The optimization of mixture formation in diesel engines requires precise knowledge of the mechanisms of spray atomization and the correlation between injection and engine operating conditions and the parameters of the injection spray. The influence of the fuel properties will be shown considering both the temperature in the high-pressure chamber and the injection pressure as important variation parameters. A global temporally resolved visualization of the injection sprays is realized and information about the droplet size distributions in the spray are obtained by means of locally highly resolved laser-based measurement techniques. The low proportion of low-boiling components in heavy fuels is a significant cause for a deteriorated mixture formation. Higher temperature in the combustion chamber and higher injection pressure have a positive influence on the spray development as well as fuel evaporation.