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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.

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