To achieve this the invention provides a pneumatic end-of-travel damping for the adjustment piston (10).

The piston (112) is provided with a cooling passageway (122) which at or adjacent the bottom dead centre position of the piston is aligned with inlet and outlet ports (124, 126) of the cylinder.

Near the end of the fluid discharge piston stroke, a connector 88 engaged with either the shaft of with the piston assembly may engage selectively engage a mating connector on the needle assembly.

This enables, without having a long cylinder of a hydraulic cylinder, impact force to be sufficiently reduced at a stroke end of the piston and, in addition, noise by the impact force can be reduced.

7 spring adjusted elements acting only at the end of the pistons stroke.

The engine further includes a piston configured to reciprocate within the cylinder between spaced stroke termination points defining a stroke of the piston.

The engine also includes a connecting rod operably coupled to the piston.

Piston displacement and compression ratio

Needle retraction is accomplished by simply reversing the movement of the plunger at the end of an injection stroke.

The stroke area of the inner piston is arranged in a centric or approximately centric manner in relation to the stroke area of the outer piston.

The exhaust valve is again closed before the end of the piston stroke which includes the working phase, whereas the intake valve continues to be open beyond the conclusion of the exhaust for this same piston stroke.

A fluid throttling arrangement is provided to decelerate the piston (12) towards the ends of its stroke.

The piston stroke is configured to provide zero or negative clearance between the piston head and the face of the outlet valve at the end of the compression stroke.

The method may also include, subsequent to completion of the compression stroke, expanding at least part of the combustion gas against the piston during an additional combustion-gas-expansion stroke (142) of the piston.

Said control mechanism can be controlled by a potentiometer and/or an elastic force, a pressure cylinder, and a pressure-controlled valve or the like, and the piston stroke and the restoring force acting on the piston can be adjusted.