An engine body may include a piston body comprising a piston chamber and a regenerator body comprising a regenerator conduit. An engine body may include a working-fluid heat exchanger body comprising a plurality of working-fluid pathways fluidly communicating between the piston chamber and the regenerator conduit. Additionally, or alternatively, an engine body may include a heater body comprising a plurality of heating fluid pathways and the plurality of working-fluid pathways. The heating fluid pathways may have a heat transfer relationship with the working fluid pathways. The working-fluid pathways may fluidly communicate between the piston chamber and the regenerator conduit. The engine body may include a monolithic body defined at least in part by the piston body, the regenerator body, and the working-fluid heat exchanger body, and/or defined at least in part by the piston body, the regenerator body, and the heater body.

An engine body may include a piston body comprising a piston chamber and a regenerator body comprising a regenerator conduit. An engine body may include a working-fluid heat exchanger body comprising a plurality of working-fluid pathways fluidly communicating between the piston chamber and the regenerator conduit. Additionally, or alternatively, an engine body may include a heater body comprising a plurality of heating fluid pathways and the plurality of working-fluid pathways. The heating fluid pathways may have a heat transfer relationship with the working fluid pathways. The working-fluid pathways may fluidly communicate between the piston chamber and the regenerator conduit. The engine body may include a monolithic body defined at least in part by the piston body, the regenerator body, and the working-fluid heat exchanger body, and/or defined at least in part by the piston body, the regenerator body, and the heater body.

Systems and methods for converting energy are provided. In one aspect, the system includes a closed cycle engine defining a cold side. The system also includes a bottoming-cycle loop. A pump is operable to move a working fluid along the bottoming-cycle loop. A cold side heat exchanger is positioned along the bottoming-cycle loop in a heat exchange relationship with the cold side of the closed cycle engine. A constant density heat exchanger is positioned along the bottoming-cycle loop downstream of the cold side heat exchanger and upstream of an expansion device. The constant density heat exchanger is operable to hold a volume of the working fluid flowing therethrough at constant density while increasing, via a heat source, the temperature and pressure of the working fluid. The expansion device receives the working fluid at elevated temperature and pressure and extracts thermal energy from the working fluid to produce work.

Systems and methods for converting energy are provided. In one aspect, the system includes a closed cycle engine defining a cold side. The system also includes a bottoming-cycle loop. A pump is operable to move a working fluid along the bottoming-cycle loop. A cold side heat exchanger is positioned along the bottoming-cycle loop in a heat exchange relationship with the cold side of the closed cycle engine. A constant density heat exchanger is positioned along the bottoming-cycle loop downstream of the cold side heat exchanger and upstream of an expansion device. The constant density heat exchanger is operable to hold a volume of the working fluid flowing therethrough at constant density while increasing, via a heat source, the temperature and pressure of the working fluid. The expansion device receives the working fluid at elevated temperature and pressure and extracts thermal energy from the working fluid to produce work.

A split Stirling cryogenic refrigerator device may include a resonant pneumatic expander comprising a resonant displacer assembly supported by a spring and configured to slide back and forth along a longitudinal axis within a housing of the resonant pneumatic expander, the resonant displacer assembly comprising a tubular displacer containing a regenerator and coupled to a sealing piston, and a driving piston coupled to the sealing piston by an elongated radially compliant and axially rigid connecting member.

A split Stirling cryogenic refrigerator device may include a resonant pneumatic expander comprising a resonant displacer assembly supported by a spring and configured to slide back and forth along a longitudinal axis within a housing of the resonant pneumatic expander, the resonant displacer assembly comprising a tubular displacer containing a regenerator and coupled to a sealing piston, and a driving piston coupled to the sealing piston by an elongated radially compliant and axially rigid connecting member.

A heat recovery engine (5) including a compressor (15) to increase pressure, density and temperature of a gas stream flowing in a closed loop within the engine, with the gas stream at base system pressure (10) at a compressor inlet; an expander (30) to reduce the pressure of said gas stream when compressed to just above said base system pressure, at the same time receiving power from the gas stream; a recuperator (20) to transfer thermal energy from downstream gas stream of said expander (30) to downstream gas stream of said compressor (15), thereby increasing the temperature of said downstream gas stream of said compressor (15) at approximately constant pressure; a heater (25) to provide further heat energy to said gas stream at approximately constant pressure after exit from said recuperator (20); a heat source (40) and a means (45) for transferring heat energy from said heat source (40) to said heater (25); a cooler (35) to cool said gas stream prior to compression in said compressor; a heat energy transfer device to transfer heat from aid cooler (35) to the environment; an operability device to ensure the operation of said compressor and said expander, and to take off surplus power either mechanically or electrically; a plurality of insulated ducts to transfer said gas stream between said compressor (15), recuperator (20), heater (25), expander (30) and cooler (35).

A heat recovery engine (5) including a compressor (15) to increase pressure, density and temperature of a gas stream flowing in a closed loop within the engine, with the gas stream at base system pressure (10) at a compressor inlet; an expander (30) to reduce the pressure of said gas stream when compressed to just above said base system pressure, at the same time receiving power from the gas stream; a recuperator (20) to transfer thermal energy from downstream gas stream of said expander (30) to downstream gas stream of said compressor (15), thereby increasing the temperature of said downstream gas stream of said compressor (15) at approximately constant pressure; a heater (25) to provide further heat energy to said gas stream at approximately constant pressure after exit from said recuperator (20); a heat source (40) and a means (45) for transferring heat energy from said heat source (40) to said heater (25); a cooler (35) to cool said gas stream prior to compression in said compressor; a heat energy transfer device to transfer heat from aid cooler (35) to the environment; an operability device to ensure the operation of said compressor and said expander, and to take off surplus power either mechanically or electrically; a plurality of insulated ducts to transfer said gas stream between said compressor (15), recuperator (20), heater (25), expander (30) and cooler (35).

A constant density heat exchanger and system for energy conversion is provided. The constant density heat exchanger includes a housing extending between a first end and a second end and defining a chamber having an inlet and an outlet. A first flow control device is positioned at the inlet of the chamber and movable between an open position in which a working fluid is permitted into the chamber and a closed position in which the working fluid is prevented from entering the chamber. A second flow control device is positioned at the outlet of the chamber and movable between an open position in which the working fluid is permitted to exit the chamber and a closed position in which the working fluid is prevented from exiting the chamber. A heat exchange fluid imparts thermal energy to the volume of working fluid as the first flow control device and the second flow control device hold the volume of working fluid at constant density within the chamber.

A constant density heat exchanger and system for energy conversion is provided. The constant density heat exchanger includes a housing extending between a first end and a second end and defining a chamber having an inlet and an outlet. A first flow control device is positioned at the inlet of the chamber and movable between an open position in which a working fluid is permitted into the chamber and a closed position in which the working fluid is prevented from entering the chamber. A second flow control device is positioned at the outlet of the chamber and movable between an open position in which the working fluid is permitted to exit the chamber and a closed position in which the working fluid is prevented from exiting the chamber. A heat exchange fluid imparts thermal energy to the volume of working fluid as the first flow control device and the second flow control device hold the volume of working fluid at constant density within the chamber.