Effects of fuel conversion ratio on cooling and drag reduction performance for supersonic film using gaseous hydrocarbon fuel

Film cooling especially combined with regenerative cooling is an effective solution to meet the heat protection and the drag reduction demands for hydrocarbon-fueled scramjet engines. Typically, fuel is the only available coolant to organize the active cooling for hypersonic vehicles, and the coolant used in the film cooling is extracted from the regenerative cooling channels; however, the fuel pre-cracking in the regenerative cooling process must be considered as it can change the initial composition and energy level of the coolant in the film cooling. Numerical simulations based on the RANS method are conducted to evaluate the effects of film pre -cracking on its cooling and drag reduction performance, by changing the fuel conversion ratio from 0 to 40 %. Results show that the influence of film inlet cracking on its drag reduction performance is limited, and the relative change of the wall friction under different conversion ratios is less than 5 %. However, the film inlet cracking has a notable negative influence on its thermal protection performance. Specifically, for every 10 % increase in the film conversion ratio, the average adiabatic wall temperature will rise by about 20 K. Further analysis reveals that although the total amount of the fuel chemical heat sink is comparable to its physical heat sink, only around 25 % of the film chemical heat sink can be effectively used to enhance the fuel film cooling performance. The loss of the effective chemical heat sink during the pre-cracking process is the main reason for the decrease of film cooling performance as the film inlet conversion ratio increases.