Combustion analysis of natural gas in a four stroke HCCI engine using experiment and elementary reactions calculation

Homogeneous charge compression ignition (HCCI) is regarded as the next generation combustion regime in terms of high thermal efficiency and low emissions. It is difficult to control autoignition and combustion because they are controlled primarily by the chemical kinetics of air/fuel mixture. In this study, it was investigated the characteristics of autoignition and combustion of natural gas in a four-stroke HCCI engine using experiment and elementary reactions calculation. The influence of equivalence ratio, intake temperature, intake pressure and engine speed on autoignition timing, autoignition temperature, combustion duration and the emissions of THC, CO, CO2 were investigated. And also, to clarify the influence of n-butane on autoignition and combustion of natural gas, it was changed the blend ratio of n-butane from 0 mol% to 10 mol% in methane/n-butane/air mixtures. The autoignition of natural gas occurs when in cylinder gas temperature reaches to 900K-1100K under these experiment and calculation conditions. To realize high combustion efficiency and low CO emissions, it is necessary to prepare operation conditions that the maximum cycle temperature is over 1500K. The autoignition temperature becomes lower with increasing the blend ratio of n-butane. As the blend ratio of n-butane increases, the maximum cycle temperature and combustion efficiency increases, and the emissions of THC, CO emissions decrease.