A revised spray-combustion diagram of diffusion-controlled burning regimes in fuel-spray clouds

Fuel droplets in combustors interact strongly with flames and turbulence in practical liquid-fueled combustors of terrestrial and aerial propulsion systems (Williams 1965; Sirignano 1999). Although a great deal of physical understanding has been achieved in purely gaseous combustion over the last century, not much is currently known about spray combustion at the fundamental level. In this short note, a revision of earlier combustionregime diagrams for non-premixed spray combustion of stationary fuel clouds (Chiu, Kim & Croke 1982) is done that includes fuel-oxidizer stoichiometry characteristics and the radius of a single-droplet flame. By doing so, this study suggests that the the groupcombustion number may not be the sole indicator of each spray-combustion mode. The resulting diagram describes the burning regimes in the fuel-spray cloud by making use of two dimensionless parameters, namely, the mass-loading ratio and the vaporization Stokes number, which appear naturally in the nondimensional form of the conservation equations.