Two-Zone Flamelet Combustion Model

In this paper, a new two-zone flamelet model is suggested. In the combustion model, each cell is divided by the flame front to two zones: unburned zone and burned zone. The unburned zone consists of air, fuel vapour and residual gases, whilst the burned zone contains combustion products. The unburned zone is further divided into two regions: segregate region and fully mixed region. The combustion is decoupled as two sequential events: mixing and burning. The turbulent mixing is governed by the large eddy structure, taking the effect of fuel drop spacing into consideration. The turbulent burning rate is further decomposed into three terms: laminar burning velocity for combustion chemistry, turbulence enhanced burning rate and flame strain factor for flame quenching. The turbulent burning rate is evaluated based on fractal geometry and basic dimensional analysis of turbulent flame. This approach gives a simple and direct relationship between turbulence and burning velocity, which can be easily compared with measurements. Low- and high-temperature reactions are treated separately. The low-temperature reactions for auto-ignition are considered as a lumped one-step reaction of one generic ignition species. The high-temperature reactions for heat release are calculated from an equilibrium condition. The model provides a unified and predictive engineering approach for both premixed and nonpremixed flames and both fuel lean and rich mixture burning regimes with all types of hydrocarbon fuel. The model is simple and easy to implement, and computationally efficient as well.