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 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, 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.

An energy conversion apparatus may include an engine assembly, such as a monolithic engine assembly, that includes a first heater body and a first engine body. The first heater body may define a first portion of a first monolithic body or at least a portion of a first monolithic body-segment. The first engine body may define a second portion of the first monolithic body or at least a portion of a second monolithic body-segment operably coupled or operably couplable to the first heater body. The engine assembly may include a second heater body and/or a second engine body. The second heater body may define a portion of a second monolithic body or a third monolithic body-segment. The second engine body may define a portion of the second monolithic body or a fourth monolithic body-segment operably coupled or operably couplable to the second heater body and/or the first engine body.

A monolithic combustor body may provide multi-stage combustion. A combustor body may include a combustion chamber body and a plurality of heating walls that include a heat sink. The combustion chamber body may be disposed annularly about a longitudinal axis and defining a combustion chamber. The plurality of heating walls may include heat sink. The plurality of heating walls may occupy a radially or concentrically outward position relative to the combustion chamber and may define a corresponding plurality of combustion-gas pathways fluidly communicating with at least a proximal portion of the combustion chamber. During operation, the combustor body may exhibit multi-stage combustion that includes a first combustion zone occupying a distal or medial position of the combustion chamber relative to the longitudinal axis, and a second combustion zone occupying a proximal position relative to the first combustion zone and a radially or concentrically outward position of the combustion chamber and/or a radially or concentrically inward position of the plurality of combustion-gas pathways.

A constant density heat exchanger 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 held at constant density within the chamber by the first and second control devices.

A monolithic heater body may include a combustor body, a hot-side heat exchanger body, and an eductor body. The combustor body may define a combustion chamber and a conditioning conduit circumferentially surrounding the combustion chamber. The conditioning conduit may fluidly communicate with the combustion chamber at a distal portion of the combustion chamber. The hot-side heat exchanger body may define a hot-side heat exchanger that includes a heating fluid pathway fluidly communicating with a proximal portion of the combustion chamber. The eductor body may define an eduction pathway fluidly communicating with a downstream portion of the heating fluid pathway and a proximal portion of the conditioning conduit.

A mechanical device includes a working medium, a hot end, a cold end, and first and second volume regulating units. The hot and cold ends are in thermal contact with the working medium during circulation thereof. The first and second volume regulating units are disposed between the hot and cold ends, and are configured to allow passage of the working medium therethrough to perform compression and expansion of the working medium. The volume of the working medium exiting the first volume regulating unit differs from that of the working medium entering the second volume regulating unit. The volume of the working medium entering the first volume regulating unit differs from that of the working medium exiting the second volume regulating unit.

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.

A system including a closed cycle engine having a piston body defining a hot side and a cold side and having a piston assembly movable within the piston body. An electric machine is operatively coupled with the piston assembly. A control system includes one or more sensors operable to detect a piston movement characteristic of the piston assembly movable within the piston body. A controller is communicatively coupled with the one or more sensors and a controllable device. The controller is configured to determine a control command based at least in part on data received from the one or more sensors. The control command is selected based at least in part to cause the electric machine operatively coupled with the piston assembly to generate a preselected electrical power output. The controller provides the determined control command to the controllable device. The controllable device is operable to control an input to an engine working fluid disposed within the piston body.