A first orifice on a first inner surface of a first annular zone of a forward-bounded annular combustor provides for injecting air forward and radially outwards thereinto, from a location aft of a fuel slinger/injector. A radial dimension of a first outer surface of the first annular zone exceeds that of a corresponding first inner surface. A radial dimension of a second outer surface of a second annular zone of the annular combustor—aft of the first annular zone—exceeds that of a corresponding second inner surface. The first and second outer surfaces, and the first and second inner surfaces, are respectively coupled by transitional outer and inner surfaces of an annular transition zone located therebetween. The radial dimensions of the transitional outer and inner surfaces at the junctions with the corresponding second surfaces exceed the corresponding radial dimensions at the junctions with the corresponding first surfaces.