Apparatus constituting part of an induction and fuel delivery system for a cylinder of a piston internal combustion engine comprising a small cyclone into which is tangentially discharged a flow of heated air to generate a sustained vortex of high rotational speed; a modulatable fuel injector delivering a flow of atomised fuel into said small cyclone wherein it underdoes flash evaporation and energetic mixing; a delivery duct connecting said small cyclone to the inlet tract of said cylinder wherein said vortex fuel-air mixture is mixed with heated induction air; and means to prevent overheating of said modulatable fuel injector.