Measurement of the droplets sizes of a flash boiling spray using an improved extended glare point velocimetry and sizing

An improved extended glare point velocimetry and sizing (EGPVS) is proposed to investigate the droplets sizes of a flash boiling spray. When a spherical droplet with a relative refractive index from 1.16 to 1.41 is illuminated by two opposite laser sheets and a charge-coupled device camera is used to collect the s-polarization light at an observation angle of 90°, the intensities of the reflected lights are much stronger than the other order scattering lights. If the intensity of incident laser is controlled appropriately, two glare points from the reflected lights for the droplet are formed at the focused plane, while the intensities of the other order scattering lights are too weak to form any glare points. Then, the droplet diameter can be derived from the distance between the two glare points. In addition, the focused image is relative small, making it possible to measure dense spray. First, the characteristics of the improved EGPVS are discussed, and a series of standard particles are measured for validating this technique. Then, the technique is applied to investigate the droplets sizes of flash boiling spray. It is found that the minimum measurable diameter of droplets is 7.1 μm, and the relative error is less than 4.7 %. The droplet size distributions of spray are different at different stages. The Sauter mean diameter (SMD) of gasoline spray decreases gradually as the fuel temperature increases, which is different from that of a single-component fuel with a sharp decrease in SMD at the flash boiling stage.