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Strategy for improved NH2 detection in combustion environments using an Alexandrite laser

Brackmann, Christian LU ; Zhou, Bo LU ; Samuelsson, Per LU ; Alekseev, Vladimir A. LU ; Konnov, Alexander A. LU ; Li, Zhongshan LU and Aldén, Marcus LU (2017) In Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy 184. p.235-242
Abstract

A new scheme for NH2 detection by means of laser-induced fluorescence (LIF) with excitation around wavelength 385 nm, accessible using the second harmonic of a solid-state Alexandrite laser, is presented. Detection of NH2 was confirmed by identification of corresponding lines in fluorescence excitation spectra measured in premixed NH3-air flames and on NH2 radicals generated through NH3 photolysis in a nonreactive flow at ambient conditions. Moreover, spectral simulations allow for tentative NH2 line identification. Dispersed fluorescence emission spectra measured in flames and photolysis experiments showed lines attributed to vibrational bands of the NH2... (More)

A new scheme for NH2 detection by means of laser-induced fluorescence (LIF) with excitation around wavelength 385 nm, accessible using the second harmonic of a solid-state Alexandrite laser, is presented. Detection of NH2 was confirmed by identification of corresponding lines in fluorescence excitation spectra measured in premixed NH3-air flames and on NH2 radicals generated through NH3 photolysis in a nonreactive flow at ambient conditions. Moreover, spectral simulations allow for tentative NH2 line identification. Dispersed fluorescence emission spectra measured in flames and photolysis experiments showed lines attributed to vibrational bands of the NH2 A2A1 ← X2B1 transition but also a continuous structure, which in flame was observed to be dependent on nitrogen added to the fuel, apparently also generated by NH2. A general conclusion was that fluorescence interferences need to be carefully considered for NH2 diagnostics in this spectral region. Excitation for laser irradiances up to 0.2 GW/cm2 did not result in NH2 fluorescence saturation and allowed for efficient utilization of the available laser power without indication of laser-induced photochemistry. Compared with a previously employed excitation/detection scheme for NH2 at around 630 nm, excitation at 385.7 nm showed a factor of ~ 15 higher NH2 signal. The improved signal allowed for single-shot NH2 LIF imaging on centimeter scale in flame with signal-to-noise ratio of 3 for concentrations around 1000 ppm, suggesting a detection limit around 700 ppm. Thus, the presented approach for NH2 detection provides enhanced possibilities for characterization of fuel-nitrogen combustion chemistry.

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author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Combustion, Laser-induced fluorescence, NH radical
in
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy
volume
184
pages
8 pages
publisher
Elsevier
external identifiers
  • scopus:85019143618
  • wos:000403742500029
ISSN
1386-1425
DOI
10.1016/j.saa.2017.05.002
language
English
LU publication?
yes
id
45168874-cada-426a-a68d-0e79d4b67b29
date added to LUP
2017-05-29 10:50:12
date last changed
2017-09-18 11:37:40
@article{45168874-cada-426a-a68d-0e79d4b67b29,
  abstract     = {<p>A new scheme for NH<sub>2</sub> detection by means of laser-induced fluorescence (LIF) with excitation around wavelength 385 nm, accessible using the second harmonic of a solid-state Alexandrite laser, is presented. Detection of NH<sub>2</sub> was confirmed by identification of corresponding lines in fluorescence excitation spectra measured in premixed NH<sub>3</sub>-air flames and on NH<sub>2</sub> radicals generated through NH<sub>3</sub> photolysis in a nonreactive flow at ambient conditions. Moreover, spectral simulations allow for tentative NH<sub>2</sub> line identification. Dispersed fluorescence emission spectra measured in flames and photolysis experiments showed lines attributed to vibrational bands of the NH<sub>2</sub> A<sup>2</sup>A<sub>1</sub> ← X<sup>2</sup>B<sub>1</sub> transition but also a continuous structure, which in flame was observed to be dependent on nitrogen added to the fuel, apparently also generated by NH<sub>2</sub>. A general conclusion was that fluorescence interferences need to be carefully considered for NH<sub>2</sub> diagnostics in this spectral region. Excitation for laser irradiances up to 0.2 GW/cm<sup>2</sup> did not result in NH<sub>2</sub> fluorescence saturation and allowed for efficient utilization of the available laser power without indication of laser-induced photochemistry. Compared with a previously employed excitation/detection scheme for NH<sub>2</sub> at around 630 nm, excitation at 385.7 nm showed a factor of ~ 15 higher NH<sub>2</sub> signal. The improved signal allowed for single-shot NH<sub>2</sub> LIF imaging on centimeter scale in flame with signal-to-noise ratio of 3 for concentrations around 1000 ppm, suggesting a detection limit around 700 ppm. Thus, the presented approach for NH<sub>2</sub> detection provides enhanced possibilities for characterization of fuel-nitrogen combustion chemistry.</p>},
  author       = {Brackmann, Christian and Zhou, Bo and Samuelsson, Per and Alekseev, Vladimir A. and Konnov, Alexander A. and Li, Zhongshan and Aldén, Marcus},
  issn         = {1386-1425},
  keyword      = {Combustion,Laser-induced fluorescence,NH radical},
  language     = {eng},
  month        = {09},
  pages        = {235--242},
  publisher    = {Elsevier},
  series       = {Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy},
  title        = {Strategy for improved NH<sub>2</sub> detection in combustion environments using an Alexandrite laser},
  url          = {http://dx.doi.org/10.1016/j.saa.2017.05.002},
  volume       = {184},
  year         = {2017},
}