U.S. patent application number 10/420640 was filed with the patent office on 2004-02-12 for fluidic-piston engine.
Invention is credited to Conde, Ricardo, Faroughy, Dara.
Application Number | 20040025489 10/420640 |
Document ID | / |
Family ID | 25299874 |
Filed Date | 2004-02-12 |
United States Patent
Application |
20040025489 |
Kind Code |
A1 |
Conde, Ricardo ; et
al. |
February 12, 2004 |
Fluidic-piston engine
Abstract
An external combustion engine includes: a plurality of cavities;
a compressible working fluid in fluid communication between each
pair of adjacent cavities; and a plurality of hydraulic linkages in
reciprocal phase communication between each pair of alternate
cavities. In an alternative embodiment the external combustion
engine includes: a plurality of cavities; a compressible working
fluid in fluid communication between each pair of adjacent
cavities; and a plurality of articulated mechanical linkages in
reciprocal phase communication between each pair of alternate
cavities. In another alternative embodiment the external combustion
engine includes: at least four upright cavities disposed
substantially equidistant from a central upright axis; a
compressible working fluid in fluid communication between each pair
of adjacent cavities; and at least one linkage in reciprocal phase
communication between each pair of alternate cavities. The at least
one linkage may comprise a hydraulic linkage. Alternatively, the at
least one linkage may comprise an articulated mechanical
linkage.
Inventors: |
Conde, Ricardo; (New Salem,
MA) ; Faroughy, Dara; (Athol, MA) |
Correspondence
Address: |
CANTOR COLBURN, LLP
55 GRIFFIN ROAD SOUTH
BLOOMFIELD
CT
06002
|
Family ID: |
25299874 |
Appl. No.: |
10/420640 |
Filed: |
April 22, 2003 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10420640 |
Apr 22, 2003 |
|
|
|
09847141 |
May 2, 2001 |
|
|
|
6568169 |
|
|
|
|
Current U.S.
Class: |
60/39.6 ; 60/517;
60/520 |
Current CPC
Class: |
F02G 2244/50 20130101;
F02G 2270/70 20130101; F01B 21/02 20130101; F02G 1/044
20130101 |
Class at
Publication: |
60/39.6 ; 60/520;
60/517 |
International
Class: |
F02C 005/00 |
Claims
What is claimed is:
1. An external combustion engine comprising: a plurality of
cavities; a compressible working fluid in fluid communication
between each pair of adjacent said cavities; and a plurality of
hydraulic linkages in reciprocal phase communication between each
pair of alternate said cavities.
2. An external combustion engine comprising: a plurality of
cavities; a compressible working fluid in fluid communication
between each pair of adjacent said cavities; and a plurality of
articulated mechanical linkages in reciprocal phase communication
between each pair of alternate said cavities.
3. An external combustion engine comprising: at least four upright
cavities disposed substantially equidistant from a central upright
axis; a compressible working fluid in fluid communication between
each pair of adjacent said cavities; and at least one linkage in
reciprocal phase communication between each pair of alternate said
cavities.
4. An engine as defined in claim 3 wherein said at least one
linkage comprises an hydraulic linkage.
5. An engine as defined in claim 3 wherein said at least one
linkage comprises an articulated mechanical linkage.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 09/847,141 filed on May 2, 2001, the contents
of which are incorporated herein in their entirety by reference
thereto.
BACKGROUND
[0002] Stirling engines refer to a specific class of external
combustion heat engines that convert heat differentials into
mechanical energy with relatively high conversion efficiencies.
Such efficiencies for a class of optimized Stirling engines can
surpass most known air-breathing internal combustion engines, and
utilize a regenerator to store or release fluid heat during the
engine cycle. Such Stirling engines can approach the efficiency of
an ideal Carnot cycle.
[0003] External combustion engines can be used in a variety of
applications. For example, as prime movers, cooling systems,
cryogenic coolers, heat pumps or pressure generators in a variety
of design forms and operating sizes. Current applications range in
size from large power generators to miniature engines for
artificial hearts. Stirling engines thus far developed vary in
output power from as little as a few watts to as much as 1 MW (1
MW=1341 hp). High temperature Stirling engines may operate at
temperatures exceeding 1000 K, with mean working fluid pressures in
the range of one atmosphere to as high as 20 MPa (1 MPa.apprxeq.10
atmospheres).
[0004] Conventional Stirling engines utilize the roughly
steady-state expansion of a highly compressed fixed number of light
molecular mass working fluid, such as helium, hydrogen or air, in
contact with a heat source at a substantially fixed temperature for
their power stroke; followed by forced convection heat transfer or
gas cooling by contact with a heat sink to generate engine speeds
ranging from low to high frequency, typically measured in
revolutions per minute.
[0005] Since the essential ingredient needed to operate a Stirling
engine is an appropriate external heat source such as, for example,
solar, natural gas, fossil fuel, oil, coal, waste heat or
geothermal energy; this makes the Stirling engine well suited for
not only terrestrial applications but also for large scale space
and underwater applications, including spacecraft and
submarines.
[0006] Any conventional (non-rotary) type Stirling engine requires
simple components for its operation. It requires internal pistons
as the means for displacing and compressing the working fluid
therein and to generate output power. The pistons receive work
during their up-stroke (compression), and generate greater work
during their down-stroke (expansion), followed by a transfer of
heat at some temperature by the working fluid to the surrounding
heat sink. The power pistons are usually equipped with high
performance fluid rings to assure and maintain a high pressure
differential between their upper and lower faces.
[0007] Regenerators, which are placed between the hot and cold heat
exchangers, optimally recycle the heat supply and transfer process
by acting as thermodynamic sponges. Their function is to receive
heat from the working fluid during the fluid passage from the high
to low temperature space, and to release heat to the working fluid
during the fluid passage back from the low to high temperature
space.
[0008] Generally, the system efficiency and the cyclic work output
are functions of both thermodynamic variables, such as pressure,
and the internal volumetric compression ratio. From a thermodynamic
standpoint, an ideal reversible four-path Stirling cycle when
depicted in the pressure (P) versus volume (V) diagram consists of
two isothermal (constant temperature) and two isochoric (constant
volume) processes in sequence. When depicted in the temperature (T)
versus entropy (S) diagram, the heat energy transfer in the process
is proportional to the area enclosed in the T-S diagram (SdT).
Likewise, the work done by the engine is proportional to the area
enclosed on the P-V diagram (PdV).
[0009] Disadvantages of conventional Stirling engines include the
use of relatively expensive and heavy materials, such as
Inconel.RTM. and other alloy steels, for the high temperature
structural components (e.g., pistons, cylinders and regenerators).
In addition, the use of seals at the piston connecting rod is a
serious factor for limiting the useful life of the engine and is a
well-known cause for downgrading the engine's overall efficiency.
Further, these seals are specialized designs and are
correspondingly expensive to produce, and typically do not perform
an adequate function in preventing leakage of high-pressure working
fluid.
[0010] Conventional high temperature Stirling engines generally
operate at high rotational velocities of typically about 3000 RPM.
This is one prime reason for the reduction of the regenerator
efficiency, and causes a marked increase in frictional losses from
the high velocity motion of the working fluid. Other adverse
effects due to high temperatures, typically about 720.degree. C.,
include the high heat losses due to the blackbody radiation.
Although the low to middle temperature types of Stirling engines
(<450.degree. C.) can alleviate some of these losses, the price
to pay is a lower Carnot efficiency. There also remain numerous
other drawbacks, deficiencies, and disadvantages associated with
conventional Stirling engines. One disadvantage is the premature
failure of the seal between the connecting rod, which exhibits
complex translational and rotational motions, and the mechanical
drive linkage, despite expensive seal designs. A further
disadvantage is the mechanical coupling of all adjacent pistons
that results in a fixed phase angle relationship, which prevents
optimization of the engine.
[0011] Since a Stirling engine is a device based on an oscillatory
and forced convection of the working fluid, parasitic losses of the
engine are related to the frequency of the operation. The higher
the frequency the worse are certain performance losses. For a fixed
target power, the lower frequency engine may be preferable.
Reduction of unnecessary dead space volumes that do not participate
in power generation and overall operation is desirable in the
design of an optimized Stirling engine.
[0012] One example of a Stirling engine is provided by U.S. Pat.
No. 4,199,945 to Finkelstein, which describes a four cylinder,
double acting engine in which the four cylinders are oriented at
least partially horizontal with the four hot heat exchangers
separated. For large engines of the design provided by Finkelstein,
separation of the heat exchangers can be several meters apart and
thus require four separate burner systems. Moreover, the horizontal
configuration taught by Finkelstein places lateral loads on piston
shaft bearings, rings and seals all reducing life of the engine.
This condition is further aggravated when high power is desired as
the size and weight of the piston can be significant. Finkelstein
also describes an eight cylinder embodiment in FIG. 5, which is
basically two four cylinder engines which are opposed to each
other. In this case, he has linked the acting power piston of one
engine to the displacement piston of the opposed, different, engine
thereby achieving the necessary input. Problematically, the heat
input on both ends has to be perfectly balanced for the engine to
have an equal stroke length in both directions. Thus, the eight
cylinder embodiment of Finkelstein would require the use of control
system to balance the piston motion in both directions.
SUMMARY
[0013] The above-described and other drawbacks and deficiencies are
overcome or alleviated by an external combustion engine comprising:
a plurality of cavities; a compressible working fluid in fluid
communication between each pair of adjacent cavities; and a
plurality of hydraulic linkages in reciprocal phase communication
between each pair of alternate cavities.
[0014] In an alternative embodiment an external combustion engine
includes: a plurality of cavities; a compressible working fluid in
fluid communication between each pair of adjacent cavities; and a
plurality of articulated mechanical linkages in reciprocal phase
communication between each pair of alternate cavities.
[0015] In another alternative embodiment an external combustion
engine includes: at least four upright cavities disposed
substantially equidistant from a central upright axis; a
compressible working fluid in fluid communication between each pair
of adjacent cavities; and at least one linkage in reciprocal phase
communication between each pair of alternate cavities. The at least
one linkage may comprise a hydraulic linkage. Alternatively, the at
least one linkage may comprise an articulated mechanical
linkage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Referring now to the drawings wherein like elements are
numbered alike in the several Figures:
[0017] FIG. 1 is a schematic representation of a prior art Stirling
engine;
[0018] FIG. 2 is a schematic representation of a first exemplary
embodiment Fluidic-Piston engine;
[0019] FIG. 3 is a schematic representation of a second exemplary
embodiment Fluidic-Piston engine;
[0020] FIG. 4 is a schematic representation of a third exemplary
embodiment Fluidic-Piston engine; and
[0021] FIG. 5 is a schematic representation of a fourth exemplary
embodiment Fluidic-Piston engine.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0022] As shown in FIG. 1, a prior art double-acting multi-cylinder
Stirling engine is indicated generally by the reference numeral 10.
The engine 10 has one reciprocating element 12a-12d per cylinder
14a-14d, respectively, and is generally designed such that the
compression space 16a-16d of each cylinder 14a-14d, respectively,
is connected through an associated heat exchanger 18a-18d,
respectively, to the expansion space 20a-20d in an adjacent
cylinder 14a-14b, respectively, via associated passageways 22a-22d,
24a-24d. As used herein, the term heat exchanger shall include a
cooler, a regenerator or a heater, or any combination thereof.
[0023] Compression space 16a of cylinder 14a is connected through
regenerator 18a via passageways 22a and 24a to the expansion space
20b of the adjacent cylinder 14b. The three adjacent cylinders
14b-14d are similarly connected. Here, each piston 12a-12d has two
functions: (1) to transmit the power to the output shafts 26a-26d,
respectively; and (2) to cause fluid motion to and from the two
sets of variable spaces 16a-16d, and 20a-20d. This configuration is
known in the art as the Rider configuration. The connecting rods
28a-28d, which are coupled to the output shafts 26a-26d,
respectively, are sealed from the environment, which tends to
decrease the engine's efficiency as will be further described.
Conventional Rider configuration Stirling engines depend on some
mechanical linkage or crankshaft 30 to transmit power from the
connecting rods 28a-28d. Such linkages include crankshafts, rhombic
drives, swash plates and slider-cranks. Because the pistons 12a-12d
are mechanically linked via the crankshaft 30, for example, the
thermodynamic state of one cylinder may not be optimized relative
to an adjacent cylinder.
[0024] Turning now to FIG. 2, an exemplary embodiment
multi-cylinder engine is indicated generally by the reference
numeral 100. Engine 100 is an external combustion engine that
includes a plurality of rigid pistons 141a-141d disposed upright in
a plurality of corresponding chambers, cavities or cylinders
140a-140d, respectively. The cylinders 140a-140d are formed in a
cylinder block (not shown), which may include cylinder heads 146d
or 146a-146cd that are also known as heater heads. As used herein,
"cylinder block" shall include a single block or a multi-component
structure, which, when coupled together, functions as the cylinder
block of the engine 100. Each rigid piston 141a-141d is in contact
along its bottom surface with a fixed mass of compressible working
gasfluidic pistons 142a-142d, which in-turn are in contact with a
fixed mass of compressible working gas in a compression space
143a-143d. The cylinders 140a-140d are physically arranged in a
two-by-two matrix with each other such that each cylinder is
vertically oriented and equidistant from each of two adjacent
cylinders.
[0025] Each cylinder 140a-140d defines a compression space
143a-143d, respectively, defined by the volume below piston
141a-141d, respectively, and below each cold heat exchanger
150a-150d, respectively; and an expansion space 145d or 145a-145cd
defined by the volume above each rigid piston 141a-141d,
respectively, and above each regenerator 144d or 144a-144cd,
respectively. The compression space 143a-143d of each cylinder
140a-140d, respectively, is thermodynamically coupled to a
corresponding heat exchanger or regenerator 144a-144d,
respectively, and connected to the expansion space 145a-145d,
respectively, of an adjacent cylinder 140ba-140d or 140a,
respectively, via associated passageways or tubes 147a-147d,
respectively. For example, the compression space 143a of cylinder
140a is connected through passageways or tubes 148a to the
regenerator 144a, and, in turn, through the tubes 147a to the
expansion space 145a of the adjacent cylinder 140b.
[0026] The compression 143a-143d and expansion spaces 145d or
145a-145cd are occupied during the engine cycle by a substantially
fixed mass of working fluid, such as, for example, air, hydrogen,
helium, or other working fluids having suitable heat-transfer and
thermodynamic properties for serving the functions of the working
fluid described herein.
[0027] The exemplary engine 100 includes a second set of pistons
149a-149d, which are directly and rigidly connected to pistons
141a-141d, respectively, in an axial relationship. Pistons
149a-149d are connected to pistons 141a-141d, respectively, via
shafts 142a-142d150a-150d, respectively, passing through shaft
ports 151a-151d, respectively, which may be formed entirely within
the cylinder block to effectively seal the shaft. The second set of
pistons 149a-149d are housed within chambers or cylinders
152a-152d, respectively.
[0028] Each cylinder 152a-152d includes a volumetric space
153a-153d, for hydraulic fluid to ingress and egress during each
stroke. For example, piston 141a in the expansion mode is rigidly
connected to piston 149a, which, in turn, transfers part of the
force to the hydraulic fluid 153a and part of the force of
expansion through an articulated mechanical linkage 155a to piston
149c. Thus, the pistons 141a and 141c are maintained in an opposite
phase relationship of 180 degrees. A second linkage (not shown)
similarly transfers expansion forces between pistons 149b and 149d
and thus maintains the pistons 141b and 141d in an opposite phase
relationship.
[0029] Each cylinder 152a-152d includes a volumetric space
153a-153d, for hydraulic fluid to ingress and egress during each
stroke. For example, piston 141a in the expansion mode is rigidly
connected to piston 149a, which, in turn, transfers the force of
expansion through an articulated mechanical linkage 155a to piston
149c. Thus, the pistons 141a and 141c are maintained in an opposite
phase relationship of 180 degrees. A second linkage (not shown)
similarly transfers expansion forces between pistons 149b and 149d
and thus maintains the pistons 141b and 141d in an opposite phase
relationship.
[0030] Although alternate pistons such as 141a and 141c are
maintained in a phase relationship of 180 degrees, the phase
relationship between adjacent pistons such as between pistons 141a
and 141b is not fixed at 90 degrees, and is gas dynamically
variable between about 0 to about 180 degrees during portions of an
engine cycle. It shall be recognized that the instantaneous phase
relationship between one pair of adjacent pistons is equal to the
instantaneous phase relationship between the other pair of adjacent
pistons. Thus, if piston 141a leads piston 141b by 135 degrees, for
example, at a point in its expansion stroke; then piston 141c leads
piston 141d by 135 degrees at an opposite point in its compression
stroke. These phase differentials between adjacent pistons will
tend towards 90 degrees or 1/4 engine cycle at about a mid-point of
the travel of each piston 141a-141d due to the balancing effect of
the linkages 155a and 155b.
[0031] Unlike with crankshafts, the linkage 155a need not make a
full rotation to guide the pistons 141a, 141c through a complete
cycle. Thus, the stroke length and corresponding compression ratio
for each piston 141a-141d is not fixed by the linkage 155a, but may
automatically vary from a relatively small stroke up to the limits
of travel of the pistons 141a-141d according to the thermodynamic
conditions in the working fluid.
[0032] At the same time that piston 141a compresses and displaces
the working fluid in the compression space 143a, piston 149c
displaces the hydraulic fluid from the volume space 153c through
valve 154c that controls the flow of hydraulic fluid into and out
of the cylinder 152c. This hydraulic fluid can then be used to
drive a conventional hydraulic motor (not shown) for production of
rotational motion.
[0033] Each fluidic piston 142a-142d is substantially
incompressible and at least partially disposed in the corresponding
cylinder 144d or 144a-144c, respectively, which is formed in the
cylinder block (not shown). Each fluidic piston 142a-142d also
extends into the tube set 148a-148d, respectively, during a portion
of each thermodynamic cycle, thereby displacing substantially all
of the working fluid from the tube set 148a-148d into the
corresponding heat-exchanger 144a-144d, respectively, when the
corresponding rigid piston 141a-141d, respectively, is at the
bottom of its travel.
[0034] Engine 100 may further include conventional features such as
piston rings connected to the rigid pistons 141a-141d and/or
149a-149d, a cooling system coupled to the cylinder block and/or
cylinder heads 146d or 146a-146c, and magnetic couplings coupled to
the pistons 149a-149d for generating power. These items have not
been shown in the drawings for the sake of clarity.
[0035] According to this exemplary multi-cylinder engine
embodiment, since the non-adjacent pistons of opposite phase are
linked to each other via the linkages 155a, the effect is that any
piston in the power or expansion mode belonging to a given cylinder
becomes, during a given half-cycle time, the complementing driving
means for the compression or displacement mode of the oppositely
disposed piston. Thus, as specifically shown in FIG. 1, pistons
141a and 141c are in the power and displacement mode, while pistons
141b and 141d temporarily not in motion until power piston 141a has
nearly finished its stroke. The arrows on the pistons 141a-141d
indicate the directional motion of each oppositely disposed piston
at this particular phase in the engine cycle. Due to the inherent
operational symmetry of the engine 100, the reversing of this
process occurs during the second half-cycle time for the engine. As
such, any pair of linked pistons belonging to two opposite phase
cylinders will oscillate substantially in reciprocal register with
one another.
[0036] Accordingly, the engine 100 provides a continuously gas
dynamically variable inter-cylinder phase relationship as well as a
dynamically variable stroke length and compression ratio, each of
which are either actively controlled or inherently varied by the
thermodynamic conditions in the working fluid to optimize the
efficiency of the thermodynamic cycle.
[0037] Engine 100 incorporates the use of intermediate zone between
the piston shaft seal 151a-151d, and the hydraulic piston
149a-149d. This area is a pressurized zone which functions as a
collection port for leaking working gas and hydraulic fluid.
Pressurizing this zone reduces the differential pressure thereby
reducing frictional losses and leakage rates. Pressure control is
provided by valves 157a-157d and can be dynamically controlled via
a pressure sensor control loop. Recycled gas can be compressed and
put back into the engine to maintain proper gas quantity.
[0038] Engine 100 is an external combustion engine that includes a
plurality of rigid pistons 141a-141d disposed upright in a
plurality of corresponding chambers, cavities or cylinders
140a-140d, respectively. The cylinders 140a-140d are formed in a
cylinder block (not shown), which may include cylinder heads 146d
or 146a-146c that are also known as heater heads. As used herein,
"cylinder block" shall include a single block or a multi-component
structure, which, when coupled together, functions as the cylinder
block of the engine 100. Each rigid piston 141a-141d is in contact
along its bottom surface with a corresponding substantially
incompressible fluidic piston 142a-142d, respectively. The
cylinders 140a-140d are physically arranged in a two-by-two matrix
with each other such that each cylinder is vertically oriented and
equidistant from each of two adjacent cylinders.
[0039] Although the fluidic pistons 142a-142d are preferably
liquid, other relatively incompressible fluids, including gels, may
be used. The material of the fluidic piston may be chosen from
water, glycols (such as ethylene glycol, propylene glycol or other
glycols), DOWTHERM.RTM., aromatics, silicones, and similar
substantially incompressible fluids for serving the function of the
fluidic piston described herein. In general, the material of the
fluidic piston will preferably exhibit substantial
incompressibility relative to a working fluid, high boiling point,
high breakdown temperature (including auto-ignition and/or
dissociation temperatures), low density, low viscosity change under
design conditions, low viscosity at lower temperatures, low vapor
pressure and immiscibility with the chosen working fluid. Functions
of the fluidic piston may include displacing a volume of working
fluid, lubricating piston and engine seals, and preventing
high-pressure gaseous working fluid from leaking between the
internal passageways of the engine and an external environment by
means of a gas to liquid barrier.
[0040] As may be recognized by those of ordinary skill in the
pertinent art, the pistons 141a-141d and/or 149a-149d may be
substituted with other displacement devices, such as, for example,
rotors in a Wankel type rotary engine chamber, for fulfilling the
functions of the pistons described herein without departing from
the teachings of this disclosure.
[0041] As shown in FIG. 3, an alternate exemplary embodiment
Fluidic-Piston engine is indicated generally by the reference
numeral 200. Engine 200 is an external combustion engine similar to
engine 100 of FIG. 2, and therefore like reference numerals
preceded by the numeral "2" are used to indicate like elements
having like functionality. Engine 200 includes a plurality of rigid
pistons 241a-241d disposed in a plurality of corresponding
cylinders 240a-240d, respectively. The cylinders 240a-240d are
formed in a cylinder block (not shown), which may include cylinder
heads 246d or 246a-246c. Each rigid piston 241a-241d is in contact
along its bottom surface with a corresponding fluidic piston
242a-242d, respectively.
[0042] Each cylinder 240a-240d defines a compression space
243a-243d, respectively, defined by the volume above each fluidic
piston 242a-242d, respectively, and below each regenerator
244a-244d, respectively; and an expansion space 245d or 245a-245c
defined by the volume above each rigid piston 241a-241d,
respectively, and above each regenerator 244d or 244a-244c,
respectively. The compression space 243a-243d of each cylinder
240a-240d, respectively, is thermodynamically coupled to a
corresponding heat exchanger or regenerator 244a-244d,
respectively, and connected to the expansion space 245a-245d,
respectively, of an adjacent cylinder 240b-240d or 240a,
respectively, via associated passageways 247a-247d, respectively.
For example, the compression space 243a of cylinder 240a is
connected through passageways 248a to the regenerator 244a, and, in
turn, through the passageways 247a to the expansion space 245a of
the adjacent cylinder 240b.
[0043] The exemplary engine 200 includes a second set of pistons
249a-249d, which are directly connected to pistons 241a-241d,
respectively, in an axial relationship. Pistons 249a-249d are
connected to pistons 241a-241d, respectively, via shafts 250a-250d,
respectively, passing through shaft ports 251a-251d, respectively,
which may be formed entirely within the cylinder block to
effectively seal the shaft. The second set of pistons 249a-249d are
housed within cylinders 252a-252d, respectively. Each cylinder
252a-252d includes a volumetric space 253a-253d, for hydraulic
fluid to ingress and egress during each stroke.
[0044] The compressive force is transferred to each piston
249a-249d by the expansive force applied to the oppositely phased
piston 249c-249d and 249a-249b, respectively, acting on a hydraulic
fluid circuit 255a-255d, respectively. Thus, the fixed phase
relationship is maintained between oppositely phased cylinders 240a
and 240c, as well as between 240b and 240d, while using a portion
of the kinetic energy produced by the expansion cycle of one
cylinder to produce the work required by the compression cycle of
an oppositely phased cylinder 240c-240d or 240a-240b, respectively.
Due to the inherent operational symmetry of the engine 200, the
reversing of this process occurs during the second half-cycle time
for the engine. Therefore, any pair of linked pistons belonging to
two oppositely phased cylinders will oscillate substantially in
reciprocal register with one another.
[0045] Turning now to FIG. 4, an alternate exemplary embodiment
Fluidic-Piston engine is indicated generally by the reference
numeral 300. The Fluidic-Piston engine 300 primarily differs from
engine 200 in that the power valve 254 of FIG. 3 has been relocated
from the expansion side of paired power piston 249 of FIG. 3 to the
compression side of power piston 241 of FIG. 3. However, new
reference numerals will be used for clarity.
[0046] Engine 300 includes a plurality of rigid pistons 361a-361d
disposed in a plurality of corresponding cavities or cylinders
360a-360d, respectively. The cylinders 360a-360d are formed in a
cylinder block (not shown), which may include cylinder heads
371a-371d. Each rigid piston 361a-361d is in contact along its
bottom surface with an hydraulic fluid in a volumetric space
362a-362d. The volumetric spaces 362a-362d are open to hydraulic
valves 363a-363d, respectively, for hydraulic fluid to ingress and
egress by pumping action during each stroke. This pumped hydraulic
fluid is used by a hydraulic motor (not shown) to generate rotary
or other designed output motion.
[0047] Each cavity 360a-360d defines a compression space 366a-366d,
respectively, defined by the volume above a fluidic piston
365a-365d, respectively, and below a regenerator 367b-367d or 367a,
respectively; and an expansion space 368a-368d defined by the
volume above each rigid piston 361a-361d, respectively, and above
each regenerator 367a-367d, respectively. The compression space
366a-366d of each cavity 360a-360d, respectively, is
thermodynamically coupled to the corresponding heat exchanger or
regenerator 367a-367d, respectively, and open to the expansion
space 368a-368d, respectively, of an adjacent cylinder 360d or
360a-360c, respectively, via associated passageways 370a-370d,
respectively. For example, the compression space 366a of cavity
360a is open through passageways 370a to the regenerator 367a, and,
in turn, to the expansion space 368a of the adjacent cylinder
360d.
[0048] The exemplary engine 300 includes a second set of pistons
364a-364d, which are directly rigidly connected to pistons
361a-361d, respectively, in an axial relationship. Pistons
364a-364d are connected to pistons 361a-361d, respectively, via
shafts 373a-373d, respectively, passing through shaft ports
372a-372d, respectively, which may be formed entirely within the
cylinder block to effectively seal the shaft. The second set of
pistons 364a-364d is housed within cavities or cylinders 369a-369d,
respectively. Each cylinder 369a-369d includes a volumetric space
spanned by the fluidic piston 365a-365d, respectively, for the
fluidic piston to ingress and egress therefrom during each stroke.
The compressive force is transferred to each piston 365a-365d by
the expansive force applied to the corresponding piston 364a-364d,
respectively.
[0049] The compressive force is transferred to each piston
364a-364d by the expansive force applied by the corresponding
piston 364c-364d or 364a-364b, respectively, acting through a
hydraulic fluid circuit 375a-375b, respectively. Thus, the fixed
phase relationship is maintained between oppositely phased pistons
361a-361d while using a portion of the kinetic energy produced by
the expansion cycle of one cylinder to produce the work required by
the compression cycle of an oppositely phased cylinder 360c-360d or
360a-360b, respectively. Due to the inherent operational symmetry
of the engine 300, the reversing of this process occurs during the
second half-cycle time for the engine. Therefore, any pair of
linked pistons belonging to two oppositely phased cylinders will
oscillate substantially in reciprocal register with one
another.
[0050] Thus, in the engine 300, the piston 364a-364d is acted on by
both the direct expansive force of 361a-361d in the expansion mode,
and the hydraulic fluid from the hydraulic passageways 375a-375b
resulting from the expansive force of pistons 361c-361d or
361a-361b, respectively.
[0051] This embodiment exhibits improved efficiency because the
power output to the hydraulic motor is not first transferred to the
coupled piston while incurring frictional losses as in engine 200,
but is received directly from the compression side of piston
364a-364d while the lesser power required to compress the
oppositely phased piston is transferred indirectly via hydraulic
passageways 375a-375b, thereby incurring reduced frictional losses
due to the reduced mass flow or power transfer. Alternate
embodiments based on engine 300 may also utilize the articulated
mechanical linkage 155a as described for engine 100.
[0052] As shown in FIG. 5, an alternate exemplary embodiment
Fluidic-Piston engine is indicated generally by the reference
numeral 400. Engine 400 is an external combustion engine similar to
engine 100 of FIG. 2, and therefore like reference numerals
preceded by the numeral "4" are used to indicate like elements
having similar functionality. Engine 400 includes a rigid power
piston 441 disposed in a first cylinder 440, and a rigid
compression piston 464 disposed in a second cylinder 478. The
cylinders 440, 478 are formed in a cylinder block (not shown),
which is connected at its upper surface to a cylinder head 446.
Alternatively, the cylinder head 446 may be formed as an integral
part of the cylinder block (not shown). The rigid power piston 441
is connected at its lower end to the upper end of a first
connecting rod 480, which, in turn, is connected at its lower end
to a crankshaft 482. The crankshaft 482 is connected to the lower
end of a second connection rod 484 having a fixed rotational phase
delay of about 90 degrees relative to the first connection rod 480.
The second connection rod 484 is connected at its upper end to the
lower end of the rigid compression piston 464. The rigid
compression piston 464 is adjacent at its upper surface to a
fluidic piston 442.
[0053] The cylinder 478 defines a compression space 443 in the
volume above the fluidic piston 442 and below a regenerator 444,
which is located at the upper end of the cylinder 478 in this
exemplary embodiment. The volume above the rigid piston 441 and
above the regenerator 444 defines an expansion space 445. The
expansion space includes the volumes within the elongated hot heat
exchanger 447, which are open at their first ends to the portion of
the expansion space immediately above the rigid power piston 441,
and at their second ends to the upper end of the regenerator 444.
The compression space 443 of the cylinder 478 is thermodynamically
coupled to the regenerator 444 via a cold heat exchanger 448. The
hot heat exchanger 447 includes three elongated tubes in this
embodiment, although any number of shaped passageways may be used
in alternate embodiments for fulfilling the functions of the hot
heat exchanger described herein. The cold heat exchanger 448
includes five elongated tubes in this embodiment, although any
number of shaped passageways may be used in alternate embodiments
for fulfilling the functions of the cold heat exchanger described
herein.
[0054] In operation, an external combustion heat source is applied
to the hot heat exchanger 447 to cause heating of a substantially
isochoric volume of working fluid as the power piston 441 travels
from about the top of its travel down to about the mid-point of its
travel while the fluidic piston travels from about the
half-displacement point of its travel to the top of its travel.
Next, substantially isothermal expansion of the working fluid takes
place as the power piston 441 travels from about the mid-point of
its travel to about the bottom of its travel while the fluidic
piston 442 travels from about the top of its travel to about the
half-displacement point of its travel. Following this expansion,
substantially isochoric cooling of this volume of working fluid
takes place as the power piston 441 travels from about the bottom
of its travel to about the mid-point of its travel while the
fluidic piston 442 travels from about the half-displacement point
of its travel to about the bottom of its travel, thereby cooling a
substantial portion of the working fluid by heat conduction and
convection with the cold heat exchanger 448. Finally, substantially
isothermal compression takes place as the power piston 441 travels
from about the mid-point of its travel to about the top of its
travel while the fluidic piston 442 travels from about the bottom
of its travel to about the half-displacement point of its travel,
thereby completing the cycle.
[0055] Thus, the fluidic piston 442 substantially increases the
thermodynamic efficiency of practical embodiments of Fluidic-Piston
Stirling engines by expelling the working fluid from the internal
passages of the cold heat exchanger during the substantially
isochoric heating phase of the cycle. In alternate embodiments,
such as, for example, those utilizing fluidic pistons having very
low thermal conductivity and density, the fluidic pistons may also
displace working fluid from the regenerators. The fluidic piston
442 is maintained separate from the working fluid by means of
gravity. Thus, the fluidic piston has a specific density greater
than that of the working fluid, and the cylinder 478 is oriented
vertically with the fluidic piston 442 disposed below the working
fluid.
[0056] When the expanding working fluid forces the power piston 441
downwards, it causes the connecting rod 480 to apply positive work
to the crankshaft 482. The crankshaft 482 has a finite rotational
inertia resulting in storage of kinetic energy in the crankshaft
482. Once the power piston 411 reaches the bottom of its travel, it
begins moving upward by means of an upward force applied by the
crankshaft 482 through the connecting rod 480. At the same time,
the fluidic piston begins moving downwards by means of a downward
force applied by the high-pressure working fluid through the
connecting rod 484 and the compression piston 464. Once, the
compression piston 464 reaches the bottom of its travel, it begins
to move upward by means of an upward force applied by the
crankshaft 482 through the connecting rod 484. This combination of
the upward motion of the power piston 441 and the downward motion
of the fluidic piston 442 results in a substantially isochoric
phase wherein the volume of the working fluid remains substantially
constant while its temperature is reduced via thermodynamic
transfer of heat to the regenerator 444 and the cold heat exchanger
448.
[0057] Although the fluidic piston is a compression piston in the
above-described exemplary embodiment, it is contemplated that the
fluidic piston may serve as an expansion piston in alternate
embodiments. As may be recognized by those of ordinary skill in the
pertinent art, other possible configurations of the fluidic piston
442 are contemplated as new fluids are encountered for serving the
purposes of the working fluid and/or the fluidic piston. For
example, a magnetorheological fluid may be used as the fluidic
piston 442 in combination with a magnetic compression piston 464 in
order to substantially eliminate the reliance on gravity to keep
the fluidic piston intact as shown in this exemplary embodiment.
Other fluids may also be substituted for the fluidic piston 442
that would generally exhibit substantial incompressibility, low
viscosity, and low thermal conductivity in order to fulfill the
functions of the exemplary fluidic piston described herein.
[0058] As may also be recognized by those of ordinary skill in the
pertinent art, an alternate fluidic piston may be added directly
above the power piston 441 along the geometrical or other minor
modifications, if necessary, to prevent the alternate fluidic
piston from substantially mixing with the working fluid and/or
substantially entering the regenerator 444. However, the type of
fluid used for the alternate piston would have more stringent
thermal breakdown requirements than that of the fluidic piston 442
due to its direct contact with the hot heat exchanger 447 and the
heated working fluidic therein.
[0059] A balancing of the overall engine torque for a four-cycle
engine constrains the "optimal" minimum number of like cylinders to
four. However, a lesser total number of cylinders is also
realizable in alternate embodiment engines if the dynamic balancing
requirement is relaxed, as is permissible for lower speed engines.
In addition, although the exemplary engine 100 shows piston sets
that are substantially identical, the coupling of two un-identical
pistons (such as, for example, having different diameters and/or
temperature ranges) that share a common linkage is possible and
contemplated as part of this disclosure. In addition, those of
ordinary skill in the pertinent art will recognize, based on the
teachings herein, that an Ericsson type engine may be provided by
incorporating associated pressure valves between the individual
passageways 147a-147d and 148a-148d.
[0060] According to these exemplary embodiments of the
Fluidic-Piston engine, the components of engines 100, 200, 300 and
400, such as the heat exchanges and regenerators, may be formed of
a high temperature conductive material to increase the overall
efficiency by allowing faster and more complete heat transfer to
occur between the various critical components. A current example of
such a high temperature conductive material is Inconel.RTM. or
nickel-based alloy steel. In addition, the Fluidic-Piston engine
operates at a relatively low frequency in order to reduce viscous
losses and enhance the heat exchanger efficiency; typically from an
upper frequency of about 50 Hz, with an upper frequency of about 35
Hz desired, and an upper frequency of about 20 Hz more desired; to
a lower frequency of about 0.5 Hz, with a lower frequency of about
2.5 Hz desired, and a lower frequency of about 5 Hz more
desired.
[0061] Thus, a Fluidic-Piston engine is configured for increased
efficiency and useful life. The engine includes mechanically and/or
hydraulically coupled piston pairs. A first set of pistons is
disposed in a first set of cylinders and a second set of pistons is
disposed in a second set of cylinders. A piston in the second set
of pistons is mechanically and/or hydraulically connected to a
piston in the first set of pistons in an opposing relation, thereby
defining a pair of connected pistons. The pair of pistons is thus
adapted to oscillate in reciprocal register with one another. Thus,
a piston in an expansion mode drives an oppositely disposed piston
in a displacement mode. Because adjacent pistons operate
independently in that no direct mechanical or hydraulic coupling
exists, adjacent pistons are driven based on substantially
optimized operating parameters.
[0062] In the external combustion engine of the present invention,
use of an articulated linkage instead of a rigid connection allows
for a co-axial vertical orientation of the cylinders. That is, each
cylinder in a single engine can be oriented vertically in a common
direction. This orientation is preferred over the at least
partially horizontal orientation of the prior art because the
vertical orientation described herein reduces lateral loads on the
piston components, such as shaft bearings, rings and seals, which
increases engine life over that possible with engines of the prior
art. Also, the vertically oriented configuration of the external
combustion engine described herein allows the cylinders to be
grouped together such that they use the same burner system,
regardless of the size of the engine. For large engines of the
prior art, separation of the heat exchangers can be several meters
apart and thus require multiple burner systems.
[0063] In prior art external combustion engines having greater than
four cylinders, multiple four cylinder engines are opposed to each
other to provide power output. With this prior art design, the
acting power piston of one engine is linked to the displacement
piston of the opposed, different, engine thereby achieving the
necessary input. Problematically, the heat input on both ends has
to be balanced for the engine to have an equal stroke length in
both directions, thus requiring the use of a control system to
balance the piston motion in both directions. In the external
combustion engine of the present invention, an articulated linkage
links the power and displacement pistons of the same side thereby
eliminating the need for any control device.
[0064] Other advantages of embodiments of the Fluidic-Piston engine
described herein is the reduced leakage of working fluid at the
engine seals due to the additional sealing provided by the liquid
to gas barrier of the fluidic piston to working fluid interface.
Another advantage of embodiments of the Fluidic-Piston engine is
reduced packaging requirements due to the similar vertical
orientation of all power pistons made possible by the provision of
the non-rigid interconnections between cylinders. Yet another
advantage of the Fluidic-Piston engine is increased engine
efficiency due to the optimization of the instantaneous phase angle
difference permissible between a power piston and an adjacent
compression piston action on the same mass of working fluid.
Another, more specific, advantage of the Fluidic-Piston engine is
increased kinetic energy output of the engine due to substantially
complete evacuation of the working fluid from the cold heat
exchanger during the compression and heating phases of the engine
cycle. Another more specific advantage of the Fluidic-Piston engine
is reduced frictional losses and wear of the seals due to
lubrication from the fluid.
[0065] While the invention has been described with reference to
exemplary embodiments, it will be understood by those of ordinary
skill in the pertinent art that various changes may be made and
equivalents may be substituted for the elements thereof without
departing from the scope of the disclosure. In addition, numerous
modifications may be made to adapt the teachings of the disclosure
to a particular object, material or situation without departing
from the essential scope thereof. Therefore, it is intended that
the Claims not be limited to the particular embodiments disclosed
as the currently preferred best modes contemplated for carrying out
the teachings herein, but that the Claims shall cover all
embodiments falling within the true scope and spirit of the
disclosure.
* * * * *