Temperature distribution and heat transfer mechanism at the upstream surface of a moving burner

Abstract

Moving fires are challenging because of their aerodynamic effects, which have gained wide attention recently. Concurrent flame spread can occur due to tilted flames, and the backward heating behavior of moving fires has not yet been addressed. To investigate these fundamental problems, a 1:10 scale burning car with an embedded propane-fueled porous burner was designed. Moving model experiments with eight heat release rates (HRRs) ranging from 6.1 to 27.3 kW and seven moving velocities varying from 2 to 10 m/s were conducted. The upstream two-dimensional temperature and the heat flux were measured by a thermocouple array and water-cooled heat flux gauges, respectively. The flame was extinguished when the velocity of the burning car (VBC) reached a threshold value, and this critical extinction VBC generally increases with the HRR. The maximum temperature on the upstream surface generally increased with the increase in VBC, and an exponential increase followed by a power law decay was observed for larger dimensionless HRRs (6.24–7.243). The upstream centerline temperature was correlated as two regimes because the difference between the intermittent and plume regions was small at higher VBCs. The exponents for the intermittent and plume regions were 0 and −7/2, respectively. Finally, the heat transfer mechanism for moving fires was elucidated. The movement effect played a dual role: accumulating and dissipating heat during the combustion process, and the cooling effect of the fuel-rich zone was more obvious for larger fuel supply flows.