Research on the effects of negative valve overlap duration on the combustion and emission of methanol, ethanol, isopropanol, and n-butanol in a spark induced compression ignition (SICI) engine by experiments and Artificial Neural Networks

In order to achieve the carbon neutrality goal, it is urgent to improve the thermal efficiency of engines and the application of carbon neutral fuels. Due to the low emissions and renewability of alcohols, which are considered as potential alternative fuels. Spark induced compression ignition (SICI) is an efficient and clean combustion mode for future engines. This article studied the differences of methanol, ethanol, isopropanol, and n-butanol in the SICI combustion modes under four different negative valve overlap (NVO). It was found that under low load, methanol exhibited higher indicated thermal efficiency (ITE) and the lowest HC emissions, while n-butanol exhibited lower NOx and CO emissions. After the load increased, the ITE of n-butanol, isopropanol, methanol, and ethanol all increased with the prolongation of NVO, increasing by 0.35 %, 0.95 %, 0.9 %, and 1.42 %, respectively. In addition, an artificial neural network SICI engines model was established, with correlation coefficients above 0.95. It was found that a correlation between fuel characteristics, auto-ignition timing and flame development. The correlation weight was 20.68 % and 48.1 %, respectively. For ITE, within the optimal ignition timing adjustment range, the contribution of latent heat of vaporization and auto-ignition temperature of alcohol was 42.5 % and 46.5 %, while NVO was 6.63 %.