Analysis of active cooling panels in a scramjet combustor considering the thermal cracking of hydrocarbon fuel

In this paper, a procedure is demonstrated for the numerical analysis of a cooling system using active panels for high-speed combustion chambers subjected to high thermo-mechanical loads. A promising alloy for high heat loads, namely, niobium Cb-752, is considered in this study. In addition to sensible heat transfer, endothermic heat absorption through the cracked hydrocarbon fuels is a viable option for cooling the chamber panels. The focus of the panel design is to minimize the weight with the safe thermo-mechanical characteristics of the panel. The present analysis is carried out in three steps. First, a one-dimensional (1D) analytical model is developed. The second and third steps are three-dimensional (3D) analyses without and with consideration of fuel endothermicity, respectively. The optimal channel dimensions obtained from the 1D analysis provide inputs for the 3D analysis. The channel dimensions obtained from the 1D analysis do not satisfy the targeted parameters in the 3D analysis. Thus, the channel is redesigned in 3D and tested with and without cracking. The channel dimensions are optimized for the ranges of heat fluxes (160–220 W/cm) in the combustor and mass flow rates (0.011–0.015 kg/s) of the fuel in the channel. Reducing the weight of the panel is sought by considering the benefit of heat absorption through the endothermic cracking process in the fuel channel. The combination of an increased width and cracking performs better than the other non-cracking cases. The study presents the most efficient configuration suitable for applications in high-speed combustion chambers under the given heat flux conditions. By increasing the channel width and cracking (for 3D), the weight of the panel is reduced by 10.58%. The fuel exit temperature, fuel cracking behavior in the channel, structural stress distribution and weight of the panel are analyzed in terms of the operating conditions.