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Title: Structural study of non-premixed tubular hydrocarbon flames

Abstract

Tubular non-premixed flames are formed by a uniquely designed opposed tubular burner. Structural measurements of hydrocarbon flames are conducted using the laser-induced Raman scattering technique. Temperature and major species concentrations are recorded for flames produced by 30% CH{sub 4}/N{sub 2} and 15% C{sub 3}H{sub 8}/N{sub 2} burning against air. Numerical simulations of these flames with detailed chemistry show good agreement between the measured and simulated results. By comparing the numerical results of the tubular curved flames to those of the opposed-jet planar flames, it is shown that flame curvature towards the fuel stream strongly effects the temperature ({+-}80 K) of flames with low fuel Lewis number (15% H{sub 2}/N{sub 2}, Le{sub f} = 0.41). The effect of curvature on flames with high (15% C{sub 3}H{sub 8}/N{sub 2}, Le{sub f} = 1.51) and near-unity (30% CH{sub 4}/N{sub 2}, Le{sub f}{approx_equal}1) fuel Lewis numbers is much less. (author)

Authors:
;  [1]
  1. Mechanical Engineering Department, Vanderbilt University, Nashville, TN 37235 (United States)
Publication Date:
OSTI Identifier:
21227374
Resource Type:
Journal Article
Resource Relation:
Journal Name: Combustion and Flame; Journal Volume: 156; Journal Issue: 1; Other Information: Elsevier Ltd. All rights reserved
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METHANE; PROPANE; FLAMES; AIR; FUELS; HYDROGEN; CONFIGURATION; LEWIS NUMBER; SIMULATION; BURNERS; COMBUSTION KINETICS; NITROGEN; TUBES

Citation Formats

Hu, Shengteng, and Pitz, Robert W. Structural study of non-premixed tubular hydrocarbon flames. United States: N. p., 2009. Web. doi:10.1016/J.COMBUSTFLAME.2008.07.017.
Hu, Shengteng, & Pitz, Robert W. Structural study of non-premixed tubular hydrocarbon flames. United States. doi:10.1016/J.COMBUSTFLAME.2008.07.017.
Hu, Shengteng, and Pitz, Robert W. 2009. "Structural study of non-premixed tubular hydrocarbon flames". United States. doi:10.1016/J.COMBUSTFLAME.2008.07.017.
@article{osti_21227374,
title = {Structural study of non-premixed tubular hydrocarbon flames},
author = {Hu, Shengteng and Pitz, Robert W.},
abstractNote = {Tubular non-premixed flames are formed by a uniquely designed opposed tubular burner. Structural measurements of hydrocarbon flames are conducted using the laser-induced Raman scattering technique. Temperature and major species concentrations are recorded for flames produced by 30% CH{sub 4}/N{sub 2} and 15% C{sub 3}H{sub 8}/N{sub 2} burning against air. Numerical simulations of these flames with detailed chemistry show good agreement between the measured and simulated results. By comparing the numerical results of the tubular curved flames to those of the opposed-jet planar flames, it is shown that flame curvature towards the fuel stream strongly effects the temperature ({+-}80 K) of flames with low fuel Lewis number (15% H{sub 2}/N{sub 2}, Le{sub f} = 0.41). The effect of curvature on flames with high (15% C{sub 3}H{sub 8}/N{sub 2}, Le{sub f} = 1.51) and near-unity (30% CH{sub 4}/N{sub 2}, Le{sub f}{approx_equal}1) fuel Lewis numbers is much less. (author)},
doi = {10.1016/J.COMBUSTFLAME.2008.07.017},
journal = {Combustion and Flame},
number = 1,
volume = 156,
place = {United States},
year = 2009,
month = 1
}
  • Centerline measurements have been made of temperature, CH{sub 4}, P{sub 2}, CO{sub 2}, and C2 to C12 nonfuel hydrocarbons in a CH{sub 4}/air nonpremixed coflowing flame and in five partially premixed coflowing flames with primary equivalence ratios varying rom 12.3 to 2.5. Partial premixing decreases the flame height and thereby compresses all of the profiles towards the burner furnace, so a nondimensional vertical coordinate has been developed to account for this and make other effects more apparent. The temperature and major species results show that partial premixing reduces radial heat and mass transfer in the lower part of the flames,more » and causes an inner rich premixed flame front to form at one-half the height of the outer flame front. Partial premixing increases the mole fractions of the oxygenated hydrocarbons CH{sub 2}O and C{sub 2}H{sub 2}O to hundreds of parts per million, and of C{sub 2}H{sub 4}O and C{sub 3}H{sub 4}O to parts per million. The mole fractions of regular hydrocarbons are decreased by partial premixing, in roughly the same proportion as they are reduced by dilution with nitrogen, which suggests that fuel dilution is the primary cause. The decrease in concentrations is progressively greater for larger hydrocarbons. In the flames that exhibit a double flame structure, nonfuel hydrocarbons are formed inside the inner rich premixed flame front, peak at this front, and are completely consumed in the region between the flame fronts.« less
  • Global emissions of NO{sub x} in a liquid-fueled lean-premixed tubular combustor with a tubular premixer operating under atmospheric pressure are studied experimentally. The effects of equivalence ratio, premixer length, residence time, fuel type, and fuel atomization and dispersion characteristics on NO{sub x} emissions are studied. Measurements of exhaust species concentrations are used as the primary indicator of the effectiveness of premixing-prevaporization upstream of the combustor. Qualitative levels of prevaporization-premixing are determined from Mie-scattering signals measured at the exit of the premixer. Emission measurements show that the equivalence ratio is the dominant operating parameter, with premixing length and residence time beingmore » less significant within the present operating range. Ultralow NO{sub x} operation (< 10 ppmv {at} 15% O{sub 2}) is feasible for equivalence ratios less than 0.5. More significantly, small drops persist beyond the premixer even for very long premixers, and Mie-scattering measurements show considerable spatial inhomogeneity, while allowing ultralow NO{sub x} operation. One-dimensional evaporation calculations for single drop trajectories confirm that complete evaporation for typical drop size distributions is not possible with reasonable premixer lengths under atmospheric pressure. Fuel dispersion is found to be the most critical parameter for high combustion efficiency, and adverse effects of poor fuel dispersion cannot be overcome by using longer premixers.« less
  • Following Seshadri and Williams solution describing the flow field for the opposed jet burner, the analytical solution is given for the flow field of two other burners: the opposed tubular burner and the tubular burner. Under plug flow boundary conditions, it is shown that the stretch rate at the stagnation surface of the opposed tubular burner is k=pV/(R{sub 2}-R{sub 1}) for the case of equal velocities and equal densities (i.e., r{sub 1}=r{sub 2} and V{sub 1}=-V{sub 2}=V). For the tubular burner, the stretch rate at the center of the burner is k=pV/R{sub 2}. The comparison of the numerical simulation andmore » analytical solution is carried out to verify the analytical solution. (author)« less
  • Tubular non-premixed flames are formed by an opposed tubular burner, a new tool to study the effects of curvature on extinction and flame instability of non-premixed flames. Extinction of the opposed tubular flames generated by burning diluted H{sub 2}, CH{sub 4} or C{sub 3}H{sub 8} with air is investigated for both concave and convex curvature. To examine the effects of curvature on extinction, the critical fuel dilution ratios at extinction are measured at various stretch rates, initial mixture strengths and flame curvature for fuels diluted in N{sub 2}, He, Ar or CO{sub 2}. In addition, the onset conditions of themore » cellular instability are mapped as a function of stretch rates, initial mixture strengths, and flame curvature. For fuel mixtures with Lewis numbers much less than unity, such as H{sub 2}/N{sub 2}, concave flame curvature towards the fuel suppresses cellular instabilities. (author)« less