ID 366

Mixing process of the fuel droplet near nozzle under high temperature and high pressure conditions

 

Abstract:

To further understand fundamental mechanisms of the mixture formation, a single component fuel (n-dodecane) was injected into a high temperature and high pressure constant volume chamber by a single-hole injector with the diameter of 0.28 mm. The high speed CMOS camera equipped with a long distance microscope and a diode pulse laser was employed to record the near-nozzle droplets behavior during the end injection (EOI). During the end-of-injection transients, the droplets oscillating, ligaments rotating and breaking up into spheres were observed, owing to the low penetration velocity and sparse distribution of the droplets. When the droplets were injected into the 900 K and 4.0 MPa ambient condition, the diameter of the droplets reduced continuously, without noticeable change in droplet shape, indicating the surface tension confining the liquid to a sphere shape. However, when the droplets were injected into 1000 K and 4.4MPa ambient condition and above, the droplets exhibited a qualitatively different behavior. After the injection, the high temperature ambient gas, the edges of the droplets became blurred, but the droplet like structure could split into small droplet like structures, indicating the reduction of the surface tension. With the droplets continued to be heated, a quick and noticeable irregular shape changing was recorded by the camera, demonstrating the diminishment of surface tension. The injected cool liquid droplets that exhibited surface tension effect at first, and then, after heated by the high temperature ambient gas, transited to a diffusion controlled supercritical regime.