Diesel engines are facing increased competition from gasoline engines in the light-duty and small non-road segments, primarily due to the high relative cost of emissions control systems for lean-burn diesel engines. Advancements in gasoline engine technology have decreased the operating cost advantage of diesels and the relatively high initial-cost disadvantage is now too large to sustain a strong business position. SwRI has focused several years of research efforts toward enabling diesel engine combustion systems to operate at stoichiometric conditions, which allows the application of a low-cost three-way catalyst emission control system which has been well developed for gasoline spark-ignited engines. One of the main barriers of this combustion concept is the result of high smoke emissions from poor fuel/air mixing. The current study focuses on improving the combustion system by investigating different fuel/air mixing strategies that enhance fuel spray - piston bowl interaction while simultaneously optimizing the fuel injection system. Computational Fluid Dynamics (CFD) simulations were carried out in conjunction with engine testing to evaluate different piston bowl designs as well as injector nozzle designs with reduced hole diameters to improve in-cylinder mixing and reduce spray over penetration. By using proposed combustion strategy, it was demonstrated that smoke emissions were reduced significantly from baseline under stoichiometric diesel operation.
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