Non-premixed Combustion: Steady Diffusion Flamelet

Non-Premixed Combustion, Steady Diffusion Flamelet, ANSYS Fluent CFD Training

Description

This project simulates non-premixed combustion inside a two-dimensional combustion chamber using ANSYS Fluent, focusing on the Steady Diffusion Flamelet model — an approach well suited to capturing the complex combustion processes commonly found in industrial applications, where fuel and air are introduced separately and mix within the chamber itself, mirroring real-world combustion behavior.

The geometry was designed in Design Modeler and meshed in ANSYS Meshing using a structured grid totaling 63,280 elements.

Methodology

The Non-Premixed Combustion model was used to represent the combustion process, applying a non-adiabatic energy treatment to realistically capture heat transfer effects, alongside the Steady Diffusion Flamelet approach for accurately predicting flame structure. A Chemkin mechanism was imported into Fluent to generate the flamelet, modeling the turbulent flame brush as an ensemble of discrete, steady laminar flames — providing a detailed representation of the underlying chemical kinetics.

To improve computational efficiency, a Probability Density Function (PDF) table was pre-generated ahead of the main simulation, storing temperature variation, mixture density, and species mass fraction data, enabling accurate representation of turbulence-chemistry interactions throughout the solution. The energy equation was enabled to accurately track temperature changes, with turbulence modeled using the standard k-epsilon model.

Conclusion

Results include temperature distribution contours, velocity profiles throughout the chamber, mass fractions for the various chemical species, and streamlines revealing the resulting flow and mixing patterns. These results offer insight into the structure and behavior of the non-premixed flame, how temperature evolves across different regions of the chamber, how species form and are consumed throughout the reaction, and how secondary flow structures enhance mixing and overall combustion efficiency.

These insights are directly applicable to designing more efficient industrial burners and furnaces, optimizing fuel injection systems in gas turbines and diesel engines, and improving combustion chamber geometry for reduced emissions in real-world non-premixed combustion applications.