Simulation of finite-rate chemical kinetics in a turbulent bluff body flame

Abstract

A turbulent combustion model using a Monte Carlo scalar PDF transport method with an adaptive number of PDF particles in each computational cell is coupled to an experimental version of a commercial CFD solver. While the molecular mixing is always modelled using a modified Curl model, the chemical source terms are calculated using a global 4-step reaction model and two different implementations of the method of intrinsic low-dimensional manifolds (ILDM), respectively. The quality of the chemistry representation by the three reduced chemical mechanisms is tested against detailed methane mechanisms using plug-flow reactor calculations. It is confirmed that the two ILDM implementations reproduce the chemical trajectories of the detailed reaction mechanism in scalar space quite well as expected, while the characteristic time scales of the global mechanism differ considerably. The full PDF transport CFD code is applied to a methane bluff-body diffusion flame stabilised by a recirculation zone. The calculations show a consistent improvement of predictions, particularly of temperature and CO concentrations of the PDF transport method compared to an presumed PDF calculation assuming equilibrium chemistry. Nevertheless, the CO concentrations are still considerably over predicted by all methods in such a highly strained flame, indicating that the mixing and turbulence models need to be improved.