Sensor and Actuator Evaluation for Liquid Rocket Engines Combustion Instability

Reliable sensing and actuation are critical to the safe, efficient, and reusable operation of liquid rocket engines (LREs), where extreme thermo-mechanical environments and fast instability growth can lead to catastrophic failure. Among LRE subsystems, the combustion chamber plays a central role in stability, as thermoacoustic instabilities originate from nonlinear coupling between unsteady heat release and chamber acoustics. Effective sensor and actuator placement in this region is therefore essential for early detection and mitigation of instability onset. This paper presents a model-based framework to evaluate sensor and actuator placement for combustion instability management in LREs, using the combustion chamber as a focused case study. A first-principles dynamic engine model is employed to capture transient engine behavior, while instability onset is characterized through a thermoacoustic instability model. Phase-based diagnostics are shown to provide early, physically meaningful indicators of instability. Candidate sensors within the combustion chamber and candidate actuators affecting equivalence ratio are evaluated based on detectability and dynamic responsiveness. Results characterize the engine-level response time resulting from feed-system actuation and motivate combustion-chamber-centric sensing strategies for instability detection and control in advanced liquid propulsion systems.