A Thickened Flame Model Adapted to Auto-Ignition/Propagation Regimes for the Large-Eddy Simulation of Dual-Fuel Combustion

Abstract Dual-fuel combustion (DFC) is a promising concept for low-emission, highly efficient internal combustion engines. Large-Eddy Simulation (LES) enables detailed analysis for engine design, but the complex combustion process in DFC, involving the transition from pilot-fuel auto-ignition to premixed flame propagation challenges existing turbulent combustion models. This study presents a new combustion model for DFC based on the Thickened Flame Model (TFM). TFM is well validated for premixed combustion but results in delayed ignition predictions. This work introduces a transported ignition sensor to relax the thickening factor, thereby modulating thickening to the combustion regime. Thickening during auto-ignition is avoided while seamlessly reverting to a classical TFM approach during flame propagation. A burnt gas criterion is also proposed to reliably detect the transition. Results obtained in one-dimensional dual-fuel cases demonstrate that the proposed approach successfully captures auto-ignition delays and flame propagation. An academic dodecane/methane jet case is proposed to validate the model under 3D turbulent conditions against fully flame resolved simulations. The model successfully predicted the heat-release rate and temperature evolution. The model underpredicted heat-release rate for cases with small pilot quantity due to thickening reducing the flame surface, highlighting the importance of efficiency models used in conjunction with TFM.