换热器预冷的空气涡轮火箭性能分析研究

Performance Study of Air Turbo Rocket Engine with Precooler

为了准确地分析以不同燃料为冷质的换热器预冷空气涡轮火箭发动机的性能,本文建立了可考虑工质组分化学平衡与工质热物性随温度和压力变化的热力循环模型。利用该模型分析了以LH2、LCH4和煤油为燃料的发动机循环性能,研究了预热温度、燃气发生器和主燃室出口温度对循环性能的影响。结果表明,换热器预冷能够降低压气机进口温度,减小相同增压比下的压缩功,提高燃料温度,减小推进剂流量,从而减小燃空比,增加比冲;燃料预热温度的提高可减小燃气发生器氧燃比,进而减小燃空比、增大比冲;较低的燃气发生器和主燃烧室出口温度可降低燃空比,提高比冲,但会造成单位推力的下降。同时,研究结果还表明,与LCH4和煤油相比,LH2的比热容与热值的比值最大,采用LH2预冷的发动机的飞行速度和比冲的增幅也最大,说明比热容与热值的比值越大,相应的预冷效果越好,即可依据燃料比热容与热值的比值定性衡量发动机的预冷效果。

A thermodynamic cycle model that considers the chemical equilibrium relationships of the fluid compositions and the effect of temperatures and pressures on the thermophysical properties of the fluid is established to investigate the performance of air turbo rocket engines with intake precooler.The cycle performances of three air turbo rocket engines,which adopt LH2,LCH4 and n-C_(10)H_(22) fuel respectively,are obtained by the model.And the effects of the preheated temperature of the fuel,the temperature at the outlet of the gas generator and the temperature at the outlet of the main burner on the cycle performance are analyzed.The results indicate that the inlet temperature of the compressor is decreased by the intake precooling using fuel.It results in a reduced compression work as the pressure ratio of the compressor is constant.Correspondingly,the temperature of the fuel is increased due to the heating effect of the air to the fuel.The higher temperature of the fuel tends to decrease the flow rate of the propellant.It causes the decrease of the ratio of the propellant flow rate to the air flow rate and the increase of the specific impulse.The results also show that the increase of the fuel temperature results in the decrease of the ratio of the oxygen flow rate to the fuel flow rate.A lower ratio of the propellant flow rate to the air flow rate is obtained.And the specific impulse of the engines is increased.The numerical results indicate that a lower outlet temperature of the gas generator and main burner trends to reduce the the ratio of the propellant flow rate to the air flow rate.It results in the increase of the specific impulse and the decrease of the specific thrust.Compared with the engines without precooler,the application of the precooler will upgrade the flight speed and the specific impulse of the engines.And the comparison among the LH2,LCH4 and n-C_(10)H_(22) fuels shows that the LH_2 fuel is more propitious to the enhancement of the flight speed and the specific impulse for the engines due to the higher ratio of the specific heat capacity to the heat value.It indicates that a higher ratio of the specific heat capacity to the heat value of the fuel will result in a better precooling effect of the engines.The ratio of the specific heat capacity to the heat value of the fuel can be used to evaluate the precooling effect of the engines.