Efficient and clean combustion of intelligent charge compression ignition (ICCI) engine at low load conditions

The efficient and clean combustion of compression ignition (CI) engines under low load conditions has always been a challenge. Intelligent charge compression ignition (ICCI) mode has been proved to be able to effectively control the combustion phase and heat release rate which has great potential to improve engine efficiency. In this paper, the combustion and emission characteristics of ICCI mode under low load conditions with indicated mean effective pressure (IMEP) from 2 to 6 bar were explored. Commercial diesel was selected as high-reactivity fuel, commercial gasoline with the research octane number (RON) of 95 and three low-octane gasolines with RON of 85, 80 and 75 were tested as the low-reactivity fuel. The results show that by optimizing the fuel injection strategies and gasoline ratio, the indicated thermal efficiency (ITE) at IMEP of 6 bar could reach above 50 % with commercial gasoline as low-reactivity fuel. For IMEP of 2 bar, increasing intake air temperature and reducing intake pressure improved ITE up to 46 %. By taking RON85 as low-reactivity fuel, the ITE at IMEP of 4 bar could reach 51.4 % with the intake air temperature of 50 degrees C. NOx and particulate emissions were maintained at low levels under ICCI mode. Based on this study, the efficient and clean combustion of ICCI mode can be reached at IMEP of 4 bar with ITE higher than 50 %.