PDF calculations of turbulent nonpremixed flames of [formula omitted] using reduced chemical mechanisms

Abstract

A three-step chemical kinetic scheme, reduced systematically from a more detailed mechanism is used to represent chemical reaction in the Monte Carlo calculations of the joint velocity-composition probability density function (pdf) for pilot-stabilized turbulent jet nonpremixed flames of H 2 CO 2 fuel mixtures. Flames with a range of fuel jet velocities and hence varying degrees of finite rate chemical kinetic effects have been calculated. The independent variables used are mixture fraction, ξ and the specific molar abundance of three reactive scalars, Γ H 2O , Γ CO 2 , and Γ H. Three multidimensional look-up tables are generated for density, other dependent properties and the composition increments due to chemical reaction. The use of these tables in all subsequent calculations is computationally efficient. Terms representing the effects of pressure fluctuations, mechanical dissipation, and scalar dissipation are modeled using an improved particle interaction model. Solutions are obtained on a Sun-Sparc1 station using 30 000 Monte Carlo particles for the low jet velocity flames and this number is increased to 50 000 at high jet velocities. The calculated velocity and turbulence fields as well as centerline velocity decay rates have not been compared with measurements but are consistent with recent experimental data collected in similar piloted jet flames of methane fuel. The calculated mixing field compares well with experimental data and the calculated flame length is slightly shorter than the observed visible flame length. For the low- and intermediate-velocity flames, the calculated temperature and mass fractions of the stable species agree reasonably well with instantaneous experimental data collected in similar flames. At high jet velocities, when the flames are close to blowoff and the finite rate chemical kinetic effects are very significant, discrepancies occur between measurements and computations and the blowoff jet velocity is underpredicted by about 20%.