Commercial Hybrid Electric Aircraft Thermal Management System Design, Simulation, and Operation Improvements

Abstract

Alternative approaches and configurations for the Thermal Management System (TMS) of a parallel hybrid electric propulsion system of a commercial single aisle aircraft have been compared to a baseline approach. A preferred configuration for the acquisition, transport and rejection of heat has been selected and a conceptual design has been completed. The Hybrid Electric Propulsion (HEP) system features a battery pack for energy storage, a low spool motor to assist the fan of a high bypass ratio geared turbofan, and an electric motor drive. The TMS services these HEP loads as well as the traditional engine heat loads including a high spool starter/generator, bearings (for shafts and fan drive system) and the accessory gearbox. The model was executed over a mission on hot day conditions (MIL-STD-210A). A proprietary, object-oriented modeling tool created at the United Technologies Research Center, REHEATS, was used to model the TMS and to optimize it for minimal fuel consumption. By separating the battery and motor drive cooling loops and by allowing battery thermal storage, ram air-cooled heat exchanger weight was reduced to one fifth of the baseline due to the higher temperature operation of the motor drive and due to colder air at the altitude where the battery heat exchanger was sized. The results predict that the TMS of a HEP aircraft increases fuel consumption due to the TMS weight, drag and power demand by approximately 49.0 lbm (~0.75%) per aircraft over a typical mission.