Stoichiometric Combustion in a HSDI Diesel Engine to Allow Use of a Three-way Exhaust Catalyst

Transcription

1 SAE TECHNICAL PAPER SERIES Stoichiometric Combustion in a HSDI Diesel Engine to Allow Use of a Three-way Exhaust Catalyst Sangsuk Lee, Manuel A. Gonzalez D. and Rolf D. Reitz University of Wisconsin - Madison Reprinted From: In-Cylinder Diesel Particulate and NOx Control 2006 (SP-2002) 2006 SAE World Congress Detroit, Michigan April 3-6, Commonwealth Drive, Warrendale, PA U.S.A. Tel: (724) Fax: (724) Web:

2 The Engineering Meetings Board has approved this paper for publication. It has successfully completed SAE's peer review process under the supervision of the session organizer. This process requires a minimum of three (3) reviews by industry experts. All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior written permission of SAE. For permission and licensing requests contact: SAE Permissions 400 Commonwealth Drive Warrendale, PA USA permissions@sae.org Tel: Fax: For multiple print copies contact: SAE Customer Service Tel: (inside USA and Canada) Tel: (outside USA) Fax: CustomerService@sae.org ISSN Copyright 2006 SAE International Positions and opinions advanced in this paper are those of the author(s) and not necessarily those of SAE. The author is solely responsible for the content of the paper. A process is available by which discussions will be printed with the paper if it is published in SAE Transactions. Persons wishing to submit papers to be considered for presentation or publication by SAE should send the manuscript or a 300 word abstract to Secretary, Engineering Meetings Board, SAE. Printed in USA

3 Stoichiometric Combustion in a HSDI Diesel Engine to Allow Use of a Three-way Exhaust Catalyst Copyright 2006 SAE International Sangsuk Lee, Manuel A. Gonzalez D. and Rolf D. Reitz University of Wisconsin - Madison ABSTRACT The objectives of this study were 1) to evaluate the characteristics of rich diesel combustion near the stoichiometric operating condition, 2) to explore the possibility of stoichiometric operation of a diesel engine in order to allow use of a three-way exhaust after-treatment catalyst, and 3) to achieve practical operation ranges with acceptable fuel economy impacts. Boost pressure, EGR rate, intake air temperature, fuel mass injected, and injection timing variations were investigated to evaluate diesel stoichiometric combustion characteristics in a singlecylinder high-speed direct injection (HSDI) diesel engine. Stoichiometric operation in the Premixed Charge Compression Ignition (PCCI) combustion regime and standard diesel combustion were examined to investigate the characteristics of rich combustion. The results indicate that diesel stoichiometric operation can be achieved with minor fuel economy and soot impact. The fuel consumption at stoichiometric operation increases about 7% compared to the best fuel economy case of standard diesel combustion. However, NOx emissions decrease to around 0.1 g/kw-hr due to oxygen deficiency at stoichiometric condition. Variations of injection timing, intake air temperature, EGR, and boost pressure did not affect the fuel consumption significantly. In general, emissions and fuel consumption were dependent strongly on the equivalence ratio under high EGR and rich operating conditions. Extending the operating range will be the subject of future studies. INTRODUCTION Stringent future emission regulations will not be met by improving diesel combustion alone, but will require the use of after-treatment devices. The use of aftertreatment devices like three-way and four-way catalysts is one of several promising candidates to meet the future regulations. Though the use of the 1 three-way catalyst is a well-established technology in spark ignition engines, it is a big challenge for use in the diesel engine since it is hard to run a diesel engine under stoichiometric conditions with acceptable fuel consumption and soot emissions. The intrinsic mixing-controlled combustion in the diesel engine produces locally rich spots which are sources of soot, unburned hydrocarbon, and carbon monoxide emissions, and also impacts fuel economy. Rich diesel combustion has been proposed for the purpose of low emission strategies [1-8] and for regenerating a lean NOx trap [8-11]. However, results have revealed that the fuel consumption and the accompanying carbon monoxide, hydrocarbon and soot emissions increase as the equivalence ratio approaches closer to the stoichiometric condition. Especially the fuel economy and carbon monoxide are marginal at stoichiometric operation, even with the premise of limited operation for the purpose of a lean NOx trap regeneration. It is still important to resolve issues related to emissions from rich spots even under normal diesel operation, where the diesel engine is operated with a lean overall equivalence ratio. Homogeneous Charge Compression Ignition (HCCI) operation is desired to minimize locally rich regions due to poor mixing. However, achieving HCCI by early injection has poor fuel economy due to liquid fuel film formation on the piston and liner surfaces due to the lower air density and the increased spray penetration under these conditions. In this study, stoichiometric operation in the Premixed Charge Compression Ignition (PCCI) combustion regime and standard diesel combustion were examined to investigate the characteristics of rich combustion. Both combustion regimes are closer to practical application and provide fairly good fuel economy [1-5]. Lee and Reitz [3] found that PCCI combustion could allow stoichiometric operation with less impact on fuel economy with optimal spray targeting to improve fuel-air mixing. When an aftertreatment device like the three-way catalyst is considered, more emphasis can be given to the fuel economy than to emissions since the emission

4 regulations can be met by selecting an adequate set of after-treatment devices. Therefore, the work in the present study is mostly devoted to estimating parameters affecting the fuel consumption at rich diesel combustion. The objectives of this study are to evaluate the characteristics of rich diesel operation and its emissions with respect to engine operating parameters, and to identify key parameters which determine fuel consumption at stoichiometric operation. The operating parameters considered in this study were the boost pressure, EGR rate, intake air temperature, fuel mass injected, and injection timing. EXPERIMENTAL SETUP The present test engine consists of a Hydra single cylinder engine from Ricardo Research and a single cylinder version of a Fiat cylinder head which was designed for 2.4L five-cylinder engine. The cylinder head is equipped with double over-head camshafts and two exhaust ports and two intake ports, which consist of a helical port and a directed port to control the swirl ratio. The original Fiat piston was replaced with an open-crater-type bowl piston which was designed using CFD and a genetic algorithm (GA) optimization [12] to realize the NADI concept [13]. Specifications of the engine are indicated in Table 1. The injection system used for this study was a Bosch common-rail injection system. The specifications of the common rail injection system are summarized in Table 2. A nozzle with a 130 degree spray included angle was chosen since the nozzle gave better soot and carbon monoxide emissions in the low emission study of Lee and Reitz [3] through a wide range of injection timings. Intake air was supplied from pressurized building air to simulate a turbocharger. The flow rate was measured with a critical orifice system. The equivalence ratio was measured with an ETAS LA4 lambda meter. EGR flow was driven by the pressure difference between the exhaust and the intake surge tanks and was controlled by regulating the openings of the valves. The emission data recorded during the experiments included the gaseous and particulate emissions. The gaseous emissions, including NO, Table 1. The Engine Specifications Engine Type 4 valve DI diesel Bore x Stroke 82.0 x 90.4 mm Compression Ratio 16.0:1 Displacement 477 cm 3 Piston Geometry Open-Crater-bowl Intake Ports 1 swirl, 1 tumble Swirl ratio (at IVC) 1.83 Bowl diameter 48 mm IVO 10 BTDC IVC 38 ABDC EVO 38 BBDC EVC 8.5 ATDC Table 2. Common rail system specifications Injector type Electro-hydraulically controlled injector Nozzle type Dual guided VCO Flow Number 400 cm 3 Number of nozzle holes 8 Hole diameter mm Included spray angle 130 Exhaust Heated Filter and Line Nicolet FTIR Exhaust Gas Analyzer Air Mass Critical Flow Orifice Measurement System Pneumatic Air Regulator Compressed Air T.C. Air Filter Pneumatic Pressure Regulator Cooling Water EGR Cooler Air Pre-Heater T.C. Exhaust Surge Tank T.C. Head Jug Intake Surge Tank T.C. T.C. Pressure Gauge Thermocouple CO 2 Analyzer Ricardo Hydra Block CO 2 Analyzer Gate Valve BOSCH RTT 100 Smoke Meter Figure 1. Open-crater type piston bowl used in this study (45 sector view with model results) Figure 2. Schematic diagram of experimental engine setup [4] 2

5 NOx, CO, HC, and Exhaust CO2, were measured with a Nicolet Rega model 7000, FTIR emissions analyzer. Intake CO2 was assessed with a Horiba PIR-9000 infrared gas analyzer. Exhaust smoke levels were sampled with a Bosch RTT100 instrument. Cylinder pressure was measured with a Kistler 6125A piezo-electric pressure transducer and the measured signal was amplified and converted into a voltage with a Kistler 5010 charge amplifier. The output signal from the charge amplifier was sampled with a National Instruments AT-MIO-16E-1 data acquisition board every quarter degree crank angle. The pressure traces were averaged over 300 cycles to compensate for cycle-by-cycle variations. The IMEP includes pumping loss during the gas exchange process by considering the whole engine cycle. Heat loss was not considered and the specific heat was assumed to be constant, 1.33, when the heat release rate was evaluated. OPERATING CONDITIONS The operating conditions in this study correspond to a representative condition for small bore HSDI engines in the New European Drive Cycle (NEDS) [4] and based on Lee and Reitz [3]. The effects of boost pressure, injection timing, and intake temperature were investigated by adjusting the energizing time (fuel amount) and EGR level to achieve the desired equivalence ratio. The boost pressure was changed as a method to control the load under stoichiometric operation, and the effects were evaluated. Two injection timings, which are representative of operation in the PCCI regime and in standard diesel Table 3. Operating Condition Summary for the Stoichiometric Tests Operating Parameter Engine Speed Exhaust Pressure Injection Pressure Intake Air Temp. Intake Pressure SOI ( ATDC) BASE 2000 rpm Intake Pressure + 18 kpa 150 MPa 90 C 40 C 130 kpa 140 kpa 130 kpa EGR 55 % Fuel Mass ~ 19 mg/cycle combustion [3], respectively, were selected to assess the effects of injection timing. Changes in intake air temperature were also evaluated to estimate the effects of combustion phasing on fuel economy by lowering the intake air temperature from 90 to 40 degrees C. The detailed conditions are compared in Table 3. RICH COMBUSTION CHARACTERISTICS There is less information available about diesel stoichiometric operation since most previous diesel studies have focused on low emissions and the application to regeneration of the lean NOx trap. In this section, the emissions and fuel consumption characteristics will be discussed to identify key parameters and to determine methods to improve the fuel economy under stoichiometric operation. FUEL ECONOMY AND CARBON MONOXIDE EMISSIONS When the fuel consumption is evaluated with respect to the equivalence ratio, as shown in Figure 3, a strong dependence on the equivalence ratio is seen. Operating conditions considered in this study do not show significant fuel economy difference especially when equivalence ratio approached unity. The fuel consumption at stoichiometric condition was about 245 g/kw-hr, which was 7% higher than the best fuel consumption (229 g/kw-hr) of, a representative of standard diesel combustion. However, the effect of operating conditions on the fuel economy becomes significant as the equivalence ratio becomes leaner. Retarding injection timing to -15 degrees ATDC () yields best fuel consumption, 229 g/kw-hr, at around 0.8 equivalence ratio while the base injection timing ISFC (g/kw-hr) Figure 3 Characteristics of fuel economy in rich diesel operation 3

6 cases (BASE and ) yield about 240 g/kw-hr regardless of boost pressure at around 0.9 equivalence ratio. Most of the fuel has burned before TDC when the injection timing is -35 degrees ATDC (BASE and ). However, the main combustion takes place after TDC when the injection timing is retarded by 20 degrees () or the intake temperature is lowered by 50 degrees (). The relative insensitivity to the phasing effect under stoichiometric conditions will be discussed later. Short ignition delay at standard diesel combustion () is believed not to provide sufficient fuel-air mixing as the equivalence ratio becomes rich. The fuel consumptions and carbon monoxide emissions of start to increase at around 0.8 equivalence ratio as shown in Figure 3 and Figure 4 while the other PCCI combustion cases (SOI = -35 degrees ATDC) start to increase at 0.9 equivalence ratio. ISCO (g/kw-hr) Figure 4. Carbon Monoxide emission characteristics as a function of equivalence ratio under rich diesel operation Energy relative to Input Energy (%) Energy in CO Energy in HC Figure 5. Energy exhausted through unburned hydrocarbon and carbon monoxide emissions for the baseline case (BASE) in Table 3 No significant difference in carbon monoxide emissions due to the operating parameters were observed up to 0.8 equivalence ratio in Figure 4. However, the emissions increase with equivalence ratio as the ratio becomes richer beyond 0.8, and the effect of late injection timing () becomes significant due to poor fuel-air mixing that resulted from the short ignition delay. The steeper increase of carbon monoxide emission of explains why shows similar fuel consumption at stoichiometric operation though it has a combustion phasing advantage compared to the other PCCI cases. Interestingly, the carbon monoxide trends of the PCCI combustion cases (BASE, CASE1, and ) is similar to that of a gasoline engine, of which carbon monoxide emissions start to increase around 0.9 equivalence ratio [14]. This suggests that PCCI combustion provides fairly good fuel-air mixing even at stoichiometric operation. The energy exhausted with carbon monoxide and unburned hydrocarbon emissions was evaluated with respect to the equivalence ratio, as shown in Figure 5, to identify how much energy was wasted in the exhaust emissions. The energy contained in the emissions was calculated using the lower heating values of the carbon monoxide and hydrocarbon emissions (C1 to C5 species). Soot was not counted since the mass of soot was negligible when it was compared to both carbon monoxide and hydrocarbon emissions. The input energy consisted of the energy contained in both EGR and fuel. Figure 5, which is for the BASE case, shows that the energy in carbon monoxide emissions becomes higher as the equivalence ratio increases. In particular, 5% of the input energy is wasted with the carbon monoxide emissions at the stoichiometric condition, while around 1% is wasted with the unburned hydrocarbon emissions. This indicates that the wasted energy through carbon monoxide emissions is one of the major contributors to the fuel consumption disadvantage at stoichiometric operation. As a result, carbon monoxide can be confirmed to be one of the most important key parameters that affect fuel economy near stoichiometric operation, while the fuel economy is usually dominated by the injection timing and combustion phasing under leaner diesel operation. SOOT AND NOx EMISSIONS When the use of after-treatment devices to treat hydrocarbon, carbon monoxide, soot and NOx is assumed, considerations of soot and NOx emissions become less important under stoichiometric operation. However, the emissions need to be estimated since the levels determine the selection of after-treatment devices. The trends of soot and NOx emissions with respect to equivalence ratio are 4

7 shown in Figure 6 and Figure 7, respectively. The soot emissions start to increase when the equivalence ratio exceeds certain limits which depend on the injection timings. Operation with standard diesel combustion (), for which the injection timing was -15 degrees ATDC, results in higher soot emissions compared to the other PCCI combustion cases. The soot emissions of PCCI cases indicate fairly low levels, around 0.2 g/kw-hr, even at stoichiometric operation. The higher soot level in standard diesel combustion may result from the lack of mixing and poor charge preparation due to the short ignition delay. The NOx emissions are seen in Figure 7 to decrease with increasing equivalence ratio, and reach about 0.14 g/kw-hr or less at the stoichiometric operating point. The significantly low level of the NOx emissions suggests the possibility that there could be no need for a reducing NOx catalyst to satisfy ISSoot (g/kw-hr) Figure 6. Soot emission characteristics as a function of equivalence ratio under rich diesel operation regulations. However, more investigations under higher load conditions are needed since the conditions in this study mostly belong to the low temperature combustion regime, which has been proven to have advantages in its NOx emissions. Indeed, stoichiometric diesel combustion at lower EGR levels is particularly attractive to minimize the complexity of the engine system. FUEL ECONOMY COMPARISON BETWEEN LEAN AND RICH OPERATION Fuel consumption results from lean to stoichiometric combustion conditions are compared in Figure 8 to help in evaluating the effect of equivalence ratio, φ, on the fuel consumption. The IMEP in this plot ranges from 270 to 590 kpa. Two ways to control equivalence ratio were compared for the case of lean operation. The equivalence ratio for the case indicated with empty circles achieved the desired equivalence ratio by reducing the EGR level from 50 to 0% while keeping the injected fuel mass at the same level of that of the 0.9 equivalence ratio case of using the same injection timing. The equivalence ratio for the other cases were achieved by reducing injected fuel mass while keeping EGR level around 55%. As seen in Figure 8, the fuel consumption shows the best values (about 229 g/kw-hr for standard diesel combustion and about 240 g/kw-hr for PCCI combustion) when the equivalence ratio is between 0.8 and 0.9. Since losses due to gas exchange process were constant and have more impact in cases of decreased fuel amount (load), lean operation sacrifices fuel consumption significantly when the equivalence ratio is controlled by fuel ISNOx (g/kw-hr) ISFC (g/kw-hr) Standard Diesel Figure 7. NOx emission characteristics as a function of equivalence ratio under rich diesel operation Figure 8. Fuel consumption for lean-to-stoichiometric operating conditions obtained by varying EGR with the fueling rate of the φ=0.9 case 5

8 amount. However, the equivalence ratio has only a minor impact when the fuel amount was kept constant while the equivalence ratio was controlled with EGR levels, as shown with empty circles in Figure 8. On the other hand, rich operation including stoichiometric operation also sacrifices fuel consumption due to incomplete combustion, as discussed in Figure 4. The parameters affecting fuel consumption can be grouped into combustion phasing and thermodynamic issues. As discussed by Kimura et al. [15] and Miles et al. [16], the fuel conversion efficiency ( η ) can be written as a product of work fc conversion efficiency and heat rejection efficiency. W W Q Q chem hl η = fc = mq Q Q mq f LHV chem hl f LHV wc hr (1) = η η (2) The first term on the right-hand-side of Eq. (1) indicates the work, W, conversion efficiency ( η ) wc which is related to the combustion phasing. The second term indicates the heat rejection efficiency ( η ) defined by dividing the integral of the apparent hr heat release rate ( Q Q ) by the chemical energy chem hl in the injected fuel ( mq ). The heat rejection f LHV efficiency indicates how much and how well the chemical energy of the fuel is released, and provides a better understanding of the effect of combustion efficiency, heat transfer losses, and gas exchange losses. The work conversion efficiency indicates how effectively the chemical energy is converted to mechanical work. Heat Rejection Efficiency Standard Diesel Figure 9. Heat rejection efficiencies for lean to stoichiometric operating conditions obtained by varying EGR with the fuel rate of the φ=0.9 case As shown in Figure 9, the heat rejection efficiency shows its best value (69%) at 0.8 equivalence ratio and is deteriorated as the equivalence ratio is changed away from the optimum. For example, the heat rejection efficiency at stoichiometric operation is around 64%, which explains most of fuel consumption impact compared to the optimum case. Heat transfer and gas exchange losses explain the lower heat rejection efficiency, resulting in higher fuel consumption at lean operation. Lower heat rejection efficiency at richer operation can be explained by the lower combustion efficiency that results in higher carbon monoxide emissions, as seen in Figure 4. The comparison between the trends of fuel consumption and heat rejection efficiency confirms that the heat rejection efficiency is a major contributor to determine and improve the fuel consumption. FUEL ECONOMY UNDER STOICHIOMETRIC OPERATION As discussed previously, no significant change in the fuel consumption was observed under stoichiometric operation with the different boost pressure, injection timings, and intake air temperatures of the present tests. A discussion of why different parameters gave no significant change in fuel consumption is important to understand the characteristics of stoichiometric combustion and to be able to expand the operating range in the future. Table 4. Fuel consumption analysis at the stoichiometric operation for the conditions of Table 3 Location of Peak HRR ( ATDC) 10 to 90% burn duration ( ) BASE CASE _1 CASE _2 CASE _ ISFC (g/kw-hr) Heat rejection efficiency (%) IMEP (kpa) SOI ( ATDC) Intake Air Temperature 90 C 40 C Boost Pressure 130kPa 140kPa 130kPa Equivalence ratio HRR: Heat Release Rate

9 As discussed with Eq. (2), the fuel conversion efficiency, or fuel economy, is divided into two factors, the heat rejection efficiency and work conversion efficiency. The work conversion efficiency was estimated by considering combustion phasing with the location of peak heat release rate (HRR) and the 10 to 90% burn duration, and is compared with the heat rejection efficiency in Table 4. Four representative stoichiometric cases in Table 4 were operated with the same fuel amount to isolate the effect of phasing and heat rejection efficiency from the effect of fuel amount (load). The heat rejection efficiencies for stoichiometric operation summarized in Table 4 are about 64%, and there is no significant difference with changes in the operating parameters including EGR, injection timing, intake temperature, and boost pressure. It might be conjectured that optimal combustion phasing could improve the fuel consumption when the ignition is delayed from the base timings of PCCI combustion by retarding the injection timing and Heat Release Rate (J/CA) Accumulated Heat Release BASE Crank Angle (degree ATDC) BASE Crank Angle (degree ATDC) Figure 10. Comparisons of heat releases rate and accumulated heat release for stoichiometric operation ( at boost pressure of 140kPa) lowering the intake air temperature. However, the delays do not give a significant benefit in fuel consumption in this study. As shown in Table 4, a retarded injection timing from -35 to -15 degree ATDC () moves the location of peak heat release rate to 0.75 degree ATDC which leads to better fuel consumption compared to -4.5 degree ATDC in the baseline PCCI operation. However, the retarded timing yielded significantly increased burn duration, and 12% of the fuel energy remains unburned even after 10 degrees ATDC, as shown in Figure 10. The 10 to 90% burn duration for the case with retarded injection timing () is about 14 crank angle degrees, as shown in Table 4. This duration is about 2.8 times longer than those for the cases of -35 degree ATDC injection timing (BASE and ). The late combustion, which mainly results from the details of the mixing controlled combustion process [3], cancels any gain obtained by moving the location of the peak heat release rate. The equivalence ratio in was maintained by increasing the EGR level when the intake air temperature was lowered to 40 degrees C from the BASE value of 90 degrees C. The higher EGR level also decelerates reactions by lowering the overall combustion temperature [17-19], as does the lower intake air temperature. In consequence, the peak heat release location of was retarded to 1.0 degree ATDC, which was similar to that of the retarded injection timing (), even with PCCI (early injection) operation. However, a significant part of the heat in was released before TDC, unlike in, and the burn duration in was extended as long as 1.4 times of the baseline PCCI cases. Both the early heat release and the extended burn duration deteriorates the advantage of delaying the location of the peak heat release and results in no significant advantage in fuel consumption. CONCLUSIONS The emissions and fuel consumption characteristics of an HSDI diesel engine operating with rich combustion were characterized by varying the boost pressure, injection timing, EGR level, fuel mass injected, and intake temperature. The fuel consumption at stoichiometric operation was scrutinized with regard to the heat rejection efficiency, combustion phasing and duration. The following conclusions are derived from the study: 1. The fuel consumption, carbon monoxide, soot, and NOx emissions characteristics are determined mostly by the equivalence ratio under rich diesel combustion conditions. 7

10 2. PCCI combustion showed a low level (0.2 g/kwhr) of soot emission even at stoichiometric operation. 3. Stoichiometric operation yielded ISFC levels of about 245 g/kw-hr which is 7% higher than that of the best fuel economy case with standard diesel combustion. 4. The fuel consumption penalty that resulted from incomplete combustion at stoichiometric operation was accompanied by carbon monoxide and unburned hydrocarbon emissions. However, the levels were acceptable when the use of a three-way catalyst is assumed. 5. The phasing of the heat release rate had only a minor influence on the fuel consumption since better phasing was accompanied by longer burn durations which canceled the gain. 6. The present study showed that diesel stoichiometric combustion is a possible way to meet future diesel emission regulations. Expanding the operating range with stoichiometric operation will be the subject of future studies. CONTACT Sangsuk Lee ACKNOWLEDGEMENTS sslee@cae.wisc.edu The authors gratefully acknowledge support for this work from the ERC Diesel Emissions Reduction Consortium member companies. NOTE ADDED IN PROOF An earlier version of this paper was found to contain errors in the fuel consumption and air flow rate measurements. These errors have been corrected in the present paper. REFERENCES 1. Lechner, G.A., Jacobs, T.J., Chryssakis, C.A., Assanis, D.N., Siewert, R.M., Evaluation of Narrow Spray Cone Angle, Advanced Injection Timing Strategy to Achieve Partially Premixed Compression Ignition Combustion in a Diesel Engine, SAE , Kanda, T., Hakozaki, T., Uchimoto, T., Hatano, J., Kitayama, N, Sono, H., PCCI Operation with Early Injection of conventional Diesel Fuel, SAE , Lee, S., Reitz, R.D., Spray Targeting to Minimize Soot and CO Formation in Premixed Charge Compression Ignition (PCCI) Combustion with a HSDI Diesel Engine, SAE , Boyarski, N. J., M.S. Thesis, Dept. of Mechanical Engineering, University of Wisconsin-Madison, Okude, K., Mori, K., Shiino, S., Moriya, T., Premixed Compression Ignition (PCI) Combustion for Simultaneous Reduction of NOx and Soot in Diesel Engine, SAE , Sluder, C.S., Wagner, R.M., Lewis, S.A., Storey, J.M.E., Exhaust Chemistry of Low-NOx, Low-PM Diesel Combustion, SAE , Wagner, R.M., Green Jr. J.B., Dam, T.Q., Edwards, K.D., Storey, J.M., Simultaneous Low Engine-Out NOx and Particulate Matter with Highly Diluted Diesel Combustion, SAE , Akihama, K., Takatori, Y., Inagaki, K., Sasaki, S., Dean, A.M., Mechanism of the Smokeless Rich Diesel Combustion by Reducing Temperature, SAE , Jacobs, T.J., Bohac, S.V., Assanis, D.N., Szymkowicz, P.G., Lean and Rich Premixed Compression Ignition Combustion in a Light-Duty Diesel Engine, SAE , Helmantel, A., Gustavsson, J.,Denbratt, I., Operation of DI Diesel Engine With Variable Effective Compression Ratio in HCCI and Conventional Diesel Mode, SAE , Tatur, D.T., Thornton, M., Development of a Diesel Passenger Car Meeting Tier 2 Emissions Levels, SAE , Boyarski, N.J., Reitz, R.D., Premixed Compression Ignition (PCI) Combustion with Modeling-Generated Piston Bowl Geomtry in a Diesel Engine, SAE , Walter, B., Gatellier, B., Development of the High Power NADI Concept Using Dual Mode Diesel Combustion to Achieve Zero NOx and Particulate Emissions, SAE , Heywood, J. B., Internal Combustion Engine Fundamentals, McGraw Hill, Kimura, S., Ogawa, H., Matsui, Y., Enomoto, Y., An Experimental Analysis of Low-Temperature and Premixed Combustion for Simultaneous Reduction of NOx and Particulate Emissions in Direct Injection Diesel Engines, International Journal of Engine Research, Vol. 3, No. 4, Miles, P. C., Choi, D., Pickett, L. M., Kook, S., Bae, C., The Influence of Charge Dilution and Injection Timing on Low-Temperature Diesel Combustion and Emissions, SAE ,

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