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 st udied in a fused silica jet-stirred reactor at I atm and at temperatures fr om 900 to 1400 K to simulate conditions in a reburning zone. The initial mo le fraction of NO was 1000 ppm, that of ethylene was 4400 ppm. The equivale nce 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 reduc tion of NO occurs slightly fuel-rich of stoichiometric conditions. Thus, op erating under optimal NO-reburning conditions is possible for particular co mbinations of equivalence ratio and temperature. The results generally agre e with previous studies involving simple hydrocarbons or natural gas as reb urn fuel. Detailed chemical kinetic modeling of the experiments was perform ed using an updated and improved kinetic scheme (877 reversible reactions a nd 122 species). Overall, reasonable agreement was obtained between the pre sent measurements and the modeling although improvements of the model are s till necessary. Also, the proposed kinetic mechanism can be successfully us ed 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 b etween NO and simple alkanes. According to this study, the main way of redu cing 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.