Modern electronic engine control systems allow manipulation of many control parameters in order to meet the emissions standards at reasonable fuel consumption. The great number of engine variables lead to very time consuming and expensive studies to determine the optimal combination at each engine operating condition. Compared with the possibilities to control the injection, the quantitative effects of parameter variations on the real processes in a operating combustion chamber and its effects on emissions and fuel consumption are little known.The first part of this paper deals with the problem of optimization of a complex engine control system in a DI-diesel engine.In the second part of this paper a novel optical diagnostic technique is proposed to detect combustion-relevant and controllable parameters such as spray propagation, droplet size and density distribution during injection in a DI-diesel engine combustion chamber. The results of an analysis of soot deposition on sapphire windows are presented. First results of in-cylinder measurements such as the spectral distribution of the combustion luminance are shown as well.