Investigation of pyrolysis effect on convective heat transfer characteristics of supercritical aviation kerosene

Abstract

By utilizing airborne hydrocarbon fuels working as coolant, active regenerative cooling method is a significant method for maintaining the reliability of the scramjet engine components. At high temperatures, the pyrolysis of hydrocarbon fuels occurs and provides extra heat absorption capacity. Investigation on coupled heat transfer and pyrolysis of fuels is essential for the design of cooling channels. This paper aims to study the pyrolysis effects on convective heat transfer of supercritical aviation kerosene RP-3 in vertical upwards. Firstly, a simple molecular kinetic model was proposed for RP-3 pyrolysis. Then the performance of two Reynolds-averaged Navier-Stokes turbulence models with three constant turbulent Prandtl numbers in predicting the fluid-thermal behaviors of reacting flow were evaluated. At last, the mechanisms of pyrolysis effect on heat transfer in the heat transfer deterioration region and the cracked region were investigated. The results showed that the pyrolysis affected heat transfer from two aspects: providing heat absorb or release capacity through the endothermic (exothermic) pyrolysis reactions, changing the fuel properties by the variations in composition. In the heat transfer deterioration region, the effect of heat absorption dominants over the effect of additional decreased in density and specific heat capacity by pyrolysis on the heat transfer, thus a lower wall temperature and larger heat transfer coefficients were observed when considering pyrolysis. In the cracked region, under the present condition, the competitive outcome of the above two led to an improved heat transfer by pyrolysis, and the improved effect first increased and then decreased as the fuel conversion increasing. This work provides a fundamental understanding of the behaviors of hydrocarbon fuel inside the cooling channels, which is valuable for the cooling structure design.