Transient Behavior of Simplified Reaction Mechanisms for Methane Nonpremixed Combustion

Abstract

The transient behaviors of three simplified methane mechanisms are numerically studied for two idealized turbulent nonpremixed combustion situations: the perfectly stirred reactor and the flamdet 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 species CH₃ leading to a five-step mechanism. Comparisons of the steady-state flame results indicate that the three reduced reaction mechanisms predict the major species concentrations and the flame extinction limits in close agreement with those from a detailed mechanism. The performances of the reduced reaction mechanisms are further assessed by examining their transient responses to a simulated turbulent environment. The results reveal that truncation of global source terms leads to unsatisfactory results especially for lean flames and the performance of the five-step reduced mechanism is found to be superior to the four-step mechanisms only for flames under rich conditions. The flame response is found to be more sensitive to the fluctuation frequency than to the amplitude.