Installed performance evaluation of an air turbo-rocket expander engine

The propulsion plant of a prospective supersonic cruise aircraft consists of an air turbo-rocket expander and a dual-mode ramjet. A comprehensive numerical model was constructed to examine the performance of the air turbo-rocket during the supersonic acceleration of the vehicle. The numerical model comprised a one-dimensional representation of the fluid paths through the dual-mode ramjet, the air turbo-rocket combustor, the regenerator and the airframe-integrated nozzle, whereas the turbomachinery and the air turbo-rocket bypass were included as zero-dimensional models. The intake operation was based on the results of time-averaged Euler simulations. A preliminary engine analysis revealed that the installation effects restricted significantly the operational envelope, which was subsequently extended bypassing the air turbo-rocket. Hence the engine was throttled varying the mixture ratio and the fan compression ratio. Nevertheless, the performance was optimal when the demand from the air turbo-rocket matched the intake air flow capture. The heat recovery across the regenerator was found critical for the operation of the turbomachinery at low speed. The transition of the air turbo-rocket to ramjet operation was identified at Mach 4.5. During this regime, the propulsion plant was rather insensitive to the mixture ratio and was throttled with the air turbo-rocket throat area.