1. DIFFUSION FLAME DYNAMICS AT ELEVATED PRESSURES J. Bassi, H.G. Darabkhani*, H.W. Huang and Y. Zhang School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester, UK, M60 1QD The 32nd International Symposium on Combustion August 3-8 2008, McGill University, Montreal, Canada Introduction  The flame dynamics of diffusion flames have been studied at elevated pressures up to 1.6 MPa.  This study addresses the influence of elevated pressures on the flickering behavior of laminar diffusion flames and particular attention has been paid to the effect of fuel variability.  The flickering of a diffusion flame could be explained by the formation of buoyancy induced toroidal vortices outside the luminous flame and small roll-up vortices inside the luminous flame. High Pressure Burner Facility Experimental Setup Results and Conclusions Current works  The High-pressure burner has been developed recently through EPSRC-funded research at the University of Manchester.  Internal height of 600 mm and internal diameter of 120 mm  Working Pressures: 1 ~ 20 bar  Glass Types: Two from fused quartz (250 nm-2500 nm) and two from silicone (Near-IR and beyond)  High speed images from Hi-Dcam Camera with framing rate of 500 fps  Flame chemiluminescence using ; 1. A bifurcated optic fibre bundle 2. Two monochromatic filters (CH* and C 2 * at wavelengths of 430±5 nm and 516±2.5 nm respectively) 3. Two photomultipliers (ORIEL model 70704)  Flow rates of Methane & Ethylene 0.21 slpm and Air 15 slpm Optic Fibre Focus Lens High Speed Camera Photomultiplier Box High Pressure Burner Gas Cylinders Flow Meters Optical Accesses Methane (Fig. A) and Ethylene (Fig. B) diffusion flame images (a) taken by a digital SLR camera at shutter speed of 1/2000s for pressures 0.1, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4 and 1.6 MPa (from left to right respectively). (b) and (c) are high speed images at pressures of 0.8 MPa and 1.6 MPa respectively.  At elevated pressures the break-up of the Methane flame tip is very uniform with a pair of equal size pockets of flame highlighting the structure of the outer toroidal vortex at the base of flame bulge. Whilst the flame tip of the Ethylene flame is burnt out in a more turbulent manner with a wrinkled flame surface consisting of small roll-up vortices of varying amplitude. Fig. C shows the frequency spectra of Methane and Ethylene diffusion flames at elevated pressures.  A linear dependency between the dominant flickering frequency of the flame and pressure was confirmed.  The harmonic frequencies were observed for both flames. Methane flame flickers with one dominant frequency and as many as six harmonic modes. In contrast, Ethylene flame flickers with at least three dominant modes together with their corresponding harmonics. * Corresponding author contact details : Hamidreza Gohari Darabkhani H.G.Darabkhani@postgrad.manchester.ac.uk Further investigating of fuel variability by using different methane/ethylene/propane fuel mixtures Using a new high speed camera (FASTCAM-Ultima APX) which can record up to 120,000 fps and ICCD spectroscopy system Modeling of flame dynamics using commercial software such as FLUENT in conjunction with CHEMKIN ABC