Abstract: CO2 dilution is a well-recognized effective strategy for combustion control. Against the backdrop of global energy structure transformation and carbon neutrality goals, developing efficient, clean, and low-carbon combustion technologies is crucial. However, the high proportion of CO2 in flue gas recirculation or the use of low-calorific-value fuels rich in CO2 can complicate the temperature field and NOx generation paths in combustion chambers, especially under lean fuel conditions. This study aimed to explore the detailed dilution effect of CO2 on the combustion of CH4 and H2, and thus numerically analyzed the combustion characteristics of jet diffusion flames. The numerical simulation was conducted under specific conditions: CO2 mixing ratio ranging from 0% to 40%, ambient temperature of 300 K, pressure of 101 325 Pa, and equivalence ratios between 0.4 and 0.9. A new triangular nozzle burner was adopted, along with the standard k-ε turbulence model and non-premixed combustion model for calculations, and grid independence verification was performed to ensure result reliability. The results showed that CO2 blending reduced the peak flame temperature, flame height, and average furnace temperature (from higher values to 1344 K at 40% CO2 mixing ratio). It inhibited the forward reactions of CO combining with O and OH, reducing O2 consumption, and achieved a maximum NOx reduction rate of 95.5% compared to pure methane combustion. In contrast, H2 enrichment increased the flame temperature, accelerated the combustion reaction, and formed a more compact flame structure. When CO2 was added to the CH4/H2 mixture, it still effectively reduced NOx emissions, though the reduction effect weakened slightly with higher CO2 blending ratios. So CO2 dilution was an effective method to achieve ultra-low NOx emissions in industrial boilers, especially suitable for hydrogen-rich natural gas combustion. Controlling CO2 blending below 30% balanced NOx reduction and combustion stability. The CH4/H2/CO2 ternary mixing strategy enabled coordinated regulation of the temperature field and pollutant emissions, providing a technical pathway for the industrial application of hydrogen-rich fuels.

Key words: CO2 dilution, NOx emissions, industrial boiler, hydrogen-rich methane combustion, numerical simulation

摘要： CO2混稀是一种有效的燃烧控制策略。为了探究CO2对CH4和H2燃烧的混稀效应，采用数值模型分析了体积分数为0%~40% CO2掺混下，环境温度300 K、压力101 325 Pa、当量比为0.4~0.9条件下射流扩散火焰燃烧特性。结果表明，CO2掺混率为0%, 10%, 20%, 30%, 40%时，炉膛的平均温度分别为1688, 1658, 1523, 1421, 1344 K，同时CO2掺混降低了火焰峰值温度与火焰高度。CO2抑制了CO与O及OH结合的正向反应，导致O2的消耗减少。添加CO2后相较于纯甲烷燃烧的NOx减排率最高可达95.5%。H2富集提高了火焰温度并促进了燃烧反应过程，从而产生更紧凑的火焰结构。同时，高比例的H2能够减少CO2稀释带来的燃烧不稳定性。CO2稀释对CH4/H2混合气体表现出优异的NOx减排效果。

关键词: CO2稀释, NOx排放, 工业锅炉, 富氢甲烷燃烧, 数值模拟