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ASME Conference Presenter Attendance Policy and Archival Proceedings

2012;():i. doi:10.1115/ICEF2012-NS.
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This online compilation of papers from the ASME 2012 Internal Combustion Engine Division Fall Technical Conference (ICEF2012) 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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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/ICEF2012-92007.

Laser ignition of natural gas engines has shown potential to improve many facets of engine performance including brake thermal efficiency, exhaust emissions, and durability as compared with traditional spark ignition. We present proof of concept of a novel fiber optic delivery approach using solid core multimode step index silica fibers with large cladding diameters (400 m core, 720 m cladding). The fibers were able to deliver high beam quality 25 nanosecond pulses of 1064 nm light with 7–10 mJ energy; sufficient to consistently ignite the engine at various air-fuel ratios and loads. Comparative tests between the laser spark plug and a traditional J-gap spark plug were performed on a single cylinder Waukesha Cooperative Fuel Research (CFR) engine running on bottled methane. Performance was measured in terms of the Coefficient of Variation (COV) of Net Mean Effective Pressure (NMEP), fuel specific efficiency, and emissions of oxides of nitrogen (NOx), carbon monoxide (CO), and total hydrocarbons (THC). Tests were run at three different NMEPs of 6, 8, and 12 bar at various air-fuel ratios. Results indicate successful operation of the fiber and improved engine performance at high NMEP and lean conditions.

Commentary by Dr. Valentin Fuster
2012;():11-21. doi:10.1115/ICEF2012-92030.

Next generation passive prechamber spark plugs for high BMEP natural gas engines require long ignition delay for durability, fast combustion for efficiency, and low COV for lean engine operation. Additionally, a successful plug should have long life, low cost, and have a robust knock margin, with best-in-class NOx vs. fuel consumption.

This paper discusses the underlying physics of the novel passive prechamber spark plug, the Woodward–Lean Quality Plug (WW-LQP.) The WW-LQP has demonstrated good ignition delay, fast combustion, and low COV at λ > 1.8+, while improving fuel consumption by more than 1% on a lean natural gas engine.

The key operating principles are developed for achieving complete combustion of the prechamber “charge”, leading to high prechamber pressure rise and resulting in high velocity turbulent flame jets, which in-turn provides for fast combustion in the main chamber. The design physics are verified by CFD simulations and on-engine experiments, including pressure measurements in both the prechamber and main combustion chamber.

Commentary by Dr. Valentin Fuster
2012;():23-33. doi:10.1115/ICEF2012-92031.

Combustion in lean large-bore natural gas engines is usually initiated by gas-scavenged prechambers. The hot reacting products of the combustion in the prechamber penetrate the main chamber as reacting jets, providing high ignition energy for the lean main chamber charge. The shape and intensity of the reaction zone in these jets are the key elements for efficient ignition and heat release in the main chamber. The influence of geometrical and operational parameters on the reaction during jet penetration was investigated in detail. As the periodically chargeable high pressure combustion cell used in the study provides full optical access to the entire main chamber the evolution of the spatial distribution of the reaction zones was investigated in terms of OH*-chemiluminescence. As jet penetration is a very fast and highly transient process the emission of OH* was recorded at a frequency of f = 30000 Hz. The macroscopic reaction zone parameters in the jet region (penetration length and angle, reacting area and light emission) reveal the influence of orifice size and prechamber gas injection on the heat release in the shear layer between the jet and the lean charge in the main chamber. In addition, the influence of the development of the reaction in these zones on the ignition probability and the main chamber pressure rise is shown. With an appropriate selection of the combination of the prechamber orifice geometry and the operating parameters significant improvements of ignition probability and heat release in the main chamber were obtained.

Topics: Gas engines
Commentary by Dr. Valentin Fuster
2012;():35-45. doi:10.1115/ICEF2012-92038.

To fulfil strict emission regulations and the need for higher efficiency of future Diesel engines require an optimized combustion process. Optical investigations represent a powerful tool for getting a better understanding of the ongoing processes. For medium speed Diesel engines, optical investigations are relatively rare or not available. The “Institut für Kolbenmaschinen” (IFKM) and MAN Diesel & Turbo SE performed extensive optical in-situ investigations of the injection and combustion process of a MAN 32/44 CR single cylinder medium speed Diesel engine that provide previously unavailable insights into the ongoing processes. The optical investigations aimed on fuel spray visualization, high-speed soot luminescence measurement and two colour pyrometry applied for five combustion chamber regions.

To apply the optical measurement techniques, two optical accesses were designed. Access no. 1 is placed near the cylinder liner. Access no. 2 is located close to the injector in a 46° angle to the cylinder vertical axis. An insert was used which consists of an illumination port and a visualization endoscope. Additionally some special nozzle designs were used beside the standard nozzle, which have one separated nozzle hole. This enables a simultaneous view from both optical accesses on the same flame cone.

For Mie-Scattering investigation a pulsed Nd:YAG-Laser with 532 nm wavelength was used for illumination and a CCD-camera with an upstream 532 nm optical filter was used for visualization. This combination allows observing the liquid fuel distribution even after start of combustion. Penetration depth of liquid fuel spray was analysed for different swirl numbers, intake manifold pressures, injection timings and injection pressures.

High-speed flame visualization was done by two CMOS cameras which were mounted at two different optical accesses with view on the same flame cone. Due to this application a simultaneous measurement of the flame distribution of two different views was possible. This enables a 3-dimensional investigation of the flame propagation process.

In addition, the advanced two colour pyrometry was applied for five different regions of the same flame cone. Due to a calibration after each measurement the absolute radiant flux can be calculated and thus the absolute temperature and soot concentration. With this procedure it was possible to give a real temperature and soot concentration distribution of the flame cone.

To provide more detailed information about the combustion process, selected engine operation points were simulated with a modified version of the CFD code KIVA3v-Release2 at the IFKM. The simulated results were compared to the measured data.

Commentary by Dr. Valentin Fuster
2012;():47-54. doi:10.1115/ICEF2012-92046.

The objective of this research was to improve the scavenging process on a heavy-duty, two-cycle, medium speed, diesel engine (710 cubic inches of displacement per cylinder) under high load. It was desired to expel as much of the residual gases in the combustion chamber during the scavenging process, without having the fresh intake air escaping through the exhaust valves. This allowed a cooler intake charge with a higher oxygen concentration to be used. Having a cooler air intake charge was beneficial for emissions and performance. The power assembly configuration for the investigation was a two-cycle engine with intake ports around the bottom portion of the cylinder liner and four exhaust valves in the cylinder head. The main variable in this study was the axial location of every other intake port on the cylinder liner. When the axial location increased, this created pseudo longer intake timing. To keep the amount of trapped mass constant, the exhaust valves remained opened longer. The effectiveness of the scavenging process was estimated by the concentration of trapped oxygen (O2), carbon dioxide (CO2), and water vapor (H2O) along with the average temperature of the intake charge at the end of scavenging. The final part of the research explored each modified cylinder liner under full load, combustion operating conditions, while varying the injection timings. Soot, nitrogen oxides (NOx) and fuel consumption were also examined. A proprietary, multi-dimensional, computational fluid dynamic (CFD) code was used for the modeling work. Sculptor™, a commercial software package, was used to morph the cylinder liner.

The results showed that by increasing the axial location of the intake ports, a cooler intake charge with higher oxygen and lower carbon dioxide and water vapor concentrations resulted. This suggested more exhaust gases were expelled from the combustion chamber and replaced with fresh air. The rate of improvement slowed down after increasing the intake port axial location by 15.0 mm. In the next step, the compression and combustion process of the different port locations was studied. The cases with higher intake port axial locations were found to have lower pressure throughout the compression and power cycles. The temperature was lower for cases with elevated intake ports, until combustion started. The final part of the research studied the modified intake port cases under combustion simulation, while varying the injection timing. Next, the results showed an improvement in soot and fuel consumption with an increase in NOx for a given injection timing. However, while injection timing was varied, it was possible to improve NOx, soot, and fuel consumption simultaneously when compared to the baseline.

Commentary by Dr. Valentin Fuster
2012;():55-60. doi:10.1115/ICEF2012-92076.

Surface temperature measurements were performed in a large bore two-stroke diesel engine used for ship propulsion. A specially designed fast-response surface thermocouple was used together with an embedded standard K-type thermocouple to measure surface temperature and heat flux with high temporal resolution.

Heat flux calculations were carried out both analytically and numerically showing good agreement between the results. Measurements were carried out at three different engine load conditions (25%, 30% and 50% load) in one of the fuel atomizers in the cylinder head. Cyclic surface temperature variations of up to approximately 80 K with a peak temperature of 860 K were observed.

The magnitude of the perturbation of the temperature field due to the presence of the thermocouples was investigated by three dimensional CFD simulations.

Commentary by Dr. Valentin Fuster
2012;():61-65. doi:10.1115/ICEF2012-92118.

Recent in Two-stroke engine development for marine applications mainly deal with better and increased overall efficiency hereby reducing the CO2 emissions. Besides a mechanical design change the service conditions play a major role in enhanced efficiency. The so increased engine parameters with higher maximum pressure during combustion will inevitable increase the load on the bearings of the reciprocating parts. Since an increase in the bearing area is not possible due to the engine design parameters the object is to increase the specific load bearing capability of the bearing alloy while keeping the tribological benevolence. In particular, the fatigue properties and the strength of the used tin based alloys, commonly known as whitemetals or babbitts.

This class of alloys stands out due to its emergency running capabilities, embedability and its high flexibility under edge load. Existing Al-based alloys like AlSn40 have improved fatigue properties but they fall behind on the named essential properties. Also, the dimensions of the AlSn40 bearings are limited due to the roll bonding process by which they are produced. On the other hand spin casting as standard production process of Babbitt bearings is limiting the alloying elements due to centrifugal segregation while solidification of the lining alloy. While tin based alloys are used in an environment of 90°C the homologue temperature is 0,7 which means that classic strengthening mechanisms like work-hardening and grain size effects are only shortly employable. Another restricting fact is the requirement of solid solubility for solid solution strengthening which also includes precipitation hardening. Hence there is a limited amount of elements dissolvable and not environmentally hazardous in tin this mechanism is already used to its maximum in the standard babbitts.

In this paper a possible way to circumvent these limits will be presented. The use of high melting elements, compared to Sn, like Co, Ni, Mn, Al and Zn which are partly dissolvable in molten Sn, where used to improve the microstructure and therefor the overall performance of the bearing alloy.

These trace elements serve as grain refinement for the primary precipitation of SbSn and CuSn during solidification. The high melting point of these elements anticipates relaxing processes in the alloy caused by diffusion at the high homologue temperature. Due to the smaller precipitations and the finer structure a better performance can be seen during tests. This leads in a higher strength while maintaining its ductility. Alternate bending tests as well as specific bearing test runs show a significant better fatigue, wear and embedability performance than standard alloys.

Commentary by Dr. Valentin Fuster
2012;():67-75. doi:10.1115/ICEF2012-92120.

Generally, two-stroke engines have inherent advantage of higher swirl, as compared to four-stroke engines. Higher swirl helps with better mixing and atomization for mechanical and low pressure, electronic, unit injectors. With the introduction of higher injection pressure, the advantage of swirl reduced to a point in which it started to have a negative impact. In this work, the goal was to optimize a high pressure, common rail injection system for heavy-duty, two-cycle, medium speed, diesel engine (710 cubic inches of displacement per cylinder) under high load. A proprietary multi-dimensional computational fluid dynamic (CFD) code was used for the modeling work. Here, we optimized the new, skewed injection system, which takes advantage of swirl and further helps in atomization of spray. The spray in this study is introduced at a radial angle, which is aligned either along or against the swirl direction. The results showed significant improvement in combustion efficiency. Combustion efficiency is estimated as a decrease in fuel consumption and CO values. Emission parameters, such as nitrogen oxide and soot were also studied and showed significant reductions.

Commentary by Dr. Valentin Fuster
2012;():77-82. doi:10.1115/ICEF2012-92128.

This paper describes the development of a low emissions upgrade kit for EMD GP20D and GP15D locomotives. These locomotives were originally manufactured in 2001, and met EPA Tier 1 locomotive emission regulations. The 1,491 kW (2,000 HP) EMD GP20D locomotives are powered by Caterpillar 3516B engines, and the 1,119 kW (1,500 HP) EMD GP15D locomotives are powered by Caterpillar 3512B engines. CIT Rail owns a fleet of 50 of these locomotives that are approaching their mid-life before first overhaul. Baseline exhaust emissions testing was followed by a low emissions retrofit development focusing on fuel injection timing, crankcase ventilation filtration, and application of a diesel oxidation catalyst (DOC), and then later a diesel particulate filter (DPF). The result was a EPA Tier 0+ certification of the low emissions upgrade kit, with emission levels below EPA Line-Haul Tier 3 NOx, and Tier 4 HC, CO, and PM levels.

Commentary by Dr. Valentin Fuster
2012;():83-89. doi:10.1115/ICEF2012-92208.

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

Fuels

2012;():91-99. doi:10.1115/ICEF2012-92041.

While engines fueled with neat or blended biodiesel have favorable combustion-emission profile in terms of carbon monoxide, particulate matter and unburned hydrocarbons emissions, they are reported to have higher NOx emissions as compared to petro-diesel. On the other hand, use of alcohols especially methanol, though limited in diesel engines, is found to decrease engine exhaust emissions including smoke and NOx emissions. The present experimental investigation evaluates the use of biodiesel-methanol blend in mitigating higher NOx emissions in biodiesel fuelled engines along with its effect on other engine performance conditions. The experimental results obtained for a blend of 90% Jatropha methyl ester and 10% methanol (J90M10) and neat Jatropha methyl ester (J100) by varying engine output load at maximum torque speed of 1400 rpm are analyzed and discussed in this paper. The experimental results at full load operation for J90M10 blend compared with neat J100 indicate a reduction in exhaust nitric oxide and smoke concentrations by 28% and 50% respectively along with a reduction of 2% in peak pressure and 0.5% in brake thermal efficiency. Also, a marginal retard in injection timing and a higher ignition delay period is observed with Jatropha methyl ester -methanol blend operation.

Commentary by Dr. Valentin Fuster
2012;():101-116. doi:10.1115/ICEF2012-92053.

In this study, the in-cylinder soot and NOx trade off was investigated in a Compression Engine by implementing Premixed Charge Compression Ignition (PCCI) coupled with Low Temperature Combustion (LTC) for selected regimes of 1–3 bars IMEP. In order to achieve that, an omnivorous (multi-fuel) single cylinder diesel engine was developed by injecting n-butanol in the intake port while being fueled with biodiesel by direct injection in the combustion chamber. By applying this methodology, the in-cylinder pressure decreased by 25% and peak pressure was delayed in the power stroke by about 8 CAD for the cycles in which the n-butanol was injected in the intake manifold at the engine speed of 800 rpm and low engine loads, corresponding to 1–3 bars IMEP. Compared with the baseline taken with ultra-low sulfur diesel no. 2 (USLD#2), the heat release presented a more complex shape. At 1–2 bars IMEP, the premixed charge stage of the combustion totally disappeared and a prolonged diffusion stage was found instead. At 3 bars IMEP, an early low temperature heat release was present that started 6 degrees (1.25 ms) earlier than the diesel reference heat release with a peak at 350 CAD corresponding to 1200 K. Heat losses from radiation of burned gas in the combustion chamber decreased by 10–50% while the soot emissions showed a significant decrease of about 98%, concomitantly with a 98% NOx reduction at 1 IMEP, and 77% at 3 IMEP, by controlling the combustion phases. Gaseous emissions were measured using an AVL SESAM FTIR and showed that there were high increases in CO, HC and NMHC emissions as a result of PCCI/LTC strategy; nevertheless, the technology is still under development. The results of this work indicate that n-butanol can be a very promising fuel alternative including for LTC regimes.

Commentary by Dr. Valentin Fuster
2012;():117-126. doi:10.1115/ICEF2012-92058.

Diesel air-fuel mixing and combustion have been investigated in a Rapid Compression Machine (RCM). The measurements were performed at high injection pressures up to 260 MPa and under reacting and non-reacting conditions. The spray was injected through solenoid-controlled multi-hole injectors. Two nozzles were applied with orifice diameters of 175 μm (D175) and 150 μm (D150), respectively. The visualization of the penetration of the liquid and the gaseous phase as well as the spray cone angle under evaporative, non-reacting conditions was carried out by the shadowgraph imaging technique in combination with a high speed camera. For combustion studies the flame luminosity of the flame as well as the chemiluminescence signals emitted by the OH radicals in the UV range were detected.

Investigations revealed different behavior of the macroscopic spray characteristics with the two applied nozzles when increasing the injection pressure from 200 MPa to 260 MPa. With the larger nozzle diameter (D175) the spray penetration and the spray propagation velocity increase as the injection pressure is increased. On the contrary to that, with the smaller nozzle diameter (D150) an increase of the injection pressure had no effect on the spray velocity. With 260 MPa a higher spray penetration was only observed at the beginning of the injection due to the faster opening of the needle. The further propagation of the tip of the spray was similar with 200 MPa and 260 MPa. With both applied nozzles the injection pressure has little effect on the penetration length of the liquid phase. At an applied injection pressure of 200 MPa the near-nozzle spray angle is wider with D175, whereas similar spray angles were observed at 260 MPa. From the measurements in reacting atmosphere an earlier ignition of the fuel and a faster combustion could be shown with nozzle D150. In addition, a higher combustion pressure was measured. This can be attributed to better air-fuel mixing and a higher premixed portion, which was confirmed by the analysis of the spray angles in the far-nozzle region obtained from the shadowgraph images at non-reacting conditions.

Commentary by Dr. Valentin Fuster
2012;():127-140. doi:10.1115/ICEF2012-92071.

This study investigates the combustion characteristics of methyl oleate (oleic FAME) produced from oleic acid. This compound is the main fatty acid component of peanut FAME, a potential renewable biofuel. Methyl oleate has been suggested in our previous work as a reference fuel or surrogate for biodiesel for advanced research (simulation and experiments), or as an enrichment compound to improve biodiesel’s fuel properties. This investigation compares the combustion and emissions characteristics of methyl oleate to peanut FAME and ultra-low sulfur diesel No. 2 (ULSD), in a single-cylinder indirect injection diesel engine intended for use as an auxiliary power unit. The dynamic viscosity of peanut FAME (P100) and Methyl Oleate (O100) was found to be 5.2 cP and 4.3 cP, respectively, at 40°C. It was determined from the ASTM standards for biodiesel that up to 50% FAME could be run in the engine. The lower heating value of P100 and O100 was 36 MJ/kg and 37 MJ/kg respectively, compared to 42.7MJ/kg for ULSD. With a combustion time of 2ms, P50 and O50 have shown similar combustion characteristics with ignition delays of about 1 ms at 2200rpm, 6.2 imep (100% load). The P50, O50, and ULSD heat release, with premixed phase combining with diffusion combustion, produced maximum values of 20.3 J/CAD, 22.7 J/CAD, and 21.9 J/CAD respectively. The heat fluxes were calculated by the Annand model, and a 2% increase in maximum total heat flux was observed for O50 compared with a maximum value of 1.95 MW/m2 for ULSD and P50. The mechanical efficiency of 77% was similar for all tested FAME blends and ULSD. The NOx increased for P20 by 6% compared with ULSD while for P50 it was similar to the ULSD values. The NOx emissions of methyl oleate showed a similar trend with that of ULSD. The soot values were relatively constant for all of the methyl oleate blends and increased by 14% for P50 when comparing both fuels to ULSD.

The findings support the use of methyl oleate as a reference or model fuel for combustion modeling, and as a compound for enriching biodiesel.

Topics: Fuels , Diesel engines
Commentary by Dr. Valentin Fuster
2012;():141-152. doi:10.1115/ICEF2012-92085.

A cavitation model has been developed for the internal two-phase flow of diesel and biodiesel fuels in fuel injectors under high injection pressure conditions. The model is based on the conventional single-fluid mixture approach with modification in the phase change rate expressions and local mean effective pressure, considering the effects of viscous stresses and turbulent pressure fluctuations, and also takes into account the effects of turbulence, compressibility and wall roughness. The model is validated by comparing the model predictions of probable cavitation regions, velocity distribution, fuel mass flow rate and pressure with the experimental measurement available in literature. It is found that cavitation inception for biodiesel occurs at a higher injection pressure, compared to diesel, due to its lower saturation pressure. However, supercavitation occurs for both diesel and biodiesel at high injection pressures. RNG k–ε model for turbulence modeling is reliable by comparing its performance with realizable k–ε and SST k–ω models. The effect of liquid phase compressibility becomes considerable for very high injection pressures. Wall roughness is not an important factor for cavitation in fuel injectors.

Commentary by Dr. Valentin Fuster
2012;():153-167. doi:10.1115/ICEF2012-92117.

In an effort towards predicting the combustion behavior of a new fuel in a conventional diesel engine, Hydrotreated Renewable Jet (HRJ) fuel was first run in a military diesel engine across the entire speed-load operating range. Ignition delay was characterized for this fuel at each operating condition. Next, a HRJ surrogate fuel was developed in order to predict the combustion performance of this new renewable fuel. A chemical ignition delay was then predicted across the speed-load range using a detailed chemical kinetic mechanism model based on an 8-component surrogate representative of HRJ. The modeling suggests that rich fuel-air parcels developed from the diesel spray are the first to ignite. The chemical ignition delay results also show decreasing ignition delays with increasing engine load and speed just as shown by the empirical data. A moderate difference between the total and chemical ignition delays was then characterized as a physical delay period which scales inversely with engine speed. The approach used in this study suggests that the ignition delay and thus start of combustion may be predicted with reasonable accuracy allowing for the analytical assessment of the acceptability of a new fuel in a conventional engine.

Commentary by Dr. Valentin Fuster
2012;():169-176. doi:10.1115/ICEF2012-92131.

Due to diminishing petroleum reserves and the environmental consequences of exhaust gases from petroleum fuelled engines, alternative fuels are becoming increasingly important for diesel engines. The processed form of vegetable oil (Biodiesel) and waste products (waste cooking oil) offer attractive alternative fuels for compression ignition engines. In this study experimental work has been carried out to investigate engine performance parameters and emissions characteristics for direct injection diesel engine using coconut biodiesel and waste cooking oil blends without any engine modifications. A total of three fuel samples, such as DF (100% low-sulfur diesel fuel), CB10 (10% coconut biodiesel and 90% DF), and C5W5 (5% CB + 5% waste cooking oil and 90% DF) respectively are used. Engine performance test was performed at 100% load keeping throttle 100% wide open with variable speeds of 1500 to 2400 rpm at an interval of 100 rpm. Whereas, emission tests were carried out at 2300 rpm at 100% and 80% throttle position. As the results of investigations, there has been a decrease in torque and brake power, where increase in specific fuel consumption has been observed for blend fuels over the entire speed range as compared to diesel fuel. In case of engine exhaust gas emissions, lower HC, CO, CO2 emissions and higher NOx emissions, were found for fuel blends compared to diesel fuel. However, sound level for both blend fuels was lower as compared to diesel fuel. It can be concluded that CB10 and C5W5 can be used in diesel engines without any engine modifications and have beneficial effects both in terms of emission reductions and alternative petroleum diesel fuel. However, C5W5 produced better results compared to CB10.

Commentary by Dr. Valentin Fuster
2012;():177-181. doi:10.1115/ICEF2012-92145.

Gaseous fuels are good alternative fuels to improve the energy crisis of today’s situation due to its clean burning characteristics. However, the incidence of backfire and knock remains a significant barrier in commercialization. With the invention of latest technology, the above barriers are eliminated. One such technique is timed injection of water into the intake port. In the present investigation, acetylene was aspirated in the intake manifold of a single cylinder diesel engine, with a gas flow rate of 390 g/h, along with water injected in the intake port, to overcome the backfire and knock problems in gaseous dual fuel engine. The brake thermal efficiency and emissions such as NOx, smoke, CO, HC, CO2 and exhaust gas temperature were studied. Dual fuel operation of acetylene induction with injection of water results in lowered NOx emissions with complete elimination of backfire and knock at the expense of brake thermal efficiency.

Commentary by Dr. Valentin Fuster
2012;():183-190. doi:10.1115/ICEF2012-92148.

Over the last couple of decade, biofuels have shown a lot of promise in terms of relatively higher combustion efficiency and lower emissions vis-à-vis conventional fuels. If mineral diesel is to be replaced by an alternate fuel in existing IC engines, compatibility of the fuel injection equipment (FIE) with these new fuels need to be ascertained because engine performance, combustion and emission characteristics are greatly affected by the FIE. It is reported that FIE components face issues such as injector deposits, injector blockage and pump plunger wear with biofuels. To experimentally investigate the compatibility of FIE with biofuels, a fuel injection simulator was developed to experimentally simulate the engine conditions as closely as possible, outside the engine environment, without the need for combustion of fuel. This simulator was operated for 250 hours with different Karanja oil blends (K100, K20, and K5) and baseline mineral diesel. New fuel pumps and injectors were used for every set of experiment. After every experiment of 250 hours, fuel injector and pumps were dismantled to assess the deposits, wear and surface texture of different components of FIE. Wear was measured by weight loss, dimensional changes and surface texture changes (analyzed by optical microscopy) of the component. For K100, injector blockage was experienced after 185 hours. During inspection, injector nozzle needles using Karanja oil blends showed higher deposits compared to mineral diesel. Dimensional changes of the plunger were highest for K100 compared to mineral diesel. Karanja oil at lower blends provided superior and improved lubricity compared to mineral diesel. In summary, FIE sub-components were damaged to a higher degree with K100, especially pump plunger. Karanja oil blends showed higher deposits on nozzle needle.

Topics: Wear , Fuels , Vegetable oils
Commentary by Dr. Valentin Fuster
2012;():191-203. doi:10.1115/ICEF2012-92151.

The molecular composition of new hydrotreated renewable fuels consists of both straight chain and branched alkanes. These new fuels do not contain aromatic or cyclo-paraffinic hydro-carbon compounds which are regularly seen in conventional petroleum fuels. Both experimental and modeling work has shown that straight chain alkanes have shorter ignition delays (e.g. higher cetane number) as compared to branched alkanes. In order to better understand the effects of branched and straight chain alkanes fuels in diesel engines, an experimental study was pursued using binary blends of iso-dodecane (iC12H26 with abbreviation: iC12) and normal-hexadecane (nC16H34 with abbreviation nC16) in a military diesel engine (AM General HMMWV ‘Humvee’ engine). Mixtures of 50% iC12 with 50% nC16 as well as 25% iC12 with 75% nC16 were compared to 100% nC16 (cetane) fueled engine operation across the entire speed-load range. Higher nC16 fuel content operation resulted in modestly earlier fuel injection events and combustion phasing that delievered slightly worse engine brake performance (torque and fuel consumption). Interestingly, ignition delay and overall burn durations were relatively insensitive to the binary blends tested. The significantly different physical properties of iC12 relative to nC16 are believed to affect the fuel injection event leading to later fuel injection with increasing iC12 content. Later injection into a hotter chamber mitigates the lower cetane number of the higher iC12 content fuel blends.

Commentary by Dr. Valentin Fuster
2012;():205-216. doi:10.1115/ICEF2012-92159.

Petroleum supply and environmental issues have increased interest in renewable low polluting alternative fuels. Published test results generally indicate decreased pollution with similar power output from internal combustion engines burning alternative fuels. More specifically, diesel engines burning biodiesel derived from plant oils and animal fats, not only reduce harmful exhaust emissions, but are renewable and environmentally friendly.

A literature review found little previous research with biodiesel in small commercial diesel engines. This paper presents the research that was conducted to study the effect of biodiesel/diesel fuel blends on engine performance and emissions for a Yanmar L100 EE (7.1 kW) engine. This is a standard commercial grade diesel engine used for small equipment such as generators.

Independent engine dynamometer and emissions testing were performed to validate the lower emission claims and assess the feasibility of alternative fuels. A testing apparatus capable of making relevant measurements was designed, built and used to perform this study.

Fuel blends used included B2, B20, B40, B60, B80, and B100 where the biodiesel component of the blend was a commercial product. An analysis of the fuel showed large percentages of linoleic acid, palmitic acid and stearic acid which is typical for a blend of soybean oil and beef tallow.

Test were performed at a constant torque (95 % of the continuously rated value) and variable engine speeds. Test results included calculated values of BMEP, BSFC, thermal efficiency, air mass flow rate, air fuel ratio, corrected NOx, energy lost to exhaust, and heat rejection, and measured values of unburned hydrocarbons, carbon monoxide, and carbon dioxide.

Results indicate an increase in thermal efficiency compared to standard diesel and significant reductions of unburned hydrocarbons and carbon monoxide at all engine speeds. Brake specific fuel consumption increased with increasing percent biodiesel consistent with the decreased energy content of blended fuel. Significantly, there were small but consistent reductions in corrected NOx for all blends at all speeds. We posit possible explanations for these results, which are contrary to the published results for larger engines which show an increase in NOx for biodiesel blends.

Topics: Engines , Biodiesel
Commentary by Dr. Valentin Fuster
2012;():217-226. doi:10.1115/ICEF2012-92176.

Previous research indicates that the low temperature combustion (LTC) is capable of producing ultra-low nitrogen oxides (NOx) and soot emissions. The LTC in diesel engines can be enabled by the heavy use of exhaust gas recirculation (EGR) at moderate engine loads. However, when operating at higher engine loads, elevated demands of both intake boost and EGR levels to ensure ultra-low emissions make engine controllability a challenging task. In this work, a multi-fuel combustion strategy is implemented to improve the emission performance and engine controllability at higher engine loads. The port fueling of ethanol is ignited by the direct injection of diesel fuel. The ethanol impacts on the engine emissions, ignition delay, heat-release shaping and cylinder-charge cooling have been empirically analyzed with the sweeps of different ethanol-to-diesel ratios. Zero-dimensional phenomenological engine cycle simulations have been conducted to supplement the empirical work. The multi-fuel combustion of ethanol and diesel produces lower emissions of NOx and soot while maintaining the engine efficiency. The experimental set-up and study cases are described and the potential for the application of ethanol-to-diesel multi-fuel system at higher loads has been proposed and discussed.

Commentary by Dr. Valentin Fuster
2012;():227-234. doi:10.1115/ICEF2012-92185.

A limited amount of information exists on the effect of higher ethanol content fuel (greater than 10 vol%) for recreational vehicle engines. The possibility exists for misfueling of these vehicles, as ethanol content may increase at gas stations in the near future. Engine management systems in the recreational vehicle market are typically not equipped with feedback controls to adapt to the increased ethanol content. To address this concern and generate preliminary data related directly to the recreational industry, a study was conducted to evaluate the impact of E22 fuel on steady-state emissions and performance of two production snowmobiles. To fully analyze the impact of higher ethanol blends, cold-start, durability, and material compatibility tests should be performed, in conjunction with emissions and performance tests. While these additional tests were not performed as part of this study, there is a test program that is assessing all these factors on E15 fuel, which will be released in fall 2012. E0 fuel was used to establish baseline performance and emissions data. A 2009 four-stroke snowmobile with a 998cc, liquid-cooled, four-cylinder, intake port-fuel injected engine and a 2009 two-stroke snowmobile with a 599cc, liquid-cooled, two-cylinder, electronically controlled, crankcase-fuel injected engine were used for this study. Neither vehicle had any feedback air-fuel controls or after-treatment devices in the exhaust system. Power, fuel consumption, relevant engine temperatures, as well as, regulated exhaust emissions were recorded using the EPA 5-mode certification test cycle.

The data showed no major impact on power output for either the four-stroke or two-stroke snowmobile. Brake specific fuel consumption varied with E22 as compared to E0. A reduction in CO emissions for both vehicles was observed for the E22 fuel. Both vehicles were factory calibrated rich of stoichiometric and hence, the addition of ethanol to the fuel effectively leaned out the air/fuel ratio and thus reduced the CO emissions. HC emissions were reduced for both the four-stroke and two-stroke engines, though certain test points of the two-stroke engine produced HC emissions that exceeded the analyzer measurement range (idle). Leaner operation reduced HC formation. Exhaust gas temperatures were observed to increase from 20°C – 50°C with E22 fuel, due to enleanment.

Topics: Fuels , Emissions
Commentary by Dr. Valentin Fuster

Advanced Combustion

2012;():235-242. doi:10.1115/ICEF2012-92027.

The effects of intake air humidity on the performance of a turbo-charged 4-cylinder diesel engine have been investigated. The relative humidity of the intake charge was varied from 31 to 80% at a fixed ambient air temperature of 26°C. The intake humidity was controlled to within ±1% of the desired value by using a steam generator-equipped intake-air conditioning system. The tests were conducted at 3 load points (4.1, 9.1 and 15 bar BMEP) at engine speeds of 1500, 2500 and 3500 RPM without exhaust gas recirculation. The results indicate that increasing the intake air moisture leads to a reduction of 3∼14% in the NOX emissions for the tested conditions. The smoke was found to increase with speed but no significant increase in the smoke values was observed with the increased humidity. The CO and HC emissions were found to be largely insensitive to the humidity levels and were otherwise extremely low. The emissions have been analyzed on both the volumetric (ppm) and brake-specific basis to provide an insight into the effect of humidity on the quantitative results.

Commentary by Dr. Valentin Fuster
2012;():243-255. doi:10.1115/ICEF2012-92049.

High-EGR diesel low temperature combustion breaks the traditional diesel NOx-PM trade-off, thereby facilitating ultra-low NOx emissions with simultaneously low smoke emissions. High-EGR LTC is currently limited to low and medium load and speed conditions. Therefore, in order to implement a high-EGR diesel LTC strategy in a passenger vehicle, a transition to conventional diesel operation is required when either a high load or high speed is demanded. This transition must be carefully managed to ensure smooth operation and to avoid excessive pollutant emissions—a task that is complicated by the markedly different response time-scales of the engine’s turbocharger, EGR, and fuelling systems.

This paper presents the results of a combination of numerical simulation and steady-state engine experiments that describe the performance and emissions of an automotive-sized 2 litre turbocharged diesel engine during a rapid transition from high-EGR LTC to conventional diesel operation. The effects of load change at constant engine speed during the Extra-Urban Drive Cycle (EUDC) part of the New European Drive Cycle (NEDC) are first evaluated using a one-dimensional engine simulation (Ricardo WAVE). The inputs to the model are; the initial and final fuelling quantities, the duration of the transient events, and the response of the engine’s control systems. The WAVE model outputs the intake manifold pressure and EGR level for each cycle during the transition.

The predicted intake pressure, EGR rate and the corresponding known injected fuel mass for each individual cycle are used to define a set of ‘pseudo-transient’ test conditions—matching the conditions encountered at discrete points within the modelled transient—for subsequent steady-state engine testing on a 0.51 litre AVL single cylinder diesel engine. These test conditions are established on the engine using independently controllable EGR and boost systems and the corresponding emissions (NOx, smoke, CO, and THC) and performance data (GISFC) were recorded. The experimental emissions and performance data are subsequently presented on a cycle-by-cycle basis. The results of this study provide significant insight into the combustion conditions that might be encountered during mode switching and their deleterious effect on emissions and performance. Strategies to mitigate these effects are examined.

Commentary by Dr. Valentin Fuster
2012;():257-265. doi:10.1115/ICEF2012-92060.

The advent of common rail technology alongside powerful control systems capable of delivering multiple accurate fuel charges during a single engine cycle has revolutionized the level of control possible in diesel combustion. This technology has opened a new path enabling low-temperature combustion (LTC) to become a viable combustion strategy. The aim of the research work presented within this paper is the understanding of how various engine parameters of LTC optimize the combustion both in terms of emissions and in terms of fuel efficiency. The work continues with an investigation of in-cylinder pressure and IMEP cycle-by-cycle variation. Attention will be given to how repeatability changes throughout the combustion cycle, identifying which parts within the cycle are least likely to follow the mean trend and why. Experiments were formulated to include rail pressure, injection settings of single injection and split-injection of varying dwell times. All injection conditions were phased across several crank-angles to demonstrate the interaction between emissions and efficiency. These tests are then repeated with blends of 30% and 50% gas-to-liquid (GTL)-Diesel blends in order to determine whether there is any change in the trends of repeatability and variance with increasing GTL blend ratio. Compression-ignition has been traditionally regarded as sufficiently stable that such investigation is irrelevant. Major improvements have been made, however, both to the understanding of compression-ignition and its control. Re-assessing and investigating how pressure repeatability fluctuates over the combustion cycle, especially in atypical engine conditions will help our understanding of combustion and facilitate a more accurate optimization of the combustion process.

Commentary by Dr. Valentin Fuster
2012;():267-276. doi:10.1115/ICEF2012-92069.

Partially premixed combustion has the potential of high efficiency and simultaneous low soot and NOx emissions. Running the engine in PPC mode with high octane number fuels has the advantage of a longer premix period of fuel and air which reduces soot emissions, even at higher loads. The problem is the ignitability at low load and idle operating conditions.

The objective is to investigate different multiple-injection strategies in order to further expand the low load limit and reduce the dependency on negative valve overlap in order to increase efficiency. The question is, what is the minimum attainable load for a given setting of negative valve overlap and fuel injection strategy. The experimental engine is a light duty diesel engine equipped with a fully flexible valve train system. The engine is run without boost at engine speed 800 rpm. The fuel is 87 RON gasoline.

A turbocharger is typically used to increase the boost pressure, but at low engine speed and load the available boost is expected to be limited. The in-cylinder pressure and temperature around top-dead-center will then be too low to ignite high octane number fuels. A negative valve overlap can be used to extend the low engine speed and load operating region. But one of the problems with negative valve overlap is the decrease in gas-exchange efficiency due to heat-losses from recompression of the residual gases. Also, the potential temperature increase from the trapped hot residual gases is limited at low load due to the low exhaust gas temperature. In order to expand the low load operating region further, more advanced injection strategies are investigated.

Commentary by Dr. Valentin Fuster
2012;():277-291. doi:10.1115/ICEF2012-92074.

The current research focuses on creating an HCCI fuel index suitable for comparing different fuels for HCCI operation. One way to characterize a fuel is to use the Auto-Ignition Temperature (AIT). The AIT can be extracted from the pressure trace. Another potentially interesting parameter is the amount of Low Temperature Heat Release (LTHR) that is closely connected to the ignition properties of the fuel.

The purpose of this study was to map the AIT and amount of LTHR of different oxygenated reference fuels in HCCI combustion at different cylinder pressures. Blends of n-heptane, iso-octane and ethanol were tested in a CFR engine with variable compression ratio. Five different inlet air temperatures ranging from 50°C to 150°C were used to achieve different cylinder pressures and the compression ratio was changed accordingly to keep a constant combustion phasing, CA50, of 3±1° after TDC. The experiments were carried out in lean operation with a constant equivalence ratio of 0.33 and with a constant engine speed of 600 rpm.

The amount of ethanol needed to suppress LTHR from different PRFs was evaluated. The AIT and the amount of LTHR for different combinations of n-heptane, iso-octane and ethanol were charted.

Commentary by Dr. Valentin Fuster
2012;():293-302. doi:10.1115/ICEF2012-92075.

The emission trade-off between soot and NOx is an issue of major concern in automotive diesel applications. Measures need to be taken both on the engine and on the aftertreatment sides in order to optimize the engine emissions while maintaining the highest possible efficiency. It is known that post injections have a potential for exhaust soot reduction without any significant influence in the NOx emissions. However, an accurate and general rule of how to parameterize a post injection such that it provides a maximum reduction of soot emissions does not exist. Moreover, the underlying mechanisms are not understood in detail.

The experimental investigation presented here provides insight into the fundamental mechanisms of soot formation and reduction due to post injections under different turbulence and reaction kinetic conditions. In parallel to the measurement of soot elementary carbon in the exhaust (using a Photo Acoustic Soot Sensor), the in-cylinder soot formation and oxidation process have been investigated with an Optical Light Probe (OLP). This sensor provides crank angle resolved information about the in-cylinder soot evolution.

The experiments confirm conclusions of earlier works that soot reduction due to a post injection is mainly based on two reasons: increased turbulence (from the post injection) during soot oxidation and lower soot formation due to lower amount of fuel in the main combustion at similar load conditions. A third effect of heat addition during the soot oxidation, which was often mentioned in the literature, could not be confirmed. In addition, the experiments show that variations of turbulence (from swirl) and reaction kinetics have a minor influence on the diffusion controlled heat release rate. However, the time phasing of the soot evolution is highly influenced by these variations with only small changes in the peak soot concentration. It is shown that the soot reduction of a post injection depends on the timing. More precisely, the soot reduction capability of a post injection decreases rapidly as soon as its timing is late in the soot oxidation phase. The soot oxidation rate can only be improved by increased turbulence and heat addition from the post injection in a time window before the in-cylinder soot peak occurs. Depending on EGR and swirl level, a maximum dwell time can be defined after which the post injection effect becomes counterproductive with respect to the soot oxidation rate.

Commentary by Dr. Valentin Fuster
2012;():303-311. doi:10.1115/ICEF2012-92094.

Stringent engine emission regulations highlight the importance of proper engine control during transient operation. In recent years, fast emissions analyzers that measure CO and CO2 simultaneously have allowed for fast air-to-fuel ratio (AFR) calculation under steady-state engine operation. However, using a steady-state methodology to calculate AFR under transient conditions can lead to significant data interpretation errors. This research introduces an experimental cycle-by-cycle AFR calculation routine developed for transient operation using cycle-resolved CO2 and CO analyzers. Need for the new technique arises when the composition of recycled exhaust gases vary significantly from expected post-combustion products corresponding to the true in-cylinder AFR. This condition commonly occurs when AFR is changed from one cycle to the next. The peak difference between the new method and traditional methods is demonstrated to be in the range of 0.1 relative air-to-fuel ratio points, or approximately 10%. These results are for low dilution conditions where the new method should show minimal difference as compared to traditional methods. If residual gas fraction levels were increased the difference in corrected to uncorrected results would become even greater, motivating the use of the new method in high-dilution engines.

Commentary by Dr. Valentin Fuster
2012;():313-326. doi:10.1115/ICEF2012-92100.

In-cylinder soot measurements obtained with a high-speed two-color method are compared to those simultaneously determined by the laser-induced incandescence (LII) technique in a single-cylinder, optically-accessible diesel engine fueled with JP-8. A double injection strategy was chosen to reduce pressure rise rates during operation at light load (2 bar IMEP) conditions. Injection timing was optimized for peak efficiency, at which point sufficient soot was produced to provide ample signal for both optical diagnostic techniques. Application of the two-color method to a high-speed CMOS camera allows the crank-angle-resolved observation of soot temperature and soot optical depth (KL) evolution, while LII provides soot volume fraction distribution at a known axial location in the cylinder independent of combustion gas temperature. Comparison of soot KL and LII signal at various stages of combustion shows high spatially-averaged correlation of the two signals near TDC. The degree of correlation decreases as the piston bowl descends and the line-of-sight soot KL value increasingly includes soot volumes not in the path of the laser sheet, the location of which is fixed 6.5 mm below the fire deck. The correlation between the two parameters again increases during the late cycle, indicating that in the later phases of combustion soot occurs in the squish zone above the piston bowl. Spatial cross-correlation of the two signals is weak, but increases in the highly luminous period immediately following heat release and illustrating a high degree of soot stratification. Soot KL and temperature evolution over a cycle are presented, which show no indication of being affected by the LII laser fluence.

Commentary by Dr. Valentin Fuster
2012;():327-338. doi:10.1115/ICEF2012-92107.

Experiments were performed to investigate injection strategies for improving engine-out emissions of RCCI combustion in a heavy-duty diesel engine. Previous studies of RCCI combustion using port-injected low-reactivity fuel (e.g., gasoline or iso-octane) and direct-injected high-reactivity fuel (e.g., diesel or n-heptane) have reported greater than 56% gross indicated thermal efficiency while meeting the EPA 2010 heavy-duty PM and NOx emissions regulations in-cylinder. However, CO and UHC emissions were higher than in diesel combustion. This increase is thought to be caused by crevice flows of trapped low-reactivity fuel and lower cylinder wall temperatures. In the present study, both the low- and high-reactivity fuels were direct-injected, enabling more precise targeting of the low-reactivity fuel as well as independent stratification of equivalence ratio and reactivity. Experiments with direct-injection of both gasoline and diesel were conducted at 9 bar IMEP and compared to results from experiments with port-injected gasoline and direct-injected diesel at matched conditions. The results indicate that reductions in UHC, CO, and PM are possible with direct-injected gasoline, while maintaining similar gross indicated efficiency as well as NOx emissions well below the EPA 2010 heavy-duty limit. Additionally, experimental results were simulated using multi-dimensional modeling in the KIVA-3V code coupled to a Discrete Multi-Component fuel vaporization model. The simulations suggest that further UHC reductions can be made by using wider injector angles which direct the gasoline spray away from the crevices.

Topics: Combustion , Diesel , Gasoline
Commentary by Dr. Valentin Fuster
2012;():339-348. doi:10.1115/ICEF2012-92109.

An experimental investigation of the thermal efficiency, combustion efficiency, and CoV IMEP, of methane fuel oxycombustion in an SI engine has been carried out. Compression ratio, spark-timing, and oxygen concentration were all varied. A variable compression ratio SI engine was operated on both wet and dry EGR working fluids, with results illustrating that the efficiency of the engine operating with a large amount of EGR was significantly reduced relative to methane-in-air operation over all oxygen concentrations and compression ratios. The maximum thermal efficiency of wet EGR, dry EGR, and air was found to be 23.6%, 24.2%, and 31.4%, respectively, corresponding to oxygen volume fractions of 29.3%, 32.7% and 21%. Combustion efficiency was above 98% for wet EGR and approximately 96% for dry EGR. CoV IMEP was low for both cases. The much lower efficiency of both EGR cases relative to air is primarily a result of the reduced specific-heat ratio of the EGR working fluids relative to air working fluid.

Commentary by Dr. Valentin Fuster
2012;():349-359. doi:10.1115/ICEF2012-92127.

This paper describes the operation of a heavy duty six-cylinder engine in a dual fuel, Low Temperature Combustion (LTC) mode with very low engine-out NOx und soot emissions according to the US EPA Tier IV final emission limits in the corresponding C1 test cycle. This operation mode makes use of a short pilot injection of diesel fuel, which is injected directly into the cylinder, to ignite a highly diluted, premixed gasoline air mixture. Multicylinder engine operation could be demonstrated over the entire engine operating map with loads of up to 2 MPa BMEP. Expensive aftertreatment systems for NOx and soot emissions are not required.

This paper also discusses the challenges involved with the implementation of this combustion system on a multicylinder engine. When transferring the dual fuel LTC from a single cylinder research engine to a multicylinder engine, the design of some engine components, e.g. the camshaft and the piston, were changed. The intake manifold is modified with port fuel injectors for ideal gasoline mixture preparation and equal distribution to all cylinders. To avoid cylinder imbalances, it is possible to control the injected masses of gasoline and diesel fuel for the pilot injection on a per-cylinder basis. Achieving high dilution for ignition delay via EGR and boosted intake pressure to avoid high pressure rise rates and knocking presents challenges for the two-stage turbocharger design. Additionally, high EGR rates and EGR cooling for increased loads are addressed. Finally, experiments to determine the significant control parameters for the combustion process are performed on the engine.

In the course of these investigations, dual fuel LTC could be transferred from a single cylinder research engine to a multicylinder engine; previously obtained single-cylinder operating conditions could be achieved even at high loads.

Commentary by Dr. Valentin Fuster
2012;():361-372. doi:10.1115/ICEF2012-92129.

HCCI combustion is highly dependent on in-cylinder thermal conditions favorable to auto-ignition, for a given fuel. Fuels available at the pump can differ considerably in composition and auto-ignition chemistry, hence strategies intended to bring HCCI to market must account for the fuel variability.

To this end, a test matrix consisting of eight gasoline fuels composed of blends made solely from refinery streams was investigated in an experimental, single cylinder HCCI engine. The base compositions were largely representative of gasoline one would expect to find across the United States, although some of the fuels had slightly lower average octane values than the ASTM minimum specification of 87. All fuels had 10% ethanol by volume included in the blend. The properties of the fuels were varied according to research octane number (RON), sensitivity (S=RON−MON) and the volumetric fractions of aromatics and olefins.

For each fuel, a sweep of the fuelling was carried out at each speed from the level of instability to excessive ringing to determine the limits of HCCI operation. This was repeated for a range of speeds to determine the overall operability zone. The fuels were kept at a constant intake air temperature during these tests.

The variation of fuel properties brought about changes in the overall operating range of each fuel, as some fuels had more favorable low load limits, whereas others enabled more benefit at the high load limit. The extent to which the combustion event changed from the low load limit to the high load limit was examined as well, to provide a relative criterion indicating the sensitivity of HCCI range to particular fuel properties.

Commentary by Dr. Valentin Fuster
2012;():373-381. doi:10.1115/ICEF2012-92142.

Premixed compression ignition (CI) combustion has attracted increasing research effort recently due to its potential to achieve both high thermal efficiency and low emissions. Dual-fuel strategies for enabling premixed CI have been a focus using a low reactivity fumigant and direct diesel injection to control ignition. Alternative fuels like hydrogen and ethanol have been used as fumigants in the past but typically with diesel injection systems that did not allow the same degree of control or mixing enabled by modern common rail systems. In this work we experimentally investigated hydrogen, ethanol and gasoline as fumigants and examined three levels of fumigant energy fraction (FEF) using gasoline over a large direct diesel injection timing range with a single cylinder diesel engine. It was found that the operable diesel injection timing range at constant FEF was dependent on the fumigant’s propensity for autoignition. Peak indicated gross cycle efficiency occurred with advanced diesel injection timing and aligned well with combustion phasing near TDC as we found in an earlier work. The use of hydrogen as a fumigant resulted in very low HC emissions compared with ethanol and gasoline, establishing that they mainly result from incomplete combustion of the fumigated fuel. Hydrogen emissions were independent of diesel injection timing and HC emissions were strongly linked to combustion phasing, giving further indication that squish and crevice flows are responsible for partially burned species from fumigation combustion.

Commentary by Dr. Valentin Fuster
2012;():383-392. doi:10.1115/ICEF2012-92143.

Interest is growing in the benefits of homogeneous charge compression ignition engines. In this paper we investigate a novel approach to the development of a homogenous charge like environment through the use of porous media. The primary purpose of the media is to enhance the spread of the high pressure fuel spray. In this paper we show through high speed visualizations of both cold and hot spray events, how porous media interactions can give rise to greater fuel air mixing and what role system pressure plays in further enhancing this process.

Commentary by Dr. Valentin Fuster
2012;():393-401. doi:10.1115/ICEF2012-92144.

The automotive sector is currently undergoing drastic changes, driven by the need to simultaneously meet increasingly stringent environmental regulations and achieve more efficient operation over a wide range of engine speeds and loads, while satisfying customer demands in terms of performance, safety, and reliability. In this study an HCCI engine is evaluated for performance and regulated and non-regulated emissions with anhydrous and hydrous ethanol. The Standard EPA Method 8315A was used to determine free carbonyl compounds by derivatization with 2,4-dinitrophenyhydrazine (DNPH). Carbonyls have been measured in emissions using DNPH impregnated cartridges and chemical analyses used high performance liquid chromatography (HPLC). Through the load range achievable, naturally aspirated lean anhydrous ethanol requires high intake temperatures. Although NOx emissions are lower with the use of hydrous ethanol, these emissions are much lower with the use of dry ethanol. The penalty of the use hydrous ethanol is an increase of unburned hydrocarbons and carbon monoxide. Total aldehyde emissions are seen to diminish when an HCCI combustion is carried out with hydrous ethanol. Our analysis gives evidence that HCCI engines can run efficiently on hydrous ethanol fuel and that utilizing hydrous ethanol fuel in HCCI engines improves the energy balance of ethanol production.

Commentary by Dr. Valentin Fuster
2012;():403-415. doi:10.1115/ICEF2012-92155.

Homogeneous Charge Compression Ignition (HCCI) combustion allows for the use of fuels with octane requirements below that of spark-ignited engines. A reference gasoline was compared with iso-octane and a low octane blend of gasoline and 40% n-heptane, NH40. Experiments were conducted on a single cylinder engine operating with negative valve overlap (NVO). The fuel flow rate per cycle was compensated based on the lower heating value to maintain a constant energy addition across fuels.

Iso-octane and gasoline demonstrated similar maximum load, achieving a gross IMEPg of ∼430 kPa, whereas the NH40 demonstrated an increased IMEPg of ∼ 460kPa. The NH40 could be operated at a later phasing compared with the higher octane fuels, and exhibited a shorter burn duration at a given fueling rate and phasing. These results could be due to compositional differences, as NH40 required less NVO compared to iso-octane and gasoline, leading to less thermal and compositional stratification, as well as a higher O2 concentration and less residual gas. Additionally, the NH40 fuel demonstrated a higher intermediate temperature heat release than the higher octane fuels, potentially contributing to the shorter burn duration. Overall, these results demonstrate clear benefits to NVO enabled HCCI combustion with low octane fuels.

Commentary by Dr. Valentin Fuster
2012;():417-426. doi:10.1115/ICEF2012-92160.

This study presents fundamentals of spray and partially premixed combustion characteristics of directly injected methane inside a constant volume combustion chamber (CVCC). The constant volume vessel is a cylinder with inside diameter of 135 mm and inside height of 135 mm. Two end of the vessel are equipped with optical windows. A high speed complementary metal oxide semiconductor (CMOS) camera capable of capturing pictures up to 40,000 frames per second is used to observe flow conditions inside the chamber. The injected fuel jet generates turbulence in the vessel and forms a turbulent heterogeneous fuel–air mixture in the vessel, similar to that in a compressed natural gas (CNG) direct injection engine. The fuel–air mixture is ignited by centrally located electrodes at a given spark delay timing of 1, 40, 75 and 110 milliseconds after fuel injection has been completed to reflect different turbulence intensities. For comparative study, by increasing the spark delay timing to five minutes, a homogeneous premixed mixture is also prepared in the vessel which provides information on laminar homogeneous mixture combustion.

Spray development and characterization including spray tip penetration, spray cone angle and overall equivalence ratio were investigated under 30–90 bar fuel pressures and 1–5 bar chamber pressure. Flame propagation images and combustion characteristics were determined via pressure-derived parameters and analyzed at a fuel pressure of 90 bar and a chamber pressure of 1 bar at different stratification ratios (from 0% to 100%) at overall equivalence ratios of 0.6, 0.8 and 1.0. Shorter combustion duration and higher combustion pressure were observed in direct injection-type combustion at all fuel air equivalence ratios compared to those of homogenous combustion.

Topics: Combustion , Sprays , Methane
Commentary by Dr. Valentin Fuster
2012;():427-437. doi:10.1115/ICEF2012-92162.

This paper reports an evaluation of various combustion strategies aiming to reduce engine-out particulate matter (PM) emissions from a natural-gas fuelled heavy-duty engine. The work is based on a Westport HPDI fuelling system, which provides direct injection of both natural gas and liquid diesel into the combustion chamber of an otherwise unmodified diesel engine. The diesel acts as a pilot to ignite the natural gas, which normally burns in a non-premixed fashion, leading to significant PM formation. The concepts to reduce PM evaluated in this work are: 1) adjusting the relative phasing of the natural gas and diesel injections to allow more premixing of the natural gas prior to ignition; 2) reducing the pilot quantity to increase the ignition delay of the gas jet; and 3) reducing the level of EGR at select modes to reduce PM formation. These strategies are evaluated at steady state using single- and multi-cylinder research engines, supported by CFD analysis. The results demonstrate that allowing limited premixing of the gas jet prior to ignition can significantly reduce PM emissions. Excessive premixing can lead to high rates of pressure rise; EGR can be used to moderate the combustion under these conditions, without causing increased PM emissions. Reducing pilot quantity is another effective technique to reduce PM, primarily by allowing more air to mix with the gas jet before ignition. These various techniques can be combined to form a new operating strategy that significantly reduces engine-out PM and NOx emissions compared to the baseline strategy without significantly impacting fuel consumption.

Commentary by Dr. Valentin Fuster
2012;():439-445. doi:10.1115/ICEF2012-92165.

This article describes a study involving new spark plug technology, referred to as pulsed energy spark plug, for use in igniting fuel-air mixtures in a spark ignition internal combustion engine. The study involves precisely controlled constant volume combustion bomb tests. The major defining difference between the pulsed energy spark plug and a conventional spark plug is a peaking capacitor that improves the electrical-to-plasma energy transfer efficiency from a conventional plug’s 1% to the pulsed energy plug’s 50%. Such an increase in transfer efficiency is believed to improve spark energy and subsequently the ignition time and burn rate of a homogeneous, or potentially stratified, fuel-air mixture.

The study observes the pulsed energy plug to shorten the ignition delay of both stoichiometric and lean mixtures (with equivalence ratio of 0.8), relative to a conventional spark plug, without increasing the burn rate. Additionally, the pulsed energy plug demonstrates a decreased lean flammability limit that is about 14% lower (0.76 for conventional plug and 0.65 for pulsed energy plug) than that of the conventional spark plug. These features — advanced ignition of stoichiometric and lean mixtures and decreased lean flammability limits — might qualify the pulsed energy plugs as an enabling technology to effect the mainstream deployment of advanced, ultra-clean and ultra-efficient, spark ignition internal combustion engines. For example, the pulsed energy plug may improve ignition of stratified-GDI engines. Further, the pulsed energy plug technology may improve the attainability of lean-burn homogeneous charge compression ignition combustion by improving the capabilities of spark-assist. Finally, the pulsed energy plug could improve natural gas spark ignition engine development by improving the ignition system. Future work could center efforts on evaluating this spark plug technology in the context of advanced internal combustion engines, to transition the state of the art to the next level.

Topics: Combustion , Ignition
Commentary by Dr. Valentin Fuster
2012;():447-455. doi:10.1115/ICEF2012-92170.

High-Pressure Direct-Injection (HPDI) combustion of Natural Gas can reduce the gaseous and Particulate Matter (PM) emissions compared to a conventional diesel engine. Upcoming EPA and EURO emission limits may restrict particle number as well as particle mass. In preparation for these upcoming limits, the PM mass, size and composition was studied from a heavy-duty Cummins ISX engine converted to HPDI operation. To characterize the PM emissions, tests were based around a mid-speed, high-load operating point. Injection timing, equivalence ratio, gas supply pressure, EGR % and diesel injection mass were isolated and varied. PM emissions were characterized by the mobility size distribution, light scattering and filter loading. In addition a novel thermodenuder was used to determine the PM volatile fraction. It was found that EQR and EGR have the greatest effect on PM mass emissions and the correlations between these parameters are evaluated. The mean particles size and number concentrations are again most effected by EGR and EQR with smaller effects from the GRP and diesel pilot. The size distributions of the parameter variations are similar and there are no nucleation mode ultrafine particles observed. The volatile fraction is fairly constant across the parameter variations and is found to be around 18% of the mass and 11% by number of particles at this high load condition.

Commentary by Dr. Valentin Fuster
2012;():457-464. doi:10.1115/ICEF2012-92178.

Premixed charge compression ignition (PCCI) engines have the potential with their attractive advanced combustion process to achieve a more homogeneous mixture and a lower peak combustion temperature resulting in both lower nitrogen oxides (NOx) and diesel particulate matter (PM) emissions. In this study, the spray characteristics for a PCCI engine according to various injection conditions were introduced and then the effects of injection strategies such as injection angles, injection timings and times on combustion and emissions were studied for a single cylinder PCCI engine using early multiple injections first. Add more, a method of early-main type split injection was used for a 4-cylinder PCCI engine and the effects of injection conditions on the combustion and emission characteristics were investigated. Finally flame visualization tests were performed to validate the result obtained from the engine test.

The experimental results showed that the mixture formation, indicated mean effective pressure (IMEP), and emission characteristics were dominantly affected by the injection conditions and the multiple injection method resulted in higher IMEP and still low smoke level characteristics. It appeared that more homogeneous mixture could be formed with decreasing of spray penetration and increasing of fuel evaporation rate for the early multiple injections. In case of the split injection, both injection timing and injected fuel ratio of the early and main injection largely affected engine combustion and emission characteristics. From the results, as the early injection rate increased premixed combustion was activated, on the other hand, as the main injection rate increased conventional diesel combustion was activated, therefore suitable split injection conditions could be selected for the 4-cylinder PCCI engine.

Commentary by Dr. Valentin Fuster
2012;():465-478. doi:10.1115/ICEF2012-92188.

Homogeneous charge compression ignition (HCCI) combustion is widely regarded an attractive option for future high efficiency gasoline engines. HCCI combustion permits operation with a highly dilute, well mixed charge, resulting in high thermal efficiency and extremely low NOx and soot emissions, two qualities essential for future propulsion system solutions.

Because HCCI is a thermo-kinetically dominated process, full understanding of how combustion chamber boundary thermal conditions affect the combustion process are crucial. This includes the dynamics of the effective chamber wall surface temperature, as dictated by the formation of combustion chamber deposits (CCD). It has been demonstrated that, due to the combination of CCD thermal properties and the sensitivity of HCCI to wall temperature, the phasing of auto-ignition can vary significantly as CCD coverage in the chamber increases.

In order to better characterize and quantify the influence of CCDs, a numerical methodology has been developed which permits calculation of the crank-angle resolved local temperature profile at the surface of a layer of combustion chamber deposits. This unique predictor-corrector methodology relies on experimental measurement of instantaneous temperature underneath the layer, i.e. at the metal-CCD interface, and known deposit layer thickness. A numerical method for validation of these calculations has also been devised. The resultant crank-angle resolved CCD surface temperature and heat flux profiles both on top and under the CCD layer provide valuable insight into the near wall phenomena, and shed light on the interplay between the dynamics of the heat transfer process and HCCI burn rates.

Commentary by Dr. Valentin Fuster
2012;():479-487. doi:10.1115/ICEF2012-92192.

Reactivity controlled compression ignition (RCCI) combustion makes use of in-cylinder blending of two fuels with differing reactivity to tailor the reactivity of the fuel charge for improved control of the combustion process. This approach has been shown in simulations and engine experiments to have the potential for high efficiency with very low NOX and particulate matter (PM) emissions. Previous multi-cylinder RCCI experiments have been completed to understand the potential of this approach under more real-world conditions in a light-duty multi-cylinder engine (MCE) with production viable hardware. MCE experiments explored fuel injection strategy, dilution levels, piston geometry (including compression ratio), and fuel properties. Many renewable fuels have unique properties which enable expanded operation of advanced combustion methods for higher engine efficiency and lower energy requirements for emissions control devices. This study investigates the effect that renewable gasoline and diesel fuel replacements have on the load-expansion of RCCI, performance and emissions. The study focuses on ethanol blends for replacement of gasoline as the port-injected fuel (PFI) and biodiesel blends as the replacement for the direct injected (DI) fuel.

Topics: Fuels , Compression , Ignition
Commentary by Dr. Valentin Fuster

Emissions Control Systems

2012;():489-498. doi:10.1115/ICEF2012-92014.

This paper details part two of the demonstration of a 2,240 kW (3,005 HP) PR30C-LE locomotive with exhaust aftertreatment containing diesel oxidation catalysts (DOC) and urea-based selective catalytic reduction (SCR). The PR30C-LE is a remanufactured and repowered, six-axle, diesel-electric, line-haul locomotive. Program objectives were to measure emission levels of the locomotive and record locomotive and aftertreatment operations during a 12 month revenue service field trial. Phase 1 of the program involved engine baseline emissions testing as well as emissions testing with the aftertreatment at the beginning of its useful life, or the 0-hour condition. Results from Phase 1 showed engine-out emission levels were within U.S. EPA Locomotive Tier 2 limits. With aftertreatment at beginning of useful life, hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) were below Tier 4 limits, and particulate matter (PM) was below Tier 3 limits.

Phase 2 consisted of a 12 month revenue service field trial and additional emissions testing completed at the midpoint and end of the field trial. On-board GPS data, aftertreatment NOx sensor data, and various locomotive operating parameters were logged continuously during the field trial. The field trial data suggests the impact SCR technology has on locomotive NOx emissions is driven primarily by locomotive utilization and loading factor. Overall the field trial included 3,082 hours of operation and PRLX3004 generated approximately 572 MW-hours of work over the 12 month period. Emission test results at the 1,500-hour and 3,000-hour conditions showed very little change from 0-hour test results. Emission levels remained below Tier 4 limits for HC, CO, and NOx, and below the Tier 3 limit for PM. Phase 2 test results suggest there was no significant degradation in emissions performance during the field trial, and no major issues with the locomotive and aftertreatment were detected. In total there are currently five PR30C-LE locomotives in operation within California and Arizona. Together they have completed a cumulative 30,800 hours of revenue service through June 2012 without report of a major issue.

Commentary by Dr. Valentin Fuster
2012;():499-504. doi:10.1115/ICEF2012-92034.

Two heavy-duty diesel vehicles operating in an underground salt mine were retrofitted with emission control systems based on selective catalytic reduction technology. The vehicles were then released for production in the mine and the emissions were measured periodically over 18 months.

The systems were very effective in reducing oxides of nitrogen (NOx) emissions from the diesel vehicle engines. The systems were able to provide NOx reductions of 60% to 65% over typical vehicle duty cycles.

This paper will describe the SCR systems, emissions reductions, operability issues and secondary emissions for both vehicles.

Commentary by Dr. Valentin Fuster
2012;():505-513. doi:10.1115/ICEF2012-92036.

Satisfying the coming International Marine Organization (IMO) NOx emissions requirements and regulations is the main focus of attention in marine engine design. Miller cycle, which reduces in-cylinder combustion temperature by reducing effective compression ratio, is the main measure to reduce NOx specific emissions on the cost of volumetric efficiency and engine power. Therefore, it is essential to combine Miller cycle with highly boosted turbocharging system, for example, two stage turbocharing, to recover the power. In this paper, different two stage turbocharging system scenarios are introduced and compared. The system design and matching process is presented. A multi-zone combustion model based one dimensional cycle simulation model is established. The intake valve closure timing and the intake exhaust valves overlap duration are optimized according to the IMO NOx emission limits by the simulation model. The high and low stage turbochargers are selected by an iterative matching method. Then the control strategies of the boost air and the high stage turbine bypass valves are also studied. As an example, a Miller cycle-regulatable two stage turbocharging system is designed for a type of highly boosted high speed marine diesel engine. The results show that the NOx emissions can be reduced 30% and break specific fuel consumption can also be improved by means of moderate Miller cycle combined with regulatable two stage turbocharing.

Commentary by Dr. Valentin Fuster
2012;():515-521. doi:10.1115/ICEF2012-92063.

The use of biodiesel has been widely accepted as an effective solution to reduce greenhouse emissions. The high potential of biodiesel in terms of PM emission reduction may represent an additional motivation for its wide diffusion. This potential is related to the oxygenated nature of biodiesel, leading to a different PM-NOx trade-off. Wide diffusion is also under debate as it may represent a solution to the highly disputed issue of the development of alternative biofuels sources not competing with the food chain. In fact, besides second generation biofuels (e.g. from algae), the transesterification of Waste Cooking Oil (WCO) is another option, that however needs additional insight. In fact, in this case, the effects on particle emissions are still not well assessed, as well as the impact of fuel distillation on engine performance and emissions.

In this paper an experimental study on particle emissions of a DEUTZ 4L off-road Diesel engine coupled to a DOC-DPF system is proposed. Experimental data have been gathered at the engine test bench of the University of Rome Tor Vergata, by using baseline fossil fuel (B06) and blends (30% vol) with both distilled and non distilled WCO biodiesel. Data have been acquired with respect to the three most probable engine points referring to the NRTC (Non-Road-Transient-Cycle), upstream and downstream of the AfterTreatment System.

Results show that B30 fuels have always lower emission on a mass and number basis, and that distillation process may have an impact especially at high power and torque operation. A slightly better behavior in terms of mass emissions has been observed for the blend with distilled fuel, while a slightly better behavior in terms of particle number has been observed for the blend with non-distilled fuel.

Commentary by Dr. Valentin Fuster
2012;():523-536. doi:10.1115/ICEF2012-92090.

Utilization of biogas is attractive from a greenhouse gas standpoint since it is carbon neutral due to the use of renewable resources. One source of biogas is anaerobic digestors. The biogas produced could be used to power IC engine-generator sets to produce electric power and heat on farms and in rural and northern communities. Use of local energy sources is particularly attractive in remote regions where liquid fuels must be shipped in via difficult terrain. Whatever the fuel, the engine must meet stringent exhaust emission standards. Biogas is typically used in spark ignition engines, where stoichiometric engine operation coupled to a three-way catalyst is a proven technology for achieving low emissions. An appropriate three-way catalyst was selected on the basis of tests with natural gas. A flow mixing system was used to create simulated biogas mixtures consisting of varying concentrations of methane, carbon dioxide, hydrogen and nitrogen. The effectiveness of the catalyst in achieving low emissions when the engine was fueled by the various simulated biogas mixtures was assessed.

Commentary by Dr. Valentin Fuster
2012;():537-549. doi:10.1115/ICEF2012-92104.

The Diesel Exhaust Filtration Analysis (DEFA) system, developed at the University of Wisconsin – Madison Engine Research Center (ERC), was used to study diesel particulate filters at the micro scale level. Previous measurements using the system have shown that there is a considerable effect of ash accumulation on the filter permeability evolution. Also the pressure drop and loading history are dependent on the number of times a filter had been filled and regenerated. The current investigation of the ash accumulation process has been done to understand its impact on the filter wall permeability over multiple loadings. Three different PM loading conditions were tested over four consecutive loading/regeneration cycles. The pressure history and particle breakthrough for each subsequent loading and regeneration has been recorded. The measurements examine the ash penetration and accumulation for the different operating conditions and for the different number of loadings and regenerations. The results show that the PM deposition mechanism has a significant impact on the ash accumulation process especially within the filter walls. The ash deposition process appears to have a distinct wall loading stage followed by ash membrane formation.

Commentary by Dr. Valentin Fuster
2012;():551-561. doi:10.1115/ICEF2012-92105.

In 2007, U.S. certification standards for heavy duty on-road diesel engine particulate matter (PM) emissions were reduced from 0.1g/bhp-hr to 0.01g/bhp-hr, representing an order of magnitude reduction in pollutant level. The Tier 4 standards for nonroad diesel engines, being phased in from 2008 through 2015, also require similar level of reduction in PM. Most conventional diesel engines could meet these low PM standards, once equipped with a diesel particulate filter (DPF). However, accurate, repeatable measurements of this PM may pose significant challenges. Gravimetric PM measurement involves diluting exhaust, then collecting the resultant aerosol sample on approved filter media. Few data exist to characterize the evolution of particulate matter (PM) in dilution tunnels, particularly at very low PM mass levels. Data are lacking as well, for PM evolution in portable dilution instruments and in exhaust plumes downstream of the tailpipe. Size distributions of ultra-fine particles in the diesel exhaust from a naturally aspirated ISUZU C240 diesel engine, equipped with a DPF, were studied. Particle size distribution data, during steady-state engine operations, were collected using a Cambustion DMS500 Fast Particulate Spectrometer. The effects of dilution ratios, dilution rates, and residence times on the diesel particulate matter (DPM) size distributions were analyzed and discussed. Measurements were made for three dilution methods: dilution in standard primary and secondary-dilution tunnels with a full scale Constant Volume Sampler (CVS) system, instrument dilution with a Portable Particulate Measurement Device (PPMD), and ambient dilution at the post-tailpipe exhaust plume centerline. Gaseous emissions measurements were utilized as surrogate confirmation of adequate mixing at the various measurement locations, as well as an indicator of dilution ratios. Tunnel sample results indicated varying size distributions at tunnel cross sections where the flow was still developing. Evolution of particle-size distributions was observed even for fully mixed primary flow conditions. Size distributions at the end of the secondary dilution tunnel were observed to vary with different secondary-dilution ratios. Particle-size distributions of post-tailpipe and PPMD test results were analyzed and compared with those results collected from the full-flow tunnel. Results from post-tailpipe sampling indicate that nucleation was the dominant process when the exhaust plume was diluted along the post-tailpipe centerline. Results from PPMD dilution measurements indicate that change of particle-size-distribution curves, including number count and mass concentration levels, were not as strongly correlated to dilution ratios as were the results from the other two sampling methods. This study shows that particle-size distributions measured inside full-flow dilution tunnel can adequately mimic freshly emitted exhaust sampled immediately post-tailpipe.

Commentary by Dr. Valentin Fuster
2012;():563-575. doi:10.1115/ICEF2012-92106.

In 2006, the ports of Long Beach and Los Angeles adopted the final San Pedro Bay Ports Clean Air Action Plan (CAAP), initiating a broad range of programs intended to improve the air quality of the port and rail yard communities in the South Coast Air Basin. As a result, the Technology Advancement Program (TAP) was formed to identify, evaluate, verify and accelerate the commercial availability of new emissions reduction technologies for emissions sources associated with port operations, [1]. Container drayage truck fleets, an essential part of the port operations, were identified as the second largest source of NOx and the fourth largest source of diesel PM emissions in the ports’ respective 2010 emissions inventories [2, 3]. In response, TAP began to characterize drayage truck operations in order to provide drayage truck equipment manufacturers with a more complete understanding of typical drayage duty cycles, which is necessary to develop emissions reduction technologies targeted at the drayage market.

As part of the broader TAP program, the Ports jointly commissioned TIAX LLC to develop a series of drayage truck chassis dynamometer test-cycles. These cycles were based on the cargo transport distance, using vehicle operational data collected on a second-by-second basis from numerous Class 8 truck trips over a period of two weeks, while performing various modes of typical drayage-related activities. Distinct modes of operation were identified; these modes include creep, low-speed transient, high-speed transient and high-speed cruise. After the modes were identified, they were assembled in order to represent typical drayage operation, namely, near-dock operation, local operation and regional operation, based on cargo transport distances [4].

The drayage duty-cycles, thus developed, were evaluated on a chassis dynamometer at West Virginia University (WVU) using a class 8 tractor powered by a Mack MP8-445C, 13 liter 445 hp, and Model Year (MY) 2011 engine. The test vehicle is equipped with a state-of-the-art emissions control system meeting 2010 emissions regulations for on-road applications. Although drayage trucks in the San Pedro Bay Ports do not have to comply with the 2010 heavy-duty emissions standards until 2023, more than 1,000 trucks already meet that standard and are equipped with diesel particulate filter (DPF) and selective catalytic reduction (SCR) technology as used in the test vehicle. An overview of the cycle evaluation work, along with comparative results of emissions between integrated drayage operations, wherein drayage cycles are run as a series of shorter tests called drayage activities, and single continuous drayage operation cycles will be presented herein. Results show that emissions from integrated drayage operations are significantly higher than those measured over single continuous drayage operation, approximately 14% to 28% for distance-specific NOx emissions. Furthermore, a similar trend was also observed in PM emissions, but was difficult to draw a definite conclusion since PM emissions were highly variable and near detection limits in the presence of DPF. Therefore, unrepresentative grouping of cycle activity could lead to over-estimation of emissions inventory for a fleet of drayage vehicles powered by 2010 compliant on-road engines.

Commentary by Dr. Valentin Fuster
2012;():577-582. doi:10.1115/ICEF2012-92130.

This paper documents the initial test results of a locomotive diesel particulate filter (DPF) retrofit project. The locomotive used for this project was BNSF1284, a 1,566 kW National Railway Equipment Company (NREC) model 3GS21B, originally manufactured in April, 2008, and designed to be an Ultra-Low Emissions Locomotive (ULEL). This genset switcher locomotive uses three Cummins QSK19 Cummins 522 kW diesel-engine driven generator sets (Genset 1, 2, and 3) to provide the power needed to drive the traction motors.

The GT Exhaust Diesel Particulate Filter (DPF) retrofit system, installed on BNSF1284, uses catalyzed DPF elements. The DPF, and its catalyzed coating, offered significant hydrocarbons (HC), carbon monoxide (CO), and particulate (PM) emissions reduction. Additionally, the catalyzed coating should allow the diesel particulate filters to passively regenerate at moderate exhaust temperatures, thus keeping the engine back pressure within allowable limits of the manufacture.

The GT Exhaust DPF’s were installed in place of the standard mufflers on each of the three engines. The GT Exhaust DPF’s are roughly the same size as the stock muffler. The only locomotive modification needed to install the GT Exhaust DPF’s was to the muffler mounting platform, directly above the engine, where the exhaust pipe opening needed to be enlarged. There are no external modifications to the locomotive car body needed to install the GT Exhaust DPF’s.

After installation of the DPF’s, they were degreened by operating the engines at rated power for 20 hours. After degreening testing was performed according to Title 40 of the U. S. Code of Federal Regulations (CFR), Part 92, Subpart B. The addition of the DPF reduced the PM emissions to 0.016 g/kW-hr or 60 percent below the locomotive Tier 4 PM limits.

BNSF1284 was returned to revenue service in Richmond, California in March 2012, where the DPF performance will be tracked for 3,000 hours of operation as part of a California Air Resources Board (CARB) verification program.

Commentary by Dr. Valentin Fuster
2012;():583-590. doi:10.1115/ICEF2012-92167.

In July 2008, Union Pacific Railroad (UP) and Electro-Motive Diesel, Inc. (EMD) began discussions to jointly investigate the potential for exhaust gas recirculation (EGR) on a small group of re-powered UP locomotives, to assess the potential for EGR as a technology to meet the oxides of nitrogen (NOx) requirement in US Environmental Protection Agency (EPA) Tier 4 locomotive emissions regulations on newly-manufactured future diesel locomotives effective January 1, 2015 [1].

After several years of research, engineering and experimental testing, EMD began delivering to UP in late-2011 nine SD59MX experimental locomotives equipped with prototype EGR technology as a first step to achieving Tier 4 NOx reductions, plus a tenth SD59MX unit equipped with both the EGR technology and an experimental whole-engine aftertreatment package to migrate toward Tier 4 particulate matter (PM) levels on future new Tier 4 locomotives. Compared to today’s Tier 2 emission limits, the EGR equipped SD59MX produces 42 percent less NOx, a significant step toward the development of new Tier 4 locomotives.

Commentary by Dr. Valentin Fuster
2012;():591-600. doi:10.1115/ICEF2012-92198.

For the first time in the locomotive industry, an advanced exhaust aftertreatment system for a locomotive application was successfully demonstrated to reduce nitrogen oxides from 6.46 g/kW·hr to 1.21g/kWhr to meet the needs of local NOx reduction requirements for non-attainment areas.

Five 2,240 kW (3,005 horsepower) PR30C line-haul repowered Progress Rail locomotives were equipped with diesel oxidation catalyst and selective catalytic reduction technologies to accumulate more than 27,000 hours in total in revenue service.

Full emissions performance including carbon monoxide, hydrocarbons, nitrogen oxides and particulate matter was conducted at Southwest Research Institute on a regular basis to measure the change of emissions performance for two selected locomotives.

The emissions performance of the aftertreatment system did not show any degradation during 3,000 hours operation. After 3,000 hours operation, 0.13 g/kW·hr carbon monoxide (89–91% reduction), 0.027 g/ kW·hr hydrocarbons (91% reduction), 1.08–1.21 g/ kW·hr nitrogen oxides (81–83% reduction) and 0.05–0.08 g/ kW·hr particulate matter (38–58% reduction) were measured on the line-haul cycle. The baseline emissions levels of the engine are within Tier 2 EPA locomotive limits. The newly developed close loop control software successfully controlled targeted nitrogen oxides reduction with minimum ammonia slip during the locomotive emission cycle tests.

Topics: Locomotives
Commentary by Dr. Valentin Fuster
2012;():601-607. doi:10.1115/ICEF2012-92199.

Exhaust gas recirculation (EGR) is an effective engine internal measure to reduce NOx emissions. This is e.g. constituted by the fact that the NOx limit of the current European on-road emission regulation EURO V can be met exclusively by the application of EGR (an overview on emissions regulations is e.g. given in [1]). However, the proposed NOx limits for the upcoming regulations have been lowered significantly which implicates much higher EGR rates compared to the EURO V applications if this strategy is further pursued. This is valid for both the future on-road regulation (EURO VI) and the off-road regulation (Stage IV). In this paper main focus is laid on off-road applications.

One of the main challenges of this task refers to transient engine operation which also requires EGR. Thus, great demands are made to the design and calibration of the charging system in order to guarantee acceptable load response characteristics during the acceleration phases.

An experimental study was carried out with a modified EURO V heavy duty engine which was operated in an engine test cell under stationary and transient conditions with various engine settings. These primarily referred to the EGR rate and smoke limitations during transient operation. In this way the NOx, soot and load response characteristics were systematically investigated. With the used test engine the NOx emissions could not be lowered below a level of approximately 0.6 g/kWh in the Non-Road Transient Test Cycle (NRTC) [1] without a significant deterioration in load response (for comparison — the proposed Stage IV NOx limit is 0.4 g/kWh in the NRTC).

Commentary by Dr. Valentin Fuster

Instrumentation, Controls, and Hybrids

2012;():609-615. doi:10.1115/ICEF2012-92018.

This paper presents a feasibility analysis on the application of Organic Rankine Cycles as a Waste Heat Recovery system for automotive internal combustion engines. The analysis is conducted considering the Ohio State University EcoCAR, a student prototype plug-in hybrid electric vehicle, as a case study for preliminary fuel economy evaluation. Starting from a energy-based powertrain simulation model validated on experimental data from the prototype vehicle, a first and second-law analysis was conducted to identify the potential for engine waste heat recovery, considering a variety of driving cycles and assuming the vehicle operating in charge-sustaining (HEV) mode. Then, a quasi-static thermodynamic model of an Organic Rankine Cycle (ORC) was designed, calibrated from data available in literature and optimized to fit the prototype vehicle. Simulations were then carried out to evaluate the amount of energy recovered by the ORC system, considering both urban and highway driving conditions. The results of the simulations show that a simple ORC system is able to recover up to 10% of the engine waste heat on highway driving conditions, corresponding to a potential 7% improvement in fuel consumption, with low penalization of the added weight to the vehicle electric range.

Commentary by Dr. Valentin Fuster
2012;():617-629. doi:10.1115/ICEF2012-92091.

Over the past few decades there has been considerable progress made in understanding the processes leading to formation and evolution of particulate matter (PM) emissions from heavy duty diesel engines (HDDE). This progress has been primarily made under controlled laboratory conditions with the use of constant volume sampling (CVS) systems and to a limited extend through on-road chase studies. West Virginia University (WVU) is attempting to close the present knowledge gap by conducting detailed experiments in a custom designed and constructed environmental wind tunnel. The understanding and knowledge has recently been further extended to new emission reduction technologies, such as the diesel particulate filter (DPF) which has dramatically changed the size distribution and chemical composition of PM. Additionally, the selective catalytic reduction (SCR) technology has shown to further enhance the formation of nucleation mode particles as well as alter their morphology. Even with advances in technology there remains a considerable gap in the current level of understanding of PM formation and evolution, since the combustion generated PM from diesel engines is not discernible from the atmospheric background PM measured beyond 300m from highways. After being emitted from the vehicle exhaust system, the process of dilution in the atmosphere leads to a multitude of PM transformation phenomena, such as volatilization, coagulation, and condensation. The work presented herein has been divided into two parts which are published separately from each another.

The first part describes the design and commissioning process of the wind tunnel focusing on both, aerodynamic and structural constraints, which ultimately led to the definition of the main characteristics of the facility. The resulting design is a subsonic, non-recirculating, suction type tunnel, with a 16ft high and 16ft wide test section capable of housing a full-size heavy-duty tractor cab. A 2,200hp suction fan is employed to provide up to 80 mph wind speeds. The 115ft test cell length guarantees for a 2 second residence time for the exhaust plume evolution (at 35 mph) and complies with turbulence intensity (less than 1%) and quality flow requirement as identified for this type of application. In addition, the West Virginia University (WVU) wind tunnel has been equipped with a custom made sampling system able to move in all three dimensions in order to measure spatially resolved plume characteristics.

The second part will describe the actual test procedures and the experimental results and will be published in a separate paper.

Commentary by Dr. Valentin Fuster
2012;():631-646. doi:10.1115/ICEF2012-92093.

Cold starting of diesel engines is characterized by inherent problems such as long cranking periods and combustion instability leading to an increase in fuel consumption and the emission of high concentrations of hydrocarbons which appear as white smoke. The ion current signal has been considered for the feedback control of both gasoline and diesel engines. However, the ion current signal produced from the combustion of the heterogeneous charge in diesel engines is weaker compared to that produced from the combustion of the homogeneous charge in gasoline engines. This presents a problem in the detection of the ion current signal in diesel engines, particularly during starting and idling operations. This paper investigates and addresses the ion current detection problems pertaining to cold starting and various idling speeds. Also, different approaches have been investigated to improve the signal detection under these conditions.

Topics: Diesel engines
Commentary by Dr. Valentin Fuster
2012;():647-656. doi:10.1115/ICEF2012-92184.

The objective of this investigation was to compare the results of metallurgical temperature sensors and thermocouples when used to measure piston temperatures in a running engine. Type J thermocouples and a microwave wireless telemetry system were used to gather real time temperature data on the piston in the vicinity of each metallurgical sensor. Eight pairs of metallurgical temperature sensors were installed in the piston with a thermocouple junction in-between. The engine was ramped up to steady state quickly and then held for approximately four hours at 1800 RPM and 1980 N-m before being quickly ramped back down in accordance with the metallurgical sensors’ recommended test cycle. During the test, continuous temperature data at each of the sensor locations was monitored and recorded using the telemetry system. After the test was complete, the metallurgical temperature sensors were removed and independently analyzed. The results indicate that readings from the metallurgical temperature sensors were similar to those of the embedded thermocouples for locations without large thermal gradients. However, when thermal gradients were present, the metallurgical sensor’s reading was influenced measurably.

Commentary by Dr. Valentin Fuster
2012;():657-666. doi:10.1115/ICEF2012-92191.

This paper describes an experimental study concerning the feasibility of monitoring the combustion instability levels of an HCCI engine based upon cycle-by-cycle exhaust temperature measurements. The test engine was a single cylinder, four-stroke, variable compression ratio Cooperative Fuel Research (CFR) engine coupled to an eddy current dynamometer. A rugged exhaust temperature sensor equipped with special signal processing circuitry was installed near the engine exhaust port. Reference measurements were provided by a laboratory grade, water-cooled cylinder pressure transducer. The cylinder pressure measurements were used to calculate the Coefficient of Variation of Indicated Mean Effective Pressure (COV of IMEP) for each operating condition tested.

Experiments with the HCCI engine confirmed that cycle-by-cycle variations in exhaust temperature were present, and were of sufficient magnitude to be captured for processing as high fidelity signal waveforms. There was a good correlation between the variability of the exhaust temperature signal and the COV of IMEP throughout the operating range that was evaluated. The correlation was particularly strong at the low levels of COV of IMEP (2–3%), where production engines would typically operate.

A real-time combustion instability signal was obtained from cycle-by-cycle exhaust temperature measurements, and used to provide feedback to the fuel injection control system. Closed loop operation of the HCCI engine was achieved in which the engine was operated as lean as possible while maintaining the COV level at or near 2.5%.

Commentary by Dr. Valentin Fuster
2012;():667-676. doi:10.1115/ICEF2012-92194.

Accurate combustion analysis at the test bed is an important tool for the development engineer. It can help engine design, efficiency improvements or emissions reduction by providing instantaneous feedback on the combustion process. It can also provide detailed combustion information to help speed-up the engine calibration process. By implementing shared memory communication, multiple core capability and streamlined calculation techniques, the calculation time of AVL gas exchange and combustion analysis software GCA (Gas Exchange and Combustion Analysis) has been dramatically reduced without significantly decreasing calculation results accuracy. This allows AVL IndiCOM (in combination with AVL GCA) to perform accurate gas exchange and combustion analysis calculations directly and promptly at the test bed. This opens the door to a number of promising new applications by erasing the bridge between measurement data acquisition and post-processing analysis. Increase of measurement data consistency and the reduction of development time are two of the most important benefits of being able to perform “on-line” plausibility checks of measurement data. The strong links connecting AVL GCA calculation results to the measurement data and the redundancy between calculation and measurement for the assessment of some highly relevant engine parameters (e.g. IMEP, air mass flow) can greatly extend the “on-line” plausibility checks functions already available in AVL IndiCom or AVL test bed automation software PUMA. Some passenger car application examples, where valve train flexibility is used to enhance fuel economy or reduce exhaust emissions of internal combustion engines, show that the immediate availability at the test bed of gas exchange related parameters (e.g. internal EGR rate, scavenged mass, mass flows through the valves) supports an intuitive optimization of the valve train parameters.

Topics: Combustion
Commentary by Dr. Valentin Fuster

Numerical Simulation

2012;():677-686. doi:10.1115/ICEF2012-92012.

Quasi-dimensional models are widely used in the design, development and analyses of automotive engines. Various phenomenological and empirical relations are used in these models to reduce the computational load compared to multi-dimensional models. These quasi-dimensional models have also been used to calculate NOx, soot and HCs using various reduced chemistry/simplified models. The extended Zeldovich mechanism is widely used for finite-rate NOx computations in these quasi-dimensional models. However, there are several simplifying assumptions in the rate equation used for the NOx computations. This paper compares the traditional method of finite-rate NOx computations with full finite-rate chemistry without the simplifying assumptions used in the former method. NOx formation in a stationary engine is studied using a single zone and two-zone (burned and unburned zone) using a 6-reaction, 7-species model. A detailed comparison of the two methods of NO computation is presented. Analyses of the temporal variation of NO predicted using these two approaches is also presented.

Commentary by Dr. Valentin Fuster
2012;():687-696. doi:10.1115/ICEF2012-92042.

In this work, a Cartesian-grid immersed boundary method using a cut-cell approach is applied to three-dimensional in-cylinder flow. A hierarchically coupled level-set solver is used to capture the boundary motion by a signed distance function. Topological changes in the geometry due to the opening and closing events of the valves are modeled consistently using multiple signed distance functions for the different components of the engine and taking advantage of a level-set reinitialization method. A continuous discretization of the flow equations in time near the moving interfaces is used to prevent nonphysical oscillations. To ensure an efficient implementation, independent grid adaptation for the flow and the level-set grid is applied. A narrow band approach and an efficient joining/splitting algorithm for the level-set functions minimize the computational overhead to track multiple interfaces. The ability of the current method to handle complex 3D setups is demonstrated for the interface capturing and the flow solution in a three-dimensional piston engine geometry.

Commentary by Dr. Valentin Fuster
2012;():697-710. doi:10.1115/ICEF2012-92043.

A state-of-the-art spray modeling methodology is presented. Key features of the methodology, such as Adaptive Mesh Refinement (AMR), advanced liquid-gas momentum coupling, and improved distribution of the liquid phase, are described. The ability of this approach to use cell sizes much smaller than the nozzle diameter is demonstrated. Grid convergence of key parameters is verified for non-evaporating, evaporating, and reacting spray cases using cell sizes down to 1/32 mm. Grid settings are recommended that optimize the accuracy/runtime tradeoff for RANS-based spray simulations.

Commentary by Dr. Valentin Fuster
2012;():711-722. doi:10.1115/ICEF2012-92045.

A skeletal mechanism with 117 species and 472 reactions for a Diesel surrogate i.e., n-heptane, was developed. The detailed mechanism for n-heptane created by Lawrence Livermore National Laboratory (LLNL) was employed as the starting mechanism. The detailed mechanism was then reduced with an enhancement of the Direct Relation Graph (DRG) technique called Parallel DRG-with Error Propagation and Sensitivity Analysis (PDRGEPSA). The reduction was performed for pressures from 20 to 80 atm, equivalence ratios from 0.5 to 2, and an initial temperature range of 600–1200 K, covering the compression ignition (CI) engine conditions. Extensive validations were performed against both 0-D simulations with the detailed mechanism and experimental data for spatially homogeneous systems. In order to perform three-dimensional turbulent spray-combustion and engine simulations, the mechanism was integrated with the multi-zone model in the CONVERGE CFD software to accelerate the calculation of detailed chemical kinetics. The Engine Combustion Network (ECN) data from Sandia National Laboratory was used for validation purposes along with single-cylinder Caterpillar engine data. The skeletal mechanism was able to predict various combustion characteristics accurately such as ignition delay and flame lift-off length (LOL) under different ambient conditions. The performance of the multi-zone solver with respect to the full cell-by-cell chemistry solver (SAGE) is compared for the Caterpillar engine simulation and a good match is obtained with significant speed-up of computational time for the multi-zone solver.

Commentary by Dr. Valentin Fuster
2012;():723-736. doi:10.1115/ICEF2012-92052.

This paper presents a detailed exergy analysis of homogeneous charge compression ignition (HCCI) engines, including a crank-angle resolved breakdown of mixture exergy and exergy destruction. Exergy analysis is applied to a multi-zone HCCI simulation including detailed chemical kinetics. The HCCI simulation is validated against engine experiments for ethanol-fueled operation. The exergy analysis quantifies the relative importance of different loss mechanisms within HCCI engines over a range of engine operating conditions. Specifically, four loss mechanisms are studied for their relative impact on exergy losses, including 1) the irreversible combustion process (16.4–21.5%), 2) physical exergy lost to exhaust gases (12.0–18.7%), 3) heat losses (3.9–17.1%), and 4) chemical exergy lost to incomplete combustion (4.7–37.8%). The trends in each loss mechanism are studied in relation to changes in intake pressure, equivalence ratio, and engine speed as these parameters are directly used to vary engine power output. This exergy analysis methodology is proposed as a tool to inform research and design processes, particularly by identifying the relative importance of each loss mechanism in determining engine operating efficiency.

Commentary by Dr. Valentin Fuster
2012;():737-745. doi:10.1115/ICEF2012-92057.

Diverse kinetic models for iso-octane, n-heptane, toluene and ethanol i.e. main gasoline surrogates, have been investigated. The models have different levels of complexity and strong and weak points. Firstly, ignition delay times for various fuel blends have been calculated and compared with published shock tube measurements. Kinetic models which are capable of distinguishing between Primary and Toluene Reference Fuels have been used further on in a zero-dimensional Homogeneous Charge Compression Ignition engine model to predict auto-ignition. The modelling results have been compared to the experimental results obtained in a single cylinder research engine. A discussion has been made on the ability of these models to predict autoignition.

Commentary by Dr. Valentin Fuster
2012;():747-756. doi:10.1115/ICEF2012-92059.

Due to the nature of the engine cycle, heat transfer has a significant role in the estimation of engine efficiency. The effects are quite well known in the classic combustion concepts, compression ignition (CI) and spark ignition (SI) combustion. But for the newer, low temperature combustion (LTC) concepts, these effects are not that well known. In this paper, a commercial computational fluid dynamics (CFD) code, AVL FIRE, is used to evaluate engine performance and emissions for different thermal settings in the engine cylinder of a LTC engine. Design of experiments (DoE) methodology is applied to model the response variables and quantify the effects from different model variables on the response. The results show that, within the parameter space chosen for this work, the strongest effect on the in-cylinder heat transfer and engine performance comes from the temperature and pressure at inlet valve closing, as well as the piston wall temperature. The values giving the best combination of low heat loss and high performance are high temperature walls along with cold inflowing air and high boost pressure.

Commentary by Dr. Valentin Fuster
2012;():757-765. doi:10.1115/ICEF2012-92087.

The interest in lasers for engine ignition is the possibility of higher efficiency and reduction of pollutants compared with conventional spark plugs. The interest in this area is to understand the laser energy needed for breakdown and ignition in order to better design practical systems. To support such development, the laser induced breakdown of air is simulated by the use of a two-dimensional computational fluid-dynamic model for 10 and 46 ns laser pulses for several pressures and focal spot sizes. The simulation includes the laser propagation, multi-photon ionization, impact ionization, electrons heating and energy loss. The dependence of breakdown irradiance on pulse duration, ambient pressure, and dimensions of the focal region is investigated and compared with experimental results.

Topics: Lasers , Simulation
Commentary by Dr. Valentin Fuster
2012;():767-779. doi:10.1115/ICEF2012-92099.

Direct injection natural gas (DING) engines offer the advantages of high thermal efficiency and high power output compared to spark ignition natural gas engines. Injected natural gas requires some form of ignition assist in order to ignite in the time available in a diesel engine combustion chamber. A glow plug — a heated surface — is one form of ignition assist.

Simple experiments show that the thickness of the heat penetration layer of a glow plug is very small (≈10−5 m) within the time scale of the ignition preparation period (1–2 ms). Meanwhile, the theoretical analyses reveal that only a very thin layer of the surrounding gases (in micrometer scale) can be heated to high temperature to achieve spontaneous ignition. A discretized glow plug model and virtual gas sub-layer model have been developed for CFD modeling of glow plug ignition and combustion for DING diesel engines.

In this paper, CFD modeling results are presented. The results were obtained using a KIVA3 code modified to include the above mentioned new developed models. Natural gas ignition over a bare glow plug was simulated. The results were validated against experiments. Simulation of natural gas ignition over a shielded glow plug was also carried out and the results illustrate the necessity of using a shield.

This paper shows the success of the discretized glow plug model working together with the virtual gas sub-layer model for modeling glow plug assisted natural gas direct injection engines. The modeling can aid in the design of injection and ignition systems for glow plug assisted DING engines.

Commentary by Dr. Valentin Fuster
2012;():781-791. doi:10.1115/ICEF2012-92133.

Dual fuel engines offer the potential for considerable reductions in emissions of carbon dioxide (CO2), as well as reducing emissions of particulate matter (PM). However, the combustion processes occurring inside a dual fuel engine are complex. This is due to the ignition of a homogeneous lean premixed charge by a pilot fuel spray, which combines elements of both conventional spark ignition and diesel combustion.

Combustion models provide an effective means of investigating the phenomena taking place inside the cylinder. This paper describes a phenomenological model used for performance and emissions predictions in a dual fuel engine. The pilot fuel spray is described using a packet model approach, which includes sub-models for spray development and mixing, swirl, spray wall impingement, ignition and combustion. Flame growth is coupled to the burning zones in the cylinder and is described using a turbulent entrainment model. Oxides of nitrogen (NOx) and PM are also evaluated.

Simulated in-cylinder pressures and rates of heat release are in good agreement with experimental data obtained from a naturally aspirated, in-line, four-cylinder, direct injection diesel engine operating with methane (CH4) as the gaseous fuel. Crank angle resolved emissions of NOx and PM are also presented. The model results give good confidence in the current approach for the description of premixed combustion following the ignition of the pilot.

Topics: Combustion , Fuels , Modeling
Commentary by Dr. Valentin Fuster
2012;():793-801. doi:10.1115/ICEF2012-92137.

While the transportation field is mostly characterized by the use of liquid fuels, gaseous fuels like hydrogen and natural gas have shown high thermal efficiency and low exhaust emissions when used in internal combustion engines (ICEs). In particular, high-pressure direct injection of a gaseous fuel within the cylinder overcomes the loss of volumetric efficiency and allows stratifying the mixture around the spark plug at the ignition time. Direct injection and mixture stratification can extend the lean flammability limit and improve efficiency and emissions of ICEs.

Compared to liquid sprays, the phenomena involved in the evolution of gaseous jets are less complex to understand and model. Nevertheless, the numerical simulation of a high-pressure gas jet is not a simple task. At high injection pressure, immediately downstream of the nozzle exit the flow is supersonic, the gas is under-expanded, and a large series of shocks occurs due to the effect of compressibility. To simulate and capture these phenomena, grid resolution, computational time-step, discretization scheme, and turbulence model need to be properly set.

The research group on hydrogen ICEs at Argonne National Laboratory has been extensively working on validating numerical results on gaseous direct injection and mixture formation against PIV and PLIF data from an optically accessible engine. While a good general agreement was observed, simulations still could not perfectly predict the mixing of fuel with the surrounding air, which sometimes led to significant under-prediction of fuel dispersion. The challenge is to correctly describe the gas dynamic phenomena of under-expanded gas jets. To this aim, x-ray radiography was performed at the Advanced Photon Source (APS) at Argonne to provide high-detail data of the mass distribution within a high-pressure gas jet, with the main focus on the under-expanded region.

In this paper, the numerical simulation of high-pressure (100 bar) injection of argon in a cylindrical chamber is performed using the computational fluid dynamic (CFD) solver Fluent. Numerical results of jet penetration and mass distribution are compared with x-ray data. The simplest nozzle geometry, consisting of one hole with a diameter of 1 mm directed along the injector axis, is chosen as a canonical case for modeling validation. A sector (90°) mesh, with high resolution in the under-expanded region, is used and the assumption of symmetry is made. Results show good agreement between CFD and x-ray data. Gas dynamics and mass distribution within the jet are well predicted by numerical simulations.

Commentary by Dr. Valentin Fuster
2012;():803-811. doi:10.1115/ICEF2012-92158.

A phenomenological model (called here “Slice Model”) has been developed to simulate non-premixed gas jet flames including soot formation in the domain. The Slice Model is based on the self-similarity solution of gas jets and forced to satisfy momentum, mass and energy balances in every cross section. The Slice Model can predict the velocity, mass fraction and temperature field of non-reacting and reacting jets over a wide range of changes in the jet parameters. A sub-model for soot formation based on Hiroyasu’ model is applied to predict soot formation in non-premixed flames. Cantera, an open-source chemical kinetics software, is integrated with the Slice Model to predict the temperature distribution (based on equilibrium composition) of reacting jets. The soot formation prediction of the Slice Model is compared with experimental data in the literature. For velocity, soot mass fraction and temperature, agreement with experiment is about as good as it is for the much more computationally intensive RANS CFD simulations. On this basis, the Slice Model is promising as the core of a non-premixed natural gas engine simulation package under development.

Commentary by Dr. Valentin Fuster
2012;():813-821. doi:10.1115/ICEF2012-92173.

Engine-out HC emissions resulting from liquid fuel, which escapes from the combustion process, provides the motivation to better understand the film vaporization in a combustion chamber. Previous work theorized that the removal of liquid fuel from the combustion cycle was a result of the increase in film vaporization time due to the Leidenfrost phenomenon. Currently, KIVA 3V predicts a continuous decrease in vaporization time for piston top films. The objective of this work is to improve the KIVA 3V film vaporization model through the inclusion of established boiling correlations, and thus, the Leidenfrost phenomenon.

Experimental results have been reviewed from which expressions encompassing high acceleration effects for the nucleate boiling regime and the film boiling regime were investigated, implemented, and validated. Validation was conducted using published experimental data sets for boiling heat flux. As a result of the implementation, a noticeable increase in heat flux occurred due to high accelerations for films in saturated film boiling in both nucleate and film boiling.

Computational simulations were conducted using a semi-infinite plate and a direct-injection spark-ignition engine. The semi-infinite plate provided a controlled environment which could separate the effects of pressure and acceleration on film boiling heat flux, film vaporization rates, and film vaporization times. The effect of decreased film vaporization rates, during the Leidenfrost phenomenon, was observed to decrease with increasing acceleration. Finally, the engine computations were used to provide the first film boiling and film vaporization rates for engine fuel films at temperatures above saturation temperature. As a result of this work, a film vaporization model capable of improved prediction of vaporization rates of piston top films in saturated boiling conditions has been created.

Commentary by Dr. Valentin Fuster
2012;():823-829. doi:10.1115/ICEF2012-92175.

A numerical study of micro-explosion in multi-component bio-fuel droplets is presented. The onset of micro-explosion is characterized by the normalized onset radius (NOR). Bubble expansion is described by a modified Rayleigh equation. The final breakup is modeled from a surface energy approach by determining the minimal surface energy (MSE). After the breakup, the Sauter mean radius (SMR) for initially small size droplets can be estimated from a look-up table generated from the current breakup model. There exists an optimal droplet size for the onset of micro-explosion. The MSE approach reaches the same conclusion as previous model determining atomization by aerodynamic disturbances. The SMR of secondary droplets can be estimated by the possible void fraction, ε, at breakup and the corresponding surface Weber number, Wes, at the minimal surface energy ratio (MSER). Biodiesel can enhance micro-explosion in the fuel blends of ethanol and diesel (which is represented by a single composition tetradecane). The simulation results show that the secondary atomization of bio-fuel and diesel blends can be achieved by micro-explosion under typical diesel engine operation conditions.

Topics: Explosions , Drops , Biofuel , Diesel
Commentary by Dr. Valentin Fuster
2012;():831-838. doi:10.1115/ICEF2012-92177.

A finite diffusion droplet evaporation model for complex liquid mixture composed of different homogeneous groups is presented in this paper. Separate distribution functions are used to describe the composition of each homogeneous group in the mixture. Only a few parameters are required to describe the mixture. Quasi-steady assumption is applied in the determination of evaporation rates and heat flux to the droplet, and the effects of surface regression, finite diffusion and preferential vaporization of the mixture are included in the liquid phase equations using an effective properties approach. A novel approach was used to reduce the transport equations for the liquid phase to a set of ordinary differential equations. The proposed model is capable in capturing the vaporization characteristics of complex liquid mixtures.

Commentary by Dr. Valentin Fuster
2012;():839-847. doi:10.1115/ICEF2012-92187.

Ensuring consistent, reliable diesel engine startups in cold temperatures is of utmost importance in a number of applications. Under extreme temperatures, the use of glow plugs is complemented by intake manifold heaters. In these, the energy released from combustion increases the intake air temperature before the air enters the main combustion chamber. Since the process also alters the stoichiometry of the fuel-air mixture at the intake ports, the pre-heater operation must be optimized in order to guarantee successful and reliable in-cylinder combustion during engine startups. This paper describes the development of an intake manifold model incorporating an air pre-heater for application in a diesel engine. The model, created using a commercial one-dimensional simulation tool, was validated against experimental data and subsequently used to quantify the concentration of combustion product species at the intake runners, as well as intake charge dilution. Results showed that the effective equivalence ratio might increase up to 2.6 after the first 25 seconds of cranking, with 12.5% reduction of the O2 concentration in the intake charge.

Commentary by Dr. Valentin Fuster

Engine Design, Lubrication, and Applications

2012;():849-857. doi:10.1115/ICEF2012-92025.

This paper presents a comprehensive lubrication model for piston skirt-liner system of internal combustion engines. In the model it is included that the effects of the surface roughness, the piston skirt surface geometry, the piston pin offset, the crankshaft offset, and the lubricant viscosity on the piston secondary motion and lubrication performance. Especially, the effects of the thermal and the elastic deformation of the piston skirt and the cylinder liner, and the piston skirt deformations due to the combustion pressure and the piston axial inertia, are considered as the key task in this study. The results show that the combustion force, the working temperature and the piston axial inertia all play important roles in the piston-skirt lubrication. Also, considering the elastic deformation of the piston skirt and the cylinder liner is beneficial to the prediction of piston-skirt lubrication more accurately. The developed program in this study can provide a useful tool for the analysis of the piston-liner system lubrication problem.

Commentary by Dr. Valentin Fuster
2012;():859-868. doi:10.1115/ICEF2012-92047.

A hydrogen-fueled two-stroke prototype demonstrator based on a 9.9 horsepower (7.4 kW) production gasoline marine outboard is presented, which, while matching the original engine’s rated power output on hydrogen, achieves a best-point gross indicated thermal efficiency (ITE) of 42.4% at the ICOMIA Mode 4 operating point corresponding to 80% and 71.6% of rated engine speed and torque, respectively. Brake thermal efficiency (BTE) at rated power is 32.3%. Preliminary exhaust gas measurements suggest that the engine could also meet the most stringent CARB 5-Star marine spark-ignition emission standards limiting HC+NOx emissions to 2.5 g/kWh without any after-treatment. Later fuel injection is found to improve thermal efficiency at the expense of increased NOx emissions and, at the extreme, increased cyclic variation. The mechanism for these observations is reasoned to be increasing charge stratification with the later timings.

All these are realized in a cost-effective concept around a proven two-stroke base engine and a low-pressure, direct-injected gaseous hydrogen (LPDI GH2) system, which employs no additional fuel pump and is adapted uniquely from volume production components. This work outlines the pathway — including investigations of several fuel delivery strategies with limited success — leading to the current status including design; modeling with GT-POWER; delivery of lube oil; lubrication issues using hydrogen; and calibration sweeps. Experimental results comprising steady-state dynamometer performance, cylinder pressure traces, NOx emission measurements, as well as heat release analyses, support the reported numbers and the key finding that late fuel injection timing and charge stratification drive the high efficiencies and the NOx trade-off; this is discussed and forms the basis for future work.

Commentary by Dr. Valentin Fuster
2012;():869-883. doi:10.1115/ICEF2012-92055.

Over the past two years, we have conducted two experimental test series aimed at examining typical performance of gasoline V-twin engines in the 25 hp class, and the suitability of assumed mechanical efficiency in correcting observed measurements. We used engines manufactured by Honda, Kawasaki, Kohler, and Subaru (Robin). The tests were conducted at the Engines Laboratory of the California Polytechnic State University, San Luis Obispo (Cal Poly). The Kohler engines are fuel injected while the others three are carbureted. We tested twenty-eight engines in total. The first series of tests included four horizontal shaft engines from each of the manufacturers (sixteen in total), and followed the general guidelines of SAE standard J1349-199506.

This paper reports primarily on the subsequent series of twelve engine tests, which included vertical shaft engines of an equivalent family (and displacement class), from three of the original manufacturers: Honda, Kawasaki and Kohler. All three engines have roughly the same engine speed range (2000–4000), and all three reportedly reach peak power at 3600rpm. This is typical of small engines, which may be used to drive small generators in addition to being installed on other equipment.

Vertical shaft engines are typically tested on a vertical shaft dynamometer, or one that converts from a horizontal to vertical position. However, these dynamometers are typically either of the water brake or eddy current type. They cannot motor the engine, and thus cannot measure friction mean effective pressure (FMEP) directly, which is the preferred method to quantify friction and mechanical efficiency for engine testing. However, testing vertical shaft engines on a horizontal shaft motoring dynamometer requires an angled gear drive to mate the engine to the dynamometer, and thus adds a loss that complicates the accurate measurement of FMEP and brake output. We present here results using a simple method with which our measurements can be corrected for this loss, in tests of this sort.

The study thus expands on our previous results, and shows the extent by which engine to engine variations are affected by shaft configurations, within a given model family, and within similar offerings by different manufacturers. We also analyzed our results to contrast the methodology of SAE J1349-199506 with that of the updated J1349-201109, specifically with respect to using an assumed value of mechanical efficiency to characterize FMEP and correct dynamometer data on small, general utility engines.

Topics: Engines
Commentary by Dr. Valentin Fuster
2012;():885-891. doi:10.1115/ICEF2012-92067.

The technology drivers for slow speed large bore engines can be summarized as follows: restrictive emission regulations, improvements in reliability, new ship designs and decreasing life cycle costs (fuel efficiency, first cost, maintenance cost). The industry mindset and development experience is traditionally driven by reliability and fuel consumption. The upcoming emission reduction calls for a focus shift and new development processes for the engine builders. The emission reduction increment is substantial and the time is short. Therefore the industry needs fast technology awareness, acceptance and implementation.

The new 2-stroke engine generations are subject to continuous performance improvements driven by new and demanding operating conditions. Higher firing pressures are required and result in higher bearing loads and larger bearing sizes. In particular for the cross-head bearing the bearing width will exceeding 400mm. Thus traditional bearing designs no longer meet the requirements. Bearing manufacturers must consequently go to the limits of feasibility.

When looking at the performance criteria of bearings for the application in 2-stroke engines, properties like emergency running capabilities, embedability and to certain extend the fatigue properties are vital to the performance of these engines.

To meet these demanding requirements a new and extremely robust cross-head bearing design based on tri-metal configuration Steel – Aluminium-Tin 40 - Synthec® for the MAN Diesel & Turbo SE Tier II engine platforms has been developed and successfully tested. The new design is called “Patch-Work-Bearing” and is currently used for long stroke engines with a minimum bore diameter of 400mm.

So far, the prefab material for steel backed aluminium based bearings is produced via well-established roll-bonding processes. If it comes to cross-head bearings for the new engine generations with a characteristic bearing diameter to bearing width ratio of approximately 1:1 ordinary processes cannot be used. The process window is already fully exploited with respect to the rolling-mills capability (width and rolling force). Currently in order to produce the needed prefab material a so called explosion bonding process is used, at which the formation of multi-layer materials is based on kinetic blasting energy [1]. Parts with a size of several square meters can be product. Anyway this technology is exceptionally expensive as high safety measures are mandatory and ordinary production facilities are insufficient. It is a single piece production process with many variable process parameters and therefore a stable and high quality level is difficult to achieve. In particular the bonding strength and bonding quality relies on a constant forming process.

This paper will focus on a new method to produce prefab material for the production of extra wide cross head-bearings which is not based on the explosion bonding process. The paper gives an insight in the new design of the cross-head bearing and the advantages resulting from that.

Topics: Engines , Bearings , Design
Commentary by Dr. Valentin Fuster
2012;():893-905. doi:10.1115/ICEF2012-92078.

The separate effects on heat transfer of 1) piston crown surface finish and 2) the use of a metal based thermal barrier coating (MTBC) on the piston crown of a spark ignition (SI) engine were quantified through experimental analysis in a single cylinder CFR engine. Measured engine parameters such as power, fuel consumption, emissions and cylinder pressure were used to identify the effects of the coating and its surface finish. Two piston coatings were tested: a baseline copper coating and a metal-based thermal barrier coating. Each coating was tested at multiple surface finishes. Tests showed that reducing surface roughness of both coatings increased in-cylinder temperature and pressure as a result of reduced heat transfer through the piston crown. For both coatings, this resulted in small improvements (∼3%) in power and fuel consumption, while also having a measurable effect on emissions. Oxides of nitrogen emissions increased while total hydrocarbon emissions generally decreased as a result of polishing. The polished coatings were also seen to increase in-cylinder peak pressures and burn rates.

Improvements attributed to the TBC were found to be small, but statistically significant. At an equivalent surface finish, the MTBC-coated piston produced slightly higher power output and peak pressures. Hydrocarbon emissions were also seen to be significantly higher for the MTBC-coated piston due to its porosity. The effectiveness of the coating was found to be highly dependent on surface finish.

Commentary by Dr. Valentin Fuster
2012;():907-914. doi:10.1115/ICEF2012-92083.

Rising fuel prices and more stringent requirements in the field of emissions such as nitrogen oxides, particulate matter and carbon dioxide are increasing the pressure on the engine manufacturers to utilize technologies that contribute to a reduction in these emissions. As a result, interest in cylinder surface coatings has risen considerably in the last three to four years, and particularly in the SUMEBore® coating solution from Sulzer Metco. Such coatings are applied by a powder-based atmospheric plasma spray process (APS). The APS method is very flexible and can also process materials to which wire-based methods do not have access, particularly high chromium containing steels, metal matrix composites (MMCs) and pure ceramics. The compositions can be tailored to the specific challenges in an engine, e.g. excessive abrasive wear, scuffing or corrosion caused by adulterated fuels and/or high exhaust gas recirculation rates (EGR). Over the past four to five years cylinder liner surfaces from trucks, diesel locomotives, marine and gas engines, for power generation and gas compression have been coated with such materials. These engines have been tested successfully. Most of the tested engines achieved significant reductions of lubrication oil consumption (LOC), sometimes in excess of 75%, reduced fuel consumption, very low wear rates and corrosion resistance on the liner surfaces. As an example the paper will highlight the coating of cylinder surfaces in a 4,000 hp EMD 16-710G3 locomotive diesel engine. Details of the application of a corrosion resistant MMC will be shown, together with results obtained with the Da Vinci DALOC measurement technique in an engine test where the lubricant oil consumption was accurately quantified at 4 steady-state operating conditions typical of North American freight locomotive and which clearly showed the significant contribution of the liner ID coating to reduction of lubricant oil consumption (LOC).

Commentary by Dr. Valentin Fuster
2012;():915-927. doi:10.1115/ICEF2012-92102.

High performance naturally-aspirated internal combustion engines require effective use of exhaust pressure waves during the gas exchange process to maximize volumetric efficiency and torque. Under certain conditions sudden increases, or steps, in exhaust runner diameter are used to control pressure wave reflections to provide appropriately timed low pressure waves to the cylinder that reduce pumping work and improve air scavenging. This research evaluates gas exchange performance for an exhaust port and an attached stepped-tube primary using unsteady conditions with 1-D and 3-D CFD. The objectives of this research are to (1) discuss the importance of using unsteady flow simulations in the design of high performance exhaust systems, (2) describe the use of stepped-runners to provide performance gains, and (3) discuss the influence of runner step geometry and the number of steps on gas exchange. Simulations are correlated with experimental data to ensure accuracy of the results. A correlation is found between the step size and the magnitude as well as phase of tuning effects. The number of steps is also found to have a direct impact on tuning. The pumping work of the cycle was significantly affected by the stepped primary design, while the scavenging efficiency was not.

Commentary by Dr. Valentin Fuster
2012;():929-934. doi:10.1115/ICEF2012-92103.

When a company designs an engine, mandates by the federal government regarding fuel efficiency, safety and emissions must be met. Consumers demand power, reliability, and creature comforts of the vehicles they choose to purchase. Car manufacturers must meet all of these needs and desires as well as maintain profitability.

The present paper reviews the application of recent advances in IC engines. It covers the four specific areas of (a) Electronic Applications (b) Air Flow Management (c) Fuel Injection / Combustion and (d) Loss Reduction technologies to address the needs of engine performance enhancement. Finally it provides a future direction of the technology for IC engine applications.

Commentary by Dr. Valentin Fuster
2012;():935-939. doi:10.1115/ICEF2012-92123.

The piston compression ring-cylinder liner contact experiences a transient regime of lubrication. This comprises hydrodynamic, mixed (partial) or boundary interactions. The regime of lubrication is influenced by contact kinematics, loading, mechanical and topographical properties of the bounding solid surfaces, as well as lubricant rheology and its supply to feed the conjunction. Ideally, a sufficient volume of lubricant would exist at the conjunctional inlet, which acts as a meniscus, from which a film of lubricant is entrained into the contact area. However, often there is an insufficient volume at the inlet to the contact or unfavourable kinematic conditions exist, such as at the dead centre reversals in the piston system. Such conditions are generally regarded as the underlying reasons for mixed or boundary regimes of lubrication. Whilst, these are the main reasons for failure to form a coherent lubricant film at dead centre reversals, poor hydrodynamic lubrication can also occur elsewhere in the piston cycle due to the lack of an inlet meniscus. This may be as the result of poor ring-bore conformability, where a meniscus cannot be formed in an increasing clearance space. Numerical analyses reported in open literature often assume an idealised fully flooded or drowned inlet. Other analyses assume starved inlet boundaries, usually based on a lubricant availability model, which itself is based on an assumed supply of lubricant on free surfaces ahead of the contact. It is, however, important to establish the limiting clearance space which would allow the lubricant to adhere to the adjacent boundary solids and, thus form a meniscus bridge. The current study is aimed at establishing inlet meniscus conditions. This would depend on the lubricant surface tension, affected by the free surface energy of liquid-vapour interface and the contact angle made between the lubricant and the bounding solids. It also depends on the solid surfaces, any coatings and their topography.

In general, the results indicate the dependence of the meniscus force on surface material and topography, through measurement of contact angles made by the various compression rings against the various cylinder liner surfaces, using an especially developed rig and in conjunction with a goniometer. Obviously, the measurements do not exactly replicate those existing in a fired engine. Nonetheless, this initial study provides a good insight into oil-surface combination in separating gaps, which is far more representative than the usually assumed idealised inlet conditions.

Commentary by Dr. Valentin Fuster
2012;():941-945. doi:10.1115/ICEF2012-92138.

NVH is a necessary consideration in engine component development. The piston pin joint can be a significant contributor of mechanical noise in SI engines. Although there is literature on this subject, most of it is dealing with measurement using accelerometers for vibration analysis. This however does not indicate the fundamentals of the piston pin to connecting rod pin bore interaction mechanism. Limited research was found on this matter which prompted this investigation.

A measurement system was designed to determine the connecting rod small end bore clearance in real-time from the base and side of the pin bore. In this system, we applied a high precision displacement sensor to measure the pin motion, and a linkage was designed and fabricated to transfer the signal output out of the engine. This information was then correlated with accelerometer impact measurements to create a baseline for piston pin motion. Impacts were linked to the load reversal of the piston pin to connecting rod interface.

Commentary by Dr. Valentin Fuster
2012;():947-952. doi:10.1115/ICEF2012-92139.

Friction reduction within the power cylinder assembly of internal combustion engines continues to be a one of the foremost focuses of engine manufactures. In an effort to better address this topic previously developed bench test rigs, such as the Falex, Cameron-Plint, and EMA-LS9 [1,2], have been utilized. These devices were formerly focused solely on wear mechanisms and material compatibility. Current development of new piston ring coatings has demanded significant refinements to the previously mentioned EMA-LS9 test rig for specific frictional characteristic evaluations. These developments have allowed for coefficient of friction ranking between various piston ring materials in addition to the influence and surface finish on coefficient of friction.

This paper examines how the test rig is utilized to characterize upper compression ring materials, surface treatments, and the impact of surface finish. The significance of these results will be examined as it applies to analytical evaluations. From these calculations a demonstration of the effect of surface finish on ring dynamics and gas flow, as well as future piston ring coating developments will be discussed.

Commentary by Dr. Valentin Fuster
2012;():953-962. doi:10.1115/ICEF2012-92164.

The paper discusses the importance of a numerical method for fast and accurate prediction of main bearing loads of inner combustion engine and its place in the concept phase of engine development process.

An approach based on linear dynamic analysis of 3D engine model in frequency domain is presented. Implemented within a separate module of AVL software package EXCITE Designer, it delivers a combination of accuracy and performance suitable for this task.

An application example illustrates the method.

Topics: Stress , Bearings
Commentary by Dr. Valentin Fuster
2012;():963-970. doi:10.1115/ICEF2012-92166.

A comprehensive piston skirt lubrication and secondary motion model that can be used for piston friction simulations was developed based on Greenwood and Tripp’s surface asperity contact model and Patir and Cheng’s modified Reynolds equation with surface flow factors. Oil flow between the skirt-liner clearances was modeled and hydrodynamic and asperity contact pressures around the skirt were calculated. Reynolds boundary conditions were applied to determine the film rupture boundaries and wetted areas. Surface roughness and roughness orientation were included in the model. Due to its important effect on pressure development in the oil film, change in the skirt profile due to elastic deformations was taken into account. Change of the skirt profile due to piston thermal expansion is also calculated using the steady-state temperature distribution of the piston corresponding to the investigated engine running conditions. A piston stiffness matrix obtained by finite element analysis was used to determine the elastic deformations of the piston skirt under the calculated oil film pressures. A two-degree-of-freedom system is formed with the forces and moments calculated by the lubrication model. These forces and moments require a coupled solution with piston position. This is achieved by applying an iterative numerical procedure based on Broyden’s scheme which seeks force and moment balance at each iteration phase making use of time step variation. The effects of various engine operating conditions and piston design parameters on piston secondary motion were investigated. Piston skirt friction force due to hydrodynamic shear forces and metal-to-metal contact is calculated.

Topics: Friction , Pistons
Commentary by Dr. Valentin Fuster

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