The break phenomenon of self-pulsation for liquid-centered swirl coaxial injectors

Abstract

Self-pulsation boundaries that spray switches between stable and self-pulsated behaviors are experimentally obtained under water and air flow conditions for a liquid-centered swirl coaxial injector configured with different recess lengths. The underlying mechanisms responsible for self-pulsation are investigated comprehensively. Results show that for the non-recessed injector, self-pulsation only occurs in a relatively narrower region, associated with weaker spray oscillation with the amplitude less than 2 mm2/Hz correspondingly. In particular, for the injector with larger recess length, a break region is generated with increasing the momentum flux ratio. It is indicated that spray transforms from the self-pulsated behavior to the stable behavior, and develops into self-pulsated behavior once again. The break phenomenon of self-pulsation reveals a destabilizing/stabilizing effect created by the violent gas-liquid flow dynamics. Self-pulsation occurring on either side of the break region is found to be caused by different mechanisms. As such, self-pulsation of the liquid-centered swirl coaxial injector is classified into two types. The first type occurs in the injectors configured with relatively small recess length, or with large recess length before the occurrence of the break phenomenon. This self-pulsation is caused by the periodic blockage of the conical liquid sheet. Whereas, the second type is attributed to the periodic squeezing influences of annular gas on the conical liquid sheet, corresponding to the self-pulsation occurring in the injectors with larger recess length and after the disappearance of the break phenomenon.