U.S. patent application number 11/344278 was filed with the patent office on 2006-06-08 for threaded sealing flange for use in an external combustion engine and method of sealing a pressure vessel.
This patent application is currently assigned to TIAX LLC. Invention is credited to Roberto O. Pellizzari, Laurence B. Penswick.
Application Number | 20060117746 11/344278 |
Document ID | / |
Family ID | 34465072 |
Filed Date | 2006-06-08 |
United States Patent
Application |
20060117746 |
Kind Code |
A1 |
Pellizzari; Roberto O. ; et
al. |
June 8, 2006 |
Threaded sealing flange for use in an external combustion engine
and method of sealing a pressure vessel
Abstract
A pressure vessel for containing a mechanical device operable to
convert heat to mechanical or electrical power, comprising: a high
temperature section, the high temperature section having a first
end and an open second end, a sealing flange, the sealing flange
having a first end and a second threaded end, the first end bonded
to the open second end of the high temperature section, and a low
temperature section having an open threaded first end, the open
first end in sealing engagement with the second threaded end of the
sealing flange. Also provided are a Stirling engine and a method of
hermetically sealing a pressure vessel of a Stirling engine.
Inventors: |
Pellizzari; Roberto O.;
(Groton, MA) ; Penswick; Laurence B.; (Stevenson,
WA) |
Correspondence
Address: |
LOWRIE, LANDO & ANASTASI
RIVERFRONT OFFICE
ONE MAIN STREET, ELEVENTH FLOOR
CAMBRIDGE
MA
02142
US
|
Assignee: |
TIAX LLC
Cambridge
MA
02140-2390
|
Family ID: |
34465072 |
Appl. No.: |
11/344278 |
Filed: |
January 31, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10943545 |
Sep 17, 2004 |
6990810 |
|
|
11344278 |
Jan 31, 2006 |
|
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60504090 |
Sep 19, 2003 |
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Current U.S.
Class: |
60/517 |
Current CPC
Class: |
F02G 2258/90 20130101;
F02G 2270/55 20130101; F02G 2253/80 20130101; F02G 1/0535 20130101;
F02G 1/055 20130101 |
Class at
Publication: |
060/517 |
International
Class: |
F02G 1/04 20060101
F02G001/04; F01B 29/10 20060101 F01B029/10 |
Claims
1. A pressure vessel for containing a mechanical device operable to
convert heat to mechanical or electrical power, comprising: a) a
high temperature section said high temperature section having a
first end and an open second end; b) a sealing flange, said sealing
flange having a first end and a second threaded end, said first end
bonded to said open second end of said high temperature section;
and c) a low temperature section having an open threaded first end,
said open first end in sealing engagement with said second threaded
end of said sealing flange.
2. The pressure vessel of claim 1, wherein said high temperature
section is constructed of a material selected from the group
consisting of thin wall stainless steel and high nickel alloys.
3. The pressure vessel of claim 2, wherein said high temperature
section is constructed of a material selected from the group
consisting of thin wall stainless steel, Inconel 600, Inconel 625,
Inconel 718, Inconel 754 and Hastelloy GMR 235.
4. The pressure vessel of claim 2, wherein said sealing flange is
constructed of a material selected from the group consisting of
thin wall stainless steel and high nickel alloys.
5. The pressure vessel of claim 1, wherein said sealing flange is
constructed of a material selected from the group consisting of
thin wall stainless steel, Inconel 600, Inconel 625, Inconel 718,
Inconel 754 and Hastelloy GMR 235.
6. The pressure vessel of claim 5, wherein said low temperature
section is constructed of aluminum alloy.
7. The pressure vessel of claim 1, wherein said low temperature
section is cast aluminum alloy.
8. The pressure vessel of claim 7, wherein an outer surface of said
open threaded first end of said low temperature section is clad
with a layer of material selected from the group consisting of
copper, nickel and electroless nickel.
9. The pressure vessel of claim 8, wherein said outer surface of
said open threaded first end of said low temperature section is
uniformly coated with solder.
10. The pressure vessel of claim 1, wherein said outer surface of
said open threaded first end of said low temperature section is
uniformly coated with solder.
11. The pressure vessel of claim 9, wherein an inner surface of
said second threaded end of said sealing flange is uniformly coated
with solder.
12. The pressure vessel of claim 1, wherein an inner surface of
said second threaded end of said sealing flange is uniformly
coating with solder.
13. The pressure vessel of claim 11, wherein said sealing flange is
effective to create a hermetic seal between said high temperature
section and said low temperature section.
14. The pressure vessel of claim 1, wherein said sealing flange is
effective to create a hermetic seal between said high temperature
section and said low temperature section.
15. A Stirling engine, comprising: a) a pressure vessel having a
high temperature section, said high temperature section having a
first end and an open second end, a sealing flange, said sealing
flange having a first end and a second threaded end, said first end
bonded to said open second end of said high temperature section;
and a low temperature section having an open threaded first end,
said open first end in sealing engagement with said second threaded
end of said sealing flange; b) a displacer cylinder formed within
said pressure vessel, said displacer cylinder having a high
temperature end and a low temperature end; and c) a displacer for
traversing said displacer cylinder from said high temperature end
to a low temperature end.
16. The Stirling engine of claim 15, further comprising a combustor
recuperator assembly for heating the high temperature end of said
displacer cylinder.
17. The Stirling engine of claim 15, wherein said high temperature
section is constructed of a material selected from the group
consisting of thin wall stainless steel and high nickel alloys.
18. The Stirling engine of claim 17, wherein said high temperature
section is constructed of a material selected from the group
consisting of thin wall stainless steel, Inconel 600, Inconel 625,
Inconel 718, Inconel 754 and Hastelloy GMR 235.
19. The Stirling engine of claim 17, wherein said sealing flange is
constructed of a material selected from the group consisting of
thin wall stainless steel and high nickel alloys.
20. The Stirling engine of claim 15, wherein said sealing flange is
constructed of a material selected from the group consisting of
thin wall stainless steel, Inconel 600, Inconel 625, Inconel 718,
Inconel 754 and Hastelloy GMR 235.
21. The Stirling engine of claim 20, wherein said low temperature
section is constructed of aluminum alloy.
22. The Stirling engine of claim 15, wherein said low temperature
section is cast aluminum alloy.
23. The Stirling engine of claim 22, wherein an outer surface of
said open threaded first end of said low temperature section is
clad with a layer of material selected from the group consisting of
copper, nickel and electroless nickel.
24. The Stirling engine of claim 23, wherein said outer surface of
said open threaded first end of said low temperature section is
uniformly coated with solder.
25. The Stirling engine of claim 15, wherein said outer surface of
said open threaded first end of said low temperature section is
uniformly coated with solder.
26. The Stirling engine of claim 24, wherein an inner surface of
said second threaded end of said sealing flange is uniformly coated
with solder.
27. The Stirling engine of claim 15, wherein an inner surface of
said second threaded end of said sealing flange is uniformly coated
with solder.
28. The Stirling engine of claim 26, wherein said sealing flange is
effective to create a hermetic seal between said high temperature
section and said low temperature section.
29. The Stirling engine of claim 15, wherein said sealing flange is
effective to create a hermetic seal between said high temperature
section and said low temperature section.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 10/943,545, filed Sep. 17, 2004 which claims priority to
Provisional Application No. 60/504,090, filed Sep. 19, 2003, the
contents of which are incorporated by reference in their
entirety.
FIELD
[0002] The present invention relates to external combustion
engines. More particularly, the invention relates to an external
combustion engine, such as a Stirling cycle engine and improved
means for sealing pressure vessels associated therewith.
BACKGROUND
[0003] The Stirling cycle engine was originally conceived during
the early portion of the nineteenth century by Robert Stirling.
During the middle of the nineteenth century, commercial
applications of this hot gas engine were devised to provide rotary
power to mills. The Stirling engine was ignored thereafter until
the middle of the twentieth century because of the success and
popularity of the internal combustion engine. Stirling cycle
machines, including engines and refrigerators, are described in
detail in Walker, Stirling Engines, Oxford University Press (1980),
incorporated herein by reference.
[0004] The principle underlying the Stirling cycle engine is the
mechanical realization of the Stirling thermodynamic cycle: 1)
isovolumetric heating of a gas within a cylinder, 2) isothermal
expansion of the gas (during which work is performed by driving a
piston), 3) isovolumetric cooling and 4) isothermal compression.
Additional background regarding aspects of Stirling cycle machines
and improvements thereto are discussed in Hargreaves, The Phillips
Stirling Engine (Elsevier, Amsterdam, 1991), incorporated herein by
reference. As such, an ideal Stirling cycle can be plotted in a
pressure volume (PV) diagram as a pair of isothermal
expansion-compression curves connected by a pair of constant volume
heating and cooling lines. In actual engines, however, such an
ideal cycle has never been achieved due to a dependent interaction
between the displacer piston and the power piston of the
engine.
[0005] The high theoretical efficiency of the Stirling engine has
attracted considerable interest in recent years. The Stirling
engine adds the additional advantages of easy control of combustion
emissions, potential use of safer, cheaper, and more readily
available fuels and quiet running operation, all of which combine
to make the Stirling engine a highly desirable alternative to the
internal combustion engine for many applications.
[0006] Despite these advantages, development of the Stirling engine
has proceeded at a much slower rate than might otherwise be
expected. Since the Stirling engine is an external combustion
engine that includes a working gas sealed in a pressurized chamber,
one of the more acute problems includes the need to seal the
working gas at a high pressure within the working space.
[0007] In operation, a displacer body is movable within the chamber
but occupies only a portion of the chamber volume so that as the
displacer body is moved towards the cold end of the chamber the
fluid is displaced towards the remaining volume at the hot end of
the chamber. Cooling of the fluid is achieved by opposite movement
of the displacer body towards the hot end, thus forcing the fluid
towards the cool end of the chamber. In this manner the fluid is
subjected to a thermodynamic cycle responsive to movement of the
displacer body.
[0008] The hot end of the chamber is externally heated by any means
desired or available, including gas burners, solar heaters, etc.
The cold end of the fluid chamber may be water or air cooled, among
other possible refrigeration schemes. The pressurized fluid is
allowed to exert force against and reciprocate a working piston
from which a useful work output may be derived through mechanical
shaft arrangements or the like.
[0009] An ideal Stirling cycle can be plotted in a pressure volume
(PV) diagram by a pair of isothermal expansion-compression curves
connected by a pair of constant volume heating and cooling lines.
In practical engines, however, such an ideal cycle has never been
achieved due to a dependent interaction between the displacer
piston and the power piston of the engine.
[0010] Stirling engines have been proposed for use in a wide range
of applications. Examples include automotive applications,
refrigeration systems and applications in outer space. The need to
power portable electronics equipment, communications gear, medical
devices and other equipment in remote field service presents yet
another opportunity, as these applications require power sources
that provide both high power and energy density, while also
requiring minimal size and weight, low emissions and cost. One
design, which is well suited, is the free-piston. Stirling engine.
The free-piston Stirling engine uses a displacer that is
mechanically independent of the power output member. Its motion and
phasing relative to the power output member is accomplished by the
state of a balanced dynamic system of springs and masses, rather
than a mechanical linkage.
[0011] To date, batteries have been the principal means for
supplying portable sources of power. However, the time required for
recharging batteries has proven inconvenient for continuous use
applications. Moreover, portable batteries are generally limited to
power production in the range of several milliwatts to a few watts
and thus cannot address the need for significant levels of mobile,
lightweight power production.
[0012] Small generators powered by internal combustion engines,
whether gasoline- or diesel-fueled have also been used. However,
the noise and emission characteristics of such generators have made
them wholly unsuitable for a wide range of mobile power systems and
unsafe for indoor use. While conventional heat engines powered by
high energy density liquid fuels offer advantages with respect to
size, thermodynamic scaling and cost considerations have tended to
favor their use in larger power plants.
[0013] As indicated above, in Stirling engines, one end of the
displacer cylinder is always hot; the other end is always
relatively cold. While this design is beneficial from an efficiency
standpoint, since repetitious heating and cooling of the same
section of the displacer cylinder is avoided, the material
requirements of the opposing ends of the displacer cylinder are
markedly different. To address these divergent needs, the use of a
two-piece piece pressure vessel, formed of dissimilar materials,
have been considered. Since helium gas is often the preferred
working fluid and the prevailing internal pressure of the pressure
vessel is high, the effective sealing of such a pressure vessel has
proven challenging.
[0014] In view thereof and despite the advances in the art, there
continues to be a need for a pressure vessel of a Stirling engine,
formed of dissimilar materials, having improved sealing
characteristics.
SUMMARY
[0015] Provided is a pressure vessel for containing a mechanical
device operable to convert heat to mechanical or electrical power.
The pressure vessel includes a high temperature section, the high
temperature section having a first end and an open second end; a
sealing flange, the sealing flange having a first end and a second
threaded end, the first end bonded to the open second end of the
high temperature section, and a low temperature section having an
open threaded first end, the open first end in sealing engagement
with the second threaded end of the sealing flange.
[0016] Also provided is a Stirling engine. The Stirling engine
includes a pressure vessel having a high temperature section, the
high temperature section having a first end and an open second end,
a sealing flange, the sealing flange having a first end and a
second threaded end, the first end bonded to the open second end of
the high temperature section, and a low temperature section having
an open threaded first end, the open first end in sealing
engagement with the second threaded end of the sealing flange, a
displacer cylinder formed within the pressure vessel, the displacer
cylinder having a high temperature end and a low temperature end,
and a displacer for traversing the displacer cylinder from the high
temperature end to a low temperature end.
[0017] Additionally provided is a method of hermetically sealing a
pressure vessel of a Stirling engine. The pressure vessel has a
high temperature section, the high temperature section having a
first end and an open second end, and a low temperature section
having an open threaded first end. The method includes the steps of
providing a sealing flange, the sealing flange having a first end
and a second threaded end, bonding the first end of the sealing
flange to the open second end of the high temperature section,
coating an outer surface of the open threaded first end of the low
temperature section uniformly with solder, coating an inner surface
of the second threaded end of the sealing flange uniformly with
solder, and heating the second threaded end of the sealing flange
until the solder coatings are uniformly melted and co-mingled,
wherein upon cooling the solder layers re-solidify so as to form a
leak-proof hermetic seal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The invention will now be described in more detail with
reference to preferred forms of the invention, given only by way of
example, and with reference to the accompanying drawings, in
which:
[0019] FIG. 1 presents a cross-sectional view of a Stirling engine
100, with its combustor/recuperator assembly removed, employing a
threaded sealing flange of the present invention;
[0020] FIG. 2 shows a combustor/recuperator in partial
cross-section, together with a partial cross-sectional view of a
threaded sealing flange, in accordance with an embodiment of the
invention;
[0021] FIG. 3A presents a top plan view of a form of a threaded
sealing flange, in accordance with an embodiment of the invention;
and
[0022] FIG. 3B presents a cross-sectional view of a threaded
sealing flange, taken along line B-B of FIG. 3A, in accordance with
an embodiment of the invention;
DETAILED DESCRIPTION
[0023] Reference is now made to the embodiments illustrated in
FIGS. 1-3B wherein like numerals are used to designate like parts
throughout.
[0024] The Stirling engine is an external combustion engine,
employing an external continuous combustion system for heating.
Generally, this continuous combustion system is comprised of an
induction system, an exhaust and a combustion chamber. In
operation, a displacer is disposed within a displacer cylinder, one
end of which is heated by the external combustion system. The
displacer cylinder exists within what may be best characterized as
a pressure vessel and contains a working fluid, which is often
helium gas. When the displacer is-positioned within the heated end
of the displacer cylinder, the working fluid moves to the opposite,
cooler end and exists at a lower temperature and pressure. When the
displacer is moved into the cold end of the displacer cylinder, the
working fluid moves around the displacer and into the hot end of
the displacer cylinder, raising the temperature and pressure of the
working fluid.
[0025] As may be appreciated, one end of the displacer cylinder is
always hot; the other end is always cooler. This design is
beneficial from an efficiency standpoint, since repetitious heating
and cooling of the same section of the displacer cylinder is
avoided. However, the material requirements of the opposing ends of
the displacer cylinder are markedly different. To address these
divergent needs, the use of a two-piece piece pressure vessel,
formed of dissimilar materials, may be advantageously employed.
Since helium gas is often the preferred working fluid and the
prevailing internal pressure of the pressure vessel is high, the
effective sealing of such a pressure vessel has proven challenging.
As will be described below, the threaded sealing flange of the
present invention addresses this challenge, providing an effective
mechanism for sealing dissimilar materials.
[0026] FIG. 1 presents a cross-sectional view of a Stirling engine
100, with its combustor/recuperator assembly removed, employing the
threaded sealing flange of the present invention. A suitable
combustor/recuperator 50 is shown in partial cross-section in FIG.
2 and is disclosed in Provisional Application Ser. No. 60/484,508,
filed on Jul. 2, 2003, contents of which are incorporated by
reference in their entirety.
[0027] Stirling engine 100 has a pressure vessel 10 which includes
a high temperature section 12 and a low temperature section 14.
High temperature section 12 is constructed of a material selected
to withstand the high temperature environment created by its close
proximity to combustor/recuperator assembly 50 (see FIG. 2), such
materials including thin wall stainless steels and high nickel
alloys, commonly known as superalloys. Other factors to consider in
material selection include the need for safety, long life, low mass
and excellent oxidation resistance at high temperature. While
stainless steel has utility in this application, the superalloys
are preferred as they possess superior strength at high
temperature, excellent fatigue resistance and oxidation resistance
when compared with the stainless steels.
[0028] The pressure vessel contains helium at very high pressures
and temperatures, which vary cyclically in both high and low
frequency modes. Low cycle fatigue has been found to be a critical
issue, such fatigue associated with the number of engine start-ups
and shut-downs. In selecting a material for use in high temperature
section 12, cost, mass, life and performance trade-offs must be
assessed. For examples, the less costly stainless steels can yield
equivalent safety and life characteristics as a superalloy if the
pressure vessel walls are made thicker and the operating
temperatures maintained at lower levels, however, lower engine
efficiency and power output are realized. What matters is strength,
creep and oxidation resistance at high temperature.
[0029] As indicated, preferred materials include the superalloys,
such as Inconel 600 (able to withstand a maximum temperature of
800.degree. C.), Inconel 625 (able to withstand a maximum
temperature of 900.degree. C.), Inconel 718 (able to withstand a
maximum temperature of more than 1000.degree. C.), Inconel 754
(able to withstand a maximum temperature of 1800.degree. C.) and
Hastelloy GMR 235 (able to withstand a maximum temperature of
935.degree. C.), with Inconel 718 being particularly preferred.
High temperature section 12 may be fabricated from by deep drawing,
hydro-forming, machining or casting, as those skilled in the art
will recognize.
[0030] In selecting a material for use in forming low-temperature
section 14, the desire for low mass, thermal growth compatibility
with the reciprocating components, and high thermal conductivity
makes aluminum alloy an excellent choice for the cold end pressure
vessel where operating temperatures permit its use. As is
well-known, aluminum is roughly one-third the density of a
superalloy, but much weaker. This creates the need for making the
pressure vessel walls much thicker, although the structure is still
significantly lighter. Another benefit that accrues through the use
of aluminum in forming low temperature section 14 is the matching
of the thermal coefficients of expansion between the piston and
displacer and their bores so that seizing does not occur when the
Stirling engine undergoes thermal changes. Yet another reason for
selecting aluminum is to more easily transfer heat through the low
temperature section 14 wall to the external heat exchanger 32 when
driving temperature differentials are low.
[0031] With regard to material selection for threaded sealing
flange 16, it should be noted that the high temperature section 12
of the pressure vessel 10 is maintained at about 650.degree. C. by
the combustor/recuperator assembly 50. The low temperature end of
pressure vessel 10 is maintained at about 100.degree. C. by an
external heat exchanger 32. Within the engine, the entire
temperature differential (650.degree. C.-100.degree. C.) is taken
along the length of the regenerator heat exchanger. It is preferred
that the positioning of the joint between the high temperature
section 12 and the low temperature section 14 be selected at about
the level of the cold end of the regenerator since this is a
natural break point in the Stirling engine and the bulk of the
temperature gradient can be taken along the superalloy high
temperature section 12 wall. It is desirable to take the bulk of
the temperature gradient along the superalloy high temperature
section 12 wall, rather than along the aluminum low temperature
section 14 wall since the higher strength and creep resistance of
the superalloy allows it to survive the combined pressure induced
loads and those associated with the thermal gradients.
Additionally, the conduction losses are reduced due to the lower
conductivity and required cross-sectional area of the superalloy
wall and any heat conducted from the hot to the cold end of the
engine represents an efficiency penalty.
[0032] In view of the aforementioned factors, threaded sealing
flange 16 may be constructed from the stainless steels and
superalloys, including Inconel 600, Inconel 625, Inconel 718,
Inconel 754 and Hastelloy GMR 235, with Inconel 718 being
particularly preferred. As will be described in more detail below,
a hermetic seal is provided between high temperature section 12 and
a low temperature section 14 through the use of threaded sealing
flange 16. As will be discussed further below, threaded sealing
flange 16 may be brazed or welded to high temperature section 12 of
pressure vessel 10. The assembly of threaded sealing flange 16 and
high temperature section 12 of pressure vessel 10 may alternatively
be machined or cast as a single component.
[0033] Referring still to FIG. 1, within pressure vessel 10 of
Stirling engine 100 is a displacer assembly 22 mounted to a
displacer rod 26. Displacer rod 26 is attached to the engine casing
30. Displacer assembly 22 consists of a displacer seal body 27, a
displacer cap assembly 21 and a spring 23. The spring 23 is
attached to the displacer seal body 27 with mounting screws (not
shown), and to the displacer rod 26 with a mounting ring 25. During
displacer reciprocation, one end of spring 23 remains fixed in
place via the mounting screws while spring 23 is free to expand and
contract in direct relationship with the movement of displacer 22.
While it is important that spring 23 be free to expand and contract
in direct relationship with the movement of displacer 22, the above
disclosed mechanism for attaching spring 23 to displacer rod 26 is
only one of many possible ways of providing attachment. Moreover,
displacer 22 and spring 23 are designed such that the moving mass
and the force constant of spring 23 provide a combination which is
mechanically resonant at a desired frequency.
[0034] Referring now to FIGS. 2, 3A and 3B, enlarged views of one
form of the threaded sealing flange 16 are shown. Threaded sealing
flange 16 has a first end 40 and a second threaded end 42. The
first end 40 may be left unthreaded for bonding to the open end 52
of high temperature section 12. Bonding may be 1o accomplished by
welding or braising, as those skilled in the art will recognize.
Second threaded end 42 is provided with a thread 44 on an inner
surface thereof. It is preferred that a machine thread, rather than
a pipe thread, be employed to assure proper sealing engagement with
low temperature section 14. A 2 MM machined thread has been found
to be particularly effective.
[0035] As shown in FIG. 2, low temperature section 14 has an open
threaded first end 60, which is provided with a thread 48 on an
outer surface thereof. It is preferred that a machine thread,
rather than a pipe thread, be employed to assure proper sealing
engagement with the threaded sealing flange 16. Once again, a 2 MM
machined thread has been found to be particularly effective.
[0036] As may be appreciated by those skilled in the art, the harsh
environment sought to be sealed makes it desirable to effect a
hermetic seal without the use of conventional sealing materials
such as O-rings and the like. As such, the threads themselves must
seal the joint. To assure hermetic sealing, thread 44 may be
uniformly coating with solder 70 before assembly. To address the
issue of flowing a solder coating on thread 48 of open threaded
first end 60 of low temperature section 14 when low temperature
section 14 is formed from aluminum, thread 48 is first
electroplated with a layer 72 of copper, nickel or electroless
nickel, with electroless nickel being preferred. Following the
application of layer 72, a uniform coating of solder 74 is applied
before assembly. Alternatively, cavities for solder pre-forms may
be machined into either the threaded sealing flange 16 or the open
threaded first end 60 of low temperature section 14 of pressure
vessel 10.
[0037] To assemble the joint, first end 40 of threaded sealing
flange 16 is braised to open second end 52 of high temperature
section 12. Second threaded end 42 of sealing flange 16 is threaded
onto open threaded first end 60 of low temperature section 14 until
fully seated thereon. Heat is applied about second threaded end 42
of sealing flange 16 until solder coatings 70 and 74 are uniformly
melted and co-mingled. The joint is allowed to cool until the
solder layers re-solidify, forming a leak-proof hermetic seal.
[0038] The threaded flange provides a simple method for joining the
hot and cold ends of the Stirling engine pressure vessel, allowing
for the mechanical coupling of dissimilar materials.
Advantageously, the threads carry the mechanical loads associated
with pressurization and thermal gradients. As may be appreciated by
those skilled in the art, the joint is configured such that the
thermal growth of the components generates hoop stresses in the
threaded flange, and compressive stresses in the aluminum.
Moreover, the joint is configured such that the axial loads align
with the threads, to the extent possible, to reduce bending
moments.
[0039] In operation of Stirling engine 100, heat is be supplied to
the heater head at between approximately 500.degree. C. and
750.degree. C. To maximize efficiency, highly preheated combustion
air should be used. To accomplish this, the air is preheated in the
recuperator of combustor recuperator assembly 50 (see FIG. 2). For
maximum combustor efficiency, high-quality heat, that is the heat
directly available from combustion, is transferred directly to the
engine heater head, while the lower quality heat, that is the heat
of the exhaust stream, is used to preheat the combustion air in the
recuperator.
[0040] As is preferred, the combustor may be fueled using a source
of gaseous fuel or may be fitted with a fuel system capable of
providing a vaporized high energy density liquid fuel for
combustion. Suitable fuels that exist as gases at standard
temperatures and pressures (ambient conditions) include such
hydrocarbon fuels as methane, ethane, propane and butane.
Alternatively, a fuel vaporizer suitable for use in the present
invention is disclosed in U.S. application Ser. No. 10/143,463, the
contents of which are incorporated by reference in their
entirety.
[0041] While the invention has been described in detail with
reference to preferred embodiments thereof, it will be apparent to
one skilled in the art that various changes can be made, and
equivalents employed, without departing from the scope of the
invention.
* * * * *