Prediction of non-premixed combustion regimes in direct injection compression ignition engines

Dissipation element analysis offers a methodology to investigate turbulence-chemistry interactions in non- premixed combustion. A dissipation element based combustion regime diagram is used to describe non- premixed combustion in terms of the scale interactions between chemistry and turbulence, i.e., flamelet-like combustion, small-scale interactions, or extinction. An analysis framework is developed to link direct numerical simulations (DNS) and Reynolds-averaged Navier-Stokes (RANS). A three-pronged approach combines universal scaling relations of turbulence and chemistry from DNS data with the mean values from RANS and 1D detailed chemistry calculations. To demonstrate the methodology, it is applied to simulations of a compression ignition internal combustion engine for various operating conditions. Spatially and temporally resolved probabilities of the combustion regimes are computed. The contributions from the different regimes are extracted and analyzed. For the largest part, combustion occurs in the flamelet regime, which confirms the suitability of the model and its wide use and validation. Some regions exist where turbulence and chemistry scales are of the same order of magnitude, rendering the flamelet assumptions inaccurate. This approach enables predictions of mixing and flamelet statistics from mean values, universal distributions, and scaling relations. Those quantities are typically not accessible in RANS.