Integrated Propulsive and Thermal Management System Design for Optimal Hybrid Electric Aircraft Performance

The use of hybrid-electric propulsion systems aboard aircraft present opportunities for improved vehicle range and endurance, reduced fuel burn, as well as lower acoustic and thermal signatures. The energy benefits anticipated by such architectures may be offset, however, by new thermal management challenges introduced by the heat generated within the components of a hybrid-electric power train. A system level modeling approach that integrates the propulsion and thermal management subsystems is therefore critical to providing insight into the various tradeoffs. The current paper explores the reduction in fuel consumption offered by a series hybrid propulsion system using an integrated system modeling approach. A numerical model of the propulsive, thermal management, and flight dynamics subsystems was developed to simulate component and system level performance of a fixed wing, 11901 lb. medium altitude long endurance (MALE) vehicle, conventionally driven by a turboprop engine.. A thermal management system was integrated with the propulsive subsystem which utilized closed loop fuel cooling for electrical devices within the hybrid drive train, as well as a Polyalphaolephin (PAO) coolant loop to absorb the heat from several aircraft level auxiliary heat loads. Ram air was utilized to provide a heat sink for the PAO cooling loop, as well as the fuel loop to ensure return-to-tank fuel temperature limits are maintained. For a notional 18 hour flight mission, with respect to the conventional propulsion system, a fuel savings of 750 lb. was obtained, despite a gain of 708 lb. associated with the added weight of electrical devices within the drive train.