Preliminary Drop Size and Velocity Measurements in a Dense Diesel-Type Spray

A single-holed round nozzle with diameter of 127 μm, length-to-nozzle diameter ratio of 4, and fuel differential pressure of 13.6 MPa was used to generate a narrow, fast, steady Diesel - type spray of hexane into nitrogen at 1.46 MPa and 65.C. Effects of instrument variables of a Phase Doppler Particle Analyzer (PDPA) on the mean and rms of the drop axial velocity and SMD at a distance-to-diameter ratio of 410 were investigated. It was found that a seemingly good choice of instrument parameters based on SMD may not necessarily be appropriate for velocity measurements. Although all measured quantities tended to level out at sufficiently high values of the photo multiplier voltage, no such tendency was exhibited by changes in the shift velocity. Optical arrangements with smaller measurement volume showed less sensitivity to the instrument parameters and produced mean and rms velocities in agreement with 8% with those obtained with a single-component, dual Bragg-cell LDV system. The SMD decreased radially from 26 μm at the axis to 24 μm and then increased to about 32 μm where the mean velocity was virtually zero. Further drop size (and velocity) measurements are necessary at various axial locations, particularly closer to the nozzle where the spray becomes denser, possibly using different instruments such as the PDPA, the Malvern particle analyzer, the pulse height and visibility: technique (and LDV).