Effects of H2 addition on the formation and emissions of CO/NO2/NOx in the laminar premixed biogas-hydrogen flame undergoing the flame-wall interaction

The overall emissions of CO, NOx and NO2/NOx ratio of laminar premixed biogas-hydrogen flames undergoing the flame-wall interaction (FWI) were measured experimentally while the emission indexes (EI) were calculated. The computational model was employed to calculate the combustion process of the biogas-hydrogen flame, and four major routes to produce the NO were isolated and calculated in the simulations. The effects of H-2 addition on the formations and emissions of CO/NO2/NOx of BG75-hydrogen impinging flames were analyzed quantitatively. The results show that, with the H-2 addition, the EICO of BG75-hydrogen flame is enhanced steadily at either small separated distance (H) or large H thanks to that the high reactivity of H-2 suppresses the CO oxidization efficiently by competing for the OH radical. The H-2 addition can improve the NO production via four routes and increase the EINOx of the BG75-hydrogen flame. Although the prompt NO is improved by the H-2 addition, its rising trend is decreased considerably as hydrogen addition is larger than 20% owing to the reduced methane proportion and improved premixed combustion. The contribution of prompt NO is decreased with the H-2 addition, while that of other routes are increased steadily. The NNH route dominates the increased EINOx at small H while the thermal route dominates the rising trend at large H. EINO2 is enhanced steadily with the H-2 addition due to the improved HO2 production in the air mixing region, while the NO2 conversion ratio is improved and suppressed with H-2 addition at small and large H, respectively.