Atomization Characteristics of High-Frequency Pulsatile Impinging Jets Based on Image Processing

In order to investigate the atomization characteristics of impinging jet injector under high-frequency pulsatile conditions, hydro-mechanical pulsator was used to generate pre-injection pressure perturbations. Backlit images of dynamic atomization field were captured by high-speed camera. An ordinary lens with long-distance focus was used to capture macroscopic atomization field, and a microscopic lens was used to capture microscopic atomization field. To solve the difficulty of the measurement of transient droplet diameter in high-frequency pulsatile atomization field, a method for capturing and measuring transient droplet size was established based on image processing. The variation rule of Sauter mean diameter (SMD) of droplets in local regions of high-frequency pulsatile atomization field with time was obtained. From a macro perspective, droplet distribution in space of natural atomization field is rather uniform. However, for the high-frequency pulsatile atomization field, the phenomenon of alternating distribution of dense and dilute region occurs. Regions with small grayscale values in macroscopic atomization field correspond to dense spray regions. From a microscopic perspective, droplet behaviors in these regions are more complex. Droplet collision and fusion, secondary breakup and other complicated physical processes occur in these regions. The appearance of complicated droplet behaviors in these regions leads to variation of droplet diameter and distribution in space, and it causes significant effects on combustion heat release. Variation of SMD in natural atomization behaves white noise characteristics. However, variation of SMD in high-frequency pulsatile atomization field behaves periodic characteristics and the frequency is consistent with that of the imposed forced perturbation. © 2022, Editorial Department of Journal of Propulsion Technology. All right reserved.