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

TLDR

Direct‑injection spark‑ignition engines improve fuel economy and power over port injection but often raise particle number emissions, raising concerns for future regulations. This study evaluates whether ethanol blends and variable valve timing strategies can reduce particle emissions in DI engines. The authors compared baseline gasoline, 20 % E20, and 85 % E85 fuels under early or late intake valve closing, measuring particle number size distributions with a scanning mobility particle sizer and filter smoke number. While PFI emissions were low for all fuels, DI with gasoline or E20 increased particle numbers by 1–2 orders of magnitude, whereas DI with E85 maintained low emissions comparable to PFI, enabling DI benefits without emission penalties.

Abstract

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.