Nonlinear Behavior Analysis For Air-turbo Ramjet Engine Under Double Compression Mechanism

Air-turbo ramjet(ATR) is a combined propulsion system. It has become a hot research topic in foreign countries because of its good performance and application potential. Unlike ramjet engine, after compressed by the shockwave in the inlet, the air flow will be further compressed by the compressor. The working substance that drives turbine is fuel-rich gas produced by a gas generator or high temperature fuel after absorbing heat in the heat exchanger. The inlet unstart and working mode conversion has always been an important content for the research of the ramjet engine. Due to introduction of the rotor system, the interaction between combustion chamber and the inlet of ATR engine as well as working mode transformation way is changed. To this end, this paper establishes the mathematical model, and analyzes the nonlinear behavior of the ATR engine under the coupling action of the multi compression mechanism.Firstly, the steady state mathematical model of non design point of ATR engine is constructed. The engine designed does not use any control system. Given flight conditions and fuel flow as the independent variables, the internal parameters of the engine and working status of the compression system can be determined by blocking mechanism, rotor system matching model and so on.Then using the steady state model, calculate the working status of the compression system with the change of fuel flow under certain conditions. A general conchusion of the operating mode conversion of ATR inlet is obtained. The working status of ATR engine under different conditions is simulated. And analyse the effects of flight conditions and nozzle throat area on operating characteristics of ATR engine. The special nonlinear phenomenon of the engine under the condition of low altitude and high Mach number, when the compressor operation is not obvious, is also obtained.Finally, based on the actual working process of ATR engine, set the isobar in which the design flight conditions locate as the flight trajectory. The working performance of ATR engine along the flight path is simulated and analysed. The operating mode conversion of the inlet and the working status of the compression system during whole process are obtained. Different modes of inlet operating conversion are classified, and different flight zones correspond to different modes. This provides a theoretical basis for the introduction of control system and the improvement of the stability for ATR engine.