Relation between Tip Penetration and Droplet Size of Diesel Spray

A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel sprays. The L2F has a micro-scale probe which consists of two foci. Diesel fuel was injected intermittently into the atmosphere by using a 6-hole injector nozzle. The diameter of the nozzle orifice was 0.135mm. The injection pressure was set at 80MPa. Measurement positions were located at 5, 7, 10 and 15mm from the nozzle exit. The measurement result showed that the velocity of droplets at the spray center was the highest, and decreased in the direction towards the spray periphery. The size of droplets at the spray periphery was larger than the one at the spray center. The size of droplets decreased in the direction of droplet flight on the near nozzle plane. It is understood that the breakup of droplets occurred. The size of droplets increased in the direction of droplet flight at the spray periphery on downstream planes. It is understood that the coalescence of droplets occurred. The image of spray was taken by a camera. Each penetration length was measured by averaging 5 images which were taken with same time. The acceleration of spray front is taken as the second derivative of time variation of penetration length. The acceleration of spray front decreased on near-nozzle planes, and increased at the spray periphery on downstream planes. The acceleration of spray front increased at the position where the size of droplets increased. It is understood that the size of droplets is related to the spray penetration.