Combustion Characteristics of a Single-Cylinder Engine Equipped with Gasoline and Ethanol Dual-Fuel Systems

The requirement of reduced emissions and improved fuel economy led the introduction of direct-injection (DI) spark-ignited (SI) engines. Dual-fuel injection system (direct-injection and port-fuel-injection (PFI)) was also used to improve engine performance at high load and speed. Ethanol is one of the several alternative transportation fuels considered for replacing fossil fuels such as gasoline and diesel. Ethanol offers high octane quality but with lower energy density than fossil fuels. This paper presents the combustion characteristics of a single cylinder dual-fuel injection SI engine with the following fueling cases: a) gasoline for PFI and DI, b) PFI gasoline and DI ethanol, and c) PFI ethanol and DI gasoline. For this study, the DI fueling portion varied from 0 to 100 percentage of the total fueling over different engine operational conditions while the engine air-to-fuel ratio remained at a constant level. It was shown in all cases that the IMEP (indicated mean effective pressure) decreases by as much as 11% as DI fueling percentage increases, except in case b) where the IMEP increases by 2% at light load. The combustion burn duration increases significantly at light load as DI fueling percentage increases, but only moderately at WOT (wide open throttle). In addition, the percentage of the ethanol in the total fueling plays a dominant role in affecting the combustion characteristics at light load; but at heavy load (WOT), the DI fueling percentage becomes an important parameter, regardless of the percentage of ethanol content in the fuel.