Transient control strategies for hydrogen supply temperature and comprehensive evaluation in a hydrogen turboprop engine at ground idle

During a hydrogen turboprop engine's transition to ground idle, the hydrogen flow rate decreases rapidly, whereas stored heat is released more slowly from the intermediate loop, causing the supply temperature to approach the upper limit of 323 K. Using a previously developed single-variable strategy as the reference, this study compares two coordinated strategies in which the second control action is applied either at the upstream heat source or at the terminal hydrogen heat exchanger. The analysis uses a coupled one-dimensional model of the engine and thermal management system and a five-dimensional evaluation of temperature control, heat sink utilization, and cold exergy utilization. The relative errors between simulation and engine-test data are 1.32% for exhaust temperature and 0.07% for mass flow rate; experiments using nitrogen as a surrogate show a deviation of approximately 2% in cold-side outlet temperature. The results show that control node placement determines how stored heat and mass transport delay affect the temperature response. Under nominal conditions, coordinated control at the terminal side reaches a quasi-steady state within 44 s and retains a temperature margin of 6 K; the investigated local parameter perturbations reduce this margin to approximately 2 K. Coordinated control at the heat source reduces total exergy destruction by approximately 8% relative to single-variable control, whereas single-variable control achieves the highest heat sink utilization. Under the investigated case-specific response-time assumptions, finite actuator dynamics consume most of the nominal safety margin. Under the conditions investigated, coordinated control at the terminal side is preferred when temperature safety and cold exergy utilization are prioritized, whereas single-variable control is more competitive when heat sink utilization is prioritized. These findings identify control node placement as a key determinant of transient heat transport and strategy applicability.