DNS with detailed and tabulated chemistry of engine relevant igniting systems

摘要

Developments in modern engine technology are moving towards a regime with fuel injection uncoupled from combustion. Auto-ignition is an essential characteristic in these systems. The accurate prediction of this chemical process is of paramount importance. Tabulation techniques can provide a detailed chemistry description which is needed to represent the subtle processes that occur during ignition. Strictly, only chemical sources are stored in a look-up table, while assumptions have been made about the mixing process in this pre-processing step. In this study, the validity of Flamelet Generated Manifolds (FGM's) in a series of canonical configurations representative for compression ignition combustion processes is investigated. To this purpose, the FGM approach is applied to OD perfectly stirred reactor (PSR), igniting ID counterflow diffusion flame (CD-flame) and igniting 2D mixing layer simulations for a wide range of relevant engine conditions. An FGM table generated with homogeneous reactor simulations is able to correctly predict reaction progress in PSR cases which include mixing. On the other hand, an FGM table generated with a single igniting CD-flame at a constant strain rate predicts the trend in auto-ignition delay for varying strain rates qualitatively correct. Ignition in a 2D mixing layer, where a straining field due to vortical structures exists, is also well predicted with this FGM. To improve the quantitative auto-ignition prediction near the ignition limit, an extra controlling variable is needed.