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

Abstract 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 H2 addition on the formations and emissions of CO/NO2/NOx of BG75-hydrogen impinging flames were analyzed quantitatively. The results show that, with the H2 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 H2 suppresses the CO oxidization efficiently by competing for the OH radical. The H2 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 H2 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 H2 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 H2 addition due to the improved HO2 production in the air mixing region, while the NO2 conversion ratio is improved and suppressed with H2 addition at small and large H, respectively.