Kinetic analysis of the chemical structure of filtration-combustion waves in fuel-lean gases

On the basis of skeleton diagrams and sensitivity analysis, the structure of the heat-release region, special features of formation of radicals, and methane-oxidation dynamics under conditions of filtration combustion of an ultralean methane–air mixture are considered in detail. It is shown that the exothermal region consists of two consecutive peaks, the first one due to oxidation of hydrocarbons and hydrogen by OH radicals and the other due to the CO oxidation reaction. Several specific regions are identified in the wave, depending on the prevailing reactions of branching of radical chains. The main chain mechanism of formation of radicals is the reaction CH$_3$ + O$_2$ = CH$_3$O + O in the region of “low” temperatures, the reaction HO$_2$ + CH$_3$ = CH$_3$O + OH in the “transitional” region, and the reaction H +O$_2$ = O + OH in the region of “high” temperatures. Two former regions correspond to the preheating zone, and the latter corresponds to the reaction zone of the wave of filtration combustion of gases.