Enhancement mechanism of impinging atomization by gas injection

Impinging atomization, which has been widely utilized in liquid rocket propulsion systems, is able to produce fine drops at a rated operation. In contrast, however, the atomization characteristics deteriorate under off design conditions when injection velocity comes to be slower. In the present study, for improving atomization characteristics at off design operation, an effective technique is verified utilizing small amount of gas injection. The gas jet is supplied from a pressurized reservoir independent of the liquid supply system, and it is injected from the center of the liquid nozzles toward the impingement point. To clarify the flow field and the mechanism of the effectivity, experimental visualizations, drop size measurements and corresponding numerical analyses are carried out. It is elucidated that atomization is drastically promoted when the dynamic pressure of gas overcomes that of liquid at the impingement point. By the gas injection with the amount of only 1% of liquid mass flow rate, Sauter Mean Diameter (SMD) becomes one-tenth of the original SMD. In addition, the optimized atomization efficiency is achieved when the gas dynamic pressure is twice as much as the liquid at the impingement point.