Research On The Dynamic Characteristic Of Injecting System In Liquid Rocket Engine

The dynamic characteristics of injecting system in liquid rocket engine is studied quantitatively for the purpose of establishing a criterion of combustion instability.The dynamic characteristics and transfer function of different types of injectors is analyzed,the influence of structure in injectors is discussed.The combustion stability of one specific liquid rocket engine is analyzed by means of the method of this paper.To build the transfer function of liquid swirl injector,the theoretical method of Bazarov and Yang Lijun is summarized.Liquid swirl injectors are divided into six types by different structures,for each the dynamical function is derived.The influence of parameters of structures on the dynamic characteristic of injectors is discussed.Rocker and Hutt's numerical method for liquid coaxial injector's dynamic characteristics is introduced,the dynamic characteristics of coaxial injector in different conditions is computed,the influence of throttling hole in coaxial injector on the dynamic characteristics is analyzed and a formula of natural frequency of coaxial injector with throttling hole is derived.The formula of natural frequency of gas coaxial injector is derived after the modeling of the dynamic system of gas coaxial injector,with the consideration of the velocity of the gas in the injector.The results of theoretical and experimental method of the gas coaxial injector are compared.The dynamic characteristics of liquid swirl injector,liquid coaxial injector and gas coaxial injector are compared and have been expressed in matrix form,the criterion of injection coupled instability is derived.Some advises for combustion instability are given.The results show that:(1)the dynamic characteristic of open-ended swirl injector is better than that of close-ended swirl injector.(2)both the length of the swirl chamber and the location of the tangential inlet can be designed for specific dynamic characteristic in swirl injector.(3)length of the injector is the most significant parameter for the dynamic characteristic in both gas and liquid coaxial injector.(4)the boundary condition of gas coaxial injector is of great significance for its dynamic characteristic.(5)the throttling hole shows important influence on the dynamic characteristic of liquid coaxial injector,which can be designed for specific dynamic characteristic in liquid coaxial injector.(6)the transmission of waves is the most important factor of the dynamic characteristic in all injectors.(7)the distribution of combustion has an impact on combustion stability.