Combustion phenomena can comprise any one of three regimes, namely: (a) homogeneous combustion of pre-mixed fuel vapour and air; (b) heterogeneous combustion of fuel droplets and air, as in spray combustion; (c) combustion of solid particles and air, as with metal dust. This paper presents a simple phenomenological model that offers a consistent method of computing the burning velocity in each of the three regimes. The effects of turbulence can be allowed for. The model can be used with multi-component fuels in conjunction with techniques that have been developed to predict instantaneous properties of vaporising petroleum fractions. The simplicity of the model makes it amenable to inclusion as a submodel in larger models used for the design of practical combustion systems.