Chemical Kinetic Structure of the Reaction Kernel of Methane Jet Diffusion Flames

Abstract

The detailed structure of the stabilizing region of an axisymmetric laminar methane jet diffusion flame has been studied numerically by solving the time-dependent full Navier-Stokes equations with buoyancy using an implicit, third-order accurate numerical scheme and two detailed C2-chemistry models. The calculated standoff distance of the flame base was comparable to that experimentally observed but chemistry-model dependent. Nevertheless, local flame structure around the base was nearly identical, except that the C -chemistry previously used overpredicted the methyl and formaldehyde concentrations. The fuel-lean, highest-reactivity spot (reaction kernel) responsible for flame stabilization was formed as a result of back-diffusion of radicals into the oxygen-abundant flame base, thereby dramatically enhancing the H2-O2 chain reactions, the CH3 formation and oxidation via formaldehyde, the C2-reaction path, and the H02 reactions at relatively low temperatures (⁢1600 K(. In particular, the H = O2 → OH = O and CH2 = O → CH20 = H reactions played a decisive role in the reaction kernel.