THE COMPUTATION OF STRETCHED LAMINAR METHANE AIR DIFFUSION FLAMES USING A REDUCED 4-STEP MECHANISM

We demonstrate that a systematically reduced four-step mechanism is able to provide the essential properties of methane-air diffusion flames such as the structure and extinction limits in a way similar to a full kinetic mechanism. The reduction is based on the C//1-chain for methane oxidation. By looking at the magnitude of the intermediate species we argue that a steady state assumption is justified for OH, O, HO//2, CH//3, CHO, and CH//2O. Furthermore, by considering which reactions are fast, we are able to assume partial equilibrium of the reactions OH plus H//2 reversible reaction H//2O plus H and OH plus OH reversible reaction H//2O plus O. Even though the maximum mole fraction of the hydrogen atom H is of the same order of magnitude as that of OH, it is not assumed to be in steady state because of its larger diffusion coefficient.