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

Near-Field Characteristics of a Rectangular Jet and Its Effect on the Liftoff of Turbulent Methane Flame

[+] Author and Article Information
Mohsen Akbarzadeh

Department of Mechanical Engineering,
University of Manitoba,
Manitoba R3T 5V6, Canada
e-mail: Mohsen.Akbarzadeh@umanitoba.ca

Madjid Birouk

Department of Mechanical Engineering,
University of Manitoba,
Manitoba R3T 5V6, Canada
e-mail: Madjid.Birouk@umanitoba.ca

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received September 12, 2014; final manuscript received November 17, 2014; published online January 28, 2015. Editor: David Wisler.

J. Eng. Gas Turbines Power 137(8), 081502 (Aug 01, 2015) (8 pages) Paper No: GTP-14-1547; doi: 10.1115/1.4029371 History: Received September 12, 2014; Revised November 17, 2014; Online January 28, 2015

Understanding the stability of turbulent flames is a key for the design of efficient combustion systems. The present paper reports an experimental study on the effect of the internal geometry of a rectangular orifice on the characteristics/stability of a turbulent methane flame. Three rectangular nozzles with different orifice lengths having an identical exit aspect ratio (AR) of 2 were used. The co-airflow strength was also varied to evaluate its effect on the jet flow emerging from the rectangular nozzle. The experimental data revealed that the jet initial conditions affect both the flow characteristics and the liftoff of turbulent diffusion methane flame. That is, increasing the orifice length of the rectangular nozzle resulted in delaying the occurrence of the axis-switching phenomenon, reducing the length of the jet potential core, and accelerating the liftoff transition of the attached flame. The co-airflow was found to reduce the velocity strain rate in the shear layer, displace the occurrence of axis-switching farther downstream of the jet, and delay flame detachment. The results revealed also that there is a clear interplay between the flame liftoff and the jet near-field molecular mixing and flow characteristics. That is, a rectangular jet which spreads faster and generates higher near-field velocity strain and turbulence intensity causes flame detachment at a lower fuel jet velocity. Based on this, a correlation was found between the flame liftoff velocity, the fuel molecular thermal diffusivity, the stoichiometric laminar flame speed, and the fuel jet strain rate at the nozzle exit. This relationship was shown to successfully predict the liftoff velocity of methane flame as well as other common gaseous hydrocarbons and hydrogen flames.

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Fig. 1

Schematic of (a) the experimental burner setup and (b) the burner and the fuel nozzle geometry (Dcoh = 21.7 mm is the hydraulic diameter of the co-airflow annulus)

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Fig. 2

Initial velocity profiles (U/Ujet, u/Ujet, and v/Ujet) along the major axis of the rectangular jet (x/De ∼ 0.25 and Uco ∼ 0.2 m/s)

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Fig. 3

Initial velocity profiles (U/Ujet and u/Ujet) along the minor axis of the rectangular jet (x/De ∼ 0.25 and Uco ∼ 0.2 m/s)

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Fig. 4

Lateral (y1/2/De) and spanwise (z1/2/De) spread of rectangular jet for a weak co-airflow (Uco ∼ 0.2 m/s)

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Fig. 5

Lateral (y1/2/De) and spanwise (z1/2/De) spread of rectangular jet for a relatively strong co-airflow (Uco ∼ 0.9 m/s)

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Fig. 6

Contours of the streamwise turbulence intensity u/Ujet (in the major plane) showing the jet’s core potential length xp/De (Uco ∼ 0.6 m/s)

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Fig. 7

Flame liftoff velocity Ul versus Uco

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Fig. 8

Initial velocity profiles (U/Ujet) along the major axis of rectangular jet with L/De = 1 for different co-airflow strengths (Uco ∼ 0.2 and 0.9 m/s)

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Fig. 9

Large-scale structures at the interface between the central jet and surrounding co-airflow (L/De = 5.6)




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