Performance Improvement of Turbofans by Electric Power Transfer

With design trends toward the more electric engine (MEE) for the more electric aircraft (MEA), novel technologies can be pinpointed for multi-spool engines. Provided that a multi-spool MEE is equipped with electrical machines connected to each of its shafts, using power electronic converters (PECs) within a common high-voltage DC bus configuration, it is possible to redistribute a desired amount of power between the engine shafts independent of their speeds. This paper presents the impact of electric power transfer (EPT) on engine performance by using a developed 0-dimensional engine model based on the inter-component volume (ICV) method and engine component maps. Generic component maps are scaled to match the design point of the CFM56-3 engine. Validating the simulation results with engine performance data from literature shows that the steady-state error of the speed and fuel consumption is within 1% and 3.5% for the high- and low-speed settings, respectively, which is acceptable for the purpose of power transfer studies. It is shown that a 400 kW EPT system is the best performing for the cases run for the CFM56-3 engine, which can halve the amount of bleed air from variable bleed valves (VBVs). Results show that EPT with the rescheduled VBVs opening improves the engine performance significantly at low-speed settings by decreasing fuel consumption and increasing surge margins. Detailed simulation results from the engine model and EPT weight penalty analysis show that fuel consumption for short- and medium-haul flights reduces by up to 0.46% and 0.79% with state-of-the-art, and 0.60% and 1.0% with future technologies, respectively. Furthermore, results show that electric power transfer can recover the surge margins of degraded engines at high-speed settings.