Identifying Flame Merging of Multiple Fires by Experimental Means

摘要

In this paper, two experimental methods, referred to as the "image method" and the "temperature method", are proposed to identify flame merging and determine the critical conditions for flame merging. The experiments were conducted in propane fire arrays by using 36 porous gas burners (side length: 5.6 cm) and the fire array size varied from 2 × 2 to 6 × 6. The heat release rate of each burner was equal and varied from 0.41 to 4.89 kW. The spacing distance between adjacent burners was changed from 0.4 to 11.2 cm. The flames were recorded from one side and the centerline flame temperatures were measured. In the image method, the critical dimensionless heat release rate of flame merging is obtained by processing of the video images, and it is also extracted by comparing the centerline temperatures with a critical value in the temperature method. It is found that for smaller fire array sizes, the critical dimensionless heat release rates for flame merging are consistent with the two methods. However, for larger fire array sizes, the critical dimensionless heat release rates extracted by the image method are lower than those with the temperature method. The differences are attributed to the superposition of different flame layers. Dimensionless correlations are proposed to predict the occurrence of flame merging by coupling the heat release rate with number of fire points, length of burner side and burner spacing. It is found that the critical dimensionless heat release rate increases with burner spacing ratio and decreases with number of fire points.