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Research Papers: Gas Turbines: Combustion, Fuels, and Emissions

Flame Extinction Limits of H2CO Fuel Blends

[+] Author and Article Information
Ahsan R. Choudhuri

Combustion and Propulsion Research Laboratory,  University of Texas at El Paso, El Paso, TX 79968-0521ahsan@utep.edu

Mahesh Subramanya

Combustion and Propulsion Research Laboratory,  University of Texas at El Paso, El Paso, TX 79968-0521msubrama@bechtel.com

Subramanyam R. Gollahalli

Combustion and Flame Dynamics Laboratory,  University of Oklahoma, Norman, OK 73019-1052gollahal@ou.edu

“The axial flow velocity U is given by ±2cz, where c is constant and z is the axial distance from the stagnation plane, which is independent of the radial coordinate r. The radial velocity V is given by cr and is independent of z. The stretch acting on the flame is the sum of the extensional strains in the two directions orthogonal to the z axis, that is, Vx+Vy=2c=Uz. Thus, the flame stretch Σ is simply the magnitude of the axial velocity gradient” (12).

J. Eng. Gas Turbines Power 130(3), 031501 (Mar 28, 2008) (8 pages) doi:10.1115/1.2835059 History: Received February 22, 2007; Revised September 26, 2007; Published March 28, 2008

The flame extinction limits of syngas (H2CO) flames were measured using a twin-flame counterflow burner. Plots of extinction limits (%f: volumetric percent of fuel in air) versus global stretch rates were generated at different fuel blend compositions and were extrapolated to determine the flame extinction limit corresponding to an experimentally unattainable zero-stretch condition. The zero-stretch extinction limit of H2CO mixtures decreases with the increase in H2 concentration in the mixture. The average difference between the measured flame extinction limit and the Le Chatelier’s calculation is around 7% of the mean value. The measured OH chemiluminescence data indicates that regardless of blend composition the OH radical concentration reduces to a critical value prior to the flame extinction. The measured laminar flame velocity close to the extinction indicates that regardless of fuel composition, the premixed flame of hydrogen fuel blends extinguishes when the mixture laminar flame velocity falls below a critical value.

Copyright © 2008 by American Society of Mechanical Engineers
Topics: Fuels , Flames
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References

Figures

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Figure 1

Counterflow twin-flame burner assembly

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Figure 2

Hotwire anemometry data on the burner exit profile analyzed without the effect of acoustic oscillations

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Figure 3

Twin-flame images of pure CH4-air flame at different stretch conditions leading to extinction (Kext∼500s−1, %f=6.2)

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Figure 4

Flat-flame burner system

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Figure 5

Flame extinction limit for pure-methane fuel at different stretch conditions

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Figure 6

Flame extinction limits of H2‐CO fuel blend composition at different stretch conditions

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Figure 7

Normalized sensitivity analysis data (Ref. 8)

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Figure 8

Extrapolation of 5%–95% H2‐CO extinctions to zero-stretch condition

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Figure 9

Zero-stretch flame extinction limits of H2‐CO and H2‐CH4 fuel blends at different H2 concentration in the fuel mixture

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Figure 10

Plot of zero-stretch flame extinction limits of H2‐CH4 fuel blends in an expanded scale

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Figure 11

Maximum flame temperature of CO‐H2 mixtures as flames approach to extinction

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Figure 12

Chemiluminescent emissions of OH* radicals measured from H2‐CO fuel blends as flames approach extinction

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Figure 13

Chemiluminescent emissions of CH* radicals measured from H2‐CO fuel blends as flames approach extinction

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Figure 14

Average laminar flame velocity of 3.77 (±0.38)cm∕s measured close to extinction for H2‐CO flames, measurements obtained using flat-flame burner

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Figure 15

OH radical concentrations measured close to extinction in 24% H2‐76% CO fuel blend compositions for various %f, as measured using flat-flame burner

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