Methane Diffusion Flame Dynamics at Elevated Pressures

Abstract

The chamber pressure and fuel flow rate effects on the flickering behavior of methane-air diffusion flames was studied over the pressure range of 1 to 10 bar. Photomultipliers and high-speed imaging techniques have been used to study the frequency and magnitude of the flame oscillation and the change in global flame shape. The instability behavior of the flame was observed to be sensitive to both the fuel flow rate and pressure. Particularly, it has been observed that the flame responds to the change of pressure more when the pressure is relatively low. High-speed imaging has shown that the periodical break-up of the methane flame at higher flow rates is almost symmetric. However, the methane flames at lower flow rates oscillate in a more waving manner due to the alternating lateral nature of the outer vortices. The average flame luminosity was observed to increase with pressure up to 6 bar and then starts to decrease with the further increase of pressure. The flame oscillation magnitude (L _f ) and oscillation wavelength (λ) were obtained from the high-speed imaging database. It has been observed that the trends of these parameters correlate well with the standard deviation (σ) of mean pixel intensity (MPI), measured from the flame high-speed images. The increase in fuel flow rate was observed to increase the magnitude of oscillation. The dominant flickering frequency of a methane diffusion flame varies with the chamber pressure as a function of P ⁿ (f = 15.7P ^0.17).

Keywords:

• Diffusion flames
• Flame dynamics
• Flickering frequency
• High-pressure

ACKNOWLEDGMENTS

The first author wants to gratefully acknowledge the School of MACE, The University of Manchester for the Ph.D. research scholarship. The first author also appreciates the general comments of Dr. Mark Jabbal and Mr. Robert Ward regarding this paper. The high-pressure burner was developed under the EPSRC Basic Technology Program.