Effects of unburned gases velocity on the CO/NO2/NOx formations and overall emissions of laminar premixed biogas-hydrogen impinging flame

Experimental measurements and numerical simulations were both conducted to study effects of unburned gases velocity on the formations and overall emissions of CO and NOx of the laminar premixed biogas-hydrogen impinging flame. Emission indexes (EI) of CO and NOx and NO2/NOx ratio were obtained based on the measured data, while four major routes to produce the NO were isolated and calculated in the simulation. The results show that EICO is decreased with Re at small H, while it is increased with Re at large H. The thermal NO is improved with Re as the flame front is affected strongly by the cold plate, while it is suppressed at larger H due to the reduced residence time and relatively insufficient oxidizer. The N2O route is decreased with Re, while the increased NO amounts of prompt route and NNH route are dominated by the higher flame temperature and more available active radicals. The contributions of thermal route and N2O route are decreased with Re while that of prompt route and NNH route are increased. With the increased Re, EINO2 and NO2/NOx ratio are decreased at small H but increased at large H. •The effects of flow field on formations and emissions of CO and NOx were investigated.•Four major routes to produce the NO were isolated and calculated.•Higher flow velocity can reduce the EICO at small H but increase it at large H.•Higher flow velocity suppresses the thermal NO while improves the prompt NO.•Higher flow velocity inhibit the NO2 production at small H but improves it at large H.