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Technical Briefs

Combustion Oscillations in Bluff Body Stabilized Diffusion Flames With Variable Length Inlet

[+] Author and Article Information
M. Madanmohan, S. Pandey, A. Kushari

Department of Aerospace Engineering, Indian Institute of Technology Kanpur, Kanpur UP 208016, India

K. Ramamurthi

Department of Mechanical Engineering, Indian Institute of Technology Madras, Chennai 600 036, India

J. Eng. Gas Turbines Power 131(5), 054501 (May 22, 2009) (4 pages) doi:10.1115/1.3078387 History: Received June 07, 2008; Revised October 15, 2008; Published May 22, 2009

This paper describes the results of an experimental study to understand the influence of inlet flow disturbances on the dynamics of combustion process in bluff body stabilized diffusion flames of liquid petroleum gas and air. The results show the influence of weak disturbances created by the change in incoming pipe length on the amplitude of pressure oscillations and the phase angle between pressure and heat release. It is seen that the phase delay increases as the entry length increases. The rms value of pressure, however, generally falls with the increase in length. The phase angle is seen to be in the second quadrant, showing that the heat release oscillations damp the pressure oscillations. Therefore, the decrease in the phase angle results in the reduction in damping and hence an increase in pressure fluctuations. The dominant frequencies of combustion oscillations are found to be the low frequency oscillations, and the frequency of oscillations increases with a decrease in the inlet pipe length and an increase in the flow Reynolds number. It is suggested that such low frequency oscillations are driven by vortex shedding at the wake of the bluff body, which energizes the diffusion and mixing process.

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Copyright © 2009 by American Society of Mechanical Engineers
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Figures

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Figure 1

Diagram of experimental setup: (1) settling chamber, (2) inlet pipe with ram, (3) cylindrical pipe housing the inlet pipe for air supply, (4) combustor inlet, (5) bluff body, (6) quartz window opening, (7) combustor, (8) location of pressure sensor, (9) combustion chamber, (10) supporting plates, and (11) exhaust section

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Figure 2

Variation in the rms pressure and the phase angle between the heat release oscillations and the pressure oscillations with inlet length for Re=4.8×103 and an equivalence ratio of 0.35

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Figure 3

Frequency domain representation of pressure and heat release oscillations for an inlet length of 14 cm and the flow Reynolds number of 4.8×103 (equivalence ratio of 0.35)

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Figure 4

Dependence of low frequency oscillations on the inlet pipe length for different Reynolds numbers

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Figure 5

Comparison of measured and estimated dominant frequency variations for 28 cm pipe length

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