skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: A computational and experimental study of coflow laminar methane/air diffusion flames: Effects of fuel dilution, inlet velocity, and gravity

Authors:
; ; ; ; ; ; ;
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1251883
Grant/Contract Number:
FG02-88ER13966
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Proceedings of the Combustion Institute
Additional Journal Information:
Journal Volume: 35; Journal Issue: 1; Related Information: CHORUS Timestamp: 2017-05-17 09:41:35; Journal ID: ISSN 1540-7489
Publisher:
Elsevier
Country of Publication:
United States
Language:
English

Citation Formats

Cao, S., Ma, B., Bennett, B. A. V., Giassi, D., Stocker, D. P., Takahashi, F., Long, M. B., and Smooke, M. D.. A computational and experimental study of coflow laminar methane/air diffusion flames: Effects of fuel dilution, inlet velocity, and gravity. United States: N. p., 2015. Web. doi:10.1016/j.proci.2014.05.138.
Cao, S., Ma, B., Bennett, B. A. V., Giassi, D., Stocker, D. P., Takahashi, F., Long, M. B., & Smooke, M. D.. A computational and experimental study of coflow laminar methane/air diffusion flames: Effects of fuel dilution, inlet velocity, and gravity. United States. doi:10.1016/j.proci.2014.05.138.
Cao, S., Ma, B., Bennett, B. A. V., Giassi, D., Stocker, D. P., Takahashi, F., Long, M. B., and Smooke, M. D.. Thu . "A computational and experimental study of coflow laminar methane/air diffusion flames: Effects of fuel dilution, inlet velocity, and gravity". United States. doi:10.1016/j.proci.2014.05.138.
@article{osti_1251883,
title = {A computational and experimental study of coflow laminar methane/air diffusion flames: Effects of fuel dilution, inlet velocity, and gravity},
author = {Cao, S. and Ma, B. and Bennett, B. A. V. and Giassi, D. and Stocker, D. P. and Takahashi, F. and Long, M. B. and Smooke, M. D.},
abstractNote = {},
doi = {10.1016/j.proci.2014.05.138},
journal = {Proceedings of the Combustion Institute},
number = 1,
volume = 35,
place = {United States},
year = {Thu Jan 01 00:00:00 EST 2015},
month = {Thu Jan 01 00:00:00 EST 2015}
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1016/j.proci.2014.05.138

Citation Metrics:
Cited by: 3works
Citation information provided by
Web of Science

Save / Share:
  • A numerical and experimental study of an axisymmetric coflow laminar methane-air diffusion flame at pressures between 5 and 40 atm was conducted to investigate the effect of pressure on the flame structure and soot formation characteristics. Experimental work was carried out in a new high-pressure combustion chamber described in a recent study [K.A. Thomson, O.L. Gulder, E.J. Weckman, R.A. Fraser, G.J. Smallwood, D.R. Snelling, Combust. Flame 140 (2005) 222-232]. Radially resolved soot volume fraction was experimentally measured using both spectral soot emission and line-of-sight attenuation techniques. Numerically, the elliptic governing equations were solved in axisymmetric cylindrical coordinates using the finitemore » volume method. Detailed gas-phase chemistry and complex thermal and transport properties were employed in the numerical calculations. The soot model employed in this study accounts for soot nucleation and surface growth using a semiempirical acetylene-based global soot model with oxidation of soot by O{sub 2}, OH, and O taken into account. Radiative heat transfer was calculated using the discrete-ordinates method and a nine-band nongray radiative property model. Two soot surface growth submodels were investigated and the predicted pressure dependence of soot yield was compared with available experimental data. The experiment, the numerical model, and a simplified theoretical analysis found that the visible flame diameter decreases with pressure as P{sub a}{sup -0.5}. The flame-diameter-integrated soot volume fraction increases with pressure as P{sub a}{sup 1.3} between 5 and 20 atm. The assumption of a square root dependence of the soot surface growth rate on the soot particle surface area predicts the pressure dependence of soot yield in good agreement with the experimental observation. On the other hand, the assumption of linear dependence of the soot surface growth rate on the soot surface area predicts a much faster increase in the soot yield with pressure than that observed experimentally. Although pressure affects the gas-phase chemistry, the increased soot production with increasing pressure seems primarily due to enhanced mixture density and species concentrations in the pressure range investigated. The increased pressure causes enhanced air entrainment into the fuel stream around the burner rim, leading to accelerated fuel pyrolysis. In the pressure range of 20 to 40 atm both the model and experiment show a diminishing sensitivity of sooting propensity to pressure with a greater decrease in the predicted sensitivity of soot propensity to pressure than the experimental results. (author)« less
  • Measured temperature and composition profiles are reported for a number of flames. Implications concerning flame structure are deduced, with emphasis on soot formation and on correlation involving conserved scalars.
  • A detailed soot growth model in which the equations for particle production have been coupled to the flow and gaseous species conservation equations has been developed for an axisymmetric, laminar, coflow diffusion flame. Results from the model have been compared to experimental data for a confined methane-air flame. The two-dimensional system couples detailed transport and finite rate chemistry in the gas phase with the aerosol equations in the sectional representation. The formulation includes detailed treatment of the transport, inception, surface growth, oxidation, and coalescence of soot particulates. Effects of thermal radiation and particle scrubbing of gas-phase growth and oxidation speciesmore » are also included, Predictions and measurements of temperature, soot volume fractions, and selected species are compared over a range of heights and as a function of radius. Flame heights are somewhat overpredicted and local temperatures and volume fractions are underpredicted. The authors believe the inability to reproduce accurately bulk flame parameters directly inhibits the ability to predict soot volume fractions and these differences are likely a result of uncertainties in the experimental inlet conditions. Predictions of the distributions of particle sizes indicate the existence of (relatively) low-molecular-weight species along the centerline of the burner and trace amounts of the particles that escape from the flame, unoxidized. Oxidation of particulates is dominated by reactions with hydroxyl radicals which attain levels approximately 10 times higher than calculated equilibrium levels. Gas cooling effects due to radiative low are shown to have a very significant effect on predicted soot concentrations.« less
  • The effects of fuel dilution with nitrogen on the propagation of tribrachial flames were studied experimentally using a multislot burner, which can stabilize lifted flames at low concentration gradients. Three fuel dilutions with nitrogen (N{sub 2} 0%, 25%, and 50% dilution) were employed. The lift-off height and OH-radical content of the flames were measured using an intensified CCD camera and an OH-PLIF scheme. Regardless of the fuel dilution mole fractions, the lift-off height of the tribrachial flames exhibited U-shaped trends with a minimal value during the increase of the concentration gradients. This implies that the propagation velocity is maximized atmore » a specific concentration gradient regardless of the fuel dilution. Overall, the propagation velocity of the tribrachial flame was reduced by the fuel dilution, and the fuel dilution weakly affected the generation of the diffusion flame. The OH radicals in the diffusion branch became prominently active at the critical concentration gradient and these phenomena were more clearly detected at higher fuel dilution mole fractions. The decrease of the three modes of the OH radicals in a streamwise direction is discussed regarding the relation of the diffusion branch to the propagation velocity of the tribrachial flames. It is suggested that the effect of the diffusion branch on the propagation velocity of tribrachial flames needs to be reconsidered, especially when the concentration gradient is small. (author)« less
  • The chemical structure of a methane counterflow diffusion flame and of the same flame doped with 1000 ppm (molar) of either jet fuel or a 6-component jet fuel surrogate was analyzed experimentally, by gas sampling via quartz microprobes and subsequent GC/MS analysis, and computationally using a semi-detailed kinetic mechanism for the surrogate blend. Conditions were chosen to ensure that all three flames were non-sooting, with identical temperature profiles and stoichiometric mixture fraction, through a judicious selection of feed stream composition and strain rate. The experimental dataset provides a glimpse of the pyrolysis and oxidation behavior of jet fuel in amore » diffusion flame. The jet fuel initial oxidation is consistent with anticipated chemical kinetic behavior, based on thermal decomposition of large alkanes to smaller and smaller fragments and the survival of ring-stabilized aromatics at higher temperatures. The 6-component surrogate captures the same trend correctly, but the agreement is not quantitative with respect to some of the aromatics such as benzene and toluene. Various alkanes, alkenes and aromatics among the jet fuel components are either only qualitatively characterized or could not be identified, because of the presence of many isomers and overlapping spectra in the chromatogram, leaving 80% of the carbon from the jet fuel unaccounted for in the early pyrolysis history of the parent fuel. Computationally, the one-dimensional code adopted a semi-detailed kinetic mechanism for the surrogate blend that is based on an existing hierarchically constructed kinetic model for alkanes and simple aromatics, extended to account for the presence of tetralin and methylcyclohexane as reference fuels. The computational results are in reasonably good agreement with the experimental ones for the surrogate behavior, with the greatest discrepancy in the concentrations of aromatics and ethylene. (author)« less