Jet fires involving releases of gas and solid particle

Abstract

The high-pressure leakage of underground pipeline could entrain the nearby sands and soils, and thus cause the jet fire of gas-solid mixtures. In addition, the thermal runaway of Lithium ion batteries could also cause a typical gas-solid jet diffusion flame. In comparison with the gaseous jet diffusion flame and the gas-solid-air jet premixed flame, the gas-solid jet diffusion flame lacks of exploration. Thus, a new facility consisting of a jet fire apparatus and a sand feeder, was designed to explore the gas-solid jet fire. The test repeatability was justified for the proposed facility. The dynamical differences of gas-solid and gaseous jet fires are clarified. It is found that the gas-solid jet fire holds a larger lift-off height, a less visible flame height and a less radiative fraction than the purely gaseous jet fire. In particular, for gas-solid jet fires at high exit velocities, the lift-off height increases, but the visible flame height and radiative fraction seem to decrease, as the particle size of sand decreases to increase the jet height of sand. (1) Inside the flame volume, the sand plays a role of heat sink to decrease the flame temperature and thus the flame burning velocity. Moreover, in the lift-off region, the sand dilutes the gas fuel and isolates the surrounding oxygen to inhibit the combustion. Both effects of sand cause a large lift-off height, especially for the sand of little particle size. (2) A large lift-off height means the increase of the air mass entrained from flame base or the portion of the premixed flame to the whole flame. In addition, the sand particle-laden flow would significantly increase the ambient air entrainment rate of fire plume. Both effects result in a less visible flame height. (3) The portion of the premixed flame increases in the bottom, which reduces the total soot amount inside the whole flame volume. The decrease of the flame temperature and the total soot amount reduces the radiative fraction. (4) The sand significantly affects the flame geometry and radiative fraction, which alters the radiant heat flux distribution and challenges the development of thermal radiation model for gas-solid jet fires. The gas-solid jet fire holds a less peak radiant heat flux but a higher positon of peak radiant heat flux than the gaseous jet fire. In addition, the line source radiation model available in literature is revised to well predict the radiant heat flux distribution of the gas-solid jet fires.