Numerical Simulation of Lean Fuel Combustion Characteristics of CH4/H2/CO2
CO2 dilution is a recognized strategy for combustion control, yet its detailed effects on CH4/H2 combustion under lean conditions remain insufficiently characterized. This study numerically investigated jet diffusion flames in a triangular nozzle burner, varying CO2 mixing ratios from 0% to 40%, equivalence ratios from 0.4 to 0.9, at 300 K and 101325 Pa. The standard k-ε turbulence model and non-premixed combustion model were employed, with grid independence verified. Results showed that increasing CO2 blending reduced peak flame temperature, flame height, and average furnace temperature from 1688 K (0% CO2) to 1344 K (40% CO2). CO2 inhibited forward reactions of CO with O and OH, reducing O2 consumption. NOx emissions decreased by up to 95.5% at φ=0.7 (from 6.7×10-5 to 3.03×10-6) and 94.3% at φ=0.9, compared to pure methane. Conversely, H2 enrichment (0% to 40%) raised peak temperature from 2018 K to 2199 K and shifted the peak location closer to the burner (from 1.16 m to 0.82 m), promoting more compact flames. In CH4/H2 mixtures, CO2 still effectively reduced NOx, though the effect slightly weakened with higher CO2 ratios. Controlling CO2 blending below 30% balances NOx reduction and combustion stability. The CH4/H2/CO2 ternary strategy enables coordinated regulation of temperature and pollutant emissions, offering a technical pathway for hydrogen-rich fuel applications.