Active Energy Management for Enhanced Engine Transient Operations

Combat aircraft often require the engine to accelerate as fast as possible in response to the demand of maneuvering. The engine acceleration rate, however, is limited by the compressor surge constraint, which prevents more fuel addition that, otherwise, could provide for higher net shaft torque, and thus, faster acceleration. This paper examines the idea of using the electric starter/generator (ES/G) system to provide additional net shaft torque during this critical phase of acceleration. The idea is examined by simulations using a quasi-one-dimensional dynamic compressor flow model coupled with a lumped combustor–turbine model. A notional single-spool turbojet with a low overall pressure ratio is modeled and simulated. Simulation results suggest that an ES/G, when used as an electric-assist motor during acceleration, can help the engine to accelerate roughly 11, 48, and 70% faster compared to the case without ES/G participation, by using electric power roughly equivalent to 0.1, 1, and 3% of full-speed fuel combustion power, respectively. Furthermore, the respective increase in the acceleration rate leads to an additional 19, 80, and 113% of propulsion impulse, respectively (i.e., thrust integrated over time), during the first 5 s following the acceleration command.