Radiative Heating in Hydrocarbon-fueled Scramjet Engines

Abstract

Radiation may play an important role in the wall heating and flow cooling of scramjet engines. There have, however, been very few studies in this area, partially due to the inherent difficulties involved. In the present study, an AFRL/RZA RC22 axisymmetric scramjet design was investigated at different fuel splits, Mach numbers, and geometric scales, in order to understand the effects of radiative heat transfer in hydrocarbon-fueled scramjet engines. The results of interest in this study are the radiative and convective heat transfer on the walls of nine components in the test section, including the facility nozzle, isolator, and combustor. For the baseline case with Mach 2.2 nozzle and φp/φs=0.32/0.58, it was found that the radiative wall heat flux was elevated in the combustor and the predicted radiative wall transfer rates were between 1-4% of the corresponding convective wall transfer rates for the five combustor components. For another two cases with the same nozzle Mach number and different fuel splits, the radiation contribution to the wall heat transfer was found to be similar to the baseline case. For the case with Mach 1.8 nozzle, the flow temperature and speed are reduced, and so are the predicted convective and radiative wall heat fluxes. The radiation contribution for this case appeared to be similar to the baseline case. With an increase of combustor scale from 1X to 10X, the radiative wall heat flux is increased while the convective wall heat flux is decreased. This opposite change trend results in a significant increase of the radiation contribution to the wall heat transfer in comparison to the convective heat transfer. For the two cases with 10X combustor scale, the radiative wall transfer rate was found to exceed 10% of the convective wall transfer rate for some combustor components. This implies that radiative heat transfer can no longer be neglected in the scramjet thermal analysis and the radiative effects on the flowfield may also have to be considered in scramjet performance analysis.