Effects of transverse air flow on burning rates of rectangular methanol pool fires

Abstract

The effects of a transverse air flow on the burning rate of square and rectangular methanol pools have been studied experimentally. The variables altered were the size and shape of the pool, and the air speed. The responding variable measured was a characteristic burning rate. Direct images of flame luminosity were collected to help interpret the burning rate data. The square pools ranged in size from 7.5 × 7.5 to 30 × 30 cm . The rectangular pools tested were the same area as a 15 × 15 cm square pool, but with aspect ratios of 4:1. The air flow ranged in speed from quiescent to 5.5 m/s and was provided by a low-turbulence wind tunnel. The pools were held outside the tunnel boundary layers, so they would experience near-uniform upstream air flow conditions, and oriented perpendicular to the pool's leading edge. The results of this study were that the quiescent burning rate per unit area was essentially constant for all pools tested. As the transverse air flow was introduced a variety of responses in burning rate were observed for different sizes and shapes of the pool. Depending on the size of the square pool, the burning rate showed a 2.5 times monotonic increase, invariance, or nonmonotonic response to increasing air speeds. The nonmonotonic burning rate response corresponded to the flame separating from the trailing edge of the pool. The use of pools of the same area, but different shape showed that the response of burning rate to air speed does not correlate to pool area, but supported an analysis based on the ratio of momentum to buoyancy forces that suggested that the characteristic dimension for combustion was the stream-wise length of the pool.