Droplet size decrease rate of secondary breakup in diesel fuel sprays

Abstract

Targeting the evaluation of the universal droplet breakup process, measurements were made on diesel fuel sprays injected from two solenoid type injectors with different specifications. The velocity and size of the spray droplets were measured using a laser 2-focus velocimeter (L2F). The velocity of small droplets that follow the flow was taken as the air velocity. The Weber number was evaluated using the velocity of the droplets relative to air as the representative velocity. Since the spray expands in a conical shape with the nozzle hole at its apex, the measurement points were placed on a straight line from the apex, which is the estimated flight direction of droplets. The change in droplet size in the flight direction was considered to be due to secondary breakup, and the rate of decrease in droplet size during this process was evaluated. It was confirmed that the velocity and size of the droplets inside the spray injected from the two injectors varied over time, and the spatial distribution of the Weber number and the rate of droplet size decrease in the middle of the injection period was non-uniform and different. It was found that there is a positive correlation between the Weber number and the rate of droplet size decrease for both sprays, and that the relationship is nearly identical despite the fact that the characteristics are different between the two sprays. The secondary breakup process was shown to be independent of the injection conditions such as the diameter and number of nozzle holes.

Keywords

• diesel engine
• spray
• droplet size decrease rate
• laser measurement
• weber number