X-ray micro-Computed Tomography for Cavitating Diesel Nozzles

The flow inside a purpose build enlarged single-orifice nozzle replica is quantified using X-ray micro-computed tomography (micro-CT) and high speed visualisation. Results have been obtained at Re and CN numbers similar to those of real-size injectors. Moreover, the effect of fuel degassing on the cavitating flow has been examined. The results indicate that the time-averaged micro-CT flow structure is comparable to the mean 2D projected image of cavitation, as captured by the high speed camera. However, the internal structure of the developing cavitation cloud exhibits significant differences. A hollow ring is formed at the hole entrance while cavitation extends only at the lower part of the hole due to the asymmetric flow entry, showing a significant gradient in cavitation volume fraction. The cavitation number seems to be the most influential operating parameter when compared to Reynolds number. At the same time, the effect of fuel degassing seems to be marginal. Overall, the study demonstrates that use of micro-CT can be a reliable tool for fundamental studies of cavitation in nozzle orifices.