Experimental study on horizontal gas temperature distribution of two propane diffusion flames impinging on an unconfined ceiling

Ceiling gas temperature is one of the most important factors for heat detection and alarm once an undesirable fire along with releasing hot and toxic smoke is erupted in a building. The impinging flame characterized by the unbumt fuel burning along the ceiling has received much attention in recent years as it poses a greater threat to the ceiling structure, devices and trapped people than the non-impinging flame. Many studies have been focused on the ceiling gas temperature induced by a single flame, while little effort has been put with respect to the multiple flames. The interaction between multiple flames might lead to flame's tilt to each other and even merge together with small spacings, resulting in different ceiling gas temperature distribution from the single flame. The aim of this experimental work is to investigate the ceiling gas temperature decay profile induced by two impinging flames. Propane was used as the fuel. The heat release rate (HRR), burner edge spacing and ceiling height above the fuel were overall changed. The ceiling gas temperatures along the direction of changing spacing were measured to determine the impingement point position and temperature decay profile. The results showed that the impingement point position is dependent on the HRR and the spacing as well as the ceiling height, while the maximum gas temperature is weakly affected by the spacing. The established correlation reveals that the maximum excess temperature increases first and then maintains unchanged with increasing the HRR normalized by the ceiling height. The plume radius proposed for the single impinging flame is not enough to characterize the ceiling gas temperature of two impinging flames. A new correlation for temperature decay profile induced by two impinging flames is therefore proposed and validated using the experimental results.