US 20060093977A1
`
`(19) United States
`(12) Patent Application Publication (10) Pub. No.: US 2006/0093977 A1
`Pellizzari et al.
`(43) Pub. Date:
`May 4, 2006
`
`(54) RECUPERATOR AND COMBUSTOR FOR
`USE IN EXTERNAL COMBUSTION ENGINES
`AND SYSTEl\I FOR GENERATING POWER
`ENIPLOYING SAME
`
`(76)
`
`Inventors: Roberto O. Pellizzari, Groton, MA
`(US); Peter Loftus, Cambridge, MA
`(US)
`
`Correspondence Address:
`Michael J. Mlotkowski
`Roberts, Mlotkowski & Hobbes, PC
`Suite 850
`8270 Greensboro Drive
`McLean, VA 22102 (US)
`
`(21) Appl. No.:
`
`10/883,511
`
`(22) Filed:
`
`Jul. 1, 2004
`
`Related U.S. Application Data
`
`(60) Provisional application No. 60/484,508, filed on Jul.
`1, 2003.
`
`Publication Classification
`
`(51)
`
`Int. Cl.
`(2006.01)
`F23D 11/44
`(52) U.S.Cl.
`............................................................ .. 431/215
`
`(57)
`
`ABSTRACT
`
`A combustor/recuperator assembly for use in an external
`combustion engine, such as a Stirling engine. The assembly
`includes a plurality of substantially hemispherical domed
`members positioned in nested uniaxial spaced relation, the
`plurality of substantially hemispherical domed members
`forming at least a first flow chamber and a second flow
`chamber, the first flow chan1ber for passing an incoming
`charge of air therethrough and the second flow chamber for
`passing an outgoing charge of con1bustion exhaust gases
`therethrough, wherein the second chamber is positioned to
`be effective to heat the incoming charge of air. Also provided
`is a system for producing power from a source ofliquid fuel.
`The system is capable of producing up to about 5,000 watts
`of mechanical or electrical power.
`
`
`
`
`/EA
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`NU MARK Ex.1011 p.1
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`Patent Application Publication May 4, 2006 Sheet 1 of 6
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`US 2006/0093977 A1
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`fig.’1
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`NU MARK Ex.1011 p.2
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`Patent Application Publication May 4, 2006 Sheet 2 of 6
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`US 2006/0093977 A1
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`NU MARK Ex.1011 p.3
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`Patent Application Publication May 4, 2006 Sheet 3 of 6
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`US 2006/0093977 A1
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`NU MARK Ex.1011 p.4
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`Patent Application Publication May 4, 2006 Sheet 4 of 6
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`US 2006/0093977 A1
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`NU MARK Ex.1011 p.5
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`Patent Application Publication May 4, 2006 Sheet 5 of 6
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`US 2006/0093977 A1
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`NU MARK Ex.1011 p.6
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`Patent Application Publication May 4, 2006 Sheet 6 of 6
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`US 2006/0093977 A1
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`NU MARK Ex.1011 p.7
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`

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`US 2006/0093977 A1
`
`May 4, 2006
`
`RECUPERATOR AND COMBUSTOR FOR USE IN
`EXTERNAL COMBUSTION ENGINES AND
`SYSTEl\I FOR GENERATING POWER
`EMPLOYING SAME
`
`RELATED APPLICATIONS
`
`[0001] This patent application claims priority fron1 Pro-
`visional Application Scr. No. 60/484,508, filcd on Jul. 1,
`2003,
`the contents of which are hereby incorporated by
`reference.
`
`FIELD
`
`[0002] The present invention relates to external combus-
`tion engines. More particularly, the invention relates to an
`external combustion engine, such as a Stirling cycle engine,
`having a combustor/recuperator assembly design adapted to
`have improved heat transfer characteristics.
`
`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, com-
`mercial 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 com-
`bustion 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 regard-
`ing aspects of Stirling cycle machines and improvements
`thereto are discussed in Hargreaves, The Phillips Stirling
`Engine (Elsevier, Amsterdam, 1 991), incorporated herein by
`reference.
`
`[0005] The high theoretical efficiency of the Stirling
`engine has attracted considerable interest i11 recent years.
`The Stirling engine adds the additional advantages of easy
`control of combustion cmissions, potential use of safcr,
`cheaper, and more readily available fuels and quiet running
`operation, all of wl1icl1 combine to make the Stirling engine
`a highly desirable altemative 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. Some of the more acute
`problems include the need to seal the working gas at a high
`pressure within the working space,
`the requirement for
`transferring heat at high temperature from the heat source to
`the working gas through the heater head, and a si111ple,
`reliable and inexpensive means for modulating the power as
`the load changes.
`
`[0007] One design, which is well suited to a variety of
`applications,
`is the free-piston Stirling engine. The free-
`piston Stirling engine uses a displacer that is mechanically
`independent of the power output member. lts motion and
`
`phasing relative to the power output member is accom-
`plished by the state of a balanced dynamic system of springs
`and masses, rather than a mechanical linkage.
`
`[0008] 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 gcar, medical devices and other equipment
`in remote field service presents yet another opportunity, as
`these applications require power sources that provide botl1
`high power and energy density, while also requiring minimal
`size and weight, low emissions and cost.
`
`[0009] 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 carmot address the
`
`need for significant levels of mobile,
`production.
`
`ligl1tweigl1t power
`
`Small generators powered by internal combustion
`[0010]
`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
`energy density liquid fuels oifer advantages with respect to
`size, thermodynamic scaling and cost considerations have
`tended to favor their use in larger power plants.
`
`In view of these factors, a void exists with regard
`[0011]
`to power systems in the size range of approximately 50 to
`500 watts. Moreover, in order to take advantage of high
`energy density liquid fuels, improved fuel preparation and
`delivery systems capable of low fueling rates are needed.
`Additionally, such systems must also enable highly efiicient
`combustion with minimal emissions.
`
`[0012] The drive to maximize engine eficiency has stimu-
`lated the introduction of several modifications to make the
`Stirling engine more suitable for a broader range of appli-
`cations. The basic Stirling engine employs a continuous
`combustion system that can waste considerable energy via
`exhaust gases released to the atmosphere. For fixed use
`Stirling engines, heavy steel heat exchangers were devised
`to return a proportion of the exhaust heat energy to the
`inducted air to facilitate combustion. In automotive use, the
`heavy steel heat exchangers were replaced by rotary ceramic
`pre-heaters of the type, which earlier found utility in gas
`turbine engine applications. The rotary preheater functioned
`to expose hot gases through a crescent shaped opening to a
`rotating ceramic wheel, and separately exposed inducted air
`to the heated wheel at
`a11 independent crescent shaped
`opening. Small free-piston Stirling engines have provided
`their own unique challenges in the quest to improve engine
`efliciency, since inherent size restrictions limit the available
`options.
`
`In view thereof and despite the advances in the art,
`[0013]
`there continues to be a need for a small free-piston Stirling
`engine having improved thermal efliciency characteristics.
`SUMMARY
`
`[0014] Provided is a combustor/recuperator assembly for
`use in an external combustion engine. The assembly
`
`NU MARK Ex.1011 p.8
`
`
`

`
`US 2006/0093977 A1
`
`May 4, 2006
`
`includes a plurality of substantially hemispherical domed
`members positioned in nested uniaxial spaced relation, the
`plurality of substantially hemispherical domed members
`forr11ir1g at least a first flow chamber and a second flow
`chamber, the first flow chamber for passing an incoming
`charge of air therethrough and the second flow chamber for
`passing an outgoing charge of combustion exhaust gases
`therethrough, wherein the second chamber is positioned to
`be effective to heat the incoming charge of air.
`
`[0015] Also provided is a burner for an external combus-
`tion engine having a heater head. The burner includes a
`combustor/recuperator assembly for use in an external com-
`bustion engine having a heater head, the combustor/recu-
`perator assembly including a plurality of substantially hemi-
`spherical domed members positioned in nested uniaxial
`spaced relation, the plurality of substantially hemispherical
`domed members forming at least a first flow chamber and a
`second flow chamber, the first flow chamber for passing an
`incoming charge of air therethrough and the second flow
`chamber for passing an outgoing charge of combustion
`exhaust gases therethrough, a fuel vaporizing device, the
`fuel vaporizing device including at least one capillary flow
`passage, the at least one capillary flow passage having an
`inlet end and an outlet end, the inlet end in fluid commu-
`nication with a source of liquid fuel; and a heat source
`arranged along the at least one capillary flow passage, the
`heat source operable to heat the liquid fuel in the at least one
`capillary flow passage to a level sufiicient to change at least
`a portion thereof from a liquid state to a vapor state and
`deliver a stream of substantially vaporized fuel from the
`outlet end of the at least one capillary flow passage and a
`combustion chamber defined by an inner surface of the
`combustor/recuperator assembly and an outer surface of the
`heater head of the external combustion engine, the combus-
`tion chamber having an igniter for combusting the stream of
`substantially vaporized fuel and air, the combustion chamber
`in communication with the outlet end of the at least one
`capillary flow passage, wherein the second chamber of the
`combustor/recuperator assembly is positioned to be eflective
`to heat the incoming charge of air.
`
`[0016] Also provided is a method of generating power.
`The method includes the steps of inducing a flow of air of
`through an intake system, supplying liquid fuel to at least
`one capillary flow passage, causing a stream of substantially
`vaporized fuel to pass through an outlet of the at least one
`capillary flow passage by heating the liquid fuel in the at
`least one capillary flow passage, combusting the air and
`vaporized fuel
`in a combustion chamber, exhausting a
`stream of combustion gases through an exhaust, exchanging
`heat from the stream of combustion gases exhausted to the
`flow of air induced for combustion through a recuperator;
`and converting heat produced by combustion of the vapor-
`ized fuel in the combustion chamber into mechanical and’or
`
`electrical power using an external combustion engine. The
`recuperator includes a plurality of substantially hemispheri-
`cal domed members positioned in nested uniaxial relation,
`the plurality of substantially hemispherical domed members
`forming at least a first flow chamber and a second flow
`chamber, the first flow chamber for passing an incoming
`charge of air therethrough and the second flow chamber for
`passing an outgoing charge of combustion exhaust gases
`therethrough and the second chamber is positioned to be
`elfective to heat the incoming charge of air.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`[0017] 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 accom-
`panying drawings, i11 which:
`
`[0018] FIG. 1 presents a schematic view of a fuel-vapor-
`izing device, combustion chamber and exhaust heat recu-
`perator;
`
`[0019] FIG. 2 shows a perspective view of a combustorl
`recuperator assembly in cross-section, in accordance with an
`embodiment of the invention;
`
`[0020] FIG. 3 presents a cross-sectional view of a com-
`bustor/recuperator assembly, in accordance with an embodi-
`ment of the invention;
`
`[0021] FIG. 4 shows an enlarged cross-sectio11al view of
`a combustor/recuperator assembly, in accordance with an
`embodiment of the invention;
`
`[0022] FIG. 5 presents a cross-sectional view of an alter-
`nate embodiment of a combustor/recuperator assembly, in
`accordance with the invention; and
`
`[0023] FIG. 6 is a schematic view of an apparatus for
`generating power in accordance with the invention wherein
`an external combustion engine is used to generate electricity
`in accordance with one embodiment of the invention.
`
`DETAILED DESCRIPTION
`
`[0024] Reference is now made to the embodiments illus-
`trated in FIGS. 1-6 wherein like numerals are used to
`designate like parts throughout.
`
`[0025] The present invention provides a con1bustor/recu-
`perator design suitable for use in external combustion
`engines, particularly Stirling engines. The design provides
`an arrangement of combustion air and exhaust flow pas-
`sages, together with low-mass thermal insulation to ensure
`maximal transfer of high-quality heat to a load, such as an
`external combustion engine heater head and efficient transfer
`of low-quality heat in the recuperator to preheat the coin-
`bustio11 air. This results in the transfer of heat to the load
`with maximum efliciency in a compact,
`lightweight and
`cost-elfective design.
`
`[0026] As is well known, the Stirling engine is an external
`combustion engine, employing an external continuous com-
`bustion system for heating. Generally, this continuous coin-
`bustio11 system is comprised of an induction system, an
`exhaust and a combustion chamber. To enhance overall
`system elficiency, it is advantageous to employ a means of
`preheating the inducted air stream.
`
`[0027] The burning of fuel to supply heat to the heater
`head is constrained ir1 many ways. For example, heat must
`be supplied at between approximately 500° C. and 750° C.
`The surface area available on the heater head requires that
`either very high heat flux rates must be generated from the
`combustion heat source or an extended heater head surface
`must be provided, or both. Moreover, it is important that heat
`transfer and head temperature should be as uniform as
`possible and combustion should be accomplished with the
`minimum generation of pollutant species, such as NOX, CO,
`and unburned hydrocarbons.
`
`NU MARK Ex.1011 p.9
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`US 2006/0093977 A1
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`May 4, 2006
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`To maximize the conversion elliciency of the sys-
`[0028]
`tem, highly preheated combustio11 air should be used. To
`accomplish this, the air is preheated in a recuperator. How-
`ever,
`the high combustion air temperature significantly
`increases the potential for forming NOX emissions from the
`combustor. The combustor should be operated at as low a
`level of excess air as possible, to minimize stack losses and
`maximize system elliciency. For maximum combustor elli-
`ciency, high-quality heat, that is the heat directly available
`from combustion, should be transferred directly to the
`engine heater head, while the lower quality heat, that is the
`heat of the exhaust stream, should be used to preheat the
`combustion air in the recuperator.
`
`[0029] Referring now to FIG. 1, a schematic View of a
`Stirling cnginc combustor/rccupcrator scction 10 is shown.
`Fuel and air enter the combustion chamber 12 at a common
`
`temperature, which is ambient temperature, TO. Combustion
`products leave at a common Lmifonn temperature, T4.
`
`[0030] The temperature at which combustion products
`make final contact with the outer surface of the expansion
`exchanger 14 must be above the nominal source tempera-
`ture, TE. As may be appreciated, to exhaust the combustion
`products at this temperature would remove any possibility of
`achieving high overall efficiency, so the combustion system
`should provide for air pre-heating by the exchange of heat
`with the exhaust. Still referring to FIG. 1, air enters the inlet
`16 of pre-heating passage 18 of recuperator 20 at T0 emerg-
`ing at outlet 24 a temperature Th after gaimng heat from the
`exhaust via the recuperator 20.
`
`is introduced at outlet 26 of fuel delivery
`Fuel
`[0031]
`device 28 at a temperature To. Optionally, it may be injected
`by entrainment with a source of high-pressure air 30 at a rate
`of m'ap. As may be appreciated, the net air/fuel ratio for such
`a system is based on the sum of both air streams, m'a=(m'ap+
`m'aS). With modest pre-heating, fuel and air may be pre-
`mixed. A particularly preferred capillary-based fuel-vapor-
`izing device for use in the practice of the present invention
`is disclosed in U.S. application Ser. No. 10/143,463, the
`contents of which are hereby incorporated in their entirety.
`
`[0032] Thereafter, combustion takes place in combustion
`chamber 12, yielding temperature T2. Combustion for this
`example is taken to be complete before the products pass
`over the expansion exchanger 14, where they exit at T3. This
`is the temperature at which the products enter the exhaust
`inlet 32 of exhaust passage 22 of recuperator 20. The exhaust
`products leave at T4 after exchanging heat with incoming air.
`
`[0033] Referring now to FIGS. 2-4, the present invention
`seeks to efficiently transfer heat to the heater head of a
`Stirling engine with maximum efficiency in a compact,
`lightweight and cost-eflfective design. As shown, the com-
`bustor housing/rccupcrator assembly is
`formcd from a
`nested set of four substantially hemispherical domes. The
`four domes include ar1 intake dome 150, which may be
`fabricated from stainless steel or one of the well-known
`super alloys having a wall thickness of from about 0.5 to
`about 1 mm, a recuperator dome 152, which may also be
`fabricated from stainless steel having a wall thickness of
`from about 0.5 to about 1 mn1, an exhaust dome 154, which
`again may be fabricated from stainless steel having a wall
`thickness of about 1 mm, and an inner dome 156, which
`again may be fabricated from stainless having a wall thick-
`ness of about 1 mm. Refractory material 160 is affixed to
`
`inner dome 156 to further insulate intake dome 150, recu-
`perator dome 152 a11d exhaust dome 154 from the heat of
`combustion and enhance the ability to transfer the highest
`amount of heat to the outer surface of Stirling engine heater
`head 170 (see FIG. 3). To further aid in the transfer of heat,
`heater head 170, which may be constructed from stainless
`steel, can be further clad with a layer of copper. As shown
`in FIG. 4, nested stainless steel domes are set in a spaced
`relation to form the passages discussed below. The stainless
`steel domes may be joined by welds or brazing, with a full
`round or half—tube welded to the ceramic shell to position
`same.
`
`[0034] Referring to FIGS. 2 and 4, combustion air is
`introduced into an inlet 180 and into upper manifold 182,
`where it flows down through a plurality of manifold runners
`184, through an outer shell passage 186 formed by the
`combination of thc intakc domc 150 and rccupcrator domc
`152. The combustion air then picks up heat by convective
`heat transfer from the exiting combustion products flowing
`through exhaust shell passage 190 formed by the combina-
`tion of the exhaust dome 154 and the inner dome 156. The
`air
`is passes through a plurality of circumferentially
`arranged slots 194 and is re-directed upwards through an
`inner shell passage 192, formed by the combination of the
`recuperator dome 152 and the exhaust dome 154, and heats
`further, finally passing via the upper manifold 182 into the
`central combustion zone 200, where it is mixed with fuel and
`is ignited. The combustor can be operated in either diflusion
`flame mode, by introducing fuel along the central axis
`through the manifold 182, or in a premixed mode, by
`introducing fuel into the recuperator passages or the mani-
`fold 182. The combustion zo11e heats the Stirling engine
`heater head 170 by a mixture of convection and radiation.
`The combustion products exit at the bottom of the heater
`head and flow upwards through the exhaust shell passage
`190 formed by the combination of the exhaust dome 154 and
`the imier dome 156, which is located behind lightweight
`refractory insulation 160.
`
`[0035] Preferred refractory materials include lightweight,
`high-purity, alumina-silica fiber, having a duty rating of at
`least about 2300’ F., with a more preferred range of duty
`ratings of at
`lcast about 2600 to about 2800° F. Such
`materials have characteristically low thermal conductivity,
`low specific heat, high therr11al-sl1ock resistance and very
`good durability. The refractory materials appropriate for use
`in the present invention possess an approximate thermal
`conductivity (ASTM C-201) value of at least about 0.8 BTU
`In/Hr/Ft2 at a mean temperature of 1000° F. A source for
`such materials is Refractory Specialties Incorporated, of
`Sebring, Ohio, which markets them under the GemcoliteTM
`brand.
`
`[0036] As may be appreciated by those skilled in the art,
`the location of the insulation adjacent to the flame zone
`increases efiiciency by not allowing the high quality heat to
`be transferred via tl1e cold recuperator walls to tl1e incoming
`air and the outside environment.
`
`[0037] 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.
`
`NU MARK Ex.1011 p.10
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`US 2006/0093977 A1
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`May 4, 2006
`
`[0038] Alternatively, a fuel vaporizer suitable for use in
`the present invention is shown schematically in FIG. 3.
`Referring now to FIG. 3, the combustor/recuperator assem-
`bly of the present
`invention may be fitted with a fuel
`vaporizer, which may include at least one capillary sized
`flow passage 300 for connection to a fuel supply (not
`shown). As disclosed i11 U.S. application Ser. No. 10/ 143,
`463, a heat source is arranged along the flow passage 300 to
`heat liquid fuel in the flow passage sufficiently to deliver a
`stream of vaporized fuel from an outlet of the flow passage
`into the combustion zone 200, wherein the vaporized fuel is
`combusted. The flow passage 300 can be a capillary tube
`heated by a resistance heater, a section of the tube heated by
`passing electrical current therethrough. As is particularly
`preferred,
`the capillary flow passage should have a low
`thermal inertia, so that capillary passage 300 can be brought
`up to the desired temperature for vaporizing fuel very
`quickly, e.g., within 2.0 seconds, preferably within 0.5
`second, and more preferably within 0.1 second. The capil-
`lary sized fluid passage is preferably fon11ed iii a capillary
`body such as a single or multilayer metal, ceramic or glass
`body. The passage l1as an enclosed volume opening to an
`inlet and an outlet either of which may be open to the
`exterior of the capillary body or may be connected to another
`passage within the same body or another body or to fittings.
`The heater can be formed by a portion of the body such as
`a section of a stainless steel tube or the heater car1 be a
`discrete layer or wire of resistance heating material incor-
`porated in or on the capillary body.
`
`[0039] FIG. 5 presents a cross-sectional View of an alter-
`nate embodiment of a combustor/recuperator assembly, in
`accordance with another aspect of the invention. The com-
`bustor housing/recuperator assembly is
`formed from a
`nested set of four substantially hemispherical domes,
`although the outer three domes are flared-out, as shown, to
`accommodate manifolding. The four domes include an
`intake dome 550, which may be fabricated from stainless
`steel having a wall thickness of from about 0.5 to about 1
`mm, a recuperator dome 552, which may also be fabricated
`from stainless steel having a wall thickness of from about
`0.5 to about 1 m, an exhaust dome 554, which again may
`be fabricated from stainless steel having a wall thickness of
`about 1 mm, and an inner don1e 556, which again may be
`fabricated from stainless steel having a wall thickness of
`about 1 mm. Refractory material 560 is aflixed to inner dome
`556 to further insulate intake dome 550, recuperator dome
`552 and exhaust dome 554 from the heat of combustion and
`enhance the ability to transfer the highest amount of heat to
`the outer surface of a Stirling engine heater head (not
`shown). As shown, nested stainless steel domes are set i11 a
`spaced relation to form intake and exhaust passages. The
`stainless steel domes may be joined by welds or braising.
`
`[0040] Advantageously, inner dome 560 may be spring
`loaded against exhaust dome 554, rather than rigidly fixed
`thereto,
`to provide flexibility during the heating of the
`assembly and thermal growth of exhaust dome 554. This
`also prevents the grinding away over time of the inner dome
`560, which results from vibratory motion of the Stirling
`engine. Another suitable arrangement includes the use of a
`cerainic/metal felt of the type employed in gas turbine
`engines, as those skilled in the art will recognize.
`
`586 formed by the combination of the intake dome 550 and
`recuperator dome 552. The combustion air then picks up
`heat by convective heat transfer from the exiting combustion
`products flowing through exhaust shell passage 590 formed
`by the combination of the exhaust dome 554 and the inner
`dome 556. The air passes through a plurality of circumfer-
`entially arranged slots 594 and is re-directed upwards
`through an inner shell passage 592, formed by the combi-
`nation of the recuperator dome 552 and the exhaust dome
`554, and heats further, finally passing via the upper manifold
`582, through a plurality of exit slots 588 i11to the central
`combustion zone 600. where it is mixed with fuel and is
`ignited. As may be appreciated, the combustion air passing
`though the plurality of exit slots 588 serves to impart a
`swirling motion to the combustion air. The swirling air
`serves to create a more homogenous mixture of air and fuel
`for combustion, producing a n1ore stable flame. The coin-
`bustio11 zone heats the Stirling engine heater head (not
`shown) by a mixture of convection a11d radiation. The
`cor11bustior1 products exit at the bottom of the heater head
`and flow upwards through the exhaust shell passage 590
`formed by the combination of the exhaust dome 554 and the
`inner dome 556, which is located behind lightweight refrac-
`tory insulation 560.
`
`[0042] Once again, preferred refractory materials include
`lightweight, high-purity, alumina-silica fiber, having a duty
`rating of at least about 2300° F., with a more preferred range
`of duty ratings of at least about 2600 to about 2800° F. The
`refractory materials appropriate for use in the present inven-
`tion possess an approximate thermal conductivity (ASTM
`C-201) value of at least about 0.8 BTU In/Hr/Ftz at a mean
`temperature of l000° F. A source for such materials is
`Refractory Specialties
`Incorporated, of Sebring, Ohio,
`which markets them under the GemcoliteTM brand.
`
`[0043] As with the embodiment of FIGS. 2-4, the location
`of the insulation adjacent to the flame zone increases effi-
`ciency by not allowing the high quality heat to be transferred
`via the cold recuperator walls to the incoming air and the
`outside environment.
`
`[0044] FIG. 6 shows a schematic of a power system 400
`in accordance with another aspect of the present invention.
`Power system 400 includes an external combustion engine
`430, such as a kinematic Stirling engine or a free-piston
`Stirling engine, a combustion chamber 434 wherein heat at
`550-750° C.
`is converted into mechanical power by a
`reciprocating piston which drives an altemator 432 to pro-
`duce electrical power. The assembly also includes a capillary
`flow passage/heater assembly 436, a controller 438, a rec-
`tifier/regulator 440, a battery 442, a fuel supply 444, a
`combustor/recuperator assembly 446, of the type disclosed
`above and depicted in FIGS. 2-4, a combustion blower 448,
`a cooler 450 and a cooler/blower 452. In operation, the
`controller 438 is operable to control delivery of fuel to the
`capillary 436 and to control combustion of the fuel in the
`chamber 434 such that the heat of combustion drives a piston
`in the Stirling engine 430 such that the engine outputs
`electricity from the alternator 432. If desired. the Stirling
`engine 430/alternator 432 can be replaced with a kinematic
`Stirling engine (not shown) which outputs mechanical
`power.
`
`In operation, combustion air is introduced into an
`[0041]
`inlet 580, where it flows down through outer shell passage
`
`In order to initiate combustion, the air-fuel mixture
`[0045]
`can be confined in an ignition zone in which an ig11iter such
`
`NU MARK Ex.1011 p.11
`
`
`

`
`US 2006/0093977 A1
`
`May 4, 2006
`
`as a spark generator ignites the mixture. The igmter can be
`any device capable of igniting the fuel such as a mechanical
`spark generator, an electrical spark generator, resistance
`heated ignition wire or the like. The electrical spark gen-
`erator can be powered by any suitable power source, such as
`a small battery. However, the battery can be replaced with a
`manually operated piezoelectric transducer that generates an
`electric current when activated. With such an arrangement,
`current can be generated electro-mechamcally due to com-
`pression of the transducer. For instance, a striker can be
`arranged so as to strike the transducer with a predetermined
`force when the trigger is depressed. The electricity generated
`by the transducer can be supplied to a spark generating
`mechanism by suitable circuitry. Such an arrangement could
`be used to ignite the fuel-air mixture.
`
`Some of the electrical power generated can be
`[0046]
`stored ir1 a suitable storage device such as a battery or
`capacitor, which can be used to power the igniter. For
`example, a manually operated switch can be used to deliver
`electrical current to a resistance—heating element or directly
`through a portion of a metal tube, which vaporizes fuel in the
`flow passage a11d/or the electrical current can be supplied to
`an igniter for initiating combustion of the fuel-air mixture
`delivered to the combustion chamber.
`
`If desired, the output of the power system could be
`[0047]
`used to operate any type of device that relies on 111ecl1a11ical
`or electrical power. For instance, electricity generated could
`be used for portable electrical equipment such as telephone
`communication devices (e.g., wireless phones), portable
`computers, power tools, appliances, camping equipment,
`military equipment,
`transportation equipment
`such as
`mopeds, powered wheelchairs and marine propulsion
`devices, electronic sensing devices, electronic monitoring
`equipment, battery chargers,
`lighting equipment, heating
`equipment, etc. The power system could also be used to
`supply power to non-portable devices or to locations where
`access to an electrical power grid is not available, inconve-
`nient or unreliable. Such loca