Simultaneous Flow Field Measurement of D.I. Gasoline Spray and Entrained Ambient Air by LIF-PIV Technique

The spray and the entrained ambient air motions produced by a swirl-type D.I. gasoline injector were simultaneously measured by combining the laser induced fluorescence (LIF) and the particle image velocimetry (PIV) techniques. For the simultaneous measurement of the spray and the ambient air velocities, the succeeding two image pairs of the fuel spray and the ambient air tracer particles were captured by using a Nd:YAG laser light sheet (wave length: 532 nm) and two high-resolution CCD cameras. The light emitted from the fluorescent tracer clouds was discriminated from the light scattered from the droplets in the fuel spray by an optical low-pass filter (>560 nm), and the Mie scattering signals from the spray particles were screened by a band-pass filter ranging from 520 to 545 nm. The spray and the tracer particle images were analyzed by the double frame cross-correlation PIV technique to obtain the droplets and ambient air velocity distributions. It was confirmed that the LIF-PIV technique is effective in the assessment of the ambient air motion in and around the spray. The ambient air motion induced by the spray is the large-scale bulk motion symmetrically to the spray axis, and there is a difference between the vortex center of the spray and the center of the ambient air bulk motion. The high relative velocity area in the main spray appears at the location a little downstream of the leading edge of the main spray, inside of the vortex-like structure, not at the leading edge of the spray.