Inlet-engine Matching Control of Rocket Based Combined Cycle Engine under Rocket-ramjet Mode

The Rocket Based Combined Cycle (RBCC) engine operates over a wide range of speeds and airspace conditions. During thrust regulation, improper control of the ramjet kerosene and rocket flow can disrupt the normal operation of the inlet, potentially leading to severe consequences such as overflow or unstart. Therefore, engine control must ensure proper matching between the inlet and the engine. This study focuses on the RBCC engine and investigates an inlet-engine matching control scheme under rocket-ramjet mode. Within this context, a control model for the RBCC engine is developed based on neural networks, component dynamics, and system identification methods, taking into account the kerosene supply system and the pressure response delay time along the engine. A hybrid control architecture integrating model predictive control (MPC) and PID control is proposed. An MPC controller is designed to achieve two-stage kerosene injection regulation with thrust tracking and inlet stability margin constraints, while a PID controller is employed to precisely regulate the flow rates of the rocket engine. Under Mach 2 and Mach 4 inflow conditions, the system adjustment time is no more than 0.15 seconds, the maximum deviation between engine thrust and demand thrust was 0.73%, and the fluctuation range of the inlet stability margin was less than 4%. Compared to the commonly used H∞ robust control method, the MPC method reduces the adjustment time by over 50% and ensures that the inlet stability margin is maintained near the critical threshold, thereby fully leveraging the performance advantages of the engine.