Numerical simulation on flame morphology and pollution emissions of methane-hydrogen diffusion flames
Hydrogen as a green and efficient clean energy source,holds significant importance in reducing carbon emissions.However,blending hydrogen can affect flame stability,morphology and pollutant emissions.Focusing on natural gas-hydrogen blending combustion technology,a non-premixed bluff body coaxial burner was designed to create a recirculation zone for flame stabilization.Based on the GRI-Mech 3.0 combustion reaction mechanism,computational fluid dynamics analysis was employed to investigate the effects of hydrogen blending ratio on the velocity and temperature fields,flame morphology,combustion reaction zone and pollutant emissions of methane-hydrogen blending combustion under lean fuel conditions.The results indicate that with a fixed equivalence ratio and hydrogen-enriched fuel volumetric flow rate,as the hydrogen blending ratio increases,the average flow velocity in the combustion chamber decreases,the recirculation zone vortex structure downstream of the bluff body becomes smaller,the combustion reaction zone is shifted forward,and the flame structure becomes more compact.The average temperature and temperature uniformity index increase with an increasing hydrogen blending ratio,rising 1.82％-16.22％and 0.59％-1.73％respectively compared to pure methane combustion.Simultaneously,the outlet NO molar fraction increases,while the outlet CO2 molar fraction gradually decreases,and both changes exhibit an increasing trend.At a hydrogen blending ratio of 20％,CO2 emissions are reduced by 6％.However,under high blending ratios,although the carbon reduction effect is significant,nitrogen oxide emissions increase exponentially.Therefore,studying the combustion characteristics of hydrogen-enriched fuels at different blending ratios provides important insights for recommending appropriate hydrogen blending ratios and designing non-premixed stable flame burners for natural gas-hydrogen blending combustion technology.
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