The objective of the injection system in Diesel engines is the delivery of a 
high-quality air-fuel mixture, in such a way that an efficient combustion is 
achieved whilst minimising pollutant emissions. Among the different parameters that 
control the injection process and the formation of the fuel spray, momentum flux 
stands as one of the most important ones. Many important spray parameters depend to 
a large extent on it (e.g. penetration, angle and air entrainment). Furthermore, 
with respect to the  injection nozzle internal flow study, the measurement of this 
parameter provides much more information than that obtained from simply measuring 
mass flow, since the use of these two measurements makes it possible to obtain such 
important parameters as exit velocity and effective flow section. However, and 
despite its proven usefulness, momentum flux measurement has not been widely used so 
far, mainly due to the difficulty in measuring it.

Basically, this thesis has met two different objectives. Firstly, the development 
and implementation of a momentum flux measurement system based on the measurement of 
the spray impact force. Secondly, and more important, the use of this measurement in 
the experimental study of injection processes, which has proved to be a very useful 
tool for understanding the different phenomena involved in the injection process. As 
a result of this research, some important conclusions are drawn about the influence 
of hole geometry and the phenomenon of cavitation on injection systems.