Author is pointing at possibilities of the utilisation of simulated computations (i.e. theoretical experiment) for research and development of The diesel engines. Modern technical potential of them is discussed in opening part of the paper with emphasis on Electronic Diesel Control with control of the electromagnetic injector valves, PLD, PDE, VP and mainly the Common Raił (CR) injection systems, the Latest Fuel Injection Technology, EGR and so on. Examples of optimisation analysis of three control parameters of TDI-CR engines arę presented in the main part. Output variables arę thermodynamic, dynamie, economic and ecological engine properties.