The Effect of Coking on Transpiration Cooling Behavior in Porous Media

Transpiration cooling method using hydrocarbon fuel is promising in the active thermal protection of scramjet engines due the high cooling efficiency. However, coke deposits derived from thermal cracking of hydrocarbon fuel in porous media severely affected the flow resistance and porosity. In order to investigate the effect of coking on transpiration cooling behavior, a transient numerical model of transpiration cooling in porous media considering coking process is established. The effect of coking on flow and heat transfer characteristics is numerically studied. The results show that coking causes a decrease in porosity, which significantly affects the flow field and coolant distribution within the porous media. With coking time increasing from 0 to 45 min, surface temperature at the leading edge of the high-temperature wall surface increases by 2.5%, while temperature at the trailing edge decreases slightly. The cooling efficiency and its uniformity at the wall surface are deteriorated due to coking. The average cooling efficiency η_avedecreases by 5.4% while the standard deviation of cooling efficiency increases by 3.3%. The flow distribution ratio increases by 13% in the trailing part of the porous zone due to the concentration effect of the coolant.