Efficiency and emissions mapping of RCCI in a light-duty diesel engine

In-cylinder blending of gasoline and diesel to achieve Reactivity Controlled Compression Ignition (RCCI) has been shown to reduce NO_X and particulate matter (PM) emissions while maintaining or improving brake thermal efficiency as compared to conventional diesel combustion (CDC). The RCCI concept has an advantage over many advanced combustion strategies in that the fuel reactivity can be tailored to the engine speed and load allowing stable low-temperature combustion to be extended over more of the light-duty drive cycle load range. Varying the premixed gasoline fraction changes the fuel reactivity stratification in the cylinder providing further control of combustion phasing and pressure rise rate than the use of EGR alone. This added control over the combustion process has been shown to allow rapid engine operating point exploration without direct modeling guidance. This paper explores the efficiency, emissions and combustion characteristics of RCCI with gasoline and ultra-low sulfur diesel fuel over a wide speed and load range in a light-duty multi-cylinder diesel engine leading to the creation of an RCCI engine map. The RCCI map was developed under self-imposed constraints which included a maximum cylinder pressure rise rate of 10 bar/deg and a CO emission limit of 5000 ppm. The RCCI map was developed using a mix of single and split diesel injections without the use of EGR for best brake thermal efficiency with lowest possible NO_X emissions. RCCI emissions and performance results are compared to CDC on the same base diesel engine.