Premixed Combustion: Eddy Dissipation/Finite Rate

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 fuel and air assumed to enter the chamber already premixed through a single boundary.

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 where reaction kinetics may become locally significant (such as near flame ignition points or in regions of low turbulence), rather than assuming mixing is always the sole limiting process, as the standalone Eddy Dissipation model does.

The 2D geometry was designed in Design Modeler and meshed in ANSYS Meshing using a structured mesh totaling 86,002 elements.

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. 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, mass fractions of the various species, and streamlines. The temperature contour shows a clear rise within the chamber, confirming that combustion has taken place.

The streamlines also reveal secondary flow structures forming within the chamber — these secondary flows enhance the mixing between fuel and air, thereby improving the overall combustion process. Because the model accounts for finite-rate kinetics alongside mixing, this simulation can also capture combustion behavior in regions where reaction rates are not purely mixing-controlled, offering a more complete picture of the flame structure than a mixing-only approach would provide.