Multi-dimensional design and thermal protection capability of a regenerative cooled RBCC variable-geometry combustor

The Rocket-based Combined-Cycle (RBCC) engine is a propulsion system that combines a ramjet engine with a rocket engine, which is capable of operating over a wide speed and space range. To ensure efficient operation throughout the flight envelope, variable geometry combustor is commonly used in RBCC engines to obtain higher performance under different operating conditions. However, non-uniform heat release during multimode operations should be considered with special attention and it is necessary to conduct research on the thermal protection system design of variable geometry combustor. This research proposes a multidimensional fast design method for regenerative cooling structure. The effectiveness of this regenerative cooling structure is simulated under different cooling equivalent ratios. The results indicate that the thermal environment is highly inhomogeneous. Results from one-dimensional design model indicate that the cooling effect of the structure is optimal when the cooling channel width is 2mm, the rib width is 3mm, and the height is 1mm. The cooling effect becomes progressively better as the cooling equivalent ratio increases. Three dimensional numerical calculations considering combustion, flow, supercritical-pressure heat transfer and fuel pyrolysis were further performed to analyze the thermal protection capability of the regenerative cooling structure at cooling equivalent ratios of 1.0, 1.5. The study indicates that when the cooling equivalent ratio is 1.0, the combustor experiences local over-temperature phenomenon, which appears at the side and bottom of the combustor. However, when the ratio is 1.5, the combustor operates normally with a maximum wall temperature of 1480 K, which is below the permissible temperature of 1500 K (assuming a Zirconia coating). Additionally, the fuel is completely cracked and the fuel heat sink is fully utilized. The results obtained here will lay the foundation for the future development of regenerative cooled RBCC engine with variable structure.