Computational and experimental investigation of a turbulent non-premixed methane flame

Abstract

Mathematical modeling of turbulent combustion processes is a challenging task, mainly because of the problem of describing the coupling of the chemical kinetics with the turbulent flow. Existing models still have to be improved, which can only be achieved by comparison and validation with experimental results. We present experimental results and numerical simulations of a piloted non-premixed methane-airflame of semitechnical size (50 kW). The experimental data comprise measurements of velocities, temperature, and species concentrations. The model used for the simulation of the turbulent flame consists of a k-ε model for the turbulent flow field combined with a Monte Carlo method for the solution of the joint probability density function (PDF) of velocities and scalars that overcomes the closure problem for the chemical kinetics. Finite-rate chemistry is incorporated in the model using a two-step reduced chemistry model obtained by an automatic mechanism reduction procedure based on intrinsic low-dimensional manifolds, together with a table look-up procedure. Comparisons of experimental and computational results show that the model is able to predict the main characteristics of the flame well. Discrepancies can be mainly attributed to deficiencies of the micromixing model and inaccuracies in the description of the turbulent flow field by the k-ε model. However, it is clearly shown that finite chemistry effects play a major role in this flame.