Effect of slot positions on multi-regime turbulent combustion of CH 4 -air flame: A numerical study

Abstract

The presence of inhomogeneities in the premixed and non-premixed fuel-air mixtures leads to the formation of multi-regime combustion. This study numerically investigates the influence of slot-2 positions on the re-circulation characteristics of a multi-regime burner (MRB) operating under premixed and non-premixed ${CH}_{4}$ -air combustion conditions. The axisymmetric, steady-state, compressible turbulent flow field was simulated using the standard $κ - ϵ$ turbulence model coupled with the Eddy Dissipation Concept (EDC) to resolve the reactive flow dynamics. Detailed chemical kinetics incorporating $36$ species and $218$ reactions based on the GRI-3.0 mechanism were implemented. Five slot-2 positions were examined by varying slot-1 wall thickness for equivalence ratios $ϕ_{j} = 1.8$ and $2.6$ at slot-1 velocity 15 m/s. Numerical results of the mixture fraction, temperature, major species, minor species, and progress variable were validated against prior experimental and numerical datasets. The analysis revealed that varying the slot-2 position significantly alters the radial width of the re-circulation zone and the flame neck thickness. The peak of the temperature ( $\approx 2200$ K) and enhanced minor species concentrations ( $Y_{CO} = 0.0465$ and $Y_{H_{2}} = 0.0031$ ) were found in the inner premixed reaction zone. The outer premixed region exhibited a gradual decline in temperature and mixture fraction due to entrainment of co-flowing air, leading to a shift of the outer reaction zone downstream. These findings highlight the strong geometric sensitivity of turbulent flame structure and stabilization in MRB configurations.

Keywords

equivalence ratio turbulence combustion modeling Eddy dissipation concept CHEMKIN-II GRI-3.0

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