Combustion and flame spreading characteristics of diesel fuel with forced air flows

Research on combustion and flame spreading behaviors in a system with forced air flow is crucial for actual fire protection design and scientific meanings. Flame spread tests over sub-flash diesel fuel are conducted by using a self-developed cross flow system, in both opposed and concurrent configurations. Some key parameters to characterize the flame spread performance, namely, flame tilt, flame spread rate, temperature distribution and scale characteristic of subsurface flow are achieved and analyzed. The variations of flame tilt angle in opposed and concurrent flame spreads follow well with Thomas's classical model, and the tangent value of the flame tilt angle is correlated with the wind Froude number with the power value of 0.8. The flame spread rate decreases monotonically with an increase in the opposed air flow velocity. By contrast, the flame spread rate decreases initially and increases afterwards as the concurrent air flow velocity increases, with the critical air velocity of 1.725 m/s. Furthermore, the step temperature rise remains stable in the range of 27 degrees C to 30 degrees C for opposed air flows, but it is not pronounced for concurrent air flows. The subsurface flow length increases with opposed air flow velocity, while it becomes irregular under concurrent air flows. The primary contribution of heat transfer to flame spread is liquid-phase thermal convection for opposed or low-speed concurrent air flow conditions, whereas it is flame radiation and gas conduction for high-speed concurrent air flow conditions. The finding of current study is favorable for the fire hazard assessment of spilling hydrocarbon fuel in air flow environments.