Autoignition and combustion of natural gas in a 4 stroke HCCI engine

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 timing and combustion duration because they are controlled primarily by the chemical kinetics of fuel-air mixture. In this study, it was investigated the characteristics of autoignition and combustion of natural gas in a 4 stroke HCCI engine. 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. Autoignition strongly depends on in-cylinder gas temperature. Autoignition of natural gas occurs when in-cylinder gas temperature reaches in a range of 1 000±100 K under this experimental condition. To realize high thermal efficiency and low CO emissions, it is necessary to prepare operation conditions that maximum cycle temperature is over 1 500 K. Autoignition temperature is 25 K lower by increasing n-butane blend ratio of 10%. As the blend ratio of n-butane increases, the maximum cycle temperature increases, and THC, CO emissions reduce.