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Title: Multiscalar imaging in partially premixed jet flames with argon dilution

Abstract

Simultaneous imaging of depolarized and polarized Rayleigh scattering combined with OH-LIF and two-photon CO-LIF provides two-dimensional measurements of mixture fraction, temperature, scalar dissipation rate, and the forward reaction rate of the reaction CO+OH=CO{sub 2}+H in turbulent partially premixed flames. The concept of the three-scalar technique for determining the mixture fraction using CO-LIF with depolarized and polarized Rayleigh signals was previously demonstrated in a partially premixed CH{sub 4}/air jet flame [J.H. Frank, S.A. Kaiser, M.B. Long, Proc. Combust. Inst. 29 (2002) 2687-2694]. In the experiments presented here, we consider a similar jet flame with a fuel-stream mixture that is better suited for the diagnostic technique. The contrast between the depolarized and the polarized Rayleigh signals in the fuel and air streams is improved by partially premixing with an argon/oxygen mixture that has the same oxygen content as air. The substitution of argon, which has a zero depolarization ratio, for the nitrogen in air decreases the depolarized Rayleigh signal in the fuel stream and thereby increases the contrast between the depolarized and the polarized Rayleigh signals. We present a collection of instantaneous 2-D measurements and examine conditional means of temperature, scalar dissipation, and reaction rates for two downstream locations. The emphasis ismore » on the determination of the scalar dissipation rate from the mixture-fraction images. The axial and radial contributions to scalar dissipation are measured. The effects of noise on the scalar dissipation measurements are determined in a laminar flame, and a method for subtracting the noise contribution to the scalar dissipation rates is demonstrated.« less

Authors:
;  [1];  [2]
  1. Combustion Research Facility, Sandia National Laboratories, Livermore, CA 94551-0969 (United States)
  2. Department of Mechanical Engineering, Yale University, New Haven, CT 06520-8284 (United States)
Publication Date:
OSTI Identifier:
20681467
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 143; Journal Issue: 4; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; FLAMES; JETS; CARBON MONOXIDE; HYDROXYL RADICALS; CARBON DIOXIDE; HYDROGEN; RAYLEIGH SCATTERING; COMBUSTION KINETICS; ARGON

Citation Formats

Frank, J.H., Kaiser, S.A., and Long, M.B.. Multiscalar imaging in partially premixed jet flames with argon dilution. United States: N. p., 2005. Web. doi:10.1016/j.combustflame.2005.08.027.
Frank, J.H., Kaiser, S.A., & Long, M.B.. Multiscalar imaging in partially premixed jet flames with argon dilution. United States. doi:10.1016/j.combustflame.2005.08.027.
Frank, J.H., Kaiser, S.A., and Long, M.B.. Thu . "Multiscalar imaging in partially premixed jet flames with argon dilution". United States. doi:10.1016/j.combustflame.2005.08.027.
@article{osti_20681467,
title = {Multiscalar imaging in partially premixed jet flames with argon dilution},
author = {Frank, J.H. and Kaiser, S.A. and Long, M.B.},
abstractNote = {Simultaneous imaging of depolarized and polarized Rayleigh scattering combined with OH-LIF and two-photon CO-LIF provides two-dimensional measurements of mixture fraction, temperature, scalar dissipation rate, and the forward reaction rate of the reaction CO+OH=CO{sub 2}+H in turbulent partially premixed flames. The concept of the three-scalar technique for determining the mixture fraction using CO-LIF with depolarized and polarized Rayleigh signals was previously demonstrated in a partially premixed CH{sub 4}/air jet flame [J.H. Frank, S.A. Kaiser, M.B. Long, Proc. Combust. Inst. 29 (2002) 2687-2694]. In the experiments presented here, we consider a similar jet flame with a fuel-stream mixture that is better suited for the diagnostic technique. The contrast between the depolarized and the polarized Rayleigh signals in the fuel and air streams is improved by partially premixing with an argon/oxygen mixture that has the same oxygen content as air. The substitution of argon, which has a zero depolarization ratio, for the nitrogen in air decreases the depolarized Rayleigh signal in the fuel stream and thereby increases the contrast between the depolarized and the polarized Rayleigh signals. We present a collection of instantaneous 2-D measurements and examine conditional means of temperature, scalar dissipation, and reaction rates for two downstream locations. The emphasis is on the determination of the scalar dissipation rate from the mixture-fraction images. The axial and radial contributions to scalar dissipation are measured. The effects of noise on the scalar dissipation measurements are determined in a laminar flame, and a method for subtracting the noise contribution to the scalar dissipation rates is demonstrated.},
doi = {10.1016/j.combustflame.2005.08.027},
journal = {Combustion and Flame},
number = 4,
volume = 143,
place = {United States},
year = {Thu Dec 01 00:00:00 EST 2005},
month = {Thu Dec 01 00:00:00 EST 2005}
}
  • We report on the application of simultaneous single-shot imaging of CH and OH radicals using planar laser-induced fluorescence (PLIF) to investigate partially premixed turbulent jet flames. Various flames have been stabilized on a coaxial jet flame burner consisting of an outer and an inner tube of diameter 22 and 2.2 mm, respectively. From the outer tube a rich methane/air mixture was supplied at a relatively low flow velocity, while a jet of pure air was introduced from the inner one, resulting in a turbulent jet flame on top of a laminar pilot flame. The turbulence intensity was controlled by varyingmore » the inner jet flow speed from 0 up to 120 m/s, corresponding to a maximal Reynolds number of the inner jet airflow of 13,200. The CH/OH PLIF imaging clearly revealed the local structure of the studied flames. In the proximity of the burner, a two-layer reaction zone structure was identified where an inner zone characterized by strong CH signals has a typical structure of rich premixed flames. An outer reaction zone characterized by strong OH signals has a typical structure of a diffusion flame that oxidizes the intermediate fuels formed in the inner rich premixed flame. In the moderate-turbulence flow, the CH layers were very thin closed surfaces in the entire flame, whereas the OH layers were much thicker. In the high-intensity-turbulence flame, the CH layer remained thin until it vanished in the upper part of the flame, showing local extinction and reignition behavior of the flame. The single-shot PLIF images have been utilized to determine the flame surface density (FSD). In low and moderate turbulence intensity cases the FSDs determined from CH and OH agreed with each other, while in the highly turbulent case a locally broken CH layer was observed, leading to a significant difference in the FSD results determined via the OH and CH radicals. Furthermore, the means and the standard deviations of CH and OH radicals were obtained to provide statistical information about the flames that may be used for validation of numerical calculations. (author)« less
  • Measurements of visible flame heights, global radiative heat loss fractions, distributions of mole fractions of stable gas species, and pollutant emission indices in laminar partially premixed flames burning various fuel-rich mixtures of CH{sub 4} and air in an overventilating co-flow of air are reported. Mole fractions of CO{sub 2}, CO, H{sub 2}, O{sub 2}, N{sub 2} CH{sub 4}, C{sub 2}H{sub 4} and C{sub 2}H{sub 2} were measured, using sampling and gas chromatography, at several radial locations at three different heights above the fuel tube for a fixed fuel flow rate and six different fuel tube equivalence ratios. Mole fractions ofmore » H{sub 2}O were inferred from the dry based measurements. With increasing levels of partial premixing following effects are observed: (1) the visible flame height decreases and the overall flame color changes from yellow to blue; (2) the radiative heat loss fraction first decreases and then reaches a constant value; (3) the mole fractions of CO decrease and those of CO{sub 2} and H{sub 2}O increase in the lean parts of the flame; (4) mole fractions of C{sub 2}H{sub 2} decrease and those of C{sub 2}H{sub 4} first increase and then decrease in the rick parts of the flame; (5) mole fractions of CO and H{sub 2} first decrease slightly and then increase in the rich parts of the flame; and (6) the O{sub 2} mole fractions at the point of negligible CH{sub 4} mole fraction decrease. Measurements of emission indices for NO, NO{sub x}, CO and HC show that, for a fixed fuel flow rate and overall equivalence ratio, an optimum level of partial premixing exists.« less
  • The authors measured emission indices for NO{sub x}, CO, and HC for turbulent partially premixed flames formed by injecting rich methane/air mixtures through a central burner tube into a co-flow of air. The operating conditions included a broad range of burner tube equivalence ratios ({Phi}{sub B}) including the limiting cases of diffusion and stoichiometric premixed flames. At sufficiently high levels of partial premixing, a double flame structure consisting of a rich premixed inner flame and an outer diffusion flame is established similar to that previously observed in laminar flames. EINO{sub x} values remain approximately constant for 5 {le} {Phi}{sub B}more » {le} {infinity} and then decrease slightly with decreasing {Phi}{sub B} at 3.5 {le} {Phi}{sub B} {le} 5. For 3.5 {le} {Phi}{sub B} {le} 1.5, EINO{sub x} decreases further with decreasing {Phi}{sub B} to a minimum at around {Phi}{sub B} = 1.5, followed by a sharp increase as {Phi}{sub B} approaches unity. The reduction in EINO{sub x} at {Phi}{sub B} = 1.5 as compared with that for the diffusion flame is approximately 25% and as compared with that for the stoichiometric premixed flame is approximately 35%. In addition, the authors measured temperature distributions and found that temperatures increase continuously with increasing partial premixing. They also estimated global residence times ({tau}{sub 0}) from flame length measurements and average velocities. The observed changes in temperatures and residence times are not sufficient to explain the observed changes in EINO{sub x}.« less