ID 101

Fluctuations of droplet characteristics in diesel fuel atomization process

 

Abstract:

Droplet characteristics near the nozzle in diesel sprays are required to understand the atomization process and also to validate numerical simulation and breakup models. The breakup of droplets near the nozzle is mainly induced by turbulence, cavitation and aero dynamic force. Not only droplet size decreasing but also fluctuations on droplet velocity and flight angle occur in the breakup region. Several measurement techniques are developed but techniques which are able to obtain droplets properties near the nozzle where the breakup occurs are quite few. Laser 2-Focus Velocimeter (L2F) is one of the techniques and it is based on the measurement of time-of-flight and time-of-scattering when a droplet flies through two foci. The L2F measurements are conducted under 50 and 100 MPa injection pressures at the spray center, periphery and the middle of them at 5, 10 and 15 mm downstream from the nozzle. Time resolved velocities on spray axis are discussed with the velocity results from X-ray Phase Contrast Velocimetry (PCV) and the estimated velocity from mass flow rate measurements on the same injector system and operating condition. The velocity results from these measurement show good agreement. The velocity and size of droplets and fluctuations of droplets flight angles are characterized to discuss the relation on fluctuations and atomization. The results show that the standard deviation of velocity and size are high near the nozzle at spray center where the droplets size is relatively large. Also, there are high fluctuations on droplets flight angle compared to that at periphery.