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Title: Laser-saturated fluorescence of nitric oxide and chemiluminescence measurements in premixed ethanol flames

Abstract

In this study, nitric oxide laser-saturated fluorescence (LSF) measurements were acquired from premixed ethanol flames at atmospheric pressure in a burner. NO-LSF experimental profiles for fuel-rich premixed ethanol flames ({phi} = 1.34 and {phi} = 1.66) were determined through the excitation/detection scheme of the Q{sub 2}(26.5) rotational line in the A{sup 2}{sigma}{sup +} - X{sup 2}{pi} (0,0) vibronic band and {gamma}(0,1) emission band. A calibration procedure by NO doping into the flame was applied to establish the NO concentration profiles in these flames. Chemiluminescent emission measurements in the (0, 0) vibronic emission bands of the OH{sup *} (A{sup 2}{sigma}{sup +} - X{sup 2}{pi}) and CH{sup *}(A{sup 2}{delta} - X{sup 2}{pi}) radicals were also obtained with high spatial and spectral resolution for fuel-rich premixed ethanol flames to correlate them with NO concentrations. Experimental chemiluminescence profiles and the ratios of the integrated areas under emission spectra (A{sub CH*}/A{sub CH*}(max.) and A{sub CH*}/A{sub OH*}) were determined. The relationships between chemiluminescence and NO concentrations were established along the premixed ethanol flames. There was a strong connection between CH{sup *} radical chemiluminescence and NO formation and the prompt-NO was identified as the governing mechanism for NO production. The results suggest the optimum ratio of themore » chemiluminescence of two radicals (A{sub CH*}/A{sub OH*}) for NO diagnostic purposes. (author)« less

Authors:
; ; ;  [1]
  1. Aerothermodynamic and Hypersonic Division, Institute of Advanced Studies - General Command of Aerospatial Technology, Rodovia dos Tamoios, km 5.5, 12228-001 Sao Jose dos Campos - SP (Brazil)
Publication Date:
OSTI Identifier:
21350384
Resource Type:
Journal Article
Resource Relation:
Journal Name: Experimental Thermal and Fluid Science; Journal Volume: 34; Journal Issue: 8; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; NITRIC OXIDE; CHEMILUMINESCENCE; ETHANOL; FLUORESCENCE; COMBUSTION; RADICALS; EMISSION SPECTRA; EXCITATION; HYDROXYL RADICALS; ATMOSPHERIC PRESSURE; BURNERS; CALIBRATION; DETECTION; CORRELATIONS; Premixed flames

Citation Formats

Marques, Carla S.T., Barreta, Luiz G., Sbampato, Maria E., and dos Santos, Alberto M. Laser-saturated fluorescence of nitric oxide and chemiluminescence measurements in premixed ethanol flames. United States: N. p., 2010. Web. doi:10.1016/J.EXPTHERMFLUSCI.2010.04.003.
Marques, Carla S.T., Barreta, Luiz G., Sbampato, Maria E., & dos Santos, Alberto M. Laser-saturated fluorescence of nitric oxide and chemiluminescence measurements in premixed ethanol flames. United States. doi:10.1016/J.EXPTHERMFLUSCI.2010.04.003.
Marques, Carla S.T., Barreta, Luiz G., Sbampato, Maria E., and dos Santos, Alberto M. 2010. "Laser-saturated fluorescence of nitric oxide and chemiluminescence measurements in premixed ethanol flames". United States. doi:10.1016/J.EXPTHERMFLUSCI.2010.04.003.
@article{osti_21350384,
title = {Laser-saturated fluorescence of nitric oxide and chemiluminescence measurements in premixed ethanol flames},
author = {Marques, Carla S.T. and Barreta, Luiz G. and Sbampato, Maria E. and dos Santos, Alberto M.},
abstractNote = {In this study, nitric oxide laser-saturated fluorescence (LSF) measurements were acquired from premixed ethanol flames at atmospheric pressure in a burner. NO-LSF experimental profiles for fuel-rich premixed ethanol flames ({phi} = 1.34 and {phi} = 1.66) were determined through the excitation/detection scheme of the Q{sub 2}(26.5) rotational line in the A{sup 2}{sigma}{sup +} - X{sup 2}{pi} (0,0) vibronic band and {gamma}(0,1) emission band. A calibration procedure by NO doping into the flame was applied to establish the NO concentration profiles in these flames. Chemiluminescent emission measurements in the (0, 0) vibronic emission bands of the OH{sup *} (A{sup 2}{sigma}{sup +} - X{sup 2}{pi}) and CH{sup *}(A{sup 2}{delta} - X{sup 2}{pi}) radicals were also obtained with high spatial and spectral resolution for fuel-rich premixed ethanol flames to correlate them with NO concentrations. Experimental chemiluminescence profiles and the ratios of the integrated areas under emission spectra (A{sub CH*}/A{sub CH*}(max.) and A{sub CH*}/A{sub OH*}) were determined. The relationships between chemiluminescence and NO concentrations were established along the premixed ethanol flames. There was a strong connection between CH{sup *} radical chemiluminescence and NO formation and the prompt-NO was identified as the governing mechanism for NO production. The results suggest the optimum ratio of the chemiluminescence of two radicals (A{sub CH*}/A{sub OH*}) for NO diagnostic purposes. (author)},
doi = {10.1016/J.EXPTHERMFLUSCI.2010.04.003},
journal = {Experimental Thermal and Fluid Science},
number = 8,
volume = 34,
place = {United States},
year = 2010,
month =
}
  • Quantitative measurements of NO concentrations ([NO]) have been obtained along the centerline of atmospheric ethane-air counterflow diffusion flames by using saturated and linear laser-induced fluorescence (LIF). In particular, four flames with strain rates varying from 5 to 48 s{sup {minus}1} were investigated while maintaining a constant fuel dilution in all cases. The utility of a broad-band laser-saturated fluorescence (LSF) technique is assessed by comparison to similar measurements of NO using linear LIF. The linear LIF measurements are corrected for variations in the local electronic quenching rate coefficient by using major species profiles generated by a diffusive flame code and availablemore » correlations for the quenching cross-sections of NO. The corrected LIF profiles compare favorably with the LSF profiles. A four-level model is used to investigate the effects of rotational energy transfer (RET) on the LSF measurements. The excellent comparison between the quenching-corrected linear LIF and the LSF measurements at locally fuel-lean to greater than stoichiometric mixture fractions verifies the validity of the LKSF technique for these conditions. The slight but consistent discrepancy between the LSF and linear LIF measurements at local equivalence ratios above 1.6 may be attributed to a change in the collisional branching ratio from lean to rich stoichiometries and/or the need for further work on the electronic quenching cross-sections required for quantitative NO measurements under fuel-rich conditions.« less
  • Inverse diffusion flames (IDFs) are a primary component of staged-air combustion processes, which are often used to achieve ultralow NO{sub x} emissions. Unfortunately, such IDFs created by mixing air with hot fuel-rich combustion products rather than the usual unreacted fuel have received little previous attention in the literature. Here, the authors use laser-saturated fluorescence (LSF) to make nonintrusive point measurements of nitric oxide concentration throughout a single atmospheric IDF of this type; thermocouple-based temperature measurements are also made at specific locations including those of the concentration measurements. These measurements demonstrate similarities between IDF and normal diffusion flame behavior, and indicatemore » that the majority of the IDF-attributable NO is generated at the IDF tip. The results suggest that the dominant NO mechanism varies throughout the flame, and provide data relevant to assessment of future kinetics models.« less
  • In recent years, there has been increased concern over the adverse effects of combustion on the environment. Much of this concern focuses on the environmental problems caused by nitric oxide. Because many combustion applications, such as gas turbines and internal combustion engines, operate at high pressure, quantitative measurements of NO at such pressures are required to gain a better understanding of practical processes leading to NO formation. Such an improved understanding could lead to new combustion strategies that would further reduce NO emissions. One of the promising techniques for making accurate NO measurements at high pressure is laser-induced fluorescence (LIF).more » In this brief communication, the authors present quantitative LIF measurements of NO in C[sub 2]H[sub 6]/O[sub 2]/N[sub 2] flames at 1-9 atm, thereby demonstrating the feasibility of such measurements at high pressure. The authors have successfully used LIF to make quantitative measurements of NO down to [approximately] 1 ppm at pressures up to 9 atm. The location of maximum NO concentration shifts towards leaner equivalence ratios with increasing pressure. Quantitative NO concentration measurements using LIF should be achievable at even higher pressures.« less
  • Quantitative laser-induced fluorescence (LIF) measurements of nitric oxide concentrations[NO] have been obtained along the centerline in atmospheric pressure methane-air and ethane-air counterflow diffusion flames. These flames are highly diluted to avoid both soot formation and the influence of radiative heat losses on NO formation, thereby ensuring NO production mostly via the prompt mechanism. Linear LIF measurements of [NO] are corrected for variations in the electronic quenching rate coefficient by using major species profiles generated by an opposed-flow flame code and quenching cross-sections for NO available from the literature. Temperature measurements are also made in the methane-air counterflow diffusion flames bymore » using thin SiC filament pyrometry. The excellent agreement between temperature measurements and model predictions verifies the efficacy of a new calibration method developed for thin filament pyrometry. Predictions using the GRI mechanism consistently underpredict peak [NO] in all flames. This result indicates a need for refinement of both the prompt-NO and CH kinetics, especially the rate coefficient for the prompt-NO initiation reaction. A modified rate coefficient proposed for the prompt-NO initiation reaction significantly improves agreement between modeling and measurements in both the methane-air and ethane-air counterflow diffusion flames. The remaining discrepancy in some flames can be attributed to a lack of refinement in the CH chemistry. Overall, the modified rate coefficient proposed here seems to be a good choice over a wide range of strain rates for both methane and ethane fuels.« less
  • A feasibility study has been performed on the application of laser-saturated fluorescence (LSF) to the measurement of OH concentration in high-pressure flames. Using a numerial model for the collisional dynamics of the OH molecule under nonuniform laser excitation, we have investigated the effect of pressure on the balanced cross-rate model and determined the sensitivity of the depopulation of the laser-coupled levels to the ratio of rate coefficients describing (1) electronic quenching of the vibrational levels for which v''>0 and (2) vibrational relaxation from v''>0 to v'' = 0. At sufficiently high pressures in near-saturated conditions, the total population of themore » laser-coupled levels reaches an asymptotic value, which is insensitive to the degree of saturation. When the ratio of electronic quenching is vibrational relaxation is small and the rate coefficients for rotational transfer in the ground and excited electronic states are nearly the same, the balanced cross-rate model remains a good approximation for all pressures. When the above ratio is large, depopulation of the laser-coupled levels becomes significant at high pressures, and thus the balanced cross-rate model no longer holds. In these conditions, however, knowledge of the asymptotic value achieved by the laser-coupled levels could be used to correct the balanced cross-rate model and thus allow LSF measurements at sufficiently high pressures.« less