Effect of momentum ratio on hypergolic propellant atomization characteristics of liquid/liquid swirl coaxial injectors

The liquid-liquid swirl coaxial injector is an important component of the liquid rocket engines, serving to atomize and supply propellant. The momentum ratio of injectors could affect the spray characteristics and stability of the injector, thus affecting the working performance of rocket engines. Thus, studying the spray characteristics of injectors with different momentum ratios is helpful to design a high-performance injector. In this paper, the spray characteristics of liquid/liquid swirl coaxial injectors are studied by numerical simulation, and the working medium uses the hypergolic propellant unsymmetrical dimethylhydrazine (UDMH)/dinitrogen tetroxide (NTO). The velocity of the liquid/liquid swirl coaxial injectors under different momentum ratios is obtained, and the spray atomization properties under different momentum ratio conditions have been analyzed. The results show that the Sauter mean diameter (SMD) is more uniform at different times when the internal and external injector momenta are similar, which is conducive to the stability of the injector. The SMD distribution under different working conditions ranges from 230-270μm. With the increase of the momentum ratio, the mass flow rate of the inner injector decreases, this subsequently influences the spray cone angle and the post-collision and coalescence fragmentation span of the inner and outer liquid films. The working condition with a momentum ratio of 0.125 has the shortest breakup length and the best atomization, indicating that simply increasing or decreasing the momentum ratio does not necessarily optimize spray characteristics.