Experimental study on flame characteristics and heat transfer analysis in flame spread in all directions over flowing n-butanol fuel surface

This work carries out a series of experiments on a 130 cm × 90 cm substrate under different leakage rates (8.9–87.1 mL/s, corresponding to the flow velocity of 5.2–35.6 mm/s) to reveal the flame spread characteristics over flowing fuel. The results show that the flame front expands gradually in an approximate circular shape, and the flame height increases continuously during the spreading process and slightly with the increase in leakage rate. Based on the parallel shear flow hypothesis, a method for calculating the surface flow structure is proposed, and the heat balance relationship and calculation method for various components in the heat transfer process are established. In the downstream, the increase of leakage rate inhibits the backflow of surface flow, which leads to increased heat transfer to the unburned zone and higher spread speed. In the upstream, the increase in leakage rate causes more heat to be carried and lost, reducing heat accumulation in the unburned area and resulting in slower spread speed or even no spread. As time progresses, the increase of flame volume enhance flame radiation, which promotes the heating of the upstream unburned area and gradually forms an opposed spread.