Towards the Use of Eulerian Field PDF Methods for Combustion Modeling in IC Engines 2014-01-1144

Detailed chemistry and turbulence-chemistry interaction need to be properly taken into account for a realistic combustion simulation of IC engines where advanced combustion modes, multiple injections and stratified combustion involve a wide range of combustion regimes and require a proper description of several phenomena such as auto-ignition, flame stabilization, diffusive combustion and lean premixed flame propagation. To this end, different approaches are applied and the most used ones rely on the well-stirred reactor or flamelet assumption. However, well-mixed models do not describe correctly flame structure, while unsteady flamelet models cannot easily predict premixed flame propagation and triple flames. A possible alternative for them is represented by transported probability density functions (PDF) methods, which have been applied widely and effectively for modeling turbulent reacting flows under a wide range of combustion regimes. For IC engine simulations, the most promising ones are the Eulerian field PDF methods (SEF) whose formulation was originally proposed by Valiño and Sabel'nikov. Such models can be easily incorporated into CFD codes and are less computationally intensive with respect to Lagrangian approaches. In particular, Lagrangian particles are replaced by stochastic fields and transport equations are solved for them including a random process as a source term. Purpose of this work is the assessment of a SEF combustion model, that has been implemented into the Lib-ICE code, which is based on the OpenFOAM technology. To make the use of detailed chemistry possible in a reasonable amount of time, a multi-zone approach was incorporated in the combustion model and coupled with the TDAC technique, combining in-situ adaptive tabulation and dynamic adaptive chemistry. Experimental validation was carried out by simulating Diesel combustion experiments at constant volume conditions.