Comparative analysis and normalization of single-hole vs. multi-hole spray characteristics: 1st report on spray characteristic comparison

The single hole injector, known for its simple design and ease of measurement, is widely utilized in optical spray experiments; however, multi-hole injectors are commonly applied in real engine applications. The structural differences between the two leads to variations in spray characteristics. This series of studies, based on the principles of similarity and normalization, proposes a theory for the transformation of spray characteristics between different hole numbers injectors. The 1st report investigates the spray characteristics of different hole numbers injectors under super high injection pressure conditions. Using the Diffuser Background Imaging (DBI) method, the experimental pressure range covers 100–300 MPa. The research indicate that the single-hole injector exhibits a shorter initial injection delay, while the multi-hole injector demonstrates a more stable injection flow rate and greater penetration. At higher pressures, the velocity increase, especially at 300 MPa. Higher ambient density has a suppressive effect on spray tip velocity and alters spray morphology. Moreover, it was observed that while the initial spray velocity of the single-hole injector is relatively higher, the penetration of the multi-hole injector significantly exceeds that of the single-hole injector in the later stages. For multi-hole injectors, interactions between adjacent sprays lead to a relatively narrower spray angle. The ratio of spray angle to cone angle for both injectors remain nearly unaffected by changes in density and injection pressure. In general, the Naber and Siebers model is better suited for predicting penetration in single-hole injectors under conditions of high density and ultra-high injection pressure (200–300 MPa). This study not only highlights the distinctive spray characteristics under super high pressure conditions but also offers valuable theoretical foundations and experimental insights for optimizing diesel engine design.