In some embodiments the disclosure is directed to a closed-loop piston engine system using a recirculating carbon dioxide (CO.sub.2) system with supercritical carbon dioxide (scCO.sub.2) as a working fluid. The closed-loop piston engine system may include a scCO.sub.2 injector; a superheating nozzle region; a first valve; a second valve; a piston moving in the cylinder and coupled with a crankshaft, the piston being driven toward a centerline of the crankshaft during a power stroke using a connecting rod and causing the crankshaft to rotate thereby causing one power stroke per piston per crankshaft rotation and thereby producing two power strokes for every single power stroke that a similar engine would produce if run as a hydrocarbon fuel powered internal combustion engine. The recirculating CO.sub.2 system recirculates the used carbon dioxide and there are no carbon dioxide emissions from the system.

A valve assembly is adjustable in three independent ways allowing it to provide a variable input volume. The valve assembly has a base and an entrance plate. An outer guide, an inner guide and a shaft, each with a passage, are held together and the shaft is rotatable between the guides. The valve is open when the passages of the inner guide plate and shaft are aligned and closed when the passages are not aligned. The shaft RPM determines how many times per minute the valve opens. The open/closed ratio of the valve assembly determines how long the valve is open during each half revolution. The location of the shaft up or down in relationship to the inner guide determines what percentage of possible flow passes through the valve during each half revolution. The valve assembly can be used with either a gas or liquid medium.

A high efficiency steam engine or steam expander includes a cylinder, cylinder head and piston in which cylinder clearance volume is zero or nearly zero together with a negligible amount of compression such that any pressure in the cylinder clearance volume just before the power stroke is as low as ambient pressure or condenser pressure to provide superior thermal efficiency in a compact compound engine having a high pressure expansion chamber within the piston and low pressure chamber in the cylinder. The inlet valve is opened slightly by piston movement and a steam assist force then drives it to its fully open position. Steam passes from the high pressure chamber to the low pressure chamber through a transfer valve located in the head of the piston and steam is released through an automatic exhaust valve in the cylinder head.

In some embodiments the disclosure is directed to a closed-loop piston engine system using a recirculating carbon dioxide (CO.sub.2) system with supercritical carbon dioxide (scCO.sub.2) as a working fluid. The closed-loop piston engine system may include a scCO.sub.2 injector; a superheating nozzle region; a first valve; a second valve; a piston moving in the cylinder and coupled with a crankshaft, the piston being driven toward a centerline of the crankshaft during a power stroke using a connecting rod and causing the crankshaft to rotate thereby causing one power stroke per crankshaft rotation and thereby producing two power strokes for every single power stroke that a similar engine would produce if run as a hydrocarbon fuel powered internal combustion engine. The recirculating CO.sub.2 system recirculates the used carbon dioxide and there are no carbon dioxide emissions from the system.

In some embodiments the disclosure is directed to a closed-loop piston engine system using a recirculating carbon dioxide (CO.sub.2) system with supercritical carbon dioxide (scCO.sub.2) as a working fluid. The closed-loop piston engine system may include a scCO.sub.2 injector; a superheating nozzle region; a first valve; a second valve; a piston moving in the cylinder and coupled with a crankshaft, the piston being driven toward a centerline of the crankshaft during a power stroke using a connecting rod and causing the crankshaft to rotate thereby causing one power stroke per crankshaft rotation and thereby producing two power strokes for every single power stroke that a similar engine would produce if run as a hydrocarbon fuel powered internal combustion engine. The recirculating CO.sub.2 system recirculates the used carbon dioxide and there are no carbon dioxide emissions from the system.

In some embodiments the disclosure is directed to a closed-loop piston engine system using a recirculating carbon dioxide (CO.sub.2) system with supercritical carbon dioxide (scCO.sub.2) as a working fluid. The closed-loop piston engine system may include a scCO.sub.2 injector; a superheating nozzle region; a first valve; a second valve; a piston moving in the cylinder and coupled with a crankshaft, the piston being driven toward a centerline of the crankshaft during a power stroke using a connecting rod and causing the crankshaft to rotate thereby causing one power stroke per piston per crankshaft rotation and thereby producing two power strokes for every single power stroke that a similar engine would produce if run as a hydrocarbon fuel powered internal combustion engine. The recirculating CO.sub.2 system recirculates the used carbon dioxide and there are no carbon dioxide emissions from the system.

A high efficiency uniflow steam engine having automatic poppet valves yieldably based by fluid such as steam held under pressure within a cavity in the engine and a cutoff control for closing a steam inlet valve at any time selected stops the flow of steam into the cylinder. Proximate the end of the exhaust stroke, around 0.12 inch before TDC the cylinder is sealed to thereby compress residual steam as the piston clearance approaches zero; typically, 0.020 inch which raises cylinder pressure enough to open an inlet valve without making physical contact to push the inlet valve open with the piston thereby eliminating a tappet type of noise, shock and wear.

A high efficiency uniflow steam engine with automatic inlet and exhaust valves rather than camshaft operated valves includes an electromagnet and cooperating armature that actuates a cutoff control valve for closing a steam inlet valve at any time selected to stop the flow of steam to the cylinder. Approaching the end of the exhaust stroke typically 0.12 inch before TDC the cylinder is sealed thereby compressing the remaining residual steam down to a minute clearance approaching zero, for example, 0.020 inch to raise cylinder steam pressure enough to open the steam inlet valve without physical contact between the piston and the steam inlet valve thereby eliminating tappet noise, shock and wear.

A high efficiency uniflow steam engine having automatic inlet and exhaust valves rather than camshaft operated valves includes an electromagnet and cooperating armature that actuates a cutoff control valve for closing a steam inlet valve at any time selected to cut off the flow of steam to the cylinder. Approaching the end of the exhaust stroke, e.g., about 0.12 inch before TDC the cylinder can be sealed to thereby compressing the remaining residual steam down to a minute clearance approaching zero, for example, 0.020 inch raising cylinder steam pressure enough to open the steam inlet valve without physical contact between the piston and the steam inlet valve eliminating tappet noise, shock and wear.

Provided herein are rotary valve assemblies, engines, and corresponding methods. A rotary valve assembly may include a valve housing defining a cylindrical bore, an inlet, and an outlet. The valve assembly may further include an intake assembly and a throttle assembly arranged concentrically within the cylindrical bore of the valve housing, and the intake assembly and the throttle assembly may rotate independently of one another with respect to a longitudinal axis. During operation of the rotary valve assembly, the valve housing may permit fluid to enter the cylindrical bore of the valve housing via the inlet, the intake assembly may rotate to permit the fluid to flow through the at least one intake inlet port and the at least one throttle inlet port into the throttle body, and the intake assembly may permit the fluid to flow to the outlet from the throttle body.