Effects of research octane number of gasoline and dual direct injection strategies on combustion and emission performance of intelligent charge compression ignition (ICCI) mode

Dual-fuel intelligent charge compression ignition (ICCI) combustion mode has been proved to be an efficient combustion mode for internal combustion engines. The properties of low reactivity fuel have a strong influence on ICCI combustion. In this paper, based on a modified ICCI engine, the effect of octane number of low reactivity fuels on ICCI combustion mode was studied under medium engine load, in which 75#, 80#, 85#, and 95# gasoline were applied as low reactivity fuels. In addition, dual-fuel injection strategies were tested and optimized. Results showed that ICCI mode performed well with gasoline research octane numbers (RON) even low as to 75. With the decrease of gasoline RON, the reactivity of mixture increased which caused the advanced combustion. This also made the peaks of heat release rate and in-cylinder pressure advance with the decrease of RON. By post-injection strategy of gasoline and diesel, the combustion phase could be delayed when fueled with low-octane fuel but significantly increased the particle number to 10 9 /cm 3. Under the respective optimized fuel injection strategies, 85# gasoline achieved ultra-low NOx emission (0.15 g/kWh), low particle numbers (under 10 7 /cm 3 ), and high indicated thermal efficiency (close to 50%).