Blowoff characteristics of bluff-body stabilized conical premixed flames with upstream spatial mixture gradients and velocity oscillations

Journal Article · Sun Jun 15 04:00:00 EDT 2008 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2007.12.008· OSTI ID:21044866

Chaudhuri, Swetaprovo; Cetegen, Baki M ^[1]

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1. Mechanical Engineering Department, University of Connecticut, Storrs, CT 06269-3139 (United States)

This experimental study concerns determination of blowoff equivalence ratios for lean premixed conical flames for different mixture approach velocities ranging from 5 to 16 m/s in the presence of spatial mixture gradients and upstream velocity modulation. Conical flames were anchored on a disk-shaped bluff body that was attached to a central rod in the burner nozzle. A combustible propane-air mixture flowed through a converging axisymmetric nozzle with a concentric insert, allowing radial mixture variation by tailoring the composition in the inner and outer parts of the nozzle. The radial mixture profiles were characterized near the location of the flame holder by laser Rayleigh light scattering. Additionally, a loudspeaker at the nozzle base allowed introduction of periodic velocity oscillations with an amplitude of 9% of the mean flow velocity up to a frequency of 350 Hz. The flame blowoff equivalence ratio was experimentally determined by continuously lowering the fuel flow rates and determining the flame detachment point from the flame holder. Flame detachment was detected by a rapid reduction of CH* emission from the flame base imaged by a photomultiplier detector. It was found that the flame blowoff is preceded by progressive narrowing of the flame cone for the case of higher inner jet equivalence ratios. In this case, the fuel-lean outer flow cannot sustain combustion, and clearly this is not a good way of operating a combustor. Nevertheless, the overall blowoff equivalence ratio is reduced by inner stream fuel enrichment. A possible explanation for this behavior is given based on the radial extent of the variable-equivalence-ratio mixture burning near the flame stabilization region. Fuel enrichment in the outer flow was found to have no effect on blowoff as compared to the case of uniform mixture. The results were similar for the whole range of mean flow velocities and upstream excitation frequencies. (author)

• OSTI ID: 21044866
• Journal Information: Combustion and Flame, Journal Name: Combustion and Flame Journal Issue: 4 Vol. 153; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
AIR
AXIAL SYMMETRY
BLOWOFF
BURNERS
Bluff-body stabilization
COMBUSTION
CONES
ENRICHMENT
EXCITATION
FLAMES
FLOW RATE
FUELS
Flow oscillation
HZ RANGE
JETS
MIXTURES
MODULATION
Mixture gradients
NOZZLES
OSCILLATIONS
PERIODICITY
PROPANE
Premixed flames
STABILIZATION
VELOCITY