Diesel Spray Structure Investigation by Laser Diffraction and Sheet Illumination 920577

Intermittent and highly transient dense diesel sprays were investigated using laser diffraction and laser sheet illumination techniques to decipher the internal spray structure. Through careful experimental design, the unperturbed structure of the dense core region of a transient full cone diesel spray was observed for the first time. Diffraction measurements showed that larger droplets exist at the spray periphery and the Sauter mean diameter decreases from the periphery to the spray centerline. The results from both laser diffraction and 2-D imaging are inconsistent with the existence of an intact liquid core extending to a few hundred nozzle diameters. The intermittent and highly transient nature of diesel sprays ensures rapid and complete atomization within no more than twenty nozzle diameters. Due to high number density and multiple scattering, two dimensional images of diesel sprays obtained using excessive laser energy and camera exposure, or using line-of-sight techniques such as shadowgraphy, can mislead the observers into interpreting the saturated region of the image as an intact liquid core.