An experimental study of jet fires in rotating flow fields

The interaction between jet flame and vortex flow is a fundamental combustion phenomenon which could occur in actual fire accidents. This paper presents a systematical investigation on such jet fire in a rotating flow field (JFRFF). A new facility was designed for the experimental study, which consists of a jet fire apparatus and a whirl generator. The test repeatability was justified for the proposed facility. The dynamical differences of JFRFF, free jet fire and fire whirl are clarified. A set of correlations are proposed for the flow circulation, flame height, lift-off height and frequency of flame wander of JFRFF. The flow circulation is found to well couple the inlet velocity and the flow guide angle as Gamma = 0.80 pi D(d)u(a)sin theta. The results have also shown that the JFRFF has a larger flame height than the free jet fire in still air, while the lift-off height is shorter than the free jet fire. Theoretical analysis identifies two competitive effects of flow circulation on the flame height of JFRFF. The enhancement of air entrainment in the ground layer reduces the flame height by decreasing the jet momentum, whereas the reduction of fuel-air mixing rate in the upper flame increases the flame height. The flow circulation reduces the vertical velocity of gas mixtures in the ground boundary layer, resulting in a less lift-off height. However, similarly as for fire whirls, the flame of JFRFF wanders as whole with the centerline being not completely perpendicular to the horizontal plane, and the appearance probability of flame fits Gauss distribution. It is also found that the frequency of flame wander can be positively correlated to the tangential component of inlet velocity. (C) 2019 The Combustion Institute. Published by Elsevier Inc. All rights reserved.