Measurements of Fuel Vapor Concentration in a Diesel Spray by Image Analysis of a Reconstructed Hologram

A diesel spray in a high-pressure and high-temperature atmosphere was recorded by pulsed-laser holography. The schlieren and shadow images of the same spray obtained from a reconstructed hologram were analyzed, and the concentrations of fuel vapor and droplets in the spray were measured. The radial distribution of the fuel vapor concentration shows a low value at the center and the edge of the spray, and takes a maximum between them. At the section where a relatively large eddy is produced around the spray, the fuel vapor concentration increases in the whole section, and takes two maximums corresponding to the structure of the eddy flow. The axial distribution of the fuel vapor concentration shows a gradual increase in the upper stream of the spray, whereas in the lower part of the spray it shows sudden increase and decrease repeatedly due to the eddies around the spray. The axial distribution of the total fuel (vapor and droplets) approximately agrees with the calculated result by the momentum theory in the lower part of the spray.