Study of Diesel Jet Variability Using Single-Shot X-Ray Radiography

Abstract

The variability of diesel jet structure, both as a function of time and between individual injection events, has important implications on the breakup and mixing of the jet. It is accepted that diesel jets become unstable due to interactions with the ambient gas, leading to breakup of the jet. This concept is the principle behind the Kelvin-Helmholtz and Rayleigh-Taylor models of diesel atomization. Very little information regarding diesel jet variability is available, however, in the near-nozzle region of the diesel jet, where primary breakup of the jet occurs. This is due to the presence of many small droplets, which strongly scatter visible light and render the spray opaque. X-ray radiography has been successfully used in recent years to probe the structure of diesel sprays with high spatial and temporal resolution. All of these previous measurements, however, were ensemble-averaged, measuring only persistent features of the spray. In the current study, measurements are performed at individual measurement points of single diesel injection events. These measurements are taken at several points near the injector exit for a non-hydroground nozzle with a single axial hole at two injection pressures (500 and 1000 bar). The variability of the start of injection, end of injection, and the time history of the spray density during the injection event are examined, as well as how these quantities change for different transverse positions across the jet.