Abstract
This study focuses on the experimental comparison of combustion phenomena and nanoparticle emission characteristics from a wall-guided direct-injection (DI) spark ignition engine for gasoline and liquefied petroleum gas (LPG). A returnless gasoline direct-injection (GDI) fuel supply system was reworked for the return-type liquid-phase LPG injection fuel supply system that was composed of an LPG tank with a brushless d.c. pump and a low-pressure regulator to supply the stable liquid-phase LPG for the DI engine. To verify the clean combustion characteristics of the LPG DI engine, nanoparticle concentrations obtained with a differential mobility spectrometer and the total hydrocarbon and nitrogen oxide emission levels were compared with those of a gasoline-fuelled engine. The maximum performance and the part-load combustion phenomena of the two fuels were evaluated. In conclusion, the nanoparticle and exhaust emissions of the LPG DI engine were much lower than those of the GDI engine. Furthermore, the combustion performance of LPG in the full-load condition was comparable with that of the gasoline fuel, and the combustion stability in a part-load condition of LPG was better than that of gasoline because it evaporated very rapidly and mixed well with the air. As a result, a substantial reduction in the fuel wetting in the combustion chamber was achieved.
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