Flame morphologic characteristics of horizontally oriented jet fires impinging on a vertical plate: Experiments and theoretical analysis

Abstract

Flame morphological characteristics of horizontal impinging jet fires are of practical importance in predicting and controlling the undesirable energy transfer to the nearby obstacle, which usually results in an escalating accident accompanied by severe consequences. But up to now, the relevant research is still very limited. The length of flame spread on the obstacle's surface for various nozzle diameters as well as the lift-off distance restricted by a vertical plane surface downstream the flame has not been quantified yet. In this work, the evolutions of flame spread length and lift-off distance of horizontal jet fires impinging on a vertical plate for different nozzle diameters at various energy (heat) release rates and nozzle-plate spacings have been quantified comprehensively. Experiments were conducted with three nozzles with different inner diameters of 2.0, 3.0 and 4.2 mm. The heat release rates of the fire source ranged between 5.7 and 32.2 kW, and the nozzle-plate spacings were varied from 0.20 to 0.40 m with a corresponding free condition. The results showed that the length of flame spread along the vertical plate increased with increasing the heat release rate and decreasing the nozzle-plate spacing for a given nozzle diameter. In addition, the large nozzle had a relatively greater increase in the flame spread length than the small one. A new correlation was proposed on physically the coupling effects of the flux ratio of buoyancy-induced air entrainment and jet momentum and the dimensionless heat release rate, showing good agreement with the experimental results. It was also found that the normalized lift-off distance under impingement can be correlated with the modified dimensionless flow number, and the correlation can well collapse all the lift-off data of this work. The present findings contribute to a better understanding of horizontal impinging jet fires, allowing predictions to be made regarding the possible threat and the establishment of the necessary safety distance for the pipeline to reduce the potential risk of such fire disasters.