Christopher Kolodziej

Computational Fluid Dynamics Simulation of Gasoline Compression Ignition

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.

Effects of injection parameters, boost, and swirl ratio on gasoline compression ignition operation at idle and low-load conditions

In this work, we study the effects of injector nozzle inclusion angle, injection pressure, boost, and swirl ratio on gasoline compression ignition combustion. Closed-cycle computational fluid dynamics simulations using a 1/7th sector mesh representing a single cylinder of a four-cylinder 1.9 L diesel engine, operated in gasoline compression ignition mode with 87 anti-knock index (AKI) gasoline, were performed. Two different operating conditions were studied—the first is representative of idle operation (4 mg fuel/cylinder/cycle, 850 r/min), and the second is representative of a low-load condition (10 mg fuel/cylinder/cycle, 1500 r/min). The mixture preparation and reaction space from the simulations were analyzed to gain insights into the effects of injection pressure, nozzle inclusion angle, boost, and swirl ratio on achieving stable low-load to idle gasoline compression ignition operation. It was found that narrower nozzle inclusion angles allow for more reactivity or propensity to ignition (determined qualitatively by computing constant volume ignition delays) and are suitable over a wider range of injection timings. Under idle conditions, it was found that lower injection pressures helped to reduce overmixing of the fuel, resulting in greater reactivity and ignitability (ease with which ignition can be achieved) of the gasoline. However, under the low-load condition, lower injection pressures did not increase ignitability, and it is hypothesized that this is because of reduced chemical residence time resulting from longer injection durations. Reduced swirl was found to maintain higher in-cylinder temperatures through compression, resulting in better ignitability. It was found that boosting the charge also helped to increase reactivity and advanced ignition timing.

CFD Simulation of Gasoline Compression Ignition

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 multi-zone 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 multi-zone 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°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°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°aTDC.© 2014 ASME

Effects of Intake Pressure on Particle Size and Number Emissions from Premixed Diesel Low Temperature Combustion

In this study, 10 premixed diesel low-temperature combustion engine operating conditions were chosen based on engine intake pressure (1.2–1.6 bar), intake oxygen concentration (10%, 11%, and 12%), and injection timing (−24° after top dead centre in all test conditions). At each intake oxygen concentration, the effects of intake pressure on combustion parameters and emission measurements (carbon monoxide, hydrocarbons, nitrogen oxides, particulate matter mass concentration, and particle size distributions) were analyzed. Although increased intake pressure resulted in higher in-cylinder charge air density that improved fuel/air premixing and late-cycle oxidation quality, higher intake pressure also advanced the start of combustion and thereby decreased the time available for fuel and air premixing. But even with the decrease in premixing time available before start of combustion, increased intake pressure caused significant decreases in carbon monoxide, hydrocarbon, particulate matter mass, and particle number emissions. Particle size distribution measurements allowed greater understanding of how higher intake pressure decreased the particulate matter mass concentrations with respect to particle size. To further investigate the experimental results, a zero-dimensional engine heat release code was used to analyze combustion temperatures, and a one-dimensional free spray model was used to estimate the relative levels of liquid fuel spray impingement on the piston surface and maximum local equivalence ratio at start of combustion for each test case. Therefore, though the premixing time was shortened by higher intake pressures, the decreased emissions were understood by combined effects of enhanced fuel and air premixing quality and improved late-cycle oxidation near the end of combustion.

Effects of Injector Nozzle Inclusion Angle on Extending the Lower Load Limit of Gasoline Compression Ignition Using 87 AKI Gasoline

Gasoline Compression Ignition (GCI) is a promising single-fuel advanced combustion concept for increased efficiency and reduced emissions in comparison with current conventional combustion modes. Gasoline fuels are advantageous in premixed combustion concepts because of their increased volatility and reduced reactivity compared to diesel. These qualities help reduce emissions of particulate matter (PM) and oxides of nitrogen (NOx), while making combustion phasing (and therefore combustion noise reduction) easier to manage. One of the challenges of using a gasoline with an anti-knock index (AKI) of 87 in a premixed combustion concept is being able to achieve stable low load operation. (Note that AKI is equivalent to (RON + MON)/2.) With such small injection quantities of a relatively more volatile and less reactive fuel than diesel, the injection timing of minimum load fueling needs to be early enough to allow the auto-ignition chemistry enough time, but late enough to keep the fuel from over-mixing and losing ignition propensity. The objective of this study was to investigate the advantages and disadvantages of reducing the injector nozzles’ inclusion angle from 148° to 120° on the combustion and emissions performance of GCI at 850 RPM and low load. To assess these effects, minimum fueling injection timing sweeps were performed with a 3% coefficient of variance of indicated mean effective pressure with each injector nozzle angle at 500 and 250 bar injection pressure. The results from these experiments revealed that both reduced injector nozzle angle and reduced injection pressure increased ignition propensity and allowed for reduced fueling and stable low load extension to 1 bar brake mean effective pressure using 87 AKI gasoline without any external boosting or heating. Combustion characteristics (such as noise) and emissions are discussed.Copyright

Development of a Virtual CFR Engine Model for Knocking Combustion Analysis

The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (Argonne). Argonne, a U.S. Department of Energy (DOE) Office of Science laboratory, is operated under Contract No. DEAC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in the said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. This research was partially funded by DOEs Office of Vehicle Technologies and Office of Energy Efficiency and Renewable Energy (EERE) under Contract No. DE-AC02-06CH11357. The authors wish to thank Gurpreet Singh, Kevin Stork, and Leo Breton, program managers at DOE, for their support. This research was conducted as part of the Co-Optimization of Fuels and Engines (Co-Optima) project sponsored by the U.S. DOE Office of EERE, Bioenergy Technologies and Vehicle Technologies Offices

Combustion characteristics of various fuels during research octane number testing on an instrumented CFR F1/F2 engine

The Cooperative Fuels Research (CFR) engine is the long-established standard for characterization of fuel knock resistance in spark-ignition internal combustion engines. Despite its measurements of RON and MON being widely used, there is little understanding of what governs the CFR octane rating for fuels of various chemical compositions compared to primary reference fuels (iso-octane and n-heptane). Detailed combustion characteristics were measured on a highly instrumented CFR F1/F2 engine during RON testing of fuels with significantly different chemical composition. The results revealed differences in the cylinder pressure and temperature conditions, as well as knocking characteristics.