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TECHNICAL PAPERS: Internal Combustion Engines

Effect of Developing Turbulence and Markstein Number on the Propagation of Flames in Methane-Air Premixture

[+] Author and Article Information
M. Z. Haq

Department of Mechanical Engineering, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladeshzahurul@me.buet.ac.bd

J. Eng. Gas Turbines Power 128(2), 455-462 (Feb 18, 2005) (8 pages) doi:10.1115/1.2056537 History: Received January 24, 2004; Revised February 18, 2005

In spark ignition engines, initial flame kernel is wrinkled by a progressively increasing bandwidth of turbulence length scales until eventually the size of the flame kernel is sufficient for it to experience the entire turbulence spectrum. In the present study, an effective rms turbulence velocity as a function of time, estimated by integrating the nondimensional power spectrum density (psd) function for isotropic turbulence, is utilized to analyze the statistical distribution of flame front curvatures and turbulent burning velocities of flames propagating in methane-air premixtures. The distributions of flame front curvatures show these to become more dispersed as the effective turbulence velocity increases, and result in increased burning of premixtures. A decrease in the Markstein number also results in a further increase in curvature dispersion and enhanced burning, in line with the flame stability analysis.

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Copyright © 2006 by American Society of Mechanical Engineers
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Figures

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Figure 1

The fan-stirred combustion vessel

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Figure 2

Experimental setup for PMS visualization of turbulent flames

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Figure 3

Flame images for the propagation in methane-air premixture with an isotropic rms turbulent velocity of 0.6m∕s. Time interval between the images is 0.67ms and real size of the full frame image is 128mm.

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Figure 4

Flame images at different initial conditions

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Figure 5

Definition of reference radii and associated masses for a flame image

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Figure 6

Generalized psd function showing the spectrum of turbulent energy

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Figure 7

Development of effective rms turbulent velocity

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Figure 8

Temporal development of the effective rms turbulent velocity

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Figure 9

Curvature pdfs for a developing methane-air flame front at three different elapsed times

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Figure 10

(a) Positive, negative, and mean flame curvatures. (b) Variance of pdf of curvatures, plotted as a function of elapsed time from ignition.

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Figure 11

Variance of curvature pdfs of methane-air flame fronts at different initial conditions of equivalence ratio, pressure, and rms turbulent velocity

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Figure 12

Variation of ut(Rv)∕ul with uk′∕ul for methane-air premixtures at different initial conditions

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Figure 13

Relationship between turbulent flame speeds and turbulent burning velocities defined at Rv

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