Cars measurements and computations of the structure of laminar stagnation-point methane-air counterflow diffusion flames

Abstract

Information on the structure of laminar diffusion flames under the influence of the strain of an inhomogeneous velocity field is essential for the understanding of tubulent diffusion flames. Coherent Anti-Stokes Raman Scattering (CARS) is used to determine temperature and concentration profiles in an atmospheric pressure CH 4 /air counterflow diffusion flame. First a comparison between thermocouple and CARS measurements is done in a high temperature furnace up to 2000 K. The temperature dependent CARS spectra of N 2 are evaluated by a simulation program. Agreement between both techniques is obtained within 40 K over the complete temperature range. The experimental data from the counterflow diffusion flame are compared with calculations where the corresponding governing equations for enthalpy, momentum, and chemical species are used in their two dimensional form. By boundary layer approximations and a coordinate transformation the equations are transformed into a one dimensional form, which is integrated with a finite differences method. Transport is described by a simplified multicomponent model. The detailed reaction mechanism consists of more than 250 elementary steps and 39 chemical species. The comparison between the experimental and simulated temperature profiles shows satisfactory agreement on the fuel rich side but deviates significantly on the fuel lean side of the mixing layer. This discrepancy is ascribed to shortcomings in the model underlying the numerical simulation. Further calculations should therefore replace the use of boundary layer approximations by true two-dimensional representations of the flow field.