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ASME Conference Presenter Attendance Policy and Archival Proceedings

2012;():i. doi:10.1115/ICES2012-NS.
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This online compilation of papers from the ASME 2012 Internal Combustion Engine Division Spring Technical Conference (ICES2012) represents the archival version of the Conference Proceedings. According to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.

Commentary by Dr. Valentin Fuster

Large Bore Engines

2012;():1-9. doi:10.1115/ICES2012-81016.

The behavior of lagrangian spray models for the application in large two stroke marine engines is investigated. 3D-CFD simulations of a Spray Combustion Chamber (SCC) with a single hole (0.875 mm diameter) injector are presented and compared with experimental results. Shadow images of the spray under evaporating and non-evaporating conditions, with and without swirl flow and for different chamber pressures are available by means of which the simulation results are validated. A novel post processing methodology for 3D CFD spray simulations is introduced, which converts the numerical data into images which allows for a more rigorous quantitative comparison with the experimental data. Good agreement of the simulation results with the experiment is reported both in terms of spray penetration as well as concerning the evaporation of the fuel. Since the appropriate discretization of the large volumes typical of 2-stroke marine engines presents a substantial challenge, the influence of the grid resolution is investigated. In addition, the influence of fuel quality on the evolution of the spray morphology is assessed. For this purpose, simulations with heavy fuel oil (HFO) are compared with experiment.

Commentary by Dr. Valentin Fuster
2012;():11-17. doi:10.1115/ICES2012-81030.

This article presents a summary of some experimental results obtained on a 1.4 MW CHP engine. Tests concern the effect of H2 and CO addition to the natural gas at the engine inlet. Hydrogen and CO were obtained through the partial oxidation of methane.

A honey-comb Platinum based catalyst was used for the partial oxidisation of methane. Part of the natural gas main stream was deviated and mixed with air to supply the catalyst. Catalyst output (mixture of H2, CO, H2O, CO2, N2 and methane) are then mixed with the main stream of natural gas supplying the engine.

Two different tests were conducted, the first one is an operation under a constant average combustion chamber temperature and the other one is an operation at a constant NOX level in the exhaust gases.

Results showed a decrease of about 10% in NOX emissions when operating under constant combustion chamber temperature (this temperature is the average temperature of the four strokes inside the cylinders); and a slight increase of engine efficiency for a constant NOX emissions level.

Commentary by Dr. Valentin Fuster
2012;():19-27. doi:10.1115/ICES2012-81041.

To satisfy the Tier-4 requirements EMD as well as other large engine manufacturers are investigating the emission reduction potentials of different technologies whether they are application ready or in concept stage. One of the recent trends is to use dedicated cylinders as EGR gas suppliers. In this study the NOx reduction potential of dedicated cylinders for the two-cycle EMD 16-710 engine is evaluated analytically.

The performance of the well known and documented 16-710 T-2 engine is chosen as the base case. An analytical model is developed to simulate the engine operation by using the commercially available GT-Power code. Model parameters are adjusted to fit predictions to test data.

The base model is then modified for a high pressure cooled EGR system. The system parameters are changed to optimize the system for selected criteria. Predicted performance of the system is compared against the base case.

The system model with EGR is further modified to accommodate the use of dedicated cylinders as the gas supplier to the EGR loop. The following dedicated cylinder variables are changed to optimize the system performance for NOx reductions; (a). Number of dedicated cylinders, (b). Location of dedicated cylinders, (c). Dedicated cylinder’s flow rate (EGR rate), (d). Compression ratio, (e). Injection timing, (f). Valve timing, (g). Valve lift profile, (h). Valve opening and closing times. Predicted results are compared against cases with and without EGR.

The study demonstrates that a 3-cylinder dedicated system, supplying the EGR gases, has the potential to reduce the tailpipe BSNOx below Tier-4 emissions level at Notch 8 operation condition of the engine. The study also suggests that designing the dedicated cylinders as if they are a different engine, for BHP while designing the normal cylinders to reduce BSNOx can be a successful strategy.

During this study the basic mechanisms of EGR in reducing the engine NOx is classified into three groups. It is shown that the Flow Diversion Effect of EGR can be above 40% of total BSNOx reduction.

Commentary by Dr. Valentin Fuster
2012;():29-36. doi:10.1115/ICES2012-81042.

The thermal efficiency of gas engines have been improved considerably in the last decade and now some of gas engines has achieved higher efficiency than diesel engines by introducing the state of the arts technologies. But at the same time, the abnormal combustion with the high peak firing pressure has been seen in recent years especially on high BMEP engines. This combustion has the unique characteristics such that it occurs temporally with the limited crank angle of advanced timing and the retarded spark ignition timing makes it worse.

As the results of researches including the visualization tests on the single cylinder engine, this combustion was confirmed to be the kind of pre-ignition caused by the auto ignition of in-cylinder lubricating oil. And it was found to be one of the causes of the cyclic variation of peak firing pressure on premixed combustion gas engine.

The lubricating oil can be ignited in the cylinder near the end of compression stroke where the temperature in cylinder is high enough for fuel oil to ignite. This is a natural phenomenon because the auto ignition temperature of lubricating oil is same level as that of fuel oil. But this phenomenon has not been considered so deeply so far because it has not caused serious combustion problems. But from now, more careful design by adding the view of the abnormal combustion caused by lubricating oil will be required for the future engines having the higher BEMP and thermal efficiency. Especially in case of gas engine ignited by fuel oil, such as Micro Pilot and Dual Fuel engine, the stable combustion window where combustion can be initiated and controlled not by lubricating oil but by fuel oil will become narrow.

In this paper, the characteristics of this abnormal combustion on production engines and the visualization data of combustions measured on a test engine are introduced and then the consideration about the mechanism and the analysis of this phenomenon are described in detail.

Commentary by Dr. Valentin Fuster
2012;():37-46. doi:10.1115/ICES2012-81049.

Pipeline natural gas composition is monitored and controlled in order to deliver high quality, relatively consistent gas quality in terms of heating value and detonation characteristics to end users. The consistency of this fuel means gas-fired engines designed for electrical power generation (EPG) applications can be highly optimized. As new sources of high quality natural gas are found, the demand for these engines is growing. At the same time there is also an increasing need for EPG engines that can handle fuels that have wide swings in composition over a relatively short period of time. The application presented in this paper is an engine paired with an anaerobic digester that accepts an unpredictable and varying feedstock. As is typical in biogas applications, there are exhaust stream contaminants that preclude the use of an oxygen or NOx sensor for emissions feedback control. The difficulty with such a scenario is the ability to hold a given exhaust gas emission level as the fuel composition varies. One challenge is the design of the combustion system hardware. This design effort includes the proper selection of compression ratio, valve events, ignition timing, turbomachinery, etc. Often times simulation tools, such as a crank-angle resolved engine model, are used in the development of such systems in order to predict performance and reduce development time and hardware testing. The second challenge is the control system and how to implement a robust control capable of optimizing engine performance while maintaining emissions compliance. Currently there are limited options for an OEM control system capable of dealing with fuels that have wide swings in composition. Often times the solution for the engine packager is to adopt an aftermarket control system and apply this in place of the control system delivered on the engine. The disadvantage to this approach is that the aftermarket controller is not calibrated and so the packager is faced with the task of developing an entire engine calibration at a customer site. The controller must function well enough that it will run reliably during plant start-up and then eventually prove capable of holding emissions under typical operating conditions. This paper will describe the novel use of a crank-angle resolved four-stroke engine cycle model to develop an initial set of calibration values for an aftermarket control system. The paper will describe the plant operation, implementation of the aftermarket controller, the model-based calibration methodology and the commissioning of the engine.

Commentary by Dr. Valentin Fuster
2012;():47-60. doi:10.1115/ICES2012-81100.

Diesel engines are almost exclusively used for propulsion of marine vessels. They are also used for power generation either on vessels or power stations because of their superior efficiency, high power concentration, stability and reliability compared to other alternative power systems. However, a significant drawback of these engines is the production of exhaust gases some of which are toxic and thus can be a threat to the environment. The most important toxic gaseous pollutants found in the exhaust gas of a marine diesel engine are NOx (NO, NO2 etc), CO and SOx. Particulate matter is also a major pollutant of diesel. Currently CO2 is considered to be also a “pollutant”, even though not being directly toxic, due to its impact on global warming.

In the Marine sector there exists legislation for marine diesel engine NOx emissions which is getting stricter as we move on towards Tier III. This brings new challenges for the engine makers as far as NOx control and its reduction is concerned. Towards this effort of NOx reduction, modelling has an important role which will become even more important in the future. This is mainly attributed to the large size of marine engines which makes the use of experimental techniques extremely expensive and time consuming. Modelling can greatly assist NOx reduction efforts at least at the early stages of development leading to cost reduction. As known NOx emissions are strongly related to engine performance and thus efforts for their reduction usually have a negative impact on efficiency and particulate matter. Modelling can play an important role towards this direction because optimization techniques can be applied to determine the optimum design for NOx reduction with the lowest impact on efficiency.

At present an effort is made to apply an existing well validated multi-zone combustion model for DI diesel engines on a 2-stroke marine diesel engine used to power a tanker vessel. The model is used to determine both engine performance and NOx emissions at various operating conditions. To validate model’s ability to predict performance and NOx emissions, a comparison is given against data obtained from the vessel official NOx file and from on board measurements conducted by the present research group. On board performance measurements were conducted using an in-house engine diagnostic system while emissions were recorded using a portable exhaust gas analyzer. From the comparison of measured against predicted data, the ability of the model to adequately predict performance and NOx emissions of the slow speed 2-stroke marine diesel engine examined is demonstrated. Furthermore, from the application are revealed specific problems related to the application of such models on large slow speed two-stroke engines which is significantly important for their further development.

Commentary by Dr. Valentin Fuster
2012;():61-71. doi:10.1115/ICES2012-81109.

Recent developments in numerical techniques and computational processing power now permit time-dependent, multi-dimensional computational fluid dynamic (CFD) calculations with reduced chemical kinetic mechanisms (approx. 20 species and 100 reactions). Such computations have the potential to be highly effective tools for designing lean-burn, high BMEP natural gas engines that achieve high fuel efficiency and low emissions. Specifically, these CFD simulations can provide the analytical tools required to design highly optimized natural gas engine components such as pistons, intake ports, precombustion chambers, fuel systems and ignition systems. To accurately model the transient, multi-dimensional chemically reacting flows present in these systems, chemical kinetic mechanisms are needed that accurately reproduce measured combustion data at high pressures and lean conditions, but are of sufficient size to enable reasonable computational times. Presently these CFD models cannot be used as accurate design tools for application in high BMEP lean-burn gas engines because existing detailed and reduced mechanisms fail to accurately reproduce experimental flame speed and ignition delay data for natural gas at high pressure (40 atm and higher) and lean (0.6 equivalence ratio (ϕ) and lower) conditions. Existing methane oxidation mechanisms have typically been validated with experimental conditions at atmospheric and intermediate pressures (1 to 20 atm) and relatively rich stoichiometry. These kinetic mechanisms are not adequate for CFD simulation of natural gas combustion in which elevated pressures and very lean conditions are typical. This paper provides an analysis, based on experimental data, of the laminar flame speed computed from numerous, detailed chemical kinetic mechanisms for methane combustion at pressures and equivalence ratios necessary for accurate high BMEP, lean-burn natural gas engine modeling. A reduced mechanism that was shown previously to best match data at moderately lean and high pressure conditions was updated for the conditions of interest by performing sensitivity analysis using CHEMKIN. The reaction rate constants from the most sensitive reactions were appropriately adjusted in order to obtain a better agreement at high pressure lean conditions. An evaluation of this adjusted mechanism, “MD19”, was performed using Converge CFD software. The results were compared to engine data and a remarkable improvement on combustion performance prediction was obtained with the MD19 mechanism.

Commentary by Dr. Valentin Fuster
2012;():73-82. doi:10.1115/ICES2012-81135.

This study investigates how injection timing affects combustion, NOx, PM mass and composition from a 2-stroke turbocharged locomotive diesel engine fitted with an early-development Tier 0+ emissions kit. The objective of the work is to gain insight into how injection timing affects combustion and emissions in this family of engines, modified to meet the newly implemented Tier 0+ emissions requirements, and to identify areas of potential future emissions reduction. For a range of injection timings at a medium load (notch 5) operating condition, the majority of PM mass is comprised of insolubles (81–89%), while the soluble component of PM (SOF) accounts for a smaller fraction (11–19%) of total PM mass. The SOF is 66–80% oil-like C22–C30+ hydrocarbons, with the remainder being fuel-like C9–C21 hydrocarbons.

A heat release analysis is used to elucidate how injection timing affects combustion by calculating mass fraction burn curves. It is observed that retarding injection timing retards combustion phasing, decreases peak cylinder pressure and temperature, and increases expansion pressure and temperature. Results show that insolubles and fuel-like hydrocarbons increase and oil-like hydrocarbons decrease with later injection timing. Analysis suggests that insolubles and fuel-like HC increase due to lower peak combustion temperature, while oil-like HC, which are distributed more widely throughout the cylinder, decrease due to higher expansion temperatures. The net result is that total PM mass increases with retarded combustion phasing, mostly due to increased insolubles.

Considering the high fraction of insoluble PM (81–89%) at all injection timings tested at notch 5, steps taken to reduce PM elemental carbon should be the most effective path for future reductions in PM emissions. Further reductions in oil consumption may also reduce PM, but to a smaller extent.

Commentary by Dr. Valentin Fuster
2012;():83-92. doi:10.1115/ICES2012-81159.

A reduction in diesel engine fuel consumption at a constant emissions level can be achieved by various means. A power turbine as a means of waste heat recovery (i.e., turbocompounding) and altered intake valve closure timing (Miller cycle) are two such mechanisms. Each of these technologies act as a means of improving the expansion process of the combustion gases, requiring reduced fueling for the same work extraction. When these embodiments are typically implemented, the timing of the exhaust valve opening is maintained. However, optimization of the timing of the exhaust valve opening presents the potential for further improvement in the expansion process. Variations in the exhaust valve opening timing will be investigated for Miller and turbocompounding cycles as well as the combination of the two features. Results will be shown to quantify the impact these variations have in system efficiency. Second law analysis will be used to show how these variations in engine configurations impact individual loss mechanisms. Finally, comparisons will be made to show the relative differences between Miller cycle and turbocompounding with and without optimization of the exhaust valve timing.

Commentary by Dr. Valentin Fuster
2012;():93-99. doi:10.1115/ICES2012-81163.

An electronic fuel injection system for a 4-stroke, 16 cylinders, V-configuration, medium speed, large bore locomotive diesel engine has been developed and successfully retrofitted on a rebuilt diesel locomotive. The engine employs a Pump-Line-Nozzle (PLN) system of fuel injection into the cylinder. Original fuel injection system used is a mechanical fuel injection pump connected to a mechanical fuel injector through a high pressure fuel line. The fuel injection pump meters the fuel delivery using a single helix machined on its plunger. The fuel injection timings are however optimized only for the rated speed and load resulting in non-optimised operation at other engine operating points. An electronic fuel injection pump having a solenoid valve for both fuel metering and injection timing along with ECU has been developed for retrofitment on rebuilt diesel locomotives. Interfacing of the ECU to the engine test cell controller has been done by developing suitable hardware and software. ECU calibration has been done and various maps of the engine have been developed. The engine was tested on the engine test bed. High pressure injector, modified fuel headers, fuel connection systems, a new high capacity fuel pump and layout of the wire harness were installed. After thorough testing and debugging, the EFI kit has been retrofitted on a rebuilt diesel locomotive and tested on load box followed by brief field trials. A savings of 4% fuel consumption over the duty cycle has been obtained. In addition there is an appreciable reduction in the smoke emissions during steady-state as well as transient operations.

Commentary by Dr. Valentin Fuster
2012;():101-110. doi:10.1115/ICES2012-81168.

Exhaust emissions from internal combustion engines are one of the leading sources of fine particulate matter emissions in urban areas. Off-road engines account for a substantial portion of the total emissions, and are subject to increasingly strict legislation as well as voluntary emissions reduction programs. The benefits of various emissions reduction programs are typically quantified with simplified, short duration field tests. In an inquiry into the suitability of such tests, this paper examines experimental data collected by portable, on-board monitoring systems on truck, tractor, construction equipment, marine and locomotive diesel engines with rated power ranging from 130 to 1550 hp and displacement ranging from 4 to 163 liters. In engines operated extensively at low load, such as some locomotive engines, substantial amounts of solids and liquids accumulate inside of the engine and in the exhaust system. These deposits are then driven off during subsequent operation at high load. As a result, the emissions of particulate matter may be elevated for a rather long time, on the order of tens of minutes, which is longer than the duration of the individual modes of most field emissions tests. Therefore, the emissions of fine particles measured during short (units of minutes per mode) tests may be affected by the accumulated deposits. If this phenomenon is overlooked and not properly accounted for, the measurements may be less repeatable or comparable, and the particulate matter emissions based on such measurements may be overestimated. On the other hand, it is not clear that the problem can be remedied if the engine is diligently preconditioned prior to the measurement — in this case, the measured values do not account for “excess” emissions associated with extended low-load operation.

Commentary by Dr. Valentin Fuster
2012;():111-120. doi:10.1115/ICES2012-81180.

Lean large-bore natural gas engines are usually equipped with gas-scavenged prechambers. After ignition and during combustion in the prechamber hot reacting jets penetrate the main chamber and provide much higher ignition energies than electric spark plugs. Although prechambers stabilize combustion, limitations of the concept are observed at very lean main chamber mixtures and large cylinder diameters, which appear as cycle-to-cycle variations of heat release and pressure.

At the Thermodynamics Institute of the Technical University of Munich cycle-to-cycle variations are investigated in an unique periodically chargeable high pressure combustion cell with full optical access to the entire main chamber. Recently, the influence of the ignition timing, the amount of scavenge-gas of the prechamber and the cross section of the prechamber exit orifices on cycle-to-cycle variations have been studied. From the pressure traces characteristic parameters of the combustion process like the ignition probability, the ignition delay and the rate of the pressure rise have been derived. By analysing the emission of OH*-chemiluminescence in terms of reacting area and light emission and on the basis of numerical simulations information on the source of cycle-to-cycle variations is obtained. Finally it is shown that cycle-to-cycle variations can be reduced remarkably by appropriate selection and combination of prechamber geometry and operating parameters.

Commentary by Dr. Valentin Fuster

Fuels

2012;():121-132. doi:10.1115/ICES2012-81048.

A vegetable oil from algae has been processed into a Hydrotreated Renewable Diesel (HRD) fuel. This HRD fuel was tested in an extensively instrumented legacy military diesel engine along with conventional Navy diesel fuel. Both fuels performed well across the speed-load range of this HMMWV engine. The high cetane value of the HRD (77 v. 43) leads to significantly shorter ignition delays with associated longer combustion durations and modestly lower peak cylinder pressures as compared to diesel fuel operation. Both brake torque and brake fuel consumption are better (5–10%) with HRD due to the cumulative IMEP effect with moderatly longer combustion durations. Carbon dioxide emmisions are considerably lower with HRD due to the improved engine efficiency as well the more advantageous hydrogen-carbon ratio of this HRD fuel.

Commentary by Dr. Valentin Fuster
2012;():133-144. doi:10.1115/ICES2012-81145.

Dual fuel pilot ignited natural gas engines are identified as an efficient and viable alternative to conventional diesel engines. This paper examines cyclic combustion fluctuations in conventional dual fuel and in dual fuel partially premixed low temperature combustion (LTC) at 1700 rev/min and 6 bar brake mean effective pressure (bmep). Conventional dual fueling with 95% (energy basis) natural gas (NG) substitution reduces NOx emissions by almost 90%t relative to straight diesel operation; however, this is accompanied by 98% increase in HC emissions, 10 percentage points reduction in fuel conversion efficiency (FCE) and 12 percentage points increase in COVimep. Dual fuel LTC is achieved by injection of a small amount of diesel fuel (2–3 percent on an energy basis) to ignite a premixed natural gas–air mixture to attain very low NOx emissions (less than 0.2 g/kWh). Cyclic variations in both combustion modes were analyzed by observing the cyclic fluctuations in start of combustion (SOC), peak cylinder pressures (Pmax), combustion phasing (Ca50), and the separation between the diesel injection event and Ca50 (termed “relative combustion phasing”). For conventional dual fueling, as % NG increases, Pmax decreases, SOC and Ca50 are delayed, and cyclic variations increase. For dual fuel LTC, as diesel injection timing is advanced from 20° to 60°BTDC, the relative combustion phasing is identified as an important combustion parameter along with SoC, Pmax, and CaPmax. For both combustion modes, cyclic variations were characterized by alternating slow and fast burn cycles, especially at high %NG and advanced injection timings. Finally, heat release return maps were analyzed to demonstrate thermal management strategies as an effective tool to mitigate cyclic combustion variations, especially in dual fuel LTC.

Commentary by Dr. Valentin Fuster
2012;():145-150. doi:10.1115/ICES2012-81155.

Experimental investigation was carried out in order to optimize the performance of a small high speed direct injection diesel engine running on Jatropha methyl ester (JME), using Taguchi methods. In the investigation three controlled parameters — injection timing, load and speed — were varied at three levels and their effect on the engine output responses — engine noise, combustion noise, smoke, NOx, HC emissions and brake specific fuel consumption were studied. Taguchi method was found to be efficient for investigating the effect of speed, load and injection timing on the engine noise, emissions and fuel economy. Analysis of variance (ANOVA) was used to find out the percentage contributions of the controlled parameters on the engine output responses. To optimize the performance, optimum combinations of the controlled parameters were found using the signal to noise (S/N) ratio. The engine output responses were predicted at those combinations. Further, confirmation runs were carried out which showed good agreement with the predicted engine output responses.

Commentary by Dr. Valentin Fuster
2012;():151-161. doi:10.1115/ICES2012-81169.

There has been an extensive worldwide search for alternate fuels that fit with the existing infrastructure and would thus displace fossil-based resources. In metabolic engineering work at Argonne National Laboratory, strains of fuel have been designed that can be produced in large quantities by photosynthetic bacteria, eventually producing a heavy alcohol called phytol (C20H40O). Phytol’s physical and chemical properties (cetane number, heat of combustion, heat of vaporization, density, surface tension, vapor pressure, etc.) correspond in magnitude to those of diesel fuel, suggesting that phytol might be a good blending agent in compression ignition (CI) engine applications. The main reason for this study was to investigate the feasibility of using phytol as a blending agent with diesel; this was done by comparing the performance and emission characteristics of different blends of phytol (5%, 10%, 20% by volume) with diesel. The experimental research was performed on a single-cylinder engine under conventional operating conditions. Since phytol’s viscosity is much higher than that of diesel, higher-injection-pressure cases were investigated to ensure the delivery of fuel into the combustion chamber was sufficient. The influence of the fuel’s chemical composition on performance and emission characteristics was captured by doing an injection timing sweep. Combustion characteristics as shown in the cylinder pressure trace were comparable for the diesel and all the blends of phytol at each of the injection timings. The 5% and 10% blends show lower CO and similar NOx values. However, the 20% blend shows higher NOx and CO emissions, indicating that the chemical and physical properties have been altered substantially at this higher percentage. The combustion event was depicted by performing high-speed natural luminosity imaging using endoscopy. This revealed that the higher in-cylinder temperatures for the 20% blend are the cause for its higher NOx emissions. In addition, three-dimensional simulations of transient, turbulent nozzle flow were performed to compare the injection and cavitation characteristics of phytol and its blends. Specifically, area and discharge coefficients and mass flow rates of diesel and phytol blends were compared under corresponding engine operating conditions. The conclusion is that phytol may be a suitable blending agent with diesel fuel for CI applications.

Topics: Fuels , Diesel engines
Commentary by Dr. Valentin Fuster
2012;():163-170. doi:10.1115/ICES2012-81171.

The effect of spray penetration distance on fuel impingement on piston bowl of a 7.4 kW diesel engine for biodiesel-diesel blend (B20) was studied using modeling and CFD simulation. As the peak inline fuel pressure increased from 460 bar with base diesel to 480 bar with B20, the spray penetration distance (fuel jet) increases. It is observed from the study that the jet tip hits on piston bowl resulting to fuel impingement which is one of durability issues for use of biodiesel blend in the diesel engine. In addition to this, the simulation of effects of different injection pressures up to 2000 bar on spray penetration distance and wall impingement were also studied. The penetration distance increases with increase the in-line fuel pressure and it decreases with decrease nozzle hole diameter. The fuel impingement on piston bowl of the engine with high injection pressure (typically 1800 bar) can be avoided by decreasing the nozzle diameter from 0.19 mm to 0.1 mm. Increase in swirl ratio could also reduce fuel impingement problem.

Commentary by Dr. Valentin Fuster
2012;():171-177. doi:10.1115/ICES2012-81178.

This study describes the effects of two-stage combustion (TSC) strategy on combustion and emission characteristics in 4 cylinder common-rail direct injection (CRDI) diesel engine fueled with biodiesel blends. In the present work, to investigate the combustion and emission characteristics, the experiments were performed under various injection pressures, first injection quantity and first injection timing of TSC strategy at constant engine speed and engine load. In addition, conventional diesel fuel (ULSD) was used to compare with biodiesel blends.

The experimental results show that combustion of biodiesel blends is stable for various test conditions regardless of blending ratio, and indicated specific fuel consumption (ISFC) was increased as biodiesel blending ratio increased. In the emission characteristics, biodiesel blends generated lower indicated specific nitrogen oxides (IS-NOx) and indicated specific soot (IS-Soot) emissions compared to those of ULSD when the first injection quantity increased.

Commentary by Dr. Valentin Fuster
2012;():179-187. doi:10.1115/ICES2012-81179.

Using CNG as an additive for gasoline is a proper choice due to higher octane number of CNG enriched gasoline with respect to that of gasoline. As a result, it is possible to use gasoline with lower octane number in the engine. This would also mean the increase of compression ratio in SI engines resulting in higher performance and lower gasoline consumption.

Over the years, the use of simulation codes to model the thermodynamic cycle of an internal combustion engine have developed tools for more efficient engine designs and fuel combustion.

In this study, a thermodynamic cycle simulation of a conventional four-stroke spark-ignition engine has been developed. The model is used to study the engine performance parameters and emission characteristics of CNG/gasoline blend fuelled engine. A spark ignition engine cycle simulation based on the first law of thermodynamic has been developed by stepwise calculations for compression process, ignition delay time, combustion and expansion processes. The building blocks of the model are mass and energy conservation equations. Newton-Raphson method has been used to solve the equations numerically and there was no need to solve them analytically. In the quasi-dimensional combustion model, the cylinder is divided into two zones separated by a thin flame front. The flame front propagates spherically throughout the combustion chamber to the point that it contacts the cylinder wall and head. The model effectively describes the thermodynamic processes and chemical state of the working fluid via a closed system containing compression, combustion, and expansion processes.

The model predicts the trends and tradeoffs the performance characteristics at various engine speeds. The variation of indicated power, ISFC and emissions are predicted by the model. Experimental data are also presented to indicate the validity of the model. The predicted results based on the model have shown reasonable agreement with the corresponding experimental data.

Commentary by Dr. Valentin Fuster
2012;():189-202. doi:10.1115/ICES2012-81187.

An experimental investigation and a burning-rate analysis have been performed on a production 1.4 liter CNG (compressed natural gas) engine fueled with methane-hydrogen blends. The engine features a pent-roof combustion chamber, four valves per cylinder and a centrally located spark plug.

The experimental tests have been carried out in order to quantify the cycle-to-cycle and the cylinder-to-cylinder combustion variation. Therefore, the engine has been equipped with four dedicated piezoelectric pressure transducers placed on each cylinder and located by the spark plug. At each test point, in-cylinder pressure, fuel consumption, induced air mass flow rate, pressure and temperature at different locations on the engine intake and exhaust systems as well as ‘engine-out’ pollutant emissions have been measured. The signals correlated to the engine operation have been acquired by means of a National Instruments PXI-DAQ system and a home developed software. The acquired data have then been processed through a combustion diagnostic tool resulting from the integration of an original multizone thermodynamic model with a CAD procedure for the evaluation of the burned-gas front geometry. The diagnostic tool allows the burning velocities to be computed.

The tests have been performed over a wide range of engine speeds, loads and relative air-fuel ratios (up to the lean operation). For stoichiometric operation, the addition of hydrogen to CNG has produced a bsfc reduction ranging between 2 to 7% and a bsTHC decrease up to the 40%. These benefits have appeared to be even higher for lean mixtures. Moreover, hydrogen has shown to significantly enhance the combustion process, thus leading to a sensibly lower cycle-to-cycle variability. As a matter of fact, hydrogen addition has generally resulted into extended operation up to RAFR = 1.8. Still, a discrepancy in the abovementioned conclusions was observed depending on the engine cylinder considered.

Commentary by Dr. Valentin Fuster
2012;():203-213. doi:10.1115/ICES2012-81239.

As part of the U.S. Maritime Administration (MARAD) marine application of alternative fuel initiative, the U.S. Navy provided neat hydrotreated renewable diesel (HRD), derived from the hydroprocessing of algal oils, for operational and exhaust emission testing onboard the T/S STATE OF MICHIGAN. This vessel has diesel-electric propulsion with four caterpillar D-398 compression ignition engines; one of these ship service diesel engines was selected as the test engine. The diesel generator sets power both the propulsion motors propelling the ship and provide the electrical power for the hotel loads of the ship. Ultra-low sulfur diesel (ULSD) was blended with the neat HRD fuel in a 50/50-by-volume blend and tested for over 440 hours on the vessel. Exhaust emissions testing was performed while underway on Lake Michigan using the baseline ULSD assessed earlier. A similar profile was run using the blended test fuel. Emission testing was conducted using the ISO 8178 (D2) test cycle. When emissions testing was completed a series of underway and pierside test runs were conducted to accumulate the remaining engine hours, After all testing, the engine conditions were assessed again using a combination of visual inspection and oil analysis. The remainder of the test fuel will be used to conduct a long-term stability test. The setup, test, and results of this testing, currently underway, are reported here with a discussion of MARAD’s alternative fuels test initiative.

Commentary by Dr. Valentin Fuster

Advanced Combustion

2012;():215-223. doi:10.1115/ICES2012-81010.

Conventional combustion techniques struggle to meet the current emissions’ regulations while retaining high engine efficiency. Specifically in automotive diesel engines, oxides of nitrogen (NOx) and particulate matter (PM) emissions have limited the utilization of diesel fuel in compression ignition engines. By comparison, throttled, knock-limited conventional gasoline operated SI engines tend not to be fuel efficient. Advanced combustion systems that simultaneously address PM and NOx while retaining the high efficiency of modern diesel engines, are being developed around the globe [1]. One of the most difficult problems in the area of advanced combustion technology development is the control of combustion initiation [2] and retaining power density [3]. During the past several years, significant progress has been accomplished in reducing emissions of NOx and PM through strategies such as LTC/HCCI/PCCI/PPCI and other advanced combustion processes; however control of ignition and improving power density has suffered to some degree — advanced combustion engines tend to be limited to the 10 bar BMEP range and under [4].

Experimental investigations have been carried out on a light duty, DI, multi cylinder, diesel automotive engine. The engine is operated in low temperature combustion technology with 87 RON (Research Octane Number) fuel [7]. Using an Ignition Quality Test (IQT) device, the equivalent Cetane Number (CN) was measured to be 25. In the present work, various EGR rates are examined to determine the effect on the combustion, emissions and performance. Experiments were conducted at three different engine load/speed combinations that are part of General Motors’ reference points for vehicle operation. To reduce the complexity, boost pressure and injection pressure and timing were kept constant while EGR percentage and intake temperature were used as parameters in this study. The intake temperature was not truly independent, as it trended with EGR level, but based upon the boost level and the available EGR cooling, Intake Air Temperature (IAT) was kept in the range of 40–80 deg C. Additional cooling capacity will be added in future work in an effort to keep IAT more consistent. EGR rates have a detrimental effect on engine efficiencies at lower load while it appears to have little effect on efficiency at higher loads. A more significant effect at very low load appears to be higher intake temperatures (hot EGR) as opposed to the very slight decrease in oxygen concentration.

Commentary by Dr. Valentin Fuster
2012;():225-237. doi:10.1115/ICES2012-81023.

Diesel knock is a phenomenon that generates undesirable noise and vibration that can be destructive to diesel engine structures and components for long-term operation. The diesel knock occurs when a large quantity of air-fuel is mixed prior to combustion when the ignition delay is long. This leads to a drastic pressure rise during the premixed phase of the combustion, which is followed by a pressure ringing. The main focus of this study is to examine effect of pilot injection on the pressure ringing and associated in-cylinder flame behaviour. In a single-cylinder small-bore optical engine, in-cylinder pressure measurement and high-speed imaging of the natural combustion luminosity have been performed. Results demonstrate that pilot injection helps reduce the in-cylinder pressure ringing by reducing the pressure rise rate of the main injection. Moreover, oscillation of the flames observed during the knocking events appears to diminish when the pilot injection is applied. How the pilot injection duration and timing affect the diesel knock behaviour is also discussed in detail.

Topics: Engines , Diesel
Commentary by Dr. Valentin Fuster
2012;():239-250. doi:10.1115/ICES2012-81059.

Spark ignition constitutes the most common way of mixture inflammation for gas engines of CHP units (combined heat and power). However, spark plug durability is limited due to spark erosion. High maintenance costs as a result of frequent spark plug replacements are the consequence. Beside the durability aspect, the inflammation of lean mixtures makes high demands on the inflammation process itself. Due to the small reactive mixture volume, the level of air-fuel ratio as well as the efficiency increase is limited. The ignition by means of a hot surface enables an increase of the reactive mixture volume and, as a result, an enhancement of the lean burn limit.

A hot surface ignition (HSI) system was developed for stationary lean burn operation in due consideration of low manufacturing costs and electrical characteristics that allow a reliable control of the ignition timing. The main component of the inflammation element is a pin-shaped glow plug, whose temperature can be regulated by adjusting the electrical power. Due to external influences such as fluctuating ambient pressure and gas quality a control unit is essential for securing an optimal combustion phasing of the engine.

Several designs of hot surface ignition, including passive prechamber and shielded versions, were tested on a single cylinder test bed engine operating with a homogeneous air-petrol mixture. The engine tests were accompanied by 3D flow simulations. The trials showed that the power consumption, and hence the temperature of the hot surface, as well as the flow conditions around the glow plug have a strong influence on the ignition timing. Furthermore, a strong correlation between the mean combustion chamber temperature and combustion phasing became evident. Based on this coherence, it was possible to develop a closed-loop control that adjusts the combustion phasing by controlling the combustion chamber temperature at a stationary operating point.

The shielded inflammation element stood out to be the target-aiming version of hot surface ignition. It is characterised by an accelerated inflammation which allows reducing the cycle-to-cycle variations compared to prechamber spark ignition and, hence, to enhance the lean burn limit. As a result, a significant improvement of the efficiency-NOx trade-off is possible.

The obtained results provide the basis for further trials on a gas engine CHP module operating with natural gas.

Topics: Ignition , Gas engines
Commentary by Dr. Valentin Fuster
2012;():251-259. doi:10.1115/ICES2012-81067.

Diesel low temperature combustion (LTC) is capable of producing diesel-like efficiency while emitting ultra-low nitrogen oxides (NOx) and soot emissions. Previous work indicates that well controlled single-shot injection with exhaust gas recirculation (EGR) is an operative way of achieving diesel LTC from low to mid engine loads. However, as the engine load is increased, demanding intake boost and injection pressure are necessary to suppress high soot emissions during the transition to LTC. The use of volatile fuels such as ethanol are deemed capable of promoting the cylinder charge homogeneity, which helps to overcome the high soot challenge and thus potentially expand the engine LTC load range.

In this work, LTC investigations have been carried out on a high compression ratio (18.2:1) engine. The engine was firstly fuelled with diesel, and LTC operation at 8 bar indicated mean effective pressure (IMEP) was enabled by sophisticated control of the injection pressure, injection timing, intake boost and EGR application. The engine performance was characterized as the baseline, and the challenges were identified. Further tests were aimed to improve the engine performance against these baseline results.

Experiments were hence conducted on the same engine with secondary ethanol port injection (PI). Single-shot diesel direct injection (DI) was applied close to top dead center (TDC) to ignite the ethanol and control the combustion phasing. The control sensitivity has been studied through injection timing sweeps and EGR sweeps. Additional tests were performed to investigate the ethanol-to-diesel ratio effects on the mixture reactivity and the engine emissions. Engine load was also raised to 10 bar IMEP while keeping the simultaneously low NOx and soot emissions. Significant improvement of engine control and emissions was achieved by the DI+PI strategy.

Commentary by Dr. Valentin Fuster
2012;():261-271. doi:10.1115/ICES2012-81079.

Continued interest in kinetically-modulated combustion regimes, such as HCCI and PCCI, poses a significant challenge in controlling the ignition timing due to the lack of direct control of combustion phasing hardware available in traditional SI and CI engines. Chemical kinetic mechanisms, validated based on fundamental data from experiments like rapid compression machines and shock tubes, offer reasonably accurate predictions of ignition timing; however utilizing these requires high computational cost making them impractical for use in engine control schemes. Empirically-derived correlations offer faster control, but are generally not valid beyond the narrow range of conditions over which they were derived.

This study discusses initial work in the development of an ignition correlation based on a detailed chemical kinetic mechanism for three component gasoline surrogate, composed of n-heptane, iso-octane and toluene, or toluene reference fuel (TRF). Simulations are conducted over a wide range of conditions including temperature, pressure, equivalence ratio and dilution for a range of tri-component blends in order to produce ignition delay time and investigate trends in ignition as pressure, equivalence ratio, temperature and fuel reactivity are varied. A modified, Arrhenius-based power law formulation will be used in a future study to fit the computed ignition delay times.

Topics: Fuels , Ignition
Commentary by Dr. Valentin Fuster
2012;():273-288. doi:10.1115/ICES2012-81094.

A predictive zero-dimensional low-throughput combustion model that was previously developed by the authors has been refined and applied to a EURO V diesel automotive engine.

The model is capable of simulating, in real time, the time-histories of the HRR (Heat Release Rate), in-cylinder pressure, in-cylinder temperatures and NOx (nitrogen oxides) concentrations, on the basis of a few quantities estimated by the ECU (Engine Control Unit), such as the injection parameters, the trapped air mass, the intake manifold pressure and temperature. It has been developed for model-based feedforward control purposes in DI (Direct Injection) diesel engines featuring an advanced combustion system or new combustion-mode concepts, such as LTC/PCCI (Low Temperature Combustion/Premixed Charge Compression Ignition) engines.

In the present work, the model has been assessed in detail by analyzing a wide set of experimental engine data that were acquired during the engine calibration phase. The experimental data set has been defined according to the DoE (Design of Experiment) methodology currently used for engine calibration purposes, and applied to six ‘key-points’ that are representative of engine working operations during an NEDC (New European Driving Cycle) for a D-class passenger car. Different injection strategies (pilot-main, double pilot-main; pilot-main-after; double pilot-main-after) have been considered for each key point, and all the main engine operating parameters (rail pressure, injected quantities, boost level, intake temperature, EGR rate,…) have been included in the DoE variation list. Therefore, about 1000 steady-state engine operating conditions have been investigated.

In addition, several NEDC driving cycles have been realized with the engine installed on a dynamic test rig, and the combustion parameters and emission levels have continuously been measured during the transient operations.

The model has been applied to all the investigated conditions. It has shown excellent accuracy in estimating the values of the main combustion parameters, and a good matching between the calculated and predicted NOx concentrations was found, for both steady-state and transient operations.

Commentary by Dr. Valentin Fuster
2012;():289-296. doi:10.1115/ICES2012-81106.

Advanced premixed compression ignition (CI) combustion using fumigation has been shown to yield significant improvements in indicated efficiency over traditional diesel combustion strategies while simultaneously reducing engine-out soot and NOX emissions. To better interpret these findings, a breakdown of the ways in which actual performance deviates from ideal engine cycles is helpful. Non-ideal combustion phasing is one cause of such deviations. In this paper, the centroid of the calculated apparent heat release rate is used to estimate an adjusted maximum possible thermal efficiency based on constant volume combustion using an effective compression ratio concept. Using these metrics, experimental engine data are evaluated from a single cylinder direct-injection diesel engine operating in premixed CI mode enabled by gasoline fumigation and a diesel pilot injection. Indicated gross cycle efficiency was found to be higher for premixed fumigation compared with a conventional diesel condition at the same load. A key finding of the work is that the peak indicated cycle efficiency for fumigated premixed CI combustion occurs with combustion phased very close to TDC. Shorter heat release duration and lower heat losses from the cylinder are thought to be the cause of differences in cycle efficiency between conventional combustion and premixed CI fumigation modes.

Commentary by Dr. Valentin Fuster
2012;():297-306. doi:10.1115/ICES2012-81107.

Cyclic variability (CV) in lean HCCI combustion at the limits of operation is a known phenomenon, and this work aims at investigating the dominant effects for the cycle evolution at these conditions in a multi-cylinder engine. Experiments are performed in a four-cylinder engine at the operating limits at late phasing of lean HCCI operation with negative valve overlap (nvo). A combustion analysis method that estimates the unburned fuel mass on a per-cycle basis is applied on both main combustion and the nvo period revealing and quantifying the dominant effects for the cycle evolution at high CV. The interpretation of the results and comparisons with data from a single-cylinder engine indicate that, at high CV, the evolution of combustion phasing is dominated by low-order deterministic couplings similar to the single-cylinder behavior. Variations, such as in air flow and wall temperature, between cylinders strongly influence the level of CV but the evolution of the combustion phasing is governed by the interactions between engine cycles of the individual cylinders.

Commentary by Dr. Valentin Fuster
2012;():307-318. doi:10.1115/ICES2012-81127.

Homogeneous charge compression ignition (HCCI) has the potential to reduce both fuel consumption and NOx emissons compared to normal spark-ignited (SI) combustion. For a relatively low compression ratio engine, high unburned temperatures are needed to initiate HCCI combustion, which is achieved with large amounts of internal residual or by heating the intake charge. The amount of residual in the combustion chamber is controlled by a recompression valve strategy, which relies on negative valve overlap (NVO) to trap residual gases in the cylinder. A single-cylinder research engine with fully-flexible valve actuation is used to explore the limits of HCCI combustion phasing at a constant load of ∼3 bar IMEPg. This is done by performing two individual sweeps of a) internal residual fraction (via NVO) and b) intake air temperature to control combustion phasing. It is found that increasing both variables advances the phasing of HCCI combustion, which leads to increased NOx emissions and a higher ringing intensity. On the other hand, a reduction in these variables leads to greater emissions of CO and HC, as well as a decrease in combustion stability. A direct comparison of the two sweeps suggests that the points with elevated intake temperatures are more prone to ringing as combustion is advanced and less prone to instability and misfire as combustion is retarded. This behavior can be explained by compositional differences (air vs. EGR dilution) which lead to variations in burn rate and peak temperature. As a final study, two additional NVO sweeps are performed while holding intake temperature constant at 30°C and 90°C. Again, it is seen that at higher intake temperatures, combustion is more susceptible to ringing at advanced timings and more resistant to instability/misfire at retarded timings.

Commentary by Dr. Valentin Fuster
2012;():319-333. doi:10.1115/ICES2012-81175.

The research described in this paper was aimed at determining any common precedents for abnormal combustion events in a gasoline engine in order that their occurrence might be predicted and ultimately corrected.

Combustion data was collected for 1200 cycles from a motorbike spark ignition engine running at 4,000rpm and 1.15 bar BMEP at fuelling conditions ranging from rich through stoichiometric to lean. The least cyclic variability occurred during slightly rich fuelling and was best characterised through the heat released per cycle.

Phase-lag plots of the heat released per cycle showed boomerang shaped patterns, indicating deterministic cyclic variability. This suggested that an algorithm capable of predicting poor cycles could be developed. It was found, however, that the majority of poor combustion events are preceded by cycles of an approximately average heat release and that poor combustion events are likely to be followed by a strong combustion event. Importantly not all poor cycles follow this pattern. This means that existing prediction algorithms which are based on preceding cycles would not be suitable in this case. An examination of the chain length of good or average combustion events between poor events did not show any chain length commonality across the AFR’s.

The findings of this paper support the view that the deterministic patterns in the cyclic variations in combustion are present but that they are complex and cannot be predicted using simple metrics based on neighbouring cycles. A more thorough understanding of the fundamental contribution of previous combustion cycles to the variability is required for predictive tools to be effective.

Commentary by Dr. Valentin Fuster
2012;():335-345. doi:10.1115/ICES2012-81184.

The impact of fuel composition on the emission performance and combustion characteristics for partially premixed combustion (PPC) were examined for four fuels in the gasoline boiling range together with Swedish diesel MK1. Experiments were carried out at 8 bar IMEPg and 1500 rpm with 53±1% EGR and λ = 1.5. This relation gave inlet mole fractions of approximately 5% CO2 and 13% O2. The combustion phasing was adjusted by means of start of injection (SOI), for all fuels, over the range with stable combustion and acceptable pressure rise rate combined with maintained λ, EGR ratio, inlet pressure, and load. The operating range was limited by combustion instability for the high RON fuels, while MK1 and the low RON fuels could be operated over the whole MBT plateau. The largest difference in engine-out emissions between the fuels was the filtered smoke number (FSN), as the gasoline fuels produced a much lower FSN value than MK1. Higher RON value gave higher levels of carbon monoxide (CO) and unburned hydrocarbon (HC) for the gasoline fuels, while MK1 had the lowest levels of these emissions.

Commentary by Dr. Valentin Fuster
2012;():347-356. doi:10.1115/ICES2012-81206.

A prototype Diesel common rail direct-acting piezoelectric injector has been used to study the influence of fuel injection rate shaping on spray behavior (liquid phase penetration) under evaporative and non-reacting conditions. This state of the art injector allows a fully flexible control of the nozzle needle, enabling various fuel injection rates typologies under a wide range of test conditions. The tests have been performed employing a novel continuous flow test chamber that allows an accurate control on a wide range of thermodynamic test conditions (up to 1000 K and 15 MPa). The temporal evolution of the spray has been studied recording movies of the injection event with a fast camera (25 kfps) by means of the Mie scattering visualization technique. The analysis of the results showed a strong influence of needle position on the behavior of the liquid length. The needle position controls the effective pressure upstream of the nozzle holes. Higher needle lift is equivalent to higher effective pressures. According to the free-jet theory, the stabilized liquid-length depends mainly on effective diameter, spray cone-angle and fuel/air properties and does not depend on injection velocity. Therefore, higher injection pressures gives slightly lower liquid length due to small change in the spray cone-angle. However, partial needle lifts has an opposite effect: lower effective pressure upstream of the nozzle holes shows a dramatic increase on the spray cone-angle, reducing the liquid length. This behavior could be explained mainly due to the fact that the flow direction upstream of the nozzle holes is affecting the area coefficient, or in other words, the effective diameter of the holes.

Topics: Sprays , Diesel
Commentary by Dr. Valentin Fuster
2012;():357-367. doi:10.1115/ICES2012-81207.

The HCCI combustion process is highly reliant upon a favorable in-cylinder thermal environment in an engine, for a given fuel. Commercial fuels can differ considerably in composition and auto-ignition chemistry, hence strategies intended to bring HCCI to market must account for this fuel variability.

To this end, a test matrix consisting of eight gasoline fuels comprised of blends made solely from refinery streams were run in an experimental, single cylinder HCCI engine. All fuels contained 10% ethanol by volume and were representative of a cross-section of fuels one would expect to find at gasoline pumps across the United States. The properties of the fuels were varied according to research octane number (RON), sensitivity (S=RON-MON) and volumetric content of aromatics and olefins.

For each fuel, a sweep of load (mass of fuel injected per cycle) was conducted and the intake air temperature was adjusted in order to keep the crank angle of the 50% mass fraction burned point (CA50) constant. By analyzing the amount of temperature compensation required to maintain constant combustion phasing, it was possible to determine the sensitivity of HCCI to changes in load for various fuels.

In addition, the deviation of fuel properties brought about variations in important engine performance metrics like specific fuel consumption. Though the injected energy content per cycle was matched at the baseline point across the test fuel matrix, thermodynamic differences resulted in a spread of specific fuel consumption for the fuels tested.

Commentary by Dr. Valentin Fuster
2012;():369-378. doi:10.1115/ICES2012-81208.

Naturally occurring thermal stratification significantly impacts the characteristics of HCCI combustion. The in-cylinder gas temperature distributions prior to combustion dictate the ignition phasing, burn rates, combustion efficiency, and unburned hydrocarbon and CO emissions associated with HCCI operation. Characterizing the gas temperature fields in an HCCI engine and correlating them to HCCI burn rates is a prerequisite for developing strategies to expand the HCCI operating range.

To study the development of thermal stratification in more detail, a new analysis methodology for post-processing experimental HCCI engine data is proposed. This analysis tool uses the autoignition integral in the context of the mass fraction burned curve to infer information about the distribution of temperature that exists in the cylinder prior to combustion. An assumption is made about the shape of the charge temperature profiles of the unburned gas during compression and after combustion starts elsewhere in the cylinder. Secondly, it is assumed that chemical reaction rates proceed very rapidly in comparison to the staggering of ignition phasing from thermal stratification. The autoignition integral is then coupled to the mass fraction burned curve to produce temperature-mass distributions that are representative of a particular combustion event. Due to the computational efficiency associated with this zero-dimensional calculation, a large number of zones can be simulated at very little computational expense.

The temperature-mass distributions are then studied over a coolant temperature sweep. The results show that very small changes to compression heat transfer can shift the distribution of mass and temperature in the cylinder enough to significantly affect HCCI burn rates and emissions.

Commentary by Dr. Valentin Fuster
2012;():379-391. doi:10.1115/ICES2012-81223.

Measuring the rate of injection of a common-rail injector is one of the first steps for diesel engine development. At the same time, this information is of prime interest for engine research and modeling as it drives spray development and mixing. On the other hand, the widely used long-tube method provides results that are neither straightforward, nor fully understood. This study performed on a 0.09 mm axially drilled single-hole nozzle is part of the Engine Combustion Network (ECN) and aims at analyzing these features from an acoustic point of view to separate their impact on the real injection process and on the results recorded by the experimental devices. Several tests have been carried out for this study including rate of injection and momentum, X-ray phase-contrast of the injector and needle motion or injector displacement. The acoustic analysis revealed that these fluctuations found their origin in the sac of the injector and that they were the results of an interaction between the fluid in the chamber (generally gases) and the liquid fuel to be injected. It has been observed that the relatively high oscillations recorded by the long-tube method were mainly caused by a displacement of the injector itself while injecting. In addition, the results showed that these acoustic features also appear on the momentum flux of the spray which means that the real rate of injection should present such behavior.

Commentary by Dr. Valentin Fuster
2012;():393-404. doi:10.1115/ICES2012-81234.

Toluene fuel-tracer laser-induced fluorescence is employed to quantitatively measure the equivalence ratio distributions in the cylinder of a light-duty diesel engine operating in a low-temperature, high-EGR, and early-injection operating mode. Measurements are made in a non-combusting environment at crank angles capturing the mixture preparation period: from the start-of-injection through the onset of high-temperature heat release. Three horizontal planes are considered: within the clearance volume, the bowl rim region, and the lower bowl. Swirl ratio and injection pressure are varied independently, and the impact of these parameters on the mixture distribution is correlated to the heat release rate and the engine-out emissions.

As the swirl ratio or injection pressure is increased, the amount of over-lean mixture in the upper central region of the combustion chamber, in the bowl rim region and above, also increases. Unexpectedly, increased injection pressure results in a greater quantity of over-rich mixture within the squish volume.

Commentary by Dr. Valentin Fuster
2012;():405-414. doi:10.1115/ICES2012-81236.

Dilution of partially-premixed combustion (PPC) using different combinations of excess air (λ>1) and exhaust gas recirculation (EGR) was investigated in a single-cylinder, heavy-duty diesel engine equipped with common-rail fuel injection. The experiments were limited to a single fuel injection event using ultra-low sulphur diesel fuel at a low engine load (∼3 bar BMEP) and engine speeds of 900 and 1350 rpm. The start of injection was varied to optimize the combustion performance and emissions.

The experimental results show that increasing air dilution at constant EGR reduced BSFC slightly. CO and HC emissions decreased significantly due to the increased oxygen concentration, but NOx and soot emissions increased. For a given level of charge dilution, there was an optimal EGR rate to minimize BSFC. NOx emissions decreased significantly as the proportion of dilution by EGR was increased, but CO and HC emissions increased due to the reduced in-cylinder temperature and oxygen concentration, which increased the combustion duration.

Topics: Combustion , Stress , Diesel , Sulfur
Commentary by Dr. Valentin Fuster

Emissions Control Systems

2012;():415-430. doi:10.1115/ICES2012-81003.

Both, the continuous tightening of the exhaust emission standards and the global efforts for a significant lowering of CO2 output in public traffic display significant developments for future diesel engines. These engines will utilize not only the mandatory Diesel oxidation catalyst (DOC) and particulate trap (DPF), but also a DeNOx aftertreatment system as well — at least for heavier vehicles. The DOC as well as actually available sophisticated DeNOx aftertreatment technologies, i.e. LNT and SCR, depends on proper exhaust gas temperatures to achieve a high conversion rates. This aspect becomes continuously critical due to intensified measures for CO2 reduction, which will conclude in a drop of exhaust gas temperatures. Furthermore, this trend has to be taken into account regarding future electrification and hybridization scenarios. In order to ensure the high NOx conversion rates in the EAS intelligent temperature management strategies will be required, not only based on conventional calibration measures, but also a further upgrade of the engine hardware.

Advanced split-cooling and similar thermal management technologies offer the merit to lower CO2 emissions on one hand and increase exhaust gas temperature at cold start and warm-up simultaneously on the other hand. Besides this, also variable valve train functionalities deliver a substantial potential of active thermal management. In the context of this paper various concepts for exhaust gas temperature management are investigated and compared. The final judgment will focus on the effectiveness concerning real exhaust temperature increase vs. corresponding fuel economy penalty. Further factors, like operational robustness, consequences on operational strategies and related software algorithms as well as cost are assessed. The utilized reference engine in this advanced program is represented by a refined I-4 research engine to achieve best combustion efficiency at minimal engine-out emissions. The detailed studies were performed with an injection strategy, featuring one pilot injection and one main injection event, and an active, advanced closed-loop combustion control. The engine used in this study allows fulfillment of Euro 6 and Tier 2 Bin 5 emissions standards, while offering high power densities above 80 kW/ltr.

As a résumé, it can be stated, that with all accomplished variations a significant increase in temperature downstream low pressure turbine can be achieved. The PI and PoI quantities define dominant parameters for emission formation under cold and warm conditions. By using an exhaust cam-phaser CO-, HC- and NOx emissions can be significantly lowered, separating VVT functions from the other investigated strategies.

Commentary by Dr. Valentin Fuster
2012;():431-443. doi:10.1115/ICES2012-81037.

Over the two last decades, gaseous and particle mass emissions of new diesel engines have been reduced effectively and progressively in response to the emissions legislation and due to the applied new technologies.

There is, however, increasing concern about whether the engine modifications, while improving combustion and reducing emissions, have increased the number emissions of ultrafine and nanoparticles. So far, emissions regulations have solely been based on particulate matter (PM) mass measurements, not on particle number. Nanoparticles, however, form a major part of the PM emissions, but they do not considerably contribute to the PM mass and can not be seen as a problem, if only PM mass is determined.

Therefore, there is increasing interest in expanding the scope of the regulations to also include particle number emissions, e.g. Euro VI for on-road engines. The PM number limit will also be enforced for non-road engines slightly later. Thus, more information is required about the particle number emissions themselves, but also about the effects of the engine technology on them.

Wall-flow diesel particulate filters (DPFs) reduce the particle number very effectively within the entire particle size range. Nevertheless, in order to keep the DPF as small as possible and to lessen the need for regeneration, the engine-out PM number should also be minimized.

If the DPF could be left out or replaced by a simpler filter, there would be greater freedom of space utilization or cost savings in many non-road applications. This might be realized in installations where the engine is tuned at high raw NOx and an SCR system is adopted for NOx reduction. However, it is not self-evident that new engine technologies would reduce the PM number emissions sufficiently.

In this study, particle number emissions were analyzed in several non-road diesel engines representing different engine generations and exploiting different emissions reduction technologies: 4- or 2-valve heads, exhaust gas recirculation (EGR), different injection pressures and strategies, etc. All engines were turbocharged, intercooled, direct-injection non-road diesel engines. Most engines used common-rail fuel injection technology. Comparisons were, however, also performed with engines utilizing either a distributor-type or an in-line fuel injection pump to see the long-term development of the particle number emissions.

In this paper, the PM number emissions of nine (9) non-road diesel engines are presented and compared. Gaseous exhaust emissions and fuel consumption figures are also provided.

Commentary by Dr. Valentin Fuster
2012;():445-450. doi:10.1115/ICES2012-81054.

Analysis of the changes in mass and size of particles formed during the diesel combustion process, the morphological characteristics, and the trace elements within these amorphous particles was carried out using a total cylinder sampling system installed on a direct injection diesel engine. Utilizing field emission transmission electron microscope technology, the results showed that the amorphous particles formed during the combustion process were abundant in metallic and non-metallic elements mainly derived from the lubrication oil, which was found to have entered the combustion process, oxidized and combusted, further increasing the absorbed carbon particles during the later stages of combustion.

Commentary by Dr. Valentin Fuster
2012;():451-459. doi:10.1115/ICES2012-81060.

Ultra-fast emission measurements can provide important information about the combustion system of an engine, especially during its development phase. The ability to measure NOx as soon as it exits the cylinder provides an insight to engine designers and combustion engineers about the in-cylinder process with regards to formation of NOx emissions. There are mainly two areas where such information can be used. First, the fast measurements can be used for the tuning of CFD models that are used during the development phase of an engine. Secondly, such a method could be useful in the first phases of engine testing during the development of the combustion system where engine tuning could lead to an overall superior compromise between an engine’s fuel economy and emission behaviour.

The current research work investigated the potential of performing ultra-fast emission measurements in the exhaust port, immediately downstream of the exhaust valve, of a specified engine cylinder of a two-stroke large engine. A methodology was therefore developed and tested, by which emission measurements with fast temporal response can be conducted for individual engine cylinders.

More specifically, an ultra-fast NOx measurement sampling probe was designed and developed to be applied mainly to 2-stroke engines, with the flexibility to also be applicable to 4-stroke engines. The development of the sampling system was done by initially performing NO measurements on the 4-stroke MAN L16/24 research engine, installed at the test bed of the Laboratory of Marine Engineering (LME), at the National Technical University of Athens (NTUA). Once developed, the final fast sampling system was then used for measurements of NO at the exhaust port of the 2-stroke MAN 4T50ME-X engine, at the MAN Diesel & Turbo test-centre in Copenhagen. The employed NO emissions measurement method provided the results on a cycle-by-cycle basis, and also as phase averaged values. The extremely fast response time of the instrument captured important details of the NO concentration in the exhaust gases, as soon as they exit the cylinder.

Commentary by Dr. Valentin Fuster
2012;():461-471. doi:10.1115/ICES2012-81146.

The concept of a hybrid braking energy recoupment system was defined for coaches of diesel-hauled regional commuter trains. Functional specifications were developed having the goal of increasing by 25 percent the acceleration rate of a commuter train consisting of 10 bi-level coaches hauled by a 3,000 hp diesel locomotive, typical of the rolling stock now in service in Canada and the U.S.A. Because increasing train acceleration was the primary aim, the concept was named the Hybrid Augmented Traction System (HATS). Analyses of HATS simulations showed that in addition to augmenting acceleration and reducing trip time, braking energy recoupment reduced fuel consumption and corresponding diesel emissions.

Examined were three alternate hybrid systems for train retardation by recoupment of braking energy, its storage and then regeneration based, respectively, on Hydrostatic, Battery and Ultracapacitor energy storage. The Ultracapacitor Hybrid system appeared the most promising due to the capability of ultracapacitors to repeatedly and rapidly accept large charges, be temperature insensitive and flexible in the placement of modules in the limited space available. The study foresees that HATS technology development could be expedited via the procurement process if railway operators specified braking energy recoupment requirements in calls-for-proposals for new capital equipment.

Topics: Braking , Diesel , Trains , Emissions
Commentary by Dr. Valentin Fuster
2012;():473-480. doi:10.1115/ICES2012-81157.

The PR30C-LE is a repowered six-axle, 2,240 kW (3,005 hp), line-haul locomotive that was introduced to the rail industry in 2009. The Caterpillar 3516C-HD Tier 2 engine is equipped with an exhaust aftertreatment module containing selective catalyst reduction (SCR) and diesel oxidation catalyst (DOC) technology. PR30C-LE exhaust emission testing was performed on test locomotive PRLX3004. Phase-1 of the test program included the following tasks: engine-out baseline emissions testing without the aftertreatment module installed, aftertreatment module installation, commissioning and degreening, and emissions testing with the aftertreatment. Emission results from testing without the aftertreatment module, referred to as the baseline configuration, indicated that PRLX3004 emissions were below Tier 2 EPA locomotive limits without aftertreatment. Emission test results with the DOC and SCR aftertreatment module showed a reduction in nitrogen oxides (NOx) of 80 percent over the line-haul cycle, and 59 percent over the switcher cycle. Particulate matter (PM) was reduced by 43 percent over the line-haul cycle and 64 percent over the switcher cycle. Line-haul cycle composite emissions of Hydrocarbon (HC) and carbon monoxide (CO) were reduced by 93 and 72 percent, respectively. The PR30C-LE locomotive achieved Tier 4 line-haul NOx, CO, HC, as well as Tier 3 PM levels. There are currently five PR30C-LE locomotives in operation in California and Arizona, and the total hour accumulation of the five PR30C-LE locomotives as of October 2011 was 20,000 hours.

Commentary by Dr. Valentin Fuster
2012;():481-486. doi:10.1115/ICES2012-81170.

A 2009 Volkswagen Jetta was tested using a Portable Emissions Measurement System (PEMS) SemtechD emissions analyzer to determine when the emissions and fuel consumption will be the smallest in regards to startup vs. idle emissions. An idle time equivalent was calculated to determine when idle emissions became equal to startup emissions at four different ambient temperatures for a cold start. The mass of Total Hydrocarbons (THC) emitted limited the idle time equivalent to less than the startup time for all ambient temperatures. The temperature of the Catalytic Converter (CC) was monitored to determine how quickly the car cools down and therefore, how beneficial it is to turn the car off after a certain time period. For the temperature range tested, it was more beneficial for reduced emissions to turn off the car compared to idling by a factor of at least four. The data suggests a trend that idling would never be the best option; however, more testing needs to be done with a greater range of CC cool down temperatures to confirm this initial assessment.

Commentary by Dr. Valentin Fuster
2012;():487-493. doi:10.1115/ICES2012-81195.

One of the California Air Resources Board’s highest priorities is to reduce NOx and PM emissions from diesel engines. To support this goal, this project evaluated two different brands of experimental diesel particulate filters (DPF’s) on a 1,500 kW GenSet Switcher locomotives to determine their efficiency at reducing PM for this application. The locomotive used for these tests was UPY2737, an NREC Model 3GS-21B Ultra Low Emissions Locomotive (ULEL) originally manufactured in 2007. This is one of 70 of this type of locomotive operating in California. These locomotives are powered by three EPA Tier 3 nonroad, 522 kW, diesel engine driven generator sets.

Upon receipt, the locomotive was baseline emission tested and the results were provided to two DPF system suppliers. Experimental DPF’s provided by these suppliers were then installed and tested using only one of the three engine-gen sets.

The experimental DPF provided by Supplier “A” reduced PM emissions by 92 percent from baseline switch cycle levels, or 77 percent below the US EPA Tier 4 locomotive PM emission limit. Additionally this system essentially did not change the NOX emissions and cycle weighted fuel consumption from the engine. The experimental DPF provided by Supplier “B” also showed no significant change in the switch cycle weighted fuel consumption and NOX emission and reduced the PM emissions by 88 percent, which is 63 percent below the Tier 4 locomotive PM emissions limit.

Based on these successful screening test results, projects are underway to equip all three engines with production intent retrofit DPF systems on two revenue service locomotives, one for each of the two DPF suppliers.

Commentary by Dr. Valentin Fuster
2012;():495-509. doi:10.1115/ICES2012-81202.

Exhaust Gas Recirculation (EGR) is extensively employed in diesel combustion engines to achieve NOx emission targets. The EGR is often cooled in order to increase the effectiveness of the strategy, even though this leads to a further undesired impact on PM and HC.

Experimental tests were carried out on a diesel engine at a dynamometer rig under steady-state speed and load working conditions that were considered relevant for the New European Driving Cycle. Two different shell and tube-type EGR coolers were compared, in terms of the pressure and temperature of the exhaust and intake lines, to evaluate thermal effectiveness and induced pumping losses. All the relevant engine parameters were acquired along EGR trade-off curves, in order to perform a detailed comparison of the two coolers. The effect of intake throttling operation on increasing the EGR ratio was also investigated. A purposely designed aging procedure was run in order to characterize the deterioration of the thermal effectiveness and verify whether clogging of the EGR cooler occurred.

The EGR mass flow-rate dependence on the pressure and temperature upstream of the turbine as well as the pressure downstream of the EGR control valve was modeled by means of the expression for convergent nozzles. The restricted flow-area at the valve-seat passage and the discharge coefficient were accurately determined as functions of the valve lift.

Commentary by Dr. Valentin Fuster
2012;():511-520. doi:10.1115/ICES2012-81203.

Newly developed Diesel engine control strategies are mainly aimed at pollutant emissions reduction, due to the increasing request for engine-out emissions and fuel consumption reduction. In order to reduce engine-out emissions, the development of closed-loop combustion control algorithms has become crucial. Modern closed-loop combustion control strategies are characterized by two main aspects: the use of high EGR rates (the goal being to obtain highly premixed combustions) and the control of the center of combustion. In order to achieve the target center of combustion, conventional combustion control algorithms correct the measured value by varying Main injection timing.

It is possible to obtain a further reduction in pollutant emissions through a proper variation of the injection parameters. Modern Diesel engine injection systems allow designing injection patterns with many degrees of freedom, due to the large number of tuneable injection parameters (such as start and duration of each injection). Each injection parameter’s variation causes variations in the whole combustion process and, consequently, in pollutant emissions production. Injection parameters variations have a strong influence on other quantities that are related to combustion process effectiveness, such as noise radiated by the engine. This work presents a methodology that allows real-time evaluating combustion noise on-board a vehicle. The radiated noise can be evaluated through a proper in-cylinder pressure signal processing. Even though in-cylinder pressure sensor on-board installation is still uncommon, it is believed that in-cylinder pressure measurements will be regularly available on-board thanks to the newly developed piezo-resistive sensors.

In order to set-up the methodology, several experimental tests have been performed on a 1.3 liter Diesel engine mounted in a test cell. The engine was run, in each operating condition, both activating and deactivating pre-injections, since pre-injections omission usually produces a decrease in pollutant emissions production (especially in particulate matter) and a simultaneous increase in engine noise. The investigation of the correlation between combustion process and engine noise can be used to set up a closed-loop algorithm for optimal combustion control based on engine noise prediction.

Commentary by Dr. Valentin Fuster
2012;():521-530. doi:10.1115/ICES2012-81232.

During research on diesel engine EGR cooler fouling a test stand giving visual access to the building deposit layer has been developed. Initial experiments reveal the presence of large particles in the exhaust. While conventional wisdom is that diesel particulates typically have log-normal size distributions ranging approximately 10–200 nm, the tests reported here observe small numbers of particles with sizes on the order of tens of μm. Such particles are not generally reported in the literature because exhaust particle sizing instruments typically have inertial separators to remove particles larger than ∼1 μm in order to avoid fouling of the nanoparticle measurement system.

The test stand provides exhaust or heated air flow over a cooled surface with Reynolds number, pressure, and surface temperature typical of an EGR cooler. A window allows observation using a digital microscope camera. Starting from a clean surface, a rapid build of a deposit layer is observed. A few large particles are observed. These may land on the surface and remain for long times, although occasionally a particle blows away.

In order to study these particles further, an exhaust sample was passed over a fiberglass filter, and the resulting filtered particles were analyzed. Samples were taken at the engine EGR passage, and also in the test stand tubing just before the visualization fixture. The resulting images indicate that the particles are not artifacts of the test system, but rather are present in engine exhaust.

MATLAB routines were developed to analyze the filter images taken on the microscope camera. Particles were identified, counted, and sized by the software.

It is not possible to take isokinetic samples and give quantitative measurement of the number and size distribution of the particles because the particles are large enough that inertial and gravitational effects will cause them to at least partially settle out of the flows. Nonetheless, the presence of particles tens of μm is documented.

Such particles are probably the result of in-cylinder and exhaust pipe deposits flaking. While these larger particles would be captured by the diesel particulate filter (DPF), they can affect intake and exhaust valve seating, EGR cooler fouling, EGR valve sealing, and other factors.

Commentary by Dr. Valentin Fuster
2012;():531-546. doi:10.1115/ICES2012-81237.

The current CJ-4 oil specification places a limit on the oil’s sulfated ash content of 1.0% to reduce the build-up of lubricant-derived ash in the diesel particulate filter (DPF). Lubricant additives, specifically detergents and anti-wear additives, contribute to most of the sulfated ash content in the oil and ash accumulation in the DPF, and hence are studied with increasing interest in the optimization of the combined engine-oil-aftertreatment system. However, characteristics of ash deposits found in the particulate filter, which are affected by a number of parameters, differ markedly from those of the ASTM-method defined sulfated ash. In addition, ash characteristics and effects on DPF performance vary substantially among the different metallic base in the additives, specifically calcium, magnesium, and zinc. Through a series of carefully-controlled tests with specially-formulated lubricant additives, this work quantified the individual and combined effects of the most common detergent and anti-wear additives on the ash properties which directly influence DPF pressure drop.

The results show that different lubricant additive formulations (Ca, Zn, Mg) produce profound differences in DPF pressure drop. It was found that DPF ash is a complex mixture of metals (Ca, Zn, Mg) in the form of sulfates, phosphates, and oxides. These ash compounds each have unique physical properties, which affect DPF pressure drop differently. In particular, ash containing calcium sulfate compounds resulted in an increase in filter pressure drop by over a factor of two, relative to the same amount of ash composed only of zinc phosphate or magnesium oxide compounds, at the same ash loading in the DPF. In addition, synergistic effects due to specific additive combinations were also explored and showed significant differences in ash composition and degree of exhaust flow restriction imposed by the ash resulting from specific additive combinations, as opposed to the individual additives themselves. Results are useful not only for lubricant formulators to design oils for improved aftertreatment system compatibility, but also to understand the practical effects of ash in the DPF in relation to the standardized sulfated ash definition in the lubricant specification.

Commentary by Dr. Valentin Fuster

Instrumentation, Controls, and Hybrids

2012;():547-556. doi:10.1115/ICES2012-81017.

In this paper, a new configuration for air hybrid engines is introduced which increases the energy storing capacity of the system during braking and simplifies significantly the valvetrain needed for the hybridized engine by relaxing the need for a fully flexible valvetrain system. The proposed configuration allows easy implementation of various air hybrid operational modes. Moreover, the specific configuration of the system avoids irreversible gas exchange in the cylinder during regenerative mode which results in the significant increase of the energy recovering efficiency. One of the most important advantages of the proposed system is that the engine torque in the regenerative braking mode is controlled by the same throttle system used in the conventional ICE mode. The performance and feasibility of the proposed configuration is shown through simulation and experimental work.

Topics: Hybrid engines
Commentary by Dr. Valentin Fuster
2012;():557-568. doi:10.1115/ICES2012-81093.

Hybrid Electric Vehicles (HEVs) can be considered one of the most promising ways of improving the sustainability of the road transport sector. They are equipped with an Internal Combustion Engine (ICE) coupled to an electro-mechanical system. This study has focused on a parallel-hybrid diesel powertrain featuring a high-voltage Belt Alternator Starter (BAS). This layout allows regenerative braking, Stop&Start, load point shift and electric power assistance to the ICE. However, a dedicated optimization of the operating strategy is required to exploit all the expected advantages of the considered HEV. The project has entailed the implementation of a zero-dimensional model of the hybrid powertrain in GT-Drive and Matlab environments. Genetic Algorithm (GA) based techniques have been used to define a novel benchmark operating strategy and to calibrate a real-time optimizer. The benchmark and real-time optimization approaches have been applied to reduce the total FC and NOx emissions as well as to diminish the local combustion noise peaks. Different mission profiles have been considered, i.e. the New European Driving Cycle (NEDC) and three Artemis driving routes. The results show the effectiveness of the proposed methods and the improvements obtained in fuel economy, NOx emissions and combustion noise.

Topics: Optimization , Cycles , Diesel
Commentary by Dr. Valentin Fuster
2012;():569-581. doi:10.1115/ICES2012-81105.

Reciprocating engines are still frequently used in aviation especially in applications such as recreation planes, taxi-planes, fire extinguishing aircraft and generally applications that do not require a high power density. For such applications they have a significant advantage against turbine engines as far as purchase and maintenance cost is concerned. The proper and efficient operation of these engines in aviation applications is critical and therefore techniques that are used to determine engine condition and to detect potential faults are extremely important. The performance of these engines depends strongly on the condition of the ignition system and the quality of the supplied mixture. For this reason in the present work it is examined the effect of mixture AFR on the combustion mechanism and engine performance using an existing diagnostic methodology for spark ignited engines developed by the present research group. The investigation is conducted on a radial, spark-ignited reciprocating engine used on the CL-215 fire extinguishing aircraft. The diagnostic technique is used to investigate the effect of AFR on the main combustion and performance characteristics of the engine and specifically brake power output, rate of heat release, cumulative heat release, peak firing pressure, ignition and injection timing and duration of combustion. Furthermore the diagnostic technique is used to derive information for spark advance, spark duration, compression condition etc. The diagnostic technique is based on a thermodynamic two-zone combustion model for spark ignited engines. To examine the effect of AFR on the combustion mechanism a detailed experimental investigation was conducted on an engine (radial, supercharged, air-cooled, eighteen-cylinders) mounted on a test bench. The measurement procedure involved measurements at various operating conditions (load and speed) and various AFR values. During the experimental investigation beyond the conventional test bench measurements, measurements were taken using a fast data acquisition system of cylinder pressure and the electric signal of both spark plugs. Engine diagnosis is established by processing of these measured data. From the results of the diagnosis procedure it is revealed that the diagnosis method provides detailed information for the operating condition of the engine and the values of parameters that cannot be measured on the field. The diagnosis results reveal that the proposed technique can determine the effect of AFR ratio on the combustion mechanism adequately and thus it can be used during engine testing to determine the optimum AFR ratio in combination with the remaining engine settings and mainly spark advance. The results obtained are positive and reveal that the proposed diagnostic technique can be easily applied on any type of spark-ignited engine and especially on aircraft piston engines (i.e. aviation applications), where the accurate estimation of the engine condition and settings is extremely important.

Commentary by Dr. Valentin Fuster
2012;():583-595. doi:10.1115/ICES2012-81110.

One of the principal issues of alternative combustion modes for Diesel engines (such as HCCI, PCCI and LTC) is related to imbalances in the distribution of air and EGR across the cylinders, which ultimately cause significant differences in the pressure trace and indicated torque for each cylinder. In principle, a cylinder-by-cylinder control approach could compensate for air, residuals, and temperature imbalance. However, in order to fully benefit from closed-loop combustion control, it is necessary to obtain feedback from each engine cylinder to reconstruct the pressure trace. Therefore, cylinder imbalance is an issue that can be detected in a laboratory environment, wherein each engine cylinder is instrumented with a dedicated pressure transducer. The objective of the work in this paper is to estimating the individual in-cylinder pressure traces in a multi-cylinder engine, relying on a very restricted sensor set, namely a crankshaft speed sensor, a single production-grade pressure sensor. In doing so, a crankshaft model will be developed and a sliding mode observer will be employed to estimate the cylinder pressure using only crankshaft speed fluctuation measurement. Furthermore, as an added enhancement, the cylinder pressure signal from one cylinder will be utilized to adapt the friction and heat release parameters for more accurate estimation in all cylinders.

Commentary by Dr. Valentin Fuster
2012;():597-604. doi:10.1115/ICES2012-81111.

Engine manufacturers and researchers in the United States are finding growing interest among customers in the use of opportunity fuels such as syngas from the gasification and pyrolysis of biomass and biogas from anaerobic digestion of biomass. Once adequately cleaned, the most challenging issue in utilizing these opportunity fuels in engines is that their compositions can vary from site to site and with time depending on feedstock and process parameters. At present, there are no identified methods that can measure the composition and heating value in real-time. Key fuel properties of interest to the engine designer/researcher such as heating value, laminar flame speed, stoichiometric air to fuel ratio and Methane Number can then be determined. This paper reports on research aimed at developing a real-time method for determining the composition of a variety of opportunity fuels and blends with natural gas. Interfering signals from multiple measurement sources are processed collectively using multivariate regression methods, such as, the principal components regression and partial least squares regression to predict the composition and energy content of the fuel blends. The accuracy of the method is comparable to gas chromatography.

Topics: Fuels , Heating
Commentary by Dr. Valentin Fuster
2012;():605-614. doi:10.1115/ICES2012-81138.

Many modern engine systems are designed using one-dimensional computational fluid dynamics (1D CFD). This same technique can be used to model these systems in real time. This real-time model can be used to create virtual sensors in places where due to environmental or cost reasons physical sensors would not be practical. Achieving real-time performance of the CFD model requires more throughput than is available on single processor systems, so an Field Programmable Gate Array (FPGA) is employed. By employing an FPGA, we can synthesize and reconfigure our system to ensure determinism and lower resource usage. We instantiate several dedicated processing cores for parallel processing of sub-volumes. The number of cores can be configured to support up to 500 fluid volumes, more than enough for common 1D CFD models used in engines. This paper evaluates the feasibility of such a system and evaluates the complexity of such models against the GT-SUITE simulation software.

Commentary by Dr. Valentin Fuster
2012;():615-626. doi:10.1115/ICES2012-81166.

A first-order lumped-parameter model for the prediction of thermal behavior of a single-cylinder gasoline engine for Hybrid Electric Vehicles (HEVs) has been implemented. The model is coupled with a zero-dimension in-cylinder model that evaluates the working cycle of the engine according to the actual operating conditions and calculates the temperature of the exhaust gases, the overall efficiency of the engine and the exhaust gases flow rate. The model takes into account the possibility of using exhaust gas heat recirculation in order to enhance engine warm-up during cold start which improves its efficiency. The supervisory strategy takes into account not only predicted speed and ambient and road conditions along a future time window but also actual battery state of the charge and engine temperature to select the optimal power split between the ICE-generator group and the batteries. The proposed model represents an improvement with respect to a previous investigation of the authors where the temperature of the engine were assumed to increase/decrease of on Celsius degree in each seconds according to the state of the engine (ON/OFF).

Commentary by Dr. Valentin Fuster
2012;():627-634. doi:10.1115/ICES2012-81173.

In this paper, a new hydraulic variable valve actuation system is proposed. Using this system, the engine valve opening and closing timings and lift are flexibly controlled with two rotary spool valves actuated by the engine crankshaft. High degree of flexibility with less control complexity and high repeatability are the advantages of this system over other camless valvetrains; however, in this system, there is a trade-off between its robustness and power consumption. A numerical model of the system is developed to study the system functionality at different operating conditions. To validate the developed model, the simulation results for a random operating condition are compared with those from the experiments. A sensitivity analysis is done to study the effects of variations in different design parameters on system robustness and power consumption. The results prove that increasing engine valve return-spring stiffness and actuator piston area will reduce the mechanism sensitivity to engine cycle-to-cycle variations; however, this results in poor energy efficiency. Therefore, a neat energy recovery strategy is developed to recuperate a portion of the energy used to compress the engine valve return-spring during valve opening interval. The results show that more than 90% of the extra energy wasted for the sake of system robustness could be regenerated through the proposed energy recovery system.

Commentary by Dr. Valentin Fuster
2012;():635-644. doi:10.1115/ICES2012-81189.

A two-degree freedom air fuel ratio controller (Model based feed forward transient plus closed loop Proportional-Integral-Derivative (PID) steady state controllers) developed for controlling the air fuel ratio of the charge in a small displacement (125 CC) SI engine is presented. The feed forward controller’s airflow and injector models were developed after conducting extensive experiments on the engine modified for the Port Fuel Injection (PFI) operation. A dynamic air fuel ratio model obtained (air fuel ratio changes measured using an UEGO sensor) by injecting the Pseudo Random Binary Signal (PRBS) signal in addition to base line fuel injection pulse, was used for designing the PID controller. Optimal PID gain values were identified using Nelfer-Mead optimization technique. The control algorithms were implemented and optimized using SIMULINK blocks that are run under dSPACE on the MicroAuto box hardware. The optimized control algorithms were ported on the specially designed, in-house built, low cost engine management system (EMS) developed around an 8-bit microcontroller. The spark timing was also controlled simultaneously for knock free operation. The two-degree freedom air fuel ratio controller could maintain the air fuel ratio under steady and transient conditions closely. High thermal efficiency and low HC & NOx emissions were achieved using the developed EMS. At higher speed elevated NOx emission was observed, due to the use of leaner mixture. The improvements are expected to be higher if a suitable smaller injector is used.

Commentary by Dr. Valentin Fuster
2012;():645-658. doi:10.1115/ICES2012-81211.

Diesel engines have to meet stringent emissions standards without penalties in performance and fuel economy. This necessitated the use of elaborate after treatment devices to reduce the tail pipe emissions. In order to decrease the demand on the after treatment devices, there is a need to reduce the emissions in the formation stage during combustion. This requires a precise control of the phasing of the combustion process. Currently, diesel engines are controlled by pre-set open loop schedules that require extensive, time consuming and costly laboratory tests and calibration tasks to meet the production target goals which are stricter than the emission standards. Such goals are set as a safe guard against the deterioration during engine life cycle. This paper presents an incremental fuzzy logic controller that adjusts the combustion phasing as per desired targets to meet production goals over the engine life period. An ion current/ glow plug sensor and its circuit are used to produce a signal indicative of different combustion parameters. Signal conditioning and filtering are applied to improve the quality of ion current.

The algorithm developed in this paper optimizes the ion current feed back to increase its reliability for stable engine control while maintaining fast controller response, and high accuracy. Experiments are carried out on a four cylinder, turbo-charged, 4.5L heavy duty diesel engine equipped with a common rail injection system and an open ECU. The response of the controller is evaluated from experimental data obtained by running the engine under different steady, and transient operating conditions. The results demonstrate the ability of the closed-loop control system in achieving the desired combustion phasing.

Commentary by Dr. Valentin Fuster
2012;():659-666. doi:10.1115/ICES2012-81235.

This work constitutes one of the last steps of a comprehensive research program in which vibration sensors are used with the purpose of developing and setting up a methodology that is able to perform a real time control of the combustion process by means of non-intrusive measurements.

Previous obtained and published results have demonstrated that a direct relationship exists between in-cylinder pressure and engine block vibration signals. The analysis of the processed data have highlighted that the block vibration signal may be used to locate, in the crank–angle domain, the combustion phases (the start of the combustion, the crank angle value corresponding to the beginning of main combustion and to the in-cylinder pressure maximum value) and to quantify the in-cylinder pressure development by evaluating the pressure peak value and the pressure rise rate caused by the combustion process.

The aim of this work is to extend and validate the developed methodology when a multiple-injection strategy is imposed on the engine.

The paper presents the results obtained during the experimentation of a two cylinder diesel engine equipped with a common rail injection system, that was performed in the Laboratory of the Mechanical and Industrial Department of ‘ROMA TRE’ University. During the tests, a wide variation of the injection parameters settings is imposed on the engine (timing and duration) in its complete operative field.

Commentary by Dr. Valentin Fuster

Numerical Simulation

2012;():667-672. doi:10.1115/ICES2012-81045.

Fuel efficiency is now the over-riding engine development objective. With approximately 50–60% of the input fuel energy in an internal combustion engine lost through thermal and mechanical inefficiencies, friction has been targeted as the arch nemesis in any engine development program. A significant portion of the parasitic frictional losses is due to the top compression ring. This suggests that optimization of tribological performance of the compression ring conjunction warrants much more attention that it has been hitherto afforded. Studies reported thus far take into account ring-bore conformance, based on static fitment of the ring within an out-of-round bore, whose out-of-circularity is affected by manufacturing processes, surface treatment and assembly. The various static fitment analyses presume quasi-static equilibrium between ring tension and gas pressure loading with the generated conjunctional pressures. This is an implicit assumption of ring rigidity whilst in situ, which is in fact not the case in practice. The transient nature of combustion variation means that mere static or quasi-static force balance is inappropriate. Furthermore, the bore is not a right circular cylinder. Thus, its radial cross-sectional out-of-roundness and its axial variation introduce further transience in the ring-bore conformance. Consequently, the net force applied to the ring induces its modal behaviour, which accounts for its instantaneous in situ shape within the bore. These considerations are not taken into account in the often idealized ring-bore tribology. The paper provides transient solution of ring-bore conjunction, when subjected to ring in-plane modal behavior, when the conjunction is subjected to a mixed regime of lubrication, comprising hydrodynamic viscous action and boundary interactions.

Commentary by Dr. Valentin Fuster
2012;():673-680. doi:10.1115/ICES2012-81065.

The aim of the present work is to investigate the possibility of using eucalyptus biodiesel and its blends with diesel fuel as an alternative fuel for diesel engines. Eucalyptus oil is converted to biodiesel with ethanol using sodium hydroxide as a catalyst. The characterization of the obtained biodiesel shows that the thermo-physical properties are in the range recommended by American Standard (ASTM D6751). Innovative biodiesel development tests on the diesel engine require a lot of time and efforts. Here, mathematical model, which is based on the thermodynamic single zone model, is developed to analyze the combustion characteristics such as cylinder pressure and the performance characteristics such as brake power, brake thermal efficiency and specific fuel consumption of a DI diesel engine.

Commentary by Dr. Valentin Fuster
2012;():681-690. doi:10.1115/ICES2012-81068.

The aim of this work is the study of the fluid dynamic structure of underexpanded hydrogen jets by using a High Performance Computing (HPC) methodology. An axial symmetric two-dimensional turbulent flow model, which solves the Favre-averaged Navier-Stokes equations for a multicomponent gas mixture, has been implemented and validated. In order to predict the decrease in spreading rate with increasing Mach number, a compressibility correction has been added to the turbulence closure model.

The flow model has been assessed by comparing spreading and centerline property decay rates of subsonic jets at different Mach numbers with those obtained both by theoretical considerations and experimental measurements. Besides, the Mach disk structure of an underexpanded jet has been analysed, thus confirming the suitability of the computational model.

To take into account the effects of real gases, both van der Waals and Redlich-Kwong equations of state have been implemented. The computations performed under ICEs conditions show that the values of Mach number and pressure just behind the Mach disk are affected by the use of real gas equations.

Commentary by Dr. Valentin Fuster
2012;():691-702. doi:10.1115/ICES2012-81074.

This paper presents an application of the mean value combustion model to simulate large bore turbocharged diesel engines, coupled with large electric AC synchronous generators, to mimic power generation within a training simulator for a ship board electrical power system. A mean value engine model has been developed to simulate the most prevalent phenomena occurring in diesel direct injection internal combustion engines. The combustion process is modeled as a mean value system where characteristics of combustion are averaged over the entire cycle. Detailed models of the air intake, fuel delivery, and internal/external cooling systems have been developed using concepts from fluid dynamics and thermodynamics. The engine model has been created in MATLAB® Simulink® to simulate actual hardware signals sent to the power management controller to facilitate the development of the power system trainer. The model has been structured so that it is highly adaptable and is capable of simulating a wide variety of engine bore sizes and cylinder numbers which has significantly increased the utility of the work presented herein.

Commentary by Dr. Valentin Fuster
2012;():703-714. doi:10.1115/ICES2012-81078.

Inner nozzle flow characteristics (e.g., cavitation, turbulence, injection velocity) are known to affect spray development and hence combustion and emissions. Our previous studies showed that petrodiesel and biodiesel (soybean-based fuels) had very different cavitation and turbulence characteristics, which caused differences in spray breakup, penetration, dispersion, etc. Specifically, the atomization characteristics of biodiesel were worse than those of diesel; they were a direct consequence of biodiesel’s reduced cavitation and turbulence levels at the nozzle exit. In this study, the nozzle flow characteristics of biodiesel (from different feedstocks like tallow, soy, rapeseed, cuphea, and hydrotreated vegetable oil [HVO]) were compared with those of diesel. The first step was to obtain data on the physical properties of these fuels (e.g., their density, viscosity, surface tension, vapor pressure) at different temperatures. At full-needle open position, the cavitation contours scaled with the vapor pressure and viscosity; hence, methyl esters such as soy (SME), rapeseed (RME), and tallow (TME) exhibited less cavitation. The nozzle discharge coefficient, exit velocity, turbulent kinetic energy, and dissipation rate at the orifice exit were also compared for these fuels. Transient effects due to needle movement upon the inception of cavitation were studied. The effects of different needle-lift profiles (pertaining to various load conditions) on the nozzle flow development of these fuels were also characterized. This study also provides data on the critical boundary conditions for spray simulations from using the Kelvin Helmholtz-aerodynamic cavitation turbulence (KH-ACT) model, which accounts for cavitation and turbulence-induced breakup in addition to aerodynamic breakup.

Commentary by Dr. Valentin Fuster
2012;():715-725. doi:10.1115/ICES2012-81095.

For increasing the thermal engine efficiency, faster combustion and low cycle-to-cycle variation are required. In PFI engines the organization of in-cylinder flow structure is thus mandatory for achieving increased efficiency. In particular the formation of a coherent tumble vortex with dimensions comparable to engine stroke largely promotes proper turbulence production extending the engine tolerance to dilute/lean mixture. For motorbike and scooter applications, tumble has been considered as an effective way to further improve combustion system efficiency and to achieve emission reduction since layout and weight constraints limit the adoption of more advanced concepts. In literature chamber geometry was found to have a significant influence on bulk motion and turbulence levels at ignition time, while intake system influences mainly the formation of tumble vortices during suction phase. The most common engine parameters believed to affect in-cylinder flow structure are:

1. Intake duct angle;

2. Inlet valve shape and lift;

3. Piston shape;

4. Pent-roof angle.

The present paper deals with the computational analysis of three different head shapes equipping a scooter/motorcycle engine and their influence on the tumble flow formation and breakdown, up to the final turbulent kinetic energy distribution at spark plug. The engine in analysis is a 3-valves pent-roof motorcycle engine. The three dimensional CFD simulations were run at 6500 rpm with AVL FIRE code on the three engines characterised by the same piston, valve lift, pent-roof angle and compression ratio. They differ only in head shape and squish areas. The aim of the present paper is to demonstrate the influence of different head shapes on in-cylinder flow motion, with particular care to tumble motion and turbulence level at ignition time. Moreover, an analysis of the mutual influence between tumble motion and squish motion was carried out in order to assess the role of both these motions in promoting a proper level of turbulence at ignition time close to spark plug in small 3-valves engines.

Commentary by Dr. Valentin Fuster
2012;():727-743. doi:10.1115/ICES2012-81101.

Over a significant period of time, efforts have been made towards a valid and accurate estimation of DI diesel engine NOx emissions. Considering the fact that experiments have a high cost in both time and money, modelling approaches have been developed in an effort to overcome these issues. It is well known that accuracy in the prediction of NOx emissions lies specifically on the accurate estimation of local temperature and O2 histories inside the combustion chamber that govern NOx formation, fulfilled by an accurate estimation of the combustion mechanism. To account for the actual effect of parameters that control NOx formation and overcome inefficiencies introduced from existing purely empirical models or artificial neural networks, valid only on the combustion systems for which they were developed [1], an alternative solution is the introduction of physically based semi-empirical models. Towards this direction, in the present work is presented and evaluated a new modelling approach, based on the combustion rate obtained from the measured cylinder pressure trace using Heat Release Rate Analysis. The model used is a semi-empirical two-zone one which makes use of the estimated elementary fuel mass burnt at each crank angle interval. The combustion process is considered to be adiabatic, while chemical dissociation is also considered. With this approach, temperature distribution throughout the combustion chamber is considered for, together with its evolution during the engine cycle. In addition, O2 availability is also considered for through the calculated charge composition. The result is an extremely fast computational model, combining the advantages of both empirical and physically based ones. In the present work is given a detailed validation of the model, from its application on two different types of diesel engines: a heavy-duty DI diesel engine and a light-duty DI diesel engine with pilot fuel injection. A significant number of cases where tested for both engine configurations, considering different operation points and variation of operating parameters, such as rail pressure and EGR. The twelve points of the European Stationary Cycle (ESC) were covered for the case of the heavy duty DI diesel engine, whilst for the light-duty DI engine a total number of forty-six operating points was studied. For both engine configurations the model reveals a very good predictive ability, considering for the effect of all operating parameters examined on NOx emissions. However, there is potential for improvement and development on its physical base for even more accurate predictions. The merits of good accuracy in prediction trends with varying engine operating parameters — even without calibration — and low computational time establish a potential for model use in engine development, optimization studies and model based control applications.

Commentary by Dr. Valentin Fuster
2012;():745-754. doi:10.1115/ICES2012-81104.

This work deals with the analysis of the performance and emissions of ethanol HCCI/PSCCI engines by means of a Dynamic Adaptive Chemistry (DAC) technique. The implementation of such a technique provides a reduction of the computational cost of the simulations without compromising the reliability of the results. Very accurate results, in terms of pressure and heat release rate profiles and CO, CO2 and UHC emissions, are obtained with ethanol as the only species for the DRGEP graph search both with the charge uniformly distributed in the combustion chamber and by directly injecting liquid fuel in the same chamber. The global speed up of DAC simulations is twice with respect to a full mechanism which consists of 57 species and 288 reactions and a further increase is expected when DAC is compared to very detailed kinetics.

Commentary by Dr. Valentin Fuster
2012;():755-764. doi:10.1115/ICES2012-81119.

Today, Reynolds Averaged Navier Stokes (RANS) simulation approach remains the most widely used method in computational fluid dynamic studies of IC-Engines because it allows a good prediction of the mean flow properties at an affordable computational cost. The main limit of the RANS approach resides in the method used to predict turbulence that fails in the reproduction of anisotropic turbulence conditions. It can result in a lack of accuracy in reproducing the main physical processes, as spray evolution (mixture formation), heat transfer, and combustion, governing the IC-Engine physics. To fix this problem, the large Eddy Simulation (LES) approach can be considered.

In LES the governing equations are filtered in space, rather than time-averaged as in RANS. It allows the direct solution of all the turbulent scales up to a cut-off length defined by the filter dimension. Therefore, in LES a more accurate description of the turbulence and of all the physical processes correlated to it has to be expected. However, even if the LES method allows an irrefutable improvement in turbulent flow solution accuracy, today its application to industrial IC-Engine design is still rare because of its high computational cost.

During the last few years, significant advances in numerical methods, sub-grid scale models, and hardware performance have supported LES applications in many industrial fields. This paper is intended to work in the same direction by presenting a new LES methodology based on the coupling between LES and an adaptive mesh refinement (AMR) procedure. The main goal of this procedure is to guarantee a good resolution of the turbulent flow field adapting the filter size to the local turbulence length scale. The developed procedure allows a significant reduction of the total mesh size and, therefore, of the computational cost. The LES-AMR method was tested on an IC-Engine geometry for which experimental results were available.

Commentary by Dr. Valentin Fuster
2012;():765-773. doi:10.1115/ICES2012-81120.

The injection of small amount of diesel fuel is mainly achieved through the shortening of energizing signal. Consequently, in such injection phases, the needle does not reach the mechanical stroke-end and its displacement may be defined as ballistic.

By means of a detailed 3D-CFD modeling, the behavior of nozzle flow is investigated under typical pilot/split injection conditions, namely high injection pressure and low needle lift. The investigation focuses on the effects of the restricted flow passage on fuel flow at hole inlets. Once the modeling details are described, the influence of different elements on the internal fuel flow is shown and discussed, pointing out the role of different driving factors; investigations take into account actual injector tip layouts and the response to the needle off-axis operating conditions. Results are presented highlighting the flow pattern features within the nozzle and their reflects on the hole-to-hole differences.

Commentary by Dr. Valentin Fuster
2012;():775-783. doi:10.1115/ICES2012-81137.

High-Speed Direct Injection (HSDI) diesel engines are increasingly used in automotive applications due to superior fuel economy. An advanced CFD simulation has been carried out to analyze the effect of injection timing on combustion process and emission characteristics in a four valves 2.0L Ford diesel engine. The calculation was performed from intake valve closing (IVC) to exhaust valve opening (EVO) at constant speed of 1600 rpm. Since the work was concentrated on the spray injection, mixture formation and combustion process, only a 60° sector mesh was employed for the calculations. For combustion modeling, an improved version of the Coherent Flame Model (ECFM-3Z) has been applied accompanied with advanced models for emission modeling. The results of simulation were compared against experimental data. Good agreement of calculated and measured in-cylinder pressure trace and pollutant formation trends were observed for all investigated operating points. In addition, the results showed that the current CFD model can be applied as a beneficial tool for analyzing the parameters of the diesel combustion under HSDI operating condition.

Commentary by Dr. Valentin Fuster
2012;():785-795. doi:10.1115/ICES2012-81150.

Porous media (PM) has interesting advantages in compared with free flame combustion due to the higher burning rates, the increased power range, the extension of the lean flammability limits, and the low emissions of pollutants. Future clean internal combustion (IC) engines should have had minimum emissions level (for both gaseous and particulate matter) under possible lowest fuel consumption permitted in a wide range of speed, loads and having good transient response. These parameters strongly depend on mixture formation and combustion processes which are difficult to be controlled in a conventional engine. This may be achieved by realization of homogeneous combustion process in engine. This paper deals with the simulation of direct injection IC engine equipped with a chemically inert PM, with cylindrical geometry to homogenize and stabilize the combustion of engine. A 3D numerical model for PM engine is presented in this study based on a modified version of the KIVA-3V code. Due to lack of any published data for PM engines, numerical results of thermal and combustion wave propagation in a porous medium are compared with experimental data of lean methane-air mixture under filtration in packed bed and very good agreement is seen. For PM engine simulation methane as a fuel is injected directly inside hot PM that is assumed, mounted in cylinder head. Lean mixture is formed and volumetric combustion occurs in PM and in-cylinder. Mixture formation, pressure and temperature distribution in both phases of PM and in-cylinder fluid with the production of pollutants CO and NO and also effects of injection time in the closed part of the cycle are studied.

Commentary by Dr. Valentin Fuster
2012;():797-808. doi:10.1115/ICES2012-81153.

Due to the vast resources of natural gas (NG), it has emerged as an alternative fuel for SI internal combustion engines in recent years. The need to have better fuel economy and less emission especially that of greenhouse gases has resulted in development of NG fueled engines. Direct injection of natural gas into the cylinder of SI internal combustion engines has shown great potential for improvement of performance and reduction of engine emissions especially CO2 and PM. Direct injection of NG into the cylinder of SI engines is rather new thus the flow field phenomena and suitable configuration of injector and combustion chamber geometry has not been investigated completely.

In this study a numerical model has been developed in AVL FIRE software to perform investigation of direct natural gas injection into the cylinder of spark ignition internal combustion engines. In this regard, two main parts have been taken into consideration aiming to convert an MPFI gasoline engine to direct injection NG engine. In the first part of study multidimensional numerical simulation of transient injection process, mixing and flow field have been performed via different validation cases in order to assure the numerical model validity of results. Adaption of such a modeling was found to be a challenging task because of required computational effort and numerical instabilities. In all cases present results were found to have excellent agreement with experimental and numerical results from literature.

In the second part, using the moving mesh capability, the validated model has been applied to methane injection into the cylinder of a direct injection engine. Five different piston head shapes have been taken into consideration in investigations. An inwardly opening multi-hole injector has been adapted to all cases. The injector location has been set to be centrally mounted. The effects of combustion chamber geometry have been studied on mixing of air-fuel inside cylinder via quantitative and qualitative representation of results. Based on the results, suitable geometrical configuration for a NG DI engine has been discussed.

Commentary by Dr. Valentin Fuster
2012;():809-827. doi:10.1115/ICES2012-81162.

A master combustion mechanism of biodiesel fuels has recently been developed by Westbrook and co-workers [1]. This detailed mechanism involves 5037 species and 19990 reactions, the size, which prohibits its direct use in computational fluid dynamic (CFD) applications. In the present work, various mechanism reduction methods included in the Reaction Workbench software [2] were used to derive a semi-detailed reduced combustion mechanism maintaining the accuracy of the master mechanism for a desired set of engine conditions. The reduced combustion mechanism for a five-component biodiesel fuel was implemented in the FORTÉ CFD simulation package [3] to take advantage of advanced chemistry solver methodologies and advanced spray models. The spray characteristics, e.g. the liquid penetration and flame lift-off distances of RME fuel were modeled in a constant-volume combustion chamber. The modeling results were compared with the experimental data. Engine simulations were performed for the Volvo D12C heavy-duty diesel engine fueled by RME on a 72° sector mesh. Predictions were validated against measured in-cylinder parameters and exhaust emission concentrations. The semi-detailed mechanism was shown to be an efficient and accurate representation of actual biodiesel combustion and emissions formation. Meanwhile, as a comparative study, the simulation based on a detailed diesel oil surrogate mechanism were performed for diesel oil under the same conditions.

Commentary by Dr. Valentin Fuster
2012;():829-836. doi:10.1115/ICES2012-81176.

A renewed interest in CNG fuelled engines, which has recently been boosted by the even more stringent emissions regulations, has generated considerable R&D activity in the last few years. In order to fulfill such limits, most current CNG vehicles combine advanced technical and control solutions such as VVA intake systems, new turbocharging solutions, enhanced ECU strategies, etc. The present work focuses on the complete fluid-dynamic characterization of a gaseous injection system so as to support the design of the related control module and devices. To that end, a numerical investigation into the fluid-dynamic behavior of a commercial CNG injection system has been extensively carried out by means of the GT-POWER code.

A detailed geometrical model including the rail, the injectors as well as the pipe connecting the pressure regulator to the rail has been built in the GT-POWER environment. The model has been validated by comparing the experimental to the numerical outputs for the rail pressure and for the injected mass quantity. The model has hence been applied to the prediction of the pressure waves produced by the injection event and of their effect on the actually injected fuel mass. Moreover, the influence of the pressure regulator dynamics has been assessed by simulating the impact on the system behavior of a pressure noise downstream from the regulator. Finally, the possibility of reducing the rail volume, thus enhancing its dynamic response, has been investigated.

The results have shown a good agreement between the predicted and the measured rail pressure and injected fuel mass flow rates over a wide range of engine operation conditions. Moreover, the dynamic simulations sketched a dependence of the injected fuel mass on the average rail pressure level, which in turn appeared to reduce for increasing engine power outputs. Finally, the reduction in the rail volume has proved not to significantly affect the injected mass flow rate.

Topics: Fluids
Commentary by Dr. Valentin Fuster
2012;():837-850. doi:10.1115/ICES2012-81181.

Increasing demands on the capabilities of engine simulation and the ability to accurately predict both performance and acoustics has lead to the development of several numerical tools to help engine manufacturers during the prototyping stage. One dimensional simulation tools are widely used during this phase and they allow the simulation of several engine configurations within a short time. Certain components, however, such as the intake and exhaust manifolds, exhibit a high degree of geometric complexity, which cannot be accurately modelled by ID codes, unless equivalent ID models are adopted. The need of achieving good accuracy, along with acceptable computational runtime, has given the spur to the development of a geometry based quasi-3D approach. This is designed to model the acoustics and the fluid dynamics of both intake and exhaust system components used in internal combustion engines. Models of components are built using a network, or grid, of quasi-3D cells based primarily on the geometry of the system. The solution procedure is an explicitly time marching pseudo staggered grid approach, where the equations of mass and energy are solved at cell centers while the momentum equation at cell connections or boundaries. The quasi-3D approach has been fully integrated into a ID research code in order to study the behavior of intake and exhaust devices under real engine pulsating flow conditions. This approach was mainly developed to model the acoustic behavior of complex shape silencers, however, in this work it has been extended and applied to the prediction of the fluid dynamic behavior of intake and exhaust systems. The validation was carried on a high performance V4 motorbike engine. In particular, the silencer and the air box have been modeled resorting to a quasi-3D reconstruction. Calculated results of instantaneous pressure traces and volumetric efficiency have been compared to measured data, highlighting a good capability in capturing dynamic effects with a computational runtime much lower than the one required by the integration of fully 3D models with the ID.

Commentary by Dr. Valentin Fuster
2012;():851-862. doi:10.1115/ICES2012-81186.

In the last few years, a significant research effort has been made for developing and enhancing Direct Injection (DI) for compressed natural gas (CNG) engines. Several research projects have been promoted by the European Community (EC) in this field with the objective of finding new solutions for the automotive market and also of encouraging a fruitful knowledge exchange among car manufacturers, suppliers and technical universities.

This paper concerns part of the research activity that has been carried out by the Politecnico di Torino, AVL List GmbH and Siemens AG within the EC VII Framework Program (FP) InGAS Collaborative Project (CP), aimed at optimizing the control phase of a new injector for CNG direct injection, paying specific attention to its behavior at small injected-fuel amounts, i.e., small energizing times. The CNG injector which was developed within the research project proved to be suitable to be used in a DI SI engine, featuring a pent-roof combustion chamber head and a bowl in piston, with reference to both homogeneous and stratified charge formation. Fuel flow measurements made by AVL on the four-cylinder engine revealed a good linearity between injection duration and fuel mass-flow rate for injection durations above a reference value.

In order to improve the injector characterization at short injection durations, an experimental and numerical activity was designed. More specifically, a multidimensional CFD model of the actual injector geometry was built by Politecnico di Torino, and purposely-designed simulation cases were carried out, in which the needle-lift time-history was defined on the basis of experimental measurements made by Siemens. The numerical model was validated on the basis of experimental data concerning the total injected-fuel amount under different conditions. Then, the model was applied in order to evaluate the dynamic flow characteristic by taking also the inner geometry of the injector valve group into account, so as to establish a correlation to the needle lift measurements done by Siemens for injector characterization.

In the paper this dynamic behavior of the injector is analyzed, under actual operating conditions, and its impact on the nozzle injection capability is discussed. The simulation results did not show significant oscillations of the stagnation pressure upstream of the nozzle throat section, and thus the resultant mass-flow rate profile is almost proportional to the needle-lift one. As a consequence, in order to characterize the injector flow behavior in the nonlinear region (short injection duration), the measurement of needle lift is sufficient.

Commentary by Dr. Valentin Fuster
2012;():863-874. doi:10.1115/ICES2012-81217.

Nowadays, environmental concerns are posing a great challenge to DI Diesel engines. Increasingly tightening emission limits require a higher attention on combustion efficiency. In this scenario, computational fluid-dynamics can prove its power guaranteeing a deeper understanding of mixture formation process and combustion. A high efficiency Diesel engine can be developed only mastering all the parameters that can affect the combustion and, therefore, NOx and soot emissions. In this work, the development of an engine in order to fulfill Tier 4i emission standard will be presented. Originally, the engine was a two-valve engine supplied with a DPF. Since no SCR aftertreatment is supplied, NOx emission target are achieved through external exhaust gas recirculation and retarding the start of injection. In order to fulfill Tier 4i emissions, the main concern is on soot emission and, thus, the combustion chamber has been re-designed, through CFD simulations, leading to a better interaction between the flow field, the fuel spray and the piston bowl geometry.

Particularly, through intake phase simulations, performed with the CFD code Fire v2009 v3, different intake ducts, with different swirl ratio, have been simulated in order to provide a flow field as realistic as possible for the combustion simulations. Through combustion process simulations, performed with the CFD code Kiva, by varying different parameters the interaction between the swirl flow field, generated by the intake duct, the reverse squish motion, and motions aerodynamically generated by spray has been investigated leading to the definition of a new engine lay-out. The study shows how, given the need of retarded injection for limiting NOx emission, the decrease of swirl ratio, when combined with a proper piston bowl design, allows a significant decrease of soot emissions and the achievement of Tier 4i emission standard.

Commentary by Dr. Valentin Fuster
2012;():875-883. doi:10.1115/ICES2012-81218.

Transient operation of engines leads to air fuel (A/F) ratio excursions, which can increase engine emissions. These excursions have been attributed to the formation of fuel films in the intake port, which are caused by a portion of the intake fuel impinging and adhering on the relatively cool port surface. These films act as a source or sink which cause the AF variations depending upon the transient condition. Gaining a fundamental understanding of the nature and quantity of such films may assist in future fuel mixture preparation designs that could aid in emission reductions, yet would not require overly expensive nor complicated systems.

The control of air to fuel ratio is a critical issue for high performance engines: due to the low stroke-to-bore ratio the maximum power is reached at very high regimes, letting little time to the fuel to evaporate and mix with air. The injector located upstream the throttle causes a lot of fuel to impinge the throttle and intake duct walls, slowing the dynamics of mixture formation in part load conditions.

The aim of this work is to present a CFD methodology for the evaluation of mixture formation dynamics applied to a Ducati high performance engine under part load conditions.

The phenomena involved in the process are highly heterogeneous, and particular care must be taken to the choice of CFD models and their validation. In the present work all the main models involved in the simulations are validated against experimental tests available in the literature, selected based on the similarity of physical conditions of those of the engine configuration under analysis.

The multi-cycle simulation methodology here presented reveals to be a useful tool for the evaluation of the mixture dynamics and for the evaluation of injection wall film compensator models.

Commentary by Dr. Valentin Fuster

Mechanical Design, Analysis, Vibration, and Lubrication

2012;():885-892. doi:10.1115/ICES2012-81021.

One of the key conjunctions in the IC engine is that made by the top compression ring to the cylinder liner. Although the compression ring has seen considerable improvements since its introduction into steam engines by John Ramsbottom in the 1850s, its multiple and often contradictory functions still remain a challenge today. The primary aim has always been to seal the combustion chamber and guard against leakage of combustion gasses. The ring is also required to conduct some of the generated heat away. These requirements call for good ring-bore conformance, but often at the expense of increased friction.

A simplified inter-ring gas flow model, as well as the measured chamber pressure using a Kistler pressure transducer is carried out under motored conditions to obtain the net gas pressure acting behind the ring. This and the elastic pressure as the result of ring restoring tension force in fitment constitute the contact load, which is usually carried by a mixed-hydrodynamic regime of lubrication. The conjunction pressures are treated as a combination of hydrodynamic generated pressures and asperity-pair interactions. The former is obtained by solution of two dimensional Reynolds equation, whilst the latter is determined assuming a Gaussian distribution of asperities on the counterfaces. Surface topography of the bounding solids; the compression ring and the liner are measured and used as appropriate statistical functions in the Greenwood and Tripp model.

Using an analytical flow model, pressure acting behind the ring (on the inner periphery of the ring) is obtained, leading to the calculation of ring-bore friction. A floating liner is used to measure friction of piston and ringpack in situ. The characteristic of the predicted variations are compared with the measured data. However, a quantitative comparison is not possible as the measured data corresponds to all the conjunctions of piston system, including the oil control rings as well as the piston skirt. The results show that variation of gas force behind the ring significantly changes the ring-bore contact, thus friction and the nature of interactions.

Commentary by Dr. Valentin Fuster
2012;():893-900. doi:10.1115/ICES2012-81026.

An experimental investigation has been carried out on a diesel 1000 cc, two-valve, three-cylinder, engine for heavy quadricycle and off-road applications. The engine was equipped with a unit-pump common rail injection system, automotive derived, with maximum pressure 140 MPa and ECU able to manage multinjection strategies in Euro 4 target for the foreseen applications.

Experimental investigations on the fuel spray have been carried out in an optically accessible vessel at engine gas density. Spatial and temporal spray behavior has been studied by image processing of the evolving jet pictures. Spray tip penetrations, cone angles and fuel spatial density analysis have been extracted and correlated to the injection and engine parameters. On the other side, visible flame propagation and soot formation process have been evaluated by digital imaging at high spatial and temporal resolution using a quartz window of the third cylinder obtained modifying the engine head. Strategies consisting of two injections per cycle, pilot and main, and typical of real engine working conditions have been investigated in the pressure range 43–116 MPa both in terms of injection rates and injected fuel dispersion. The effects of different injection strategies on soot formation and exhaust emissions have been evaluated.

Commentary by Dr. Valentin Fuster
2012;():901-906. doi:10.1115/ICES2012-81028.

The regime of lubrication changes in a transient manner in many load bearing conjunctions. This is particularly true of any conjunction which is subjected to changes in contact kinematics as the result of stop-start or motion reversals and loading. One such conjunction in the IC engine is the piston-bore contact. A repercussion of these transient events under otherwise perceived steady operating condition is the underlying changes in the mechanisms giving rise to engine efficiency, such as parasitic losses, mainly due to friction. Understanding the nature of these losses is the prelude to any form of palliation.

A single cylinder motocross motorbike engine’s cylinder barrel is redesigned to accept wet liners with various incorporated instrumentation. The paper describes one such barrel which incorporates an instrumented floating liner for the purpose of measurement of in-cylinder friction. The principle and design of the floating liner is described. A series of tests are carried out in order to ensure the operational integrity and repeatability of the device. The basic test includes motorised running of the engine without the cylinder head installed. This renders simplified motion of the liner, subject to resistance by friction only. In a sense, under this type of motion, the liner should undergo a form of simple harmonic motion, which is verified using a number of suitably positioned accelerometers.

Some more representative tests are reported under motorised conditions with the cylinder head installed. Thus, the effect of chamber pressure is introduced. However, with no combustion pressure, heat output and resulting side forces, a better understanding of tribological conditions is accrued owing to the reduced physical interactions. The results show the dominance of a mixed regime of lubrication at the dead centre reversals.

Topics: Friction , Cylinders
Commentary by Dr. Valentin Fuster
2012;():907-916. doi:10.1115/ICES2012-81044.

Variable displacement lubricant pumps allow oil flow to be matched to engine requirements over the whole operating range, reducing energy losses through excessive pumping work. An experimental investigation has been performed on-engine to understand the effects of such devices. Significant instrumentation was fitted to the production, EURO IV specification, 2.4L Diesel engine to assess the impacts of lubricant flow on thermal state. The reduced oil flow was measured as a reduction in engine oil pressure with the production pump supplying 4–6bar whereas the variable flow device provided pressures as low as 1–2bar.

The reduction in oil flow significantly reduced the oil pump energy consumption, measured as a change in indicated work, resulting in a 4% benefit in fuel economy over both hot and cold start NEDC. The reduced oil flow also impacted oil and metal temperatures: during engine warm-up, oil temperatures were approximately 4°C colder with the lower flow as a result of less work input from the oil pump. Conversely, cylinder liner temperatures were 2–6°C hotter both during warm-up and fully warm conditions as a result of reduced piston cooling from piston cooling jets. The changes in thermal state were reflected by changes in emissions with a 3% increase in NOx and a 3–5% reduction in HC and CO.

The calibration of the variable flow device follows a fuel consumption/NOx trade-off that is more favourable to fuel economy than conventional control parameters. However, these benefits are strongly linked to engine duty cycle with larger benefits at higher engine speeds.

Commentary by Dr. Valentin Fuster
2012;():917-923. doi:10.1115/ICES2012-81050.

The tribology of cam-roller follower conjunction is highly dependent on the engine type and working conditions. The interface experiences transient conditions due to variations in contact geometry and kinematics, as well as loading. These lead to instantaneous and capricious behavior of the lubricant through the contact, which determines the regime of lubrication. The resulting frictional characteristics are affected by the shear of the lubricant film and the interaction of rough surfaces themselves. Thus, specific analysis is required for any intended new engine configuration. Therefore, a tribo-dynamic model, combining valve train dynamics, contact kinematics and tribological analysis is required. An important issue is to develop a simple yet reliable and representative model to address the above mentioned pertinent issues. This would make for rapid scenario-building simulations which are critical in industrial design time-scales.

The current model has been developed in response to the above mentioned requirements. A multi-body dynamic model for the valve train system based on the key design parameters is developed and integrated with an EHL tribological model for the cam-follower contact. To keep the model simple and easy to use and to avoid time-consuming computations, the analytical EHL model makes use of Grubin’s oil film thickness equation. Viscous and boundary contributions to friction are obtained as these account for the losses which adversely affect the engine fuel efficiency.

Commentary by Dr. Valentin Fuster
2012;():925-932. doi:10.1115/ICES2012-81052.

In order to investigate the possible environmental and economic benefits of lubricants optimized for stationary natural gas engine efficiency, a decision was made to develop a test stand to quantify the effects of lubricant viscosities and formulations on the brake specific fuel consumption.

Many fuel economy tests already exist for evaluating gasoline and heavy duty diesel motor oils which have proven the benefit of fuel economy from different lubricant formulations. These engines would not be suitable tools for evaluating the fuel economy performance of lubricating oils formulated specifically for stationary natural gas engines, since there are significant differences in operating conditions, fuel type, and oil formulations. This paper describes the adaptation of a Waukesha VSG F11 GSID as a tool to evaluate fuel consumption performance. The performance of brake specific fuel consumption when using different formulations was measured at selected high loads and rated speed.

The results of the testing program discuss the viscosity and additive effects of stationary natural gas engine oil formulations on brake specific fuel consumption. The results will detail the change in brake specific fuel consumption between natural gas engine oil formulations blended to varying viscosities and compared to a typical natural gas engine oil formulation with a viscosity of 13.8 cSt @ 100°C. The second portion of the test program explores the effect of different additive packages that were blended to the same finished oil viscosity.

It was acknowledged that there were statistical differences in brake specific fuel consumption characteristics between lubricants different in viscosity and additive formulations.

Commentary by Dr. Valentin Fuster
2012;():933-943. doi:10.1115/ICES2012-81090.

The paper proposes a cost-saving analytical methodology using empirical based models to efficiently evaluate design alternatives in the optimization of a CNG converted diesel engine. The procedure is performed in five steps. Firstly, a database of different combustion chambers that can be obtained from the original piston is obtained. The chambers in the database differ for the shape of the bowl, the value of the compression ratio, the offset of the bowl and the size of the squish region. The second step of the procedure is the selection, from the first database, of the combustion chambers able to resist to the mechanical stresses due to the pressure and temperature distribution at full load. For each combination of suitable combustion chamber shape and ignition timing, a CFD simulation is used to evaluate the combustion performance of the engine. Then, a post-processing procedure is used to evaluate the detonation tendency and intensity of each combination. All the tools developed for the application of the method have been linked in the ModeFrontier optimization environment in order to perform the final choice of the combustion chamber.

The overall process requires not more of a week of computation on the 4 processor servers considered for the optimization. Moreover, the selected chambers can be obtained from the original piston of the engine. Therefore, the conversion cost of the engine is quite small compared with the case of a completely new piston. The procedure can be applied to diesel engines to be converted to either CNG dedicated or dual fuel combustion. The main aspects and challenges to be taken into account in both cases are also analyzed.

Commentary by Dr. Valentin Fuster
2012;():945-956. doi:10.1115/ICES2012-81112.

In the past decade automotive industries have focused on the development of new technologies to improve the overall engine efficiency and lower emissions in order to satisfy the always more stringent emission standards introduced all around the world. Technical progress has primarily focused on two aspects; the optimization of the air-fuel mixture in the combustion chamber as well as the combustion process itself, leading to simultaneous improvements in both, efficiency (lowering fuel consumption for same power output) and emissions levels which ultimately result from the optimized combustion process. Although engine technology has made significant progress, even modern Diesel combustion engines do not exceed a maximum efficiency of approximately 40%. Hence, around 60% of the available energy carried by the fuel and entering the combustion chamber is dissipated as heat to the environment. The next steps in engine optimization will see the integration of waste heat recovery systems (WHRS) to increase the overall energy efficiency of the propulsion system by means of recovering parts of the waste heat generated during normal engine operation. The presented was aimed at analyzing the availability as well as the quality of heat to be used in WHRS for the case of heavy-duty Diesel (HDD) engines employed in Class-8 tractors, which are suitable candidates for optimization via WHRS implementation as their engines spend most of their time operating at quasi steady state conditions, such as highway cruise. Three different primary energy sources have been considered: exhaust gas recirculation (EGR) cooling system, engine cooling system and exhaust gas stream. Experimental data has been gathered at West Virginia University’s Engine and Emissions Research Laboratory (EERL) facility in order to quantify individual heat flows in a model year (MY) 2004 Mack® MP7-355E HDD engine operated over the 13 modes of the European Stationary Cycle (ESC). Analysis based on second law efficiency underlined that not the whole amount of waste heat can be successfully used for recovery purposes and that heat sources which offer a large amount of waste energy reveal to be inappropriate for recovery purposes in case of low operating temperature. Time integral analysis revealed that engine modes which appear to offer high recovery potential in terms of waste power may not be suitable engine operating conditions when the analysis is performed in terms of waste energy, depending on the particular engine cycle. Finally a simple thermodynamic model of a micro power unit running on an Organic Rankine Cycle (ORC) has been used to assess the theoretical improvement in engine efficiency during steady state operations based on a second law efficiency analysis approach.

Commentary by Dr. Valentin Fuster
2012;():957-963. doi:10.1115/ICES2012-81115.

The continuous focus on improving engine efficiency and fulfilling new emissions legislations in high speed large bore (HSLB) applications is demanding higher performance of cylinder power cell. Regarding piston rings, this can be translated into the need for increased wear and scuff resistance in conjunction with low friction. However, there is no room to jeopardize the engine performance in terms of lube oil control and combustion gas sealing (i.e. blow-by).

The reduction in ring friction is linked with three main factors: reduction of ring tangential load, reduction of ring axial width and use of low friction coefficient materials. To enable load and axial width reduction the use of a steel ring pack becomes almost mandatory. The structural strength of steel is needed in the narrower cross-section which at the same time requires good resistance to temperature and loads. For better wear resistance and lower friction coefficient the use of improved materials is important on all three rings in the pack. The improved performance of nitriding treatment and CrN PVD coatings will be presented.

Results indicate a potential ring friction reduction of more than 30% combined with wear improvements of up to 50% depending on the engine operation. Evaluations of rig and engine tests are presented supporting the technical case.

Topics: Steel
Commentary by Dr. Valentin Fuster
2012;():965-972. doi:10.1115/ICES2012-81121.

Exhaust manifold is an individual part of conventional internal combustion engines which is made of cast iron. Furthermore expensive alloys are needed to increase its thermal resistance. In the Integrated Exhaust Manifold into Cylinder Head (IEMCH), the exhaust manifold is manufactured as one part with the cylinder head. Thus its material changes from cast iron to aluminum which has a much lower thermal resistance than the cast iron. IEMCH has many advantages such as, low cost, lower weight and volume, less fuel consumption and faster warm-up. But due to its lower thermal resistance, it must be cooled.

Here a new exhaust manifold is designed for IEMCH. Thermo-fluid analysis is carried out numerically to evaluate temperature limitation of the new exhaust manifold. The obtained results are compared to the standard exhaust manifold which indicates that by means of cooling, the new exhaust manifold can be remained at its proper temperature limitation. Thus no expensive alloys are needed in the new exhaust manifold.

Commentary by Dr. Valentin Fuster
2012;():973-978. doi:10.1115/ICES2012-81125.

The in situ profiles of the piston skirt and cylinder bore surface are subject to thermo-elastic global deformation due to differential operating temperatures and forces. In operation, a lubricant film is entrained into and pressurized within the gap between these profiles. This film not only supports the prevailing contact load, but also inhibits direct interaction of surfaces, thus reducing friction and thereby improving fuel efficiency. The reduction of reciprocating mass in motorsport applications has been achieved through the use of partial circumferential skirts for a number of years now. The response of the shape to both mechanical and structural loadings differs from the classic full circumferential skirt studies. This paper provides a ‘snapshot’ into how the inherent piston side load is supported by the piston skirt. It highlights the importance of the operational temperature on the skirt profile, conjunctional gap and the lubricant film. Additionally, it shows how a given piston skirt shape and its structural stiffness perform in operation.

Topics: Lubrication , Pistons
Commentary by Dr. Valentin Fuster
2012;():979-984. doi:10.1115/ICES2012-81134.

This paper presents experimental data comparing the thermal performance of aqueous ethylene-glycol mixtures with and without additives. These additives are used to provide corrosion protection, but their presence can also improve the coolant thermal performance. The experimental results show that the coolant with additives yields wall temperatures approximately 50°C lower than the non-additive coolant at the maximum heat flux condition.

Commentary by Dr. Valentin Fuster
2012;():985-992. doi:10.1115/ICES2012-81160.

Up to 65% of the energy produced in an internal combustion engine is dissipated to the engine cooling circuit and exhaust gases [1]. Therefore, recovering a portion of this heat energy is a highly effective solution to improve engine and drivetrain efficiency and to reduce CO2 emissions, with existing vehicle and powertrain technologies [2,3].

This paper details a practical approach to the utilization of powertrain waste heat for light vehicle engines to reduce fuel consumption. The “Systems Approach” as described in this paper recovers useful energy from what would otherwise be heat energy wasted into the environment, and effectively distributes this energy to the transmission and engine oils thus reducing the oil viscosities. The focus is on how to effectively distribute the available powertrain heat energy to optimize drivetrain efficiency for light duty vehicles, minimizing fuel consumption during various drive cycles. To accomplish this, it is necessary to identify the available powertrain heat energy during any drive cycle and cold start conditions, and to distribute this energy in such a way to maximize the overall efficiency of the drivetrain.

Commentary by Dr. Valentin Fuster
2012;():993-1001. doi:10.1115/ICES2012-81192.

A steady state test procedure has been developed and implemented on an extensively instrumented production diesel engine to estimate the total energy transfer to coolant over a New European Drive Cycle. The test procedure involved segmenting the drive cycle into 26 operating conditions, each with a corresponding weighting factor. The test program consisted of both the steady state tests and a series of transient tests for comparison. The engine instrumentation consisted of a bespoke measurement device to calculate the rate of heat transfer through the combustion chamber walls. The sensors were located vertically down both the inlet and exhaust sides of one cylinder. It was found that the steady state approximation method estimated the total energy transfer to the coolant to within 10% of the transient tests. Differences in the idle speed condition were found to have the largest effect due to 21.7% of the drive cycle occurring at this condition. The steady state approximation method can therefore be used to sufficiently estimate the drive cycle performance for energy transfer if an exact condition is used for a region where the weighting factor is significant, i.e. greater than 15%. Subsequently it could also be used for other parameters, such as fuel consumption.

Commentary by Dr. Valentin Fuster
2012;():1003-1008. doi:10.1115/ICES2012-81201.

Both the piston ring and cylinder bore experience wear throughout their life cycle. Therefore change occurs in the geometrical profile and topography of the ring. In addition, coating on the ring is also subject to wear, thus altering the physical/mechanical property of the contacting surface. These changes affect the tribological performance of the ring-bore conjunction. Geometrical changes often alter the ring contacting profile, which affects the entrainment of the lubricant into the conjunction. This can affect the regime of lubrication, thus mechanisms that contribute to friction. Wear of surfaces also plays some role in boundary friction in terms of topographical changes as well as surface properties such as hardness and asperity shear strength. Most analysis does not take into account changes in tribological conditions which occur as the result of these salient changes in practice. The paper intends to bridge this gap in the fundamental knowledge and provide explanations for some in-field experiences noted with wear of a compression ring in a typical engine test. The method of solution used is based on the average flow factors which are indicative of entrainment of the lubricant through the rough ring-bore conjunction. This approach was initiated by Patir and Cheng, for which realistic topographical parameters according to the stage of the wear process is included. Changes in friction and fuel energy consumed are predicted.

Commentary by Dr. Valentin Fuster
2012;():1009-1013. doi:10.1115/ICES2012-81209.

Increasing strict regulation on the sulfur content of diesel fuels results in decreases the lubricity of these fuels. The lubricity of the fuel is an indication of the amount of wear or scarring that occurs between two metal parts covered with the fuel as they come in contact with each other. Low lubricity fuel may cause high wear and scarring and high lubricity fuel may provide reduced wear and longer component life. Previous studies have shown that alkyl esters of triglycerides derived from vegetable oils have increased diesel fuel lubricity at concentration of less than 1%. The major objective of this study was to analyze the effectiveness of indigenous non-edible feedstocks such as jatropha (Jatropha curcas) as an additive in petroleum based diesel fuels. Jatropha oil, and its alky esters (methyl and ethyl ester) and oil-ester blends with diesel were tested as an additive to enhance the lubricity of diesel fuels. In case of fuels, the lubricating behavior is associated with boundary film-forming properties. The analysis was carried out by using ASTM 6079-4 test method using High Frequency Reciprocating Rig (HFRR model D1377) as an analytical tool. The coefficient of friction and wear was observed higher for the low lubricity diesel fuel (LLDF) and it decreases with the addition of additive dose of oil, methyl and ethyl ester of jatropha. It may be due to the better lubricating behavior of non-edible based oil and ester compare to LLDF. During the HFRR test 2±0.20 ml of fluid sample under test is placed in reservoir which is maintained at a specified temperature of 60±2 °C. The HFRR test uses a vertically mounted steel ball to apply force to a horizontally mounted stationary steel disk with an applied load (200±1 g). The test ball is oscillated at a fixed frequency (50 ± 1 Hz) with a fixed stroke length (1 ± 0.02 mm) while the disk is fully immersed in the fluid reservoir. The whole test rig was placed in the humidity cabin with transparent enclosure. The test was kept for 75 minutes and the wear scar on the ball was measured by electronic microscope. It is believed that the high concentration of the particular fatty acid in oil and alkyl ester could be responsible for enhancing the lubricity and subsequent lower wear scar.

Topics: Diesel , Ester
Commentary by Dr. Valentin Fuster

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