In a jet spray flame a jet of liquid fuel spray emerges from a small orifice of a burner into a stagnant air environment. The fuel jet entrains air from the surroundings and a mixing layer is formed between the evaporating fuel and the oxygen in the air. Under appropriate operating conditions, a diffusion flame can be established throughout this mixing layer. Although jet spray flames are widely used in many engineering applications, such as gas turbines, jet engines and other energy production systems, a fundamental theoretical understanding of these flames and their characteristics has yet to appear in the literature.
In the current work, a laminar jet polydisperse spray diffusion flame is nalysed mathematically for the first time using an extension of classical similarity solutions for gaseous jet flames. The analysis enables a comparison to be drawn between conditions for flame stability or flame blow-out for purely gaseous flames and for spray flames. It is found that, in contrast to the Schmidt number criteria relevant to gas flames, droplet size and initial spray polydispersity play a critical role in determining potential flame scenarios. Some qualitative agreement for lift-off height is found when comparing predictions of the theory and sparse independent experimental evidence from the literature.
