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

ABSTRACT

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 $\mathit{k}-\mathit{\epsilon }$ 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 (${\varphi }_j$ = 1.4, 1.8, 2.2, and 2.6) where, slot-1 velocity varied as $7.5$ $\mathrm{m}/\mathrm{s}$ and $15$ $\mathrm{m}/\mathrm{s}$. The grid independent results of the temperature $\left(\mathit{T}\right)$ and mixture fraction $\left(\mathit{Z}\right)$ are found in a good agreement with the experimental data. The qualitative and quantitative study of the temperature $\left(\mathit{T}\right)$, mixture fraction $\left(\mathit{Z}\right)$, mass fraction of carbon monoxide $\left(Y_{\mathrm{CO}}\right)$, mass fraction of methane $\left(Y_{\mathrm{C}{\mathrm{H}}_4}\right)$ and progress variable $\left(Y_c\right)$ 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 $\left({\varphi }_j\right)$ reduces the temperature and extends the internal premixed reaction zone. This is due to the mixture fraction ratio $\left(\mathit{Z}\right)$ exceeding the flammability limit near the jet exit, which occurs when $\mathit{Z}$ is within the range of $0.027$ to $0.09$. The maximum temperature value of approximately $2125$ K is consistent with the variation in ${\varphi }_j$. The re-circulation zone shows a constant temperature of $2000$ K, where methane is completely burned and is not affected by the values of jet equivalent ratios.

KEYWORDS:

• Methane-air premixed combustion
• turbulence combustion modeling
• eddy dissipation concept
• equivalence ratio
• CHEMKIN-II
• GRI-3.0

Disclosure statement

No potential conflict of interest was reported by the author(s).

Authors contributions

The work of research, analysis of data, and writing of the manuscript has been done by Mr. Ganamatayya K Hikkimath. Dr. Devendra Kumar Patel conceptualized, selected methodology, supervised and edited the manuscript.

Novelty and significance statement

In the present study an attempt has been made to present a comprehensive numerical study of the multi-regime burner introduced by Butz et al (2019) at four equivalence ratios (${\varphi }_j=1.4$, $1.8$, $2.2$ and $2.6$.) and two different slot-1 velocities (Case-A: $7.5$ $\mathit{m}/\mathit{s}$ and Case-B:$15$ $\mathit{m}/\mathit{s}$). A comparative study among that different configuration of the present problem is presented using the contour and line plots of velocity, streamline, temperature and the mass fractions of the reactants and products of combustion. The standard $\mathit{k}-\mathit{\epsilon }$ model with eddy dissipation concept (EDC) and CHEMKIN-II, GRI-3.0, has been used to investigate the multi-regime burner flame. The present RAND-EDC approach predicts well the recirculation zone compared to the inner and outer premixed reaction zone. The change in the equivalence ratio significantly influences the inner premixed reactions zone. A significant increase in carbon monoxide values near the burner axis is observed with the change in jet equivalence ratio.