The composition PDF transport model, like the EDC model (see Section 14.1.1), should be used when you are interested in simulating finite-rate chemical kinetic effects in turbulent reacting flows. With an appropriate chemical mechanism, kinetically-controlled species such as CO and NOx, as well as flame extinction and ignition, can be predicted. PDF transport simulations are computationally expensive, and it is recommended that you start your modeling with small grids, and preferably in 2D.
A limitation that applies to the composition PDF transport model is that you must use the pressure-based solver. The composition PDF transport model is not available with either of the density-based solvers.