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The Development of Throttled and Unthrottled PCI Combustion in a Light-Duty Diesel Engine

GM R&D and Planning-Patrick G. Szymkowicz
University of Michigan-Timothy J. Jacobs, Alexander Knafl, Stanislav V. Bohac, Dennis N. Assanis
Published 2006-04-03 by SAE International in United States
Present-day implementations of premixed compression ignition low temperature (PCI) combustion in diesel engines use higher levels of exhaust gas recirculation (EGR) than conventional diesel combustion. Two common devices that can be used to achieve high levels of EGR are an intake throttle and a variable geometry turbocharger (VGT). Because the two techniques affect the engine air system in different ways, local combustion conditions differ between the two in spite of, in some cases, having similar burn patterns in the form of heat release. The following study has developed from this and other observations; observations which necessitate a deeper understanding of emissions formation within the PCI combustion regime.This paper explains, through the use of fundamental phenomenological observations, differences in ignition delay and emission indices of particulate matter (EI-PM) and nitric oxides (EI-NOx) from PCI combustion attained via the two different techniques to flow EGR. PCI attained via the use of a VGT to flow EGR, i.e. unthrottled PCI, has significantly less EI-PM emissions than PCI attained via the use of a throttle to flow EGR, i.e.…
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Characterizing Light-Off Behavior and Species-Resolved Conversion Efficiencies During In-Situ Diesel Oxidation Catalyst Degreening

GM R&D and Planning-Patrick G. Szymkowicz, Richard D. Blint
University of Michigan-Alexander Knafl, Stephen B. Busch, Manbae Han, Stanislav V. Bohac, Dennis N. Assanis
Published 2006-04-03 by SAE International in United States
Degreening is crucial in obtaining a stable catalyst prior to assessing its performance characteristics. This paper characterizes the light-off behavior and conversion efficiency of a Diesel Oxidation Catalyst (DOC) during the degreening process. A platinum DOC is degreened for 16 hours in the presence of actual diesel engine exhaust at 650°C and 10% water (H2O) concentration. The DOC's activity for carbon monoxide (CO) and for total hydrocarbons (THC) conversion is checked at 0, 1, 2, 3, 4, 6, 8, 10, 12, and 16 hours of degreening. Pre-and post-catalyst hydrocarbon species are analyzed via gas chromatography at 0, 4, 8, and 16 hours of degreening. It is found that both light-off temperature and species-resolved conversion efficiencies change rapidly during the first 8 hours of degreening and then stabilize to a large degree. T50, the temperature where the catalyst is 50% active towards a particular species, increases by 14°C for CO and by 11°C for THC through the degreening process. The shapes of the conversion versus DOC inlet temperature curves are preserved. With respect to species-resolved hydrocarbons,…
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Lean and Rich Premixed Compression Ignition Combustion in a Light-Duty Diesel Engine

GM R&D and Planning-Patrick G. Szymkowicz
University of Michigan-Timothy J. Jacobs, Stanislav V. Bohac, Dennis N. Assanis
Published 2005-04-11 by SAE International in United States
Lean Premixed Compression Ignition (PCI) low-temperature combustion promises to simultaneously reduce NOx and PM emissions, while suffering a moderate penalty in fuel consumption. Similarly, opportunities exist to develop rich PCI combustion strategies which can provide the necessary exhaust constituents for aggressive regeneration of a Lean NOx Trap (LNT). The current work highlights the development of lean and rich PCI combustion strategies. It is shown that the lean PCI combustion strategy successfully operates with low NOx and PM, at the expense of a 5% increase in fuel consumption over conventional diesel operation. The rich PCI combustion strategy similarly operates with low NOx and PM, and produces enough CO (up to 5% by volume in exhaust) for aggressive regeneration of an LNT.
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Evaluation of a Narrow Spray Cone Angle, Advanced Injection Timing Strategy to Achieve Partially Premixed Compression Ignition Combustion in a Diesel Engine

GM R&D and Planning-Robert M. Siewert
University of Michigan-Guntram A. Lechner, Timothy J. Jacobs, Christos A. Chryssakis, Dennis N. Assanis
Published 2005-04-11 by SAE International in United States
Simultaneous reduction of nitric oxides (NOx) and particulate matter (PM) emissions is possible in a diesel engine by employing a Partially Premixed Compression Ignition (PPCI) strategy. PPCI combustion is attainable with advanced injection timings and heavy exhaust gas recirculation rates. However, over-advanced injection timing can result in the fuel spray missing the combustion bowl, thus dramatically elevating PM emissions. The present study investigates whether the use of narrow spray cone angle injector nozzles can extend the limits of early injection timings, allowing for PPCI combustion realization. It is shown that a low flow rate, 60-degree spray cone angle injector nozzle, along with optimized EGR rate and split injection strategy, can reduce engine-out NOx by 82% and PM by 39%, at the expense of a modest increase (4.5%) in fuel consumption. This PPCI strategy has the potential for meeting upcoming stringent fuel specific NOx emission levels of less than 1 g/kg-fuel and fuel specific PM levels less than 0.25 g/kg-fuel.
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Fuel Economy and Engine-Out Emissions from a Single-Cylinder Two-Valve Direct-Injection S.I. Engine Operating in the Stratified-Combustion Regime

GM R&D and Planning-A. C. Alkidas, A. M. Lippert, D. L. Reuss
GM Powertrain-J. Liedtke, K.-J. Wu
Published 2002-10-21 by SAE International in United States
This study is an experimental and computational investigation of the influence of injection timing, fuel spray orientation, and in-cylinder air motion on the combustion, fuel economy, and engine-out emissions of a single-cylinder, 2-valve, spark-ignition direct-injection (SIDI) engine, operating under stratified-charged conditions. For the best compromise between fuel consumption, combustion stability, engine-out hydrocarbon emissions and smoke, the engine required relatively retarded injection timings (in comparison to other charge- or wall-controlled DI engines), high swirl levels, and a spray orientation that is directed towards the intake-valve side and targets the ridge wall of the piston. The stratified combustion was thus found to be a combination of wall and charge control, as indicated by the indirect spray targeting relative to the spark location coupled with the high swirl requirements of the engine, as well as the crucial role of the piston ridge in deflecting the fuel vapor towards the spark gap. The CFD computations, which showed close agreement with the experimental results, suggest that minimizing the amount of fuel deposited on the piston surface is a requirement for…
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Modifying an Intake Manifold to Improve Cylinder-to-Cylinder EGR Distribution in a DI Diesel Engine Using Combined CFD and Engine Experiments

GM R&D and Planning-Robert M. Siewert, Roger B. Krieger, Mark S. Huebler, Prafulla C. Baruah, Bahram Khalighi
Opel Powertrain GmbH-Markus Wesslau
Published 2001-09-24 by SAE International in United States
Improved cylinder-to-cylinder distribution of EGR in a 2-L Direct-Injection (DI) Diesel engine has been identified as one enabler to help reach more stringent emission standards. Through a combined effort of modeling, design, and experiment, two manifolds were developed that improve EGR distribution over the original manifold while minimizing design changes to engine components or interfering with the many varied vehicle platform installations.One of the modified manifolds, an elevated EGR entry (EEE) approach, provided a useful improvement over the original design that meet Euro-II emission standards, and has been put into production as it enabled meeting the Euro III emissions requirements a year early. The second revision, the distributed EGR entry (DEE) design, showed potential for further improvement in EGR distribution. This design has two EGR outlets rather than the one used in the original and EEE manifolds, and was first identified by modeling to be a promising concept. Using rapid prototype parts with variable geometry, over 40 variations of the DEE concept were studied experimentally in an attempt to identify an improved configuration. Parallel CFD…
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Intake-Valve Temperature Histories During S.I. Engine Warm-Up

GM R&D and Planning-Alex C. Alkidas
Published 2001-05-14 by SAE International in United States
The present study is an experimental investigation on the influence of engine operational parameters on the temperature history of intake valves. During the initial stage of the warm-up process, the temperature history of the intake valve followed an exponential behavior with a time constant that ranged from about 23 to 39 s for the test conditions examined. In contrast, the temperature history of the coolant varied linearly with time suggesting that the net heat input to the coolant is roughly constant during the initial stage of the engine warm-up process. After the initial transient phase that lasted about one minute, the temperature rise of the intake valve was quasi-steady. During this latter period, the measured intake valve temperature was predicted by the steady-state temperature correlation developed in an earlier study.
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Effects of Advanced Fuels on the Particulate and NOx Emissions from an Optimized Light-Duty CIDI Engine

GM R&D and Planning-Patrick G. Szymkowicz, Donald T. French, Chris C. Crellin
Published 2001-03-05 by SAE International in United States
A compression ignition direct injection (CIDI) engine was used to evaluate the engine-out emissions from four advanced CIDI fuels that define a broad range of properties. The fuels include a market-averaged California fuel (designated CARB) to serve as a benchmark, a petroleum-based low sulfur, low aromatic hydrocracked fuel (LSHC), the LSHC fuel blended with 15% dimethoxy methane (DMM15), and a neat Fischer-Tropsch fuel (FT100).Engine-out particulate matter (PM), oxides of nitrogen (NOx), and performance data were collected at 5 steady-state operating conditions. The engine calibration was optimized for each fuel and operating condition. Fuel injection timing was optimized for best fuel economy and the injection pressure was optimized for minimum smoke. The PM-NOx trade-off for EGR dilution was established for each fuel and operating condition with the optimum injection timing and pressure.Modal averaged mass emission results were computed for each fuel using a weighted combination of the data from each of the 5 operating conditions. Weighted results simplified the relative emission comparisons and improved the confidence in the statistical analysis. Dunnett statistical techniques, for multiple-comparisons to…
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Overall Results: Phase I Ad Hoc Diesel Fuel Test Program

GM R&D and Planning-Patrick G. Szymkowicz
BP Amoco-John C. Eckstrom, Leslie R. Wolf
Published 2001-03-05 by SAE International in United States
The future of diesel-engine-powered passenger cars and light-duty vehicles in the United States depends on their ability to meet Federal Tier 2 and California LEV2 tailpipe emission standards. The experimental purpose of this work was to examine the potential role of fuels; specifically, to determine the sensitivity of engine-out NOx and particulate matter (PM) to gross changes in fuel formulation. The fuels studied were a market-average California baseline fuel and three advanced low sulfur fuels (<2 ppm). The advanced fuels were a low-sulfur-highly-hydrocracked diesel (LSHC), a neat (100%) Fischer-Tropsch (FT100) and 15% DMM (dimethoxy methane) blended into LSHC (DMM15). The fuels were tested on modern, turbocharged, common-rail, direct-injection diesel engines at DaimlerChrysler, Ford and General Motors.The engines were tested at five speed/load conditions with injection timing set to minimize fuel consumption. Data from each fuel and test engine were statistically analyzed at each speed/load condition. The results were weighted and combined to provide an estimate of cycle average engine-out emissions at two EGR levels: 0% EGR and moderate EGR (which corresponds to the inflection region…
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Evaluation of New Volatility Indices for Modern Fuels

GM R&D and Planning-Scott Jorgensen
BP Amoco-David Whelan, Eric Ziegel
Published 1999-05-03 by SAE International in United States
From 1995 to 1997, the Coordinating Research Council (CRC) conducted a cold-start driveability program to evaluate the behavior of lower volatility fuels at cold, intermediate, and warm ambient temperatures. The program used 135 vehicles to evaluate 87 hydrocarbon, MTBE blended, and ethanol blended fuels. Evaporative driveability index equations (EDIs) were developed using the test design fuel variables (E158°F, E200°F, E300°F), and three other variable sets: (E158°F, E250°F, E330°F), (T10, T50, T90), and (E70°C, E100°C, E140°C). The models that best fit the data contained oxygenate offsets. Overall, the best indices are the E70°C, E100°C, E140°C equation and the DI equation with offsets.
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