Mission analysis and operational optimization of adaptive cycle micro-turbofan engine in surveillance and firefighting scenarios

The current work focuses on mission based evaluation of a novel engine architecture arising from the conversion of a micro turbojet to a micro turbofan via introduction of a variable speed fan and bypass nozzle. The solution significantly improves maximum thrust by 260%, reduces fuel consumption by as much as 60% through maintaining the core independently running at its optimum, and enables a wider operational range, all the meanwhile preserving a simple single spool configuration. Particularly, the introduction of a variable speed fan, enables real-time optimization for both high speed cruise and low speed loitering. In order to characterize the performance of the adaptive cycle engine with increased number of controls (engine speed, gear ratio, bypass opening), a component map based thermodynamic study is used to contrast it against other similar propulsion systems with incrementally reduced input variables. In following, a shortest path based optimization is conducted over the locally minimum fuel consumption operating points, based on a set of gradient driven connectivity constraints for changes in gear ratio and bypass nozzle area. The resultant state transition graphs provide global optimum for fuel consumption at a thrust range in a given altitude and Mach flight envelope. Then, the engine model is coupled to a flight mechanics solver supplied with a conceptual design for a representative multipurpose UAV. Lastly, the associated mission benefits are demonstrated in surveillance and firefighting scenarios.