Reduced kinetic models for methane flame simulations

The present paper describes the development of two reduced kinetic schemes suitable for multidimensional turbulent flame simulations in high-temperature oxidation of methane. Formal reduction of the USC Mech II $\mathrm{C1}$–$\mathrm{C4}$ detailed kinetic model by using the directed relations graph mechanism results in a $31$-species derivative scheme for lean to near-stoichiometric conditions. To deduce a still shorter, simpler, and less stiff kinetic model, further species elimination is based on combined sensitivity and chemical time scale information to arrive at a $22$-species scheme. The kinetic rates of lumped reactions are here expressed as simple Arrhenius rates, avoiding nonlinear algebraic combinations of excluded elementary steps or species. The accuracy is maintained by tuning pre-exponential constants in the global Arrhenius rate expressions and computing a range of target data. A more compact, quasi-global $14$-species scheme is subsequently formulated by modeling fuel decomposition to a methyl radical pool, followed by $\mathrm{CH}_3$ oxidation with $\mathrm{O}$ and $\mathrm{OH}$ toward $\mathrm{CH}_2$ and $\mathrm{CO}$, and retaining a full $\mathrm{CO}/\mathrm{H}_2/\mathrm{O}_2$ subset. The $\mathrm{C}_2$-chain with recombination of $\mathrm{CH}_3$ into $\mathrm{C}_2\mathrm{H}_6$ and production of $\mathrm{C}_2\mathrm{H}_2$ is also represented in both schemes. Equilibrium $0\mathrm{D}$ and $1\mathrm{D}$ propagating premixed flames and axisymmetric co-flowing lifted laminar jet flames are computed through an iterative validation process. Accompanying computations with the USC Mech II mechanism, as well as available experimental results, are exploited for optimization. The comparisons demonstrate that the derived schemes ensure satisfactory agreement with data over the investigated parameter space.