Simulation Based Development of Combustion Concepts for Large Diesel Engines

The development of low-emission combustion concepts for large Diesel engines requires a specially adapted methodology. In all phases of the development process, it is essential that appropriate tools are used so that an optimized solution can be found within a short time. This paper will describe the methodology used for developing combustion concepts for large Diesel engines. In general, the development of a combustion concept for Diesel engines comprises the definition of the system (e.g. combustion chamber geometry, injection system, EGR system and charging system) and the calibration of engine parameters (e.g. injection parameters, EGR rate, charge pressure, excess air ratio and valve timing) for an application and its emission scenario. In the present case, the main objective was to develop concepts for applications to comply with emissions standards according to EU Stage III B and US EPA Tier 4. To this end, the LEC has developed the LDM method (LEC Development Methodology). This method is based on the intensive interaction of simulation with experimental investigations on single-cylinder research engines. As part of this development methodology, 3D CFD simulation as well as 0D and 1D engine cycle calculation are employed. Another approach used to handle the complexity of the systems is Design of Experiments (DoE) for simulation and experimental work. While 3D CFD simulation is used to optimize the details of the combustion and pollutant formation processes in the combustion chamber, 0D and 1D engine cycle simulation is applied to select the concepts and to pre-optimize important engine parameters. One great advantage of 0D and 1D models is their short calculation time, which allows the investigation of a great amount of variations in parameters. In order to apply the methodology, it must be guaranteed that the results from tests on the single-cylinder engine (SCE) can be transferred to the multi-cylinder engine (MCE). Therefore, it is necessary that the boundary conditions of the SCE are comparable to those of the MCE. Not only the same thermal boundary conditions but also the same conditions at the beginning of the high-pressure cycle (charge composition, pressure and temperature) must be maintained. The SCE measurement results that are generated serve to verify and calibrate the simulation models and deliver the necessary boundary conditions for further simulations. All in all, the paper comprises an evaluation of the different simulation models used and the applied development methodology in order to optimize fuel consumption and to reduce the emissions of large Diesel engines.