Novel Tabulated Combustion Model Approach for Lifted Spray Flames with Large Eddy Simulations

In this work, a turbulent combustion model is developed for large eddy simulation (LES) using a novel flamelet tabulation technique based on the framework of the multi-flamelet representative interactive flamelet (RIF) model. The overall aim is to develop a detailed model with elaborate chemistry mechanisms, LES turbulence models and highly resolved grids leveraging the computational cost advantage of a tabulated model. A novel technique of implementing unsteady flamelet libraries by using the residence time instead of the progress variables is proposed. In this study, LES of n-dodecane spray flame is performed using the tabulated turbulent combustion model along with a dynamic structure subgrid model. A high-resolution mesh is employed with a cell size of 62.5 microns in the entire spray and combustion regions. This model is then validated against igniting n-dodecane sprays under diesel engine conditions. For these constant volume combustion cases, 4-dimensional flamelet libraries based on scalar dissipation rate, residence time, mixture fraction variance and filtered mixture fraction are generated using a highly scalable parallel code. The flamelet libraries are generated using a 106-species and 420-reactions chemistry mechanism for n-dodecane. The transient flame development and the grid dependency shown by the tabulated model are analyzed. The results from the model show excellent agreement with the experimental measurements for ignition delay and flame liftoff across a wide range of ambient temperature conditions. The tabulated combustion modeling approach is also shown to have better agreements with the experiments than the homogenous reactor approach (typically used in the engine modeling community), while the computational expenses were significantly lower.