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Research Papers: Fuel Combustion

Computational Fluid Dynamics Simulation of Gasoline Compression Ignition

[+] Author and Article Information
Janardhan Kodavasal

Argonne National Laboratory,
9700 S. Cass Avenue,
Argonne, IL 60439
e-mail: jkodavasal@anl.gov

Christopher P. Kolodziej

Argonne National Laboratory,
9700 S. Cass Avenue,
Argonne, IL 60439
e-mail: ckolodziej@anl.gov

Stephen A. Ciatti

Argonne National Laboratory,
9700 S. Cass Avenue,
Argonne, IL 60439
e-mail: sciatti@anl.gov

Sibendu Som

Argonne National Laboratory,
9700 S. Cass Avenue,
Argonne, IL 60439
e-mail: ssom@anl.gov

1Corresponding author.

Contributed by the Internal Combustion Engine Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received January 21, 2015; final manuscript received February 10, 2015; published online April 2, 2015. Editor: Hameed Metghalchi.

This work has been authored by an employee of the UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”) under Contract No. DE-AC02-06CH11357 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the published form of this work, or allow others to do so, for United States Government purposes.

J. Energy Resour. Technol 137(3), 032212 (May 01, 2015) (13 pages) Paper No: JERT-15-1029; doi: 10.1115/1.4029963 History: Received January 21, 2015; Revised February 10, 2015; Online April 02, 2015

Gasoline compression ignition (GCI) is a low temperature combustion (LTC) concept that has been gaining increasing interest over the recent years owing to its potential to achieve diesel-like thermal efficiencies with significantly reduced engine-out nitrogen oxides (NOx) and soot emissions compared to diesel engines. In this work, closed-cycle computational fluid dynamics (CFD) simulations are performed of this combustion mode using a sector mesh in an effort to understand effects of model settings on simulation results. One goal of this work is to provide recommendations for grid resolution, combustion model, chemical kinetic mechanism, and turbulence model to accurately capture experimental combustion characteristics. Grid resolutions ranging from 0.7 mm to 0.1 mm minimum cell sizes were evaluated in conjunction with both Reynolds averaged Navier–Stokes (RANS) and large eddy simulation (LES) based turbulence models. Solution of chemical kinetics using the multizone approach is evaluated against the detailed approach of solving chemistry in every cell. The relatively small primary reference fuel (PRF) mechanism (48 species) used in this study is also evaluated against a larger 312-species gasoline mechanism. Based on these studies, the following model settings are chosen keeping in mind both accuracy and computation costs—0.175 mm minimum cell size grid, RANS turbulence model, 48-species PRF mechanism, and multizone chemistry solution with bin limits of 5 K in temperature and 0.05 in equivalence ratio. With these settings, the performance of the CFD model is evaluated against experimental results corresponding to a low load start of injection (SOI) timing sweep. The model is then exercised to investigate the effect of SOI on combustion phasing with constant intake valve closing (IVC) conditions and fueling over a range of SOI timings to isolate the impact of SOI on charge preparation and ignition. Simulation results indicate that there is an optimum SOI timing, in this case −30 deg aTDC (after top dead center), which results in the most stable combustion. Advancing injection with respect to this point leads to significant fuel mass burning in the colder squish region, leading to retarded phasing and ultimately misfire for SOI timings earlier than −42 deg aTDC. On the other hand, retarding injection beyond this optimum timing results in reduced residence time available for gasoline ignition kinetics, and also leads to retarded phasing, with misfire at SOI timings later than −15 deg aTDC.

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Figures

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Fig. 1

1/7th sector mesh at TDC for simulations showing grid refinement from fixed embedding (nozzle and wall) and AMR

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Fig. 2

Comparison of motoring pressure predictions from simulation with experiments

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Fig. 3

Grid convergence study with a RANS turbulence model for the baseline conditions shown in Table 3 with different resolutions based on minimum cell size

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Fig. 9

Comparison of “EI” emissions, NOx, HC, and CO, between experiments and simulations

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Fig. 8

Comparison of TIVC (left) and PIVC (right) from experiments and simulations. PIVC and TIVC were adjusted in the simulations to match experimental compression curves as well as the ignition timing. Note that there is significant uncertainty in the experimental TIVC obtained from heat release.

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Fig. 7

Comparison of in-cylinder pressure and ROHR between experiments (left) and simulations (right) for the SOI sweep. Legends indicate SOI timing in degrees aTDC.

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Fig. 6

Comparison of in-cylinder pressure predictions from the 48-species PRF mechanism based on Liu et al. ([43]) and the four-component, 312-species gasoline mechanism ([48]). Note that the IVC pressures and temperatures are different for both cases, and adjusted to match phasing.

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Fig. 5

Comparison of in-cylinder pressure predictions from RANS and LES with 0.175 mm minimum cell size. Note that IVC pressures and temperatures are different for both cases, and adjusted to match phasing.

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Fig. 4

Evaluation of the multizone solutions for chemical kinetics against detailed solution. Simulation time on 64 processors indicated within parentheses in the legend.

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Fig. 10

In-cylinder pressure traces at various SOI timings from simulations with all other operating conditions fixed. Dashed lines indicate SOI timings later than the −30 deg aTDC.

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Fig. 11

Ignition timing (represented by CA10) versus SOI timing with all other operating conditions fixed

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Fig. 12

Minimum allowable fueling (where COV of IMEP is >3%) versus SOI from experiments ([14])

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Fig. 21

Tradeoff between shorter ignition delays and reduced residence time for ignition kinetics (relative to SOI at −30 deg) as SOI is retarded beyond its optimum value

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Fig. 13

Pre-ignition reaction space (shown at TDC) for the SOI at −30 deg aTDC. Both reacting and nonreacting cases are shown.

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Fig. 14

Plot of a 2D section of the mesh at TDC showing the “squish” region, which is comprised of squish and crevice

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Fig. 15

Fuel mass percentage trapped in the squish region at TDC versus SOI timing from nonreacting simulations

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Fig. 16

Average temperatures in the squish and bowl regions for different SOI timings

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Fig. 17

TDC fuel mass distribution at different temperatures for the optimum SOI (−30 deg) and an early SOI (−42 deg)

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Fig. 18

Fuel mass distribution versus equivalence ratio: (a) within the whole cylinder and (b) only in the bowl, shown at TDC from nonreacting simulations at −30 deg and −42 deg SOI cases

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Fig. 19

Fuel mass distribution versus ϕ (whole cylinder) at TDC from nonreacting simulations with −30 deg and −18 deg SOI

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Fig. 20

Cumulative fuel mass distribution over constant volume ignition delays (a metric of reactivity) shown at TDC from nonreacting simulations at −30 deg and −18 deg SOI cases

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Fig. 22

Pressure traces and ROHR from simulations at an early SOI (−36 deg), and a late SOI (−21 deg)—these cases have similar combustion phasing, but different burn rates

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Fig. 23

Pre-ignition equivalence ratio distribution (at TDC) for the early (−36 deg) and late (−21 deg) SOI timings. The early SOI timing has a significant amount of fuel in the squish region, while the late SOI case has all the fuel in the bowl.

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Fig. 24

Temperature distribution near CA10 ignition timing (4 deg aTDC) showing ignition location for the early (−36 deg) and late (−21 deg) SOI cases

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Fig. 25

Temperature distribution near the 60% burn point for the early (−36 deg) and late (−21 deg) SOI timing cases—most of the combustion for the early SOI case happens in the squish (slower) while combustion for the late SOI case happens solely in the bowl (faster)

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