Ethanol Blends and Engine Operating Strategy Effects on Light-Duty Spark-Ignition Engine Particle Emissions

Spark-ignition (SI) engines with direct-injection (DI) fueling can improve fuel economy and vehicle power beyond that of port fuel injection (PFI). Despite this distinct advantage, DI fueling often increases particle number emissions, such that SI exhaust may be subject to future particle emissions regulations. In this study, ethanol blends and engine operating strategy are evaluated for their effectiveness in reducing particle emissions in DI engines. The investigated fuels include a baseline emissions certification gasoline, a blend of 20 vol % ethanol with gasoline (E20), and a blend of 85 vol % ethanol with gasoline (E85). The operating strategies investigated reflect the versatility of emerging cam-based variable valve actuation technology capable of unthrottled operation with either early or late intake valve closing (EIVC or LIVC). Particle emissions are characterized in this study by the particle number size distribution as measured with a scanning mobility particle sizer (SMPS) and by the filter smoke number (FSN). Particle emissions for PFI fueling are very low and comparable for all fuels and breathing conditions. When DI fueling is used for gasoline and E20, the particle number emissions are increased by 1-2 orders of magnitude compared to PFI fueling, depending upon the fuel injection timing. In contrast, when DI fueling is used with E85, the particle number emissions remain low and comparable to PFI fueling. Thus, by using E85, the efficiency and power advantages of DI fueling can be gained without generating the increase in particle emissions observed with gasoline and E20.