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

Combustion Characteristics of a Two-Dimensional Twin Cavity Trapped Vortex Combustor

[+] Author and Article Information
P. K. Ezhil Kumar

Combustion Laboratory,
Department of Aerospace Engineering,
Indian Institute of Technology,
Kanpur 208016, India
e-mail: pkezhil@iitk.ac.in

D. P. Mishra

Combustion Laboratory,
Department of Aerospace Engineering,
Indian Institute of Technology,
Kanpur 208016, India
e-mail: mishra@iitk.ac.in

1Corresponding author.

Contributed by the Combustion and Fuels Committee of ASME for publication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received December 15, 2014; final manuscript received December 16, 2016; published online March 7, 2017. Assoc. Editor: Joseph Zelina.

J. Eng. Gas Turbines Power 139(7), 071504 (Mar 07, 2017) (10 pages) Paper No: GTP-14-1666; doi: 10.1115/1.4035739 History: Received December 15, 2014; Revised December 16, 2016

Trapped vortex combustor (TVC) is a relatively new concept, having potential application in gas turbine engines. In this work, an attempt has been made to characterize the 2D twin cavity TVC experimentally in terms of its visible flame length, pollutant emission level, and exit temperature profile. Besides this, numerical results are also discussed to explain certain intricacies in flow and flame characteristics. Experimental results reveal that visible flame length value is sensitive to mainstream Reynolds number (Rems), primary (cavity) air velocity (Vp), and cavity equivalence ratio (Φc). For a particular Rems and Φc, an increase in Vp results in longer flame length; whereas, flame length gets shortened at higher mainstream Reynolds number cases. Numerical studies indicate that shortening of flame length at higher Rems cases is caused due to quenching of flame at the shear layer by the incoming flow. An attempt has been made to correlate flame length data with the operating parameters and Damkohler number (Da); Da takes care of flame quenching effects. Moreover, it is also brought out that the emission profile at the combustor exit is dependent on primary air velocity, mainstream Reynolds number, and cavity equivalence ratio. Emission studies indicate that higher primary air velocity cases make the carbon monoxide (CO) and unburned hydrocarbon (UHC) emission levels to lower values. Reduction in emission level is caused mainly due to the flame merging effects. Besides this, the influence of cavity flame merging on the exit temperature profile uniformity is also brought out. This study reveals that merging of cavity flames is essential for the optimized operation of a 2D trapped vortex combustor.

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Figures

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Fig. 1

Schematic of trapped vortex combustor (TVC) and the associated flow structure

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Fig. 2

Schematic of 2D trapped vortex combustor (TVC)

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Fig. 3

Influence of threshold value on the flame length (Case: Rems = 20,000, ϕms = 0.25, Vp = 70 m/s, ϕc = 1.4): (a) flame luminous intensity along the combustor centerline with various threshold values marked on it and (b) flame surface edge detected by using various threshold values

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Fig. 4

Effects of primary air velocity on flame length for two cavity equivalence ratios: namely, (a) ϕc = 1.2 and (b) ϕc = 1.4

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Fig. 5

Variation of aerodynamic strain rate magnitude (numerical result) along y-direction at x = 42 mm for Rems = 20,000, Vp = 60 m/s and Rems = 40,000, Vp = 60 m/s

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Fig. 6

Effect of primary air velocity on flame length for twomainstream Reynolds numbers Rems = 20,000, and Rems = 40,000

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Fig. 7

Effect of momentum flux ratio on the normalized flame length for two cavity equivalence ratio cases: (a) ϕc = 1.2 and (b) ϕc = 1.4

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Fig. 8

(a) Normalized flame length versus correlation parameter and (b) measured versus predicted flame length by the proposed correlation

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Fig. 9

Variation of CO and UHC emission level along y-directions at the combustor exit for various primary air velocities and for mainstream equivalence ratio of 0.25: (a) EICO profile for Rems = 20,000, (b) EICO profile for Rems = 40,000, (c) EIUHC profile for Rems = 20,000, and (d) EIUHC profile for Rems = 40,000

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Fig. 10

Direct flame images under stable operating conditions for ϕms = 0.25, ϕc = 1.2 and for two mainstream Reynolds numbers: (a) Rems = 20,000 and (b) Rems = 40,000

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Fig. 11

Predictions of (i) CO concentration within the cavity for (a) Rems = 20,000, Vp = 40 m/s case and (b) Rems = 20,000, Vp = 60 m/s case and (ii) CO2 concentration for (c) Rems = 20,000, Vp = 40 m/s case and (d) Rems = 20,000, Vp = 60 m/s case

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Fig. 12

Temperature profile along y direction at z = 0 mm and at 5 mm inside the exit plane for (a) Rems = 20,000 case and (b) Rems = 40,000 case

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Fig. 13

Temperature contour at the y–z plane at 5 mm inside the exit plane for Rems = 20,000 case: (a) Vp = 60 m/s (MFR = 22.89), (b) Vp = 80 m/s (MFR = 58.6), and (c) Vp = 100 m/s (MFR = 91.6)

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Fig. 14

Temperature contour at the y–z plane at 5 mm inside the exit plane for Rems = 40,000 case: (a) Vp = 100 m/s, (b) Vp = 140 m/s, and (c) Vp = 160 m/s

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