Effect of slot positions on multi-regime turbulent combustion of CH4-air flame: A numerical study

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 ( ≈ 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.