Design and operation variables as well as fluid properties in fuel injection systems are investigated in an experiment that studies their influence, mutual interactions, and optimum values for atomization. Discussion is centered on measurements of discharge coefficient and spray angle for the typical range of diesel injection. Both plain-orifice and swirl atomizers are investigated and compared. It was found that, although producing a narrower spray angle, plain-orifice atomizers had, in some cases, as good a performance as swirl atomizers while allowing for a considerably higher flow rate.Correlations are obtained for discharge coefficient and spray angle for fuel injection as a function of eight different dimensionless variables. Recommendations are made for improved design of fuel injectors.