Simulation of dynamic methane jet diffusion flames using finite rate chemistry models

Detailed calculations for methane jet diffusion flames under laminar and transitional conditions are made using an axisymmetric, time-dependent computational fluid dynamics code and different chemical kinetics models. Comparisons are made with experimental data for a steady-state flame and for two dynamic flames that are dominated by buoyancy-driven instabilities. The ability of the three chemistry models-namely, 1) the modified Peters mechanism without C-2 chemistry, 2) the modified Peters mechanism with C(2)chemistry, and 3) the Gas Research Institute's Version 1.2 mechanism-in predicting the structure of coaxial jet diffusion flames under different operating conditions is investigated. It is found that the modified Peters mechanisms with and without C-2 chemistry are sufficient for the simulation of jet diffusion flames for a wide range of fuel-jet velocities. Detailed images of the vortical structures associated with the low- and transitional-speed methane jet flames are obtained using the reactive-Mie-scattering technique. These images suggest that a counter rotating vortex is established upstream of the buoyancy-induced toroidal vortex in the low-speed-flame case and that the shear-layer vortices that develop in the transitional-speed flame are dissipated as they are convected downstream. The time dependent calculations made using the modified Peters chemistry model have captured these unique features of the buoyancy-influenced jet flames. Finally, the unsteady flame structures obtained at a given height are compared with the steady state flame structures.