Experimental study on the flame length and burning behaviors of pool fires with different ullage heights

Abstract

Floating-roof tanks are widely used in chemical parks and in case of fires, it is common to form pool fires with varying ullage height. This paper is aimed at examining experimentally and analytically the effects of ullage height on the burning and flame behaviors of heptane pool fires. A series of pool fire tests with four fuel tray sizes (D = 20–35 cm) and five ullage heights (h = 3 cm, 5 cm, D/2, D, 2D) was conducted. The flame characteristics (length and position) and mass burning rate were measured. Experimental results indicate that the total flame length can be divided into (i) a down-reaching flame length, (Lf,down), and (ii) an upper flame length (Lf,upper). The data shows that Lf,down increases as the ullage height increases whereas Lf,upper shows an opposite trend. For the tests with very large ullage heights (h/D = 1.93), it was found that the flame fluctuated periodically and, in some cases, self-extinguishing of the flame occurred due to lack of oxygen inside the fuel tray. A theoretical model is developed to calculate the total flame length by considering the influence of ullage height on air entrainment and heat feedback and subsequently validated against the experimental data.