An Experimental Study on the Effect of Direct-injection Ratio on the Combustion and Emission of Dual-injection Gasoline Engine

The test on a gasoline engine equipped with dual-injection system is conducted to investigate the effects of direct-injection ratio rDI on the combustion and emission of that engine with stoichiometric mixture under different load conditions. The results show that with the increase of rDI, the pressure and temperature in cylinder are almost kept unchanged when rDI is less than 40%, and they obviously fall when rDI is more than 40%; CO emission increases first and then decreases, and the trend of THC emission is just the opposite, while NOx emission constantly lowers. With the increase of rDI, the distribution of particle size changes from single peak to double peaks, and the total particle emission rises first then falls, the emission of accumulation mode particle constantly raises, while that of nucleation mode particle depends on load, and there is an optimal rDI to make it minimum. With the increase of load, all the emissions of particle and pollutant gases fall except NOx, which rises with load going up. © 2017, Society of Automotive Engineers of China. All right reserved.