The reactions supporting or opposing the development of explosive modes: Auto-ignition of a homogeneous methane/air mixture

The development of time scales that characterize the initiation of an auto-ignition processes is supported by specific reactions and is opposed by some others. An algorithmic tool which identifies these two sets of reactions is validated on the basis of the auto-ignition of a homogeneous stoichiometric methane/air mixture at 50 bar and 1100 K. It is shown that this process is characterized by two time scales, the fastest of which relates to the generation of the required for ignition radical pool and the temperature increase. This time scale associates mainly to carbon chemistry, except the very last period of its presence where it relates to hydrogen/oxygen-chemistry. The analysis allows for the quantitative assessment of several chemical phenomena that have been associated with the abnormal long ignition delay of methane, such as the formation of C2H6 and the relative importance of the formation of CH2O and CH3O as means of consumption of CH3 radicals. The identification of the reactions supporting or opposing the initiation of the auto-ignition is most useful when it is desired to control the ignition process.