Time-resolved droplet size and velocity distributions in a dilute region of a high-pressure pulsed diesel spray

The principal objective of the present work is to experimentally investigate the time-resolved spray characteristics. Droplets data in a dilute region of a high-pressure diesel spray were obtained by employing the PDIA (particle/droplet image analysis) method with double pulse laser illumination. Eulerian specification was adopted to describe the transient spray microscopic behavior within a fixed test window at ten representative instants after triggering the injection. The experimental results indicate that the transient spray evolution can be characterized in three distinct stages. During stage I (the latency stage), the spray tip develops and reaches the test location, but no discrete droplets were clearly observed. During stage II, the spray passes through the test window, from which discrete droplets are observed to disperse in the dilute region and the SMD of the droplets increases rapidly. During stage III, bulk spray disappears in the test window and only discrete droplets were observed. The SMD of the droplets is decreased to a “steady-state” value. Based on these sampled and processed data, the droplet size distribution functions were obtained and compared with the Rosin-Rammler and the Nukiyama-Tanasawa function. Finally, the Stokes number and the Weber number of each droplet were determined, and the movement of the droplets were analyzed. The measured time dependent droplet behaviors are believed to provide important data for spray modeling and simulation.