The reduction of NO by ethylene in a jet-stirred reactor at 1 atm: Experimental and kinetic modelling

The kinetics of the reduction of nitric oxide (NO) by ethylene have been studied in a fused silica jet-stirred reactor at I atm and at temperatures from 900 to 1400 K to simulate conditions in a reburning zone. The initial mole fraction of NO was 1000 ppm, that of ethylene was 4400 ppm. The equivalence ratio was varied from 0.75 to 2. It was found that the reduction of NO varies with temperature and that for a given temperature, the maximum reduction of NO occurs slightly fuel-rich of stoichiometric conditions. Thus, operating under optimal NO-reburning conditions is possible for particular combinations of equivalence ratio and temperature. The results generally agree with previous studies involving simple hydrocarbons or natural gas as reburn fuel. Detailed chemical kinetic modeling of the experiments was performed using an updated and improved kinetic scheme (877 reversible reactions and 122 species). Overall, reasonable agreement was obtained between the present measurements and the modeling although improvements of the model are still necessary. Also, the proposed kinetic mechanism can be successfully used to model the reduction of NO by ethane, acetylene, a natural gas blend (methane-ethane 10:1) and HCN, as well as the low temperature interactions between NO and simple alkanes. According to this study, the main way of reducing NO by ethylene involves the ketenyl radical, HCCO. The model indicates that the reduction of NO proceeds through the reactions: C2H4 --> C2H3 --> HCCO; HCCO + NO --> NCNO + CO and HCN + CO2; HCNO + H --> HCN + OH; HCN + O --> NCO --> HNCO --> NH2; NCO + H --> NH; NHi(i =1,2) + NO --> N-2; NH + NO --> N2O followed by N2O + H --> N-2. (C) 1999 by The Combustion Institute.