Abstract: An engine includes a crankshaft, rotating about a crankshaft axis of the engine. A power piston is received within a first cylinder and operatively connected to the crankshaft such that the power piston reciprocates through a power stroke and an exhaust stroke during a single rotation of the crankshaft. A compression piston is received within a second cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke during a single rotation of the crankshaft. A gas passage interconnects the first and second cylinders. The gas passage includes an inlet valve and an outlet valve defining a pressure chamber therebetween. The outlet valve permits substantially one-way flow of compressed gas from the pressure chamber to the first cylinder. The power piston descends to a firing position from its top dead center position.

Abstract: An engine has a crankshaft, rotating about a crankshaft axis of the engine. An expansion piston is slidably received within an expansion cylinder and operatively connected to the crankshaft such that the expansion piston reciprocates through an expansion stroke and an exhaust stroke of a four stroke cycle during a single rotation of the crankshaft. A compression piston is slidably received within a compression cylinder and operatively connected to the crankshaft such that the compression piston reciprocates through an intake stroke and a compression stroke of the same four stroke cycle during the same rotation of the crankshaft. A ratio of cylinder volumes from BDC to TDC for either one of the expansion cylinder and compression cylinder is fixed at substantially 26 to 1 or greater.