Investigation of Methods and Devices for Active Thrust Profile Control in Hybrid Rocket Engines through Oxidiser Flow Management
Research on thrust control in hybrid rocket engines (HREs) has gained renewed interest due to the growing demand for microsatellites and small launch vehicle operations, as well as the limitations of solid and liquid propulsion technologies. The ability to optimise the thrust profile is a key advantage of HREs, influencing flight safety, stability, and operational, environmental, and economic factors. By controlling the oxidiser flow into the combustion chamber, the thrust profile of HREs can be tailored to meet specific mission requirements. This study designs both the engine and a control methodology for regulating oxidiser flow HREs. It details the development of an ABS/N2O hybrid rocket engine, capable of producing 500N of thrust. Throttling is achieved by using a ball valve as the throttle mechanism. Advanced modelling techniques, including MATLAB/Simulink and ANSYS FLUENT, were employed to analyse engine dynamics and the effects of varying oxidiser mass flow rates, and to develop system models for controller design. The numerical models accurately captured the system dynamics, with pressure chamber errors ranging from 9.32% to 39.57%, increasing at lower oxidiser flow rates due to the absence of a radiation model and simplified chemical reaction mechanisms. The controller’s performance was evaluated under various throttle profiles (step changes, multiple steps, gradual decreases, rapid changes) and oxidiser-to-fuel (o/f) ratio profiles (constant, ramp, sine inputs). The controller performed well in gradual and step changes, exhibiting minimal overshoot and steady-state error. However, it struggled with rapid changes, showing steady-state errors and overshoot between 15% and 25%. These results indicate that while the proposed controller is effective for boost and sustain profiles and gradual decrease throttling, it faces challenges in responding to disturbances and unexpected changes.
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