Combustion and emission characteristics of LPG(Liquefied Petroleum Gas) and gasoline fuels were compared in a single cylinder engine with direct fuel injection. While fuel injection pressure and IMEP(indicated mean effective pressure) were varied with 60, 90, 120 bar and 2 to 10 bar, another parameters for the engine operation as engine speed, air excess, and fuel injection timing were fixed at 1500 rpm, 1.0, and BTDC 300 CA respectively.
Experimental results showed that MBT timing for LPG was less sensitive to IMEP, and high injection pressure made combustion stability worse at IMEP=2 bar. Through heat release analysis LPG showed shorter 10 and 90% MBD(mass burn duration) than gasoline due to fast flame speed and for both fuels injection pressure hardly affected burn duration. It was also found that thermal efficiency of LPG had a little higher than that of gasoline.
Hydrocarbon emissions of gasoline rose to a level of three-fold than those of LPG. Nitric oxides had higher values for gasoline but carbon monoxide for both fuels showed similar level for all test conditions. A number of particles were normally much higher values for gasoline at all load conditions and changed a little with injection pressure. The peaks of particle size distribution were found near 80 nm for gasoline and that for LPG were shifted to smaller size, 40 nm.