Numerical analysis of multi-regime combustion using flamelet generated manifolds - a highly-resolved Large-Eddy Simulation of the Darmstadt multi-regime burner

Abstract

Multi-regime effects occur due to the interaction of combustion phenomena such as partial premixing of reactants or product-recirculation and lead to the invalidity of idealization of local reaction zones by purely premixed or purely non-premixed flame structures. The recently proposed multi-regime burner (MRB) at the Hochschule Darmstadt and the TU Darmstadt is investigated using highly-resolved Large-Eddy Simulation (LES) regarding the present combustion modes – with focus on MILD combustion – and overall flame characteristics. Thermochemical experimental data and highly resolved LES are compared for two selected operating conditions MRB18b and MRB26b. The experimental investigation focuses on the overall flame structure by examining radial profiles of temperature and mixture fraction, as well as scatter plots of temperature and CH4 versus mixture fraction. The objective of this analysis is to provide insights into the reaction zone structure which are difficult to extract by experimental means, by using highly-resolved Large-Eddy Simulations under flow conditions representative of MRB18b and MRB26b. The generated database was used to allow for a separate analysis of the inner and outer flame branches. SO2 measurements were analyzed together with the simulated temperature fields to further assess the flame stabilization mechanism in this configuration. The importance of different flame zones and burning modes was analyzed using the flame index and temperature locus diagrams. The effects of the flame zones are found to evolve with the downstream distance and show distinct differences between the two operating conditions. The applied diagnostics reveal the spatial and thermodynamical state of the different regimes.