Abstract: The invention seeks to improve the functioning of a piston internal combustion engine which uses heat vaporization of the fuel, already in the starting and cold running phase. This is achieved by using a fuel preheater having at least one glow plug fitted directly in the nozzle-holder shank. The glow plug protrudes into the modified fuel chamber of the valve body, and is in direct contact with the fuel. In this way, the fuel is instantaneously heated to a temperature far above boiling point at atmospheric pressure. As a result, the combustion process of the internal combustion engine is considerably more efficient in the starting and cold running phase. In addition, fuel consumption is lower and cleaner exhaust gases are given off.