Experiment on effect of free jet length on impinging atomization of gel propellant

In order to study the effect of free jet length on impinging atomization of gel propellant, an impinging atomizer was designed, and gelled kerosene and corresponding waterbased simulant were prepared. Discharge coefficient of the injector and the viscosity and stability of the simulant were measured. Impinging atomization experiments were conducted under different free jet lengths for three jet velocities. Spray behavior of the jet and impinging sheet was observed. The breakup length, droplet distribution and SMD(Sauter mean diameter) were obtained. Relative results indicated that increasing free jet length resulted in great change of spray behavior of impinging sheet when jet velocity was low. But spray behavior nearly kept the same at high jet velocity. For three jet velocities, breakup length located between 45mm and 9mm, and decreased with the free jet length. Droplet distribution was in accordance with RosinRammler relation with a high fitting accuracy. All the evenness indexes were between 3 and 4, and gradually declined with the free jet length implying a reduced evenness of droplet diameter. SMD increased with the free jet length at higher jet velocity. In the case of lower jet velocity, SMD decreased at first and then increased slowly. There is an optimal value for free jet length, and the value equals to 25/3 at present. As a result, when designing an impinging injector, better atomization quality can be reached by applying an optimal free jet length.