Gas-liquid hydrodynamics and vortex motion of flame spread over jet fuel in longitudinal air stream

Abstract

The gas-liquid hydrodynamic characteristics and pulsation behaviors of flame spread over jet fuel are investigated in various longitudinal air streams. The experiments are conducted in concurrent and opposed air streams by igniting fuels at opposite extremes of the tray. Six magnitudes of air stream speeds are used for the tests, namely 0.45, 0.88, 1.3, 1.73, 2.15 and 2.57 m/s. The liquid convection flow is monitored using a rainbow schlieren deflectometry which confirms that the liquid flows in vertical and horizontal direction act together to form a clockwise vortex. Based on non-dimensional parameter group, the effect of longitudinal air stream on liquid hydrodynamics is revealed. The movement of liquid convective flow is primarily driven by thermocapillary force, while the effect of buoyancy is relatively small, regardless of direction and magnitude of air stream speeds. Combined with the boundary layer theory, the flow velocities driven by expansion of hot gas product and opposed thermal buoyancy and local air stream are quantified. The threshold value of air flow speed for establishing gas-phase recirculation cell is determined, and the transformation mechanism of flame pulsation mode is analyzed.