Abstract: An engine may include a cylinder having a first combustion chamber at one end thereof and a second combustion chamber at an opposing end thereof, first and second cylinder heads at an end of the first combustion chamber and the second combustion chamber, respectively, and a double-faced piston slidably mounted within the cylinder. The piston may be configured to move in a first stroke from the first end to the second end of the cylinder. The piston and the cylinder may be configured such that the first stroke includes an expansion stroke portion during which chemical energy from combustion in the first combustion chamber is converted into mechanical power of the piston, and a momentum stroke portion during which the piston continues to move to the second end of the cylinder and gases are exchanged between the first combustion chamber and a location outside the cylinder.