Experimental analysis of flame dynamic evolution and heat transfer mechanism of ethanol spill fire with different channel width in tunnel environment

Abstract

When liquid fuel leaks onto a busy road tunnel, it initially spreads in a two-dimensional manner, leading to a two-dimensional spill fire if ignited. As the tunnel width increases, the two-dimensional spreading and burning process becomes more enduring. This study aims to investigate the impact of tunnel width on flame dynamics, thermal feedback mechanisms, and heat loss mechanisms in ethanol spill fires. The results indicate that as the tunnel width increases, both the maximum combustion area (MCA), the increase rate of combustion area (IRCA) and stable combustion area (SCA) increase, but heat release rate per unit area (HRRPUA) decrease. As the channel width expands, the flame plume height and flame oscillation frequency rise. A new flame oscillation model considering flame shape ratio is introduced. Both channel width and flame length-to-height ratio influence flame oscillation behavior. Heat transfer analysis reveals that when the discharge rate increases and the width is between 0.05 m and 0.15 m, the fraction of radiant thermal feedback ${\chi }_{\text{rad}}$ significantly increases with discharge rate. However, when the width is between 0.2 m and 0.3 m, the ${\chi }_{\text{rad}}$ difference between different widths is minimal. Under the same discharge rate, as the channel width expands, both the convective thermal feedback ${\chi }_{\text{conv}}$ and heat loss ${\chi }_{\text{loss}}$ fractions tend to rise. A novel dimensionless burning rate model is developed, when the dimensionless heat release rate $Q_{hrr}^{*}$ increase, the burning rate ${m^{″}}^{*}$ exhibit an upward trend, albeit at a reduced growth rate. Once $Q_{hrr}^{*}$ reaches a sufficient magnitude, ${m^{″}}^{*}$ stabilizes at a constant value.