The present invention directly affects two primary limitations of diesel fuel: poor vaporization and ease of auto-ignition. Superheated fuel is injected within a cone of steam. As a result, fuel is fully vaporized and steam controls ignition by momentarily isolating fuel from air. In order to achieve high vapor velocities, the present invention uses momentum of circulating fuel and water to propel them through the injector. Momentum is preserved by transfer valves that transfer moving liquids between through paths and injection paths. Momentum is further preserved by an injector design that minimizes turbulence that would absorb energy and reduce injected velocity. The fuel and water may be superheated before injection to convert to steam and vapor upon the release of pressure when injected into the combustion chamber. The injector may also be used to achieve high injection velocity for liquid fuel injection without heating.