Investigation of droplet disintegration in diesel spray core by advanced laser 2-focus velocimeter

In order to get fundamental information about the droplet disintegration in the core region of diesel fuel spray, an advanced laser 2-focus velocimeter (L2F) was used for the measurements of velocity and size of droplets. The L2F with micro-scale probe has high optical SN ratio and high spatial resolution. Measured was the fuel spray injected into the atmosphere intermittently from a single hole nozzle. The diameter of the orifice was 0.2 mm. Measurements were conducted on four planes where the axial distances were 10, 20, 30, and 40 mm respectively downstream from the orifice exit. As the injection pressure and needle valve lift change unsteadily in case of the intermittent injection spray, time change of spatial distributions of velocity and size was measured and time change of the joint probability density associated with velocity and size was examined. It is confirmed that droplets with higher velocity and larger size increase with needle valve opening and also increase with injection pressure after the needle valve opens fully. The droplets with low velocity and small size injected at early stage of injection are caught up and passed by faster droplets injected later on near the position about 30 to 40 mm downstream from the nozzle orifice exit. It is found that droplets disintegrate and decelerate simultaneously in the core region.