Experimental study on flame length and pulsation behavior of n-heptane continuous spill fires on water

Continuous spill fires pose significant risks to the storage and transportation industries of liquid fuels. To investigate the flame length and pulsation behavior of continuous spill fires, large-scale spill fire experiments were conducted on water to simulate the burning fuel on a water surface that could occur during firefighting of tank fires or due to leaked fuels on water during transportation, with varying discharge rates (3, 6, 9, 14 mL/s) and ignition delays (0, 10, 20, 30 s). The results suggest that the flame length increased initially with the spread area and reached the maximum at the end of the spreading stage, then followed by a decrease at the shrinking stage and kept nearly constant at the steady stage. For the steady flame length, a new correlation (Ls/D=3.1(Q˙*)0.42) was established based on dimensionless analysis, which was higher than that for pool fires, highlighting the important differences between spill and pool fires. This developed model was also used to predict the maximum flame length with a maximum deviation of 19.2%, as the heat transfer mechanism and air entrainment are expected to be similar at the shrinking and steady stages. The flame pulsation frequency was determined through the fast Fourier transform (FFT) method, which shows a gradual decrease during the spreading stage while remaining higher than that of pool fires at the steady stage. Subsequently, two new correlations (fi=0.525g/D and fs=0.724g/D) were derived from experimental data to predict the pulsation frequency at both spreading and steady stages. The higher frequencies during the steady stage can have a significant influence on the radiation impact to adjacent equipment or personnel. This study not only provides insights into the flame and pulsation behaviors of spill fires but lays a solid foundation for the thermal hazard and risk assessment analysis in the liquid fuel storage and transportation industries. •The flame length change during the liquid spread is clearly displayed.•The flame pulsation frequency decreases gradually during the spreading stage and is higher than that of pool fires for the steady stage.•Two new correlations were built to predict the flame pulsation frequency for the spreading and steady stages, respectively.