Experimental investigation on flame spread over diesel fuel near sea level and at high altitude

Abstract

Flame spread over a petroleum-based diesel fuel was experimentally examined at two different altitude conditions (Lhasa plateau 3658m, and Hefei Plain, 50m). Based on the test results, the flame appearance, velocity of flame spread and temperature profile near oil surface were comprehensively characterized. Two types of flame are observed during the flame spread: a blue precursor flame and a yellow main flame. The main flame possesses a flame shape under diffusion combustion, whereas the precursor flame belongs to premixed combustion. The liquid temperature initiating flame propagation over diesel fuel is lower in Lhasa, indicating that oils can more easily catch fire at a higher altitude. For a wide range of fuel temperatures, the velocity of flame spread at low-pressure region is considerably larger than that near sea level. The intrinsic reasons are predicted by variations in flashpoint and surface tension of liquid fuel with altitude. Theoretical analyses confirm that the flashpoint of liquid fuel decreases with altitude while the surface tension increases. Moreover, the measured temperature distributions normal to the oil surface reveal that the oil surface temperature as well as the liquid temperature inside the subsurface convection flow is larger at high altitude, while the time interval between the flame leading edge and the subsurface convection flow front is smaller.