Chemistry reduction and thermokinetic criteria for ignition of hydrogen–air mixtures at high pressures

Abstract

A systematic methodology consisting of sensitivity analysis, principal component analysis, quasi-steady-state analysis, and reaction path analysis is applied at bifurcation points to deduce the kinetic and thermal interactions at ignition of H₂–air mixtures at high pressures in a flow reactor. Singularity theory is subsequently used to derive thermokinetic ignition criteria, capable of accurately predicting ignition temperature over a wide range of pressure along the second and third ignition limits. Comparison of thermokinetic criteria to the second ignition branch isothermal kinetic criterion shows the importance of HO₂ and H₂O₂ chemistry and reaction exothermicity at high pressures. Thermally, ignition along the third branch is shown to be primarily driven by the exothermicity of the H+O₂+M→HO₂+M reaction. Transport analysis indicates that the outflow of H₂O₂ becomes quite important at high pressures, causing the shift in the third ignition branch with respect to residence time. A revised isothermal kinetic criterion for the higher pressures of the second ignition limit is also proposed.