Formations and emissions of CO/NO2/NOx in the laminar premixed biogas-hydrogen flame undergoing the flame-wall interaction: Effects of the variable CO2 proportion

Experimental and numerical studies were conducted to investigate the effects of CO2 proportion on the formation processes and overall emissions of CO and NOx of the laminar premixed biogas-hydrogen flames undergoing the flame-wall interaction (FWI). The overall EICO, EINOx, EINO2 and NO2/NOx ratio were obtained. The near-wall combustion processes of the wall-impinging flame at different separated distance (H) were simulated numerically using a computational model, and four major routes (thermal route, prompt route, NNH intermediate route and N2O intermediate route) of the NO production were calculated separately. The results show that the EICO decreases at small H but increases at large H with the increased CO2 proportion, which is dominated by the cooling plate and dilution/chemical effects of CO2, respectively. This indicates that the overall EICO of biogas fuel can be reduced effectively with the enhanced CO2 proportion when the FWI effects are intensive. The overall EINOx is decreased obviously with the increased CO2 proportion owing to the declined temperature and reduced active radicals. With the increased CO2, the contributions of thermal route and N2O route are decreased considerably while the importance of prompt route and NNH route are increased evidently. The strong FWI effects can increase the importance of prompt route while decrease the contribution of thermal route effectively. The EINO2 of biogas-H-2 flame is decreased with the increased CO2 proportion. The dilution effects of CO2 can improve the NO2 conversion efficiently but this NO2 conversion process can be suppressed effectively by the intensive FWI effects.