Experimental study on flame interaction and geometrical features of two identical fires on a slope

Multiple fire interaction is a fundamental combustion phenomenon which often occurs in forest fires and urban fires. This paper presents a systematical study of two identical buoyant fires on a slope in a facility consisting of a slope apparatus and a couple of gas burner systems. The test repeatability is justified for the proposed facility. The effects of fire spacing, fire power, slope angle and burner layout are intensively investigated on the flame merging probability and flame geometry of two interactive fires. The flame merging probability is found to well correlate the spacing normalized by the flame height of no spacing, and the variation of flame merging behavior with spacing can be divided into the consistent, intermittent, and independent regimes. However, the burner layout affects the critical dimensionless spacing that distinguishes the three regimes, due to the difference of air flow field between the side by side and tandem layouts. Data analysis clarifies the effect of slope and spacing on the flame length, flame tilt angle and flame attachment length, and a semi-empirical correlation is developed for the flame height of no spacing.