Engine with gas exchange through piston rod

A linear reciprocating engine, comprising:

• a cylinder having a first combustion chamber at a first end thereof and a second combustion chamber at an opposing second end thereof;
• a first cylinder head located at an end of the first combustion chamber;
• a second cylinder head located at an end of the second combustion chamber;
• a double-faced piston slidably mounted within the cylinder and configured to travel in a first stroke from a first position in a region of the first combustion chamber to a second position in a region of the second combustion chamber, the piston including a first face and a second face;
• a first piston rod portion extending from the first face of the piston through the first combustion chamber, the first piston rod portion having at least one port;
• a second piston rod portion extending from a second face of the piston through the second combustion chamber, the second piston rod portion having at least one port;
• a first recess in the first piston rod portion configured to communicate gases between the first combustion chamber and a first location outside the cylinder opposite the first cylinder head, the first recess being in fluid communication with the at least one port of the first piston rod portion;
• a second recess in the second piston rod portion configured to communicate gases between the second combustion chamber and a second location outside the cylinder opposite the second cylinder head, the second recess being in fluid communication with the at least one port of the second piston rod portion;
• a peripheral port in a wall of the cylinder, wherein the peripheral port is configured such that when the piston is in the first combustion chamber, the peripheral port communicates with the second combustion chamber, and when the piston is in the second combustion chamber, the peripheral port communicates with the first combustion chamber;
• and
• a chamber surrounding the first piston rod portion or the second piston rod portion, the chamber configured to be supplied with gas and the chamber being isolated from the first combustion chamber and the second combustion chamber.