An internal combustion engine includes a hollow cylinder, a piston within the hollow cylinder, and a cylinder head. A base valve assembly at a base of the hollow cylinder permits or restricts fluid flow from an intake manifold into a sub-chamber below the piston. The piston includes at least one intake port connecting a combustion chamber above the piston with the sub-chamber, and a transfer valve that opens and closes the at least one intake port. When the transfer valve opens the at least one intake port, fluid is permitted to flow from the sub-chamber to the combustion chamber. The internal combustion engine operates according to a four-stroke piston cycle, wherein multiple intake stages are provided. The intake stages may include intake of air into the sub-chamber during a compression stroke, transfer of air from the sub-chamber to the combustion chamber during a power stroke, intake of air-fuel mixture into the sub-chamber during an exhaust stroke, and transfer of air-fuel mixture from the sub-chamber to the combustion chamber during an intake stroke.

An internal combustion engine includes a hollow cylinder, a piston within the hollow cylinder, and a cylinder head. A base valve assembly at a base of the hollow cylinder permits or restricts fluid flow from an intake manifold into a sub-chamber below the piston. The piston includes at least one intake port connecting a combustion chamber above the piston with the sub-chamber, and a transfer valve that opens and closes the at least one intake port. When the transfer valve opens the at least one intake port, fluid is permitted to flow from the sub-chamber to the combustion chamber. The internal combustion engine operates according to a four-stroke piston cycle, wherein multiple intake stages are provided. The intake stages may include intake of air into the sub-chamber during a compression stroke, transfer of air from the sub-chamber to the combustion chamber during a power stroke, intake of air-fuel mixture into the sub-chamber during an exhaust stroke, and transfer of air-fuel mixture from the sub-chamber to the combustion chamber during an intake stroke.

An internal combustion engine includes a hollow cylinder, a piston within the hollow cylinder, and a cylinder head. A base valve assembly at a base of the hollow cylinder permits or restricts fluid flow from an intake manifold into a sub-chamber below the piston. The piston includes at least one intake port connecting a combustion chamber above the piston with the sub-chamber, and a transfer valve that opens and closes the at least one intake port. When the transfer valve opens the at least one intake port, fluid is permitted to flow from the sub-chamber to the combustion chamber. The internal combustion engine operates according to a four-stroke piston cycle, wherein multiple intake stages are provided. The intake stages may include intake of air into the sub-chamber during a compression stroke, transfer of air from the sub-chamber to the combustion chamber during a power stroke, intake of air-fuel mixture into the sub-chamber during an exhaust stroke, and transfer of air-fuel mixture from the sub-chamber to the combustion chamber during an intake stroke.

An internal combustion engine includes a hollow cylinder, a piston within the hollow cylinder, and a cylinder head. A base valve assembly at a base of the hollow cylinder permits or restricts fluid flow from an intake manifold into a sub-chamber below the piston. The piston includes at least one intake port connecting a combustion chamber above the piston with the sub-chamber, and a transfer valve that opens and closes the at least one intake port. When the transfer valve opens the at least one intake port, fluid is permitted to flow from the sub-chamber to the combustion chamber. The internal combustion engine operates according to a four-stroke piston cycle, wherein multiple intake stages are provided. The intake stages may include intake of air into the sub-chamber during a compression stroke, transfer of air from the sub-chamber to the combustion chamber during a power stroke, intake of air-fuel mixture into the sub-chamber during an exhaust stroke, and transfer of air-fuel mixture from the sub-chamber to the combustion chamber during an intake stroke.

An internal combustion engine has at least one piston configured to reciprocate within a combustion chamber. The engine has a transfer port, and exhaust port and a secondary port which may be adapted as either a secondary air transfer port, a secondary exhaust port, or as a two-way port acting selectively as i) an air transfer port and ii) an exhaust port. The engine may operate on a two stroke cycle. The engine may be for use submerged in a body of water, e.g. in an outboard motor, and with a cowling defining a volume near an outer wall of the combustion chamber. The volume can be selectively filled with water or exhaust gas for engine temperature optimisation.

An internal combustion engine has a cylinder with a combustion chamber and a piston supported reciprocatingly in the cylinder and delimiting the combustion chamber. A crankcase is connected to the cylinder and a crankshaft is rotatably supported therein. The piston is operatively connected to the crankshaft so as to drive the crankshaft in rotation. A transfer passage provides flow communication between crankcase interior and combustion chamber when the piston is at bottom dead center. The transfer passage has a port opening connecting the transfer passage to the crankcase interior and has a transfer port connecting the transfer passage to the combustion chamber. A fuel supply device supplies fuel into the transfer passage at a location between the transfer port and the port opening. The transfer passage has a connecting opening and is connected to the crankcase interior at the connecting opening. A control element controls the connecting opening.

A mixture-lubricated four-stroke engine has a cylinder and a piston. On the piston, at least one piston ring is arranged. Between valve drive chamber and crankcase interior, at least one first channel is arranged. The first opening of the first channel lies in the bottom dead center position of the piston below each piston ring. At the first opening, the first channel defines a first middle flow direction for mixture flowing into the crankcase interior. The first middle flow direction extends inclined towards the combustion chamber and in a viewing direction perpendicular to the cylinder longitudinal plane intersects the longitudinal center axis above the first opening of the first channel.

A mixture-lubricated four-stroke engine has a cylinder and a piston. On the piston, at least one piston ring is arranged. Between valve drive chamber and crankcase interior, at least one first channel is arranged. The first opening of the first channel lies in the bottom dead center position of the piston below each piston ring. At the first opening, the first channel defines a first middle flow direction for mixture flowing into the crankcase interior. The first middle flow direction extends inclined towards the combustion chamber and in a viewing direction perpendicular to the cylinder longitudinal plane intersects the longitudinal center axis above the first opening of the first channel.

Internal combustion engines that operate in an inverted orientation in which the piston is closer to the local gravitationally dominant terrestrial body's center of gravity at top dead center position than at bottom dead center position are disclosed. The engines may have non-circular, preferably rectangular, cross-section pistons and cylinders, and the pistons may include a skirt with a field of pockets that provide a ringless, non-lubricated, seal equivalent. The pistons also may have a domed piston head with depressions thereon to facilitate the movement of air/charge in the cylinder. The engines also may use multi-stage poppet valves in lieu of conventional poppet valves, and a split crankshaft. The engines may use the pumping motion of the engine piston to supercharge the cylinder with air/charge.

Internal combustion engines that operate in an inverted orientation in which the piston is closer to the local gravitationally dominant terrestrial body's center of gravity at top dead center position than at bottom dead center position are disclosed. The engines may have non-circular, preferably rectangular, cross-section pistons and cylinders, and the pistons may include a skirt with a field of pockets that provide a ringless, non-lubricated, seal equivalent. The pistons also may have a domed piston head with depressions thereon to facilitate the movement of air/charge in the cylinder. The engines also may use multi-stage poppet valves in lieu of conventional poppet valves, and a split crankshaft. The engines may use the pumping motion of the engine piston to supercharge the cylinder with air/charge.