Integrated assessment of parallel hybrid electric aircraft propulsion architectures

Advisory Council for Aeronautical Research in Europe (ACARE) has published ambitious goals for reduction in emissions from aircraft applications by the year 2050. Hybrid-electric and alternative fuelled powerplants have been proposed as one of the major solutions to resolve this problem. There has been significant industrial push to build and test viable hybrid-electric propulsion systems onboard aircraft and certify them for flight, with Rolls-Royce ACCEL, Airbus E-Fan X and Boeing SUGAR VOLT being some recent examples. Despite this, there exists significant uncertainty around the potential fuel burn benefits from these architectures across the different aircraft classes, the impact on gas turbine design, thermal management and aircraft integration, as well as fleet technology penetration. The work in open literature has focussed on individual aspects mentioned above but no study was found considering all these aspects in a common design and optimization loop. The aim of this thesis is to develop robust integrated design and optimization methods, to help industry examine future application scenarios in a more objective, systematic and therefore, more cost-effective manner. The regional to single aircraft design space is explored with ATR 72, Fokker 100 and A320 being the baseline aircraft platforms. Initially, a design space exploration is performed for the Fokker 100 style airframe utilizing lithium ion batteries in a parallel hybrid configuration. The impact of hybrid gas turbine cycle redesign strategies are benchmarked and compared to retrofit hybrid gas turbine. A power management optimization loop is set up to optimize the power split for varying battery pack sizes and motor powers on different mission ranges. This sweep is also performed for varying technology levels on gas turbine, motor power density and battery energy density. It is demonstrated that the benefit from electrification improves with improvement in gas turbine technology level. The integrated hybrid gas turbine cycle design and power management optimization ANN method is applied to all three aircraft platforms for EIS 2035 time frame. The optimal power management strategies favour take-off and initial climb for redesigned gas turbines while they favour cruise for retrofit gas turbines. Incorporation of direct operating cost modules show retrofit hybrid systems having a lower direct operating cost as compared to redesigned hybrid systems owing to reduced gas turbine maintenance cost. The multi-mission method is applied to the test cases showing the penalty paid in carrying a fixed battery pack. Two thermal management architectures, ram air-liquid coolant heat exchanger and vapour compression cycles are utilized to reject the heat load from the electrical systems. The design space of both the systems are first explored for varying levels on quantity of heat load, quality of heat load and flight mission conditions. The method to integrate optimal combinations of thermal management architectures in terms of, coolant mass flow rate, condenser pinch, condenser geometry and compressor pressure ratio is utilized and applied to different propulsion configurations. The full framework is also expanded to include proton exchange membrane fuel cells and hydrogen-powered gas turbines. A final technological assessment is performed for the regional ATR 72 style aircraft platform for both thermal management architectures. A pure electric, battery and fuel cell powered aircraft with an optimal power split is identified as a suitable candidate against kerosene and hydrogen powered gas turbines to power EIS 2035 regional turboprop. While for single-aisle applications, there is a case for mild hybridization to reduce NOx and improve gas turbine operability at part load settings.