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This paper focuses on particulate emissions from direct injection spark ignition engines running on controlled ethanol-gasoline splash-blended fuels. Study objectives include understanding the relationship between ethanol concentration and particulate emissions, as well as assessing the impact of distillation characteristics and aromatic content of the base fuel. Model year 2011 vehicles equipped with GM Ecotec, Ford EcoBoost, and Chrysler PentaStar engines were evaluated on FTP75 and US06 drive cycles. Both gravimetric and particle number data were recorded with the vehicles running on controlled splash-blended fuels with a range of ethanol concentrations. A high T90 commercial gasoline served as a template in defining a consistent gasoline fraction that was used in preparing many of the ethanol blends. A controlled gasoline was used to avoid distillation and aromatic content variability seen in commercial blends.

Ethanol and other high heat of vaporization (HoV) fuels result in substantial cooling of the fresh charge, especially in direct injection (DI) engines. The effect of charge cooling combined with the inherent high chemical octane of ethanol make it a very knock resistant fuel. Currently, the knock resistance of a fuel is characterized by the Research Octane Number (RON) and the Motor Octane Number (MON). However, the RON and MON tests use carburetion for fuel metering and thus likely do not replicate the effect of charge cooling for DI engines. The operating conditions of the RON and MON tests also do not replicate the very retarded combustion phasing encountered with modern boosted DI engines operating at low-speed high-load. In this study, the knock resistance of a matrix of ethanol-gasoline blends was determined in a state-of-the-art single cylinder engine equipped with three separate fuel systems: upstream, pre-vaporized fuel injection (UFI); port fuel injection (PFI); and DI.