Effect of the reaction mechanism on the numerical prediction of the performance of a scramjet combustor at cruise flight 8 Mach number

Abstract

Abstract A numerical investigation of the effect of the hydrogen-air reaction mechanism on the prediction of supersonic combustion was conducted. Different reaction mechanisms with different number of species and reactions were investigated at a Scramjet hypersonic flight trajectory. A generic three-dimensional supersonic combustor was investigated at flight 8 Mach number condition and at an altitude of 30 km. Numerical simulations were performed to determine the influence of the size of the reaction mechanism on the prediction of supersonic lifted flames, in a Scramjet flight trajectory were the combustor inflow conditions are close to the hydrogen-air self-ignition limit. Results showed significant influence of the number of species and reactions involved in the mechanism on the prediction of the ignition length. Shorter ignition delays were obtained with a reduced mechanism. Similarly, combustion efficiency was affected by the reduced mechanism dropping nearly 15%, compared to the reference scheme. On the other hand, no significant influence of the reaction mechanism was observed on the combustor pressure drop. Pressure losses nearly converge to the same values by the exit of the combustor. The present data suggest that the main observed differences are on the different prediction of the location where self-ignition occurred. We show how the ignition delay is affected by the omission of secondary species and steps reactions leading to shorter ignition delays or even attached flames which are not expected to occur at the investigated hypersonic flight condition.