Abstract
Abstract
The requirements of reduced emissions and improved fuel economy led to the introduction of direct-injection (DI) spark ignition (SI) engines. A dual-fuel injection system (DI and port fuel injection (PFI)) was also used to improve engine performance at high-speed high-load conditions. 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 fuelling cases: case A, gasoline for both PFI and DI; case B, gasoline PFI and ethanol DI; case C, ethanol PFI and gasoline DI. For this study, the DI fuelling portion varied from 0 per cent to 100 per cent of the total fuelling 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 indicated mean effective pressure (IMEP) decreases by as much as 11 per cent as the DI fuelling percentage increases, except in case B where the IMEP increases by 2 per cent at a light load. The combustion burn duration increases significantly at a light load as the DI fuelling percentage increases, but only moderately at wide-open throttle (WOT). In addition, the percentage of the ethanol in the total fuelling plays a dominant role in affecting the combustion characteristics at a light load but, at a heavy load (WOT), the DI fuelling percentage becomes an important parameter, regardless of the percentage of ethanol content in the fuel.
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