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.

An engine apparatus, in which each piston assembly includes a piston attached to a connection member at a first end and a second end. Each piston of the piston assembly defines a first chamber and a second chamber separated by the piston. The first chamber and the second chamber are each defined at the first end and at the second end. Each first chamber of one piston assembly is fluidly connected to the second chamber at a different piston assembly. At least one first chamber at the first end is fluidly connected to a respective second chamber at the second end. At least one first chamber at the second end is fluidly connected to a respective second chamber at the first end.

A monolithic heat exchanger body for inputting heat to a closed-cycle engine may include a plurality of heating walls and heat sink, such as a plurality of heat transfer regions. The plurality of heating walls may be configured and arranged in an array of spirals or spiral arcs relative to a longitudinal axis of an inlet plenum. Adjacent portions of the plurality of heating walls may respectively define a corresponding plurality of heating fluid pathways therebetween, for example, fluidly communicating with the inlet plenum. At least a portion of the heat sink may be disposed about at least a portion of the monolithic heat exchanger body. The heat sink may include a plurality of working-fluid bodies, for example, including a plurality of working-fluid pathways that have a heat transfer relationship with the plurality of heating fluid pathways. Respective ones of the plurality of heat transfer regions may have a heat transfer relationship with a corresponding semiannular portion of the plurality of heating fluid pathways. Respective ones of the plurality of heat transfer regions may include a plurality of working-fluid pathways fluidly communicating between a heat input region and a heat extraction region.

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.

A monolithic engine assembly may include an engine body that includes a regenerator body. The engine body and the regenerator body may respectively define at least a portion of a monolithic body, or the engine body may define at least a portion of a first monolithic body-segment and the regenerator body may define at least a portion of a second monolithic body-segment operably coupled or operably couplable to the first monolithic body-segment. The regenerator body may include a regenerator conduit, and a plurality of fin arrays adjacently disposed within the regenerator conduit and respectively supported by the regenerator conduit in spaced relation to one another. The spaced relation of the plurality of fin arrays may define a gap longitudinally separating adjacent ones of the plurality of fin arrays.

An energy conversion apparatus may include an engine assembly, such as a monolithic engine assembly. The engine assembly may include a first monolithic body segment and a plurality of second monolithic body segments directly coupled or directly couplable to the first monolithic body segment. The first monolithic body segment may define a combustion chamber and a recirculation pathway in fluid communication with the combustion chamber. The recirculation pathway may be configured to recirculate combustion gas through the combustion chamber. The plurality of second monolithic body segments may respectively define at least a portion of a piston chamber and a plurality of working-fluid pathways fluidly communicating with the piston chamber.

A piston apparatus may include a plurality of piston assemblies respectively having a first piston body and a first piston disposed within a first volume defined by the first piston body, a second piston body and a second piston disposed within a second volume defined by the second piston body, and a connection member coupled to the first piston and the second piston. The first and second volume may respectively include an expansion chamber and a compression chamber defined by opposite sides of the corresponding piston. The respective expansion chambers may fluidly communicate with a corresponding compression chamber of another one of the piston assemblies. The first volume of a first piston assembly may fluidly communicate with the first volume and the second volume of a second piston assembly, and the first volume of a third piston assembly may fluidly communicate with the first volume and the second volume of the second piston assembly.

A monolithic heat exchanger body for inputting heat to a closed-cycle engine includes heating walls and heat sink, such as heat transfer regions. The heating walls are configured and arranged in an array of spirals or spiral arcs relative to a longitudinal axis of an inlet plenum. Adjacent portions of the heating walls respectively define corresponding heating fluid pathways fluidly communicating with the inlet plenum. At least a portion of the heat sink is disposed about at least a portion of the monolithic heat exchanger body. The heat sink includes working-fluid bodies including working-fluid pathways that have a heat transfer relationship with the heating fluid pathways. Respective ones of the heat transfer regions have a heat transfer relationship with a corresponding semiannular portion of the heating fluid pathways. Respective ones of the heat transfer regions include working-fluid pathways fluidly communicating between a heat input region and a heat extraction region.

A system for energy conversion including a closed cycle engine containing a volume of working fluid is provided. The engine includes a double-ended piston assembly including a pair of pistons coupled to a connection member. An expansion chamber is separated from a compression chamber by the piston. The engine defines an outer end and an inner end relative to a lateral extension of the piston assembly. A heater body is positioned thermally proximal to the expansion chamber and thermally distal to the compression chamber, and the heater body is positioned at the outer end of the engine. A load device is operably coupled to the piston assembly at the inner end of the engine. The load device is positioned between the pair of pistons of the piston assembly.

A system for energy conversion, the system including a closed cycle engine containing a volume of working fluid, the engine comprising a first chamber defining an expansion chamber and a second chamber defining a compression chamber each separated by a piston attached to a connection member of a piston assembly, and wherein the engine comprises a heater body in thermal communication with the first chamber, and further wherein the engine comprises a cold side heat exchanger in thermal communication with the second chamber, and wherein a third chamber is defined within the piston, wherein the third chamber is in selective flow communication with the first chamber, the second chamber, or both.