TRANSIENT-BEHAVIOR OF SIMPLIFIED REACTION-MECHANISMS FOR METHANE NONPREMIXED COMBUSTION

The transient behaviors of three simplified methane mechanisms are num erically studied for two idealized turbulent nonpremixed combustion si tuations: the perfectly stirred reactor and the flamelet model. Two of the simplified mechanisms contain four global steps, and one of them has truncated source terms. The third mechanism is an improved version of the four-step mechanisms with the inclusion of an additional speci es CH3 leading to a five-step mechanism. Comparisons of the steady-sta te flame results indicate that the three reduced reaction mechanisms p redict the major species concentrations and the flame extinction limit s in close agreement with those from a detailed mechanism. The perform ances of the reduced reaction mechanisms are further assessed by exami ning their transient responses to a simulated turbulent environment. T he results reveal that truncation of global source terms leads to unsa tisfactory results especially for lean flames and the performance of t he five-step reduced mechanism is found to be superior to the four-ste p mechanisms only for flames under rich conditions. The flame response is found to be more sensitive to the fluctuation frequency than to th e amplitude.