An experimental study on the burning rates of n-heptane pool fires with various lip heights in cross flow

Abstract

This paper presents an experimental investigation into the burning rates of pool fires with different lip heights in cross flows for which data are not previously reported. Square pool fires with side lengths (D) of 5, 10, 15 and 20 cm and dimensionless lip heights (h⁎ = h/D) of 0.25, 0.5, 1.0, 1.5 and 2.0 were tested burning n-heptane using a system that maintains the fuel level. The mass burning rates were measured with cross flow air speeds of 0–∼3.0 m/s. Previous works have mostly been concerned with pool fires with similar lip heights (h⁎) in still air for relative smaller pools, or in cross flows with very small lip heights (i.e., h⁎ ≤ 0.1). It was found that the burning rate behavior differs with pool size and h⁎. For small pools (D = 5 and 10 cm), the burning rate increased monotonically with cross flow air speed when h⁎ was small, but first decreased then increased with large h⁎. For larger pools (D = 15 and 20 cm), the burning rate first increased, then decreased, followed by a final increasing trend with small h⁎; while for larger h⁎, the burning rate first decreased and then increased with increasing cross flow air speed. These different trends were discussed in terms of the considerable change in the distance from the flame to the fuel surface, which affected the conduction, convection and radiation feedbacks to the fuel. It was observed that the flame was “pushed down” into the fuel-containing vessels by relatively strong cross flows, which further changed the heat feedback. A burning rate correlation was proposed to characterize the combined effects of cross flow air speed and lip height.