L2F Measurements of Diesel Fuel Spray for Numerical Simulation of Atomization

抄録

L2F (Laser 2-Focus Velocimeter) has been utilized for the measurement of velocity and size of droplets in diesel fuel spray injected from a single-hole nozzle. The L2F had a micro-scale probe which consists of two foci. The focal diameter was about 3 μm, and the distance between two foci is 20 μm. Diesel fuel sprays were injected intermittently by using a common rail injector. The diameter of the nozzle orifice was 0.125 mm. The injection pressure was 100 MPa, and the ambient pressure was changed from 0.1 to 0.7 MPa. The spray image was taken by a CMOS camera with a resolution of 1.62 million pixels in the xenon lamp lighting with a period of 180 ns. The L2F measurement was conducted at 13 mm downstream from the nozzle exit. The velocity of droplets near the spray center was higher than the one at the spray periphery. The change of droplet velocity was small with the increase of ambient pressure at the spray center, and the velocity of droplets at spray periphery decreased with the increase of ambient pressure. The size of droplets at the spray center was larger than the one at the spray periphery. The size of droplets decreased with the increase of ambient pressure inside the spray, especially, the amount of decrease in size was larger at the spray center. The characteristic velocity of the Weber number was the difference between the droplets velocity and the air flow velocity which was defined as the velocity of droplets less than 3 μm. It is understood that the increase in the Weber number due to the increase in the ambient density enhances the atomization of large droplets. These findings are thought to be applied to the initial condition and evaluation of numerical simulation of atomization.