Combustion of partially premixed spray jets

The burning behavior of partially premixed sprays was experimentally studied with a newly developed spray burner. A fuel spray and an oxidizer, diluted with nitrogen, were injected into the air. n-Decane was used as a liquid fuel. The overall equivalence ratio of the spray jet was set larger than unity to establish partially premixed spray combustion. In the present burner, the mean droplet diameter of the atomized liquid fuel could be varied without varying the overall equivalence ratio of the spray jet. Two combustion modes with and without an internal flame were observed. As the mean droplet diameter was increased or the overall equivalence ratio of the spray jet was decreased, the transition from spray combustion only with an external group flame to that with the internal premixed flame occurred. The internal flame was supported by flammable mixture through the vaporization of fine droplets, and the passage of droplet clusters deformed the internal flame and caused internal flame oscillation. The existence of the internal premixed flame enhanced the vaporization of droplets in the post-premixed-flame zone within the external diffusion flame. This is an abstract of a paper presented at the 30th International Symposium on Combustion (Chicago, IL 7/25-30/2004).