PDF CALCULATIONS OF TURBULENT NONPREMIXED FLAMES OF H-2 CO2 USING REDUCED CHEMICAL MECHANISMS/

A three-step chemical kinetic scheme, reduced systematically from a mo re detailed mechanism is used to represent chemical reaction in the Mo nte Carlo calculations of the joint velocity-composition probability d ensity function (pdf) for pilot-stabilized turbulent jet nonpremixed f lames of H-2/CO2 fuel mixtures. Flames with a range of fuel jet veloci ties and hence varying degrees of finite rate chemical kinetic effects have been calculated. The independent variables used are mixture frac tion, xi and the specific molar abundance of three reactive scalars, G AMMA(H2O), GAMMA(CO2), and GAMMA(H). Three multidimensional look-up ta bles are generated for density, other dependent properties and the com position increments due to chemical reaction. The use of these tables in all subsequent calculations is computationally efficient. Terms rep resenting the effects of pressure fluctuations, mechanical dissipation , and scalar dissipation are modeled using an improved particle intera ction model. Solutions are obtained on a Sun-Sparc1 station using 30 0 00 Monte Carlo particles for the low jet velocity flames and this numb er is increased to 50000 at high jet velocities. The calculated veloci ty and turbulence fields as well as centerline velocity decay rates ha ve not been compared with measurements but are consistent with recent experimental data collected in similar piloted jet flames of methane f uel. 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, t he calculated temperature and mass fractions of the stable species agr ee reasonably well with instantaneous experimental data collected in s imilar flames. At high jet velocities, when the flames are close to bl owoff and the finite rate chemical kinetic effects are very significan t, discrepancies occur between measurements and computations and the b lowoff jet velocity is underpredicted by about 20%.