A heat exchanger, internal to an injector for a variable spray fuel injection system, uses nucleate boiling to maximize the heat flux from the heated metal to the fuel, wherein the nucleate boiling occurs along a control surface characterized by features conducive to generating detaching bubbles to transfer heat energy in a vapor flux. The source of heat flux may be an induction heater coil magnetically coupled to an appropriate loss component so that fuel inside a fuel component is heated to a desired temperature.