Premixed Combustion: Eddy Dissipation / Finite Rate Model

Premixed Combustion, Eddy Dissipation/Finite Rate Model, ANSYS Fluent CFD Simulation Training

Description

This project simulates premixed combustion inside a combustion chamber using ANSYS Fluent, with a particular focus on pollutant formation. The 2D geometry was designed in Design Modeler and meshed in ANSYS Meshing using a structured mesh totaling 86,002 elements.

The Eddy Dissipation/Finite Rate model combines two distinct approaches to reaction rate calculation: the Eddy Dissipation model, which assumes combustion is limited purely by turbulent mixing, and the Finite Rate model, which calculates reaction rates directly from Arrhenius chemical kinetics. At each computational cell, the model takes the smaller of the two calculated rates — meaning the reaction proceeds at whichever rate is the limiting factor, mixing or chemistry. This makes the model particularly useful for cases like this one, where pollutant formation depends on capturing reaction kinetics accurately rather than assuming mixing is always the dominant limiting process, as the standalone Eddy Dissipation model does.

Methodology

The Species Transport model is used to represent the combustion process, applying a single-step methane-air reaction with the volumetric option enabled to capture combustion throughout the chamber. Turbulence-chemistry interaction is handled using the Eddy Dissipation/Finite Rate model, evaluating both the turbulent-mixing-limited rate and the kinetics-limited rate at each point in the domain and applying the smaller of the two — balancing mixing effects against reaction rates to more accurately capture pollutant formation mechanisms. The energy equation is enabled to capture temperature changes driven by combustion, with turbulence modeled using the standard k-epsilon model.

Conclusion

The simulation results include contours of temperature, velocity, and mass fractions of the various species — including pollutant species — along with streamlines throughout the chamber. The temperature contour shows a clear rise within the chamber, confirming that combustion has taken place, while the species mass fraction results reveal where and how pollutants form as reaction byproducts.

The streamlines also reveal secondary flow structures forming within the chamber, which enhance the mixing between fuel and air and directly influence both combustion completeness and pollutant formation. Because this model accounts for finite-rate kinetics alongside mixing, it can capture pollutant formation more accurately in regions where reaction rates are not purely mixing-controlled — offering insight directly applicable to designing cleaner combustion systems, optimizing existing combustion chambers for reduced emissions, and predicting pollutant formation in industrial combustion processes.