2.2 Review of drop sizing techniques and spray characteristics

The atomisation of liquids is a process of great practical importance. It finds application in many branches of industry: mechanical, chemical, aerospace, metallurgy, medicine, agriculture. For different applications, people attempt to manipulate the spray by changing the operating conditions to satisfy their own demands. In order to understand how and why changes in operating conditions change spray characteristics, studies on the spray characterisation and the basic physical mechanisms involved in the formation of spray have to be carried out while the application is considered. Currently, the physical mechanisms of the Diesel spray formation are not completely understood. Also, in response to the demand on improving the performance of the sprays, new technologies are being explored. The sprays generated by these new technologies need to be characterised to provide necessary information for their applications.

In this study, sprays generated by a technically advanced injection system (common-rail injection system) are examined. Investigations into Diesel sprays characteristics have concentrated on the effect of the injection system parameters and ambient conditions (pressure, temperature, density, viscosity) and on global parameters such as the spray tip penetration, break-up length and droplet size and velocity distributions (Figure 2.2.1).

Figure 2.2.1: Spray parameters diagram