Chemical Reactions & Combustion

Whether simulating combustion design in gas turbines, automotive engines, or coal-fired furnaces or assessing fire safety in and around buildings and other structures, ANSYS CFX software provides a rich framework to model chemical reactions and combustion associated with fluid flow.

There is a complete range of options for all situations: a rich library of predefined chemical reactions that can be easily edited and extended by users as well as the integration of ANSYS reactive integrated flamelet (RIF) for detailed chemistry tables. These are rounded out with models for auto and spark ignition, pollutant formation (NOx, soot), residual exhaust gases, knock, wall quenching, flame extinction and more.

The eddy-dissipation model (EDM) and finite-rate chemistry (FRC) models are provided in ANSYS CFX software for relatively fast and slow reactions, respectively, when compared to the mixing of reactants due to turbulent fluid flow. Simulations are not limited, however, to either extreme, as the two models can be combined, with the reaction rate being taken as the minimum of the two, both for single and multi-step reactions, from pre-defined or user-defined reactions.

In situations in which fuel and oxidant are fed into a system separately and the chemistry is assumed to be relatively fast, the laminar flamelet model with presumed probability density function (PDF) offers a practical and efficient means to depict the detailed chemistry of hundreds of species without having to solve hundreds of transport equations.

The burning velocity model (BVM) is well suited for combustion in which oxidant and fuel are premixed or partially premixed and the flames are steady, such as in gas turbines. BVM is coupled with the laminar flamelet PDF model to model post-flame front mixing and reaction.

Like the BVM model, the extended coherent flamelet model (ECFM) is suited for premixed or partially premixed fuel/oxidant combinations. It can capture post-flame front mixing using the laminar flamelet PDF model. However, an additional degree of freedom makes it more suitable for unsteady flames and moving geometries, as found for example in internal combustion engines. It includes an option to incorporate the quenching effect walls can have on flames.

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View Larger ImageInstantaneous and time-averaged temperature predictions in combustion chamber simulation using scale-resolving SAS turbulence modelCourtesy German Aerospace Center (DLR), Institute of Combustion Technology.