Spray characteristics of an impinged diesel fuel spray.

摘要

The purpose of this study was to investigate the effect of utilizing the spray impingement technique as a method of secondary atomization by intentionally impinging a diesel fuel spray on a raised surface (pedestal) in order to enhance the fuel injection process. The specific goal was to observe a non-vaporizing spray under a variety of pedestal parameters and ambient conditions and to measure droplet size, velocity, and spray distribution before and after spray impingement in both a quiescent spray chamber and motored single-cylinder engine.; The pre-impingement (free-) spray was investigated in order to verity if any obvious characteristics in the pre-impinged spray might influence the post-impingement results. It was found that a free-spray which appears symmetric can exhibit high degrees of asymmetry after impingement. Since high momentum goes with dense spray/liquid core regions, the asymmetry of these regions in the free-spray could be the source of post-impingement asymmetry.; In the atmospheric pressure spray chamber, two distinct post-impingement spray formations were identified by the laser light sheet spray visualization technique. Both spray formations contained both a dense spray region as well as what appeared as “bigger” droplets penetrating outward at small angles of incidence. The spray penetration was much greater for the “bigger” droplets than for the dense spray region.; In the motored engine, contours of the spray images showed that spray penetration proceeds quickly at first and then slows down for later times. For all cases, higher boost pressure (higher ambient density) yielded shorter spray penetration. For higher pedestal heights, the post-impingement spray is bounded by the engine head on the upper side which restricts spray development in that direction and causes much of the spray cloud to form below the top of the pedestal.; PDPA data was acquired for both post-impingement spray formations in the atmospheric pressure spray chamber. Positive/negative normal velocities for both formations identified a spray vortex as it passed the measurement location. Radial velocities peaked in the same plane as the top of the pedestal, which is the location of the highest spray momentum based on the spray images. Magnitudes of raw droplet diameters appeared essentially uniform across all radial locations, and most droplet diameters were 25 μm.