SAE PUBLICATIONS
Tuesday 4/13/2010 – COBO Room W2-68, 10:00AM:
Liang, L., Naik, C.V., Puduppakkam, K.V., Wang, C., Modak, A., Meeks, E., Ge. H.-W., Reitz,
R.D., Rutland, C.J., "Efficient Simulation of Diesel Engine Combustion Using Realistic
Chemical Kinetics in CFD," SAE paper 2010-01-0178, 2010.
Detailed knowledge of hydrocarbon fuel combustion chemistry has grown tremendously in
recent years. However, the gap between detailed chemistry and computational fluid dynamics
(CFD) remains, because of the high cost of solving detailed chemistry in a large number of
computational cells. This paper presents the results of applying a suite of techniques aimed at
closing this gap. The techniques include use of a surrogate blend optimizer and a guided
mechanism reduction methodology, as well as advanced methods for efficiently and accurately
coupling the pre-reduced kinetic models with the multidimensional transport equations. The
advanced methods include dynamic adaptive chemistry (DAC) and dynamic cell clustering
(DCC) algorithms. These techniques are demonstrated by determining a multi-component diesel
fuel surrogate mechanism, reducing it as appropriate for the conditions of interest, and then
employing the reduced (but still quite detailed) mechanism in a multidimensional CFD
calculation of diesel engine combustion. The CFD simulation employs the newly developed
FORTÉ simulation package, which was designed to take advantage of the advanced chemistry
solver methodologies as well as advanced spray models. We start with a detailed diesel-surrogate
mechanism that contains 26 model-fuel components, for which an extensive set of validation
studies have been performed to verify predictions of ignition-delay and flame properties. The
diesel surrogate mechanism contains ~3,800 species and ~16,000 reactions. Given the cetane
number and physical properties of a specific blend of diesel fuel, a surrogate-blend optimizer
was used to obtain multi-component diesel surrogates that match the properties of the diesel.
With this diesel surrogate composition, a guided mechanism reduction method was used to
reduce the 3,800-species diesel mechanism to a 437-species mechanism, maintaining accuracy of
fundamental predictions over a wide range of conditions. Then the 437-species mechanism was
used directly in a CFD simulation of diesel engine combustion using a sector mesh. The
combined use of the DAC and DCC methods offers a speed-up factor of two to three orders of
magnitude compared to conventional computational approaches, making the once-prohibitive
computational task achievable within a reasonable time frame. Calculated in-cylinder pressure,
heat release rates, and emissions were analyzed against experimental data. The chemistry
solution techniques demonstrated in this paper prove highly efficient and accurate, and they pave
the way for including sophisticated combustion kinetics in computational engine combustion
research.
--------------------------------------------------------------------------------------------------------------------Tuesday 4/13/2010 – COBO Room W2-68, 10:00AM:
Liang, L., Naik, C.V., Puduppakkam, K., Wang, C., Modak, A., Meeks, E., Reaction Design; Ge,
H., Reitz, R.D., Rutland, C.J., Univ. of Wisconsin-Madison, “Efficient Simulation of Diesel
Engine Combustion Using Realistic Chemical Kinetics in CFD,” SAE paper 2010-01-0178
Detailed knowledge of hydrocarbon fuel combustion chemistry has grown tremendously in
recent years. However, the gap between detailed chemistry and computational fluid dynamics
(CFD) remains, because of the high cost of solving detailed chemistry in a large number of
computational cells. This paper presents the results of applying a suite of techniques aimed at
closing this gap. The techniques include use of a surrogate blend optimizer and a guided
mechanism reduction methodology, as well as advanced methods for efficiently and accurately
coupling the pre-reduced kinetic models with the multidimensional transport equations. The
advanced methods include dynamic adaptive chemistry (DAC) and dynamic cell clustering
(DCC) algorithms. These techniques are demonstrated by determining a multi-component diesel
fuel surrogate mechanism, reducing it as appropriate for the conditions of interest, and then
employing the reduced (but still quite detailed) mechanism in a multidimensional CFD
calculation of diesel engine combustion. The CFD simulation employs the newly developed
FORTÉ simulation package, which was designed to take advantage of the advanced chemistry
solver methodologies as well as advanced spray models. We start with a detailed diesel-surrogate
mechanism that contains 26 model-fuel components, for which an extensive set of validation
studies have been performed to verify predictions of ignition-delay and flame properties. The
diesel surrogate mechanism contains ∼3,800 species and ∼16,000 reactions. Given the cetane
number and physical properties of a specific blend of diesel fuel, a surrogate-blend optimizer
was used to obtain multi-component diesel surrogates that match the properties of the diesel.
With this diesel surrogate composition, a guided mechanism reduction method was used to
reduce the 3,800-species diesel mechanism to a 437-species mechanism, maintaining accuracy of
fundamental predictions over a wide range of conditions. Then the 437-species mechanism was
used directly in a CFD simulation of diesel engine combustion using a sector mesh. The
combined use of the DAC and DCC methods offers a speed-up factor of two to three orders of
magnitude compared to conventional computational approaches, making the once-prohibitive
computational task achievable within a reasonable time frame. Calculated in-cylinder pressure,
heat release rates, and emissions were analyzed against experimental data. The chemistry
solution techniques demonstrated in this paper prove highly efficient and accurate, and they pave
the way for including sophisticated combustion kinetics in computational engine combustion
research.
--------------------------------------------------------------------------------------------------------------------Tuesday 4/13/2010 – COBO Room W2-68, 10:40AM:
Lee, C.-W., Reitz, R.D., and Kurtz, E.J., "The Impact of Engine Design Constraints on Diesel
Combustion System Size Scaling," SAE paper 2010-01-0180, 2010.
A set of scaling laws were previously developed to guide the transfer of combustion system
designs between diesel engines of different sizes [1-4]. The intent of these scaling laws was to
maintain geometric similarity of key parameters influencing diesel combustion such as incylinder spray penetration and flame lift-off length. The current study explores the impact of
design constraints or limitations on the application of the scaling laws and the effect this has on
the ability to replicate combustion and emissions. Multi dimensional computational fluid
dynamics (CFD) calculations were used to evaluate the relative impact of engine design
parameters on engine performance under full load operating conditions. The base engine was
first scaled using the scaling laws. Design constraints were then applied to assess how such
constraints deviate from the established scaling laws and how these alter the effectiveness of the
scaling effort. The considered design parameters included engine speed, fuel injection pressure,
nozzle hole size, injection duration, compression ratio, intake valve closing, squish height and
effective compression ratio. For each test case a start of injection (SOI) sweep was carried out.
The impact of the engine parameters on engine-out emissions was evaluated using averaged
deviation of the emission data over the range of the SOI tests. The results revealed that duration
of injection (DOI) has the biggest impact, followed by the injection velocity both of which are
parameters that are related to local equivalence ratio. Injection velocity was found to affect the
mixing as well. It was also found that engine speed had a negligible effect on the combustion
characteristics within the tested range. This is attributed to the rapid fuel vaporization and the
short ignition delay characteristic of the tested conditions.
--------------------------------------------------------------------------------------------------------------------Tuesday 4/13/2010 – COBO Room W2-68, 1:00PM:
Ge, H.-W., Shi, Y., Reitz, R.D., and Willems, W., "Engine development using multi-dimensional
CFD and computer optimization," SAE paper 2010-01-0360, 2010.
The present work proposes a methodology for diesel engine development using multidimensional CFD and computer optimization. A multi-objective genetic algorithm coupled with
the KIVA3V Release 2 code was used to optimize a high speed direct injection (HSDI) diesel
engine for passenger car applications. The simulations were conducted using high-throughput
computing with the CONDOR system. An automated grid generator was used for efficient mesh
generation with 11 variable piston bowl geometry parameters. The first step in the procedure was
to search for an optimal nozzle and piston bowl design. In this case, spray targeting, swirl ratio,
and piston bowl shape were optimized separately for two full-load cases using simpler efficient
combustion models (the characteristic time scale model and the shell ignition model). The
optimal designs from the two optimizations were then validated using a combustion model with
detailed chemistry (KIVA-CHEMKIN model and ERC n-heptane mechanism). Next, the best
design was selected, which simultaneously reduces fuel consumption and pollutant emission for
the two cases. Its nozzle design and piston bowl shape were fixed and real-time controllable
parameters were optimized for each representative operating condition, including full-load, midload, and low-load operation. The controllable parameters, SOI, swirl ratio, boost pressure, and
injection pressure, were optimized using a recently developed adaptive multi-grid chemistry
(AMC) model that allows for efficient simulations with the detailed chemistry combustion
model. Optimal designs which simultaneously reduce fuel consumption and pollutant emissions
were obtained for all the operating conditions except a very low-load case. Averaged optimal
boost pressure and injection pressure were found to increase with the engine load.
--------------------------------------------------------------------------------------------------------------------Tuesday 4/13/2010 – COBO Room W2-64, 1:00PM:
Splitter, D.A.,, Hanson, R., Kokjohn, S., Rein, K., Sanders, S., and Reitz, R.D., "An Optical
Investigation of Ignition Processes in Fuel Reactivity Controlled PCCI Combustion," SAE paper
2010-01-0345, 2010.
The ignition process of fuel reactivity controlled PCCI combustion was investigated using engine
experiments and detailed CFD modeling. The experiments were performed using a modified all
metal heavy-duty, compression-ignition engine. The engine was fueled using commercially
available gasoline (PON 91.6) and ULSD diesel delivered through separate port and direct
injection systems, respectively. Experiments were conducted at a steady state-engine load of 4.5
bar IMEP and speed of 1300 rev/min. In-cylinder optical measurements focused on
understanding the fuel decomposition and fuel reactivity stratification provided through the
charge preparation. The measurement technique utilized point location optical access through a
modified cylinder head with two access points in the firedeck. Optical measurements of natural
thermal emission were performed with an FTIR operating in the 2-4.5 mm spectral region.
Measured spectra were indexed to engine crank-angle, thus enabling cycle-averaged, crankangle-resolved in-cylinder spectroscopy. The measured spectra were compared to emission
spectra from the HITRAN database for qualitative species formation. Experimentally measured
spectra of fuel decomposition and the formation of aldehydes, water, and carbon dioxide were
observed. The reaction extent of the measurements was calculated and compared to that of
predictions from the CFD modeling. The modeling predictions used the KIVA 3v Release 2 code
coupled with the CHEMKIN II solver and a reduced primary reference fuel mechanism.
Comparison of the experimental and CFD modeling results showed good agreement of measured
species both spatially and temporally. Reaction extent comparisons were used to provide
quantitative evidence for spatially and temporally staged combustion established via in-cylinder
reactivity blended charge preparation. The results demonstrated that, at the tested conditions, the
charge preparation strategy delayed combustion by approximately 4-5 CAD in areas of lower
fuel reactivity as compared to areas of higher fuel reactivity, thus extending the combustion
duration. This establishes the well controlled ultra-low emission, high efficiency PCCI-type
combustion with reasonable pressure rise rates described by references [14, and 15].
--------------------------------------------------------------------------------------------------------------------Tuesday 4/13/2010 – COBO Room W2-68, 2:20PM:
Banerjee, S., Liang, T., Rutland, C.J., Hu, B., “Validation of an LES Multi Mode Combustion
Model for Diesel Combustion,” SAE paper 2010-01-0361
Diesel engine combustion is simulated using Large Eddy Simulation (LES) with a multi-mode
combustion (MMC) model. The MMC model is based on the combination of chemical kinetics,
chemical equilibrium, and quasi-steady flamelet calculations in different local combustion
regimes. The local combustion regime is identified by two combustion indices based on the local
temperature and the extent of mixture homogeneity. The LES turbulence model uses the dynamic
structure model (DSM) for sub-grid stresses. A new spray model in the LES context is used, and
the Reynolds-averaged Navier-Stokes (RANS) based wall model is retained with the LES
derived scales. These models are incorporated in the KIVA3V-ERC-Release 2 code for engine
combustion simulations.
A wide range of diesel engine operating conditions were chosen to validate the combustion
model. The engine operating conditions include both the Low Temperature Combustion (LTC)diesel and the conventional diesel combustion with a variety of injection timing, boost pressure,
and Exhaust Gas Recirculation (EGR). Diesel engine combustion typically exhibits both partially
premixed and non-premixed characteristics. In the low temperature premixed combustion
regimes, combustion is calculated by chemical kinetics. At higher temperatures, combustion is
calculated by the quasi steady flamelet time scale combustion model supplemented with the
chemical equilibrium calculations. The MMC model is able to predict a wide range of diesel
combustion regimes. The simulation results of pressure and heat release compared well with the
experimental measurements of the ignition delay, heat release phasing, peak pressure, and engine
exhaust emissions. The MMC model required lower CPU cost than using the CHEMKIN in
these simulations.
--------------------------------------------------------------------------------------------------------------------Tuesday 4/13/2010 – COBO Room W2-63, 3:20PM:
Swor, T.A., Kokjohn, S.L., Andrie, M.J., and Reitz, R.D., "Improving Diesel Engine
Performance Using Low and High Pressure Split Injections for Single Heat Release and TwoStage Combustion," SAE paper 2010-01-0340, 2010.
This study explores an Adaptive Injection Strategy (AIS) that employs multiple injections at both
low and high pressures to reduce spray-wall impingement, control combustion phasing, and limit
pressure rise rates in a Premixed Compression Ignition (PCI) engine. Previous computational
studies have shown that reducing the injection pressure of early injections can prevent spray-wall
impingement caused by long liquid penetration lengths. This research focuses on understanding
the performance and emissions benefits of low and high pressure split injections through
experimental parametric sweeps of a 0.48 L single cylinder test engine operating at 2000 rev/min
and 5.5 bar nominal IMEP. This study examines the effects of 2nd injection pressure, EGR,
swirl ratio, and 1st and 2nd injection timing, for both single heat release and two-peak high
temperature heat release cases. In order to investigate the AIS concept experimentally, a
Variable Injection Pressure (VIP) system was developed. The VIP system is capable of both low
and high pressure injections (~300 bar and ~1200 bar respectively) through one injector in the
same cycle. For both the single heat release and TSC experiments, optimal operating conditions
were found. The single heat release cases tended to have better fuel economy and lower
emissions than the TSC cases. However, the peak pressure rise rates (PRR) for the single heat
release cases were typically above 6 bar/deg whereas TSC peak PRR were typically under 3
bar/deg. Further, for the single heat release cases, it was found that high EGR rates sufficiently
suppressed the first stage of combustion allowing the combustion phasing to be controlled by the
second injection. The TSC combustion phasing of both heat releases could be controlled with
injection timing and EGR. Emission and engine performance trade-offs were observed over the
injection timing ranges for all cases. Variable pressure injection was also compared to a highly
dilute (~67 % EGR) low temperature combustion (LTC) and was found to produce slightly
higher emissions while maintaining the same engine performance at a lower EGR rate (~55 %).
--------------------------------------------------------------------------------------------------------------------Wednesday 04/14/2010 – COBO Room W2-68, 8:20AM:
Zhang, Y., Petersen, B., Ghandhi, J.B., Rutland, C.J., “Large Eddy Simulation of Scalar
Dissipation Rate in an Internal Combustion Engine,” SAE paper 2010-01-0625
A novel algebraic similarity model for subgrid scalar dissipation rate has been developed as part
of the Large Eddy Simulation (LES) package KIVA3V-LES for diesel engine study. The model
is proposed from an a priori study using Direct Numerical Simulation (DNS) of forced isotropic
turbulence. In the a posteriori test, fully resolved turbulent passive scalar field measurements are
used to validate the model in actual engine flows. For reason of the length limit by SAE and the
specific interest in engine applications, only a prior test and a posteriori test in engine flows are
included in this paper. A posteriori tests in isotropic cube flow, turbulent round jet and flame
cases
will
be
presented
in
separate
papers.
An engine LES simulation of multi consecutive cycles was performed in this study. In multicycle analysis, the LES simulations show the capability of capturing cycle-to-cycle variations in
addition to correctly estimating the ensemble averaged scalar dissipation rate in the sampling
domain. The averaged magnitude of resolved scalar dissipation rate as well as subgrid scalar
dissipation rate is quantified for the experiments and LES simulation. The accurate prediction of
the mixing at resolved level, in combination with reasonable scaling relation between the
resolved dissipation and residual dissipation, contributes to the satisfactory prediction of the
model.
--------------------------------------------------------------------------------------------------------------------Wednesday 4/14/2010 – COBO Room W2-68, 8:40AM:
Wang, Y., Ge, H.-W., and Reitz, R.D., "Validation of Mesh- and Timestep-Independent Spray
Models for Multidimensional Engine CFD Simulations," SAE paper 2010-01-0626, 2010.
Resolution of droplet-scale processes occurring within engine sprays in multi-dimensional
Computational Fluid Dynamics (CFD) simulations is not possible because impractically refined
numerical meshes or time steps would be required. As a result, simulations that use coarse
meshes and large time steps suffer from inaccurate predictions of mass, momentum and energy
transfer between the spray drops and the combustion chamber gas, or poor prediction of droplet
breakup and collision and coalescence processes. Several new spray models have been proposed
to address these deficiencies, including use of an unsteady gas jet model to improve momentum
transfer predictions in under-resolved regions of the spray, a vapor particle model to minimize
numerical diffusion effects, and a Radius of Influence drop collision model to ensure consistent
collision computations on different meshes. The present work combines these models with
improved KH-RT models to improve the consistency of drop breakup predictions. A modified
mean collision time model is also proposed to reduce timestep dependency of droplet collision
prediction. The models have been implemented into the KIVA CFD code and are demonstrated
to achieve independency with respect to both mesh sizes and time steps. The code was validated
for non-evaporating and evaporating sprays, and also for diesel engine simulations with
variations of larger than one order of magnitude in mesh cell volume and around two orders of
magnitude in time steps. The numerical results were found to match available experimental
measurements very well, including spray tip penetration, local drop velocity and Sauter mean
diameter (SMD) and averaged mean diameter (AMD) of non-evaporating diesel sprays. The new
spray models were also applied to simulate evaporating sprays and good agreement was found
with measured liquid and vapor penetration lengths. Finally, the engine simulations were also
found to agree well with experimental engine data.
---------------------------------------------------------------------------------------------------------------------
Wednesday 4/14/2010 – COBO Room W2-66, 10:20AM:
Hanson, R., Reitz, R.D., Splitter, D., and Kokjohn, S., "An Experimental Investigation of Fuel
Reactivity Controlled PCCI Combustion in a Heavy-Duty Engine," SAE paper 2010-01-0864,
2010.
This study investigates the potential of controlling premixed charge compression ignition (PCCI)
combustion strategies by varying fuel reactivity. In-cylinder fuel blending using port fuel
injection of gasoline and early cycle, direct-injection of diesel fuel was used for combustion
phasing control at a medium engine load of 9 bar net IMEP and was also found to be effective to
prevent excessive rates of pressure rise. Parameters used in the experiments were guided from
the KIVA-CHEMKIN code with a reduced primary reference fuel (PRF) mechanism including
injection timings, fuel percentages, and intake valve closing (IVC) timings for dual-fuel PCCI
combustion. The engine experiments were conducted with a conventional common rail injector
(i.e., wide angle and large nozzle hole) and demonstrated control and versatility of dual-fuel
PCCI combustion with the proper fuel blend, SOI and IVC timings. For example, at the 9 bar
operating point, NOx and soot were 0.012 g/kW-hr and 0.008 g/kW-hr, respectively. That is, US
EPA 2010 heavy-duty NOx and PM emissions regulations are easily met without after-treatment,
while achieving 53% net indicated thermal efficiency.
--------------------------------------------------------------------------------------------------------------------Wednesday 4/14/2010 – COBO Room W2-63, 10:20AM:
Brakora, J., and Reitz, R.D., “Investigation of emissions predictions from biodiesel-fueled engine
simulations using a reduced chemical kinetic mechanism,” SAE paper 2010-01-0577, 2010.
A numerical study was performed to compare the formation of nitric oxide (NO) and nitrogen
dioxide (NO2), collectively termed NOx, resulting from biodiesel and diesel combustion in an
internal combustion engine. It has been shown that biodiesel tends to increase NOx compared to
diesel, and to-date, there is no widely accepted explanation. Many factors can lead to increased
NOx formation and it was of interest to determine if
fuel chemistry plays a significant role. Therefore, in order to isolate the fuel chemistry from
mixing processes typical in a compression ignition engine, sprays were not considered in the
present investigation. The current study compares the NOx formation of surrogates for biodiesel
(as represented by methyl butanoate and n-heptane) and diesel (n-heptane) under completely
homogeneous conditions. Combustion of each fuel was
simulated using the Senkin code for both an adiabatic, constant volume reactor, and an adiabatic,
single-zone HCCI engine model. The fuel chemistry is represented using an updated version of a
mechanism that combines reduced mechanisms for methyl butanoate and n-heptane. NOx
chemistry is predicted using a 19-step model that includes species and reactions for both thermal
and prompt NOx. It was found that biodiesel can cause a
slight NOx increase when compared to diesel fuel under certain conditions. The largest NOx
increase was seen at very lean conditions (f<0.6), but the differences in initial temperatures
required to match ignition time make it difficult to definitively link the NOx increase to the
oxygen in the fuel. As equivalence ratios rose above 0.6, the fuel-bound oxygen in biodiesel did
not increase NOx to the extent that the same amount of oxygen would create if it were available
in the surrounding air. While the presence of O2 in biodiesel does slightly impact NOx
formation, it does not appear to be a dominant factor.
--------------------------------------------------------------------------------------------------------------------Wednesday 4/14/2010 – COBO Room W2-66, 10:40AM:
Dunbeck, P.B., and Reitz, R.D., "An Experimental Study of Dual Fueling with Gasoline Port
Injection in a Single-Cylinder, Air-Cooled HSDI Diesel Generator," SAE paper 2010-01-0869,
2010.
An experimental study was conducted on an air cooled high-speed, direct-injection diesel
generator that investigated the use of gasoline in a dual fuel PCCI strategy. The single-speed
generator used in the study has an effective compression ratio of 17 and runs at 3600 rev/min.
Varying amounts of gasoline were introduced into the combustion chamber through a port
injection system. The generator uses an all-mechanical diesel fuel injection system that has a
fixed injection timing. The experiments explored variable intake temperatures and fuel split
quantities to investigate different combustion phasing regimes. Results from the study showed
low combustion efficiency at low load. Low load operation was also characterized by high
levels of HC and CO (in excess of 20 g/kwh and 50 g/kwh respectively). Operation at 75% load
was more efficient, and displayed three different combustion regimes that are possible with PIG
(port injected gasoline) dual fuel PCCI. At full load, PIG operation provided vast improvements
in the emissions of soot. The reduction of soot was likely the result of improvements in fuel
mixture homogeneity leading to lower local equivalence ratios. Gasoline was also found to both
delay and advance the ignition timing, depending on the fueling rates and intake temperatures.
--------------------------------------------------------------------------------------------------------------------Wednesday 4/14/2010 – COBO Room W2-69, 1:20PM:
Sridharan, S., Rutland, C.J., “Model-Based Diesel HCCI Combustion Phasing Controller in
Integrated System Level Modeling,” SAE paper 2010-01-0886
This work integrated a CA10 (crank angle at 10% heat release) controller into an integrated
engine, emissions and aftertreatment model platform. Two CA10 phasing targets were chosen to
analyze how advancing (or retarding) the target combustion phasing (CA10) affect the formation
of NOx and CO. The effect of intake valve closure (IVC) timing, which is the control mechanism
for maintaining the target combustion phasing, on the cylinder trapped mass, and hence the
charge temperature after compression is detailed. Finally, the relation between combustion
phasing and the blow-down process leading to the exhaust process is discussed. Retarding the
target combustion phasing by two degrees saw a 330 K drop in compressed charge temperature
and a quadrupled reduction of peak NO emitted. Peak NO2 emission reduced three times on
account of the same. However, an increase in CO emission was observed when the combustion
phasing was advanced. An integrated engine, emissions and aftertreatment models platform was
used for this study. A low-temperature combustion (LTC) cylinder model was linked to serve the
purpose of studying homogeneous charge compression ignition (HCCI) operation. Control over
combustion phasing was made possible by linking a previously developed model-based
controller to the integrated model.
---------------------------------------------------------------------------------------------------------------------
Wednesday 4/14/2010 – COBO Room W2-69, 1:40PM:
Gong, J., Rutland, C.J., “Study the DPF Regeneration at Transient Operating Conditions Using
Integrated System-Level Model,” SAE paper 2010-01-0892
System level models containing engine model, emission models, and aftertreatment device
models have been developed. All the sub-models have been developed separately and come from
a variety of different sources. A new phenomenological CO model recently has been coupled
into the previous integrated model. The emission models, including PM (particulate matter),
NOx, and CO are also calibrated from experimental data. Some modification has been added to
improve the integrated model and accept different aftertreatment device models for future work.
The objective of this work is to study the DPF (Diesel Particulate Filter) regeneration during
transient operating conditions using the integrated model.
The integrated system-level model is used to studying the dynamic performance between engine
and aftertreatment system. In this study, the calibrated emission models are validated at transient
operating conditions. Passive and active DPF regenerations are also conducted for load and
speed transients to study the transient effects on regeneration. The effects of exhaust mass flow
rate, and temperature on pressure drop across the DPF during regeneration are investigated.
--------------------------------------------------------------------------------------------------------------------Thursday 4/15/2010 – COBO Room W2-66, 9:20AM:
Dolak, J., Shi, Y., and Reitz, "A Computational Investigation of a Stepped-Bowl Piston
Geometry for a Light Duty Engine Operating at Low Load," SAE paper 2010-01-1263, 2010.
The objective of this investigation is to optimize a light-duty diesel engine in order to minimize
soot, NOx, carbon monoxide (CO), unburned hydrocarbon (UHC) emissions and peak pressure
rise rate (PPRR) while improving fuel economy in a low oxygen environment. Variables
considered are the injection timings, fractional amount of fuel per injection, half included spray
angle, swirl and a stepped-bowl piston geometry. The KIVA-CHEMKIN code, a multidimensional computational fluid dynamics (CFD) program with detailed chemistry is used and is
coupled to a multi-objective genetic algorithm (MOGA) along with an automated grid generator.
The stepped-piston bowl allows more options for spray targeting and improved charge
preparation. Results show that optimal combinations of the above variables exist to
simultaneously reduce emissions and fuel consumption. Details of the spray targeting were
found to have a major impact on the combustion process. With the stepped-bowl and split
injection strategy, combustion can occur in two distinctly different regions of the bowl. When
the first injection targeted the top portion and second injection targeted the bottom portion of the
stepped-bowl a low emission combustion process with improved fuel economy resulted. This is
because combustion takes place in two different areas, allowing better use of the oxygen, thus
limiting the production of soot. The stepped-bowl has less surface area than the conventional
reentrant bowl resulting in less heat transfer out causing the fuel consumption to be lower in the
stepped-bowl. Swirl, and spray angle along with the bowl geometry details affected the precombustion mixing process. Second injection timing and amount of exhaust gas recirculation
(EGR) affected the objectives as well. These parameters were varied and showed the steppedbowl piston allowed better use of the oxygen. This investigation shows the importance of the
bowl geometry, spray targeting, injection timing, split fuel amounts and swirl had on emissions
and fuel efficiency in direct injection diesel engines.
--------------------------------------------------------------------------------------------------------------------Thursday 4/15/2010 – COBO Room W2-66, 10:00AM:
Musu, E., Rossi, R., Gentili, R., and Reitz, R.D., "Clean Diesel Combustion by means of the
HCPC Concept," SAE paper 2010-01-1256, 2010.
Homogeneous-charge, compression-ignition (HCCI) combustion is triggered by spontaneous
ignition in dilute homogeneous mixtures. The combustion rate must be reduced by suitable
solutions such as high rates of Exhaust Gas Recirculation (EGR) and/or lean mixtures. HCCI is
considered a very effective way to reduce engine pollutant emissions, however only a few HCCI
engines have entered into production. HCCI combustion currently cannot be extended to the
whole engine operating range, especially to high loads, since the use of EGR displaces air from
the cylinder, limiting engine mean effective pressure, thus the engine must be able to operate
also in conventional mode.
This paper concerns a study of an innovative concept to control HCCI combustion in dieselfuelled engines. The concept consists in forming a pre-compressed homogeneous charge outside
the cylinder and in gradually admitting it into the cylinder during the combustion process. In this
way, combustion can be controlled by the transfer flow rate and high pressure rise rates, typical
of standard HCCI combustion, can be avoided. This new combustion concept was called
Homogenous Charge Progressive Combustion (HCPC). The paper illustrates a CFD analysis
focused on improving efficiency and reducing pollutant emissions at medium and heavy load.
Different geometries of the transfer duct were considered. Results show negligible soot emission
up to equivalence ratios around 0.85, with indicated efficiency around 46 %. As well, a moderate
level of external cooled EGR allows reducing NOx emissions up to levels that are typical of lowtemperature combustion.
--------------------------------------------------------------------------------------------------------------------Thursday 4/15/2010 – COBO Room W2-70, 3:20PM:
Strzelec, A., Foster, D.E., Rutland, C.J., Univ. of Wisconsin; Lewis, S., Storey, J., Daw, C., Oak
Ridge National Laboratory, “Effect of Biodiesel Blending on the Speciation of Soluble Organic
Fraction from a Light Duty Diesel Engine,” SAE paper 2010-01-1273
Soy methyl ester (SME) biodiesel was volumetrically blended with 2007 certification ultra low
sulfur diesel (ULSD) fuel and run in a 1.7L direct-injection common rail diesel engine at one
speed-load point (1500rpm, 2.6bar BMEP). Engine fueling rate and injection timing were
adjusted to maintain a constant load, while particulate samples were collected in a diesel
particulate filter (DPF) and with a dilution tunnel sampling train. The samples collected at these
two locations were found to contain different levels of soluble organic fraction (SOF) and the
different hydrocarbon species in the SOF. This observation indicates that traditional SOF
measurements, in light of the specific sampling procedure used, may not be appropriate to DPF
applications
---------------------------------------------------------------------------------------------------------------------
Butts, R.T., Ra, Y., Andrie, M.J., Krieger, R., Foster, D.E., “Investigation of the Effects of
Centane Number, Volitlity, and Total Aromatic Content on Highly-Dilute Low Temperature
Diesel Combustion,” SAE paper 2010-01-0337
The objective of this study is to increase fundamental understanding of the effects of fuel
composition and properties on low temperature combustion (LTC) and to identify major
properties that could enable engine performance and emission improvements, especially under
high load conditions.
A series of experiments and computational simulations were conducted under LTC conditions
using 67% EGR with 9.5% inlet O2 concentration on a single cylinder version of the GM 1.9L
direct injection diesel engine. This research investigated the effects of Cetane number (CN),
volatility and total aromatic content of diesel fuels on LTC operation. The values of CN,
volatility, and total aromatic content studied were selected in a DOE (Design of Experiments)
fashion with each variable having a base value as well as a lower and higher level. Timing
sweeps were performed for all fuels at a lower load condition of 5.5 bar net IMEP at 2000 rpm
using a single-pulse injection strategy. Selected fuels were also run under a higher load condition
of 10 bar net IMEP at 2000 rpm with roughly 90dB combustion noise using a split injection
strategy.
For this engine and the operating conditions tested, at 5.5 bar net IMEP, results show that
increasing CN reduces CO and UHC, improves ISFC and reduces combustion noise due to more
favorable combustion phasing. The results at higher load with split injection indicate that the two
injection timings and respective fuel quantity delivered in each injection must be varied
significantly to reach optimum conditions for fuels with different CN. Numerical simulation
results also demonstrate the effects of fuel property differences on combustion. In-cylinder flow
fields and distributions of temperature and species depict the reasons for different combustion
performance of the fuels considered in the study.