Reaction mechanisms for methane ignition

To help understand hove methane ignition occurs in gas turbines, dual fuel diesel engines, and other combustion devices, the present study addresses reaction mechanisms with the objective of predicting autoignition times for temperatures between 1000 K and 2000 K. pressures between 1 bar and 150 bar, and equivalence ratio between 0.4 and 3. It extends our previous methane flame chemistry, and refines earlier methane ignition work. In addition to a detailed mechanism, short mechanisms are presented that retain essential features of the detailed mechanism. The detailed mechanism consists of 127 elementary reactions among 31 species and results in nine intermediate species being most important in autoignition, namely, CH3, OH, HO2, H2O2, CH2O, CHO. CH3O, H, O. Below 1300 K the last three of these are unimportant. but above 1400 K all are significant. To further simplify the computation, systematically reduced chemistry is developed, and an analytical solution for ignition delay tunes is obtained in the low-temperature range. For most fuels, a single Arrhenius fit for the ignition delay is adequate, but for hydrogen the temperature sensitivity becomes stronger at low temperatures. The present study predicts that, contrary to hydrogen, for methane the temperature sensitivity of the autoignition delay becomes stronger at high temperatures, above 1400 K, and weaker at loin temperatures, below 1300 K. Predictions are in good agreement with shock-tube experiments. The results tray be employed to estimate ignition delay tunes in practical combustors.