ASME Conference Presenter Attendance Policy and Archival Proceedings

2015;():V002T00A001. doi:10.1115/ICEF2015-NS2.

This online compilation of papers from the ASME 2015 Internal Combustion Engine Division Fall Technical Conference (ICEF2015) 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to ASME’s conference presenter attendance policy, if a paper is not presented at the Conference, the paper will not be published in the official archival Proceedings, which are registered with the Library of Congress and are submitted for abstracting and indexing. The paper also will not be published in The ASME Digital Collection and may not be cited as a published paper.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

Emissions Control Systems

2015;():V002T04A001. doi:10.1115/ICEF2015-1019.

A 1600 cc direct injected turbocharged Euro 5 diesel engine was operated on standard diesel fuel from a gas station in Denmark for evaluation of the test bench procedure. The NEDC (New European Driving Cycle), FTP-75 (Federal Test Procedure) and WLTP (World Harmonized Light Vehicle Test Procedure) driving cycles were simulated in the engine test bench in two ways: 1) by transient engine operation were the inertia of the vehicle during deceleration was simulated by addition of power from an electric motor mounted on the crank shaft, and 2) by steady state measurements where the total driving pattern was simulated from an integration of multiple steady state measurements. The mathematical model that calculates equivalent NEDC driving cycle vehicle emissions from the engine steady state measurements in the test bench, starting with warm engine, is presented. By applying this model any driving cycle emissions can be calculated from the presented tabulated steady state measurements, starting with warm or cold engine.

Both engine test methods showed acceptable agreement with measurement in an NEDC vehicle test on chassis dynamometer where the vehicle was equipped with a similar engine as the test bench engine. The two engine test bench methods gave very similar results, but the transient engine test procedure showed a little higher emission of CO2 and NOx, results that were closest to the vehicle measurements. This is interpreted as a result of extra emissions when the engine adjusts from one operating point to the next during transient operation. These extra emissions are not caught in the steady state method. Application of the two engine test procedures on the FTP-75 procedure and the newer WLTP showed that the steady state engine test method gave significantly lower emissions of NOx and a little lower CO2 emissions compared to the transient engine test. The results indicated that this was mainly an effect of the time delay on the engines EGR system adjustment, which is not caught in the steady state method.

The advantages and disadvantages of applying the different measurement methods and test procedures are discussed in relation to introduction of new test procedures in order to reduce engine/vehicle emissions.

Commentary by Dr. Valentin Fuster
2015;():V002T04A002. doi:10.1115/ICEF2015-1026.

Stringent emission regulations mandated by California air regulation board (CARB) require monitoring the upstream exhaust gas oxygen (UEGO) sensor for any possible malfunction causing the vehicle emissions to exceed standard thresholds. Six faults have been identified that may potentially cause the UEGO sensor performance to deteriorate and lead to instability of the air-fuel ratio (AFR) closed-loop control system. These malfunctions are either due to an additional delay or an additional lag in the transition of the sensor response from lean to rich or rich to lean. In this paper, a novel non-intrusive approach is developed to diagnose these faults using a combination of a statistical method and a system identification process. In the second part of this work, a control strategy is presented that utilizes the type, the direction and the magnitude of the fault present to update the gains of the controller for the closed-loop air-fuel ratio control system. The proposed strategy does not require modifying the controller structure and only adapts the baseline gains of the controller and delay compensator to match the actual system dynamics (in presence of fault). The proposed approach has been demonstrated on a vehicle (Mustang V6 3.7L) where different faults were induced, and the emissions associated with each fault were measured to show the improvement.

Topics: Sensors , Fuels , Oxygen
Commentary by Dr. Valentin Fuster
2015;():V002T04A003. doi:10.1115/ICEF2015-1038.

As a way of reducing the amount of Particulate Matter (PM) contained in the exhaust gas, Diesel Particulate Filter (DPF) is widely used. To keep the condition of DPF normal and effective, estimation of the amount of PM deposits in the DPF is important. The estimation is mainly conducted based on the value of pressure drop across the DPF. Occasionally, the value of the pressure drop rises suddenly and it leads to overestimation of the amount of PM deposits.

In order to elucidate the cause of the sudden pressure drop increase phenomenon, this paper firstly reveals the engine operating conditions which invoke this phenomenon. The authors also have developed a visualization method to realize the wide-perspective internal observation of the DPF. The observation experiment has been conducted with a commercial engine and DPF under the revealed conditions. Experimental results make clear that the phenomenon is caused by PM deposit layer collapse and channel plugging.

Commentary by Dr. Valentin Fuster
2015;():V002T04A004. doi:10.1115/ICEF2015-1050.

The use of natural gas in spark-ignited internal combustion engines optimized for minimum emissions has repeatedly shown a significant reduction in exhaust emissions over that of gasoline. Pronounced variations in unprocessed natural gas composition can however present an emissions problem for engines used in natural gas recovery where unrefined wellhead gas is used as the fuel. This study is twofold involving both experimental analysis and theoretical development with a computer model that simulates wellhead gas combustion. On the experimental side, Fourier transform infrared spectroscopy (FTIR) was used to analyze emissions of a 2.4L four-cylinder spark-ignited natural gas engine operating on fuels of varying composition. A comparative assessment is made between CO, NO, THC, CH4, and CH2O emissions of the engine operating on refined pipeline natural gas and those of the engine operating on the same gas with added CO2, N2, and C3H8 diluents. Diluents were added to the fuel individually to isolate the effect of each and to approximate wellhead gas. Additionally, a burn rate analysis was conducted which shows changes in the rate of fuel energy liberation with changes in diluent concentration. On the theoretical side, a two zone computer model of engine operation was developed that would simulate operation of the engine under varying fuel composition as found in various natural gas recovery wells throughout the United States. Results show that exhaust concentrations of NO and THC were strongly affected by addition of both inert and reactive diluent due to their strong dependence on in-cylinder temperature. Emissions of CO, CH4, and CH2O were also found to depend on diluent concentration; however, to a much lesser extent with emissions of CO being seemingly unaffected by addition of N2 for the compositions tested. Burn rate analysis shows that the introduction of inert constituents to the fuel decreases the fuel burn rate while addition of propane increases the burn rate. The whole of the analysis indicates a strong dependence of emissions on fuel composition and that significant potential exists for emissions reduction of engines operating on unprocessed natural gas.

Commentary by Dr. Valentin Fuster
2015;():V002T04A005. doi:10.1115/ICEF2015-1059.

There are many NOx removal technologies: exhaust gas recirculation (EGR), selective catalytic reduction (SCR), selective non-catalytic reduction (SNCR), miller cycle, emulsion technology and engine performance optimization. In this work, a numerical simulation investigation was conducted to explore the possibility of an alternative approach: direct aqueous urea solution injection on the reduction of NOx emissions of a biodiesel fueled diesel engine. Simulation was performed using the 3D CFD simulation software KIVA4 coupled with CHEMKIN II code for pure biodiesel combustion under realistic engine operating conditions of 2400 rpm and 100% load. To improve the overall prediction accuracy, the Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) spray break up model was implemented in the KIVA code to replace the original Taylor Analogy Breakup (TAB) model for the primary and secondary fuel breakup processes modeling. The KIVA4 code was further modified to accommodate multiple injections, different fuel types and different injection orientations. A skeletal reaction mechanism for biodiesel + urea was developed which consists of 95 species and 498 elementary reactions. The chemical behaviors of the NOx formation and Urea/NOx interaction processes were modeled by a modified extended Zeldovich mechanism and Urea/NOx interaction sub-mechanism. Developed mechanism was first validated against the experimental results conducted on a light duty 2KD FTV Toyota car engine fueled by pure biodiesel in terms of in-cylinder pressure, heat release rate. To ensure an efficient NOx reduction process, various aqueous urea injection strategies in terms of post injection timing and injection rate were carefully examined. The simulation results revealed that among all the four post injection timings (10 °ATDC, 15 °ATDC, 20 °ATDC and 25 °ATDC) that were evaluated, 15 °ATDC post injection timing consistently demonstrated a lower NO emission level. In addition, both the urea/water ratio and aqueous urea injection rate demonstrated important roles which affected the thermal decomposition of urea into ammonia and the subsequent NOx removal process, and it was suggested that 50% urea mass fraction and 40% injection rate presented the lowest NOx emission levels.

Commentary by Dr. Valentin Fuster
2015;():V002T04A006. doi:10.1115/ICEF2015-1110.

The use of exhaust gas recirculation (EGR) in internal combustion engines has significant impacts on engine combustion and emissions. EGR can be used to reduce in-cylinder NOx production, reduce fuel consumption, and enable advanced forms of combustion. To maximize the benefits of EGR, the exhaust gases are often cooled with liquid to gas heat exchangers. However, the build up of a fouling deposit layer from exhaust particulates and volatiles result in the decrease of heat exchanger efficiency, and increase the outlet temperature of the exhaust gases, and decrease the advantages of EGR.

This paper presents experimental data from a novel in-situ measurement technique in a visualization rig during the development of a 378 micron thick deposit layer. Measurements were performed every 6 hours for up to 24 hours. Results show a non-linear increase in deposit thickness with an increase in layer surface area as deposition continued. Deposit surface temperature and temperature difference across the thickness of the layer was shown to increase with deposit thickness while heat transfer decreased. The provided measurements combine to produce deposit thermal conductivity.

A thorough uncertainty analysis of the in-situ technique is presented and suggests higher measurement accuracy at thicker deposit layers and with larger temperature differences across the layer. The interface and wall temperature measurements are identified as the strongest contributors to the measurement uncertainty. Due to instrument uncertainty, the influence of deposit thickness and temperature could not be determined. At an average deposit thickness of 378 microns and at a temperature of 100°C, the deposit thermal conductivity was determined to be 0.044 ± 0.0062 W/mK at a 90% confidence interval based on instrument accuracy.

Commentary by Dr. Valentin Fuster
2015;():V002T04A007. doi:10.1115/ICEF2015-1118.

In some regions of the world, emissions of total organic carbon (TOC), including methane and non-methane hydrocarbons (NMHCs), from the tail pipe of natural gas or biogas fuelled combustion equipments are strictly regulated (e.g. 150 mg/Nm3 of exhaust gas in Italy). Post combustor has been widely chosen in response to the TOC emission targets. TOC typically consists of >90% methane — a strong greenhouse gas and the most challenging compound to remove due to its highly stable form. Thus, more gas is being consumed to burn the TOC present in the exhaust, resulting in higher operating (or power production) costs.

A passive catalytic approach is an alternative to post combustor. Palladium based oxidation catalyst is known to actively remove TOC, providing no sulfur compounds present. Sulfur poisons and deactivates the catalyst in a short time. This paper presents a concept to extend the life of the oxidation catalyst by using an exhaust post conditioning system. The system is designed to eliminate and withstand contaminants, yielding a protection to the catalyst. Consequently, the catalyst life is prolonged by about 50 times.

Commentary by Dr. Valentin Fuster
2015;():V002T04A008. doi:10.1115/ICEF2015-1122.

Increasingly stringent emissions standards have accounted for continuing increases in the end-user cost of a modern diesel engine, most of which due to complex and expensive emissions after treatment devices such as selective catalytic reduction (SCR), which relies on urea to be injected into a catalyst bed to remove nitrogen oxide emissions from the engine exhaust.

Prior to the current emissions standards the diesel industry had been able to meet NOx levels by reducing the combustion temperature in the engine via charge gas dilution, through cooled EGR. Although successful in reducing emissions, large levels of EGR have undesirable effects on oil quality, engine longevity, overall efficiency and warranty returns. There is also a limit to the efficacy of EGR in lowering NOx emissions such that at the current EPA mandated 0.2g/kWh, it is no longer sufficient.

Another well-known NOx mitigating solution has been the introduction of water into the diesel engine combustion chamber. This has been known to decrease peak combustion temperatures and decrease NOx emissions but usage so far has been limited to stationary and marine applications due to the requirement of a separate water tank and thereby a two-tank system. Combustion of hydrocarbon fuels produces between 1.35 and 2.55 times their mass in water. As an enabler to water injection, this paper will also demonstrate a technique where the exhaust is first cooled via a heat exchanger, and then passed through a cyclonic separator to separate heavier liquid particles from the exhaust gas flow. Through vortex separation over 100% of the burned fuel mass can be recovered as liquid water from the exhaust. A prototype system was developed and installed on a VW TDI diesel engine. Tests were conducted with and without after-treatment and results have been discussed in subsequent sections. The water was then utilized in conjunction with EGR to control NOx emissions, allowing a reduction of over 97%, thus achieving the 0.2g/kWh standard with no after treatment.

Commentary by Dr. Valentin Fuster
2015;():V002T04A009. doi:10.1115/ICEF2015-1133.

This paper describes the development, testing, and application of a low emissions upgrade kit for 1.5 MW EMD GP20D locomotives. Low emissions development focused on changes to fuel injection timing combined with the application of crank case ventilation system (CCV) and catalyzed diesel particulate filters (DPF). Composed of a porous cordierite ceramic material, the diesel particulate filters are specifically designed for entrapment of diesel particulates while allowing exhaust gases to flow through. Furthermore, the filters are coated with a proprietary catalyzed washcoat that promotes the oxidation of soot within the exhaust gas temperature range observed under normal engine operation. In addition to the low temperature oxidation of soot, the catalyzed filter also reduces carbon monoxide and unburned hydrocarbons.

The test locomotive used for this development, which is owned by CIT Rail, was powered by a recently rebuilt Caterpillar 3516B engine with a rated power of 1.5 MW (2,000 HP). Baseline exhaust emission testing was performed, followed by low emissions retrofit development. In combination with the CCV and new fuel injection calibrations, the DPF system netted significant emissions reductions. The result of the final low emissions upgrade kit was an EPA Tier 1+ certification, with emissions levels that were below EPA Tier 3 locomotive switch cycle standards for oxides of nitrogen (NOx) and below EPA Tier 4 switch cycle standards for hydrocarbons (HC), carbon monoxide (CO), particulate matter (PM), and smoke.

Commentary by Dr. Valentin Fuster
2015;():V002T04A010. doi:10.1115/ICEF2015-1140.

Stringent emission regulations (e.g., Euro-6) force automotive manufacturers to equip DPF (diesel particulate filter) on diesel cars. Generally, post injection is used as a method to regenerate DPF. However, it is known that post injection deteriorates specific fuel consumption and causes oil dilution for some operating conditions. Thus, an injection strategy for regeneration becomes one of key technologies for diesel powertrain equipped with a DPF.

This paper presents correlations between fuel injection strategy and exhaust gas temperature for DPF regeneration. Experimental apparatus consists of a single cylinder diesel engine, a DC dynamometer, an emission test bench, and an engine control system. In the present study, post injection timing covers from 40 deg aTDC to 110 deg aTDC and double post injection was considered. In addition, effects of injection pressures were investigated. The engine load was varied from low-load to mid-load and fuel amount of post injection was increased up to 10mg/stk.

Oil dilution during fuel injection and combustion processes were estimated by diesel loss measured by comparing two global equivalences ratios; one is measured from Lambda sensor installed at exhaust port, the other one is estimated from intake air mass and injected fuel mass. In the present study, the differences in global equivalence ratios were mainly caused from oil dilution during post injection.

The experimental results of the present study suggest an optimal engine operating conditions including fuel injection strategy to get appropriate exhaust gas temperature for DPF regeneration. Experimental results of exhaust gas temperature distributions for various engine operating conditions were summarized.

In addition, it was revealed that amounts of oil dilution were reduced by splitting post injection (i.e., double post injection). Effects of injection pressure on exhaust gas temperature were dependent on combustion phasing and injection strategies.

Commentary by Dr. Valentin Fuster
2015;():V002T04A011. doi:10.1115/ICEF2015-1146.

It is well known that biodiesel may reduce engine-out particulate matter (PM) emissions and result in PM which has more favorable oxidation characteristics relative to PM derived solely from petroleum diesel. This study investigated the use of neat biodiesel, as well as blends, with a light-duty diesel engine equipped with a catalyzed diesel particulate filter (DPF) and radio frequency particulate filter sensor. The results show a reduction in engine-out PM emissions with increasing biodiesel blend levels and a corresponding increase in the duration between DPF regenerations. In situ measurements of the PM oxidation rates on the DPF using the radio frequency sensor further indicated more rapid oxidation of the biodiesel-derived PM with lower light-off temperatures relative to the petroleum-derived PM. The conclusions indicate considerable potential to extend DPF regeneration intervals and decrease regeneration duration when biodiesel blends are used in conjunction with advanced DPF sensing and control systems, thereby reducing the DPF-related fuel consumption.

Commentary by Dr. Valentin Fuster
2015;():V002T04A012. doi:10.1115/ICEF2015-1170.

Sintered metal fiber (SMF) diesel particulate filters (DPF) systems efficiently remove particulate matter (PM) emission from diesel engine exhaust with low flow resistance. The permeability of DPF filtration media is the key property determining DPF fuel penalty to the engine. To advance the understanding and optimization of SMF filtration media, a general model to compute SMF media permeability based on 3D digital structure from computed tomography scan (CT-Scan) is developed in this study. An open source computational fluid dynamics (CFD) tool, OpenFOAM, is used to calculate the SMF porous media permeability. The media samples computation domain is approximately 0.9mmx0.9mmx1.8mm (depth) and one hour is needed for each simulation with 8–9 million mesh cells. The study reveals variations of permeability among different SMF media samples. The computed permeability from the 3D simulation has a good agreement with experiment data and achieves a much better accuracy than previous analytical models. In addition, through this study, a significant amount of in-depth information of flow field across the porous media is obtained, which is beneficial to improve the understanding of DPF fibrous media and builds the foundation for more advanced filtration model development.

Commentary by Dr. Valentin Fuster

Instrumentation, Controls, and Hybrids

2015;():V002T05A001. doi:10.1115/ICEF2015-1061.

An electric compressor and an electrically assisted turbocharger have been applied to a 2.0L Gasoline and a 2.2L Diesel engine 1D wave dynamic models. A novel approach is presented for evaluating transient response using swept frequency sine wave functions and Fourier Transforms.

The maximum electrical power was limited to 6% of the maximum engine power (12kW and 5kW respectively). The systems were evaluated under steady state and transient conditions. Steady state simulations showed improved Brake Mean Effective Pressure (BMEP) at low engine speeds (below 2500rpm) but electric power demand was lower (3kW vs 8kW) when the electric compressor was on the high pressure side of the turbocharger. This was due to the surge limitation of the turbocharger compressor. The electrically assisted turbocharger offered little opportunity to increase low speed BMEP as it was constrained by compressor map width. Re-matching the turbo could address this but also compromise high engine speeds.

BMEP frequency analysis was conducted in the region of 0.01–2Hz. This was repeated at fixed engine speeds between 1000rpm and 2000rpm. Spectral analysis of the simulated response showed that the non-assisted turbocharger could not follow the target for frequencies above 0.1Hz whereas the electrically-assisted device showed no appreciable drop in performance. When assessing the electric power consumption with the excitation frequency, a linear trend was observed at engine speeds below 1500rpm but more complex behavior was apparent above this speed where BMEP levels are high but exhaust energy was scarce.

Commentary by Dr. Valentin Fuster
2015;():V002T05A002. doi:10.1115/ICEF2015-1069.

At the present time, both control and estimation accuracies of engine torque are causes for under-achieving optimal drivability and performance in today’s production vehicles. The major focus in this area has been to enhance torque estimation and control accuracies using existing open-loop torque control and estimation structures. Such an approach does not guarantee optimum torque tracking accuracy and optimum estimation accuracy due to air flow and efficiencies estimations errors. Furthermore, current approach overlooks the fast torque path tracking which does not have any related feedback. Recently, explicit torque feedback control has been proposed in the literature using either estimated or measured torques as feedback to control the torque using the slow torque path only. We propose the usage of a surface acoustic wave (SAW) torque sensor to measure the engine brake torque and feedback the signal to control the torque using both the fast and slow torque paths utilizing an inner-outer loop control structure. The fast torque path feedback is coordinated with the slow torque path by a novel method using the potential torque that is adapted to the sensor reading. The torque sensor signal enables a fast and explicit torque feedback control that can correct torque estimation errors and improve drivability, emission control, and fuel economy. Control-oriented engine models for the 3.6L engine are developed. Computer simulations are performed to investigate the advantages and limitations of the proposed control strategy, versus the existing strategies. The findings include an improvement of 14% in gain margin and 60% in phase margin when the torque feedback is applied to the cruise control torque request at the simulated operating point. This study demonstrates that the direct torque feedback is a powerful technology with promising results for improved powertrain performance and fuel economy.

Topics: Torque , Engines , Feedback
Commentary by Dr. Valentin Fuster
2015;():V002T05A003. doi:10.1115/ICEF2015-1096.

This paper presents the analysis of a Rankine cycle unit applied to improve overall efficiency of a hybrid electric vehicle (HEV). Exhaust waste heat is recovered from the internal combustion engine (ICE) and is converted into electrical power that is fed into the electrical system on board. The discontinuously available exhaust waste heat from the ICE operating cycle is stored as sensible heat in a pressurized working fluid applying the principle of a Ruths storage tank. Thus, it can provide almost constant mass flows to the expansion device during discharge in contrast to the standard Rankine cycle. It is also shown that the outlined system configuration leads to faster engine warm up resulting in optimum ICE operating conditions improving fuel economy. The benefits of a mild HEV versus conventional car powertrain are outlined step by step in a vehicle simulation. Additionally, improvement in fuel economy achieved by applying an additional Rankine cycle is demonstrated in the New European Driving Cycle (NEDC).

Commentary by Dr. Valentin Fuster
2015;():V002T05A004. doi:10.1115/ICEF2015-1099.

Optimal combustion control has become a key factor in modern automotive applications to guarantee low engine out emissions and good driveability. In order to meet these goals, the engine management system has to guarantee an accurate control of torque delivered by the engine and optimal combustion phasing.

Both quantities can be calculated through a proper processing of in-cylinder pressure signal. However, in-cylinder pressure on-board installation is still uncommon, mainly due to problems related to pressure sensors’ reliability and cost. Consequently, over the last years, the increasing request for combustion control optimization spawned a great amount of research in the development of remote combustion sensing methodologies, i.e. algorithms that allow extracting useful information about combustion effectiveness via low cost sensors, such as crankshaft speed, accelerometers or microphones.

Based on the simultaneous acquisition of two crankshaft speed signals, this paper analyses the information that can be extracted about crankshaft’s torsional behavior through a proper processing of the acquired signals. In particular, the correlations existing between such information and indicated quantities (torque delivered by the engine and combustion phasing) have been analysed. In order to maximize the signal-to-noise ratio, each speed measurement has been performed at an end of the crankshaft, i.e. in correspondence of the flywheel and the distribution wheel. The presented approach has been applied to a light-duty L4 Diesel engine mounted in a test cell. Nevertheless, the methodology is general, and it can be applied to engines with a different number of cylinders, both CI and SI.

Topics: Engines
Commentary by Dr. Valentin Fuster

Numerical Simulation

2015;():V002T06A001. doi:10.1115/ICEF2015-1002.

The gas exchange process is known to be a significant source of cyclic variability in Internal Combustion Engines (ICE). Traditionally, Large Eddy Simulations (LES) are expected to capture these cycle-to-cycle variations. This paper reports a numerical effort to establish best practices for capturing cyclic variability with LES tools in a Transparent Combustion Chamber (TCC) spark ignition engine. The main intention is to examine the sensitivity of cycle averaged mean and Root Mean Square (RMS) flow fields and Proper Orthogonal Decomposition (POD) modes to different computational hardware, adaptive mesh refinement (AMR) and LES sub-grid scale (SGS) models, since these aspects have received little attention in the past couple of decades. This study also examines the effect of near-wall resolution on the predicted wall shear stresses. LES is pursued with commercially available CONVERGE code. Two different SGS models are tested, a one-equation eddy viscosity model and dynamic structure model. The results seem to indicate that both mean and RMS fields without any SGS model are not much different than those with LES models, either one-equation eddy viscosity or dynamic structure model. Computational hardware results in subtle quantitative differences, especially in RMS distributions. The influence of AMR on both mean and RMS fields is negligible. The predicted shear stresses near the liner walls is also found to be relatively insensitive to near-wall resolution except in the valve curtain region.

Commentary by Dr. Valentin Fuster
2015;():V002T06A002. doi:10.1115/ICEF2015-1003.

A state-of-the-art spray modeling methodology, recently presented by Senecal et al. [1,2,3], is applied to Large Eddy Simulations (LES) of vaporizing gasoline sprays. Simulations of non-combusting Spray G (gasoline fuel) from the Engine Combustion Network are performed. Adaptive mesh refinement (AMR) with cell sizes from 0.09 mm to 0.5 mm are utilized to demonstrate grid convergence of the dynamic structure LES model for the gasoline sprays. Grid settings are recommended to optimize the accuracy/runtime tradeoff for LES-based spray simulations at different injection pressure conditions typically encountered in gasoline direct injection (GDI) applications. Twenty different realizations are simulated by changing the random number seed used in the spray sub-models. It is shown that for global quantities such as spray penetration, comparing a single LES simulation to experimental data is reasonable. Through a detailed analysis using the relevance index (RI) criteria, recommendations are made regarding the minimum number of LES realizations required for accurate prediction of the gasoline sprays.

Commentary by Dr. Valentin Fuster
2015;():V002T06A003. doi:10.1115/ICEF2015-1004.

For a pilot-main injection strategy in a single cylinder light duty diesel engine, the dwell between the pilot- and main-injection events can significantly impact combustion noise. As the solenoid energizing dwell decreases below 200 μs, combustion noise decreases by approximately 3 dB and then increases again at shorter dwells. A zero-dimensional thermodynamic model has been developed to capture the combustion-noise reduction mechanism; heat-release profiles are the primary simulation input and approximating them as top-hat shapes preserves the noise-reduction effect. A decomposition of the terms of the underlying thermodynamic equation reveals that the direct influence of heat-release on the temporal variation of cylinder-pressure is primarily responsible for the trend in combustion noise. Fourier analyses reveal the mechanism responsible for the reduction in combustion noise as a destructive interference in the frequency range between approximately 1 kHz and 3 kHz. This interference is dependent on the timing of increases in cylinder-pressure during pilot heat-release relative to those during main heat-release. The mechanism by which combustion noise is attenuated is fundamentally different from the traditional noise reduction that occurs with the use of long-dwell pilot injections, for which noise is reduced primarily by shortening the ignition delay of the main injection. Band-pass filtering of measured cylinder-pressure traces provides evidence of this noise-reduction mechanism in the real engine.

When this close-coupled pilot noise-reduction mechanism is active, metrics derived from cylinder-pressure such as the location of 50% heat-release, peak heat-release rates, and peak rates of pressure rise cannot be used reliably to predict trends in combustion noise. The quantity and peak value of the pilot heat-release affect the combustion noise reduction mechanism, and maximum noise reduction is achieved when the height and steepness of the pilot heat-release profile are similar to the initial rise of the main heat-release event. A variation of the initial rise-rate of the main heat-release event reveals trends in combustion noise that are the opposite of what would happen in the absence of a close-coupled pilot. The noise-reduction mechanism shown in this work may be a powerful tool to improve the tradeoffs among fuel efficiency, pollutant emissions, and combustion noise.

Commentary by Dr. Valentin Fuster
2015;():V002T06A004. doi:10.1115/ICEF2015-1008.

Late fuel during closing of the valve of a fuel-injector and fuel films stuck on the wall around the nozzle outlets are sources of PM. In this study, we focused on effects of the valve motions on the late fuel and the fuel films stuck on the walls around the nozzle outlets. We previously developed a particle/grid hybrid method: fuel flows within the flow paths of fuel injectors were simulated by a front capturing method, and liquid-column breakup at the nozzle outlets was mainly simulated by a particle method. The velocity at the inlet boundary of a fuel injector was controlled in order to affect the valve motions on the late-fuel behavior. The simulated late fuel broke up with surface-tension around the time of zero-stroke position of the valve, then liquid columns and coarse droplets formed after the bounds of the valve, and finally only coarse droplets were left. We found that the late fuel was generated by low-speed fuel-flows through the nozzles during the bounds of the valve. The effect of the bounds of the valve on the fuel films stuck on the wall around the nozzle outlets was also studied with a simulation that removed the bounds of the valve. The volume of the fuel films stuck on the wall of the nozzle outlets decreased without the bounds of the valve.

Commentary by Dr. Valentin Fuster
2015;():V002T06A005. doi:10.1115/ICEF2015-1018.

Turbulent spray combustion of n-dodecane fuel was studied numerically in current paper. The ignition delay, lift-off length, combustion chamber pressure rise, fuel penetration and vapor mass fraction were compared with experimental data. n-Dodecane kinetic model was studied by using a recently developed mechanism. The combustion chamber pressure rise was modeled and compared with experiments; the result was corrected for speed-of-sound to find the ignition delay timing in comparison with pressure-based ignition delay measurement. Species time histories and reaction paths at low and high temperature combustion are modeled and studied at two conditions, 900 K and 1200 K combustion chamber temperatures. The modeled species mass histories were discussed to define the first-stage and total ignition delay timings. Among all of the studied species in this work, including OH, Hydroperoxyalkyl mass history can be utilized to determine the exact timing of luminosity-based ignition delay. Moreover, n-dodecane vapor penetration can be used to determine the luminosity-based ignition delay.

Commentary by Dr. Valentin Fuster
2015;():V002T06A006. doi:10.1115/ICEF2015-1022.

In Computational Fluid Dynamics (CFD) simulations of internal combustion engines, one of the critical modeling parameters is the valve setup. A standard workaround is to keep the valve opens at a certain clearance (minimum valve lift), while imposing a solid boundary to mimic valve closure. This method would yield a step change in valve lift during opening and closing event, and different valve event timing than hardware. Two parametric studies were performed to examine a) the effect of the minimum valve lift and b) the effect of grid resolution at the minimum valve lift on predicted in-cylinder flow fields in Reynolds Averaged Navier-Stokes (RANS) simulations. The simulation results were compared with the state-of-art PIV measurement from a two-valve transparent combustion chamber (TCC-3) engine. The comparisons revealed that the accuracy of flow simulation are sensitive to the choice of minimum valve lift and grid resolution in the valve seat region. In particular, the predicted in-cylinder flow field during the intake process was found to be very sensitive to the valve setup. A best practice CFD valve setup strategy is proposed as a result of this parametric studies. The proposed CFD valve setup was applied to Large Eddy Simulation (LES) of TCC-3 engine and preliminary results showed noticeable improvement already. Further evaluation of the valve setup strategy for LES simulations is on-going and will be reported in a separate report.

Commentary by Dr. Valentin Fuster
2015;():V002T06A007. doi:10.1115/ICEF2015-1033.

We performed Large Eddy Simulation (LES) of a turbulent non-reacting n-Heptane spray jet, referred to as Spray H in the Engine Combustion Network (ECN), and executed a data analysis focused on key LES metrics such as fraction of resolved turbulent kinetic energy and similarity index. In the simulation, we used the dynamic structure model for the sub-grid stress, and the Lagrangian-based spray-parcel models coupled with the blob-injection model. The finest mesh-cell size used was characterized by an Adaptive Mesh Refinement (AMR) cell size of 0.0625 mm. To obtain ensemble statistics, we performed 28 numerical realizations of the simulation. Demonstrated by the comparison with experimental data in a previous study [7], this LES has accurately predicted global quantities, such as liquid and vapor penetrations. The analysis in this work shows that 14 realizations of LES are sufficient to provide a reasonable representation of the average flow behavior that is benchmarked against the 28-realization ensemble. With the current mesh, numerical schemes, and sub-grid scale turbulence model, more than 95% of the turbulent kinetic energy is directly resolved in the flow regions of interest. The large-scale flow structures inferred from a statistical analysis reveal a region of disorganized flow around the peripheral region of the spray jet, which appears to be linked to the entrainment process.

Commentary by Dr. Valentin Fuster
2015;():V002T06A008. doi:10.1115/ICEF2015-1034.

An n-dodecane spray flame was simulated using a dynamic structure large eddy simulation (LES) model coupled with a detailed chemistry combustion model to understand the ignition processes and the quasi-steady state flame structures. This study focuses on the effect of different ambient oxygen concentrations, 13%, 15% and 21% at an ambient temperature of 900 K and an ambient density of 22.8 kg/m3, which are typical diesel-engine relevant conditions with different levels of exhaust gas recirculation (EGR). The liquid spray was treated with a traditional Lagrangian method. A 103-species skeletal mechanism was used for the n-dodecane chemical kinetic model. It is observed that the main ignitions occur in rich mixture and the flames are thickened around 35 to 40 mm off the spray axis due to the enhanced turbulence induced by the strong recirculation upstream, just behind the head of the flames at different oxygen concentrations. At 1 ms after the start of injection, the soot production is dominated by the broader region of high temperature in rich mixture instead of the stronger oxidation of the high peak temperature. Multiple realizations were performed for the 15% O2 condition to understand the realization to realization variation and to establish best practices for ensemble-averaging diesel spray flames. Two indexes are defined. The structure-similarity index analysis suggests at least 5 realizations are needed to obtain 99% similarity for mixture fraction if the average of 16 realizations are used as the target at 0.8 ms. However, this scenario may be different for different scalars of interest. It is found that 6 realizations would be enough to reach 99% of similarity for temperature, while 8 and 14 realizations are required to achieve 99% similarity for soot and OH mass fraction, respectively. Similar findings are noticed at 1 ms. More realizations are needed for the magnitude-similarity index for the similar level of similarity as the structure-similarity index.

Commentary by Dr. Valentin Fuster
2015;():V002T06A009. doi:10.1115/ICEF2015-1035.

A closed-cycle gasoline compression ignition engine simulation near top dead center (TDC) was used to profile the performance of a parallel commercial engine computational fluid dynamics code, as it was scaled on up to 4096 cores of an IBM Blue Gene/Q supercomputer. The test case has 9 million cells near TDC, with a fixed mesh size of 0.15 mm, and was run on configurations ranging from 128 to 4096 cores. Profiling was done for a small duration of 0.11 crank angle degrees near TDC during ignition. Optimization of input/output performance resulted in a significant speedup in reading restart files, and in an over 100-times speedup in writing restart files and files for post-processing. Improvements to communication resulted in a 1400-times speedup in the mesh load balancing operation during initialization, on 4096 cores. An improved, “stiffness-based” algorithm for load balancing chemical kinetics calculations was developed, which results in an over 3-times faster run-time near ignition on 4096 cores relative to the original load balancing scheme. With this improvement to load balancing, the code achieves over 78% scaling efficiency on 2048 cores, and over 65% scaling efficiency on 4096 cores, relative to 256 cores.

Commentary by Dr. Valentin Fuster
2015;():V002T06A010. doi:10.1115/ICEF2015-1045.

Dilute combustion is an effective approach to increase the thermal efficiency of spark-ignition (SI) internal combustion engines (ICEs). However, high dilution levels typically result in large cycle-to-cycle variations (CCV) and poor combustion stability, therefore limiting the efficiency improvement. In order to extend the dilution tolerance of SI engines, advanced ignition systems are the subject of extensive research.

When simulating the effect of the ignition characteristics on CCV, providing a numerical result matching the measured average in-cylinder pressure trace does not deliver useful information regarding combustion stability. Typically Large Eddy Simulations (LES) are performed to simulate cyclic engine variations, since Reynold-Averaged Navier-Stokes (RANS) modeling is expected to deliver an ensemble-averaged result.

In this paper it is shown that, when using RANS, the cyclic perturbations coming from different initial conditions at each cycle are not damped out even after many simulated cycles. As a result, multi-cycle RANS results feature cyclic variability. This allows evaluating the effect of advanced ignition sources on combustion stability but requires validation against the entire cycle-resolved experimental dataset.

A single-cylinder GDI research engine is simulated using RANS and the numerical results for 20 consecutive engine cycles are evaluated for several operating conditions, including stoichiometric as well as EGR dilute operation. The effect of the ignition characteristics on CCV is also evaluated. Results show not only that multi-cycle RANS simulations can capture cyclic variability and deliver similar trends as the experimental data, but more importantly that RANS might be an effective, lower-cost alternative to LES for the evaluation of ignition strategies for combustion systems that operate close to the stability limit.

Commentary by Dr. Valentin Fuster
2015;():V002T06A011. doi:10.1115/ICEF2015-1057.

A compact and accurate primary reference fuel (PRF) mechanism which consists of 46 species and 144 reactions was developed and validated to consider the fuel chemistry in combustion simulation based on a homogenous charged compression ignition (HCCI) mechanism. Some significant reactions were updated to ensure its capabilities for predicting combustion characteristics of PRF fuels. To better predict laminar flame speed, the relevant C2-C3 carbon reactions was coupled in. This enhanced PRF mechanism was validated by available experimental data references including ignition delay times, laminar flame speed, premixed flame species concentrations in jet stirred reactor (JSR), rapid compression machine and shock tube. The predicted data was calculated by CHEMKIN-II codes. All the comparisons between experimental and calculated data indicated high accuracy of this mechanism to capture combustion characteristics. Also, this mechanism was integrated into KIVA4-CHEMKIN. The engine simulation data (including in-cylinder pressure and apparent heat release rate (HRR)) was compared with experimental data in PRF HCCI, partially premixed compression ignition (PCCI) and diesel/gasoline dual-fuel engine combustion data. The comparison results implied that this mechanism could predict PRF and gasoline/diesel combustion in CFD engine simulations. The overall results show this PRF mechanism could predict the conventional fuel combustion characteristics in engine simulation.

Commentary by Dr. Valentin Fuster
2015;():V002T06A012. doi:10.1115/ICEF2015-1070.

Common rail injection system (CRIS) is an advanced technology which meets the stringent emission standards of diesel engines and satisfies consumer demand for better fuel efficiency and increased power. The coherence of fuel injection quantity is the key injection characteristic for CRIS to match diesel engines successfully. As a critical component for CRIS, the variation of injector characteristic parameters has significant influence on the coherence of fuel injection quantity of the system. In this paper, combining numerical modeling and design of experiments, the response predicted relation between fuel injection quantity fluctuation of CRIS and its influence factors had been investigated. A numerical model of common rail injector was presented for the purpose of creating a tool for simulation experiments. The model is developed using power bond graph method, which is a modeling method that has shown its superiority in modeling systems consisting of sub-models from several energy domains in a unified approach. Experiments were conducted at the same model conditions to validate the model. The results are quite encouraging and in agreement with model predictions, which imply that the model can accurately predict the fuel injection quantity of CRIS and it can be used to simulation and design experiments. Experiments were designed using D-optimal method in which the characteristic parameters of common rail injector were chosen as design factors and the fuel injection quantity fluctuation was selected as the response. The fuel injection quantity fluctuation responses at different design factor levels were obtained using the developed numerical model which had been validated. A regressive prediction model of fuel injection quantity fluctuation was suggested according to the simulation experiments by means of partial least-squares regression (PLR) analysis. Analysis of variance, normal distribution of standardized residuals and relation between observed and predicted fuel injection quantity fluctuation for the regressive prediction model were analyzed which demonstrate the favorable goodness of fit and significance of the regressive model to predict fuel injection quantity fluctuation of the system. By changing design factor levels, the comparisons between numerical results of the bond graph model and the predicted fuel injection quantity fluctuation of the regressive prediction model were conducted. Results show that the regressive prediction model can reliably predict the fuel injection quantity fluctuation caused by the variation of characteristic parameters of common rail injector. Research results of this paper can provide novel ideas to predict fuel injection quantity fluctuation and a theoretical guidance for design and parameters optimization of CRIS.

Commentary by Dr. Valentin Fuster
2015;():V002T06A013. doi:10.1115/ICEF2015-1097.

A numerical study of ignition and combustion in a glow plug (GP) assisted direct-injection natural gas (DING) engine is presented in this paper. The glow plug is shielded and the shield design is an important part of the combustion system development. The results simulated by KIVA-3V indicated that the ignition delay (ID) predicted by an in-cylinder pressure rise was different from that based on a temperature rise, attributed to the additional time required to burn more fuel to obtain a detectable pressure rise in the combustion chamber. This time difference for the ignition delay estimation can be 0.5 ms, which is significant relative to an ignition delay value of less than 2 ms. To further evaluate the time difference between the two different methods of ignition delay determination, sensitivity studies were conducted by changing the glow plug temperature, and rotating the glow plug shield opening angle towards the fuel jets. The results indicated that the ID method time difference varied from 0.3 to 0.8 ms for different combustion chamber configurations. In addition, this study also investigated the influences of different glow plug shield parameters on the natural gas ignition and combustion characteristics, by modifying the air gap between the glow plug and its shield, and by changing the shield opening size. The computational results indicated that a bigger air gap inside the shield can delay gas ignition, and a smaller shield opening can block the flame propagation for some specific fuel injection angles.

Commentary by Dr. Valentin Fuster
2015;():V002T06A014. doi:10.1115/ICEF2015-1103.

Multi-cycle Large-eddy simulations (LES) of motored flow in an optical engine housed at the University of Michigan have been performed. The simulated flow field is compared against particle image velocimetry (PIV) data in several cutting planes. Circular statistical methods have been sued to isolate the contributions to overall turbulent fluctuations from changes in flow direction or magnitude. High levels of turbulence, as indicated by high velocity root-mean square (RMS) values, exist in relatively large regions of the combustion chamber. But, the circular standard deviation, a measure of the variability in flow direction independent of velocity magnitude, is much more limited to specific regions or points, indicating much of the turbulence is from variable flow magnitude rather than variable flow direction. Using the circular standard deviation is also a promising method to identify critical points, such as vortex centers or stagnation points, within the flow, which may prove useful for future engine designers.

Commentary by Dr. Valentin Fuster
2015;():V002T06A015. doi:10.1115/ICEF2015-1112.

A numerical study of two-phase flow inside the nozzle holes and the issuing spray jets for a multi-hole direct injection gasoline injector has been presented in this work. The injector geometry is representative of the Spray G nozzle, an eight-hole counterbore injector, from the Engine Combustion Network (ECN). Simulations have been carried out for a fixed needle lift. Effects of turbulence, compressibility and non-condensable gases have been considered in this work. Standard k–ε turbulence model has been used to model the turbulence. Homogeneous Relaxation Model (HRM) coupled with Volume of Fluid (VOF) approach has been utilized to capture the phase change phenomena inside and outside the injector nozzle. Three different boundary conditions for the outlet domain have been imposed to examine non-flashing and evaporative, non-flashing and non-evaporative and flashing conditions. Noticeable hole-to-hole variations have been observed in terms of mass flow rates for all the holes under all the operating conditions considered in this study. Inside the nozzle holes mild cavitation-like and in the near-nozzle region flash boiling phenomena have been predicted when liquid fuel is subjected to superheated ambiance. Under favorable conditions considerable flashing has been observed in the near-nozzle regions. An enormous volume is occupied by the gasoline vapor, formed by the flash boiling of superheated liquid fuel. Large outlet domain connecting the exits of the holes and the pressure outlet boundary appeared to be necessary leading to substantial computational cost. Volume-averaging instead of mass-averaging is observed to be more effective, especially for finer mesh resolutions.

Commentary by Dr. Valentin Fuster
2015;():V002T06A016. doi:10.1115/ICEF2015-1114.

High-resolution single-plume JP-8 spray simulations have been performed to characterize detailed mixture formation process of high-pressure sprays for several common rail fuel injectors of interest to the Army. The first phase of the study involves examining the spray-induced turbulent mixing and global penetration parameters to present experimentally validated results across several computationally challenging length scales. Statistical convergence effects on the spray behavior and penetration profiles are presented by conducting several realizations for each injection case study. The second phase of the project adopts the grid-criteria approach developed for evaporating conditions to model turbulent combustion of a JP-8 reacting spray at compression-ignition engine conditions. A coupled Eulerian Lagrangian formulation is used to model the ensuing spray primary and secondary atomization regions using classical Kelvin Helmholtz - Rayleigh Taylor (KH-RT) wave type models. The flow turbulence subgrid scale microstructure is modeled via Dynamic Structure Large Eddy Simulation (DSLES) approach, largely resolving the anisotropic flow structures. The simulations are conducted across several fuel injector nozzle orifice dimensions ranging from 40–147 μm at a rail pressure of 1000 bar and typical compression-ignition engine operating condition of 900K and 60 bar, which is denoted as ECN Spray A. Liquid fuel physical properties are prescribed using a JP-8 surrogate mixture containing 80% n-decane and 20% trimethylbenzene (TMB) by volume.

The reacting gas phase kinetics is modeled using the Aachen mechanism [26–27] and a detailed chemistry approach of a kerosene surrogate mixture. Measurements from the Army Research Laboratory (ARL) Constant Pressure Flow (CPF) chamber provide global spray and combustion parameters for comparison, including spray penetration profiles, ignition delay and flame lift-of-lengths (LOL) for JP-8 fuels. The simulation results present validated non-reacting and reacting spray simulations (ignition delay agreed within 4% and flame LOL agreed within 5% of measured data) and provide insights into the atomization and mixing characteristics across several orifice dimensions.

Commentary by Dr. Valentin Fuster
2015;():V002T06A017. doi:10.1115/ICEF2015-1120.

The objective of the present work is to establish a framework to design simple Arrhenius mechanisms for simulation of Diesel engine combustion. The goal is to predict auto-ignition and flame propagation over a selected range of temperature and equivalence ratio, at a significantly reduced computational cost, and to quantify the accuracy of the optimized mechanisms for a selected set of characteristics. The methodology is demonstrated for n-dodecane oxidation by fitting the auto-ignition delay time predicted by a detailed reference mechanism to a two-step model mechanism. The pre-exponential factor and activation energy of the first reaction are modeled as functions of equivalence ratio and temperature and calibrated using Bayesian inference. This provides both the optimal parameter values and the related uncertainties over a defined envelope of temperatures, pressures, and equivalence ratios. Non-intrusive spectral projection is then used to propagate the uncertainty through homogeneous auto-ignitions. A benefit of the method is that parametric uncertainties can be propagated in the same way through coupled reacting flow calculations using techniques such as Large Eddy Simulation to quantify the impact of the chemical parameter uncertainty on simulation results.

Commentary by Dr. Valentin Fuster
2015;():V002T06A018. doi:10.1115/ICEF2015-1142.

The Kelvin-Helmholtz/Rayleigh-Taylor (KH-RT) wave breakup model is a commonly used model in predicting primary and secondary atomization and breakup processes in Lagrangian-Eulerian Diesel spray simulations. Droplet sizes predicted by this model are dependent on several parameters. The parameters include fuel physical properties, such as density, viscosity, and surface tension, and a number of adjustable model constants, such as KH and RT time constants, KH and RT size constants, and the breakup length constant. The purpose of this study is to investigate the effects of these parameters on predicting spray motions using large-eddy simulation with the dynamic structure sub-grid stress model. The code used in this study is OpenFOAM. This study has three major parts. Firstly, effects of the model constants on the prediction of momentum exchange process were examined by comparing liquid and gas momentum fluxes. Drag Forces exerted on liquid spray by gas phase can be determined from the slopes of gas and liquid momentum fluxes plotted against axial distance. We found that the prediction of momentum exchange between gas and liquid is most sensitive to the KH time constant, B1, among the other model constants. Secondly, effects of fuel physical properties were investigated by using four different fuels in the simulations of non-vaporizing and vaporizing sprays. The four fuels used were n-dodecane, F76 fuel, n-hexadecane, and methyl tetradecanoate. The F76 fuel is a multi-component fuel containing twenty-one hydrocarbons. Global spray quantities such as liquid and vapor penetrations, Sauter mean diameter, total liquid mass, number of parcels, and breakup model quantities such as Ohnesorge number and KH wave speed were compared. The key finding is that not all of these quantities monotonically increase or decrease with fuel molecular weight. Lastly, effects of fuel physical properties on sensitivities of the breakup model constants were studied. We compared liquid penetration and vapor penetration for each fuel using different values of the model constants. We found that the prediction of vapor penetrations is more sensitive to the KH time constant B1 when a fuel with lighter molecular weight was used, and the prediction of liquid penetrations is sensitive to the breakup length constant, Cb, in all of the four fuels. The computational investigations in this study reveal some limitations of the current spray breakup model, and motivate us to develop more advanced models to overcome these limitations.

Commentary by Dr. Valentin Fuster
2015;():V002T06A019. doi:10.1115/ICEF2015-1159.

Gasoline compression ignition (GCI), also known as partially premixed compression ignition (PPCI) and gasoline direct injection compression ignition (GDICI), engines have been considered an attractive alternative to traditional spark ignition engines. Lean burn combustion with the direct injection of fuel eliminates throttle losses for higher thermodynamic efficiencies, and the precise control of the mixture compositions allows better emission performance such as NOx and particulate matter (PM). Recently, low octane gasoline fuel has been identified as a viable option for the GCI engine applications due to its longer ignition delay characteristics compared to diesel and lighter evaporation compared to gasoline fuel [1]. The feasibility of such a concept has been demonstrated by experimental investigations at Saudi Aramco [1, 2]. The present study aims to develop predictive capabilities for low octane gasoline fuel compression ignition engines with accurate characterization of the spray dynamics and combustion processes. Full three-dimensional simulations were conducted using CONVERGE as a basic modeling framework, using Reynolds-averaged Navier-Stokes (RANS) turbulent mixing models. An outwardly opening hollow-cone spray injector was characterized and validated against existing and new experimental data. An emphasis was made on the spray penetration characteristics. Various spray breakup and collision models have been tested and compared with the experimental data. An optimum combination has been identified and applied in the combusting GCI simulations. Linear instability sheet atomization (LISA) breakup model and modified Kelvin-Helmholtz and Rayleigh-Taylor (KH-RT) break models proved to work the best for the investigated injector. Comparisons between various existing spray models and a parametric study have been carried out to study the effects of various spray parameters. The fuel effects have been tested by using three different primary reference fuel (PRF) and toluene primary reference fuel (TPRF) surrogates. The effects of fuel temperature and chemical kinetic mechanisms have also been studied. The heating and evaporative characteristics of the low octane gasoline fuel and its PRF and TPRF surrogates were examined.

Commentary by Dr. Valentin Fuster
2015;():V002T06A020. doi:10.1115/ICEF2015-1166.

Computational fluid dynamics (CFD) is now a ubiquitous computational tool for engine design and diagnosis. It is often necessary to provide well-known initial cycle conditions to commence the CFD computations. Such initial conditions can be provided by experimental data. To create an opportunity to computationally study engine conditions where experimental data are not available, a zero-dimensional quasi-predictive thermodynamic simulation is developed that uses well-established spray model to predict rate of heat release and calculated burned gas composition and temperature to predict nitric oxide (NO) concentration. This simulation could in turn be used in reverse to solve for initial cylinder conditions for a targeted NO concentration. This paper details the thermodynamic simulation for diesel engine operating conditions. The goal is to produce a code that is capable of predicting NO emissions as well as performance characteristics such as mean effective pressure (MEP) and brake specific fuel consumption (BSFC). The simulation uses general conservation of mass and energy approaches to model intake, compression, and exhaust. Rate of heat release prediction is based on an existing spray model to predict how fuel concentrations within the spray jet change with penetration. Rate of heat release provides predicted cylinder pressure, which is then validated against experimental pressure data under known operating conditions. An equilibrium mechanism is used to determine burned gas composition which, along with burned gas temperature, can be used for prediction of NO in the cylinder. NO is predicted using the extended Zeldovich mechanism. This mechanism is highly sensitive to temperature, and it is therefore important to accurately predict cylinder gas temperature to obtain correct NO values. Additionally, MEP and BSFC are determined. The simulation focuses on single fuel injection events, but insights are provided to expand the simulation to model multiple injection events.

Commentary by Dr. Valentin Fuster
2015;():V002T06A021. doi:10.1115/ICEF2015-1172.

Combustion instabilities in dilute internal combustion engines are manifest in cyclic variability (CV) in engine performance measures such as integrated heat release or shaft work. Understanding the factors leading to CV is important in model-based control, especially with high dilution where experimental studies have demonstrated that deterministic effects can become more prominent.

Observation of enough consecutive engine cycles for significant statistical analysis is standard in experimental studies but is largely wanting in numerical simulations because of the computational time required to compute hundreds or thousands of consecutive cycles. We have proposed and begun implementation of an alternative approach to allow rapid simulation of long series of engine dynamics based on a low-dimensional mapping of ensembles of single-cycle simulations which map input parameters to output engine performance.

This paper details the use Titan at the Oak Ridge Leadership Computing Facility to investigate CV in a gasoline direct-injected spark-ignited engine with a moderately high rate of dilution achieved through external exhaust gas recirculation. The CONVERGE™ CFD software was used to perform single-cycle simulations with imposed variations of operating parameters and boundary conditions selected according to a sparse grid sampling of the parameter space. Using an uncertainty quantification technique, the sampling scheme is chosen similar to a design of experiments grid but uses algorithms designed to minimize the number of samples required to achieve a desired degree of accuracy. The simulations map input parameters to output metrics of engine performance for a single cycle, and by mapping over a large parameter space, results can be interpolated from within that space. This interpolation scheme forms the basis for a low-dimensional ‘metamodel’ (or model of a model) which can be used to mimic the dynamical behavior of corresponding high-dimensional simulations.

Simulations of high-EGR spark-ignition combustion cycles within a parametric sampling grid were performed and analyzed statistically, and sensitivities of the physical factors leading to high CV are presented. With these results, the prospect of producing low-dimensional metamodels to describe engine dynamics at any point in the parameter space will be discussed. Additionally, modifications to the methodology to account for nondeterministic effects in the numerical solution environment are proposed.

Commentary by Dr. Valentin Fuster

Engine Design and Mechanical Development

2015;():V002T07A001. doi:10.1115/ICEF2015-1023.

Generally, the turbulent-flame velocity of natural gas is significantly lower than diesel in the combustion process, which results in the thermal loads of natural gas engines being significantly higher than those of diesel engines under the same stoichiometric condition without EGR. In this study, a heavy-duty natural gas engine is taken as the research object, which is used to measure the temperatures to analyze the heat transfer characteristics in the cylinder head water jacket around the valve bridges, under different speeds and loads, as well as different coolant temperatures and pressures. Twelve thermocouples are inserted by drilling through the metal in the cylinder head with different heights to measure the metal temperatures at thermally critical areas such as the valve-bridge regions. Therefore, the local heat flux and the extrapolation to coolant wall temperatures are obtained by Fourier’s Law under different engine operating conditions. In addition, the thermal balance tests of the engine are also carried out, and the energy distributions are analyzed in different parts of the engine. The results of the research show that: a) the engine cooling condition has a direct impact on the engine cylinder head temperature. If the cooling temperature is low, the temperatures of the cylinder head’s measuring points have the same increases as the increasing coolant temperature. When the coolant temperature is high, the measuring temperatures have hardly any difference from the increases in cooling temperature. With increasing cooling pressure, the temperature increase at all measuring points, and the temperature of the measuring points varies substantially under high load conditions compared with the low load condition. The results indirectly indicated that local nucleate boiling appeared in the water jacket. b) The heat transfer characteristic curve of the water jacket was obtained from the processing of experimental data. Wall heat flux increases with increasing load, and the relationship between wall heat flux and wall temperature is no longer linear. The heat transfer characteristic curve indicates that the convective heat transfer and boiling heat transfer both appeared in the cooling water jacket. c) With the decrease of engine load, the percentage of crankshaft power in the combustion heat gradually decreases, then the percentage of the heat taken away by the cooling water increases gradually. At the same time, the percentage of the heat taken away by exhaust has changed little. d) The engine cooling temperature has a substantial influence on the engine thermal balance, and the cooling pressure has little effect on the engine thermal balance. With increasing cooling temperature, the heat taken by the cooling water decreased, which lead to an increase in the proportion of crankshaft power. It can be concluded that properly increasing the coolant temperature of the engine can improve the fuel economy of the machine.

Topics: Cooling , Gas engines
Commentary by Dr. Valentin Fuster
2015;():V002T07A002. doi:10.1115/ICEF2015-1027.

In 2006, an automatic lube oil filtration system with an automatic backflushing filter and a centrifuge for railway engines was already presented at the ASME spring technical conference in Aachen. The technical benefit of a centrifuge compared to a cartridge filter is the ability to collect smaller particles.

The power to drive the centrifuge comes from the engine oil pressure. This engine oil pressure is dependent from the engine speed. Many operating profiles of locomotives are showing low engine speed and load e.g. while waiting in switchyard and under arctic weather conditions the engines keep idling even during “downtime”. Under those conditions a centrifuge is ineffective or even out of operation.

Commentary by Dr. Valentin Fuster
2015;():V002T07A003. doi:10.1115/ICEF2015-1029.

Small-displacement, single-cylinder, diesel engines employ mechanically actuated fuel injection systems. These mechanically governed systems, while robust and low-cost, lack the ability to fully vary injection parameters, such as timing, pulse duration, and injection pressure. The ability of a particular injection system to vary these injection parameters impacts engine efficiency, power, noise, and emissions. Modern, multi-cylinder automotive engines employ some form of electronically controlled injection to take advantage of the benefits of fully variable injection, including advanced strategies such as multi-pulse injections and rate shaping. Modern diesel electronic fuel injection systems also operate at considerably higher injection pressures than mechanical fuel systems used in small-bore industrial engines. As the cost of electronic fuel systems continues to decrease and the demand for high-efficiency engines increases, electronic fuel injection becomes a more viable option for incorporation into small industrial diesel engines. In particular, this technology may be well-suited for demanding and critical applications such as military power generation.

In this study, a small-bore, single-cylinder diesel was retrofit with a custom, four-hole, high-pressure electronic fuel system. Compared to the mechanical injector, the electronic, common-rail injector had a 50% smaller orifice diameter and was designed for a 4x higher injection pressure. The mechanical governor was also replaced with an electronic speed controller. The baseline and modified engines were installed on a dynamometer, and measurements of exhaust emissions, fuel consumption, brake torque, and in-cylinder pressure were made. The electronic injector led to lower smoke opacity and NOx emissions, while CO and hydrocarbon emissions were observed to increase slightly, likely due to some wall wetting of fuel with the initial prototype injector. Testing with low ignition quality fuels was also performed, and the electronic fuel system enabled the engine to operate with fuel having a cetane number as low as 30.

Commentary by Dr. Valentin Fuster
2015;():V002T07A004. doi:10.1115/ICEF2015-1042.

Modern SI (spark ignition) engines are continuing to evolve for improved fuel economy by utilizing increased peak cylinder pressure, reduced section size piston rings, reduced cylinder bore surface finish, reduced lubricating oil viscosity, usage of alternative fuels, and with potentially increased fuel dilution. These changes all increase the potential for asperity contact between the top ring outer periphery and the cylinder wall, thereby creating a more challenging operational environment for the top ring.

To evaluate the resistance of new advanced top ring coatings, a new aggressive test cycle promoting ring face fatigue and scuffing was developed. The test cycle has been shown to be successful in failing a production GNS (gas nitride steel) coating in 10 hrs of run time.

This paper also presents relative performance data for different top ring face materials and ring features. The ring coatings evaluated include traditional coatings such as GNS and PVD (physical vapor deposition) coating as well as thermal spray coatings consisting of conventional plasma, HDAP (high density air plasma), and HVOF (high velocity oxygen fuel).

Commentary by Dr. Valentin Fuster
2015;():V002T07A005. doi:10.1115/ICEF2015-1047.

Recent engine developments towards higher loads (downsizing) and thinner oil films have increased the severity of plain bearing operating conditions 1. These factors, combined with lower viscosity oils, have resulted in a greater sensitivity of bearings to damage by foreign debris particles. Traditional highly embeddable materials, such as lead, are being progressively phased out. This lead-free trend observed in the passenger car market is likely to spread to the truck market in the future. As a result, it is becoming increasingly challenging to balance the conflicting hard and soft requirements of bearing materials. Although new generations of bearing materials, particularly polymeric overlays, have shown excellent fatigue and wear capabilities 2, they would benefit from enhanced embeddability properties. This demand has led MAHLE to take a new approach with the development of a polymeric overlay material that has both hard and soft characteristics. This newly developed soft-phase co-polymer resin has been synthesized from monomers selected to give the desired properties. Conventional Polyamide-imide (PAI) monomers have been combined with Polydimethylsiloxane (PDMS) macromonomers. PDMS was selected to improve embeddability as it is softer and offers more flexibility than PAI. Via a polymerization reaction, chains of hard, fatigue resistant PAI are alternately combined with short chains of PDMS. This produces a polymer matrix which has a very fine distribution of soft phase due to the micro-phase segregation created as the soft and hard segments of neighboring polymer chains preferentially align with each other 3, 4. The relative lengths of the hard and soft sections can be ‘tuned’ to produce domains of differing size and therefore adjust the balance of properties. Experiments have been carried out varying the overall percentage of PDMS and also with the molecular weight of the PDMS segments. Initial embeddability testing has shown an improvement in embedment over current polymer products and further work is ongoing to optimize this new resin system.

Commentary by Dr. Valentin Fuster
2015;():V002T07A006. doi:10.1115/ICEF2015-1071.

This paper describes the development of a water cooled, lean burn, gaseous fueled engine designed for distributed power installations. Electric generators have become popular because they provide a portable supply of electrical power at consumer demand. They are used in critical need areas such as hospitals and airports, and have found their way into homes frequented with power outages or homes in remote locations. Gensets are available in a wide variety of sizes ranging from 1 kilowatt (kW) to thousands of kilowatts. In the mid-range the power sources are typically spark ignition, automotive type internal combustion engines. Since engines designed for automotive use are subject to different emission regulations, and are optimized for operation at RPMs and BMEPs above that of electric generator engines, modifications can be made to optimize them for gensets. This work describes modifications which can be made during remanufacturing an automotive engine to optimize it for use as a generator engine. While the work recognizes the potential for cost savings from the use of remanufactured automotive engines over that of using new automotive engines and the majority of the design constraints were adopted to reduce engine cost, the main focus of the work is quantifying the increase in fuel efficiency that can be achieved while meeting the required EPA emission requirements.

This paper describes the seven combustion chamber designs that were developed and tested during this work. Friction reduction was obtained in both valve train and journal bearing design. The engine optimized for fuel efficiency produced a maximum brake thermal efficiency of 37.5% with λ= 1.63. This yielded an EPA test cycle average brake specific fuel consumption (BSFC) of 325 g/kW-hr. Modification of the spark advance and low load equivalence ratio to meet EPA Phase III emission standards resulted in an EPA test cycle average BSFC of 330 gm/kW-hr. When the engine used in this research was tested in its unmodified, automotive configuration under the EPA Compliant Test Cycle it’s EPA test cycle average brake specific fuel consumption was 443.4 gm/kW-hr. This is a 34% increase in fuel consumption compared to the modified engine.

Commentary by Dr. Valentin Fuster
2015;():V002T07A007. doi:10.1115/ICEF2015-1074.

An experimental and theoretical study is presented to study the effect of surface texturing in the form of circumferential oil grooves on improving the tribological properties of piston ring-cylinder liner tribosystem. Tests were performed on a reciprocating test rig with actual piston rings and cylinder liner segments, and a numerical model has been developed. A comparison was made between the performance of the textured cylinder liners and un-textured cylinder liners. It was found that with the smaller oil groove area density, the reduction in friction force is more obvious, Parabolic and triangular oil grooves are more efficient in friction reducing, and the prediction results by numerical model match the experimental results well in most case.

Commentary by Dr. Valentin Fuster
2015;():V002T07A008. doi:10.1115/ICEF2015-1087.

The development of combustion engines is heavily influenced by environmental regulations and efficiency. Since the environmental regulation have influenced engine design already with special combustion system and exhaust gas treatments, efficiency and the greenhouse gas CO2 has become a major issue for further development.

CO2 emissions and fuel efficiency are linked and are directly influenced by the internal friction of the combustion engine. One major part of this internal friction is coming from the crank train bearings. Since we have to consider different operating conditions for the crank train bearings like hydrodynamic and mixed friction (hydrodynamic in combination with boundary contact), working principles as well as different engine operating conditions like full load, idle, start stop etc. different measures need to be employed for a friction reduced crank train.

The optimal dimensioning of the bearings in combination with oil viscosity reduction are already known to a certain extent. Nevertheless they result in changes of bearing loads and may in consequence increase the share of boundary friction. Therefore, only looking on these two optimization steps is not enough. In addition the friction coefficient between bearing and shaft as well as the interaction between bearing surface and lubricant need to be addressed to reduce friction loss.

In order to gain a complete picture, influences and the interaction of

• geometric properties and bearing dimensions,

• friction coefficient of bearings in combination with crankshaft materials,

• oil formulation, viscosity and their interaction with engine application and duty cycle as well as

• losses caused by the lubrication system design and components

are investigated and analyzed based on simulation and testing. At first the different steps are investigated individually and secondly combinations and interactions are derived on basis of parameters derived on tribological tests and material data. Oil viscosity as major driver during hydrodynamic operation but also the influence of additive packages during mixed friction is roughly estimated on basis of tribological investigations.

Since the overall friction system and its optimization are very complex, an example for a truck engine in different applications shows advantages and disadvantages of the different approaches. Also border lines given by operational risk and improvement limits are explained. The improvement options given by bearing materials and special coatings are explained in combination with different engines and engine applications.

Further development activities, ways of collaboration between engine manufacturer and bearing supplier and an outlook on up-coming bearing system are completing the picture for a holistic approach on friction reduction in crank train bearings.

Commentary by Dr. Valentin Fuster
2015;():V002T07A009. doi:10.1115/ICEF2015-1121.

Durability is a prime concern in the design of hydraulic systems and fuel injectors [1–3] thus an accurate prediction of impact velocities between components and the flow through them is essential to assessing concepts. Simulation of these systems is difficult because the geometries are complex, some volumes go to zero as the components move, and the flow at a single operating condition generally spans Reynolds numbers less than 1 to more than 104[4–8]. As a result of these challenges, experimental testing of prototypes is the dominant method for comparing concepts. This approach can be effective but is far more costly, time consuming, and less flexible than the ability to run simulations of concepts early in the design cycle.

A validated model of a fuel injector built from publicly available data [1] is used to present a new approach to modelling hydraulic systems which overcomes many of these obstacles. This is accomplished by integrating several commercially available tools to solve the physics specific to each area within the fuel injector. First, the fuel injector is simulated using a 3D CFD simulation integrated with a 1D CFD system model. The flow in various regions of the injector is then analyzed to determine if the fluid models in these areas can be simplified based on the flow regime. Based on this analysis, a combination of models is assembled to improve the quality of the simulation while decreasing the time required to run the model.

The fuel injector is simulated using a multibody dynamics model coupled to a reluctance network model of the solenoid and several fluid models. The first is a 3D CFD simulation which uses novel mesh refinement techniques during runtime to ensure high mesh quality throughout the motion of components, to resolve the velocity profile of laminar flows, and to satisfy the requirements of the RNG k-ε turbulence model and wall functions. This approach frees the analyst from defining the mesh before runtime and instead allows the mesh to adapt based on the flow conditions in the simulation. Due to the highly efficient meshing algorithm employed, it is possible to re-mesh at each timestep thus ensuring a high quality structured mesh throughout the simulation duration. Then a 3D FEM solution to the Reynolds Equation and a statistical contact model is employed to solve for the squeeze films between components and to allow separation and contact between bodies in the control valve. These detailed simulations are integrated with a 1D flow model of the fuel injection system.

The results from the detailed coupled simulations are compared to the results from simpler 1D models and measured data to illustrate under which operating conditions a more advanced technique incorporating 3D CFD is worth the additional computational expense versus a traditional 1D model.

Commentary by Dr. Valentin Fuster
2015;():V002T07A010. doi:10.1115/ICEF2015-1126.

Natural gas is an attractive option for transportation applications in the United States due to its abundant availability and potential for reduced emissions. The scarcity of refueling resources imposes a barrier to widespread use of natural gas in internal combustion engines. The development of a novel bi-modal engine capable of operating in a compressor mode provides refueling capabilities without any supplemental devices and attempts to overcome this infrastructure limited barrier. Heat generated in the compression process however results in undesirable effects such as increased work input for compression, pre-heating of natural gas stored in the fuel tank, and thermal loads in the components used in the modified cylinder head. In order to make the system self-contained, heat exchangers that utilize engine coolant as a heat sink are included in the system design to maintain natural gas temperatures at an acceptable level in between compression stages. This is planned to be done in a novel fashion so as to make the system self-regulating permitting the cooling of natural gas while maintaining the coolant temperature in the cylinder head at acceptable levels to maintain combustion efficiency. To this end, an EES model of the system that incorporates elements of the original vehicle coolant system and modifications made to incorporate the heat exchangers is developed and analyzed to ensure satisfactory performance. Parametric studies of system performance as a function of varying heat loads are used to determine the best strategy to maintain acceptable natural gas temperatures without causing a drop in engine performance.

Commentary by Dr. Valentin Fuster
2015;():V002T07A011. doi:10.1115/ICEF2015-1161.

The noise of diesel engines is dependent upon numerous factors such as: load, speed, fuel injection strategies and fuel type, design of the piston, piston-pin and cylinder and their tolerances, bearings, valves and rocker arm clearances, and designs of the manifolds.

In this study, engine sound and vibrations analysis have been conducted using two types of fueling and combustion strategies: classical ULSD combustion and the new RCCI with n-butanol injected in the intake manifold. The analyses add to the understanding of the influence of combustion characteristics’ effect on mechanical noise and vibrations throughout the engine’s operating cycle.

The sound and vibration signals were both analyzed in the frequency and angle domain spectrum. Overall NVH spectrum from ULSD combustion was compared to that of RCCI with 50% by mass PFI of n-butanol (the 50% remaining ULSD fuel was directly injected).

Frequency analyses were performed using the FFT and CPB methods with Bruel & Kjaer’s Pulse sound and vibrations analysis software. Angle domain analyses were performed, referencing 0 CAD as TDC in combustion.

The engine tests were conducted at 1500 rpm and 4 bar IMEP. The COV of IMEP for DI ULSD and RCCI were 2.4 and 2.2, respectively. The correlations between sound, three dimensional vibration levels, and timings were found for: pressure gradients from combustion process, intake and exhaust valve actuations and gas exchange, and piston slap on the cylinder liner.

The measurements were extracted and analyzed, and the results determined that virtually all the noise and vibration values pertinent to RCCI were lower than those of ULSD classical combustion.

Commentary by Dr. Valentin Fuster
2015;():V002T07A012. doi:10.1115/ICEF2015-1169.

In a medium term scenario Internal Combustion Engine (ICE) downsizing and hybrid powertrain will represent the actual trend in vehicle technology to reduce fuel consumption and CO2 emission. Concerning downsizing concept, to maintain a reasonable power level in small engines, the application of turbocharging is mandatory both for spark ignition (SI) and compression ignition (CI) engines. Following this aspect, the possibility to couple an electric machine to the turbocharger (electric turbo compound, ETC) to recover the residual energy of the exhaust gases is becoming more and more attractive, as demonstrated by several studies around the world and by the current application in the F1 Championship.

The present paper shows the first numerical results of a research program focused on the comparison of the benefits resulting from the application of an ETC to a small twin-cylinder SI engine (900 cm3) and to a four cylinders CI engine (1600 cm3), both of the same maximum power. Starting from the experimental maps of several turbines and compressors, complete model of both turbocharged engines were created using the AVL BOOST one-dimension code.

Concerning the SI engine, first numerical results show that ETC can improve the average overall efficiency at the highest engine speeds and loads. Besides, boost range extension in the lowest engine rotational speed region and a possible reduction of turbo lag represent other benefits related to ETC application.

On the other hand, the adoption of an ETC to a CI engine shows larger benefits in term energy recovery at the highest engine speeds, with consequent reduction of fuel consumption, mainly due to the absence of throttling effects in the intake manifold and related pumping losses.

Commentary by Dr. Valentin Fuster
2015;():V002T07A013. doi:10.1115/ICEF2015-1175.

The engine vibration and noise induced by a valve train element are analyzed through the modeling and experiment method. The valve train dynamics are firstly studied to make clear the sources of the valve train noise. The component flexibility and inertia of mass are all taken into consideration as well as the contact or impact behaviors. The contact or impact forces are applied on the combined model of a combined structure. The resulting vibration responses at the outer surfaces are considered to be the boundary conditions of the acoustic model. The acoustic model is built by the boundary element method. The analysis results show the noise induced by the valve train element is mainly in the 500–800Hz 1/3 octave bands. The noise in this frequency range is related to not only the resonance of oil pan and valve cover but the overall combined structure stiffness. And moreover, the resonance of the valve train element excited by the harmonic of the camshaft rotational frequency has heightened the noise radiation in this frequency range. The noise in the low frequency range is determined by the exciting components of the cam profile, and that in the high frequency range are produced mainly by the valve-seat impact and by the cam-tappet impact. The analysis results are proved well by comparison with the experimental results. Thus the results are very useful for understanding the source characteristics of valve train noise.

Commentary by Dr. Valentin Fuster

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