IGNITION IN THE SUPERSONIC HYDROGEN AIR MIXING LAYER WITH REDUCED REACTION-MECHANISMS/

Asymptotic analysis of ignition within the supersonic hydrogen/air mix ing layer is performed using reduced mechanisms. Two distinct reduced mechanisms for the high-temperature and the low-temperature regimes ar e used depending on the characteristic temperature of the reaction zon e relative to the crossover temperature at which the reaction rates of the H + O-2 branching and termination steps are equal. Each regime fu rther requires two distinct analyses for the hot-stream and the viscou s-heating cases, depending on the relative dominance of external and i nternal ignition energy sources. These four cases are analysed separat ely, and it is shown that the present analysis successfully describes the ignition process by exhibiting turning point or thermal runaway be haviour in the low-temperature regime, and radical branching followed by thermal runaway in the high-temperature regime. Results for the pre dicted ignition distances are then mapped out over the entire range of the parameters, showing consistent behaviour with the previous one-st ep model analysis. Furthermore, it is demonstrated that ignition in th e low-temperature regime is controlled by a larger activation energy p rocess, so that the ignition distance is more sensitive to its charact eristic temperature than that in the high-temperature regime. The igni tion distance is also found to vary non-monotonically with the system pressure in the manner of the well-known hydrogen/oxygen explosion lim its, thereby further substantiating the importance of chemical chain m echanisms in this class of chemically reacting boundary layer flows.