Combustion Characteristics of Partially Premixed n-Decane Spray Jets

Partially premixed sprays have not been studied systematically although they are of practical importance. In the present study, burning behaviors of partially premixed sprays were experimentally studied with a newly developed spray burner. A fuel spray and oxidizer diluted with nitrogen was injected into air. The overall equivalence ratio of the spray jet was set quite 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 an internal flame and without it 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 results also suggested that the internal flame was a premixed flame 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.