Flame extension scale and flow characteristics of inclined tunnel fires with various separation distances from sidewall

A series of model-scale tests was conducted to investigate the influence of various separation distances from sidewall on ceiling jet flame characteristics in an inclined tunnel, considering various burner-ceiling heights (0.35 m and 0.45 m), burner-sidewall distances (0 similar to 0.5 m), tunnel inclination slopes (0 % similar to 12 %) and heat release rates (28.56 kW, 35.28 kW and 42.00 kW). It can be found that the transverse flame length of celling jet caused by tunnel fires initially increases, then decreases, and ultimately stabilizes with the increasing burnersidewall distances. However, the longitude flame length initially decreases, then remains constant with the increasing burner-sidewall distances. In addition, the transverse flame length is slightly affected by the tunnel inclination slopes. In contrast, for the longitudinal direction, the upward flame length increases as the tunnel slope rises, while the downward flame length decreases with increasing tunnel inclination slopes. Numerical simulations were performed to assist analyze the flow field and temperature contour distribution of the transverse flame of ceiling jet in inclined tunnel fires, which display the effect of various tunnel slopes and burnersidewall distances on the physical mechanism of flame behavior. Finally, a new correlation of nondimensional flame length in transverse direction was proposed, and a non-dimensional correlation for the experimental value of the upward and downward flame length in the longitudinal direction was presented as well, which were consistent with the experimental results.