| An experimental investigation of the turbulent flow in a scale model of a high pressure diesel fuel injector nozzle has been conducted. Instantaneous velocity measurements were made in a fifty-times scale transparent model of one hole of the injector nozzle using an Aerometrics Phase Doppler Particle Analyzer (PDPA) in the velocity mode. The velocity data were analyzed for both average and spectral characteristics.; Length to diameter ratio (L/D) values of 1.3, 2.4, 4.9, and 7.7 and inlet radius to diameter ratio (R/D) values of approximately 0 and 0.3 were investigated. Two steady flow average Reynolds numbers (10,500 and 13,300), analogous to fuel injection velocities of 320 and 405 m/s and sac pressures of approximately 67 and 107 MPa (10,000 and 16,000 psi), were investigated. Also, a transient flow was investigated. Spatially resolved mean and rms axial velocities and discharge coefficients were obtained for steady flow in both sharp and rounded inlet geometries and varying L/D. Also, the spatial variation of the turbulence spectra was obtained for both steady and transient flows.; The results showed significant differences between the sharp and rounded geometry rms velocity characteristics. The sharp inlet geometries had, in general, higher rms velocities than the rounded inlet geometries. Also, for the sharp inlet geometries, the near-exit rms velocities near the wall showed an inflection in behavior L/D. The lowest exit near-wall rms values were seen at L/D of 4.9, and the rms values increased for L/D above and below 4.9. The spectral analysis results also showed differences between the turbulence spectra of the rounded and sharp inlets. The rounded inlet geometries had little effect on the spectral characteristics established upstream of the hole, which persisted to the exit of the longest rounded inlet hole investigated. The sharp inlet geometries, by contrast, "erased" the upstream spectral characteristics within approximately two diameters of the entrance. In short sharp-inlet holes, the upstream characteristics were "erased" at a location nearer to the inlet than in longer holes. |
