Effects of Pressure on Flame Structure and Droplet Behaviour of Coaxial Jet Spray Flames(Thermal Engineering)

Coaxial jet spray flames of kerosene/oxygen are studied experimentally in the pressure range of 0.1-1.0MPa. The flame shapes are observed directly, and the spray cross-section is visualized using laser sheet imaging. The droplet size distributions and axial velocity components are measured by phase Doppler anemometry. Direct observation of flames indicates that, as the ambient pressure increases, the flame length decreases, the luminous flame region moves upstream, and the blue flame region at the top of the flame expands. Mie scattering images show that under high pressure, the spray region becomes narrower and shorter. The droplet mean velocity decreases as the droplets move downstream for each pressure condition; however, under high pressure, a region in which the droplet mean velocity decreases moderately appears near the burner port. The droplet mean diameter increases as the distance from the burner port increases, due to a decrease in the number of small droplets and an increase in the ratio of small to large droplets caused by evaporation of the small droplets. In addition, at high pressure, a region appears in which the droplet mean diameter does not change significantly. These results show that spray flame shapes and droplet behavior are strongly affected by ambient pressure.