On the role of C2O radicals in the prompt-NO mechanism

Abstract

The measurements of NO concentrations in the post-flame zone of different hydrocarbon + O 2 + N 2 flames at standard temperature and atmospheric pressure available in the literature are compared with predictions of the original Konnov reaction mechanism and with the same mechanism extended by the reaction of C 2 O with N 2 . The goal was to investigate the possible role of this reaction proposed by Williams and Fleming [P roc. Combust. Inst., Vol. 31 (2007), pp. 1109-1117]. This new reaction of C 2 O with N 2 seems to be a reasonable explanation of the deficiencies in the prompt-NO route. Direct comparisons of the experimental measurements performed in different flames with the modeling strongly suggests that the upper limit of this reaction rate constant is k = 7 · 10 11 exp(−17,000/RT ) [cm 3 /(mole · sec)].

Experimental and numerical study of the role of NCN in prompt-NO formation in low-pressure CH4–O2–N2 and C2H2–O2–N2 flames

“…Additionally, the revised GDFkin Ò 3.0_NCN mechanism has been validated against experimental measurements of Berg et al [42,43], Sutton et al [4], and Pillier et al [17]. The C 2 O route has also been considered by including the reaction C 2 O + N 2 = NCN + CO, to which rate constants proposed either by Williams and Fleming [24] or by Konnov [26] have been applied. The best compromise was found with Konnov's.…”

“…The obtained database has allowed testing chemical mechanisms for prompt-NO predictions incorporating the recent routes and rate constants proposed in the literature [9,12,13,24,26,53]. For the methane flame we have used the GDFkin Ò 3.0_NCN mechanism which was developed for natural gas oxidation in various reactors.…”

“…The N-species submechanism is (see numbers of patterns at top of Fig. 12a) (1) initial one, (2) revised one according to Table 3, (3) where the rate constant of the CH 2 + N 2 = HCN + NH is replaced by the one from Sanders et al [21], (4) includes the reaction C 2 O + N 2 = NCN + CO with the rate constant from Williams and Fleming [24], (5) includes the reaction C 2 O + N 2 = NCN + CO with the rate constant from Konnov [26]. acetylene flame, suggesting that a parallel route could be important in this flame.…”

“…Later on, Williams et al [18] gave up the C 2 O route due the fact that in the lean and ultralean methane-air mixtures, the concentration of C 2 O is extremely small. Konnov [26] examined the possible role of C 2 O, including the reaction C 2 O + N 2 = products. Here, the products were assumed to be either NCO + CN or CNN + CO, for which Konnov proposed a rate constant.…”

“…Sensitivity analysis for labeled species at the NCN peak value location in: (a) the rich CH 4 -O 2 -N 2 flame using the initial GDFkin Ò 3.0_NCN mechanism[7], (b) the rich, and (c) the stoichiometric C 2 H 2 -O 2 -N 2 flame using the LSN mechanism[26,28].…”