Laminar flame speeds and kinetic modeling of H₂/O₂/diluent mixtures at sub-atmospheric and elevated pressures

Adiabatic flame temperature and composition laminar flame speeds extracted from constant-pressure expanding flames were studied for H₂/O₂/diluent flames spanning the considered parameter range. A new kinetic model HP-Mech based on evaluation of the rate coefficients from recent high-level quantum chemistry calculations and shock tube measurements was developed and employed to evaluate the controlling reaction steps of these flames. Specifically the overall reaction order was extracted allowing for the pressure dependence of the adiabatic flame temperature. The results showed that the model could assume values not only less than zero at high pressures but also values larger than 2 at lower pressures. Sensitivity and reaction path analyses presented that these responses are controlled by the competition between two opposing pathways.