Effects of combustion on supersonic film cooling using gaseous hydrocarbon fuel as coolant

For hydrocarbon fueled scramjet engine, gaseous hydrocarbon fuel has been promoted to conduct supersonic film cooling. During the continuous mixing in the cooling process, the possibility of the coolant film combustion must be seriously considered. In this paper, a numerical model of gaseous hydrocarbon fueled supersonic film cooling in terms of the coolant combustion has been developed and validated. The results indicate that the combustion of the coolant film occurs in the boundary layer. The combustion flame is formed apart from the wall and restricted near the boundary layer edge. The interesting thing is that the combustion first reduces and then increases the wall temperature rather than only increases the wall temperature significantly as expected, which brings double effects on film cooling. The combustion reduces the wall temperature due to low-temperature endothermic chemical reactions occur and dominate the near wall region over a long distance after the film injection. Moreover, the turbulent energy transport to the wall is suppressed due to the combustion heat release. Furthermore, after the combustion flame occurs, the skin friction is reduced. The skin friction reduction by combustion is attributed to the combined effects of Reynolds stress reduction and the viscosity stress reduction.