On the boundary conditions and stability of moderately dense spray flames

This paper presents a mapping of boundary conditions for moderately dense spray flames stabilized on a new variant of the piloted burner which uses a needle to inject liquid fuel into an air-blasting stream. The needle tip may be translated upstream of the jet exit plane such that the spray exiting the burner may develop from dense at zero recess distance to dilute when the needle is sufficiently recessed. Global stability limits of the burner are generated for a range of recess distances and are compared to a fully dilute spray studied earlier [1]. High speed shadowgraph imaging is employed to highlight details of the boundary conditions and reveal the evolution of various shapes of liquid fragments over a range of recess distances. Such information is presented for three types of liquid fragments: spherical droplets, ligaments and unbroken 'irregular' shapes. The information presented here will assist modelers in advancing current capabilities to compute the structure of moderately dense spray flames.