Experimental study on characteristics of flame spread over diesel and n-butanol pool fires in tunnel

Comparative tests were conducted to investigate the flame spread characteristics of a typical hydrocarbon fuel mixture (0# diesel) and a typical pure alcohol fuel (n-butanol) in a reduced-scale (1:10) tunnel model. Experimental data with regard to flame spread appearance, flame spread rate, temperature profile, and subsurface convection flow were obtained and discussed in this study. Results showed that: (1) The diffusion flame of n-butanol propagated in a forward-stop-forward pattern, while diesel fuel pulsated in a forward-back-forward manner with less stability. The flash flame of diesel appeared periodically with significant higher spreading velocity than the enduring flash flame of n-butanol. (2) The average main flame spread rate of n-butanol was faster than that of diesel fuel, whereas the transient flame spread rate showed an opposite trend. (3) No sensitive difference was found in surface temperature profile between two fuels, but n-butanol retained higher vertical temperature due to its higher flame height than diesel. The infrared images discovered that the subsurface convection flow of diesel had a larger size and noticeable temperature gradient. Diesel burned with more luminous flame and denser soot than n-butanol, owing to its more complex fuel components.