Combustion analysis of natural gas/air mixture in an HCCI engine using experiment and chemical reactions calculation

Homogeneous charge compression ignition (HCCI) combustion is regarded as next generation combustion method in terms of high thermal efficiency and low emissions. Natural gas is regarded as the most promising alternative fuel due to its clean burning and abundant supply. In this study, it was inventigated characteristics of autoignition and combustion of natural gas in an HCCI engine by using chemical reactions calculation and experimental study. And also, the operation conditions to realize combustion completion in an HCCI engine were suggested. The influences of n-butane blend ratio on autioignition and combustion was clarified in methane/n-butane/air mixtures. As a results of experiment and chemical reactions calculation, it becomes clear the following facts; i) Autoignition temperature of natural gas is in a range of 1 000=100 K without relations of equivalence ratios, intake temperatures and intake pressures, ii) 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. iii) As blend ratios of n-butane are increased in Methane/n-butane/air mixtures, autoignition temperature and autoignition pressure become lower.