Abstract
Combustion and heat release characteristics of biogas non-premixed flames under various hydrogen-enriched and oxygen-enriched conditions were investigated through chemical kinetics simulation using detailed chemical mechanisms. The heat release rates, chemical reaction rates, and molar fraction of all species of biogas at various methane contents (35.3–58.7%, mass fraction), hydrogen addition ratios (10–50%), and oxygen enrichment levels (21–35%) were calculated considering the GRI 3.0 mechanism and P1 radiation model. Results showed that the net reaction rate of biogas increases with increasing hydrogen addition ratio and oxygen levels, leading to a higher net heat release rate of biogas flame. Meanwhile, flame length was shortened with the increase in hydrogen addition ratio and oxygen levels. The formation of free radicals, such as H, O, and OH, are enhanced with increase in hydrogen addition ratio and oxygen levels. Higher reaction rates of exothermic elementary reactions, especially those with OH free radical are increased, are beneficial to the improvement in combustion and heat release characteristics of biogas in practical applications.
Highlights
With continuous depletion of fossil fuels and worsening pollution, research and development of renewable energy sources have attracted considerable interest [1,2,3,4,5,6,7]
The results showed that OH + H2 ⇔ H + H2 O was major endothermic reaction for biogas-hydrogen premixed flames
To enhance the combustion and heat release characteristics, hydrogen addition and oxygen enriched combustion are selected for biogas combustion in future practical application
Summary
With continuous depletion of fossil fuels and worsening pollution, research and development of renewable energy sources have attracted considerable interest [1,2,3,4,5,6,7]. Zhen et al [18] experimentally investigated the effect of H2 addition on the characteristics of a biogas diffusion flame. Wei et al [19] numerically investigated the effects of equivalence ratio, H2 , and CO2 on the heat release characteristics of the premixed laminar biogas-hydrogen flames. The improvement of heat release characteristics of biogas flame at various condition are necessary. The above results show that numerous studies have investigated the combustion characteristics of biogas premixed flame. The non-premixed flames of biogas under various hydrogen-enriched and oxygen-enriched conditions are studied, and the combustion and heat release characteristics of biogas non-premixed flames are numerically investigated. To enhance the combustion and heat release characteristics, hydrogen addition and oxygen enriched combustion are selected for biogas combustion in future practical application. The mass contents of CH4 in biogas, hydrogen addition ratios, and oxygen enrichment levels are ranged from 35.3% to 58.7%, 0% to 50%, and 21% to 35%, respectively
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