Establishment of a Confined Swirling Natural Gas/Air Flame as a Standard Flame: Temperature and Species Distributions from Laser Raman Measurements

A prototype of an industrial burner for confined swirling natural gas diffusion flames with thermal powers in the range of 100 to 300 kW is presented. Within the TECFLAM research cooperation, a well-defined "standard flame" was investigated in this burner with complementary measuring techniques to yield a comprehensive characterization of the combustion process. The aims of the investigations were a better understanding of the complex physical and chemical processes, their interactions in turbulent swirling flames, and the establishment of a database that can be used as a test case for numerical simulations. The results from single-pulse Raman measurements of the temperature, mixture fraction, and major species concentrations are presented. The global flame behavior is illustrated by the spatial distributions of the mean values and fluctuations of the temperature and mixture fraction. The different flame regions and their characteristic features are discussed. The main objective is the investigation of finite-rate chemistry effects, which can be deduced from the correlations between the various simultaneously measured quantities (scatterplots). Within the shear layers and the region of flame reactions, large deviations from chemical equilibrium are observed, which can be attributed to local flame extinction and ignition delay. Further discussion points are the stabilization mechanism of the flame and the influence of turbulent mixing on the thermochemical state. Finally, the effect of increased swirl on the flame behavior is illustrated and discussed.