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

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T1 - Strategy for improved NH2 detection in combustion environments using an Alexandrite laser

AU - Brackmann, Christian

AU - Zhou, Bo

AU - Samuelsson, Per

AU - Alekseev, Vladimir A.

AU - Konnov, Alexander A.

AU - Li, Zhongshan

AU - Aldén, Marcus

PY - 2017/9/5

Y1 - 2017/9/5

N2 - 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.

AB - 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.

KW - Combustion

KW - Laser-induced fluorescence

KW - NH radical

UR - http://www.scopus.com/inward/record.url?scp=85019143618&partnerID=8YFLogxK

U2 - 10.1016/j.saa.2017.05.002

DO - 10.1016/j.saa.2017.05.002

M3 - Article

C2 - 28501744

AN - SCOPUS:85019143618

VL - 184

SP - 235

EP - 242

JO - Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

JF - Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

SN - 1386-1425

ER -