The rate constant of the reaction NCN + H-2 and its role in NCN and NO modeling in low pressure CH4/O-2/N-2-flames.

Fassheber, Nancy, Lamoureux, Nathalie and Friedrichs, Gernot (2015) The rate constant of the reaction NCN + H-2 and its role in NCN and NO modeling in low pressure CH4/O-2/N-2-flames. Physical Chemistry Chemical Physics, 17 (24). pp. 15876-15886.

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Abstract

Bimolecular reactions of the NCN radical play a key role in modeling prompt-NO formation in hydrocarbon flames. The rate constant of the so-far neglected reaction NCN + H-2 has been experimentally determined behind shock waves under pseudo-first order conditions with H2 as the excess component. NCN3 thermal decomposition has been used as a quantitative high temperature source of NCN radicals, which have been sensitively detected by difference UV laser absorption spectroscopy at (nu) over tilde = 30383.11 cm(-1). The experiments were performed at two different total densities of rho approximate to 4.1 x 10(-6) mol cm(-3) and rho approximate to 7.4 x 10(-6) mol cm(-3) (corresponding to pressures between p = 324 mbar and p = 1665 mbar) and revealed a pressure independent reaction. In the temperature range 1057 K < T < 2475 K, the overall rate constant can be represented by the Arrhenius expression k/(cm(3) mol(-1) s(-1)) = 4.1 x 10(13) exp(-101 kJ mol(-1)/RT) (Delta log k = +/- 0.11). The pressure independent reaction as well as the measured activation energy is consistent with a dominating H abstracting reaction channel yielding the products HNCN + H. The reaction NCN + H-2 has been implemented together with a set of reactions for subsequent HNCN and HNC chemistry into the detailed GDFkin3.0_NCN mechanism for NOx flame modeling. Two fuel-rich low-pressure CH4/O-2/N-2-flames served as examples to quantify the impact of the additional chemical pathways. Although the overall NCN consumption by H-2 remains small, significant differences have been observed for NO yields with the updated mechanism. A detailed flux analysis revealed that HNC, mainly arising from HCN/HNC isomerization, plays a decisive role and enhances NO formation through a new HNC -> HNCO -> NH2 -> NH -> NO pathway.

Document Type: Article
Additional Information: Times Cited: 3
Research affiliation: Kiel University
Kiel University > Kiel Marine Science
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
ISSN: 1463-9076
Projects: Future Ocean
Date Deposited: 20 Oct 2016 10:52
Last Modified: 21 Mar 2017 11:51
URI: http://oceanrep.geomar.de/id/eprint/32469

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