Reduced Reaction Mechanisms for Methanol-Air Diffusion Flames

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Abstract
Reduced reaction mechanisms for methanol-air diffusion fiames are developed by systematic reduction of a skeletal mechanism. By examining the magnitude of the net production rates for the intermediate species, it is shown that for stagnation point diffusion flames the steady state assumption is reasonable for CH2OH, HCO, O, OH, H02, and H2O2, but not for CH2O. By eliminating these species from the skeletal mechanism, a five-step reduced mechanism is derived CH3OH + 2H = CH2O + 2H2, (R1) CH2O = CO + H2, (R2) CO + H2O = CO2 + H2,(R3) 2H2 + O, + M = 2H2O + M, (R4)O2 + 3H2 = 2H + 2H2O. (R5) To explore the impact of making the steady state assumption for CH2O, this five-step mechanism is further reduced to four steps by eliminating CH2O from the mechanism. Comparisons of calculated results for the stagnation point diffusion flame show a reasonable agreement among the different mechanisms. However, the four-step mechanism yields peak CH2O concentrations about six limes those predicted by the skeletal mechanism or by the five-step mechanism. Application of the reduced mechanisms to the perfectly-stirred reactor (PSR) indicates that both CH2O and the H atom are in the steady state. Therefore, it is possible to model the kinetics in the PSR by a three-step mechanism.