Experimental and theoretical study on the break phenomenon of self-pulsation for liquid-centered swirl coaxial injectors

Experimental observations together with theoretical analysis were conducted to investigate the break phenomenon and the corresponding mechanisms of self-pulsation for a liquid-centered swirl coaxial injector with recess number of RN=1.Instantaneous spray images were obtained based on background light imaging technology with a high-speed camera.By dynamic analysis of the flow process of the liquid sheet in the recess chamber,a 1D self-pulsation theoretical model was established,and the self-sustaining mechanisms of self-pulsation were analyzed in depth.The results show that the increase of the momentum flux ratio will lead to the occurrence of the break phenomenon of self-pulsation for the injector with a larger recess length,and the frequency and intensity of self-pulsation before and after the break phenomenon differ significantly.The flow dynamics in the recess chamber sequentially transform from a periodic expansion-dominated flow to a stable flow,and then develop to a periodic contraction-dominated flow during the break process of self-pulsation.With the occurrence of self-pulsation before the break phenomenon,the liquid sheet has little effect on the pressure disturbance in the recess chamber.In contrast,with the occurrence of self-pulsation after the break phenomenon,the pressure disturbance is obviously affected by the liquid sheet.Based on the theoretical analysis model of self-pulsation,the self-pulsation frequency can be predicted.Furthermore,the self-sustaining mechanism of self-pulsation before and after the break phenomenon is preliminarily confirmed.The energy transfer between the gas-and liquid-phase is an important factor for maintaining the self-pulsation process.