Intracavity laser absorption spectroscopy of NH2 in methane/air flames doped with N2O, NO, and NH3

I. Rahinov, N. Ditzian, A. Goldman, S. Cheskis

Research output: Contribution to journalConference articlepeer-review

Abstract

Intracavity laser absorption spectroscopy (ICLAS) was used to measure concentration profiles of NH2 in low pressure (30 Torr) methane/oxygen/nitrogen flames doped with small amounts of N2O, NO, and NH3. The effective optical length of ICLAS, which dictates the sensitivity of the method, is controlled by the generation time of the quasi-cw-laser. The effective optical length of 0.87 km, reached at generation time of 75 μs, provides very high sensitivity: from 5×1010 molecules/cm3 at 500 K in the vicinity of burner up to 2×1011 molecules/cm3 in the burned gas zone (T∼ 1800 K). The radial profile of NH2, measured using a tomographic technique, indicates that the radical is located mainly inside a cylinder with diameter equal to the burner diameter. For the first time, the absolute mole fraction profiles of NH2 were measured in hydrocarbon flames with different dopants and compared with one-dimensional calculations based on the GRI-3.0 mechanism. The dependence of the NH2 concentrations on the equivalence ratio is in excellent agreement with the model prediction. The absolute NH2 concentration values for different dopants are predicted very well by the calculations apart from the NO-doped flame where GRI-Mech 3.0 overpredicts the NH2 concentration by a factor of 2. In the ammonia-doped flame, the calculations predict an additional concentration maximum located close to the burner. This maximum is not observable in the experiment. All the experimental profiles exhibit 1-2 mm shift further from the burner surface in comparison with the predicted ones. The reasons of those discrepancies are discussed.

Original languageEnglish
Pages (from-to)1575-1582
Number of pages8
JournalProceedings of the Combustion Institute
Volume30
Issue number1
DOIs
StatePublished - 2005
Event30th International Symposium on Combustion - Chicago, IL, United States
Duration: 25 Jul 200430 Jul 2004

Keywords

  • Laminar flames
  • Laser diagnostics
  • Nitrogen chemistry
  • Spectroscopy

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