Cryogenic Flow and Atomization from a Coaxial Injector

The global flow characteristics of the cryogenic flow injected from a single-element coaxial injector have been examined experimentally to simulate the flow andmixing behavior before ignition and combustion in characteristic rocket engines. The injector simulated one element of the cryogenic rocket engine injectors under realistic operating conditions. This work focuses specifically on the evolution of liquid nitrogen jet instability, spreading, and its atomization and mixing with the surrounding coaxial gaseous jet under steady-state atmospheric conditions. The effect of some important flow parameters, such as velocity ratio and momentum ratio between jets, on the potential core length of the liquid nitrogen jet and shear angle of the flow have been analyzed. The results showed a significant role of these parameters on the instability and breakup of the liquid nitrogen jet, along with the strong heat transfer effect of the surrounding atmosphere on the cryogenic liquid nitrogen jet. The shear angle of the flow remained constant along the longitudinal axis of the injector, thus confirming fully developed steady-state jet under atmospheric conditions. The mean value of the shear angle showed the transcritical nature of the liquid nitrogen jet under atmospheric conditions. The shear angle of the flow also reduced with introduction of the helium jet and decreased uniformly with increase in helium jet velocity, which supports the effect of surrounding gas density on the jet spreading as predicted by previous researchers. The potential core length of the cryogenic liquid nitrogen showed a local peak as a function of velocity of the gaseous jet and decreased exponentially with momentum ratio for values close to and higher than one.