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

Flame Structure and Combustion Capability of Non-Premixed Rifled Nozzles

[+] Author and Article Information
Kuo C. San

Department of Aircraft Engineering,
Air Force Institute of Technology,
Kaohsiung, Taiwan 820, China
e-mail: d90543001@ntu.edu.tw

Shun C. Yen

Department of Mechanical and Mechatronic Engineering,
National Taiwan Ocean University, Keelung,
Taiwan 202, China

1Corresponding author.

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the Journal of Engineering for Gas Turbines and Power. Manuscript received August 10, 2012; final manuscript received October 27, 2012; published online June 10, 2013. Assoc. Editor: Joseph Zelina.

J. Eng. Gas Turbines Power 135(7), 071501 (Jun 10, 2013) (9 pages) Paper No: GTP-12-1325; doi: 10.1115/1.4024060 History: Received August 10, 2012; Revised October 27, 2012

The target of this study is to promote combustion capability using a novel rifled nozzle which was set at the outlet of a conventional (unrifled) combustor. The rifled nozzle was utilized to adjust the flow swirling intensity behind the traditional combustor by changing the number of rifles. The rifle mechanism enhances the turbulence intensity and increases the mixing efficiency between the central-fuel jet and the annular swirled air-jet by modifying the momentum transmission. Specifically, direct photography, Schlieren photography, thermocouples, and a gas analyzer were utilized to document the flame behavior, peak temperature, temperature distribution, combustion capability, and gas-concentration distribution. The experimental results confirm that increasing the number of rifles and the annular swirling air-jet velocity (ua) improves the combustion capability. Five characteristic flame modes—jet-flame, flickering-flame, recirculated-flame, ring-flame and lifted-flame—were obtained using various annular air-jet and central fuel-jet velocities. The total combustion capability (Qtot) increases with the number of rifles and with increasing ua. The Qtot of a 12-rifled nozzle (swirling number (S) = 0.5119) is about 33% higher than that of an unrifled nozzle. In addition, the high swirling intensity induces the low nitric oxide (NO) concentration, and the maximum concentration of NO behind the 12-rifled nozzle (S = 0.5119) is 49% lower than that behind the unrifled nozzle.

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Fig. 1

Experimental setup

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Fig. 2

Variations of swirl number (S) against the annular-jet velocity (ua)

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Fig. 3

Photographs of flame configurations for a unrifled nozzle at (a) ua = 0 m/s, (b) ua = 0.23 m/s, (c) ua = 0.42 m/s, (d) ua = 1.22 m/s, (e) ua = 1.98 m/s, and (f) ua = 2.16 m/s with a constant uc of 2.5 m/s. Shuttle speed = 1/2000 s.

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Fig. 4

Distribution of characteristic flame modes

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Fig. 11

Variations of radial-concentrations at x/D = 3.75 when uc = 2.5 m/s. (a)–(c) ua = 0.23 m/s and (d)–(f) ua = 2.16 m/s.

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Fig. 10

Total combustion capability (Qtot) versus ua when uc = 2.5 m/s

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Fig. 9

Variations of combustion capability (Q) versus x/D for various ua when uc = 2.5 m/s. (a) Behind an unrifled nozzle, (b) behind a 6-rifled nozzle and (c) behind a 12-rifled nozzle.

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Fig. 8

Variations of nondimensional peak-temperature coordinate (xp.t./D) versus ua when uc = 2.5 m/s

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Fig. 7

Temperature distributions along the x-axis at uc = 2.5 m/s and 0 ≤ ua ≤ 2.16 m/s

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Fig. 6

Radial-temperature distributions along the axial positions at uc = 2.5 m/s. (a)–(c): ua = 0.23 m/s and (d)–(f) ua = 2.16 m/s.

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Fig. 5

Flame patterns visualized using the Schlieren photography when uc = 2.5 m/s



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