Development of a Gas Turbine Concept for Electric Power Generation in a Commercial Hybrid Electric Aircraft

Abstract

Civil aviation is growing 4.7% per annum. Alternative propulsion systems are necessary to reduce emissions causing global warming. The electrification of aircraft propulsion systems has the potential to use renewable energy and reduce the environmental footprint of aviation. At present, full electric flight appears to be feasible for small aircraft only, due to the power density of batteries which is approximately 45-times lower than that of kerosene. Hybrid electric concepts may present a bridging technology towards more electrified aviation for short/mid-range aircraft. The hybrid concept combines the benefits of electrical power with conventional turboshaft engine technology. Within the framework of the ‘HyFly’ project (supported by the German Luftfahrtforschungsprogramm LuFo V-3), a hybrid electric concept for a short/mid-range 19 PAX aircraft is studied. In this paper the results of a preliminary design exercise of the gas turbine used in this concept is presented. Conventional aircraft gas turbines deliver maximum power only at take-off for a short period of time. At this power setting temperature and stress levels are at the extreme and dominate overall engine life consumption. In the HyFly concept, the gas turbine inlet temperature is kept constant during the entire flight. The engine is not driven into the extreme take-off power setting, resulting in a significant increase of engine life. The constant power setting also offers the opportunity to optimize efficiency especially around the base load point. For take-off and an emergency power rating, extra power is provided by batteries. In this paper, a survey of existing engine technology is presented considering suitability for the concept. The impact of improvement of component efficiencies, increase in cycle pressure ratio and turbine inlet temperature, relative to the state-of-the-art, is analyzed using a B&B-AGEMA in-house gas turbine simulation tool. In addition, a weight model is presented for preliminary estimation of engine mass. Finally, requirements for the individual gas turbine sub-component design and performance are defined. This will build the basis for further component design.