Fuel effects on diffusion flames at elevated pressures

This study addresses the influence of elevated pressures up to 1.6 MPa on the flame geometry and the flickering behavior of laminar diffusion flames and particular attention has been paid to the effect of fuel variability. It has been observed that the flame properties are very sensitive to the fuel type and pressure. The shape of the flame was observed to change dramatically with pressure. When the pressure increases, the visible flame diameter decreases. The height of a flame increases first with pressure and then reduces with the further increase of pressure. The cross-sectional area of the flame (A.) shows an average inverse dependence on pressure to the power of n (A(cs) alpha P-n), where n = 0.8 +/- 0.2 for ethylene flame, n = 0.5 +/- 0.1 for methane flame and n = 0.6 +/- 0.1 for propane flame. It was observed that the region of stable combustion was markedly reduced as pressure was increased. High speed imaging and power spectra of the flame chemiluminescence reveal that an ethylene flame flickers with at least three dominant modes, each with corresponding harmonics at elevated pressures. In contrast methane flames flicker with one dominant frequency and as many as six harmonic modes at elevated pressures. (C) 2008 Published by Elsevier Ltd.