Comparison of conjugate heat transfer characteristics between regenerative cooling and recooling system for a methane-fueled scramjet

Methane-fueled scramjet engines are considered the ideal powerplant for next-generation reusable hypersonic vehicles. However, conventional methane regenerative cooling systems cannot meet the thermal protection requirement for high-Mach-number scramjets due to limited coolant. To maximize the utilization of fuel heat sink, this study proposes a recooling system which divides the cooling channel into two sections, with a turbine introduced as an intermediate cooling device between the two sections. To precisely evaluate the performance of this recooling system, a three-dimensional conjugate heat transfer numerical model integrating the cooling channel and the supersonic combustor is developed. Compared to traditional regenerative cooling configurations, the results show that the recooling design effectively prevents overtemperature in downstream walls due to the lower temperature and higher Reynolds number of subcritical methane. Especially the second-stage injection of subcritical methane generates a pronounced impingement cooling effect, reducing the average wall temperature by nearly 120 K. Further parametric analysis reveals that increasing the turbine inlet pressure continuously lowers the peak temperature in this recooling configuration. However, when the pressure exceeds 10 MPa, the resultant temperature reduction can be ignored. For practical designs, optimal channel pressures are determined to be 10 MPa (front) and 2 MPa (rear).