UW-Madison | College of Engineering | Search

SAE 2013 World Congress

Tuesday, April 16

Engine Flows and Combustion Diagnostics (Part 1 of 2)
(Session Code: PFL212)

Room W2-69  9:30 a.m.

9:50 a.m.

2013-01-0562

Simultaneous Measurements of In-Cylinder Temperature and Velocity Distribution in a Small-Bore Diesel Engine Using Thermographic Phosphors
Nicholas James Neal, Jonny Jordan, David Rothamer, University of Wisconsin-Madison

In-cylinder temperature and velocity fields were quantified simultaneously in an optically accessible, small-bore diesel engine. A technique utilizing luminescence from Pr:YAG phosphor particles aerosolized into the intake air was used for temperature determination while particle image velocimetry (PIV) on the aforementioned phosphor particles was used to simultaneously measure the velocity field. The temperature and velocity fields were measured at different points throughout the compression stroke up to -30 CAD. Systematic interference due to emission from the piston window reduced the accuracy of the measurements at crank angles closer to TDC. Single-shot simultaneous measurements of the temperature and velocity fields were made using both unheated and heated intake temperatures. In both cases, cycle-to-cycle variations in the temperature and velocity fields were visible. The single-shot temperature precision was estimated to be 30 K and 20 K respectively for the unheated and heated intake air cases at -30 CAD. Temperature determined with the diagnostic agreed with conventionally accepted methods for estimating the in-cylinder bulk gas temperature.

Engine Flows and Combustion Diagnostics (Part 1 of 2)
(Session Code: PFL212)

Room W2-69  9:30 a.m.

10:10 a.m.

2013-01-0567

High Resolution In-Cylinder Scalar Field Measurements during the Compression and Expansion Strokes
Yizhou Zhang, University of Wisconsin-Madison; David Jesch, Budapest University of Technology; Jason Oakley, Jaal Ghandhi, University of Wisconsin-Madison

High-resolution planar laser-induced fluorescence (PLIF) measurements were performed on the scalar field in an optical engine. The measurements were of sufficient resolution to fully resolve all of the length scales of the flow field through the full cycle. The scalar dissipation spectrum was calculated, and by fitting the results to a model turbulent spectrum the Batchelor scale of the turbulent flow was estimated. The scalar inhomogeneity was introduced by a low-momentum gas jet injection. A consistent trend was observed in all data; the Batchelor scale showed a minimum value at top dead center (TDC) and was nearly symmetric about TDC. Increasing the engine speed resulted in a decrease of the Batchelor scale, and the presence of a shroud on the intake valve, which increased the turbulence intensity, also reduced the Batchelor scale. The effect of the shrouded valve was less significant compared to the effect of engine speed. The results were also compared with high-resolution particle image velocimetry (PIV) measurements of the velocity field previously made in the same engine. The kinetic and scalar energy spectra were found to agree well, but the dissipation spectra differed significantly at high wavenumber due to the insufficient spatial resolution of the PIV data. The velocity data allow a direct comparison of the relative role of turbulence intensity, integral length scale, and viscosity on the Batchelor scale evolution. The reduction in turbulence intensity and integral length scale were found to nearly balance, allowing the reduction in kinematic viscosity at TDC to have a significant effect on the Batchelor scale behavior. The quantitative comparison between the Batchelor scale determined from the scalar data and the Komogorov scale determined from the velocity data was good, differing by less than 30% despite the independent estimation methods. But, some scaling relations using the velocity data were found to incorrectly predict the magnitude of the changes observed in the Batchelor scale.

Multi-Dimensional Engine Modeling (Part 2 of 4)
(Session Code: PFL209)

Room W2-67  1:00 p.m.

1:20 p.m.

2013-01-1082

Knock Tendency Prediction in a High Performance Engine Using LES and Tabulated Chemistry
Stefano Fontanesi, Stefano Paltrinieri, Alessandro D'Adamo, Giuseppe Cantore, Univ of Modena and Reggio Emilia; Christopher Rutland, Univ of Wisconsin Madison

The paper reports the application of a look-up table approach within a LES combustion modelling framework for the prediction of knock limit in a highly downsized turbocharged DISI engine. During experimental investigations at the engine test bed, high cycle-to-cycle variability was detected even for relatively stable peak power / full load operations of the engine, where knock onset severely limited the overall engine performance. In order to overcome the excessive computational cost of a direct chemical solution within a LES framework, the use of look-up tables for auto-ignition modelling perfectly fits with the strict mesh requirements of a LES simulation, with an acceptable approximation of the actual chemical kinetics.

The model here presented is a totally stand-alone tool for autoignition analysis integrated with look-up table reading from detailed chemical kinetic schemes for gasoline. The look-up table access is provided by a multi-linear interpolating routine internally developed at the “Gruppo Motori (GruMo)” of the University of Modena and Reggio Emilia. As the experimental tests were conducted operating the engine at knock-limited spark advance, the tool is at first validated for three different LES cycles in terms of knock tolerance, i.e. the safety margin to knock occurrence. As a second stage, the validation of the methodology is performed for discrete spark advance increases in order to assess the sensitivity of the modelling strategy to variations in engine operations. A detailed analysis of the unburnt gas physical state is performed which confirms the knock-limited condition suggested by the experimental tests.

High Efficiency IC Engines (Part 1 of 3)
(Session Code: PFL216)

Room W2-64  1:00 p.m.

1:40 p.m.

2013-01-0263

Efficiency and Emissions performance of Multizone Stratified Compression Ignition Using Different Octane Fuels
Stephen Ciatti, Michael Johnson, Argonne National Laboratory; Bishwadipa Das Adhikary, Rolf Reitz, University of Wisconsin Madison; Aaron Knock, Columbia University

Advanced combustion systems that simultaneously address PM and NOx while retaining the high efficiency of modern diesel engines, are being developed around the globe. One of the most difficult problems in the area of advanced combustion technology development is the control of combustion initiation and retaining power density. During the past several years, significant progress has been accomplished in reducing emissions of NO x and PM through strategies such as LTC/HCCI/PCCI/PPCI and other advanced combustion processes; however control of ignition and improving power density has suffered to some degree – advanced combustion engines tend to be limited to the 10 bar BMEP range and under. Experimental investigations have been carried out on a light-duty DI multi-cylinder diesel automotive engine. The engine is operated in low temperature combustion (LTC) mode using 93 RON (Research Octane Number) and 74 RON fuel. The presented approach uses multiple injections of low cetane (gasoline-like) fuels in a Multizone, Stratified Compression Ignition (MSCI) approach in an effort to improve control of combustion phasing and increase the engine load such that the practicality of the combustion system is increased compared to other LTC approaches. In the present work, different ignition quality (RON) fuels are examined to determine the effect on the combustion, emissions and performance. Considering the operational complexity of a multi-cylinder engine, an effort was made to reduce the variability of the boost pressure and injection timing, while EGR percentage and injection pressure were used as parameters in this study. At low load operation, the lower RON (i.e. easier to ignite) fuel displayed improved performance while at higher loads, the higher RON fuels displayed improved performance - primarily due to managing the ignition propensity, or ease of auto-ignition, of each operating condition.

Modeling of SI and Diesel Engines - SI Combustion
(Session Code: PFL208)

Room W2-61  1:00 p.m.

1:40 p.m.

2013-01-1311

A Quasi-Dimensional NOx Emission Model for Direct Injection Spark Ignition (DISI) Gasoline Engines
Jian Gong, Christopher Rutland, University of Wisconsin-Madison

A physical based quasi-dimensional NOx emission model for direct injection spark ignition gasoline engines (DISI) is developed. Physically, NOx emission in the DISI engines correlates to chemical mechanism of NOx formation and destruction, air-fuel mixing in the combustion chamber and flame temperature. The classical extended Zeldovich mechanism and N2O path way for NOx formation are employed as the chemical mechanism. A characteristic time model for the radical species H, O and OH is incorporated to account for non-equilibrium of radical species during the combustion. A model of homogeneity which correlates the fundamental dimensionless number and mixing time is developed to model the air-fuel mixing and homogeneity during the combustion. Since temperature has dominant effect on NOx emission, a flame temperature correlation is developed to model the flame temperature for NOx generation. Measured NOx emissions data from a single cylinder DISI research engine at different operating conditions was used to validate the NOx model. Comparison between the experimental data and modeling results shows the model gives very good predictions of NOx emissions. The effects of fuel injection timing, injection pressure, spark timing, overall engine AFR, and intake temperature are explored to validate the model. The NOx model is a good tool for NOx emissions prediction in DISI engines.

Multi-Dimensional Engine Modeling (Part 2 of 4)
(Session Code: PFL209)

Room W2-67  1:00 p.m.

2:40 p.m.

2013-01-1097

Improved Engine Wall Models for Large Eddy Simulation (LES)
Chalearmpol Plengsaard, Christopher Rutland, Univ of Wisconsin Madison

Improved wall models for LES are presented in this paper. The classical Werner-Wengle (WW) wall shear stress model was used along with the eddy viscosity near walls. A sub-grid scale turbulent kinetic energy was employed in a model for the eddy viscosity. To provide heat flux results, a modified classical variable-density wall heat transfer model, which includes the variation of the turbulent Prandtl number in the boundary layer, was also employed. The fully turbulent developed flow in a square duct with constant wall temperature was used to validate the model and the friction factor and Nusselt number predictions are in good agreement with experimental results. The resulting time and spatially averaged velocity and temperature wall functions from the new wall models match well with the law-of-the-wall experimental data. Additionally, the model was validated using experimental data from a Caterpillar engine operated with conventional diesel combustion. The computational pressure and heat release are well predicted when comparing with the experimental measurements. There is successful matching between the predicted wall heat fluxes and measurements taken at ten points on the piston surface. Compared with the previous RANS-based wall models, the new models generate more accurate predictions, which agree better with experimental data.

Wednesday, April 17

High Efficiency IC Engines (Part 2 of 3)
(Session Code: PFL216)

Room W2-64  8:00 a.m.

8:00 a.m.

2013-01-0279

RCCI Engine Operation Towards 60% Thermal Efficiency
Derek Splitter, Martin Wissink, Dan DelVescovo, Rolf Reitz, Univ of Wisconsin

The present experimental study explored methods to obtain the maximum practical cycle efficiency with Reactivity Controlled Compression Ignition (RCCI). The study used both zero-dimensional computational cycle simulations and engine experiments. The experiments were conducted using a single-cylinder heavy-duty research diesel engine adapted for dual fuel operation, with and without piston oil gallery cooling. In previous studies, RCCI combustion with in-cylinder fuel blending using port-fuel-injection of a low reactivity fuel and optimized direct-injections of higher reactivity fuels was demonstrated to permit near-zero levels of NOx and PM emissions in-cylinder, while simultaneously realizing gross indicated thermal efficiencies in excess of 56%. The present study considered RCCI operation at a fixed load condition of 6.5 bar IMEP an engine speed of 1,300 [r/min]. The experiments used a piston with a flat profile with 18.7:1 compression ratio. The results demonstrated that the indicated gross thermal efficiency could be increased by not cooling the piston, by using high dilution, and by optimizing in-cylinder fuel stratification with two fuels of large reactivity differences. The best results achieved gross indicated thermal efficiencies near 60%. By further analyzing the results with zero-dimensional engine cycle simulations, the limits of cycle efficiency were investigated. The simulations demonstrated that the RCCI operation without piston oil cooling rejected less heat, and that ~94% of the maximum cycle efficiency could be achieved while simultaneously obtaining ultra-low NOx and PM emissions.

High Efficiency IC Engines (Part 2 of 3)
(Session Code: PFL216)

Room W2-64  8:00 a.m.

8:20 a.m.

2013-01-0264

Effect of Piston Bowl Geometry on Dual Fuel Reactivity Controlled Compression Ignition (RCCI) in a Light-Duty Engine Operated with Gasoline/Diesel and Methanol/Diesel
Adam B. Dempsey, N. Ryan Walker, Rolf Reitz, Univ. of Wisconsin

A single-cylinder light-duty diesel engine was used to investigate dual fuel reactivity controlled compression ignition (RCCI) operated with two different fuel combinations: gasoline/diesel fuel and methanol/diesel fuel. The engine was operated over a range of conditions, from 1500 to 2300 rpm and 3.5 to 17 bar gross IMEP. Using the stock re-entrant piston bowl geometry, both fuel combinations were able to achieve low NOx and PM emissions with a peak gross indicated efficiency of 48%. However, at light load conditions both gasoline and methanol yielded poorer combustion efficiencies. Previous studies have shown that the high-levels of piston induced mixing that are created by the stock piston are not required, and in fact are detrimental due to increased heat transfer losses, for premixed combustion. Thus a modified piston featuring a shallow, flat piston bowl with nearly no squish land was also investigated. Using the modified piston, the gross indicated efficiency of RCCI combustion was significantly improved at light loads due to increases in combustion efficiency and decreases in heat transfer losses. At higher loads the modified piston also performed better than the stock piston, but the improvements were not as significant. Over the entire load and speed range, the modified piston yielded low NOx and PM emissions with a peak gross indicated efficiency of nearly 51%.

Multi-Dimensional Engine Modeling (Part 3 of 4)
(Session Code: PFL209)

Room O2-43  8:00 a.m.

8:20 a.m.

2013-01-1092

Surrogate Diesel Fuel Models for Low Temperature Combustion
Anand Krishnasamy, Rolf D. Reitz, University of Wisconsin; Werner Willems, Ford Forschungszentrum Aachen GmbH; Eric Kurtz, Ford Motor Co

Diesel fuels are complex mixtures of thousands of hydrocarbons. Since modeling their combustion characteristics with the inclusion of all hydrocarbon species is not feasible, a hybrid surrogate model approach is used in the present work to represent the physical and chemical properties of three different diesel fuels by using up to 13 and 4 separate hydrocarbon species, respectively. The surrogates are arrived at by matching their distillation profiles and important properties with the real fuel, while the chemistry surrogates are arrived at by using a Group Chemistry Representation (GCR) method wherein the hydrocarbon species in the physical property surrogates are grouped based on their chemical classes, and the chemistry of each class is represented by using up to two hydrocarbon species. The developed surrogate models were applied to predict conventional and low temperature combustion (LTC) characteristics of the three fuels in a single cylinder diesel engine using the KIVA-ERC-CHEMKIN code incorporated with a “MultiChem” mechanism having 120 species and 459 reactions. The predictions compared well with the measured data and engine trends with the three fuels with cetane numbers ranging from approximately 40 to 57. To examine the advantages of using the present multi-component models, the results were also compared with a conventional single component model, viz., n-tetradecane representing physical properties and n-heptane representing chemistry. It was found that although the single component fuel model reproduces the combustion and emission characteristics of the three diesel fuels under conventional combustion operation, it was unable to predict combustion and emission processes in LTC operation, especially, for lower cetane diesel fuels. It was also observed that there was a lack of sensitivity to changes in fuel properties in conventional combustion due to favorable charge conditions in terms of higher oxygen fraction and higher temperatures as compared to LTC.

High Efficiency IC Engines (Part 2 of 3)
(Session Code: PFL216)

Room W2-64  8:00 a.m.

8:40 a.m.

2013-01-0289

Efficiency and Emissions Mapping of RCCI in a Light-Duty Diesel Engine
Scott Curran, Reed Hanson, Robert Wagner, Oak Ridge National Laboratory; Rolf Reitz, University of Wisconsin

In-cylinder blending of gasoline and diesel to achieve Reactivity Controlled Compression Ignition (RCCI) has been shown to reduce NO X and particulate matter (PM) emissions while maintaining or improving brake thermal efficiency as compared to conventional diesel combustion (CDC). The RCCI concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. Varying the premixed gasoline fraction changes the fuel reactivity stratification in the cylinder providing further control of combustion phasing and pressure rise rate than the use of EGR alone. This added control over the combustion process has been shown to allow rapid engine operating point exploration without direct modeling guidance. This paper explores the efficiency, emissions and combustion characteristics of RCCI with gasoline and ultra-low sulfur diesel fuel over a wide speed and load range in a light-duty multi-cylinder diesel engine leading to the creation of an RCCI engine map. The RCCI map was developed under self-imposed constraints which included a maximum cylinder pressure rise rate of 10 bar/deg and a CO emission limit of 5000 ppm. The RCCI map was developed using a mix of single and split diesel injections without the use of EGR for best brake thermal efficiency with lowest possible NOX emissions. RCCI emissions and performance results are compared to CDC on the same base diesel engine.

Mixing-Controlled CI Combustion (Part 3 of 3) Fuel Effects
(Session Code: PFL204)

Room W2-65  9:00 a.m.

9:20 a.m.

2013-01-0900

Study of In-cylinder Combustion and Compression Ignition Engine Performance Using Different RON Fuels
Bishwadipa Das Adhikary, Univ. of Wisconsin-Madison; Rolf Reitz, Univ of Wisconsin-Madison; Stephen Ciatti, Argonne National Laboratory

The effects of different Research Octane Number [RON] fuels on a multi-cylinder light-duty compression ignition [CI] engine were investigated at light load conditions. Experiments were conducted on a GM 1.9L 4-cylinder diesel engine at Argonne National Laboratory, using two different fuels, i.e., 75 RON and 93 RON. Emphasis was placed on 5 bar BMEP load, 2000 rev/min engine operation using two different RON fuels, and 2 bar BMEP load operating at 1500 rev/min using 75 RON gasoline fuel. The experiments reveal difficulty in controlling combustion at low load points using the higher RON fuel. In order to explain the experimental trends, simulations were carried out using the KIVA3V-Chemkin Computational Fluid Dynamics [CFD] Code. The numerical results were validated with the experimental results and provided insights about the engine combustion characteristics at different speeds and low load conditions using different fuels. It was observed that cycle-to-cycle and cylinder-to-cylinder variability issues complicate the multi-cylinder engine operation to a significant extent. Effective compression ratios [CR] of all 4 cylinders were found to be different, which indicates the variability in injected fuel amount as well. With all these differences, validating the experimental emission trends with the simulations appeared to be somewhat difficult. Experiments indicated that to operate the engine using a higher RON fuel more premixing is required. Also 93 RON fuel injection at 5 bar BMEP load suggested that multi-cylinder engine operation at a higher injection pressure needed the injection strategy to be altered.

Multi-Dimensional Engine Modeling (Part 3 of 4)
(Session Code: PFL209)

Room O2-43  8:00 a.m.

 

9:20 a.m.

2013-01-1105

A Computational Investigation of the Effects of Swirl Ratio and Injection Pressure on Mixture Preparation and Wall Heat Transfer in a Light-Duty Diesel Engine
Federico Perini, Adam Dempsey, Rolf Reitz, University of Wisconsin-Madison; Dipankar Sahoo, Sandia National Laboratories; Benjamin Petersen, Ford Motor Company; Paul Miles, Sandia National Laboratories

In a recent study, quantitative measurements were presented of in-cylinder spatial distributions of mixture equivalence ratio in a single-cylinder light-duty optical diesel engine, operated with a non-reactive mixture at conditions similar to an early injection low-temperature combustion mode. In the experiments a planar laser-induced fluorescence (PLIF) methodology was used to obtain local mixture equivalence ratio values based on a diesel fuel surrogate (75% n-heptane, 25% iso-octane), with a small fraction of toluene as fluorescing tracer (0.5% by mass). Significant changes in the mixture’s structure and composition at the walls were observed due to increased charge motion at high swirl and injection pressure levels. This suggested a non-negligible impact on wall heat transfer and, ultimately, on efficiency and engine-out emissions. In this work, the extensive and quantitative local information provided by the PLIF experiments was used as the reference for assessing the accuracy of the CFD modeling of the engine. The KIVA3V-ERC code was used, with a sector mesh featuring high spatial resolution (about 0.1 cm). A compressible model for the extended piston and connecting rod assembly was introduced, and observed to significantly improve modeling of motored engine operation. The validation was then further extended by comparison with measured in-cylinder equivalence ratio distributions over a broad parameter range, and with measured average pressure and apparent heat release rate traces. Finally, an analysis of the effects of varying fuel injection pressures (500 - 2000 bar) and nominal swirl ratios (1.55 – 4.5) on the heat losses caused by different flow fields at the liner and piston bowl walls was conducted. The results showed the sensitivity of the combustion timing to swirl- or injection-induced wall heat transfer, and its interaction with equivalence ratio stratification.

Multi-Dimensional Engine Modeling (Part 3 of 4)
(Session Code: PFL209)

Room O2-43  8:00 a.m.

 

10:40 a.m.

2013-01-1099

A Comprehensive Combustion Model for Biodiesel-fueled Engine Simulations
Jessica Brakora; Rolf Reitz, Univ of Wisconsin

A comprehensive biodiesel combustion model is presented for use in multi-dimensional engine simulations. The model incorporates realistic physical properties in a vaporization model developed for multi-component fuel sprays and applies an improved mechanism for biodiesel combustion chemistry. Previously, a detailed mechanism for methyl decanoate and methyl-9-decenoate was reduced from 3299 species to 85 species to represent the components of biodiesel fuel. In this work, a second reduction was performed to further reduce the mechanism to 69 species. Steady and unsteady spray simulations confirmed that the model adequately reproduced liquid penetration observed in biodiesel spray experiments. Additionally, the new model was able to capture expected fuel composition effects with low-volatility components and fuel blend sprays penetrating further. A new biodiesel chemistry modeling strategy was implemented that utilizes n-heptane to improve ignition behavior and two biodiesel xperiments were chosen to validate the model under engine operating conditions. First, a low-speed, high-load, conventional combustion experiment was simulated and the model was able to predict the performance and NOx formation seen in the experiment. Second, high-speed, low-load, low-temperature combustion conditions were successfully modeled and the HC, CO, NOx, and fuel consumption were well-predicted for a sweep of injection timings. The LTC results included a comparison of biodiesel composition (palm vs. soy) and fuel blends (neat vs. B20). The model effectively reproduced trends observed in the experiments including a reduction in NOx with neat biodiesel at these conditions.

Fuel Injection and Sprays (Part 1 of 3)
(Session Code: PFL210)

Room W2-65  1:00 p.m.

2:40 p.m.

2013-01-1605

Use of Low-Pressure Direct-Injection for Reactivity Controlled Compression Ignition (RCCI) Light-Duty Engine Operation
N. Ryan Walker, Adam B. Dempsey, Michael J. Andrie, Rolf D. Reitz, University of Wisconsin-Madison

Reactivity controlled compression ignition (RCCI) has been shown to be capable of providing improved engine efficiencies coupled with the benefit of low emissions via in-cylinder fuel blending. Much of the previous body of work has studied the benefits of RCCI operation using high injection pressures (e.g., 500 bar or greater) with common rail injection (CRI) hardware. However, low-pressure fueling technology is capable of providing significant cost savings. Due to the broad market adoption of gasoline direct injection (GDI) fueling systems, a market-type prototype GDI injector was selected for this study. Single-cylinder light-duty engine experiments were undertaken to examine the performance and emissions characteristics of the RCCI combustion strategy with low-pressure GDI technology and compared against high injection pressure RCCI operation. Gasoline and diesel were used as the low-reactivity and high-reactivity fuels, respectively. GDI injection pressures range from 150 to 200 bar, while the CRI pressures range from 250 to 500 bar. Start of injection (SOI) timings ranged from −35° aTDC and −115° aTDC. The experimental results show comparable engine performance and emissions output, but with slight reductions in overall combustion efficiency when using low-pressure fueling with the stock re-entrant piston. CFD simulations were also performed to aid in visualization of the in-cylinder fuel distributions, which are controlling factors for RCCI combustion. By utilizing an optimized RCCI piston geometry, equivalent RCCI combustion performance can be achieved under low-pressure fueling, at moderate and high loads. The optimized geometry also allows for significant increases in thermal efficiency, with peak efficiencies over 47% observed.

Particle Emissions from Combustion Sources (Part 1 of 2)
(Session Code: PFL409)

Room O3-45  1:00 p.m.

3:00 p.m.

2013-01-1560

Effect of Equivalence Ratio on the Particulate Emissions from a Spark-Ignited, Direct-Injected Gasoline
Stephen Sakai, Mitchell Hageman, David Rothamer, University of Wisconsin-Madison

The effect of equivalence ratio on the particulate size distribution (PSD) in a spark‑ignited, direct-injected (SIDI) engine was investigated. A single-cylinder, four-stroke, spark-ignited direct-injection engine fueled with certification gasoline was used for the measurements. The engine was operated with early injection during the intake stroke. Equivalence ratio was swept over the range where stable combustion was achieved. Throughout this range combustion phasing was held constant. Particle size distributions were measured as a function of equivalence ratio. The data show the sensitivity of both engine out particle number and particle size to global equivalence ratio. As equivalence ratio was increased a larger fraction of particles were due to agglomerates with diameters > 100 nm. For decreasing equivalence ratio smaller particles dominate the distribution. The total particle number and mass increased non-linearly with increasing equivalence ratio. High sensitivity of particulate number to even small equivalence ratio changes was seen. These changes may be attributed to changes in fuel and oxygen availability, as well as changes in the flame temperature and heat release. The results have implications for fuel/air ratio dithering, enrichment, and cold start in spark-ignition direct-injection engines.

Thursday, April 18

Heat Transfer and Advances in Thermal & Fluid Sciences - In-cylinder Heat Transfer, Cooling and Exhaust Systems (Part 1 of 2) Engine Heat Transfer
(Session Code: PFL214)

Room W2-64  8:00 a.m.

8:20 a.m.

ORAL ONLY

Experimental Investigation of Piston Heat Transfer During Conventional Diesel and Reactivity Controlled Compression Ignition Combustion Regimes
Terry Hendricks, Sandia National Laboratories; Jaal Ghandhi, Univ of Wisconsin Madison

This work compares experimentally measured heat fluxes obtained while operating in two different combustion regimes on a single cylinder research engine. Engine performance, heat transfer, and emissions trends are compared between conventional diesel combustion (CDC) and reactivity controlled compression ignition (RCCI) combustion regimes for matched operating conditions. Thermocouples were embedded in the piston surface to track dynamic heat flux and enhance understanding of the differences that occur between the two different combustion regimes. To overcome load limitations that would be encountered on this engine with a mechanical linkage system, a commercial wireless system was used to transmit the thermocouples signals. The engine geometry required a sophisticated data processing scheme to convert the raw thermocouple data into a more usable form due to signal blockage. An inverse heat conduction method utilizing regularization was used to convert the temperature data into transient heat fluxes. The heat flux data demonstrates that RCCI displays enhanced thermal uniformity when compared to CDC. Heat release rates and other performance data were analyzed to compare the two combustion regimes and a heat transfer performance metric was developed to compare all the matched data sets. The data show that when comparing RCCI to CDC with matched loads, RCCI shows an approximately 15-50% decrease in piston heat transfer at moderate to high engine speed (1300 and 1750 RPM) and a slight advantage at lower engine speed. When examining start of injection (SOI) timing, the increase in mixing time for RCCI generates a more volumetric combustion event that maintains optimal phasing and burn duration under a wide range of timing conditions compared with CDC. Finally, a boost sweep demonstrated that CDC can be characterized by highly localized events that drive heat transfer patterns at the piston surface while RCCI, owing to its enhanced uniformity, is more uniform at the global and local level.

Fuel Injection and Sprays (Part 2 of 3)
(Session Code: PFL210)

Room W2-67  8:00 a.m.

9:40 a.m.

2013-01-1601

Effect of Physical Properties on Spray Models
Sarangarajan Vijayraghavan Iyengar, Christopher Rutland, University of Wisconsin Madison

In this work the modeling aspects of fuel vaporization are studied. To start with, the effects of vaporization model on engine simulations are studied. This is done by using two different fuel surrogates. Next a set of non-reacting spray simulations were performed under different ambient and operating conditions and for two different fuels. This was done for spray model validation and to look at the effect of vaporization model on liquid penetration length. Following an observed discrepancy in one of the spray cases, effect of ambient temperature on liquid length, two sensitivity analyses were performed. These analyses take into account the effects of each spray-sub model on vaporization and effects of spray breakup constants on liquid penetration. Using the results from the sensitivity analyses and linearized stability theory an empirical correction factor was developed to correct the spray behavior at low ambient temperatures. This factor corrects the Rayleigh-Taylor breakup time based on the fuel viscosity and empirical data for liquid length. To validate the correction factor a set of reacting and non-reacting cases were run with different fuels and it was observed that with the empirical correlation, the results are in good agreement with experimental data, which is encouraging.

Fuel Injection and Sprays (Part 2 of 3)
(Session Code: PFL210)

Room W2-67  8:00 a.m.

10:00 a.m.

2013-01-1595

Validating Non-Reacting Spray Cases with KIVA-3V and OpenFoam
Sarangarajan Vijayraghavan Iyengar, Chi-Wei Tsang, Christopher Rutland, Univ of Wisconsin Madison

In this work non-reacting spray simulations are performed using two Computational Fluid Dynamic (CFD) codes, KIVA and OpenFoam. The metric used is the liquid tip penetration which is compared with experimental data from the Engine Combustion Network at Sandia National Laboratories. Some important spray sub-models, available in KIVA, are implemented in OpenFOAM so that the two codes have more common models. In addition, model coefficients and computations cells used in the simulations are the same in both codes. The differences in spray source terms formulations and other spray sub models between the codes and their effect on liquid penetration are discussed.

Exhaust Emission Control: Modeling (Part 1 of 2)
(Session Code: PFL407)

Room O3-46  8:20 a.m.

10:20 a.m.

2013-01-1572

Three Way Catalyst Modeling with Ammonia and Nitrous Oxide Kinetics for a Lean Burn Spark Ignition Direct Injection (SIDI) Gasoline Engine
Jian Gong, Christopher Rutland, University of Wisconsin-Madison

A Three Way Catalyst (TWC) model with global TWC kinetics for lean burn DISI engines were developed and validated. The model incorporates kinetics of hydrocarbons and carbon monoxide oxidations, NOx reduction, water-gas and steam reforming and oxygen storage. Ammonia (NH3) and new nitrous oxide (N2O) kinetics were added into the model to study NH3 and N2O formation in TWC systems.

The model was validated over a wide range of engine operating conditions using various types of experimental data from a lean burn automotive SIDI engine. First, well controlled time-resolved steady state data were used for calibration and initial model tests. In these steady state operations, the engine was switched between lean and rich conditions for NOx emission control. Then, the model was further validated using a large set of time-averaged steady state data. Temperature dependencies of NH3 and N2O kinetics in the TWC model were examined and well captured by the model. Finally, the model was tested in a highly transient FTP drive cycle with cold start conditions. Comparisons between the data and simulation results indicate that the model is able to predict the experimental data fairly well. The global TWC kinetics in this study are a good starting point for further refinement.

Kinetically Controlled CI Combustion (Including HCCI) (Part 2 of 2)
(Session Code: PFL206)

Room W2-65  1:00 p.m.

1:00 p.m.

2013-01-0896

Experimental Investigation of Light-Medium Load Operating Sensitivity in a Gasoline Compression Ignition (GCI) Light-Duty Diesel Engine
Paul Loeper, Youngchul Ra, Cory Adams, David Foster, Jaal Ghandhi, Michael Andrie, Roger Krieger, Univ. of Wisconsin Madison; Russ Durrett, General Motors Company

The light-medium load operating range (4-7 bar net IMEP) presents many challenges for advanced low temperature combustion strategies utilizing low cetane fuels (specifically, 87-octane gasoline) in light-duty, high speed engines. The overly lean overall air-fuel ratio (Φ<0.4) sometimes requires unrealistically high inlet temperatures and/or high inlet boost conditions to initiate autoignition at engine speeds in excess of 1500 RPM. The objective of this work is to identify and quantify the effects of variation in input parameters on overall engine operation. Input parameters including inlet temperature, inlet pressure, injection timing/duration, injection pressure, and engine speed were varied in a ~0.5L single cylinder engine based on a production GM 1.9L 4-cylinder high speed diesel engine.

With constraints of combustion efficiency, noise level (pressure rise rate) and emissions, engine operation sensitivity due to changes in inlet temperature between 50-90C was first examined for fixed fueling rates. This experiment was then repeated at different inlet pressures and engine speeds. Finally, constant load experiments were performed in which perturbations in injection strategies (timing, duration, and pressure) were executed to assess overall system sensitivity. These experiments revealed primary and secondary effects with respect to changes in engine operation. In addition, an assessment of combustion robustness was made as well. Based on the results, we conclude that input parameters can be effectively manipulated to maintain low NOx emissions <0.6 g/kg-fuel with good combustion stability (COV of IMEP <3%) over a wide inlet temperature range. Further optimization (with respect to combustion efficiency and CO/UHC emissions) was realized with additional adjustment of these input parameters. Interestingly, gross ISFC remained relatively unaffected by changes in input parameters (185-190 g/kWh). This last observation leads to the assessment that GCI combustion can provide robust, high-fuel-efficiency, low emissions light-medium load operation in a light-duty engine application.

Kinetically Controlled CI Combustion (Including HCCI) (Part 2 of 2)
(Session Code: PFL206)

Room W2-65  1:00 p.m.

1:40 p.m.

2013-01-1652

Investigation of Pressure Oscillation Modes and Audible Noise in RCCI, HCCI, and CDC
Martin Wissink, Univ of Wisconsin; Zhi Wang, Tsinghua Univ; Derek Splitter, Arsham Shahlari, Rolf Reitz, Univ of Wisconsin

This study uses Fourier analysis to investigate the relationship between the heat release event and the frequency composition of pressure oscillations in a variety of combustion modes. While kinetically-controlled combustion strategies such as HCCI and RCCI offer advantages over CDC in terms of efficiency and NO X emissions, their operational range is limited by audible knock and the possibility of engine damage stemming from high pressure rise rates and oscillations. Several criteria such as peak pressure rise rate, ringing intensity, and various knock indices have been developed to quantify these effects, but they fail to capture all of the dynamics required to form direct comparisons between different engines or combustion strategies. Experiments were performed with RCCI, HCCI, and CDC on a 2.44 L heavy-duty engine at 1300 RPM, generating a significant diversity of heat release profiles. Fourier and statistical analyses were used to examine the effect of both the average heat release as well as cyclic variations on the frequency and amplitude of pressure oscillations, and these were compared to existing knocking criteria. The results indicate that for this engine platform, the first two resonant frequency modes contain the majority of the spectral power contributing to the ringing effect, and that the relative power contained in these modes is strongly influenced by the heat release event and operating conditions when operating with premixed combustion strategies.

Kinetically Controlled CI Combustion (Including HCCI) (Part 2 of 2)
(Session Code: PFL206)

Room W2-65  1:00 p.m.

2:00 p.m.

2013-01-1659

Comparison of Compression Ignition Engine Noise Metrics in Low-Temperature Combustion Regimes
Arsham J. Shahlari, Univ. of Wisconsin Madison; Chris Hocking, Eric Kurtz, Ford Motor Co; Jaal Ghandhi, Univ of Wisconsin Madison

Many combustion researchers use peak pressure rise rate or ringing intensity to indicate combustion noise in lieu of microphone data or using a combustion noise meter that simulates the attenuation characteristics of the engine structure. In this paper, peak pressure rise rate and ringing intensity are compared to combustion noise using a fully documented algorithm similar to the ones used by combustion noise meters. Data from multiple engines operating under several low-temperature combustion strategies were analyzed. The results suggest that neither peak pressure rise rate nor ringing intensity provides a direct correlation to engine noise over a wide range of operating conditions. Moreover, the estimation of both metrics is often accompanied by the filtering of the pressure data, which changes the absolute value of the results. Thus, all ringing intensity and peak pressure rise rate data should be provided with the filter characteristics to allow an independent assessment of the noise potential. The major difference between ringing intensity and peak pressure rise rate on the one hand and noise on the other appears to be in the speed scaling relationship.

Kinetically Controlled CI Combustion (Including HCCI) (Part 2 of 2)
(Session Code: PFL206)

Room W2-65  1:00 p.m.

2:20 p.m.

2013-01-1653

Effects of Biofuel Blends on Light-Duty Multi-Cylinder RCCI Operation
Reed Hanson, Scott Curran, Robert Wagner, Oak Ridge National Laboratory; Rolf Reitz, Univ of Wisconsin

Reactivity Controlled Compression Ignition (RCCI) is an engine combustion strategy that utilizes in-cylinder fuel blending to produce low NO x and PM emissions while maintaining high thermal efficiency. Previous RCCI research has been investigated in single-cylinder heavy-duty engines [1-6]. The current study investigates RCCI operation in a light-duty multi-cylinder engine over a wide number of operating points representing vehicle operation over the US EPA FTP test. Similarly, previous RCCI engine experiments have used petroleum based fuels such as ultra-low sulfur diesel fuel (ULSD) and gasoline, with some work done using high percentages of biofuels, namely E85 [7]. The current study was conducted to examine RCCI performance with moderate biofuel blends, such as E20 and B20, as compared to conventional gasoline and ULSD. The engine experiments consisted of in-cylinder fuel blending using port fuel-injection (PFI) of gasoline or E20 and early-cycle, direct-injection (DI) of ultra-low sulfur diesel (ULSD) or B20 fuel. At the selected load points, the results from RCCI combustion using biofuels and petroleum fuels are compared. Preliminary results show that with E20, the peak load was able to be raised from 8 to 10 bar BMEP, due to ethanol’s lower propensity for auto-ignition. Ethanol’s low reactivity enabled an increased reactivity gradient and reduced the pressure rise rate (PRR) compared to gasoline. This increase in peak load also allowed for a 5% relative increase in brake thermal efficiency (BTE). Replacing ULSD with B20 was shown to increase combustion efficiency at low loads. The unique fuel properties of these biofuel blends increases the benefits of the use of RCCI combustion compared to conventional diesel combustion (CDC).

Kinetically Controlled CI Combustion (Including HCCI) (Part 2 of 2)
(Session Code: PFL206)

Room W2-65  1:00 p.m.

2:40 p.m.

2013-01-1661

Particle Size and Number Emissions from Dual-Fuel Reactivity Controlled Compression Ignition
Christopher Kolodziej, Argonne National Laboratory; Martin Wissink, Derek Splitter, Reed Hanson, Rolf Reitz, Univ of Wisconsin; Jesus Benajes, Universitat Politècnica de València

Many concepts of premixed diesel combustion at reduced temperatures have been investigated over the last decade as a means to simultaneously decrease engine-out particle and oxide of nitrogen (NO x ) emissions. To overcome the trade-off between simultaneously low particle and NO x emissions versus high “diesel-like” combustion efficiency, a new dual-fuel technique called Reactivity Controlled Compression Ignition (RCCI) has been researched. In the present study, particle size distributions were measured from RCCI for four gasoline:diesel compositions from 65%:35% to 84%:16%, respectively. Previously, fuel blending (reactivity control) had been carried out by a port fuel injection of the higher volatility fuel and a direct in-cylinder injection of the lower volatility fuel. With a recent mechanical upgrade, it was possible to perform injections of both fuels directly into the combustion chamber. Particle size distributions were measured at four different gasoline injection timings for each gasoline:diesel fuel reactivity blend, while the ignition-controlling diesel injection timings remained constant. Increased particle mass and number emissions were measured for increased diesel fueling and advanced in-cylinder gasoline injection timing (especially from -340 to -360 °aTDC). In addition, effects of heated primary dilution ratio on the particle size distribution from one of the “standard” RCCI engine operating conditions was measured to provide some information of the particles’ volatility and how high of dilution ratio would be necessary to ensure stable measurements.

Kinetically Controlled CI Combustion (Including HCCI) (Part 2 of 2)
(Session Code: PFL206)

Room W2-65  1:00 p.m.

4:40 p.m.

2013-01-1678

Effect of Cetane Improvers on Gasoline, Ethanol, and Methanol Reactivity and the Implications for RCCI Combustion
Adam B. Dempsey, N. Ryan Walker, Rolf Reitz, Univ. of Wisconsin

The focus of the present study was to characterize the fuel reactivity of high octane number fuels (i.e., low fuel reactivity), namely gasoline, ethanol, and methanol when mixed with cetane improvers under lean, premixed combustion conditions. Two commercially available cetane improvers, 2-ethylhexyl nitrate and di-tert-butyl peroxide, were used in the study. First, blends of the primary reference fuels iso-octane and n-heptane were port injected under fixed operating conditions. The resulting combustion phasings were used to generate effective PRF number maps. Then, blends of the aforementioned base fuels and cetane improvers were tested under the same lean premixed conditions as the PRF blends. Based on the combustion phasing results of the base fuel and cetane improver mixture, the effective PRF number, or octane number, could be determined. In all three base fuels it was found that 2-ethylhexyl nitrate is more effective at increasing fuel reactivity compared to di-tert-butyl peroxide. However, 2-ethylhexyl nitrate has a potential disadvantage due its nitrate group, which can manifest itself as NOx emissions. The relationship between the fuel-bound nitrate group and the engine-out NOx emissions was extensively characterized in the present study. It was also observed that methanol’s response to cetane improvers was better than that of ethanol, in spite of the fact that they have similar octane numbers in their neat form. Once the reactivity of the base fuels was characterized, two mixtures of methanol and cetane improvers were selected and compared to diesel fuel as the high reactivity fuel (i.e., direct injected) for RCCI combustion.