A Numerical Investigation on Turbulent CH4-air Combustion Flames of a Multi-Regime Burner

The interaction between premixed and non-premixed methane-air mixtures affect the flame structure. The flow field is improved by supplying the lean and rich mixture. The objective of this work is to study the effect of the re-circulation zone on premixed and non-premixed methane-air mixture in a multi-regime burner using numerically. The two-dimensional, axis symmetric, steady state, compressible turbulent reactive flow is simulated using standard k-epsilon model with the eddy dissipation concept (EDC). The chemical kinetics developed by the Gas Research Institute (CHEMKIN-II, GRI-3.0) has been combined with the governing equations using the open source CFD-tool box OpenFOAM. The flames have been tested for different equivalence ratios of jet (phi(j)= 1.4, 1.8, 2.2, and 2.6) where, slot-1 velocity varied as 7.57.5 m/sm/s and 1515 m/sm/s. The grid independent results of the temperature (T) and mixture fraction (Z) are found in a good agreement with the experimental data. The qualitative and quantitative study of the temperature (T), mixture fraction (Z), mass fraction of carbon monoxide (Y-CO), mass fraction of methane (Y-CH4) and progress variable (Y-c) have been presented. The results show that a lifted reaction zone close to the jet, and a re-circulation zone between the inner and outer premixed reaction zones, which stabilizes the combustion between slot-1 and slot-2. Increasing the jet equivalent ratio (phi(j)) reduces the temperature and extends the internal premixed reaction zone. This is due to the mixture fraction ratio (Z) exceeding the flammability limit near the jet exit, which occurs when Z is within the range of 0.0270.027 to 0.090.09. The maximum temperature value of approximately 21252125 K is consistent with the variation in phi(j). The re-circulation zone shows a constant temperature of 20002000 K, where methane is completely burned and is not affected by the values of jet equivalent ratios.