Mixture Formation and Pollution Emissions of Ethanol-Gasoline/Ethanol-LPG PI Motorcycle Engines

Mixture formation, soot and HC emissions of a spark-ignition (SI) engine fueled with ethanol-gasoline and with ethanol-liquid petroleum gas (LPG) under effects of intake air temperature and injection methods were investigated numerically. The simulation was performed on an 110cc motorcycle engine with a retrofitted intake system to adopt new fuel supply modes. The results show that ethanol-LPG dual injection (ELDI) mode produces a better homogeneous mixture as compared to that of ethanol-gasoline pre-blended injection (EGBI) mode. The diffusion combustion of liquid fuel droplets in a heterogeneous mixture is the main factor affecting soot emission. Either ELDI or EGBI mode, the higher Tint leads to the lower unburned fuel concentration in the exhaust gas. At a low Tint, the unburned fuel concentration increases with ethanol content, whereas the rate of this increase is reduced gradually at high Tint. At a given engine operating condition, the unburned fuel concentration and the soot volume fraction in the exhaust gas of EGBI mode are nearly 1.3 times and 2.5 times, respectively, higher than those of ELDI mode. The over-fueling is required for EGBI mode, while no start-aids system is needed for ELDI mode under the cold start condition.