of the injector 15 as an alternative to the above stated fraction of the cobalt of the first material this may be replaced with a nickel chromium fraction or a nickel chromium cobalt fraction such that the first material has at least 70 percent preferably 90 percent tungsten carbide and 1 to 30 percent preferably 1 to 10 percent nickel chromium or nickel chromium cobalt by virtue of the fact that the control plate 60 is composed of steel it exhibits similar warming up characteristics to the injector housing 25 at the same time the gap 150 is reduced in terms of its gap width b by the control piston 70 composed of hard metal when the latter is warmed up even though the invention has been illustrated and described in more detail on the basis of the preferred exemplary embodiment the invention is not restricted to the examples disclosed and other variations may be derived therefrom by a person skilled in the art without departing from the scope of protection of the invention it is emphasized that as an alternative to the configuration of the injector 15 described above it is also the case that only one or two of the three combinations of piston guide control plate 60 leakage pin plate 106 nozzle needle 110 and piston control piston 70 leakage pin 100 nozzle needle sleeve 115 has the above stated material combination what is particularly simple to implement is the configuration in which only the control piston 70 has the first material and the control piston plate 60 has the second material in order to limit the second leakage 170 between the spring chamber 85.