EP0101565A1

EP0101565A1 - Thermocompressor with pressure actuated heating chamber bypass

Info

Publication number: EP0101565A1
Application number: EP83107126A
Authority: EP
Inventors: Mark Schuman
Original assignee: Individual
Current assignee: Individual
Priority date: 1982-07-23
Filing date: 1983-07-20
Publication date: 1984-02-29
Also published as: IL69312A0; JPS5929784A; ES8406631A1; BR8303891A; ES524390A0; AU1711083A; DK334683A; DK334683D0; ZA835293B

Abstract

A thermocompressor utilizing a modified Stirling cycle is disclosed having a self-oscillating free piston driven by a thermal lag heating chamber connected to the hot end of the cylinder. A cylinder bypass containing a regenerator and cooling chamber provides a coasting region of the cylinder for the piston. The cylinder bypass is connected to the heating chamber via a conduit passing through a nipple in the hot end of the cylinder, with a very thin gap around the nipple to allow thermal lag driving of the cup-shaped free piston by the heating chamber without losing very much compressible fluid along the gap, from the conduit. The small amount of lost fluid is merely not heated thoroughly. During the cooling portion of the Stirling cycle, a check valve and short conduit in the nipple allow the gas in the cylinder hot space to bypass the heating chamber and flow directly through the nipple to the first-mentioned conduit and thence to the regenerator in the cylinder bypass for cooling, thereby avoiding unnecessary fluid drag and heating in the heating chamber during the cooling portion of the Stirling cycle.

Description

The present invention relates generally to energy converters, more particularly to heat engines utilizing a regenerative fluid cycle, and still more particularly to a Stirling type free piston thermocompressor for pumping fluid or otherwise supplying a differential or cyclical pressure to a load.
The closest prior art appears to be my own U.S. Patent No. 4,132,505 issued January 2, 1979 entitled "Thermocompressor Utilizing a Free Piston Coasting between Rebound Chambers" which has, like the present invention but in contrast with typical Stirling cycle engines, a self-oscillating displacer piston, which can be useful in driving a load and can provide stability in driving a variable load, such as a free piston linear alternator. Possible loads include-a heat pump, water pump and most any fluid driven motor.
The present invention is basically similar to my just-mentioned prior patent except for the addition, within the nipple in the hot end of the cylinder, of a short conduit and check valve, the check valve being optionally double-acting and optionally spring-biased, providing automatically a heating chamber bypass during Stirling cycle .cooling so that most or virtually all of the gas or compressible fluid between the nipple and the piston as the piston is coasting downward toward and eventually over the nipple can take the easier (lower impedance) and cooler path through the short vertical conduit and thence through a short segment of the heating chamber inlet conduit toward the hot end of the cylinder bypass for cooling, and very little gas, ten per cent or even less if desired, will have to take the higher impedance and hotter path through the heating chamber toward the hot (lower) end of the cylinder bypass for subsequent cooling. This is in contrast with the thermocompressor of my above-mentioned prior patent wherein, depending partly on the chosen thickness of the annular region between the nipple and the cylinder sidewall, a substantial fraction of such gas, typically perhaps more than one-half, returns to the hot end of the cylinder bypass via the heating chamber. In typical Stirling cycle engines virtually all such gas must return through the heating chamber, i.e., gas flowing from the hot (expansion) space to the cold (compression) space for Stirling cycle cooling.
By substantially reducing unnecessary fluid drag and heating in the heating chamber during the regenerative cooling portion of the cycle, thereby reducing the heat load on, and temperature differential across the regenerator in the cylinder bypass, the heating chamber can be smaller and require less heat, and thus produce less fluid drag, while the regenerator can also be smaller and produce less thermal and viscous losses (fluid drag). Thus the present invention facilitates the use of a thermocompressor or Stirling type engine of smaller size, higher efficiency, and greater specific power output than prior art devices of this type, e.g., free piston, Stirling cycle engines.
Figure 1 is a partly schematic, elevational, cross-sectional view of a free piston Stirling type thermocompressor employing the principles of the present invention. In Figure 1 there is illustrated a thermocompressor, or thermally driven oscillating piston apparatus designed for utilizing thermal energy to cyclically heat and cool a compressible fluid, such as a gas, thereby developing a cyclical pressure for driving a load. The apparatus includes a substantially closed cylinder I having a side-wall 2 of circular cross-section and end-walls or end-plates 3 and 4 at the upper and lower ends of the cylinder. The lower or hot end wall 4 includes a nipple or plug or projection 5 of circular cross-section projecting upwardly toward the free piston 6. Piston side- wall 7 forms a loose sliding seal with the sidewall 2 of cylinder 1, thereby dividing the cylinder into variable volume hot and cold ends of the cylinder below and above the piston. The free piston 6 is cup-shaped with the open end of the cup facing downward toward the nipple 5 so that the piston can pass almost completely over the outer cylindrical surface 9 of the nipple.
Cylinder 1 has a cylinder bypass means 10 connecting the hot and cold cylinder ends thereby providing a bypass region of the cylinder for the coasting of the free piston as the piston oscillates along the cylinder axis. The cylinder bypass includes, in seriatim, cold cylinder bypass ports 11 defined in the cylinder sidewall in the cold cylinder end; cooling chamber means 13, possibly including a fan, for cooling the working gas by external cooling means; thermal regenerator 15 for conserving heat by storing heat from and releasing heat to the working gas each cycle (e. g., stainless steel wool); and hot bypass conduits 16 which terminate in hot bypass ports 17 defined in cylinder sidewall 2 in the hot end of the cylinder. Figure 1 illustrates the thermocompressor as being symmetrical with respect to the cylinder axis, and thus having two of each off-axis port or conduit, but it should be understood that one of each would be sufficient; alternatively, more than two of each off-axis port or conduit can also be used.
Figure 1 shows the piston coasting upward in the bypass region of the cylinder during the first coasting portion, or first power portion, of the oscillatory cycle, forcing cool gas from the cold cylinder end downward through the cylinder bypass (see arrows) for heating and build-up of pressure. The gas exits the hot end of the cylinder bypass in a substantially defined stream flowing out of each hot cylinder bypass conduit 16 via each hot cylinder bypass port 17 into the hot cylinder end after being partially heated by the annular-shaped regenerator 15 in the annular-shaped cylinder bypass 10. The two fluid streams flowing out of ports 17 at_the hot end of the cylinder bypass flow perpendicularly through a very thin annular region or gap 18 defined in the hot cylinder end between outer cylindrical surface 9 of the nipple and the inner surface of cylinder wall 2; thence into two heating chamber inlet ports 20 of T-shaped heating chamber inlet conduit 21 having two short horizontal T-arm conduit segments 22 connecting ports 20 with the common vertical central or trunk segment of heating chamber inlet conduit 21, which central or axial trunk segment of T-shaped inlet conduit 21 conducts the gaseous stream, which flowed into T-arm segments 22 via inlet ports 20, downward into heating chamber 24, heated by external heat source 25. Thus heating cham-21 ber inlet conduit passes through the nipple 5 and terminates in heating chamber inlet ports 20 in the outer cylindrical surface 9 of the nipple in the hot cylinder end. Inlet ports 20 are positioned directly in the paths of the fluid streams flowing out of hot cylinder bypass ports 17, at a distance from ports 17 equal to a very small fraction, such as one-tenth or less, of the cylinder radius, and the conduit portions adjoining each pair of ports 17 and 20 are in-line or coaxial, as described in my above-mentioned U.S. Patent No. 4,132,505, to minimize loss of fluid from the gas streams crossing annular region or gap 18, so that virtually all of the gas in the streams is heated in the nipple and heating chamber before leaving the heating chamber, during this first.power portion, or Stirling cycle heating portion, of the cycle.
To facilitate good heating of the gas, cylinder hot end-wall 4 has a cup-shaped projection 26 projecting downward toward the heat source 25, which can be almost any reasonably hot source of heat, and around the projection 26 is a double-walled, cup-shaped envelope or can 27 heated by the heat source 25 and forming hot passageways with cup 26 for heating the fluid stream flowing through or into the heating chamber 24. For good heat transfer the heating chamber 24 as well as the cooling chamber can have internal/external fins (not shown). The can 27 extends upwardly around the thermocompressor to provide a good, low temperature seal at the cold cylinder end for sealing in the high pressure working fluid, e.g., helium, for a long period of time. The cylinder hot end-plate 4, with its two projections 5 and 26, is heated only indirectly by the heat source, and thus is not quite as hot as the hottest portions of can 27. The gas stream, after being heated in the heating chamber, flows upward through ports 28 of heating chamber outlet conduits 29 and thence into the hot cylinder end below the piston, via outlet ports in the upper face 30 of the nipple. Conduits 29 pass behind T-arm conduits 22.
The free piston 6,coasts upwardly until a cold rebound conduit 39 of cold rebound chamber 40 in the free piston becomes blocked by cold rebound plug 43 projecting downward toward the free piston from cylinder cold endplate 3 whereupon, during a cold rebound portion of the oscillatory cycle, compression of gas in piston chamber 40 by plug 43 causes the free piston to rebound and then begin coasting downwardly toward the hot cylinder end during a second coasting portion, or second power portion, of the cycle.
The pressure increase throughout the thermocompressor during the first power portion of the cycle allows some of the working gas to be fed via load ports 46 of load conduits 45 in cylinder cold endwall 3 to a fluid driven load (not shown). This pressure increase, which results from raising the average temperature of the working gas in the thermocompressor by heating as much of the gas as possible, is facilitated by labyrinth grooves 36 on the upper portion of the outer cylindrical surface 9 of the nipple, just below upper nipple face 30, which grooves reduce leakage of gas upward along annular region 18 from the above-mentioned gas stream or jet flowing out of hot cylinder bypass conduit or nozzle 16 toward the heating chamber 24. This leakage is also minimized by the thinness of thin-walled piston segment 37 which serves as the thin wall of the upside down cup formed by the cup-shaped free piston 6. Thin-walled piston segment 37 is needed later in the cycle to block the hot bypass ports 17 of the cylinder bypass 10 during a hot rebound portion of the cycle following the second power portion of the cycle.
Returning to the first power portion of the cycle, the pressure rise throughout the thermocompressor is further facilitated by the blockage of heating chamber bypass conduit 50, leading from port 51 in upper nipple face 30 downward along the cylinder axis to port 52, by check valve wafer 60. Port 52 connects the short, vertical, low impedance, heating chamber bypass conduit 50 with the mid-point or node of T-shaped heating chamber inlet conduit 21. The upward movement of the piston and the pressure drop through the heating chamber means due to fluid drag on the gas stream result in a greater pressure in inlet conduit 21 than in the heating chamber bypass conduit 50 and in the cylinder space between conduit 50 and the upward moving free piston. This differential fluid pressure across check valve wafer 60 holds the - wafer upward against port 52 of the short heating chamber bypass conduit 50 during upward movement of the free piston 6, thereby blocking port 52 and conduit 50 and thus facilitating the flow of the fluid stream into the heating chamber for heating therein during the first coasting portion of the cycle and even during an initial portion of the cold rebound portion of the cycle.
During a final portion of the cold rebound portion of the cycle, and during the second coasting portion of the cycle, the downward movement of the piston forces gas from the hot cylinder end upward through the cylinder bypass for cooling by the regenerator 15 and _Lurther cooling by the cooling chamber 13 before the gas flows out of the cold end of the cylinder bypass via cold cylinder bypass ports 11 into the cold cylinder end, along with perhaps some gas returning from the load via conduits 45 in response to the decreasing gas pressure throughout the thermocompressor as a result of the cooling process (gas flow arrows reverse). The downward movement of the piston and the reversed fluid friction in heating chamber 24, including its inlets and outlets, now produce a greater fluid pressure in heating chamber bypass conduit 50 and in the hot space just above upper nipple face 30 than the fluid pressure in heating chamber inlet conduit 21. As mentioned above, check valve wafer 60 is positioned centrally within nipple 5 and four-way horizontal T-shaped at the_Aintersection of the two arms 22 of heating chamber inlet conduit 21; the vertical, common flow, axial, trunk portion of T-shaped heating chamber inlet conduit 21, extending from the intersection downwardly toward the heat source; and, lastly, the short, vertical, axial (along the cylinder axis), low impedance, heating chamber bypass conduit 50 extending upwardly from the intersection. Check valve wafer 60 sees, therefore, the above-mentioned higher pressure above it in conduit 50, and the lower pressure below it in conduit 21, and responds to this differential fluid pressure by moving downward away from port 52 toward the trunk portion of conduit 21, thereby unblocking heating chamber bypass conduit 50 and allowing most of the gas in the hot cylinder end to flow through conduits 50 and 22, thereby bypassing the higher fluid flow impedance and hotter paths through the heating chamber, as it travels to the hot cylinder bypass ports 17 for cooling in the cylinder bypass. Thus, conduit 50 and check valve wafer 60 combine to form a pressure actuated heating chamber bypass, having the advantages discussed earlier.
Thin-walled piston segment 37, after passing as a sleeve over the upper portion of the outer cylindrical surface 9 of the nipple including the labyrinth grooves 36, begins blocking the hot end of the cylinder bypass by passing over and thus blocking the hot cylinder bypass ports 17, whereby the second coasting portion, or second power portion, of the cycle ends and the hot rebound portion of the cycle begins, wherein gas trapped in the hot cylinder end below the piston is compressed and forced by the piston into the nipple and heating chamber for thermal lag heating of the gas and thus a thermally augmented spring effect which drives the free piston back toward the cold cylinder end with a greater speed and momentum when the piston unblocks hot cylinder bypass ports 17 at the end of the hot rebound portion of the cycle than the speed and momentum of the piston when it blocked ports 17 at the beginning of the hot rebound. "Thermal lag" means that the times of occurrence of the maximum instantaneous temperature and pressure of the trapped gas will lag the time of occurrence of the maximum instantaneous compression ratio (bottom of the piston stroke), thereby producing a greater average pressure on the piston face after maximum compression ratio than before maximum compression ratio occurs (averaged over equal portions of the stroke, chosen symmetrically with respect to the point of maximum instantaneous compression ratio). Thermal lag driving of an oscillatory wall of a closed chamber is discussed in various of my patents, including my U.S. Patent No. 3,807,904 issued April 30, 1974, entitled"Oscillating Piston Apparatus". Heating chamber means 24 can combine the qualities needed for both Stirling cycle type heating of fluid and thermal lag driving of a free piston. Cold rebound chamber 40, being warmer than the gas in the cold cylinder end in general, may also provide some thermal lag driving of the free piston. I have built a thermally driven partial model which demonstrates coasting of a free piston in a cylinder bypass region, and thermal lag driving of the free piston. The model is powered by waste thermal energy from a standard 200 watt incandescent light bulb.
Returning now to the free piston in Figure 1, the downward motion of the piston during the first half of the hot rebound portion of the cycle continues to exert some downward force on check valve wafer 60 as a result of the continued downward flow of gas in heating chamber bypass conduit 50 and the continued inertial effect of the gas having to change direction roughly 90° when it "hits" the wafer 60, both of which effects also occurred during the second half of the cold rebound and during the second coasting portion of the cycle, but now the cylinder bypass ports 17 are blocked by piston segment 37, and the gas flow in the axial or trunk portion of heating chamber inlet conduit 21 is now downward in parallel with gas flow in heating chamber outlet conduits 29. Also the piston is now slowing down and the trapped gas is heating up. Thus the gas forces on wafer 60 will initially still be downward but will diminish to zero and reverse, during the first half of the hot rebound. Upon upward movement of piston 6, the now upward flow of gas in conduit 21 will increase, carrying wafer 60 upward to block port 52 of conduit 50, and wafer 60 will be held there by a differential pressure roughly equal to the pressure drop along the path of fluid flowing from inlet conduit 21 toward piston 6 via heating chamber 24 and its outlet conduits 29.
Therefore the heating chamber bypass conduit 50 would be blocked by check valve wafer 60 by the time cylinder bypass ports 17 at the hot end of the cylinder bypass become unblocked by the piston segment 37, and conduit 50 will remain blocked, for reasons of pressure difference discussed earlier, during at least the first coasting portion of the cycle, and also during at least an initial portion of the first half of the subsequent cold rebound portion of the cycle.
Check valve wafer 60 is guided by its loose fit in the nipple housing, which allows relatively free fluid flow around the wafer 60 when the wafer moves away from port 52. If desired, the wafer can be guided, or supported, or even spring-biased, by means such as spring-arm 61 of spring 62 mounted in a slightly enlarged upper section 64 of the axial, common flow, trunk portion of T-shaped inlet conduit 21 of the heating chamber means 24. However, the thermocompressor, including the check valve within the nipple, will operate without any mechanical spring. Thus, spring 62 is not required. The check valve can be considered to be the wafer 60 plus the adjoining or proximate structure of the nipple acting as the walls or housing of the check valve, and including the four conduit ports of the four-way intersection at which the check valve wafer 60 is located. If four hot cylinder bypass conduits are used instead of two, check valve wafer 60 can be centrally disposed at a six-way intersection of conduits on the cylinder axis within the nipple 5. Other combinations are of course possible.
The enlarged but very short cylinder section in which wafer 60 is loosely fit can be extended either upward or downward to get the wafer out of the way of the main body of fluid flow by forming a recessed valve seat at either port 52 of conduit 50 or at the top of the axial portion of inlet conduit 21, or at both of these locations, in which latter case it is evident that wafer 60 is being utilized as a moving member of a double-acting check valve within the nipple (which can be true whether or not the - valve seats are recessed). However, it is not necessary for wafer 60 to block the lower or trunk portion of the T-shaped inlet conduit 21. In fact, small raised portions or standoffs can be provided on top of the trunk portion of conduit 21, underneath wafer 60, to keep the wafer from seating against the trunk portion and blocking flow in the trunk portion. The standoffs could be provided to allow a small flow of gas through the heating chamber in parallel with the flow through heating chamber bypass conduit 50 during the second power portion of the cycle in order to further reduce fluid drag; or the standoffs could improve the thermal lag driving of the free piston during the subsequent hot rebound; or, the standoffs could facilitate the timely and proper blocking of port 52 and conduit 50 by the wafer upon subsequent upward movement of the free piston during the hot rebound. It is, after all, the main purpose of the check valve wafer to block and unblock the heating chamber bypass conduit at the proper times in the cycle without restricting fluid flow in the required or critical portions of the heating chamber inlet conduit in the nipple.
After the burner 25 supplies sufficient heat to heating chamber 24, the device can be easily started by either a single pressure pulse or an oscillatory pressure, applied below the piston, i.e., to any portion of the gas volume below the free piston, as illustrated in my U.S. Patents 3,489,335 and 3,807,904. Or a suction pulse or oscillatory suction can be applied above the piston. As part of a thermally driven, free piston, linear alternator, a voltage applied to a coil of the alternator could produce such a suction. However, such an alternator is likely to be self-starting, if suitably designed. Based on my calculations and certain design considerations, I believe that the Stirling lag angle between the phases of the two free pistons of such an alternator would automatically shift toward 90⁰ lag under increasing load, and that the alternator would run at a relatively constant amplitude and frequency under variable load, at a thermal-to-electric efficiency of around forty per cent or more, if properly designed and adequately heated. It is also expected that the energy converter of the present invention would be safe, silent, clean, low in cost, very low in pollution, and could be powered by most any fuel or even solar energy or waste heat.
Considering various Stirling cycle engines, it appears that a thermocompressor having a thermal lag driven (self-oscillating), coasting free piston is particularly suited to the pressure actuated, heating chamber bypass of the present invention, for the following reasons.
First, in taking the heating chamber out of its usual position in the Stirling cycle cylinder bypass and locating it beyond the hot end of the cylinder for thermal lag driving of the free piston, a good size conduit is needed between the regenerator and heating chamber to easily and rapidly carry fluid between the two in order to facilitate good Stirling cycle heating and cooling of the working fluid. The heating chamber bypass of the present invention also needs such a conduit to easily and rapidly conduct fluid directly from the cylinder hot space to the regenerator during Stirling cycle cooling. Thus the heater-regenerator conduit (conduits 16 and 21 in Figure 1) serves both purposes simultaneously.
Secondly, since the self-oscillating free piston needs to block the conduit each cycle in order to trap and compress fluid into the heating chamber for thermal lag driving of the piston, the heater-regenerator conduit preferably passes through the hot end of the cylinder, whereby it passes very close to the gas in the cylinder hot space below the piston. This closeness also benefits the heating chamber bypass of the present invention, since the heating chamber bypass conduit (conduit 50) can thus be very short and therefore be of very low fluid flow impedance and add very little dead volume to the hot cylinder end. Thus the passage of the heater-regenerator conduit through the hot end of the cylinder also serves two purposes at once.
Third, the thermal lag driven, coasting free piston apparatus preferably includes a projection or nipple in the hot cylinder end to provide a convenient housing through which both the heater-regenerator conduit and a heating chamber outlet conduit may pass, to reduce loss of fluid from the fluid stream flowing across the gap in the heater-regenerator conduit (the gap between ports 17 and 20), and to fill up odd-shaped dead space in the hot cylinder end adjacent the two just-mentioned conduits, filling up the dead space with an axially symmetric form over which a simple, cup-shaped free piston can pass. This same nipple provides a convenient housing, at just the right location, for the check valve and short heating chamber bypass conduit of the present invention, without requiring fittings and conduits external to the cylinder, and without introducing significant fluid drag or dead space or new thermal losses. Therefore, in these respects, the nipple, too, serves multiple purposes at once.
For these reasons, the typical Stirling cycle type thermocompressor or engine would not benefit nearly as much, if indeed at all, from a heating chamber bypass synchronized with the cycle, such as the pressure actuated heating chamber bypass of the present invention.
Thus, for the above reasons, there appears to be a strong synergism between the pressure actuated heating chamber bypass of the present invention and the thermal lag driven, coasting free piston thermocompressor of my prior U.S. Patent No. 4,132,505, which patent itself represents a synergism between the cup-shaped free piston, the conduit-containing nipple,and some of the features of my earlier piston patents - mainly, the self-oscillating free piston driven by a thermal lag heating chamber, the coasting of a free piston in a cylinder bypass region, and the use of a nozzle or jet effect to carry a compressible fluid in a stream from one conduit across a gap and into and through another conduit leading to a heating chamber.
It should be understood that, depending on the exact design of the thermocompressor and especially on the nature of the load, the thermodynamic cycle may deviate substantially from the Stirling cycle. However, the thermodynamic efficiency can still be very high, and should be significantly higher with the inclusion of the automatically synchronized heating chamber bypass of the present invention than without it, for virtually any type of load. For a typical free piston load, such as when driving a linear alternator or heat pump, the cycle can be considered a modified Stirling cycle with a very high thermal efficiency and a variable Stirling lag angle between the phases of the two pistons. The lag angle would automatically shift to increase power as the magnitude of the load increases. I was able to determine this by analogy with an RLC circuit (resistance-inductance-capacitance).
Various modifications and variations of the embodiment of the present invention specifically described herein can obviously be made that would still fall within the above teachings and within the scope of the appended claims.
For example, if the hot cylinder bypass conduits 16 are angled, as in my recent U.S. Patent No. 4,132,505, the heating chamber inlet conduit 21 would be basically Y-shaped rather than T-shaped. Or if each hot cylinder bypass conduit had its own heating chamber inlet conduit, there could be one or more elbow- shaped heating chamber inlet conduits, each with a heating chamber bypass conduit and check valve. Also, the check valve might be replaced by another form of pressure sensitive valve or valve suitably synchronized to the cycle.

Claims

1. A thermocompressor comprising a cylinder, a free piston dtvid- ing the cylinder into variable volume hot and cold cylinder ends at opposite ends of the piston, cylinder bypass means containing a regenerator and connecting the hot and cold cylinder ends thereby providing a bypass region of the cylinder for the .piston as the piston oscillates along the cylinder axis, heating chamber means disposed outside of the cylinder bypass and communicating with the cylinder bypass via a heating chamber inlet conduit originating at a heating chamber inlet port disposed in the hot cylinder end proximate a hot cylinder bypass port at the hot end of the cylinder bypass, said heating chamber means communicating with the hot cylinder end via a heating chamber outlet conduit, characterized by a heating chamber bypass means including heating chamber bypass valve means, said heating chamber bypass means connecting said heating chamber inlet conduit with the variable volume space of the hot cylinder end proximate the hot end of the piston, the heating chamber bypass valve blocking the heating chamber bypass during at least a substantial segment of a first power portion of the oscillation cycle as the piston moves in the cylinder bypass region toward the cold cylinder end.

2. A thermocompressor as in Claim 1 wherein said heating chamber bypass means is disposed in said hot cylinder end.

3. A thermocompressor as in Claim 1 or 2 wherein said heating chamber bypass valve means includes a pressure-sensitive valve disposed in said hot cylinder end.

4. A thermocompressor as in one of the claims 1 to 3 wherein said valve includes a wafer with a stem.

5. A thermocompressor as in one of the preceding claims wherein said hot cylinder end includes a hot end plate and said hot end plate has a projection extending from said hot end plate toward the hot end of said free piston, and wherein said heating chamber bypass means and at least a portion of said heating chamber inlet conduit are disposed in said projection.

6. A thermocompressor as in one of the preceding claim wherein said heating chamber - bypass valve means includes a heating chamber bypass valve which is sensitive to cyclical fluid flow in said projection.

7. A thermocompressor as in one of preceding claims wherein said heating chamber bypass valve means includes a valve having a flow-restricting moving element, said element being disposed approximately at a junction between said heating chamber inlet conduit and a heating chamber bypass conduit of said heating chamber bypass means.

8. A thermocompressor as in Claim 7 wherein said valve means and said junction are formed such that the cyclical motion of said element takes place primarily in said heating chamber inlet conduit approximately at said junction.

9. A thermocompressor as in Claim 7 or 8 wherein said element of said valve is a wafer which cyclically moves across the approximate mid-point of said heating chamber inlet conduit at said junction with said heating chamber bypass conduit.

10. A thermocompressor as in Claim 9 wherein said wafer is connected to a stem capable of guiding and modifying the motion of said wafer.

11. A thermocompressor as in one of the preceding Claims wherein said heating chamber inlet conduit includes, disposed in said projection, a common trunk connected to, at an intersection within said projection, at least two inlet arms originating at heating chamber inlet ports on a surface of said projection proximate the hot end of the cylinder bypass, said heating chamber bypass means including a heating chamber bypass conduit which is connected, at said intersection, to said common trunk and said at least two inlet arms of said heating chamber inlet conduit, whereby said intersection is at least a 4-way intersection within said projection in said hot end of the cylinder.

12. A thermocompressor as in Claim 11 wherein said heating chamber bypass conduit originates at at least one heating chamber bypass conduit inlet port on a surface of said projection proximate and communicating with said variable volume space of the hot cylinder end proximate the hot end of the piston, and said heating chamber outlet conduit terminates at a heating chamber outlet conduit outlet port on. a surface of said projection proximate and communicating with said variable volume space, whereby said heating chamber bypass means bypasses the heating chamber, said trunk and at least a portion of said heating chamber outlet conduit.

tone of the preceding, 13. A thermocompressor as in one of preceding Claims wherein the heating chamber bypass valve includes a flow-restricting element which undergoes cyclical motion in said intersection during operation of the thermocompressor.

14. A thermocompressor as in one of the preceding Claims wherein the heating chamber bypass valve includes an internal surface of said projection at said intersection.

15. A thermocompressor as in one of the preceding Claims wherein said heating chamber bypass valve means includes a wafer disposed at said intersection.

16. A thermocompressor as in Claim 15 wherein said wafer has a stem which is connected to a spring.

17. A thermocompressor as in Claim 15 or 16 wherein said heating chamber inlet conduit and said heating chamber bypass means are designed such that, during operation of the thermocompressor, said wafer cyclically crosses the approximate mid-point of said intersection in said projection in said hot cylinder end.

18. A thermocompressor as in one of the Claims 5 to 17 wherein the body of the heating chamber bypass valve is provided by said projection.

19. A thermocompressor as in one of the preceding Claims wherein said heating chamber inlet conduit in cross-section is approximately T-shaped.

20. A thermocompressor as in one of the preceding Claims. wherein the piston at its hot end has a concave hot piston face, said heating chamber bypass means being disposed within said hot cylinder end such that the moving volume within and defined by said concave hot piston face completely encloses said heating chamber bypass means during a hot rebound portion of the oscillation cycle while the wall structure of said face is blocking said hot end of said cylinder bypass.

21. A thermocompressor as in one of the preceding Claims wherein said heating chamber means and said heating chamber bypass means are designed so that, before the end of a hot rebound portion of the oscillation cycle immediately preceding said first power portion of the oscillation cycle, the heating chamber bypass valve begins said blocking of the heating chamber bypass.

22. An energy converter utilizing a modified Stirling cycle comprising a cylinder, a piston dividing the cylinder into first and second cylinder ends at opposite ends of the piston, a cylinder bypass containing a regenerator communicating with said first and second cylinder ends via first and second cylinder bypass ends, a first heat exchanger means communicating with said first cylinder end via first port means disposed in said first cylinder end, said first heat exchanger means communicating with said first cylinder bypass end via a conduit which passes through a portion of said first cylinder end, means for sustaining oscillation of the piston in the cylinder, characterized by a first heat exchanger bypass means including valve means connecting said conduit with the variable volume space of said first cylinder end proximate the piston, said valve means blocking the first heat exchanger bypass means during a portion of the oscillation cycle.

23. An energy converter as in Claim 22 wherein said valve means includes a pressure sensitive valve.

24. An energy converter as in Claim 22 or 23 wherein said valve means includes a wafer with a stem and a means for guiding the stem.

25. An energy converter as in Claim 24 further including spring means acting on said stem.