Exploring Design Trade-Offs For Installed Parallel Hybrid Powertrain Systems

The parallel hybrid (or boosted) turbofan engine alleviates the system complexity of radical electrified powertrain architectures, while also demonstrates substantial benefits in reducing specific fuel consumption. This conservative, yet promising, electrified configuration incorporates an electrical drive coupled with the engine low-pressure or gearbox fan spool. Sophisticated models for the gas turbine and the electrical drive system are developed. The former deploys a multi-point design matching scheme coupled with an installed engine performance approach, as well as an engine sizing and weight estimation tool. The latter incorporates an analytical electrical machine sizing and performance methodology. The objective of this paper is to shed light on the optimal parallel hybrid engine design, considering installed cycle performance and tight coupling of engine and electrical drive systems. The impact of installation drag components on the integrated powertrain system performance is analyzed and design trade-offs are explored. Electrical machine efficiency, propulsion system weight and installed specificfuelconsumptiondemonstrateopposingtrendswithvaryingspecificthrustfordifferent electrical drive installation positions and mechanical connections. It is shown that fan spinner-mounted electrical machine which is mechanically coupled to the low-pressure spool presents the greatest potential in terms of electrical machine efficiency and propulsion system installed performance. A 11.23% and 15.11% increase in installed specific fuel consumption at Top of Climb and Cruise, respectively, is observed for the Cruise-based optimal specific thrust variant, rendering installation effects and electrical drive considerations critical for future low-specific thrust hybrid-electric aero-engine concepts.