| In this thesis,aiming at the working characteristics of RBCC engine,the rule of energy utilization and conversion during RBCC ejector/ramjet mode transition process was studied with the method of exergy analysis based on the second law of thermodynamics.The effects on available energy during RBCC ejector/ramjet transition mode were investigated by changing ejector rocket propellant mixture ratio and proportion of fuel distribution between ejector rocket and afterburning chamber.Then the optimization scheme of realizing the efficient RBCC transition process from rocket ejector mode to ramjet mode was proposed.Firstly,the thermodynamic calculation model of RBCC internal flow passage and regenerative cooling system in rocket ejector mode were established.And the rule of RBCC energy utilization and conversion during this mode in different flight height and Mach number range was studied.It is indicated that the ejector rocket is the component which has the most exergy loss in RBCC and the exergy loss of regenerative cooling system is mainly caused by the convection heat transfer between kerosene in the cooling channel and exterior surface of thrust chamber.Moreover,such loss reaches the maximum near the throat of the nozzle in the ejector rocket.From the second law of thermodynamics,exergy efficiency can reflect the energy utilization and conversion of RBCC engine more accurately and comprehensively.Besides,it reveals the essence of energy loss in the system thermal process profoundly.Secondly,on the basis of the calculation model of RBCC ejector/ramjet transition mode,the effects on the fuel consumption of main components or subsystems and engine performance were investigated by changing ejector rocket propellant mixture ratio and proportion of fuel distribution between ejector rocket and afterburning chamber.The results show that when the combustion chamber of LOX/kerosene ejector rocket engine is in the state of oxygen enrichment,the exergy efficiency of RBCC engine can be enhanced by increasing the ejector rocket propellant mixture ratio and the chemical exergy can be transformed into kinetic exergy to the utmost at the same time.From the point of energy optimized utilization,with the purpose of reducing energy loss caused by the irreversible process in the RBCC engine,it is suggested that the fuel flow should be distributed reasonably between the ejector rocket and afterburning chamber.And the RBCC is recommended to work in the condition that the proportion of fuel distribution to the ejector rocket is 0.6~0.8.Furthermore,from the perspective of engine optimum structural design,when the propulsive efficiency of RBCC engine is at a certain level,the proportion of fuel distribution and the size of ejector rocket should be minified properly so as to reduce the flow resistance in the internal flow passage.It will also be helpful to broaden the speed domain of RBCC and improve the engine performance.Finally,based on criteria of thrust smoothing,the transition scheme of RBCC from rocket ejector mode to ramjet mode under the condition of specific flight mission and typical trajectory was presented.According to the fact that the exergy efficiency of RBCC engine experiences large step change at each mode transition point in this scheme,which wastes a great amount of available energy,an optimization scheme of realizing ejector/ramjet mode transition process was put forward from the view of decreasing the exergy loss of RBCC engine.The simulation results show that this proposed optimization scheme can not only ensure the thrust smoothing transition among different modes,but also reduce the exergy loss of engine at each mode transition point,which realizes the efficient RBCC transition process from rocket ejector mode to ramjet mode. |
