U.S. patent application number 12/685893 was filed with the patent office on 2010-07-29 for heat engine and method of operation.
This patent application is currently assigned to REGEN POWER SYSTEMS, LLC. Invention is credited to Ricardo Conde.
Application Number | 20100186405 12/685893 |
Document ID | / |
Family ID | 42353023 |
Filed Date | 2010-07-29 |
United States Patent
Application |
20100186405 |
Kind Code |
A1 |
Conde; Ricardo |
July 29, 2010 |
HEAT ENGINE AND METHOD OF OPERATION
Abstract
A closed cycle heat engine is provided. The heat engine includes
first and second expansion pistons that are fluidly coupled to a
heater. The expansion pistons are also fluidly and operably coupled
to a compression piston. A regenerator extracts heat from a working
fluid flowing from the expansion cylinders to the compression
cylinders to preheat the working fluid flowing to the heater. A
cooler is arranged in between the regenerator and the compression
cylinder to remove additional heat before the working fluid reaches
the compression cylinder. The heat engine is arranged such that the
working fluid travels unidirectionally within the engine. The heat
engine may further include one or more actuated valves for
controlling the flow of the working gas. In one embodiment, the
pressure of the crankcase is controlled to be at or less than the
heat engine minimum pressure.
Inventors: |
Conde; Ricardo; (New Salem,
MA) |
Correspondence
Address: |
CANTOR COLBURN, LLP
20 Church Street, 22nd Floor
Hartford
CT
06103
US
|
Assignee: |
REGEN POWER SYSTEMS, LLC
New Salem
MA
|
Family ID: |
42353023 |
Appl. No.: |
12/685893 |
Filed: |
January 12, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61147493 |
Jan 27, 2009 |
|
|
|
Current U.S.
Class: |
60/526 |
Current CPC
Class: |
F02G 2270/80 20130101;
F02G 1/043 20130101; F02G 2270/20 20130101; F02G 2244/06
20130101 |
Class at
Publication: |
60/526 |
International
Class: |
F01B 29/10 20060101
F01B029/10 |
Claims
1. A closed cycle heat engine comprising: a first expansion piston
arranged in a first cylinder; a second expansion piston arranged in
a second cylinder and operably coupled to said first expansion
piston, wherein said second cylinder is fluidly coupled to said
first cylinder; a compression piston arranged in a third cylinder
and operably coupled to said first expansion piston, wherein said
third cylinder is fluidly coupled to received a working fluid from
said second cylinder and transfer said working fluid to said first
cylinder.
2. The heat engine of claim 1 further comprising a drive linkage
coupled to said first expansion piston, said second expansion
piston and said compression piston.
3. The heat engine of claim 2 wherein said drive linkage is a cam
plate.
4. The heat engine of claim 2 wherein said drive linkage is an
articulated crankshaft.
5. The heat engine of claim 2 further comprising: a drive case
coupled to said drive linkage, said drive case being operated at a
pressure less than or equal to a minimum pressure of said working
fluid that occurs in said first cylinder and said second cylinder
during operation of said heat engine.
6. The heat engine of claim 1 further comprising a regenerator
arranged to transfer thermal energy from said working fluid flowing
from said second cylinder to said third cylinder to said working
fluid flowing from said third cylinder to said first cylinder.
7. The heat engine of claim 6 wherein said regenerator is a counter
flow heat exchanger.
8. The heat engine of claim 6 further comprising: a heater
thermally coupled between said regenerator and said first cylinder;
and, a cooler thermally coupled between said third cylinder and
said regenerator.
9. The heat engine of claim 8 further comprising: a first valve
fluidly coupled between said heater and said first cylinder; a
second valve fluidly coupled between said second cylinder and said
regenerator; a first check valve fluidly coupled to said third
cylinder to allow said working fluid to flow into said third
cylinder; and a second check valve fluidly coupled to said third
cylinder to allow said working fluid to flow from said third
cylinder.
10. A heat engine having a working fluid comprising: a first set of
cylinders having a first expansion piston fluidly and operably
coupled to a second expansion piston and a first compression piston
fluidly and operably coupled to said first expansion piston and
said second expansion piston, wherein said first set of cylinders
is arranged in a first closed cycle to provide a first
unidirectional flow of said working fluid.
11. The heat engine of claim 10 further comprising: a second set of
cylinders operably coupled to said first set of cylinders, said
second set of cylinders having a third expansion piston fluidly and
operably coupled to a fourth expansion piston and a second
compression piston fluidly and operably coupled to said third
expansion piston and said fourth expansion piston, wherein said
second set of cylinders is arranged in a second closed cycle to
provide a second unidirectional flow of said working fluid.
12. The heat engine of claim 11 wherein said first set of cylinders
and said second set of cylinders are arranged 90 degrees apart.
13. The heat engine of claim 12 further comprising a regenerator
thermally coupled to said first closed cycle and said second closed
cycle.
14. The heat engine of claim 13 further comprising a heater coupled
to said first closed cycle and said second closed cycle to transfer
thermal energy to said working fluid.
15. The heat engine of claims 14 further comprising a radiator
coupled to said first closed cycle and said second closed cycle to
transfer thermal energy from said working fluid.
16. The heat engine of claim 15 wherein said regenerator is
arranged in a first portion of the first closed cycle between the
second expansion piston and the first compression piston, and is
arranged in a second portion of the second closed cycle between the
fourth expansion piston and the second compression piston.
17. The heat engine of claim 11 further comprising a drive case
operably coupled to said first set of cylinders and said second set
of cylinders, said drive case having an operating pressure less
than or equal to a minimum pressure of said working fluid in said
first set of cylinders and said second set of cylinders during
operation of said heat engine.
18. A method of operating a closed cycle heat engine comprising:
heating a working fluid; expanding said heated working fluid into a
first cylinder to move a first expansion piston to a first
position; flowing said heated working fluid into a second cylinder
to move a second expansion piston to a second position; flowing
said working fluid from said first cylinder and said second
cylinder to a third cylinder; compressing said working fluid in
said third cylinder with a compression piston; and, flowing said
working fluid from said third cylinder to said first cylinder.
19. The method of claim 18 further comprising transferring thermal
energy from said working fluid flowing from said second cylinder to
said third cylinder to said working fluid flowing from said third
cylinder to said first cylinder before said step of heating said
working fluid.
20. The method of claim 19 further comprising cooling said working
fluid before said step of compressing said working fluid in said
third cylinder.
21. The method of claim 20 further comprising dwelling said first
expansion piston at said first position during said step of flowing
said heated working fluid into said second cylinder.
22. The method of claim 21 further comprising the step of dwelling
said second expansion piston at said second position during said
flowing of said working fluid from said first cylinder to said
third cylinder.
23. The method of claim 18 further comprising: adjusting a drive
case to a first pressure less than or equal to a pressure of said
working fluid in said first cylinder and said second cylinder when
said second expansion piston is in said second position.
24. A heat engine comprising: at least two expansion pistons
fluidly coupled to each other, each expansion piston being arranged
in an expansion cylinder; at least one compression piston fluidly
coupled to said at least two expansion pistons, each compression
piston being arranged in a compression cylinder; a drive linkage
operably coupled to said at least two expansion pistons and said at
least one compression piston, said drive linkage arranged in a
crankcase, wherein said crankcase is fluidly coupled to said
expansion cylinder and said compression cylinder; and, a
pressurized vessel fluidly coupled to said crankcase, wherein said
pressurized vessel is arranged to add pressurized gas to said
crankcase in response to a change in operation of said heat engine.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Patent Application 61/147,493, filed Jan. 27, 2009 entitled "Heat
Engine and Method of Operation", which is hereby incorporated
herein in its entirety.
BACKGROUND OF THE INVENTION
[0002] The subject matter disclosed herein relates to closed system
heat engine, and in particular to a heat engine providing for
unidirectional flow of a working gas and for controlling gas
pressure within the heat engine.
[0003] External heat engines refer to several cycles that extract
heat from an external source, such as solar or waste heat from a
furnace, and deliver it to a working fluid inside the engine to
produce useful work. Stirling cycle and Ericson cycles are some of
the cycles that utilize external heat sources. Both cycles use
regenerators, although the Stirling cycle is a closed system while
the Ericson cycle is an open system. To date Stirling cycle engines
have achieved the highest efficiency for a simple cycle due to the
use of the regenerator that recovers heat that would normally be
rejected from one cycle and delivers the thermal energy to the
working gas in a subsequent cycle.
[0004] Stirling engines have traditionally been operated at high
temperatures (750.degree. C.) and high speeds (30-50 Hz), in an
attempt to achieve high power to weight ratios. High temperature
Stirling engines suffer from premature failure due to creep stress
from high operating temperatures and pressures even when using
exotic metals alloys, such as Inconel for example. Recent
developments in Stirling engines have been directed to utilizing
low temperature heat sources such as industrial waste heat, solar
or geothermal for conversion into electricity. However, very few
successful engines have been demonstrated and only at small power
output levels.
[0005] Traditional Stirling engines operate by oscillating a
working gas between a hot and cold heat exchanger and the expansion
and compression pistons. The major deficiency of oscillating flow
engines is that the hot and cold heat exchangers have a volume that
is tied to the swept volume of the piston. In one half of the cycle
it is necessary to compress and expand from this volume. Although
during the other half of the cycle, it is considered dead space
that has an adverse affect. The compression piston compresses the
gas into the cold heat exchanger in order to achieve an isothermal
compression (constant temperature). Further motion of the
compression piston displaces some of the cold gas up through the
regenerator and into the hot heat exchanger. The gas in the hot
heat exchanger heats up while the expansion piston starts to
expand. As such the gas expands from the hot heat exchanger volume
in an isothermal expansion. The deficiency in this arrangement is
that a large amount of working gas mass is left in the cold heat
exchanger volume while expansion is occurring.
[0006] In high temperature engines leaving working gas in the cold
heat exchanger is acceptable due to the volume ratio of the heat
exchanger to the swept volume of the piston. In high temperature
engines this is typically 1:3 but in low temperature engines this
can be as low as 1.25:1. This means that in low temperature engines
the heat exchanger volume is much larger than the swept volume and
an excessive amount of gas is left in the cold heat exchanger. In
effect more work is put in to compressing a gas that does not make
it to the hot side of the engine to deliver useful work. This is
the primary reason why traditional oscillating Stirling engines
usually do not effectively operate below 300.degree. C.
[0007] While existing heat engines are suitable for either intended
purposes there remains a need for improvements in closed cycle heat
engines to provide high efficiency operation at low engine
temperatures.
BRIEF DESCRIPTION OF THE INVENTION
[0008] According to one aspect of the invention, a closed cycle
heat engine is provided. The heat engine includes a first expansion
piston arranged in a first cylinder. A second expansion piston is
arranged in a second cylinder and operably coupled to the first
expansion piston, wherein the second cylinder is fluidly coupled to
the first cylinder. A compression piston is arranged in a third
cylinder and operably coupled to the first expansion piston,
wherein the third cylinder is fluidly coupled to received a working
fluid from the second cylinder and transfer the working fluid to
the first cylinder.
[0009] According to another aspect of the invention, a heat engine
having a working fluid is provided. The heat engine includes a
first set of cylinders having a first expansion piston fluidly and
operably coupled to a second expansion piston. A first compression
piston is fluidly and operably coupled to the first expansion
cylinder and the second expansion cylinder. Wherein the first set
of cylinders is arranged in a first closed cycle to provide
unidirectional flow of the working fluid.
[0010] According to yet another aspect of the invention, a method
of operating a closed cycle heat engine is provided. The method
includes heating a working fluid. Expanding the heated working
fluid into a first cylinder to move a first expansion piston to a
first position. The heated working fluid is flowed into a second
cylinder to move a second expansion piston to a second position.
The working fluid is flowed from the first cylinder and the second
cylinder to the third cylinder. The working fluid is compressed in
the third cylinder with the compression piston. The working fluid
is flowed from the third cylinder to the first cylinder.
[0011] According to yet another aspect of the invention, a heat
engine is provided. The heat engine includes at least two expansion
pistons fluidly coupled to each other, each expansion piston being
arranged in an expansion cylinder. At least one compression piston
is fluidly coupled to the at least two expansion pistons, each
compression piston being arranged in a compression cylinder. A
drive linkage is operably coupled to the at least two expansion
pistons and the at least one compression piston, the drive linkage
arranged in a crankcase, wherein the crankcase is fluidly coupled
to the expansion cylinders and the compression cylinders. A
pressurized vessel is also provided that is fluidly coupled to the
crankcase, wherein the pressurized vessel is arranged to add
pressurized gas to the crankcase in response to a change in the
operation of the heat engine.
[0012] According to yet another aspect of the invention, a closed
cycle heat engine is provided. The closed cycle heat engine
includes a first expansion piston arranged in a first cylinder. A
second expansion piston arranged in a second cylinder and operably
coupled to the first expansion piston, wherein the second cylinder
is fluidly coupled to the first cylinder. A compression piston is
arranged in a third cylinder and operably coupled to said first
expansion piston, wherein the third cylinder is fluidly coupled to
received a working fluid from the second cylinder and transfer the
working fluid to the first cylinder. A drive linkage is coupled to
the first piston, the second piston and the third piston, wherein
the drive linkage is a cam plate or an articulated crankshaft. A
drive case is coupled to the drive linkage, the drive case being
operated at a pressure less than or equal to a minimum pressure of
the working fluid that occurs in the first cylinder and the second
cylinder during operation of the engine. A regenerator is arranged
to transfer thermal energy from the working fluid flowing from the
second cylinder to the third cylinder to the working fluid flowing
from the third cylinder to the first cylinder, wherein the
regenerator is a counter flow heat exchanger. A heater thermally
coupled between the regenerator and the first cylinder. A cooler is
thermally coupled between the third cylinder and the regenerator. A
first valve fluidly coupled between the heater and the first
cylinder. A second valve is fluidly coupled between the second
cylinder and the regenerator. A first check valve is fluidly
coupled to the third cylinder to allow the working fluid to flow
into the third cylinder. A second check valve is fluidly coupled to
the third cylinder to allow the working fluid to flow from the
third cylinder.
[0013] According to yet another aspect of the invention, a heat
engine having a working fluid is provided. A heat engine includes a
first set of cylinders having a first expansion piston fluidly and
operably coupled to a second expansion piston and a first
compression piston fluidly and operably coupled to the first
expansion cylinder and the second expansion cylinder, wherein the
first set of cylinders is arranged in a first closed cycle to
provide unidirectional flow of the working fluid, wherein the first
set of cylinders and said second set of cylinders are arranged 90
degrees apart. A second set of cylinders is operably coupled to the
first set of cylinders, the second set of cylinders having a third
expansion piston fluidly and operably coupled to a fourth expansion
piston and a second compression piston fluidly and operably coupled
to the third expansion cylinder and the fourth expansion cylinder,
wherein the second set of cylinders is arranged in a second closed
cycle to provide unidirectional flow of the working fluid. A
regenerator is thermally coupled to the first closed cycle and the
second closed cycle, wherein the regenerator is arranged in the
portion of the first closed cycle between the second expansion
piston and the first compression piston, and is arranged in the
portion of the second closed cycle between the fourth expansion
piston and the second compression piston. A heater is coupled to
the first closed cycle and the second closed cycle to transfer
thermal energy to the working fluid. A cooler is coupled to the
first closed cycle and the second closed cycle to transfer thermal
energy from the working fluid. A drive case is operably coupled to
the first set of cylinders and the second set of cylinders, the
drive case having an operating pressure less than or equal to a
minimum pressure of the working fluid in the first cylinder and the
second cylinder during the operation of the heat engine.
[0014] According to yet another aspect of the invention, a method
of operating a closed cycle heat engine is provided. The method
includes the steps of heating a working fluid. Expanding the heated
working fluid into a first cylinder to move a first expansion
piston to a first position. Flowing the heated working fluid into a
second cylinder to move a second expansion piston to a second
position. Flowing the working fluid from the first cylinder and the
second cylinder to the third cylinder. Compressing the working
fluid in the third cylinder with the compression piston. Flowing
the working fluid from the third cylinder to the first cylinder.
Transferring thermal energy from the working fluid flowing from the
second cylinder to the third cylinder to the working fluid flowing
from the third cylinder to the fourth cylinder before the step of
heating the working fluid. Cooling the working fluid before the
step of compressing the working fluid in the step where the heated
working fluid is flowed into the second cylinder. Dwelling the
second expansion piston at the second position when the working
fluid flows from the first cylinder to the third cylinder. Finally
a drive case is pressurized to a first pressure less than or equal
to a pressure of the working fluid in the first cylinder and the
second cylinder when the second expansion piston is in the second
position.
[0015] These and other advantages and features will become more
apparent from the following description taken in conjunction with
the drawings.
BRIEF DESCRIPTION OF THE DRAWING
[0016] The subject matter, which is regarded as the invention, is
particularly pointed out and distinctly claimed in the claims at
the conclusion of the specification. The foregoing and other
features, and advantages of the invention are apparent from the
following detailed description taken in conjunction with the
accompanying drawings in which:
[0017] FIG. 1 is a schematic block diagram illustration of a heat
engine in accordance with an embodiment of the invention;
[0018] FIG. 2 is a schematic block diagram illustration of the heat
engine of FIG. 1 with the first expansion piston in the bottom dead
center position;
[0019] FIG. 3 is a schematic block diagram illustration of the heat
engine of FIG. 1 with the second expansion piston in the bottom
dead center position;
[0020] FIG. 4 is a schematic block diagram illustration of the heat
engine of FIG. 1 during the adiabatic compression of the working
fluid by the compression piston and the first expansion piston at
the top dead center position;
[0021] FIG. 5 is a schematic block diagram illustration of the heat
engine of FIG. 1 with the first and second expansion pistons at the
top dead center position;
[0022] FIG. 6 is an illustration of an exemplary pressure-volume
diagram for the thermodynamic cycle of the heat engine of FIGS.
1-5.
[0023] FIG. 7 is a plan view illustration of an alternate
embodiment heat engine having eight expansion pistons;
[0024] FIG. 8 is another plan view illustration of the heat engine
of FIG. 7;
[0025] FIG. 9 is a schematic illustration of the heat engine of
FIG. 7;
[0026] FIG. 10 is a schematic illustration of another embodiment
heat engine having crankcase pressure control;
[0027] FIG. 11 is a partial perspective view illustration of an
alternate embodiment heat engine having a crank arrangement;
[0028] FIG. 12 is a side plan view illustration of the heat engine
of FIG. 11;
[0029] FIG. 13 is a partial perspective view illustration of an
alternate embodiment heat engine having six sets of cylinders;
and,
[0030] FIG. 14 is a top plan view illustration of the heat engine
of FIG. 13.
[0031] The detailed description explains embodiments of the
invention, together with advantages and features, by way of example
with reference to the drawings.
DETAILED DESCRIPTION OF THE INVENTION
[0032] Referring to FIGS. 1-5 and exemplary embodiment of an
external heat engine 20 is shown. The heat engine 20 utilizes an
external heat source 22 to deliver heat energy to a working gas in
the heat engine 20. The heat engine 20 is a closed system that
incorporates a hot heat exchanger 24, a cold heat exchanger 26, and
a regenerator 28. The heat engine 20 further includes a housing 30
that includes at least three of cylinders 34, 36, 38. The first or
compression cylinder 34 contains a compression piston 32, for
compressing the cold working gas. The compression piston 32 is
coupled to two expansion pistons 40, 42 that are contained within
expansion cylinders 36, 38 respectively. Each of the pistons is
coupled to a drive linkage 44. The heat engine 20 also includes
valves 46, 48, 50, 52 to control the flow of the working gas
through the heat engine 20.
[0033] The heat engine 20 utilizes a unidirectional flow of the
working gas from the compression cylinder 34 through the
regenerator 28 to the hot heat exchanger 24 and to the expansion
cylinders 36, 38 and back again. As will be made clearer herein,
the unidirectional flow of the gas provides advantages by causing
substantially all of the compressed working gas through the hot
heat exchanger 24, since all of the working gas has to propagate
through the heat engine 20 in one direction. The heat engine 20
also provides advantages by utilizing adiabatic compression
followed by an isobaric heating process in the hot heat exchanger
24.
[0034] Referring now to FIG. 1, the first expansion piston 40 has
an intake valve 46 which opens and allows high pressure (Pmax),
high temperature (Tmax) working gas to flow into the first
expansion cylinder 36 as the first expansion piston 40 moves. Since
the compression piston 32 and the first expansion piston 40 move
together there is a small overall volume change in this first
expansion of the working gas. The effect is that the pressure and
temperature of the working gas remains substantially constant which
resembles an isobaric/isothermal expansion. Once the first
expansion piston 40 reaches the bottom dead center position shown
in FIG. 2, the intake valve 46 closes and the second expansion
piston 42 that was dwelling at top dead center position is allowed
to move. As will be explained in more detail herein, the movement
of the pistons 32, 40, 42 are defined by the drive linkage 44. In
the exemplary embodiment, the drive linkage 44 is a cam plate
having at least one profile.
[0035] The volume in the first expansion cylinder 36 makes up the
initial expansion volume for the second expansion cylinder 38. The
expansion of the working gas in the second expansion cylinder 38
occurs substantially adiabatically. FIG. 3 illustrates that while
the second expansion piston 42 is moving, the first expansion
piston 40 is dwelling at the bottom dead center position. After the
second expansion piston 42 reaches the bottom dead center position,
the working gas will have expanded to the minimum pressure (Pmin)
of the heat engine 20.
[0036] After the second expansion piston 42 reaches the bottom dead
center position, an exhaust valve 48 opens to allow displacement of
the working gas towards the cold heat exchanger 26. It should be
appreciated that the heat engine 20 may be arranged, through the
configuration of the drive linkage 44 for example, to displace the
working gas from the expansion cylinders 36, 38 either
simultaneously, or sequentially as is shown in FIG. 4. When the
working gas is displaced from the expansion cylinders 36, 38 it
still contains a substantial amount of thermal energy. The working
gas first passes through the regenerator 28, which extracts the
thermal energy of the working gas flowing towards the cold heat
exchanger 26. In the exemplary embodiment, the regenerator 28 is a
counter flow heat exchanger, which can be a multiple plate or tube
in tube type exchanger where hot gas is flowing in one direction
through a chamber and cold gas is flowing in the opposite direction
in an adjacent chamber. The primary function of regenerator 28 is
to extract heat from the exhaust working gas (i.e. the working gas
flowing toward the cold heat exchanger 26) before it gets to the
cold heat exchanger 26 and deliver it to the cold compressed
working gas flowing from the compression cylinder 34 before it gets
to the hot heat exchanger 24.
[0037] After the working gas passes through the regenerator 28 it
then goes to the cold heat exchanger 26 where substantially all of
the non-recoverable thermal energy is extracted and rejected to the
atmosphere through a radiator 54. The cold working gas leaving the
cold heat exchanger 26 then enters the compression cylinder 34
where the compression piston 32 compresses the working gas
adiabatically, as is shown in FIG. 5. Once the pressure in the
compression cylinder 34 reaches a maximum pressure (Pmax) a check
valve 50 opens and allows the compressed working gas to be
displaced out of the compression cylinder 34 towards the
regenerator 28. A second check valve 52 is arranged adjacent to the
inlet to the compression cylinder 34 to prevent flow back towards
the cold heat exchanger 26. The cold working gas flowing through
the regenerator 28 is heated by the exhaust working gas flowing in
the opposite direction as discussed above, and leaves the
regenerator 28 at a temperature below the maximum operating
temperature (Tmax). The working gas then passes through the hot
heat exchanger 24 where thermal energy from an external source is
once again used to heat the working gas to the maximum temperature
(Tmax) and the thermodynamic cycle repeats.
[0038] Another way of describing the operation of the heat engine
20 is with a pressure-volume ("PV") diagram 100 as illustrated in
FIG. 6. A PV diagram is typically used to describe thermal cycles.
The PV diagram 100 is useful in the calculation of the amount of
work done by the heat engine 20, which is the integral of the
pressure with respect to volume. The work can be quickly calculated
from the PV diagram 100 by determining the area enclosed by the
cycle. In general, when the operation of the heat engine moves
clockwise about the PV diagram, positive work is created.
[0039] The cycle starts at point 102, which corresponds to the
position of the heat engine 20 in FIG. 1. At this point, the heat
engine 20 is at its minimum pressure and volume. As the hot working
gas is allowed to pass through the intake valve 46 into the
expansion cylinder 36, the pressure in the heat engine 20 increases
while maintaining the volume substantially constant. Once the
maximum pressure has been reached, the intake valve 46 closes and
the cycle is at point 104, which corresponds to FIG. 2.
[0040] The drive linkage 44 is arranged to allow the second
expansion piston 42 to then move, thereby allowing the working gas
to expand into the second expansion cylinder 38. This allows the
volume of the heat engine 20 to increase, while also decreasing the
pressure as the cycle moves from point 104 to point 106. After
reaching point 106, the exhaust valve 48 is opened, allowing the
working gas to flow from the expansion cylinders 36, 38, through
the regenerator 28 and cold heat exchanger 26, and into the
compression cylinder 34. It should be appreciated that while FIGS.
4 and 5 illustrate the expansion pistons 40, 42 moving serially,
the drive linkage 44 may also be arranged to move both expansion
pistons 40, 42 simultaneously. As the working gas flows from the
expansion cylinders 36, 38 to the compression cylinder 34, the
pressure drops and the volume increases until the cycle reaches
point 108, which corresponds to the position of the heat engine 20
shown in FIG. 5.
[0041] To finish the thermodynamic cycle, the cold working gas
flows from back from the compression cylinder 34, absorbing heat in
the regenerator 28 and hot heat exchanger 24. As the heat engine 20
returns to the position shown in FIG. 1, the volume drops while the
pressure is maintained at a nearly constant level. As discussed
above, since the cycle illustrated in FIG. 6 moves in a clockwise
direction, the heat engine 20 creates positive or useful work.
[0042] An alternate embodiment heat engine 200 is shown in FIGS.
7-10. In this embodiment, the heat engine 200 includes four sets of
pistons 202. Each set of pistons 202 includes a compression piston
32, a first expansion piston 40 and a second expansion piston 42.
Each set of pistons 202 individually operates in the same
thermodynamic cycle as described herein above with respect to FIGS.
1-5. The sets of pistons 202 are arranged radially about center
axis 204 of the engine housing 206 such that the sets of pistons
are 90.degree. apart.
[0043] As best seen in FIG. 8 and FIG. 9, the heat engine 200
includes a drive linkage 208, such as a cam plate for example,
having at least a first cam profile 210 and a second cam profile
212. In this embodiment, the motion of the first expansion piston
40 and the compression piston 32 are determined by followers 214,
216 that engage the first cam profile 210. Similarly, the second
expansion piston 42 has a follower 218 that engages the second cam
profile 212. The cam profiles 210, 212 are arranged to have
geometry suitable to provide the timing and motion of pistons 32,
40, 42 to facilitate the thermodynamic cycle illustrated in FIG. 6.
In this embodiment, the followers 214, 216, 218 include a tie rod
and a roller. Other components (not shown) may also be utilized in
maintaining the followers 214, 216, 218 engaged with the drive
linkage 208 as is known in the art. It should be appreciated that
in other embodiments, the heat engine 200 includes a third cam
profile for the compression piston 32, such that compression piston
32 is not in phase with the expansion pistons 40, 42. It should
further be appreciated that the drive linkage 208 may also be in
the form of a camshaft instead of a cam plate.
[0044] Referring now to FIG. 9, it can be seen that each of the
sets of pistons 202 are in a different phase of the thermal cycle
of FIG. 6. This allows the heat engine 200 to operate smoothly at a
substantially constant revolutions-per-minute ("RPM"). Each of the
expansion pistons 40, 42 are fluidly coupled to valves 46, 48 as
described herein above. Opposite each of the first expansion
pistons 40, the intake valves 46 are coupled together by a manifold
to a single conduit 220 that allows each of the first expansion
pistons 40 to be coupled to a single hot heat exchanger 24.
Similarly, opposite each of the second expansion pistons 42, the
exhaust valves 48 are coupled together by a manifold to a conduit
222 that provides a single connection to the regenerator 28.
[0045] The regenerator 28 is coupled to a conduit 224 that connects
the regenerator 28 to the cold heat exchanger 26. The cold heat
exchanger 26, in turn is coupled together by a manifold a single
conduit 226 that distributes the working gas to the compression
cylinders 34 via second check valve 52. After compressing the
working gas, each of the compression cylinders 34 is coupled to a
manifold 228 via check valves 50. A conduit 230 couples the
manifold 228 to the regenerator 28. The regenerator 28 in turn is
coupled to the hot heat exchanger 24 by conduit 232 to complete the
fluid circuit.
[0046] Another embodiment of a heat engine 300 is illustrated in
FIG. 10. Similar to the embodiments described above, the heat
engine 300 includes one or more sets of pistons 302 having a first
expansion piston 40, a second expansion piston 42 and a compression
piston 32. The heat engine 300 also includes a hot heat exchanger
24, a cold heat exchanger 26 and a regenerator 28 as described
herein above.
[0047] The expansion pistons 40, 42 and the compression piston 32
are operably coupled to a drive linkage 304 positioned within a
crankcase 306. Fluidly coupled to the crankcase 306 is a first high
pressure vessel or tank 308 (e.g. 2000 psi) and a second
low-pressure vessel or tank 310 (e.g. 100 psi). The tanks 308, 310
are arranged to add and subtract gas from the heat engine 300
depending on the desired operating speed. It should be appreciated
that the tanks 308, 310 may include one or more components (not
shown), such as valves 312, pumps 314 and sensors 316 for example,
to facilitate the flow of gas. In one embodiment, the pressure in
the crankcase 306 is maintained at or less than the minimum
pressure realized by the heat engine during the thermodynamic
cycle, such as the pressure at points 102, 108 on the PV diagram of
FIG. 6. In one embodiment, the pressure sensor 316 measures the
pressure in conduit 318 between the cold heat exchanger 26 and the
compression cylinder 34. By adjusting the pressure of the crankcase
306 at this level, any leakage of the working gas from the
cylinders will flow into the crankcase 306 where it can be
recycled. The maintaining of pressure in the crankcase 306 also
provides advantages in that it also minimizes the differential
pressure across the piston seals (not shown) reducing the force on
the drive linkage 304.
[0048] The tanks 308, 310 are also coupled to conduit 320 between
the regenerator 28 and the compression piston 32. A pump 324 is
coupled between the tanks 308, 310 to transfer working gas from the
low-pressure tank 310 to the high-pressure tank 308. It should be
appreciated that the conduits connecting the tanks 308, 310 to the
crankcase 306 and conduit 320 are illustrated as being separately
connected to the tanks 308, 310, however, it is contemplated that
other arrangements may also be utilized.
[0049] During operation, the tanks 308, 310 are arranged to remove
working gas from the conduit 320 into low-pressure tank 310 when
power needs to be reduced. Once the valve that connects
low-pressure tank 310 to conduit 320 is closed, the pump 314
transfers the working gas to high-pressure tank 308. As the demand
for power increases, working gas flows from high-pressure tank 308
back into conduit 320. This provides an advantage in maintaining
the heat engine 300 at a constant RPM while varying the output
power. This also provides advantages in balancing the amount of
working gas in the heat engine 300 at any given time.
[0050] Another embodiment heat engine 350 is illustrated in FIGS.
11-12. Similar to the embodiments described above, the heat engine
has a plurality of cylinders arranged in a housing 30. It should be
appreciated that the heat engine 350 also includes a regenerator
28, heat exchangers 24, 26 and valves 46, 48, 50, 52 as described
herein, however these components are not illustrated in FIGS. 13-14
for purposes of clarity. Alternately, heat engine 350 may also
include tanks 308, 310 as described herein. The heat engine 350
further includes a set of pistons including first expansion piston
40, second expansion piston 42 and compression piston 32. Each
piston 32, 40, 42 has an associated connector rod 352. Unlike the
embodiments described above, in this embodiment the compression
piston 32 and second expansion piston 42 are coupled to a first
drag link 354. The first drag link 354 pivots about a shaft 356.
The coupling of the second expansion piston 42 and the compression
piston 32 provides advantages in allowing the use of a drive
linkage 44 that includes a crank assembly 362 where the second
expansion piston 42 can dwell at the top-dead-center position and
the compression piston 32 can dwell at the bottom-dead-center
position. The first expansion piston 40 is coupled to a second drag
link 358, which pivots on a shaft 360.
[0051] The drive linkage 44 includes a top linkage 364, a bottom
linkage 366 and a crank arm 368 which are coupled for rotation
about a pin 370. The bottom linkages 366 are coupled to the drag
link 354 adjacent the connector rod 352 for the first expansion
piston 40 and the compression piston 32. The top linkage 364 pivots
about a shaft 372 that fixes the end of the top linkage 364 to the
crankcase 306. Each crank arm 368 in turn is coupled one of the
lobes 374 in the crank assembly 362. It should be appreciated that
the motion of the pistons 32, 40, 42 is defined by the linkages
354, 366, the crank arm 368 and the trajectory of the connection
point on lobes 374. In this embodiment, the motion of the expansion
pistons 40, 42 is arranged such that the working fluid is exhausted
from both expansion cylinders 36, 38 simultaneously. The crank
assembly 362 further includes a drive shaft 376 that transfers the
rotational movement generated by the heat engine 350. It should be
appreciated that the heat engine 350 also includes bearing housings
that are not shown for purposes of clarity.
[0052] In this embodiment, the thermodynamic operating cycle is
defined by the operating modes of the compression piston 32 and
expansion pistons 40, 42. The cycle starts by adiabatically
compressing a cold working fluid. The working fluid then passes
through a heat exchanger, such as hot heat exchanger 24 (FIG. 1)
for example, where it is heated. Valve 46 (FIG. 1) over the first
expansion piston 40 opens to allow the hot working fluid to flow
into the first expansion cylinder 36. While the first expansion
piston 40 is moving down the working fluid is expanding
isothermally (working fluid pressure reduces while the temperature
stays constant). Once the first expansion piston 40 reaches the
bottom of travel path, the valve 46 that was opened then closes.
The volume of the working fluid within first expansion cylinder 36
becomes the initial expansion volume for the working fluid in the
second expansion cylinder 38. While the second expansion piston 42
is moving down the working fluid is expanding adiabatically (e.g.
both the pressure and temperature of the working fluid will be
reduced). Once the second expander piston 42 reaches the bottom of
its travel path, the exhaust valve 48 (FIG. 1) opens and both the
expansion pistons 40, 42 substantially simultaneously exhaust the
lower pressure and temperature working fluid from the expansion
cylinders 36, 38 to the regenerator 28. While the exhaust working
fluid passes through the regenerator 28, heat is transferred to the
cold compressed working fluid that is flowing from the compression
cylinder 34 to the hot heat exchanger 24. After leaving the
regenerator 28, any residual heat remaining in the working fluid is
rejected through a cold heat exchanger 26 by an appropriate medium,
such as cooling water for example. The cold working fluid is then
in a position to start the cycle again.
[0053] In this embodiment, the second expansion piston 42 has a
smaller cross-sectional area than the first expansion piston 36.
The sizing of the expander pistons 40, 42 and compression piston 32
may be determined by the temperature differential between the
heating source 22 (FIG. 1) and the cold medium that removes heat
from the radiator 54 (FIG. 1). The cold medium is typically the
atmosphere (e.g. atmospheric air temperature), but alternately may
use other types of mediums such as river water or even liquid
propane for example. The expansion ratio is defined as
T.sub.hot/T.sub.cold. For example, if the hot side is 700 K and the
cold side is 300 K then the expansion volume ratio is 2.333:1. In
this example, the ratio between the initial expansion volume in the
first expansion cylinder 36 and the total expansion volume in both
expansion cylinders 36, 38 is large. For high temperature
differentials between the hot heat exchanger 24 and the cold heat
exchanger 26, the second expansion piston 42 will have a larger
surface area than the first expansion piston 40. For low
temperature differentials, such as for steam condensing, the ratio
is approximately 1:1.25. In these low temperature differentials,
the hot side may be between 370 K and 425K with the cold side being
at atmospheric temperature. In these embodiments, the first
expansion piston 40 will be larger than the second expansion piston
42. Further, the piston diameters and stroke lengths may be
determined by the desired amount of power generated at a specific
frequency. The higher the frequency, the smaller the expansion
pistons 40, 42 will be for a given power. In some embodiments, the
desired operating frequency is between 5-10 Hz. Operation of the
heat engine at this frequency provides advantages in diminishing
flow losses and maintenance issues associated with wear items.
[0054] Another embodiment heat engine 380 is illustrated in FIGS.
13-14. In this embodiment, the heat engine 380 is comprised of
multiple sets of pistons 382 each of which are substantially the
same as the embodiment described with reference to FIGS. 11-12. It
should be appreciated that the heat engine 380 also includes a
regenerator 28, heat exchangers 24, 26 and valves 46, 48, 50, 52 as
described herein, however these components are not illustrated in
FIGS. 13-14 for purposes of clarity. Alternately, heat engine 380
may also include tanks 308, 310 as described herein. Each set of
pistons 382 includes a compression piston 32, a first expansion
piston 40, and a second expansion piston 42. The compression piston
32 and the second expansion piston 42 are coupled by a drag link
354 as described above Each set of pistons 382 is coupled by a
drive linkage 44 to a crank assembly 384 having a crankshaft 386.
The crankshaft 386 couples each of the sets of pistons 382 to
transfer the power generated during operation to an external
process, such as an electrical generator for example. It should be
appreciated that the sets of pistons 382 cooperate to operate in
sequence to provide substantially continuous rotation of the
crankshaft 386.
[0055] It should be appreciated that while the embodiments
described herein refer to a heat engine having a single compression
piston and cylinder, however the claimed invention should not be so
limited. In other embodiments, the heat engine may have multiple
compression cylinders while still providing the unidirectional flow
of the working fluid. In one embodiment, the working fluid is
divided between two compression cylinders.
[0056] The heat engine disclosed herein provides a number of
advantages over oscillating flow engines of the prior art. The heat
engine eliminates the problem of mass transfer efficiency in that
all of the working gas that is compressed gets to the hot side of
the heat engine to deliver useful work. Utilizing unidirectional
flow a counter flow heat exchanger instead of the traditional
regenerators used in oscillating flow engines provides another
advantage. Counter flow heat recovery is more efficient than
oscillating flow regenerators due to the ability of counter flow
heat exchangers to maintain a higher thermal gradient across the
length of the regenerator.
[0057] While the invention has been described in detail in
connection with only a limited number of embodiments, it should be
readily understood that the invention is not limited to such
disclosed embodiments. Rather, the invention can be modified to
incorporate any number of variations, alterations, substitutions or
equivalent arrangements not heretofore described, but which are
commensurate with the spirit and scope of the invention.
Additionally, while various embodiments of the invention have been
described, it is to be understood that aspects of the invention may
include only some of the described embodiments. Accordingly, the
invention is not to be seen as limited by the foregoing
description, but is only limited by the scope of the appended
claims.
* * * * *