<p>The apparatus has a fuel tank (5) for storage fuel i.e. liquid gas. A combustion chamber (2) is connected with the tank. The combustion chamber comprises a movable piston for driving a driving plunger. A dosing device (4) is arranged between the tank and the chamber. A defined amount of the fuel from dosing volumes is passed into the chamber by the dosing device. The dosing device has a movable displacement element e.g. reciprocating piston, for discharging the fuel from the dosing volume. Movement of the displacement element is driven by pressure of the fuel as a power supply.</p>
