Investigation On Design And Performance Of Scramjet Feed System Scheme

Fuel feed system is an indispensable part of scramjet system, and reseach on the fuel supply and control is very significant for the development of scramjet system integrated design and integration technology, and it has very important significance on the promotion of scramjet engineering process. In this paper, based on the kerosene regenerative cooling scramjet engine for working long hours, the fuel feed system scheme design and performance study is carried out.The fuel feed system design methods of kerosene regenerative cooling scramjet engine are developed, and the fuel feed system design flow chart is given. Its fuel tank pressurization system and turbo pump system design model are established. The particularity of scramjet fuel feed system is pointed out, and then fuel feed system of different pressurized ways are compared and the advantages and disadvantages of them are analyzed. The cycle way design of pump-fed system is carried out, and the characteristics of different cycle ways are analyzed. The pump-fed systems scheme through ethylene auxiliary start is designed. The start-up process and expansion cycle process during steady operation state are analyzed. Ultimately, the results show that, compared to pressurize-fed system, pump-fed system is more suitable for long working engine; thrust chamber exhaust cycle does not apply for scramjet, staged combustion cycle and gas generator cycle put forward higher requirements for engine design and spatial arrangement, increasing the complexity of the system; expander cycle engine coupled thermal protection and fuel supply system has higher advantages, such as simple structure, small quality, low turbo temperature, high reliability; the selection for switching point has important implications on the system start-up successfully, whether expander cycle is fully closed or not depends largely on the turbopump power matching balance.The analysis methods for thermophysical properties of supercritical kerosene are proposed. Number of the thermal cracking conversion rates based on moles and quality are respectively defined. The thermal cracking reaction model of supercritical kerosene is established, which is lumped single step reaction model based on temperature control. The thermal cracking characterristics of supercritical kerosene are analyzed. The calculation method for average molar mass of supercritical cracked state kerosene is established. Supercritical kerosene thermal properties model is built. The thermophysical property parameters of cracked and non-cracked kerosene under the supercritical pressure are calculated, and the thermalphysical properties of cracked kerosene under the supercritical pressure are fitted nonlinearly. Besides, based on the state equation, the calculation method of supercritical cracked kerosene density is established. What’s more, the analytic expression of supercritical cracked kerosene density is obtained with pressure and temperature varying.Supercritical cracked kerosene turbopump performance analysis model is built, and the kerosene pump power characteristics are analyzed, pump power requirements are obtained, the supercritical cracked kerosene turbine performance characteristics are analyzed. Moreover, turbopump performance test study is performed, the acting performance of different state working fluid turbopump are evaluated, and based on the experimental data, the flow coefficient of the turbine, the turbopump power and efficiency characteristics, the pump similarity laws and kerosene state influences on the turbine performance are analyzed. Results found, pump power requirement is within the output power of the turbine, the supercritical cracked state kerosene turbine can meet the power requirements of the pump; pump pressure head ratio and speed ratio of the square has a good similarity; the similarity law between pump flow and pump speed has relevance on throttle, and the flow rate ratio and speed ratio has better similarity under the the same pump throttling; the similarity law between pump power and pump speed has dual relevances on the turbo throttle and pump throttle; the thermal cracking conversion rate of kerosene below 800 K is very low, and the gas constant is smaller, expansion acting capacity is insufficient.The analysis methods for thermodynamic cycle characteristic of fuel supply system are presented, and thermodynamic cycle process of fuel feed system with kerosene as working fluid is ananlyzed. Then the regenerative cooling backheating model, the pressure loss model and hydrocarbon fuels endothermic model are established, the system balance parameters, turbopump power matching characteristics and cycle performance parameters are analyzed. The results show that, the coolant flow during expansion cycle need to meet the two conditions, that’s to say, the fuel flow rate of the cooling channel need to meet the cooling requirements of the engine, while cooling passage outlet supercritical cracked fuel reaches turbo expander acting needs; the pump pressurize performance is determined by pump speed; the performance of the cracked state kerosene turbine are mainly determined by the turbo expansion ratio and the outlet temperature of the cooling channel; turbo pump flow ratio must be less than one; increasing expansion ratio and thermal cracking conversion helps to improve thermal power conversion efficiency.