Parametric Study on the Cycle of an electric Hybrid Adaptive Cycle Engine

Authors

Philipp Jäger  - University of the Bundeswehr, Munich, Germany
Marcel Stößel - University of the Bundeswehr, Munich, Germany
Michael Krummenauer - Bundeswehr Technical Center for Aircraft and Aeronautical Equipment (WTD61), Manching, Germany
Dragan Kožulović - University of the Bundeswehr, Munich, Germany

Abstract

One of the main fields of research and development in the aviation industry is increasing the efficiency of propulsion systems and optimizing them for a wide range of flight conditions. Especially for flight missions with operating points at the opposing end of the flight velocity spectrum, variable cycle or adaptive cycle engines have shown to provide a significant increase in performance and propulsive efficiency. In the last year a novel engine concept for an electric Hybrid Adaptive Cycle Engine (eHACE) was developed at the Institute of Jet Propulsion (IJP). This concept consists of an electrically driven fan, a single spool core engine with a directly driven generator and variable nozzles for the core engine and the bypass stream. For continuous operation, the electric energy required to drive the fan is provided by the generator of the core engine. For peak power, additional energy can be supplied by a battery storage. With this setup, the fan operating point can be varied independently from the operating point of the core engine to some extent. By varying the nozzle area of the core‐ and bypass nozzles, the bypass ratio of the engine and therefore the specific thrust of the engine can be adapted to maximise the propulsive efficiency for different flight velocities. A first demonstrator of the eHACE concept was built using “off the shelf” components, mainly derived from the RC hobby sector. With the tests conducted at the engine test facility of the IJP, the feasibility of the concept and its coherence with the models developed in parallel was proven. The tests also highlighted the limitations of the used, nonmatched components. Especially the fan stage has dedicated potential to contribute to the overall performance and efficiency of the system, when optimized for a variable bypass ratio. Furthermore, the power of the generator should be maximized, while staying within the speed and temperature limits of the core engine. For the design of a new demonstrator engine, a new core engine was selected and coupled to a generator, capable of converting up to 10% of the maximum turbine power to electrical power. To analyse the boundary conditions for the design of a new fan stage and optimized core‐ and bypass nozzles, the eHACE with the new core engine is modelled using the Numerical Propulsion System Simulation (NPSS). With this model, a parametric study is conducted to evaluate the effects of the concept’s main variables on the engine cycle. These variables are core engine speed, fan power, core nozzle area and bypass nozzle area. Further, the engine cycle is modelled in varying flight conditions to determine the required operating range of the components and the engine settings for maximum thrust and greatest efficiency.