Patent Publication Number: US-6336326-B1

Title: Apparatus for cooling a heat engine

Description:
This application claims the benefit of U.S. Provisional Application No. 60/182,050, filed Feb. 11, 2000, U.S. Provisional Application No. 60/182,105, filed Feb. 11, 2000, and U.S. Provisional Application No. 60/182,106, filed Feb. 11, 2000. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to a heat engine. 
     BACKGROUND OF THE INVENTION 
     The heat engine is an alternate engine to the internal combustion engine. Various designs for heat engines have been developed in the past. Despite its potential for greater thermodynamic efficiency compared to internal combustion engines, heat engines have been used in only limited applications in the past due to several factors including the complexity of the designs, the weight of the engine per unit of horse power output as well as the difficulty in starting a heat engine. 
     SUMMARY OF THE INVENTION 
     In accordance with the instant invention, an improved design for a heat engine is disclosed. In one embodiment, the heat engine is made from lightweight sheet metal. By using a plurality of cylindrical containers, one nested inside the other, for the displacer, the combustion and cooling chambers as well as to create an air flow path between the heating and cooling chambers, a rugged durable lightweight construction is achieved. 
     In another embodiment, the heat engine utilizes a power piston which is biased to a first position. By biasing the piston, several advantages are obtained. First, the heat engine may be self starting provided the power piston is biased so as to be initially positioned in the cooling chamber. A further advantage is that by using an electrical means (eg. a solenoid, an electromagnet or the like) to move the displacer, preferably in response to the position of the power piston, a complicated mechanical linkage between the power piston and the displacer is not required thus simplifying the design. Further, by using an electrical linkage, the phase angle between the displacer and the power piston may be adjusted. 
     The heat engine of the instant invention may be combined with a fuel source (eg. butane), a linear generator and an electrically operated light emitting means to create a flashlight or other portable light source. It will be appreciated that due to the simplicity of the design of the instant invention, the heat engine as well as the linear generator are each adapted to be scaled up or down so as to produce greater or lessor amounts of power. Accordingly, in another embodiment, the heat engine together with a linear generator and a fuel source may be used as a generator. It will further be appreciated that by connecting a linear generator to a source of electricity (eg. standard electrical outlet) the electricity from a power grid may be used to run the linear generator as a motor whereby the power piston effectively drives the displacer. In such a case, the heat engine may be used as a refrigerator or a cryogenic cooler. In such an embodiment, the heating and cooling chambers of the heat engine are effectively reversed and no combustion chamber is required. 
     In accordance with one aspect of the instant invention, there is provided a heat engine comprising a container defining a sealed region within which a working fluid is circulated when the heat engine is in use, the sealed region having a heating chamber and a cooling chamber, the heating and cooling chambers being in fluid flow communication via a working fluid passageway; a combustion chamber thermally connected to the heating chamber; a displacer movably mounted in the sealed region; a piston movably mounted in the sealed region; at least one cooling fin having first and second opposed sides and positioned exterior of the cooling chamber; and, a heat exchanger having a combustion air passageway for providing air for combustion to the combustion chamber, at least some of the cooling fins are positioned in the heat exchanger whereby heat withdrawn from the cooling chamber is a used to preheat the air for combustion. 
     In one embodiment, the at least one fin is configured and arranged to permit fluid to flow from the first opposed side to the second opposed side and to direct fluid from the second opposed side to the first opposed side. 
     In another embodiment, the at least one fin has main directing members and fluid flow passages through which the fluid may pass through the fin, the main directing members are configured and arranged to cause a portion of the fluid which has passed through the fin from the first opposed side to the second opposed side to then pass from the second opposed side to the first opposed side. 
     In another embodiment, the at least one fin is configured and arranged to cause at least a portion of the fluid to swirl around the combustion air passageway. 
     In another embodiment, the at least one fin has a deformable collar for lockingly engaging the wall to which the fin is attached. 
     In another embodiment, the at least one fin is mechanically mounted to at least one wall of the heat exchanger by a pressure which is exerted between the fin and the at least one wall which is sufficient to ensure that the rate of heat transfer between the at least one wall and the fin is maintained over the normal operating temperature of the at least one wall. 
     In another embodiment, the at least one fin comprises a plurality of longitudinally spaced apart fins. 
     In another embodiment, the at least one fin comprises a helical fin. 
     In another embodiment, the at least one fin has at least one main directing member which is configured and arranged to cause a portion of the fluid to pass at least twice through the main directing member as the fluid flows through the fin. 
     In another embodiment, the at least one fin has at least one main directing member which has a first side, a second side and is configured and arranged to cause a portion of the fluid to flow unidirectionally from the first side of a main directing member to the second side of the main directing member as the fluid flows through the fin. 
     In another embodiment, the at least one fin has a hub adjacent a wall of the combustion air passageway and an annular body portion extending away from the hub, and openings and main directing members are provided in the annular body portion. 
     In another embodiment, the at least one fin has a hub adjacent a wall of the combustion air passageway and a plurality of blades extending away from the hub, the blades defining passages through which air for combustion flows. 
     In another embodiment, the heat engine further comprises a motor driven fan mounted in fluid flow communication with the combustion air passageway for assisting in producing air flow through the combustion air passageway. Preferably, the motor and the fan encircle the heat engine. 
     In accordance with another aspect of the instant invention, there is also provided a heat engine comprising container means having first and second portions; fluid conduit means for connecting the first and second portions in fluid flow communication, the first portion is at a higher temperature than the second portion when the heat engine is in use; combustion means for receiving air for combustion and providing heat to the first portion; and, heat exchanger means for transferring heat from the second portion of the container means to the air for combustion, the heat exchanger means comprising fin means positioned in the heat exchanger means. 
     In one embodiment, the heat engine further comprises outer container means positioned exterior to the container means wherein each of the container means and the outer container means are thin walled, and positioning means, for dimensionally stabilizing the container means and outer container means, the heat exchanger means is positioned on the outer container means. 
     In another embodiment, the positioning means extends between the inner and outer container. 
     In another embodiment, the fin means is constructed to generate a generally longitudinal flow of fluid through the heat exchanger means. 
     In another embodiment, the fin means is constructed to generate a rotational flow of fluid through the heat exchanger means. 
     In another embodiment, the fin means comprises a plurality of rows of fins having first and second opposed sides, at least some of the fins having fluid directing means for directing the fluid from the first opposed side to the second opposed side and from the second opposed side to the first opposed side. 
     In another embodiment, the fin means comprises a plurality of rows of fins having first and second opposed sides, at least some of the fins having fluid directing means for directing fluid to flow rotationally through the heat exchanger means. 
     In another embodiment, the fin means has mounting means for producing a sufficient pressure between the fin means and the portion of the heat engine to which the fin means is mounted to ensure that the rate of heat transfer between the heat engine and the fin means is maintained over the normal operating temperature of the heat engine. 
     In another embodiment, the heat engine a further comprises fan means for providing forced convection in the heat exchanger means. 
     In another embodiment, the fan means is mounted in the heat exchanger means. 
     In another embodiment, the fin means have first and second opposed sides and first directing means for generating a main flow of fluid through the fin means as the fluid flows from the first opposed side to the second opposed side and second directing means for generating a secondary fluid flow which passes through at least some of the first directing means whereby the heat transfer between the fluid and the heat exchanger means is enhanced. 
     In another embodiment, the first directing means generates an axial flow of fluid through the heat exchanger means. 
     In another embodiment, the first directing mean generates a rotational flow of fluid through the heat exchanger means. 
     In another embodiment, at least some of the first directing means direct the fluid from the first opposed side to the second opposed side and from the second opposed side to the first opposed side. 
     In another embodiment, the fin means comprises a plurality of individual longitudinally spaced apart annular fins and/or a helical fin. 
     In another embodiment, the second directing means are configured and arranged to cause a portion of the fluid to pass at least twice through the first directing means with which the second directing means are associated as the fluid flows through the fin means. 
     In another embodiment, the main directing means has a first side, a second side, the second directing means is configured and arranged to cause the fluid to flow unidirectionally from one side of a main directing means with which the second directing means is associated to the other side as the fluid flows through the fin means. 
     In accordance with another aspect of the instant invention, there is also provided a heat engine comprising container means having first and second portions; fluid conduit means for connecting the first and second portions in fluid flow communication, the first portion is at a higher temperature than the second portion when the heat engine is in use; combustion means for receiving air for combustion and providing heat to the first portion; heat exchanger means for transferring heat from the second portion of the container means to the air for combustion; and, fan means for providing forced convection in the heat exchanger means. 
     In one embodiment, the fan means is mounted in the heat exchanger means. 
     In another embodiment, the fin means have first and second opposed sides and first directing means for generating a main flow of fluid through the fin means as the fluid flows from the first opposed side to the second opposed side and second directing means for generating a secondary fluid flow which passes through at least some of the first directing means whereby the heat transfer between the fluid and the heat exchanger means is enhanced. 
     In another embodiment, the first directing means generates an axial flow of fluid through the heat exchanger means. 
     In another embodiment, the first directing mean generates a rotational flow of fluid through the heat exchanger means. 
     In another embodiment, the second directing means are configured and arranged to cause a portion of the fluid to pass at least twice through the first directing means with which the second directing means are associated as the fluid flows through the fin means. 
     In another embodiment, the main directing means has a first side, a second side, the second directing means is configured and arranged to cause the fluid to flow unidirectionally from one side of a main directing means with which the second directing means is associated to the other side as the fluid flows through the fin means. 
    
    
     DESCRIPTION OF THE DRAWINGS 
     For a better understanding of the present invention, and to explain more clearly how it may be carried into effect, reference will now be made by way of example to the accompanying drawings which show preferred embodiments of the present invention, in which: 
     FIG. 1 is a partially cut away perspective view of a heat engine according to the instant invention; 
     FIG. 2 a  is a cross section along the line  2 — 2  of FIG. 1 of a heat engine configured as a flashlight with the heat exchanger for the fresh air for combustion removed, with the displacer positioned adjacent the heater cup and the power piston positioned at the end of the power stroke; 
     FIG. 2 b  is a cross section along the line  2 — 2  of FIG. 1 configured as a flashlight with the heat exchanger for the fresh air for combustion removed, with the displacer positioned distal to the heater cup and the power piston positioned at the beginning of the power stroke; 
     FIG. 2 c  is a cross section along the line  2 — 2  of FIG. 1 of an alternate embodiment with the displacer positioned adjacent the heater cup and the power piston positioned at the end of the power stroke; 
     FIG. 2 d  is a cross section along the line  2 — 2  of FIG. 1 of an alternate embodiment with the displacer positioned distal to the heater cup and the power piston positioned at the beginning of the power stroke; 
     FIG. 2 e  is a cross section along the line  2 — 2  of FIG. 1 of a further alternate embodiment configured as a flashlight with the displacer positioned adjacent the heater cup and the power piston positioned at the end of the power stroke; 
     FIG. 3 is an enlargement of the heating and regeneration zones of the cross section of FIG. 2 c;    
     FIG. 4 is an enlargement of the cooling zone and linear generator of FIG. 2 c;    
     FIG. 5 is an exploded view of the displacer and electromagnet of FIG. 2; 
     FIG. 6 a  is a perspective view of the heat exchanger for the heating zone and the regeneration zone; 
     FIG. 6 b  is a perspective view of the air flow through an alternate version of the heat exchanger for the heating zone; 
     FIG. 6 c  is an cross section along the line  6 — 6  in FIG. 6 b  showing the air flow through the heat exchanger for the heating zone of FIG. 6 b;    
     FIG. 6 d  is an enlargement showing the air flow through the heat exchanger for the regeneration zone of FIG. 6 a;    
     FIG. 7 is a perspective view of the working components of FIG. 2 a  with the inner and outer cylinders removed; 
     FIG. 8 is a schematic drawing of the control circuit for the electromagnet of FIG. 5; 
     FIG. 9 is a partially cut away perspective view of a heat engine according to a second embodiment of the instant invention which employs a magnetic drive system wherein the electronic control shown in FIGS. 9 and 10 has been removed; 
     FIG. 10 is a cross section of the heat engine of FIG. 9 with the heat exchanger for the fresh air for combustion removed, with the displacer positioned adjacent the heater cup and the power piston positioned at the end of the power stroke; 
     FIG. 11 is a cross section of the heat engine of FIG. 9 with the heat exchanger for the fresh air for combustion removed, with the displacer positioned distal to the heater cup and the power piston positioned at the beginning of the power stroke; 
     FIG. 12 is a perspective view of a louvred fin; 
     FIG. 12 a  is a perspective view of another louvred fin; 
     FIG. 12 b  is a cross section of a cylindrical tube with the louvred fin of FIG. 12 a  attached thereto; 
     FIG. 12 c  is a perspective view of an alternate louvred fin; 
     FIG. 12 d  is a perspective view of an alternate louvred fin; 
     FIG. 12 e  is a perspective view of a portion of a heat exchanger with louvred fins and cyclonic flow in the circulating fluid as the fluid travels axially through the heat exchanger; 
     FIG. 12 f  is a perspective view of a portion of a heat exchanger with louvred fins and cross flow in the circulating fluid as the fluid travels axially through the heat exchanger; 
     FIG. 13 is a perspective view of a radial blade; 
     FIG. 14 is a perspective view of a further embodiment of a spacer ring; 
     FIG. 15 is a perspective view of a further embodiment of a spacer ring; 
     FIG. 16 is a perspective view of a helical fin; 
     FIG. 17 is an enlarged view of the helical fin of FIG. 16 with an alternate louvre; 
     FIG. 18 a  is an enlarged perspective view of a louvre of the helical fin of FIG. 16 showing the sublouvres; 
     FIG. 18 b  is an enlarged perspective view of a louvre of the helical fin of FIG. 16 showing alternate sublouvres; 
     FIG. 19 is a cross section of a further alternate embodiment of the heat engine; 
     FIG. 20 is a cross section of a further alternate embodiment of the heat engine; 
     FIG. 21 is an assembly for a power piston or a displacer wherein the power piston of displacer is constructed from two containers that are welded together; 
     FIG. 22 is an assembly for a power piston or a displacer wherein the power piston of displacer is constructed from two containers that are threadedly engaged; 
     FIG. 23 is an assembly for a power piston or a displacer wherein the power piston of displacer is constructed from a first and second containers wherein the second container is press fitted into the opening of the first container; and, 
     FIGS. 24 a  and  b  are graphs of the movement of the power piston compared to the movement of the displacer in one embodiment of the invention. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The heat engine described herein contains several novel design innovations including the construction of the heat engine from sheet metal or the like, the construction and positioning of the heat exchangers (including the regenerator), the drive system for the displacer and the power piston so as to allow different cycles for the displacer and the power piston, the feedback system for controlling the amount of heat (energy) provided to the working fluid and the ability to synchronize the frequency of several generators to allow their series or parallel connection to a load. 
     In the preferred embodiments of FIGS. 1-4,  7 ,  9 - 11 ,  19  and  20  the heat engine includes a linear generator as the power piston. In an alternate preferred embodiment the heat engine includes a mechanical linear to rotary converter, which is known in the art. Design innovations of this disclosure may be used with either preferred embodiment. Accordingly, similar parts have been referred to by the same reference numeral in all embodiments. 
     In accordance with the embodiments of FIGS. 2 a,    2   b,    2   e  and  7 , a light bulb is incorporated into the housing of the heat engine so as to provide a portable flashlight. The heat engine is drivingly connected to a linear generator which is used to create current to power one or more incandescent light bulbs, fluorescent light bulbs, LEDs, gas plasma discharge light sources or the like. It will be appreciated that the heat engine may be powered by any heat source known in the art. In a preferred embodiment, the flashlight housing includes a fuel reservoir which, upon combustion, provides heat to power the heat engine. Accordingly, the flashlight comprises four main components namely a heat source, a heat engine, a linear generator and a light emitting device (eg. a light bulb). It will also be appreciated that the linear generator may be used to provide power for any required purpose and that the heat engine and the linear generator may be configured as an electric generator or may be connectable to an electric motor or any other application that requires electricity (i.e. the load). In any such application, the component to which the linear generator provides electricity may be housed with the heat engine and the linear generator or may be a separate discrete component. 
     As shown in the drawings attached hereto, the components are shown set out in a linear array (i.e. they are positioned sequentially along longitudinal axis A of the flashlight). However, it will be appreciated that the components may be set up in various configurations. For example, the fuel reservoir need not be positioned directly in line with the heat engine. Similarly, the light bulb or other powered component need not be positioned along longitudinal axis A of the flashlight but may be positioned at any desired point by adjusting the shape of the outer housing and providing a sufficient length of wire to connect the light bulb or other powered component to the linear generator. Alternately, the housing of the heat engine and the linear generator may have an electrical outlet for receiving a standard electric plug. 
     The following description is based on the flashlight model which has a single light bulb. However, the device, complete with an on-board heat source (eg. a reservoir filled with a combustible fuel and a combustion chamber), creates a self contained, lightweight light source which may be in the form of a flash light, a portable camping light, a lamp or the like. In this application, the flashlight has been described as if it were standing vertically on a table with bulb  48  positioned at the bottom. References to upper and lower, vertical or horizontal in this application are for reasons of convenience based upon this orientation of the flashlight in the drawings. It will be appreciated that the heat engine and the linear generator may be used when the housing of the apparatus is in any particular orientation. 
     Thin Walled Construction 
     According to one aspect of the instant invention, a novel construction of a heat engine is provided which uses thin walled structures to house the working or moving components of the heat engine (i.e. displacer  46  and power piston  50 ) within a working container having first and second ends. The working fluid is circulated between the first end of the working container which is warmer than the second end. In contrast to earlier designs wherein the working container is prepared from a block of metal which is machined to produce a space within which the working fluid circulates or which is forged, this design uses sheet metal and the like to form a container. Positioning members are provided to dimensionally stabilize the walls of the container thereby providing a durable structure. Due to the construction materials used, the heat engine is light weight and has good thermal efficiency since the thin walled construction allows for faster heat transfer to and from the working fluid and significantly reduced heat retention by the components of the heat engine. 
     In a more preferred embodiment, the working container is an inner container which is housed within an outer housing and the positioning members extend between the outer housing and the working container at a plurality of locations along the length of the working container. The positioning members may be provided only at the longitudinally opposed ends of the inner container. For example, the positioning means may be affixed to the opposed ends of the inner and/or outer containers and extend generally parallel to the longitudinal axis of the heat engine to draw the opposed ends together (eg. a bolt and a butterfly nut), in which case they function as clamping means to draw the opposed ends together and seal the inner cavity. Preferably, the positioning means extends generally transverse to the longitudinal axis of the heat engine. In such a case, if the passageway through which the working fluid travels between the first and second ends of the inner container is positioned in the space between the outer housing and the inner container, then the positioning members are configured to allow fluid flow there through. The positioning members may also function as heat exchangers and/or a regenerator thereby reducing the number of components required for constructing a heat engine. More preferably, the outer housing is also of a thin walled construction. 
     As in the embodiment of FIG. 1, the container may be open topped wherein the combustion chamber is positioned at least partially within and preferably wholly within the inner container and is used to dimensionally stabilize the top of the inner container. The combustion chamber is constructed from materials which will maintain their structural integrity at combustion temperatures and therefore, the combustion chamber may be prepared by standard construction techniques for turbine engine components (eg. stamping components out of a super nickel alloy to maximize heat transfer by minimizing the wall thickness). 
     FIGS. 1,  2   a,    9 - 11 ,  19  and  20  exemplify this construction. Referring to FIG. 2 a,  a flashlight  10  is shown with each of the components set out in a longitudinally extending array inside outer wall  12 . Outer wall  12  has a first end  14  and a second end  16 . A start or ignition button  18  is provided, preferably on the longitudinally outer wall  12 . 
     As shown in FIGS. 2 a - 2   d,  flashlight  10  comprises a heating zone  22 , a regeneration zone  24 , a cooling zone  26  and an electrical generation zone  28 . Flashlight  10  is provided with a housing to include the components for each of these four zones. The housing comprises outer wall  12  and inner wall  30  which are preferably co-axially positioned about longitudinal axis A (see FIG.  1 ). While the housing which is shown in the drawings comprises nested cylinders, it will be appreciated that the housing may comprise inner and outer containers that may be of any shape and need not be coaxially mounted. Further, the housing may allow any configuration of the components provided the electrical generation means is drivenly connected to the heat engine. 
     Outer wall  12  has an outer surface  32  and an inner surface  34 . Inner wall  30  has an outer surface  36  and an inner surface  38 . Inner surface  34  of outer wall  12  and outer surface  36  of inner wall  30  are spaced apart to define an outer cavity which may be used as annular fluid flow path  40  within which regenerator  42  is preferably positioned. The construction techniques of this design may be used in configurations of heat engines that do not include a regenerator or which do not position the regenerator in an annular passageway exterior to the inner cavity within which the displacer is positioned. 
     In the preferred embodiment of FIGS. 2 a  and  2   b,  positioned inside inner wall  30  are heater cup  44 , displacer  46 , driver  48  for moving displacer  46 , power piston  50  and a linear generator comprising a plurality of magnets  52 , ferrite beads  54  and coils  56 . Light bulb  58  is mounted at second end  16  of outer wall  12 . 
     As shown in FIG. 3, heater cup  44  has an inner surface  60  and an outer surface  62 . Outer surface  62  is spaced from inner surface  38  of inner wall  30  so as to define a fluid flow path  64 . Fluid flow path  64  is a first passageway that is in fluid flow communication with fluid flow path  40  by means of a plurality of spaced apart openings  66  which are provided in inner wall  30 . Accordingly, fluid flow path  64  and openings  66  define a passageway connecting the interior of the upper portion of inner wall  30  (i.e. heating chamber  140 ) with fluid flow path  40 . In the embodiment of FIG. 1, inner wall  30  terminates prior to top  90  of heater cup  44  thereby providing an annular space  64  through which the upwardly flowing working fluid passes as it travels from heating chamber  140  to annular fluid flow path  40 . A plurality of positioning members to dimensionally stabilize the end of inner wall  30  adjacent heater cup  44  are provided in fluid flow paths  64  and  40 . These positioning members may be in the form of rings that extend continuously around outer surface  62  and engage inner surface  38  of inner wall  30  to prevent inner wall  30  from contracting inwardly when the heat engine is operating. These positioning members may also be constructed to assist in the transfer of heat to the working fluid. Examples of such positioning members are protrusions  106  (see FIG.  3 ), contact with wall of burner cup  44  (see FIG. 2 a ), spacer rings  164 ,  476  (see FIGS.  14  and  15 ), louvred fins  428 ,  440 ,  468  (see FIGS. 12,  12   a,    12   c,    12   d  and  13 ) and helical louvred fin  448  (see FIG.  16 ). In another alternate embodiment, inner and outer walls  30  and  12  may be two containers that are prepared by die stamping and then connected together at their open (top) ends by placing one container inside the other and spin welding the top ends together to form a double walled vessel. The portions of the containers that are spun welded together define an intermediate portion and openings  66  may be provided therein to allow heating chamber  140  to be in fluid flow communication with fluid flow path  40  (see eg. FIG.  3 ). 
     In the embodiment of FIGS. 2 a  and  2   b,  inner wall  30  has a swedged portion  204  at which point inner wall  30  has an increased diameter thereby bringing inner and outer walls  30  and  12  into engagement. This method of assembly is advantageous if inner wall  30  is prepared from a preformed cylindrical tube. 
     This engagement, for example over the length of the electrical generator zone  28 , maintains the co-axial alignment of the cylinders. In the embodiment of FIG. 4, outer wall  12  has a uniform diameter along its length and accordingly is maintained in a spaced apart relationship from inner wall  30  by, for example, a sealant which is inserted in gap  166  below openings  158  or by spacer rings  164 . As shown in FIG. 15, spacer rings  164  may be generally annular members having a generally U shaped profile in cross section. As such, ring  164  has a pair of opposed edges  262  extending from upper end  264  to trough portion  266  to define an open area  268 . Preferably, opposed edges  262  extend outwardly at a sufficient angle α to central axis B which extends through ring  164  so that upper ends  264  are compressed towards each other when ring  164  is inserted between outer and inner walls  12  and  30  thus providing a tight sliding fit to mechanical lock the cylinders together. A plurality of rings  164  which are spaced apart in gap  166  provides sufficient mechanical connection between outer and inner walls  12  and  30  so as to coaxially align them. 
     As is exemplified by FIG. 1, providing any such positioning members between spaced apart inner and outer walls creates a sandwiched construction wherein the inner and outer walls become mutually self supporting. By including a plurality of such spaced apart members, longitudinally spaced apart portions of, for example, outer wall  12  and inner wall  30  (e.g. positioned adjacent each of heater cup  44  and piston  50 ), may be in contact with each other and transmit stresses (either inwardly directed or outwardly directed forces) between the inner wall and the outer wall. By maintaining the relative position of the inner and outer walls, the positioning members allow the mechanical strength of the inner and outer walls to be combined. 
     For example, in the embodiment of FIG. 1, at the lower end of the heat engine, a plurality of rings  164  are provided. At the upper end, inner wall  30  is dimensionally stabilized by louvred fins which are provided in both passageways  64  and  88  to thereby hold inner wall  30  and outer wall  12  at fixed positions with respect to heater cup  44 . 
     In the embodiments of FIGS. 2 a - 2   d,  a gap  166  exists between inner and outer walls  30  and  12  below the upper extent of travel of piston  50 . The gap between inner and outer walls  30  and  12  is sealed so as to cause the working fluid to enter cooling chamber  160  and act on piston  50 . Preferably, the gap is sealed immediately below openings  158  so as to prevent working fluid from entering gap  166  which would function as a dead zone in the heat engine. This gap may be sealed in several ways. For example, one or more rings  164  may be provided to seal gap  166 . In an alternate embodiment, a sealant (eg. epoxy) may be applied to fill all or a portion of gap  166 . In the alternate embodiment of FIG. 2 e,  inner wall  30  is swedged outwardly immediately below openings  158  such that inner and outer walls  30  and  12  are positioned adjacent each other in the cooling zone. The positioning of inner and outer walls  30  and  12  adjacent each other or the use of epoxy are additional examples of positioning members as they utilize the interplay between the inner and outer walls  30  and  12  to stabilize inner and outer walls  30  and  12 . 
     In a preferred embodiment, inner wall  30  and outer wall  12  are each of a “thin walled” construction. For example, each of inner wall  30  and outer wall  12  may be made from a metal such as aluminum, stainless steel, super metal alloys and the like, and are preferably made from stainless steel and the like. The wall thickness of cylinders  12  and  30  may vary from about 0.001 to about 0.250 inches, preferably from about 0.005 to about 0.125 inches, more preferably from about 0.01 to about 0.075 inches and most preferably from about 0.02 to about 0.05 inches. Similarly, the walls of displacer  46  as well as the walls of piston  50  may be made from the same or similar materials. In larger heat engines (eg. those over 12 inches in diameter), the wall thickness is preferably selected so as to be greater than one sixtieth of the diameter of inner wall  30  and preferably about one thirtieth of the diameter of inner wall  30  when the wall is constructed from super nickel alloys and other similar materials whose strength will not be significantly compromised at 600° C. 
     Accordingly, the main components of the heat engine may be constructed from sheet metal or the like using the same materials and in a manner that is similar to the containers which are used for soft drink cans or the like. In this preferred embodiment, inner and outer walls  30  and  12  are formed from prefabricated components (prepared eg. by stamping or drawing) which are then assembled together to form the heat engine. For example, inner and outer walls  30  and  12  may be prepared from sheet metal by roll forming the sheet metal and then laser welding the sheet metal to form a longitudinally extending tube. Alternately, metal may be drawn through a die to form a cylindrical tube. Openings  66  and  158  in inner wall  30  may then be made by stamping, drilling, laser cutting or the like. A circular bottom plate may be obtained from sheet metal by stamping and then roll formed or welded to the tube to produce an opened top container into which the power piston and the displacer may be placed. Alternately, a prefabricated open topped container may be formed by stamping metal using a high speed carbide die. This is in contrast to existing techniques for forming engines wherein a block of metal is cast and subsequently bored or the like to prepare the engine body thus resulting in an engine which is much heavier than is structurally required for a heat engine. 
     Similarly, displacer  46  may be manufactured from roll formed sheet metal which is then laser welded together. Bottom  146  and top  136  may then be affixed to the side walls by roll forming, welding, brazing, the use of an adhesive or the like. Divider plates  144  may be added as required in the manufacturing operation. Once sealed, displacer  46  provides a rugged construction which will withstand the heat and stresses applied to displacer  46  in the heat engine. A power piston may be constructed in a similar fashion. 
     As shown in FIGS. 21-23, displacer  46  or power piston  50  may be constructed from two open topped containers  498  which are joined together, such as at the mid point of displacer  46  by welding along seam line  500 . Each container comprises longitudinally extending side walls  502  and an end wall  504 . Side walls and end walls  502  and  504  may be integrally formed such as by high speed carbide die stamping or, alternately, side walls  502  may be prepared by drawings metal through a die to form a preformed longitudinally extending cylindrical tube and end wall  504  may be affixed thereto by roll forming or the like. It will be appreciated that welding seam  500  may be provided at any position along side walls  502 . By providing end walls  504  to dimensionally stabilize the opposed ends of displacer  46 , and by sealing side walls and end walls  502  and  504  of displacer  46  so as to contain a sealed cavity  506 , the overall exterior structure of displacer  46  is sufficiently strong to act as a displacer (or a power piston) in a heat engine. 
     FIG. 22 shows an alternate embodiment wherein cap  508  is provided with walls  510  which have a thread  512  provided on the inner surface thereof. The distal portion of walls  502  from end  504  are recessed inwards slightly and have a mating thread  514  provided thereon. Accordingly, displacer  46  (or a power piston  50 ) may be constructed by providing an open topped vessel and screwing a cap  508  thereon. 
     A further alternate construction is shown in FIG.  23 . In this case, a cap  516  is provided. Cap  516  has walls  518 . Portion  520  of walls  518  are recessed inward slightly so as to provide a seat for the distal end of walls  502  to be received thereon. The diameter of the outer surface of walls  520  is slightly larger than the diameter of the inner surface of walls  502  so that portions  520  lockingly engage the inner surface of walls  502 . In this way, a sealed displacer  46  (or power piston  50 ) may be provided. It will be appreciated that in the embodiments of FIGS. 22 and 23, one opposed end of walls  502  is stabilized by end wall  504  and the other opposed end of walls  502  is stabilized by cap  508 ,  518 . 
     In order to reduce thermal transfers due to radiation and convection within displacer  46 , displacer  46  may be divided into a plurality of chambers  142  by a plurality of divider plates  144  as is shown in FIGS. 1 and 3. 
     Pressurization 
     The durability of displacer  46  and/or the power piston may be further improved by pressurizing the interior of displacer  46  or the power piston. The degree to which displacer  46  and/or the power piston is pressurized is preferably based on the degree of pressurization of the working fluid in the heat engine. Preferably, displacer  46  and the power piston has a pressure from about −2 to about 10 atm, more preferably from about 1 to about 10 atm and, most preferably, from about 2 to about 4 atm greater than the pressure of the working fluid in the heat engine. In a similar manner, the structural integrity of walls  12  and  30  may be similarly enhanced by pressurizing the interior of the heat engine once it has been constructed. Preferably, the interior of the heat engine (i.e. where the working fluid circulates) is pressurized to a pressure from about 1 to about 20 atm, more preferably from about 4 to about 10 atm. Thus, if the pressure of the working fluid is 4 atm, then the displacer may be at a pressure from 2 to 14 atm. 
     The working fluid may be any working fluid known in the art. For example, the working fluid may be selected from air and helium, and, is preferably helium. Helium has a high thermal conductivity which allows the heat engine to be operated at a higher operating frequency thus increasing the power output per unit volume of interior working space of the heat engine (i.e. the volume within which the working fluid circulates). 
     Dual Flow Heat Exchanger 
     In another aspect of this design, the heat engine includes a heat exchanger which uses the heat exchange fins described herein for transferring heat between the exhaust gas and at least one of the air for combustion and the working fluid and, preferably, for transferring heat between the exhaust gas and both the air for combustion and the working fluid. To this end, the heat exchanger comprises a first heat exchanger mounted in a first passageway comprising at least one fin having first and second opposed sides and constructed to direct the working fluid as it flows through the first heat exchanger to enhance heat transfer between the working fluid and the first heat exchanger; and, a second heat exchanger mounted in a second passageway comprising at least one fin having first and second opposed sides and constructed to direct the working fluid as it flows through the second heat exchanger to enhance heat transfer between the working fluid and the second heat exchanger. Optionally, the heat exchanger comprises a third heat exchanger mounted in the exhaust gas passageway and comprises at least one fin having first and second opposed sides and constructed to direct the exhaust gas as it flows there through to enhance heat transfer between the exhaust gas and the third heat exchanger. 
     Referring to the embodiment of FIG. 3, heater cup  44  is a combustion chamber which is surrounded by a heat exchanger  67  comprising inner burner shield  68  having inner surface  74  and outer surface  76 , outer burner shield  70  having inner surface  78  and outer surface  80  and air preheat shield  72  having inner surface  82  and outer surface  84  (see, eg., FIGS.  1  and  3 ). Outer surface  84  of air preheat shield  72  is preferably at a temperature which may be comfortably handled by a user. It can be seen that when a flame is present, bottom  138  of burner cup  44  becomes hot and this heat is transferred to the working fluid. Wall  62  of the burner cup  44  is heated both by direct radiation from the flame and by contact with the hot exhaust gas  316  which comes from the flame. 
     Inner surface  74  is spaced from outer surface  32  of outer wall  12  to define a first pass  86  for the exhaust gases. As the exhaust gas travels through first pass  86  (a combustion gas passageway), the working fluid in flow path  64  is heated. Similarly, inner surface  78  of outer burner shield  70  is spaced from outer surface  76  of inner burner shield  68  so as to define a second pass  88  for the exhaust gases (a combustion gas passageway). Inner surface  82  of air preheat shield  72  is spaced from outer surface  80  of outer burner shield  70  so as to define a preheat air flow path  102  (a combustion air passageway). The lower portions of outer burner shield  70  and air preheat shield  72  define entry port  104  to preheat air flow path  102 . As the exhaust gas travels through second pass  88 , the air for combustion in preheat air flow path  102  is heated. Depending upon the temperature of the exhaust gas and the thermal efficiency which is desired, a fewer number of passes or a greater number of passes may be utilized. 
     Heater cup  44  defines a combustion chamber  92 . Inner burner shield  68  may be spaced from top  90  of heater cup  44  so as to define a manifold  94  through which the exhaust gases travel prior to entering first pass  86 . At the bottom of first pass  86 , an annular member  96  is positioned so as to force the exhaust gases to travel through second pass  88 , if a second pass is desired, prior to entering second manifold  98  where the exhaust gases are redirected through cylindrical exit ports  100 . Alternately, as shown in FIG. 1, outer burner shield  70  may have a transverse portion  97  to close the bottom of first pass  86 . 
     Inner burner shield  68 , outer burner shield  70  and air preheat shield  72  may be affixed together by any means Known in the art. In the preferred embodiment of FIG. 3, the three shields and annular member  96  are constructed so as to be press fitted together. To this end, inner surfaces  74 ,  78  and  82  are each provided with a plurality of discrete protrusions which are spaced apart around each of the inner surfaces. The protrusions abut against the outer surface which is positioned immediately inwardly thereof so as to provide a seating means for positioning each shield with respect to the next inner member. For example, inner surface  74  of inner burner shield  65  is provided with a plurality of protrusions  106  which engage, at discrete locations, outer surface  32  of outer wall  12 . The protrusions thereby allow inner burner shield  68  to be press fitted onto outer wall  12  and to remain seated at a spaced distance from outer surface  32  to define the fluid flow path. Similarly, annular member  96  may be installed by press fitting onto outer wall  12  prior to shields  68 ,  70  and  72  being installed. In the preferred embodiment of FIG. 1, a plurality of positioning members comprising one or more of spacer rings  164 ,  476 , louvred fins  428 ,  440 ,  468  and helical louvred fin  448  are provided in first and second passes  86  and  88  and preheat air flow path  102  to dimensionally stabilize shields  68 ,  70  and  72 . These positioning members may also be constructed to assist in the transfer of heat. 
     In the preferred embodiment, a fuel, preferably an organic fuel, is combusted in heater cup  44  so as to provide heat for the heat engine. As shown in FIG. 3, the fuel may be a gaseous fuel (eg. butane). However, it will be appreciated that liquid or solid fuel (eg. paraffin) may be used. However, the heat engine may use any heat source (eg. a non-combustion exothermic chemical reaction that is preferably reversible) and in such a case, heat exchanger  67  may not be required. 
     In an alternate embodiment, the heat engine may be run in reverse with chamber  160  which is positioned adjacent piston  50  operating at a higher temperature than chamber  140 . In such a case, heater cup  44  is replaced with a heat sink and a heat exchanger  67  may be provided to withdraw heat from chamber  140 . Such a heat exchanger would not require a preheat air flow path but is otherwise preferably of a similar design. 
     Fuel Reservoir 
     As shown in FIG. 7, a fuel reservoir  108  is provided. Fuel reservoir may be of any size which is sufficient to render flashlight  10  portable. For example, fuel reservoir  108  may comprise a storage tank having a volume from about 25 ml to 1 litre or more. One litre of fuel weighs about the equivalent of about 6 D cell batteries. Commercially available flashlights typically use up to 8 such batteries. The total weight of a portable long life flashlight may be from about 300 g (for a unit with about 25-50 ml of fuel and a life of about 100 hours) to about 2 kg (for a unit with about 1 litre of fuel and a life of about 2000 hours). Conduit  110  extends from reservoir  108  to annular burner  112 . Conduit  110  extends through shield  68 ,  78  and  72  and has openings  114  through which fresh air for combustion may be drawn, via preheat air flow path  102 , for mixing with the fuel prior to combustion in burner  112 . A valve  116  is provided in conduit  110  so as to selectively connect reservoir  108  and burner  112  in fluid flow communication when it is desired to power flashlight  10 . In an alternate embodiment, the heat engine may be connected to an external fuel source via conduit  110  and the fuel flow control valve may be provided as part of the external fuel source (eg. a regulator on a fuel tank). 
     Burner 
     Burner  112  may be of any type known in the art. Preferably, burner  112  has a top  118 , a bottom  120  and a circumferential sidewall having a plurality of recesses  124  provided therein through which the mixture of air and fuel may pass and be combusted (see FIGS.  3  and  7 ). Each recess  124  is defined by a pair of opposed radial walls  126  and an inner circumferential wall  128 . The air fuel mixture may be ignited by a piezo electric member positioned in housing  220  in which button  18  is mounted and an electric spark may be transmitted to a position adjacent burner  112  by means of wire  222  and spark plug  224 . Buttons to open fuel valves, and to hold them open, are known in the art and any such device may be incorporated into this design. 
     In operation, when button  18  is depressed into housing  220 , drive rod  228  (which is affixed to button  18  by eg. screw  229 ) causes connecting rod  226  (which is pivotally mounted to drive rod  228  by pivot  230 ) to move laterally transmitting this lateral force to valve  116  via drive rod  232  (which is pivotally connected to connecting rod  226  by pivot  234  and to valve  116  by pivot  238 ) causing valve  116  to pivot about pivot  236  to the open position. This allows pressurized fuel to pass through conduit  110  drawing air for combustion through openings  114  into conduit  110 . The mixed fuel and air passes through burner  112  where it is ignited by any means known in the art such as spark plug  224 . The combustion of the fuel produces heated exhaust gases which pass through heater cup  44 . In the embodiment of FIG. 3, the exhaust gases exit flashlight  10  by means of first manifold  94 , first pass  86 , second pass  88 , second manifold  98  and exit port  100 . Button  18  may be locked in this “on position” by a locking means in housing  220 . Alternately, the fuel valve may be controlled by a thermomechanical member, an electrothermomechanical member or electric control. 
     Displacer Control 
     According to another aspect of the instant invention, the upstroke and downstroke of the displacer are different. Preferably, the heat engine includes means for operating displacer  46  and piston  50  to provide the working fluid with greater residence time in cooling chamber  160  than in heating chamber  140 . This may be accomplished by controlling displacer  46  so that upstroke and the downstroke portions of the displacer cycle vary, eg., by varying the rate of movement of displacer  46  during the upstroke as compared to the downstroke or by pausing displacer  46  during its cycle to provide the additional residence time in cooling chamber  160 . Such movement of displacer  46  provides improved thermodynamically efficient heat transfer to and from the working fluid. By allowing an additional 40%, preferably 30% and more preferably 20% of time for the air in the cold region, improved thermodynamic efficiency can be achieved. Exemplary means for operating the displacer include the use of a solenoid or a magnetic drive system. This may be achieved by attenuating the pulse width and phase delay of the signal sent to the driver by means of a phase delay circuit  326  (see, eg. FIG.  10 ). 
     For example, referring to FIGS. 24 a  and  b,  the displacement of displacer  46  and piston  50  from the central positions of their cycle is plotted against time. In FIG. 24 a,  the phase angle between displacer  46  and piston  50  is 180° and the rate of expansion and the rate of compression by each of displacer  46  and piston  50  are the same. Traditionally in heat engines, the movement of the displacer  46  and piston  50  are physically linked together by a mechanical coupling and can not be varied. According to one aspect of the instant invention, the phase angle between displacer  46  and piston  50  may be varied. In addition, the rate of expansion and the rate of compression of one, and preferably both, of displacer  46  and piston  50  may be varied. The compression and expansion of the working fluid, and the phase angle between displacer  46  and piston  50 , may be varied to optimize the cooling capacity of a heat engine under different thermal loads and different thermal conditions. By way of example, in FIG. 24 b,  the phase angle between displacer  46  and piston  50  is 180° but the rate of expansion and the rate of compression by piston  50  are different. In this example, rapid compression is followed by a slower rate of compression then by a rapid rate of expansion followed by a slower rate of expansion. The expansion and compression rates are independent and are each individually adjusted to maximize heat transfer between the working fluid and the heat engine. The actual cycle profile will vary for different configurations of the heat engine. An advantage of the instant invention is that the electronic control of piston  50  permits the cycle profile to be easily adjusted to meet different configurations of the heat engine as well as different uses of the heat engine (eg. electricity production, refrigeration, cryocooling). In this way, the compression and expansion of the working fluid may be controlled to be conducted at thermodynamically optimum rates and the heat engine may be used not only to generate work using a heat source but to generate cooling using work input to a linear generator operating as a piston. 
     Referring to FIGS. 2 a - 2   d,  the heat engine has a first portion  240  in which displacer  46  is movably mounted and a second portion  242  in which power piston  50  is movably mounted. The portion within which displacer  46  is movable is the hot end of the heat engine and the portion within which the power piston is movable is the cool end of the heat engine. Driver  48  has an internal circumferential wall  130  defining an opening  132  into which displacer rod  134  is received. Displacer  46  is mounted for movement within inner wall  30  between the alpha position shown in FIG. 2 b  wherein displacer  46  is withdrawn from heater cup  44  and the omega position as shown in FIG. 2 a  in which displacer  46  is distal to driver  48  and advanced towards heater cup  44 . As shown in FIGS. 2 a  and  2   c,  when displacer  46  is positioned in the omega position, there is a chamber  244  between displacer  46  and driver  48 . In this position, displacer rod  134  is substantially removed from opening  132 . As shown in FIGS. 2 b  and  2   d,  when displacer  46  is in the alpha position, effectively all of displacer rod  134  is received in opening  132  leaving heating chamber  140  (defined by top  136  of displacer  46 , bottom  138  of heater cup  44  and inner surface  38  of inner wall  30 ) between displacer  46  and heater cup  44 . 
     Heating chamber  140  is heated by the combustion occurring in heater cup  44 . As displacer  46  moves upwardly to the position shown in FIG. 2 a,  the heated working fluid in heating chamber  140  is forced upwardly through fluid flow path  64  where it is heated by the heated heater cup  44 , and through opening  66  into fluid flow path  40  (a portion of the working fluid passageway) where it is heated by the exhaust gasses, thus increasing the pressure of the working gas. When displacer  46  is in the distal position shown in FIGS. 2 a  and  2   c,  effectively all of the working fluid has been forced out of heating chamber  140 . To this end, it is preferred that bottom  138  of heater cup  44  and top  136  of displacer  46  are constructed so as to intimately fit adjacent each other so as to force as much of the working fluid out of the heating chamber  140  as possible. Preferably, as shown in FIG. 2 a,  bottom  138  is curved so as to transfer heat to the working fluid. Alternately, as shown in FIG. 3, bottom  138  may be flat and, accordingly, top  136  of displacer  46  may also be flat. 
     Inner circumferential wall  130  of driver  48  provides a guide for displacer rod  134  so as to maintain the longitudinal alignment of displacer  46  along axis A as displacer  46  moves between the alpha and omega positions. Displacer rod  134  and inner circumferential wall  130  may be dimensioned and constructed so as to allow relatively frictionless movement of displacer rod  134  into and out of opening  132 . In order to further assist in the reduction of frictional forces, bottom  146  of displacer  46  may have a recessed circumferential wall  148 . A teflon bushing  150  or the like may be mounted around recessed circumferential wall  148  for engagement with inner surface  38  of inner wall  30  as displacer  46  moves. Further, a second teflon bushing or the like  152  may be provided on inner circumferential wall  130 . 
     Driver  48  may be any means known in the art which is drivingly connected to displacer  46  to cause displacer  46  to move in a cycle that is complementary to the cycle of power piston  50  so as to optimize the thermal efficiency of the heat engine. This may be achieved by moving displacer  46  in response to an external stimulus such as an electrical impulse caused by the movement of power piston  50 . Preferably, driver  48  is a solenoid or an electromagnet and, more preferably, an electromagnet. If driver  48  is a solenoid, current may be provided to the solenoid by means of wire  154  (see FIG. 2 e ). Accordingly, when current is supplied to the solenoid, displacer  46  will move due the current (i.e. the external force) supplied thereto. If driver  48  is an electromagnet, then, displacer  46  and/or displacer rod  134  includes a permanent magnet for moving displacer  46  due to a magnetic field produced by the electromagnet. Accordingly, when current is supplied to the coils of the electromagnet, the coils may be charged in a reverse polarity to the portion of displacer rod  134  in opening  132  thus forcing displacer rod  134  outwardly from opening  132  thus driving the working fluid from heating chamber  140 . When the current is reversed in the coils, displacer rod  134  is attracted to driver  48  and accordingly displacer rod  134  is pulled downwardly into opening  132  (thus drawing the working fluid into heating chamber  140 ). 
     In a preferred embodiment, displacer  46  is biased, preferably to the alpha position shown in FIG. 2 b.  This may be achieved, for example, by means of spring  156  as shown in FIGS. 2 c  and  3 . In such a case, driver  48  may act only to move displacer  46  to the omega position (i.e. towards heater cup  44 ) thus pushing heated working fluid to cooling chamber  160 . When the working fluid is cooled to a sufficient degree, the current to driver  48  may be switched off allowing the biasing means (eg. spring  156 ) to move the displacer to the alpha position thus drawing the working fluid into heating chamber  140 . When the working fluid is heated, the current to driver  48  may be switched on thus moving displacer  46  against spring  156  to the omega position. In one embodiment, driver  48  may be powered at all times once the heat engine is running. 
     It will be appreciated that driver  48  need not completely extend to inner wall  38  of inner wall  30 . For example, driver  48  may have a smaller diameter than inner wall  30  and be mounted thereto by, eg., brackets. If the outer wall of driver  48  contacts inner wall  38  as shown in FIGS. 2 a - 2   e,  then chamber  244  is preferably in fluid flow communication with cooling chamber  160 , such as by passage  260 , to prevent a reduced pressure region from forming in chamber  244 . Thus, when displacer  46  moves to the extended position shown in FIG. 2 a,  cooled working fluid in cooling chamber  160  may travel through passage  260  into chamber  244  to maintain an equilibrium pressure between chambers  244  and  160 . Further, when displacer  46  moves to the retracted position as shown in FIG. 2 b,  cooled fluid is pushed from chamber  244  by displacer  46  into cooling chamber  160  via passage  260  and then to heating chamber  140 . 
     Inner wall  30  is provided with a passageway, eg. a plurality of openings  158  adjacent the top of cooling zone  26 . Openings  158  define an entry port for the working fluid to enter second portion  242  of the heat engine after passing through air flow path  40 . As shown in FIG. 5, the lower portion of driver  48  may have a chamfered surface  168 . The chamfered surface assists in directing the working fluid into and out of cooling chamber  160 . Power piston  50  is not physically connected to displacer  46  but is moved due to the change of pressure in cooling chamber  160 . Accordingly, when displacer rod  134  moves displacer  46  to the withdrawn position shown in FIGS. 2 a  and  2   c,  working fluid is forced through flow path  40 , through opening  158  into cooling chamber  160 . The action of the working fluid on top  162  of piston  50  forces piston  50  downwardly into open area  246 . As the working fluid cools in cooling chamber  160 , the pressure of the working fluid decreases thus drawing piston  50  upwardly and reducing the volume of the working zone of the heat engine (i.e. chambers  140 ,  160 ,  244  and fluid flow paths  64  and  40 ). When displacer  46  moves away from heater cup  44  to the position shown in FIGS. 2 b  and  2   d,  eg. in response to driver  48  or the spring, the working fluid is drawn from cooling chamber  160  through openings  158  through flow path  40  through openings  66 , through flow path  64  into heating chamber  140 . 
     In the alternate embodiment of FIGS. 9-11,  19  and  20 , driver  48  comprises a magnetic field that is imposed on displacer  46 . As exemplified in these Figures, displacer  46  has a magnet  286  affixed to it, preferably on bottom  146 . Displacer magnet  286  and displacer  46  affixed thereto are held concentrically in place and their range of motion limited by two magnets  284  and  288  which are preferably circular and which repel the displacer magnet  286 . Thus displacer  46  sits on a magnetic bearing caused by the mutual repulsion of magnet  288  to displacer magnet  286  and the mutual repulsion of magnet  284  to displacer magnet  286 . The repulsive magnetic field between magnets  286  and  288  serves to store kinetic energy from the upstroke of displacer  46  and limits the travel of displacer  46 . The stored kinetic energy from the upstroke of displacer  46  is returned to displacer  46  on the downstroke. 
     Linear Generator 
     In another aspect of the design, the apparatus includes a linear generator. Preferably, piston  50  comprises part of the linear generator. The linear generator in electrical generation zone  28  may be of any construction known in the art. The following description is of the preferred embodiment of the linear generator which is shown in FIGS. 2 a,    2   b,    2   c,    2   d  and  4 . In these embodiments, the linear generator is positioned in a sealed chamber. In the embodiment of FIGS. 2 a  and  2   b,  the upper end of the linear generator is isolated from the working fluid by piston  50  and the lower end is sealed by closure member  195 . In the embodiments of FIGS. 2 c,    2   d  and  4 , the upper end of the linear generator is isolated from the working fluid by top  162  and the lower end is sealed by closure member  195 . As shown in FIGS. 2 a  and  2   b,  piston  50  is a sealed member having a top  162 , a bottom  170  and sidewalls  172 . Drive rod  174  may accordingly be affixed to bottom  170  by any means known in the art. In the embodiment of FIGS. 2 c,    2   d  and  4 , piston  50  comprises top  162  and sidewalls  172 . In this embodiment, drive rod  174  is affixed to inner surface  176  of top  162 , by any means known in the art, such as by threaded engagement therewith. As shown in FIG. 4, inner surface  176  may be provided with a splined shaft  178  which is received in a mating recess in drive rod  174 . 
     A plurality of magnets  52  are fixedly attached to drive rod  174  by any means known in the art, such as by use of an adhesive or by mechanical means (eg. the interior opening through which drive rod passes in magnet  152  may be sized to produce a locking fit with drive rod  174  or drive rod  174  may be threaded and magnet  152  may be positioned between spacers that are threadedly received on drive rod  174 ). A mating number of coils  56  of electrically conductive wire are provided at discrete locations along the length of electrical generation zone  28 . Coils  56  are affixed to inner wall  34  of outer wall  12  by any means known in the art, such as by means of an adhesive or by mechanical means (eg. coils  56  may be provided in a housing which is affixed to inner wall  34  by welding or by brackets). Thus coils  56  are stationary as drive rod with magnets  52  affixed thereto is moved by power piston  50 . It will be appreciated that coils  56  may be affixed in a stationary manner by any other means known in the art. In an alternate embodiment, coils  56  may be affixed to drive rod  174  and magnets  52  may be stationary. 
     An annular ferrite bead  54  is positioned centrally within each set of coils  56 . Each ferrite bead  54  has a central opening through which drive rod  174  passes. One of the coils  56  has wires  180  extending outwardly therefrom. The remainder of the coils  56  have wires  182  extending outwardly therefrom (see FIG.  7 ). It will be appreciated by those skilled in the art that only one ferrite bead  54  and one coil  156  may be provided. It will further be appreciated that the output wires from any of the coils  56  may be grouped together in parallel or series as may be desired. 
     As power piston  50  moves into area  246  away from driver  48  in response to working fluid impinging upon top  162 , magnets  52  move longitudinally along axis A so as to cause current to flow in coils  56  (see FIG. 2 b ). When piston  50  moves upwardly due to the cooling of the working fluid in cooling chamber  160 , magnets  52  are then driven in the reverse direction causing current to again flow in coils  56 . 
     In the preferred embodiment, each magnet  152  moves between a pair of ferrites  54  In particular, referring to FIG. 4, magnet  52   a  is movably mounted in the linear generator between ferrite  54   a  and ferrite  54   b.  As drive rod  174  moves with piston  50 , magnet  52   a  moves from a position adjacent ferrite  54   a  as shown in FIG. 4 to a position adjacent ferrite  54   b.  Similarly, magnet  52   b  moves from a position adjacent ferrite  54   b  to a position adjacent ferrite  54   c.  In this way, it will be seen that at the end of each strode of piston  50 , ferrite  54   b  is acted upon at any one time by only one magnet  152 . Similarly, magnet  52   a  will first act upon ferrite  54   a  and then upon ferrite  54   b.  In this way, ferrite  54   b  is sequentially exposed to, eg., a north field from magnet  52   a  and then a south field from magnet  52   b.    
     One advantage of the instant design is that there is a higher rate of change of flux per unit time due to ferrites  54  first being acted upon by one field and then the opposed field. Further, since ferrite  54  is acted upon by opposed poles of different magnets, the magnetic field induced on ferrite  54   b  by magnet  52   a  will completely collapse as magnet  52   a  moves to the position shown in FIG.  4  and ferrite  54   b  is acted upon by magnet  52   b.    
     An alternate construction of a linear generator is shown in FIGS. 9-11,  19  and  20 . In these embodiments, the magnets are positioned within inner wall  30  and the coils are positioned exterior thereto (eg. on outer surface  36  of inner wall  30  or on outer surface  32  of outer wall  12 ). Power piston  50  consists of a plurality of spaced apart magnets, eg. four magnets  270 ,  272 ,  274  and  276  and three non-magnetic spacers  278 ,  280  and  282 . The non-magnetic spacers may be made of plastic which surrounds and encases the magnets. It will be appreciated that the assembly of magnets and spacers may be connected to the power piston of FIGS. 2 a  or  2   c  by a drive rod  174 . Preferably, the assembly comprises piston  50 . 
     Power piston  50  of FIGS. 9-11,  19  and  20  is held concentrically in place and its range of motion limited by two magnets  284  and  190  which are preferably circular permanent magnets and which repel magnets  270  and  276  respectively. Thus the power piston  50  sits on a magnetic bearing caused by the mutual repulsion of magnets  284  and  270 , and magnets  190  and  276 . The repulsive magnetic field between magnets  276  and  190  serves to store kinetic energy from the downstroke of the power piston  50  and will return this energy to the power piston  50  on the upstroke of power piston  50 . Thus the magnets  276  and  190  act as a magnetic spring at the bottom of the stroke, and, similarly, magnets  284  and  270  form a repulsive magnetic field at the top of the power piston stroke which also acts as a magnetic spring. 
     Heat Engine Cycle 
     The following is a description of the operation of the heat engine based on the embodiment of FIGS. 9-11 wherein fin means are provided in various fluid flow passageways to assist in heat transfer. Heating chamber  140 , cooling chamber  160  and passageways  64 ,  312  and  40  are a sealed region within which the working fluid circulates. This heat engine cycle begins with displacer  46  positioned towards the cold end of the engine, that is, in the alpha position. This causes most of the working fluid to be forced into heating chamber  140 . Wall  62  of burner cup  44  heats the inner heat exchanger  310  which in turn heats the working fluid in passage  64 . The hot exhaust gas  316  then passes through manifold  94  and then through the exhaust outer heat exchanger  314  (to which the hot exhaust gas imparts most of its heat energy) and exit as cooled exhaust gas  332 . The heat energy from the exhaust outer heat exchanger  314  is then transferred through the heat engine outer wall  12  and into the exhaust inner heat exchanger  312  which in turn imparts this heat into the working fluid. 
     The heating of the working fluid causes the working fluid to expand. The expansion takes place through heat exchangers  310  and  312 , through the regenerator  42 , through openings  158  and into cooling chamber  160  where pressure begins to build against power piston  50 . This causes power piston  50  to move downwards towards magnet  190  and causes the magnets  270 ,  272 ,  274  and  276  to induce voltages and current in the generator coils  318 ,  320 ,  322  and  324  respectively. 
     The electrical energy from one or more of the coils, eg. generator coil  318 , provides power via wires  180  to the phase delay circuit  326  which modifies the power signal from the generator coil  318  and then feeds it through wires  154  to the displacer control coil  328 . Circuit  326  may comprise, eg., either of a variable capacitor and a fixed inductor or of a variable inductor and a fixed capacitor. Phase delay circuit  326  may be any circuit that will drive displacer  46  to move in a cycle that is out of phase to the cycle of power piston  50 . Circuit  326  modifies the power signal from the generator coil  318  and then feeds it through wire  154  to displacer control coil  328 . This signal, sent to the displacer control coil  328 , causes an upward force on the magnet  286  which in turn causes magnet  286  and displacer  46  affixed thereto to move upwards towards magnet  288 . 
     The upstroke of displacer  46  causes the working fluid to flow through the heat exchangers  312  and  310 , through the regenerator  42 , through the openings  158  and into the cold end of the engine  160 . As the working fluid passes through the regenerator  42 , most of the heat of the working fluid is transferred to the regenerator  42 . The remaining heat from the working fluid now located in the cold end  160  of the engine is dissipated by heat exchanger  330 . Heat from the working fluid now located in cooling chamber  160  is dissipated by heat exchanger  330  which preferably comprises a plurality of cooling fins  331  which may be louvred fins  428 ,  440 ,  468  or helical louvred fin  448 . This causes the working fluid to contract and reduces the pressure within the engine. This causes power piston  50  to move upwards under the influence of the magnetic energy stored between magnets  276  and  190 . 
     The upward motion of power piston  50  causes magnet  270  to induce a reverse current pulse in the generator coil  318 . This reverse current pulse from generator coil  318  provides power to the phase delay circuit  326  which modifies the power signal from the generator coil  318  and then feeds it through wires  154  to the displacer control coil  328 . This signal sent to the displacer control coil  328  causes a downward force on displacer magnet  286  which in turn causes displacer magnet  286  and displacer  46  affixed thereto to move downwards towards magnet  284 . The repulsive magnetic field between displacer magnet  286  and magnet  288  serves to impart the stored kinetic energy from the upstroke of the displacer  46  to the downstroke. The repulsive magnetic field between displacer magnet  286  and magnet  284  serves to store kinetic energy from the downstroke of displacer  46  for the next upstroke. The repulsion of displacer magnet  286  and magnet  284  also serves to limit the travel of displacer  46 . 
     In an alternate embodiment, phase delay circuit  326  may be replaced by a controller that senses when the voltage from the generator coil  318  is approaching zero which is the bottom of the stroke of the power piston  50 . At this point, the controller may cut the signal to the displacer control coil  328  and begin a reverse (negative) pulse which causes the displacer  46  to move downwards towards magnet  284 . Alternately, the controller may cut the signal and allow displacer  46  to move downwardly under tile influence of a biasing member, eg. a spring or the magnetic fields to which it is exposed. 
     If displacer is to be directly driven by piston  50  (eg. without any phase angle modification) electrical energy from generator coil  318  may provide power via wires  180  to displacer control coil  328 . 
     The downward movement of the displacer  46  causes the working fluid to be forced from the cold end of the engine  160  through openings  158 , through regenerator  42  through the heat exchangers  312  and  310 , and into the hot end of the engine near bottom  138  of burner cup  44 . As the working fluid passes through regenerator  42 , most of the heat stored in regenerator  42  is transferred into the working fluid. The cycle then repeats itself. 
     Self Starting 
     Piston  50  is preferably biased to the alpha position shown in FIGS. 2 b,    2   c  and  4  such as by means of a spring  184  (see FIG. 2 b ) or by a magnetic bushing (eg.  186 ,  190 ) as shown in FIGS. 2 c  and  4 . In particular, as shown in FIG. 4, a magnet  186  is attached to distal end  188  of drive rod  174  from piston  50 . Distal end  188  travels through a central opening in closure member  195  which may be installed in outer wall  12  by a press fit. A second magnet  190  is affixed to inner surface  192  of closure member  194 . To prevent the magnets from touching each other, an elastomeric member  196  may be affixed to the distal end of magnet  190  from inner surface  192 . End  198  of magnet  186  is of an opposite polarity to end  200  of magnet  190 . Accordingly, magnets  190  and  186  will repel piston  50  to the alpha position shown in FIG.  4 . Piston  50  moves between the alpha position and the omega position (shown in FIG. 2 d ) due to the influence of the working fluid on top  162  of piston  50 . 
     By biasing displacer  46  and piston  50  to the alpha positions, the heat engine may be self starting. In particular, when heat is applied to heating chamber  92  (eg. combustion is initiated in heater cup  44 ), the working fluid in heating chamber  140  will commence expanding. The expansion of the working fluid will cause some of the working fluid to pass out of heating chamber  140  into cooling chamber  160 . The entrance of the working fluid into cooling chamber  160  will cause piston  50  to move downwardly. Provided piston  50  moves downwardly by a sufficient amount and/or at a sufficient rate, an electrical current will be generated which may be transmitted by wires  180  to driver  48 . The signal will cause driver  48  to move displacer  46  towards the omega position thus initiating a first stroke of displacer  46  and evacuating additional heated working fluid from heating chamber  140  into cooling chamber  160  thus further driving piston  50  downwardly to generate further amounts of current. 
     The working fluid is isolated in the heat engine. To this end, the opposed ends of inner wall  30  are sealed and fluid flow path  40  is also sealed. Heater cup  44  is preferably used to seal the end of inner wall  30  adjacent heating chamber  140 . Piston  50  is preferably used to seal the end of inner wall  30  adjacent cooling chamber  160  such as by creating a seal with inner surface  38  of inner wall  30  thus isolating the linear generator from the working fluid. 
     It will be appreciated that the linear generator need not be sealed. For example, air may be able to pass through the central opening in closure member  195  as well as past coils  56  so as to prevent significant pressure build up in the linear generator as magnets  52  move. 
     Closure members  194  and  195  assist in the construction of flashlight  10  as well as to protect coils  56  from the incursion of foreign material which would damage the linear generator. Closure members  194  and  195  may be affixed to the bottom of the one of the cylinders by any means known in the art. For example, referring to FIG. 2 a,  closure member  195  is integrally formed as part of outer wall  30  whereas, for example, closure member  194  is welded to the distal end of outer wall  12  from heater cup  44 . In the embodiment shown in FIG. 4, closure member  194  has an annular flange  202  which is threadedly received on outer surface  32  of outer wall  12 . However, if the inner container, or the outer container, are prepared by high speed die stamping, then closure members may be integrally formed as part of the inner/outer container. 
     Referring to FIG. 8, wires  180  from the first set of coils  56  are electrically connected to wires  154  of driver  48 . Wires  180  pass through controller  206  (which is preferably phase delay circuit  326 ). Wires  180  and  154  as well as controller  206  (which may be a phase delay circuit) may be positioned between inner and outer walls  30  and  12  (i.e. in gaps  166  and fluid flow path  40 ). 
     Thermomechanical Control 
     A cross sectional view of a preferred embodiment of a heat exchanger utilizing thermomechanical control is shown in FIGS. 9-11. 
     To start the engine, the start switch  18  is engaged. The start switch  18  is operatively linked to the fuel switch lever  290  by means of linking member  291  which is preferably mechanical. Fuel switch lever  290  is activated such that the fuel flow control valve  292  and the variable flow fuel control valve  294  are both momentarily opened. Preferably fuel switch lever  290  is a mechanical switch drivenly moveable by linking member  291  between two positions and which is mechanically linked to fuel flow control valve  292  and the variable flow fuel control valve  294 . When the lever switch  290  is released, the variable flow fuel control valve  294  closes and the fuel flow control valve  292  remains open. This ensures starting fuel reserve  296  is full and fuel from the starting fuel reserve  296  begins to flow. The fuel in the starting fuel reserve is sufficient for a short period of operation (eg. 1-2 minutes). In the event that the burner  298  fails to ignite, then the amount of fuel which may accidentally escape into the environment is limited to the small harmless amount in the starting fuel reserve  296 . Hence the starting fuel reserve  296  and its associated mechanisms acts as a safety device to prevent the spillage or release of large quantities of fuel. 
     When start switch  18  is depressed, piezo crystal high voltage power supply  300  produces high voltage which flows along conductor  302  to the electrode  304  where a spark is created which ignites the fuel in the burner  298  and causes a flame to form. Optionally, the fuel switch lever  290  and the start switch  18  need not be linked together but may be sequentially operated by the user. 
     The flame immediately begins to heat burner cup  44  as well as heating fuel flow control member  308  which, on heating, begins to open the variable flow fuel control valve  294 . Fuel flow control member  308  may be any member that will reconfigure itself on heating so as to adjust the position of variable flow fuel control valve  294 . Examples of such members include members that deform on heating (eg. a bimetal strip), significantly contract or elongate with temperature changes (eg. muscle wire) or significantly alter their spring constant with temperature changes thereby exerting variable force based on temperature (eg. homeostat type devices). 
     Fuel flow control member  308  is configured such that as the temperature in combustion chamber  92  reaches the optimum operating temperature, the variable flow fuel control valve  294  will be fully open so that the heat engine will provide full power. If full power is not required, the burner cup will begin to overheat because the available thermodynamic energy is not being converted to mechanical or electrical energy. The overheating will cause the variable flow fuel control valve  294  to begin to close over its central maximum flow point thereby reducing the fuel flow and thereby reducing the temperature to the optimal range. Thus a self regulating system is established wherein the amount of fuel delivered by the variable flow fuel control valve  294  is controlled by the temperature of combustion chamber  92  which always remains within its optimum operating range as controlled by the bimetal fuel flow control member  308 . 
     Thermoelectromechanical Control 
     A cross sectional view of the preferred embodiment of this invention is shown in FIG.  19 . 
     To start the engine, the start switch  18  is preferably engaged as with the embodiment of FIGS. 9-11 to commence ignition and the heating of heater cup  44 . When the power piston  50  begins to move and the generator coils  318 ,  320 ,  322  and  324  begin to generate power, electricity flows through wires  334 ,  336  and  338  which are electrically connected to low resistance resistor  342  via wire  340 . Electricity flows from low resistance resistor  342  to internal load resistor  344  via wire  346  and to external load  348  via wire  350 . 
     Electricity from the generator coils  320 ,  322  and  324  also flows through wires  352 ,  354  and  356 , through wire  358 , through the low resistance resistor  360 , through wires  362  and  364  to the internal load resistor  344  and to the external load  348 . The internal load resistor  344  ensures that a small amount of current is always being withdrawn from the generator. This ensures that a small amount of current is always flowing through the low resistance resistor  360  which supplies heat to fuel flow control member  308  which opens the variable flow fuel control valve  294  by means of lever  366 . The current drawn by the internal load resistor causes the low resistance resistor  360  to heat slightly which causes the fuel flow control member  308  to be reconfigured (eg. to bend or contract or deform) thereby opening the variable flow fuel control valve  294  enough to maintain the fuel flow required for standby operation. 
     When the current drawn by the external load  348  increases, the amount of heat created by the low resistance resistor  360  increases which causes the fuel flow control member  308  to be further configured (eg. to bend further) thereby opening the variable flow fuel control valve  294  further so as to provide enough fuel to provide the thermal energy required to generate the power drawn by the load. Thus a fuel control system which proportions the fuel flow to the load has been developed. 
     Upon ignition, the flame immediately begins to heat the burner cup  44 . As the temperature of burner cup  44  becomes sufficient to cause the cyclic operation of the heat engine, the electrical current produced by generator coils  318 ,  320 ,  322  and  324  begins to flow. As the current begins to flow through low resistance resistor  360 , through interal load resistor  344  via wire  346 , low resistance resistor  360  begins to heat and supplies heat to fuel flow control member  308  which begins to open the variable flow fuel control valve  294  by means of lever  366 . As the temperature of low resistance resistor  360  reaches its optimum operating temperature, the variable flow fuel control valve  294  will be open fully for full power. If full power is not required, the low resistance resistor  360  will become cooler thereby causing the variable flow fuel control valve  294  to begin to close thereby reducing the fuel flow. Conversely, if the load  348  draws more power, variable fuel flow control valve  294  will again be opened due to the increased heat of low resistance resistor  360  being supplied to the fuel flow control member  308  which in turn opens variable fuel flow control valve  294 . Thus a self regulating system is established wherein the amount of fuel delivered by the variable flow fuel control valve  294  is controlled by the temperature of low resistance resistor  360  whose temperature is proportional to the power required by load  348 . Alternately, if the system does not include internal load resistor  344 , and if the external load  348  requires no power, then the mechanism associated with low resistance resistor  360  will cause variable fuel flow control valve  294  to shut off the fuel supply and cause the engine to stop once fuel reservoir  296  is exhausted. 
     The internal load resistor  344  ensures that a small amount of current is always being withdrawn from the generator. This ensures that a small amount of current is always flowing through the low resistance resistor  360  which supplies heat to the heat reconfigurable member  368  which operates the variable inductor  370 . Heat reconfigurable member  368  may be any member that will reconfigure itself on heating (eg. a bimetal strip, muscle wire or homeostat type devices). The current drawn by internal load resistor  344  causes the low resistance resistor  360  to heat slightly which causes the heat reconfigurable member  368  to bend thereby operating the variable inductor  370  so as to maintain an optimal phase angle between the displacer  46  and the power piston  50 . When the current drawn by the external load  348  increases, the amount of heat created by the low resistance resistor  360  increases which causes the heat reconfigurable member  368  to deform further thereby further changing the setting of the variable inductor  370  thereby again changing the phase angle relationship between the displacer  46  and the power piston  50 . It has been found that a given engine with a given displacer and power piston phase angle relationship has an energy efficiency curve which varies for different power levels or different burner/ambient temperatures. Similarly, it has been found that by varying the phase angle relationship between the displacer and the power piston, an efficient operating point can be established for any power and/or burner/ambient temperatures. Thus a simple displaceripower piston phase control system has been developed which modifies the phase angle under varying load conditions to maintain the efficiency of the system. 
     In an alternate embodiment, solid state electronics may be used to control a transistor which drives resistor  360  and fuel flow control member  308  of the variable fuel flow valve  294  and the variable inductor  370 . 
     Electric Modulation Control 
     A cross sectional view of the preferred embodiment of this invention is shown in FIG.  20 . 
     When the start switch  18  is depressed, a signal is sent from the primary controller  372  to the fuel flow controller  374  by means of wire bundle  376 . The signal to the fuel flow controller  374  causes the fuel flow controller  374  to energize a valve, eg. spring loaded normally closed solenoid fuel valve  382 , to open by means of wire pair  384 . The opening of the spring loaded normally closed solenoid fuel valve  382  allows fuel to flow from the small staring fuel reservoir  296  along passage  110  and along to the burner  298 . 
     The primary controller  372  also supplies power to the high voltage power supply  378  by means of the wire pair  380  which causes high voltage to be generated which then passes along wire  302  to the high voltage electrode  304  where sparks are created which causes the vaporized fuel in the burner  298  to be ignited. The resulting flame immediately begins to heat the bottom of the burner cup  44 . 
     The hot exhaust gases and radiation from the flame heats the temperature sensing means  386  (eg. a thermocouple) which is connected to the fuel flow controller  374  by means of the wire pair  388 . In response to the fuel flow controller  374  interpreting a high temperature present, the fuel flow controller  374  energizes another valve, eg. spring loaded normally closed solenoid fuel valve  390 , by means of wire pair  392 . The fuel flow controller  374  also sends a signal to the primary controller  372  by means of wire bundle  376  which in turn causes the primary controller  372  to de-energize the high voltage power supply and stop the sparking at electrode  304 . The temperature in burner cup  44  is constantly measured by the temperature measuring means  386  and monitored by the fuel flow controller  374  by means of the connection through wire pair  388 . If at any point the temperature drops below a preset temperature of for example 400° F., the fuel flow controller  374  sends a signal to the primary controller  372  by means of wire bundle  376 . If the primary controller  372  registers the fact that the fuel flow is on and the temperature has fallen below the preset temperature of for example 400° F., the primary controller  372  will re-energize the high voltage power supply  378  causing high voltage to flow along wire  302  to electrode  304  where sparks will again be created in order to relight the fuel in the burner  298  and to re-establish the flame. The heat from the flame will again heat the temperature measuring means  386  which is monitored by the fuel flow controller  374  through wire pair  388 . 
     Once the preset temperature of for example 400° F. is reached, the fuel flow controller  374  will send a signal to the primary controller  372  by means of the wire bundle  376  which will in turn cause the primary controller  372  to de-energize the high voltage power supply and stop the sparking at electrode  304 . If the temperature is not re-established within a preset amount of time, the fuel flow controller  374  preferably de-energizes spring loaded normally closed solenoid valves  382  and  390  by de-energizing wires  384  and  392  respectively. Thus, a safety means for ensuring that the burner is lit is incorporated in the design. 
     The electrical energy from one or more coils, eg. generator coil  318 , provides power to the rechargeable battery  394  by means of the wire pair  180 . The battery  394  in turn provides power to the primary controller  372  to which it is attached. The primary controller  372  senses the input to the battery from the generator coil  318  which causes the primary controller  372  to send a signal to the displacer control coil  328  by means of wire  154 . This positively polarized signal sent to the displacer control coil  328  causes an upward force on the magnet  286  which in turn causes the magnet  286  and the displacer  46  affixed thereto to move upwards towards magnet  288 . 
     In addition to the basic cycle, the new heat engine optionally incorporates means to modulate the fuel burn and optimize energy efficiency. There are a plurality, eg. four, solenoid fuel valves  390 ,  396 ,  398  and  400  which are connected to the fuel flow controller  374  by means of wire pairs  392 ,  402 ,  404 , and  406  respectively. The primary controller  372  senses the current flowing to the load  408  through wire pairs  410 ,  412 , and  414  by means of the hall effect current sensor  416  which is connected to the primary controller  372  by means of wire pair  418 . The power from the generator coils flows out to the load  408  (eg. an outlet or an electric apparatus) by means of wires  420  and  422 . When the primary controller  372  determines that the current flowing to the load is, eg., between 0 to 25 percent of the maximum output power of the heat engine and generator, it ensures that only solenoid fuel valve  390  is energized by sending a signal along two of the eight wires in the wire bundle  376  which connects the primary controller  372  to the fuel flow controller  374 . The fuel flow controller  374  in turn energizes only the spring loaded normally closed solenoid valves  382  and  390 . 
     When the primary controller  372  determines that the current flowing to the load is, eg., between 26 to 50 percent of the maximum output power of the heat engine and generator, it sends a signal to the primary fuel controller  374  along two of the wires in the wire bundle  376 . This signal causes the primary fuel controller  374  to energize an additional spring loaded normally closed solenoid fuel valve  396  by means of the wire pair  402  which causes the spring loaded normally closed solenoid fuel valve  396  to open thereby increasing the fuel flow to the burner  298 . 
     When the primary controller  372  determines that the current flowing to the load is, eg., between 51 to 75 percent of the maximum output power of the heat engine and generator, it sends a signal to the primary fuel controller  374  along two of the wires in the wire bundle  376 . This signal causes the primary fuel controller  374  to energize yet another spring loaded normally closed solenoid fuel valve  398  by means of the wire pair  404  which causes the spring loaded normally closed solenoid fuel valve  398  to open thereby further increasing the fuel flow to the burner  298 . 
     When the primary controller  372  determines that the current flowing to the load is, eg., greater than 75 percent of the maximum output power of the heat engine and generator, it sends a signal to the primary fuel controller  374  along two of the wires in the wire bundle  376 . This signal causes the primary fuel controller  374  to energize yet another spring loaded normally closed solenoid fuel valve  400  by means of the wire pair  406  which causes the spring loaded normally closed solenoid fuel valve  400  to open thereby further increasing the fuel flow to the burner  298 . Conversely, if the power level decreases to the range below which the burner is operating, the system closes excess spring loaded normally closed solenoid fuel valves until the number of open valves and the load are matched. 
     Under normal operating conditions the output voltage controller  424  connect to the primary controller  372  by means of wire  426  and the voltage controller connects the wire pairs  410 ,  412  and  414  from generator coils  320 ,  322  and  324  in parallel and the output frequency of the generator is equal to the displacer frequency. If an overload occurs as sensed by current sensor  416 , the voltage controller preferably disconnects the load  408  thereby protecting the generator. In the case where the output from the generator is being rectified, the frequency of operation of the displacer will also be varied so as to optimize efficiency of the system. 
     Regenerator 
     In accordance with another aspect of this invention, a novel construction for a regenerator is provided. As shown in FIG. 6 a,  regenerator  42  is preferably also of a thin wall construction. In particular, regenerator  42  may be manufactured from copper (which may be coated with an inverting layer such as silicon monoxide and/or silicon dioxide), aluminum (which is coated with an inverting layer such as silicon monoxide and/or silicon dioxide), stainless steel or a super nickel alloy and have a thickness from about 0.0005 to about 0.005 inches, more preferably from about 0.001 to about 0.002 inches. 
     As shown in FIG. 6 a,  regenerator  42  may comprise a one and preferably a plurality of sections  208  which are joined together by a plurality of longitudinally extending members  210 . Longitudinally extending members  210  are spaced apart on opposed sides of openings  212 . Openings  212  define thermal breaks between sections  208  so as to minimize the heat conducted from hot end  214  to cool end  216 . Accordingly, longitudinally extending members  210  are preferably as thin as possible in the circumferential direction so as to minimize the heat transferred between sections  208  while still maintaining sufficient structural integrity of regenerator  42  so that regenerator  42  may be handled as a single member. In the embodiment of FIG. 1, regenerator  42  comprises a plurality of individual sections  208 . 
     Regenerator  42  may be made from sheet metal which is roll formed. Then louvres (directing members)  218  and openings  212  are preferably formed (eg. by stamping). Subsequently, the material is formed into a cylindrical tube and may be spot welded together to form regenerator  42 . Sublouvres (secondary directing members) may be provided as are shown in FIGS. 17,  18   a  and  18   b.  Regenerator  42  is positioned in fluid flow path  40  between outer and inner walls  12  and,  30  as exemplified in FIG. 2 a,  the regenerator preferably extends along a substantial portion of fluid flow path  40 . As shown in FIG. 2 a,  regenerator  42  commences at about the top  136  of displacer  46  when displacer  46  is positioned distal to driver  48 . Further, regenerator  42  preferably ends adjacent opening  158  in inner wall  30 . 
     In order to improve the heat transfer between the working fluid and regenerator  42 , regenerator  42  may have a plurality of louvres  218  provided therein. Exemplary louvres  218  are shown in more detail in FIG. 6 d.  Regenerator  42  comprises a main body portion  248 . Louvres may be formed such as by stamping or other means known in the art. As shown in FIG. 6 d,  each louvres  218  comprises an angled panel which extends outwardly from main body portion  248  and has opposed flanges  250  extending between front portion  256  of angled panel  252  and main body portion  248 . As shown in FIG. 6 d,  some of the louvres may have angled panels that extend in a first direction (e.g. upwards in FIG. 6 d ) and another set of louvres may extend in the opposite direction (e.g. downwards as shown in FIG. 6 d ). The designs which are shown in FIGS. 12 d,    17 ,  18   a  and  18   b  may be used for louvres  218 . 
     In FIGS. 6 b  and  6   c,  a heat exchanger using a coil of the material used to form regenerator  42  of FIG. 6 a  is shown. Regenerator is preferably fixed in position such as by spot welding regenerator  42  to one of outer and inner walls  12  and  30 . Referring to FIG. 6 c,  arrows represent the flow of fluid through louvres  218 . Louvres  218  direct the fluid to pass first from one side of main body portion  248  to the opposed side and, subsequently, a portion to flow from the opposed side back to the initial side of main body portion  248 . The continual flow of fluid through main body portion  248  (from one side to the other) produces an improved heat transfer between the working fluid and regenerator  42 . In particular, when the working fluid is passing through the regenerator from heating chamber  140  to cooling chamber  160 , regenerator  42  accumulates heat which is transferred back to the working fluid when the working fluid travels from cooling chamber  160  to heating chamber  140 . 
     It is to be appreciated that louvred fins may be used in place of part or all of regenerator  42 . Further, a section  208  of the regenerator material may be used as a heat exchanger in passageway  64  or in the upper portion of passageway  40  provided that positioning members are provided to dimensionally stabilize the upper end of inner and outer walls  30  and  12 . For example, one or more rings  476  may be provided adjacent the upper end of inner wall  30 . 
     Heat exchanger  258  may also be incorporated into the portion of fluid flow path  40  which is positioned in heating zone  22 . This is shown in particular in FIG. 2 a.  This heat exchanger assists in transferring heat from the exhaust gases in first pass  86  of heat exchanger  67  to the working fluid as it travels from heating chamber  140  to cooling chamber  160 . 
     Heat exchanger  258  may be made from the same material as regenerator  42 . This is shown in particular in FIG. 6 a.  In FIG. 6 b,  a heat exchanger  258  is shown comprising a plurality of layers of the louvres material shown in FIG. 6 a.  The number of layers of louvred main body portion  248  which is utilized as regenerator  42  or as heat exchanger  258  may vary depending upon the desired thermal efficiency of heat exchanger  258  as well as regenerator  42 . For example, if the radial thickness of fluid flow path  40  is about 0.05 inches, then only a single layer heat exchanger  258  may be required as is shown in FIG. 6 a.    
     Fins 
     In accordance with another aspect of this invention, there is provided a novel construction for heat exchangers. As discussed above, means to assist in transferring heat between the structural components of the heat engine and a fluid may be provided in any of the air flow passages of the heat exchanger. For example, they may be provided in passages  64 ,  40 ,  86 ,  88  and  102 . At least one heat exchange member or fin is preferably provided in each fluid flow passage. In one embodiment. as exemplified by FIG. 14, the fins are constructed to allow the flow of fluid through the fin as the fluid flows axially through the heat exchanger. In another embodiment, the fins are constructed and arranged to produce a directed fluid flow as the fluid passes through the heat exchanger (e.g. see FIGS. 12. 12 a,    13  and  16 ). A plurality of individual annular fins may be provided. Alternately, one or more continuous helical fins as shown in FIG. 16 may be provided. In either case, the fins define a plurality of rows of fins in the heat exchanger that the fluid encounters as it flows through the heat exchanger and thus the fluid is acted on by the fins several times as it flows through the heat exchanger. In a further embodiment, the fins are preferably provided with directing members whereby the fin is configured and arranged to produce a main flow of fluid which flows through the fin and to produce a secondary fluid flow which passes through the main directing members whereby the transfer of heat between the fluid and the heal exchanger is enhanced. Examples of such directing members are shown in FIGS. 16. 17,  18   a  and  18   b.  The directing members may be configured and arranged to produce a cyclonic or swirling flow of air (see FIGS. 12 e ) or a cross-flow pattern. (see FIGS. 12 f.    
     In the preferred embodiment of the heat exchanger, as exemplified by FIG. 1, the fins are positioned between two concentric cylinders which are spaced apart to define an air flow passage. A second air flow passage is positioned interior of the inner of the two concentric cylinders or exterior of the outer of the two concentric cylinders. The fins may be affixed to the wall of the heat exchanger by any means known in the heat exchanger art but are preferably mechanically affixed to one or both of the inner wall and the outer wall and extend all the way across the air flow passage. However, the instant fin design may be used in a passage of any particular configuration for a heat exchanger. For example, the heat exchanger could have a square cross-section defining a first fluid flow passage with the fins longitudinally spaced apart in the passage. A plurality of generally parallel tubes (for containing a fluid at a second temperature) could extend longitudinally through the fins to thereby define a heat exchanger with a square cross-section. 
     Referring to FIG. 12, annular fin  428  has a top surface  430  and inner edge  432 , an outer edge  434  and a lower surface  436 . Top and bottom surfaces  430  and  436  are opposed surfaces of fin  428 . Inner and outer edges  432  and  434  are curved and have a portion which abuts against the longitudinally extending surface of a wall. See for example surface  438  of FIG. 12 b.  Such rings may be used in a fluid flow passage which exists between spaced apart cylindrical tubes. For example, such rings may be inserted in passageways  64  or  102  (see FIG.  1 ). In order to provide a plurality of annular fins  428  in passageway  102 , outer burner shield  70  could be placed inside air preheat shield  72  to define passageway  102 . Any desired number of rings, preferably a plurality thereof, could be inserted into passageway  102  one at a time with edges  432  and  434  pointing towards entry port  104 . Rings would then slide along the inner walls of shields  70  and  72  until they were positioned in the desired location. Annular fins  428  are preferably sized such that edges  432  and  434  are drawn towards each other upon insertion into passageway  102 . The pressure between edges  432  and  434  mechanically lock annular fins  428  in position. Preferably, the pressure which is exerted between fin  428  and shields  70  and  72  is sufficient to ensure that the rate of heat transfer between shields  70  and  72  and annular fin  428  is maintained over the normal operating temperature of shields  70  and  72 . In this way, as the dimension of passageway  102  may change under different thermal conditions, sufficient contact will be maintained between the annular fins and the walls of passageway  102  to ensure that the desired rate of heat transfer is maintained. 
     Another embodiment of such an annular fin is shown in FIG. 12 a.  In this embodiment annular fin  440  has opposed surfaces (i.e. top surface  446  and the bottom surface) which is generally flat (so as to be generally transverse to the longitudinal fluid flow path through the heat exchanger) and an outer edge  444  which is curved as in the case of annular fin  428  to define a collar. Inner edge  442  is not curved. Examples of such fins are shown in passage  102  of FIG.  1 . The outer diameter of fin  440  is selected such that when inserted into annular passage  102 , the pressure which is exerted between outer edge  444  and inner surface of outer burner shield  72  will deform the collar and lockingly hold annular fin  440  in position. It will be appreciated that a curved edge (or collar) may be provided instead only on the inner edge. For example, referring to the fins shown in passageway  88  of FIG. 1, inner edge  442  may be curved so as to have the collar like portion of fin  440  of FIG. 12 a  so as to lockingly engage a wall positioned on the interior of the ring (in this case, inner burner shield  68 ). The top surface of the fin preferably extends horizontally to have a blunt nosed edge. In this embodiment, the inner diameter of the annular fin is selected so as to be slightly smaller than inner burner shield  68  so as to lockingly engage inner burner shield  68  when inserted therein. Accordingly, in accordance to one aspect of this invention, fins which have air flow passages there through are provided to lockingly engage one or both walls of an annular passage to thereby maintain contact with the selected walls over the operating temperature of the heat exchanger. The passages may be provided as openings  456  in a fin or by passages  474  between blades  472  of a fin (see FIG.  13 ). 
     As shown in FIG. 16, one or more helical fins  448  may be provided instead of a plurality of individual annular fins such as fins  428  or  440 . Helical fin  448  is shown in FIG. 16 in an embodiment where it is positioned in the annular passage between outer and inner walls  12  and  30 . In this embodiment, helical fin  448  has curved inner and outer edges  450  and  452  for locking engagement with surfaces  36  and  34  respectively. It will be appreciated that helical fin  448  need have only one curved edge (either inner out outer) so as to lockingly engage only a single wall  12  or  30 . 
     When used in a heat exchanger, the fins are preferably constructed to allow a fluid to flow there through to enhance the heat transfer between the fluid and the heat exchanger. In the embodiment of FIGS. 12 and 12 a,  fins  428  and  440  are designed to extend fully across the annular gap between and inner and an outer wall. Therefore, fin  428  is provided with a plurality of openings  456 . In order to improve the heat transfer between the fluid and the heat exchanger, comprising fin  428  and the surface of the walls with which fin  428  is in contact, a plurality of directing members  458  may be provided. As the air travels longitudinally, in the direction of axis A of FIG. 2 a,  the air encounters top or bottom surface  430  or  436  of fin  428  and passes through openings  456 , heat is transferred between fin  428  and the fluid passing through the heat exchanger. 
     As shown in FIGS. 12 and 12 a,  each of the direction members  458  extends upwardly in the same direction. Accordingly, as fluid travels longitudinally (or axially) through the heat exchanger, the fluid will be deflected by directing members  458  to swirl around in a cyclonic type flow. Accordingly, for example, referring to the embodiment of FIG. 12 e,  a plurality of fins  428  may be positioned on outer surface  32  of outer wall  12 . As fluid travels upwardly through openings  456 , directing members  458  will cause the air to flow cyclonically around outer wall  32 . 
     As exemplified by FIGS. 12 c  and  12   d,  some of the directing members  458  extend upwardly from top surface  446  and some extend downwardly. As shown in FIG. 12 c,  directing members  458  may extend away from surface  446  in the same direction or, alternately, as shown in FIG. 12 d,  they may extend towards each other. Preferably, directing members  458  extend towards each other as shown in FIG. 12 d.    
     Directing members  458  have a distal end  460  spaced circumferentially from the position where directing member  458  contacts top surface  446 . As air travels through opening  456 , it travels along the bottom surface of directing member  458  until it encounters distal end  460 . When the fluid encounters distal end  460 , turbulent flow is created. As a result of the turbulent flow, a portion of the fluid, preferably at least about 65%, continues to travel upwardly through the heat exchanger while the remainder of the fluid is caused to travel in a reverse manner through an adjoining opening  456  to the lower surface of fin  440 . Accordingly, directing members  458  cause a portion of the fluid travelling through the heat exchanger to pass at least twice, and preferably three times, through a fin  440  as the fluid travels axially through the heat exchanger. For example, as the fluid flows through the heat exchanger, a portion of the fluid which has travelled through a fin  440  from lower surface  436  to top surface  430  will travel in the reverse direction from top surface  430  to lower surface  436 . This portion of the fluid may then be reentrained in the longitudinal flow of fluid through the heat exchanger and travel again from lower surface  436  to top surface  430  and continue on flowing through the heat exchanger to encounter another fin  440 . This is shown in particular in FIG. 12 f.  This type of flow wherein the directing members are configured and arranged to cause a portion of the fluid which has passed through the a fin from the first opposed side to the second opposed side to then pass from the second opposed side to the first opposed side is referred to as “cross-flow”. This flow is advantageous as it causes a portion of the fluid to be in contact with fin  440  for a greater period of time thereby increasing the heat transfer between fin  440  and the fluid. 
     Directing members may be formed in several ways. As shown in FIGS. 12 c  and  12   d,  directing members  458  constitute a flange which may be cut or stamped from surface  446 . In such a case, only one edge of directing member  458  may be in contact with the remainder of the fin. An alternate construction of a directing member is shown in FIGS. 17,  18   a  and  18   b.  In this case, directing member  462  is in contact with the fin over more than one surface. In particular, as shown in FIGS. 17,  18   a  and  18   b,  directing member  462  has a transverse or radial side  464  which is in contact with top surface  454  as well as opposed longitudinal edges  466  which are in contact with top surface  454 . The increased contact surface between directing member  462  and the fin permit a greater amount of heat to be transferred between directing member  462  and the fin thus improving heat transfer between directing member  462  and the fluid flowing through opening  456 . Directing members  462  may be produced by a stamping operation. Directing members  462  may be provided on any of the fins described herein. 
     In an alternate embodiment, the fin may comprise an annular member which comprises a radial blade. In particular, as shown in FIG. 13, fin  468  may have a hub (which may be a curved inner edge or collar  470 ) and a plurality of blades  472  which extend outwardly, and preferably radially outwardly, therefrom (or a hub and a plurality of blades which extend inwardly). Blades  472  are preferably angled with respect to the plane of fin  468  so as to direct air to flow in a prescribed pattern through the heat exchanger. The spacing between adjacent blades  472  comprises a passage  474  through which a fluid may flow. It will be appreciated that blades  472  may be oriented in the same direction (as is the case with directing members  458  in FIG.  12 ), thus causing a swirling flow of the fluid in the heat exchanger as is represented by FIG. 12 e.  It will be appreciated that some of blades  472  may direct the fluid upwardly whereas others may direct the fluid downwardly (in the same manner as directing members  458  of FIGS. 12 c  or  12   d ) to create a cross-flow as shown by FIG. 12 f.  It will further be appreciated that, as with fin  440 , radial blades  472  preferably extend substantially all and preferably all the way across the annular space between the concentric cylinders so as to direct as much air as possible to flow through passages  474 . 
     In some circumstances, a limited amount of heat may need to be transferred between the fluid and the fin. In such a case, the fin may be provided with openings without any directing members. An example of such a fin is shown in FIG.  14 . In this case, the fin comprises a ring  476  having a plurality of openings (for example circular openings  478 ) provided in top surface  480 . Once again, inner and/or outer edge  482  and  484  may be curved as shown in FIG.  14 . 
     In a further preferred embodiment, the directing members are themselves provided with directing members so as to cause the fluid to travel through the directing member as the fluid passes through the heat exchanger. An example of such a directing member is shown in FIG.  16 . In this case, directing member  458  is provided with at least one and preferably a plurality of openings  486  provided therein. For example, referring to FIG. 17, directing member  462  has a plurality of openings  486  provided therein. Some of the fluid will travel through openings  486  as the fluid travels through openings  456  in the fin. Preferably, as shown in FIGS. 18 a  and  18   b,  the directing member is a main directing member and has a plurality of secondary directing members  488  or sublouvres provided thereon. It will be appreciated that the secondary directing members may use the construction techniques of fins  440  (eg. it may be a flanged or stamped opening) or of fins  468  (eg. it may be a passage through a blade). As in the case with the main directing members, a secondary directing member is preferably associated with each secondary opening  486 . As shown in FIG. 18a, secondary directing members  488  may all be oriented in the same direction such that as the fluid flows axially through the fin from lower surface  490  to upper surface  492 , the fluid passes only once (i.e. unidirectionally) from lower or inner surface  494  of directing member  462  to upper or outer surface  496  of directing member  462  (inner surface  494  and outer surface  496  are opposed surfaces). In the alternate embodiment of FIG. 18 b,  some of the secondary directing members  488  extend upwardly from upper surface  496  and some extend downwardly from lower surface  494 . As shown in FIG. 18 b,  directing members may alternately extend upwardly and downwardly or they may be in any other random pattern (as is also the case with main directing members  458  in the embodiments of FIGS. 12 c  and  12   d ). In this case, as the fluid travels axially through the heat exchanger from lower surface  490  to upper surface  492  of the fin, a portion of the fluid will be caused to pass at least twice through main directing member  462  due to turbulent flow created by secondary directing members  488  thus creating cross flow of fluid similar to that shown in FIG. 12 f.  It will be appreciated that openings and preferably openings with associated secondary directing members  488  may also be provided on blades  472 . In another embodiment, blades  472  may be provided as secondary directing members. 
     In accordance with another aspect of this invention, any of these fin designs may be provided on the outer surface of outer wall  12  as shown in FIG. 1 to assist in cooling chamber  160 . These fins may define the outer perimeter of the heat engine. Alternately, as shown in FIG. 1, a further outer cylindrical sleeve  522  may be provided. This may be an extension of air preheat shield  72 . Air flow path  524  is an extension of preheat air flow path  102  and is used to transfer heat from the cooling chamber to the air for combustion. As shown in FIG. 1, the cooling fins of heat exchanger  330  transfer heat from outer wall  12  to the air for combustion. A fan is optionally provided for producing forced convection flow through air flow path  524 . The fan may be mounted at any position to provide this flow. As shown in FIG. 1, the fan is provided adjacent the entrance to air flow path  524 . The fan comprises a motor  526  and a fan blade  528  driven by the motor. Preferably, both motor  526  and fan blade  528  are annular. They may be mounted on one or both of the walls that define air flow path  524  (i.e., outer wall  12  and/or sleeve  522  in the embodiment of FIG.  1 ). If fan  528  is annular, then it may be mounted on an annular fan mount  530  which is drivenly connected to annular motor  526 . 
     In accordance with another aspect of this invention, any of these fin designs may be provided on the inner surface  60  of heater cup  44  as shown in FIG. 1 to assist in transferring heat from the combustion gas in combustion chamber  92  to the wall of heater cup  44  (the combustion chamber housing) as exemplified by reference numeral  532  in FIG.  1 ). 
     It will be appreciated by those skilled in the art that other modifications may be made to a heat engine and the flashlight disclosed herein and all of these are within the scope of the following claims. For example, the construction of regenerator  42  and the construction of the louvred heat exchanger may be used in any application heat exchange application. 
     Any heat exchanger construction known in the art may be used with the thin walled design provided herein to provide a heat exchanger means between the hot exhaust gases produced in burner cup  44  and the working fluid in the heat engine. In order to increase the thermal efficiency of the heat engine, the air for combustion may be preheated such as by use of the exhaust gas.