Study on Fuel Droplet Disintegration at early Stage of Injection by means of Semiconductor Laser 2-Focus Velocimeter

摘要

In order to investigate the droplet disintegration in diesel fuel spray in the early stage of injection, a laser 2-focus velocimeter (L2F) was adopted for the measurements of velocity and size of droplets. The distance of two foci of the L2F was only 36μm. The droplet velocity was estimated by dividing the distance between two foci by the measured time-of-flight between two foci. The droplet size was estimated by the measured time-of-scattering based on the relation that the ratio of the time-of-flight and the time-of-scattering corresponds to the ratio of the distance between two foci and the droplet size. The fuel spray injected atmosphere intermittently from a single hole nozzle. The diameter of the orifice was 0.2 mm. Measurement was conducted on 4 planes where the axial distances are z = 10, 20, 30, and 40 mm respectively downstream from nozzle orifice exit. The disintegration process of the fuel droplet was investigated by the difference in the probability density of droplet velocity and size between measurement planes. It is found that the disintegration of fuel droplet on the spray axis occurs remarkabley between the measurement planes of z = 20 and 30 mm. On the other hand, the disintegration occurs at the spray off-axis region between z = 10 and 20 mm. It is deduced that disintegrated droplets on the spray axis reach the spray off-axis region on the plane of z = 40 mm.