Experimental and numerical study of the role of NCN in prompt-NO formation in low-pressure CH sub(4)-O sub(2)-N sub(2) and C sub(2)H sub(2)-O sub(2)-N sub(2) flames

We report an experimental and modeling study on prompt-NO formation in low-pressure (5.3 kPa) premixed flames. Special emphasis is given to the quantitative detection (and prediction) of NCN, whose role in prompt-NO formation has recently been confirmed in alkane flames. Here a rich ([Phi] = 1.25) C...

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Veröffentlicht in:Combustion and flame 2010-10, Vol.157 (10), p.1929-1941
Hauptverfasser: Lamoureux, N, Desgroux, P, El Bakali, A, Pauwels, J F
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Sprache:eng
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Zusammenfassung:We report an experimental and modeling study on prompt-NO formation in low-pressure (5.3 kPa) premixed flames. Special emphasis is given to the quantitative detection (and prediction) of NCN, whose role in prompt-NO formation has recently been confirmed in alkane flames. Here a rich ([Phi] = 1.25) CH sub(4)-O sub(2)-N sub(2) flame and rich ([Phi] = 1.25) and stoichiometric C sub(2)H sub(2)-O sub(2)-N sub(2) flames have been investigated. Absolute concentration profiles of CH and NCN radicals and NO species are obtained by combining laser-induced fluorescence (LIF) and cavity ring-down spectroscopy (CRDS). Temperature profile is determined in each flame using OH and NO-LIF thermometry. Flame modeling is performed to determine the role of NCN in prompt-NO formation and to test the capacity of the present chemical mechanisms to predict some intermediate species involved in prompt-NO formation. The methane flame is modeled using GDFkin[registered]3.0_NCN mechanism [El Bakali et al., Fuel 85 (2006), 896-909]. The acetylene flames are modeled using the Lindstedt and Skevis C/H/O mechanism [Lindstedt and Skevis, Proc. Combust. Inst. 28 (2000), 1801-1807], completed by the submechanism issued from GDFkin[registered]3.0_NCN for nitrogen chemistry. This submechanism includes the initiation reaction CH + N sub(2) = NCN + H. Rate constants of NO-sensitive reactions of the submechanism are modified by taking into account the recent literature. In particular, the C sub(2)O route could be explored thanks to a significant presence of C sub(2)O in acetylene flames. Globally, the modified submechanism of nitrogen chemistry coupled with the two hydrocarbon mechanisms leads to a satisfying prediction of NCN and NO mole fraction profiles, even though refinements of rate constant determination is still required. The role of NCN in prompt-NO formation in acetylene flames is demonstrated.
ISSN:0010-2180
DOI:10.1016/j.combustflame.2010.03.013