Combustion of partially premixed spray jets

Gas turbines, liquid rocket motors, and oil-fired furnaces utilize the spray combustion of continuously injected liquid fuels. In most cases, the liquid spray was mixed with an oxidizer prior to combustion, and further oxidizer was supplied from the outside of the spray to complete diffusion combustion. This rich premlxed spray is called partially premixed spray. The burning behavior of partially premixed sprays was experimentally studied with a newly developed spray burner. A fuel spray and oxidizer diluted with nitrogen was injected into the air. The overall equivalence ratio of the spray jet was set larger than unity to establish partially premixed spray combustion. 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).