Study on the dynamic response of a pressure swirl injector to ramp variation of mass flow rate

Abstract

The response of a pressure swirl injector to ramp variation of mass flow rate is numerically and experimentally investigated. Numerical simulation based on volume of fluid method was conducted to obtain the response of the two-phase flow inside the injector. In experiments, ramp variations of mass flow rate with different slope were introduced into the swirl injector through a throttleable cavitating venturi nozzle. Backlit photography technique and laser diffraction technique were adopted to capture the spray and measure the size distribution of droplets respectively. The relationships between mass flow rate at the injector inlet and transient parameters (such as mass flow rate, air core diameter, axial and tangential velocities) at the injector exit were analyzed. Besides, the effects of throttling rate were discussed. The results indicate that the mass flow rate, air core diameter, velocities at the injector exit, spray angle and the sauter mean diameter vary almost linearly with mass flow rate at the inlet. It is found that the responses of inner flow, spray and size distribution of droplets are delayed. Larger throttling rate results in larger time lag. The numerical results show that the inner flow response quickly and the time delay is small when compared with the external flow. Phenomena, such as anti-regulation and overshoot of the film thickness at the exit, are observed. The anti-regulation was thought to be related with the anti-regulation of combustion which was observed in hot tests.