The influence of cavitation on the internal flow and the spray characteristics in diesel injection nozzles

A study was carried out on the influence of cavitation on the internal flow and the macroscopic behaviour of the spray in Diesel injection nozzles. For this study, two bi-orifice nozzles were used, one cylindrical, and the other convergent (conical). From the point of view of cavitation, the two chosen nozzles are very different, as the first nozzle is much more inclined to cavitate, whereas the second nozzle inhibits the cavitation phenomenon. First, in order to find the exact internal geometry of the two nozzles, a non-destructive characterisation method is used, which is based on the creation of silicone moulds. Once the nozzles are characterised dimensionally, a hydraulic characterisation is made. The results of this hydraulic characterisation, together with the predetermined dimensional characterisation, enable the discharge coefficient and the critical cavitation conditions to be determined. By identifying the critical cavitation conditions, it is possible to complete a study of the macroscopic parameters of the spray, with cavitating and non-cavitating conditions, and therefore a study can be carried out examining the influence of cavitation on the macroscopic spray behaviour. From the point of view of the spray macroscopic behaviour, the main conclusion of the paper is that cavitation leads to an increment of the spray cone angle. On the other hand, from the point of view of the internal flow, the hole outlet velocity increases when cavitation appears. This phenomenon can be explained by the reduction in the cross section of the liquid phase in the outlet section of the hole.