Numerical and Experimental Investigation of Hydrogen Enrichment Effect on the Combustion Characteristics of Biogas

In the present work, the combustion characteristics like adiabatic flame temperature (AFT) and laminar burning velocity (LBV) of methane (CH4) diluted with carbon dioxide (CO2), representing biogas, is investigated in detail. The laboratory prepared biogas samples containing CH4 and CO2 were also enriched with hydrogen (H-2) to realize the change in their combustion behaviour. The experiments were conducted on flat flame burners based on heat flux method at 1 bar, 298 K and at stoichiometric and off-stoichiometric conditions. The experimental results were also compared with the numerical predictions of ANSYS Chemkin-Pro (R) with full GRI Mech. 3.0 reaction mechanism. The results revealed that the presence of CO2 in biogas dominates on richer mixtures, i.e., the CO2 dilution affects the combustion characteristics of richer biogas mixtures more strongly than for leaner or stoichiometric mixtures. The simulated results of hydrogen-enriched biogas showed that the slope of the laminar burning velocity (LBV) curve for biogas containing the highest percentage of CO2 sharply rises with about 33% H-2, whereas the slope of the mixture with least CO2 and more CH4, sharply changes its nature around 40% H-2-enrichment. This signifies that even with a small amount of H-2 in biogas, may be a suitable option to improve its combustion characteristics. Some preliminary correlations for H-2-enriched biogas were also derived to estimate the effect of H-2 presence in biogas fuels with higher Hydrogen concentrations.