The Chemical and Physical Effect of Diluent H2O on NO and CO Emissions in Computational CH4 / Air Laminar Diffusion Flames

Yuqi Yang, Lei Zhang, Rui Sun, Zhuozhi Wang, Yupeng Li, Xiaohan Ren

Abstract


The chemical and physical effects of H2O addition on the NO and CO emissions of CH4 / air diffusion laminar flames are numerically investigated at atmospheric pressure with the reduced mechanism. The reduced mechanism removes the mad components from GRI - mech 3.0 by the Directed Relation Graph ( DRG ) method and the Sensitivity Analysis ( SA ) method, then adds the virtual molecules FH2O, which have the same physical properties as an H2O molecule but no chemical properties. To distinguish the chemical and physical effects of H2O addition on NO and CO formation in flames, this study adds the same amount of H2O and FH2O additions to the fuel side and oxidant side, respectively. The simulation results are obtained for an equivalence ratio of 1 and addition ratios of 0, 10 %, 20 %, and 30 % ( θ ) of the fuel mixture volume. As a result, the temperature and the NO and CO emissions decrease with H2O addition increasing. When θ is 30 % in the fuel side, the NO and CO peak proportion along axis decreases 24 % and 16%, respectively. When the same amount of H2O and FH2O are added, the difference between the components identifies the chemical and physical effects of addition significantly, and the NO and CO pollutant reduction from methane burning with FH2O diluent is 0.5 ~ 0.8 of that with H2O diluent, because H2O addition affects the reaction paths, the high heat capacity and the dilution effect. H2O addition promotes NO consumption reactions by HCCO + NO = HCNO + CO and NO + CH2 = HNCO + H. And H2O addition changes the main route of CO production. When no diluent is added, CO is created by CH4 → CH3 → CH2O → HCO → CO and CH4 → CH3 → CH2(S) → CH2 → CH → CH2O → HCO → CO. However, the reaction rate of second route is decreased clearly by H2O diluent in fuel side.

Keywords


laminar diffusion flame, reduced mechanism, the chemical and physical influence, H2O addition, NO and CO emission


DOI
10.12783/dteees/iceee2018/27889

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