A New Approach to Model DI-Diesel HCCI Combustion for Use in Cycle Simulation Studies

An approach to accurately capture overall behavior in a system level model of DI Diesel HCCI engine operation is presented. The modeling methodology is an improvement over the previous effort [36], where a multi-zone model with detailed chemical kinetics was coupled with an engine cycle simulation code. This multi-zone technique was found to be inadequate in capturing the fuel spray dynamics and its impact on mixing.

An improved methodology is presented in this paper that can be used to model fully and partially premixed charge compression ignition engines. A Computational Fluid Dynamics (CFD) driven model is used where the effects of fuel injection, spray evolution, evaporation, and turbulent mixing are considered. The modeling approach is based on the premise that once the initial spray dynamics are correctly captured, the overall engine predictions during the combustion process can be captured with good accuracy. In this technique two numerical grids of different resolution are used sequentially during the closed portion of the engine cycle. The initial spray evolution is captured on a refined grid and the solution is later mapped on to a coarse grid when chemical kinetics dominates. The closed portion of the engine cycle is interfaced with a commercial cycle simulation code to account for the gas exchange process. The whole process is automated and the improvements in computing time results in a practical tool for controls modeling in Diesel HCCI applications. The results from this new approach show good agreement of the overall cylinder predictions when compared with experimental data and detailed numerical simulations. The benefits and deficiencies of using this approach in cycle simulation studies are discussed. An example of using this methodology in DI-HCCI transient simulations is also presented by comparing two effective control strategies.