Flame height and lift-off of turbulent buoyant jet diffusion flames in a reduced pressure atmosphere

This paper reports new experimental findings at a reduced atmospheric pressure (at high altitude in Tibet) for turbulent buoyant jet diffusion flames and global correlations for both normal and this reduced atmospheric pressure. Comparative experiments are carried out in Hefei (50 m, 100 kPa) and Lhasa (3650 m, 64 kPa) in China to measure the mean flame height and lift-off behaviors. The turbulent jet diffusion flame is produced by nozzles with diameters of 4, 5, 6, 8 and 10 mm using propane as fuel. A series of new findings are revealed and their interpretations are presented in this work. Results show that the normalized mean flame height is higher in the lower pressure atmosphere. A theory of diffusion flame height based on flame Froude number for the transition from buoyancy to momentum controlled turbulent jets can still successfully collapse the flame height data, although a 0.8 factor is needed globally to include effects of reduced entrainment and larger fluctuation in reduced pressure. The lift-off heights are revealed to be higher, while the lift-off velocities are smaller, in the reduced pressure atmosphere. The lift-off heights are correlated based on different theories. The present work provides new findings supplementary over previous classical knowledge on buoyant turbulent jet diffusion flame behaviors.