To meet the future demands on internal combustion engines regarding efficiency emissions and durability all design parameters must be optimized together.As a result of progress in material engineering fuel injection technology turbo charging technology exhaust gas after treatment there arise a multiplicity of possible parameters, such as: design parameters (compression ratio, dimensioning depending on peak firing pressure and mean effective pressure), injection system (rate shaping, split injection, injection pressure, hole diameter), air management (turbo charging with or without VTG, EGR rate) combustion optimization (timing, air access ratio). The interaction of all these parameters can not be over-looked without simulation and optimization tools. This is valid for the concept layout, the optimization and the application process later on.This paper will present the use of advanced engine cycle simulation tools to build up a virtual engine combined with an optimization tool to pick out the optimized combinations of parameters under defined restrictive conditions using the example of a Diesel engine. Besides the advantage of an integrated consideration of all relevant engine parameters this method helps to save time in development and cost.This paper presents a conceptual engine design using simulation techniques, that describes the whole thermodynamic working process of internal combustion engines, including NOx emissions. The investigated concept of an engine was a heavy-duty Diesel for use in trucks. The methods and procedures used here are also applicable to engine's using other fuels. The objective of the task described here was to determine the engine specification that provides the best possible fuel consumption for future emissions scenarios.