The objective of the present study is to propose a consistent procedure to describe the hydrodynamics of the droplet and gas phases within a liquid spray. To illustrate the method, the characteristics of a full cone spray are finely measured by using the phase Doppler interferometry for different operating conditions. A laser tomography
technique is applied as visualisation support. On the basis of the extensive local data base, it can be shown that
appropriate choice of relevant dimensionless quantities reveals similarity behaviour in the profiles of the local
mean droplet diameter, liquid and gas velocity. It becomes possible to formulate a general description of the spray
development as is usually done for free single jets and to derive correlations for macroscopic quantities as for
instance gas flow entrainment. Such a methodology allows to gain more comprehensive physical understanding of
this two-phase flow and leads to efficient analytical tools providing a strong support for validation of numerical
codes and for industrial design.