Note: Descriptions are shown in the official language in which they were submitted.
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HYBRID SYSTEM FOR GENERATING POWER
[0001] The need to power electronics equipment, communications
gear, medical devices and other equipment in remote field service has
been on the rise in recent years, increasing the demand for highly efficient,
mobile power systems. These applications require power sources that
provide both high power and energy density, while also requiring minimal
size and weight, low emissions and cost.
[0002] To date, batteries have been the principal means for
supplying portable sources of power. However, due to the time required
for recharging, batteries have 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.
[0003] 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.
[0004]
Photovoltaic and thermoelectric generators are the only
commercially available energy conversion technologies below 2 kilowatts.
While the benefits of photovoltaic are clear, the drawbacks are obvious.
With respect to thermoelectric generators, they tend to be large, expensive
and relatively inefficient.
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[0005] In view of these factors, a void exists with regard to power
systems in the size range of approximately 5.1 to 204 kg-m/sec (50 to
2000 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 efficient combustion with minimal emissions. A quiet, clean power
source below 204 kg-m/sec (2 kilowatts) could advantageously
supplement current technologies, such as those based on photovoltaic
arrays, and yield an advantageous hybrid system for generating electrical
power.
[0006] In one aspect, the present invention is directed to a hybrid
system for generating electrical power comprising:
(a) a photovoltaic array for collecting and converting solar radiation
into electrical power;
(b) an apparatus for producing power from a source of liquid fuel,
the apparatus comprising (i) at least one capillary flow passage, said at
least one capillary flow passage having an inlet end and an outlet end,
said inlet end in fluid communication with the source of liquid fuel; (ii) a
heat source arranged along said at least one capillary flow passage, said
heat source operable to heat the liquid fuel in said at least one capillary
flow passage to a level sufficient to change at least a portion thereof from
a liquid state to a vapor state and deliver a stream of substantially
vaporized fuel from said outlet end of said at least one capillary flow
passage; (iii) a combustion chamber in communication with said outlet end
of said at least one capillary flow passage; and (iv) a conversion device
operable to convert heat released by combustion in said combustion
chamber into electrical power; and
(c) a storage device electrically connected to said photovoltaic array
and said conversion device for storing the electrical power produced by
said photovoltaic array and said conversion device.
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[0007] In another aspect, the present invention is directed to a
method of generating electrical power, comprising;
(a) converting solar radiation into electrical power through the use
of a photovoltaic array;
(b) supplying liquid fuel to at least one capillary flow passage;
(c) 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;
(d) combusting the vaporized fuel in a combustion chamber;
(e) converting heat produced by combustion of the vaporized fuel in
the combustion chamber into electrical power using a conversion device;
and
(f) storing electrical power generated in steps (a) and (e) in a
storage device.
[0008] According to one preferred form, the capillary flow passage
can include a capillary tube and the heat source can include a resistance-
heating element, a section of the tube heated by passing electrical current
therethrough. Further, in another preferred form, the conversion device
includes a micro-turbine with electrical generator, a Stirling engine with
electrical generator, a thermoelectric device or a thermophotovoltaic
device that outputs up to about 510 kg-m/sec (5,000 watts) of power. An
igniter can be provided to ignite the vaporized fuel upon start-up of the
apparatus. The fuel supply can be arranged to deliver pressurized liquid
fuel to the flow passage at a pressure of preferably less than 7.0 kg-m/sec
(100 psig), more preferably, less than 3.5 kg-m/sec (50 psig), even more
preferably 0.7 kg-m/sec (10 psig), and most preferably less than 0.35 kg-
m/sec (5 psig). The preferred form can be operated with low ignition
energy upon start up of the apparatus since it can provide a stream of
vaporized fuel which mixes with air and forms an aerosol in the
combustion chamber having a mean droplet size of 25 pm or less,
preferably 10 pm or less.
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[0009] To address problems associated with the formation of
deposits during the heating of liquid fuel, one preferred form provides a
method and means for cleaning deposits formed during the operation of
the apparatus.
[0010] 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:
[0011] FIG. 1
presents a fuel-vaporizing device, in partial cross
section, which includes a capillary flow passage in accordance with an
embodiment of the invention;
[0012] FIG. 2
shows a multi-capillary arrangement that can be used
to implement the device and system of FIG. 4;
[0013] FIG. 3 shows an end view of the device shown in FIG. 2;
[0014] FIG. 4
shows details of a device that can be used to
vaporize fuel and oxidize deposits in a multi-capillary arrangement to
deliver substantially vaporized fuel for use in the practice of the present
invention;
[0015] FIG. 5
shows a schematic of a control device to deliver fuel
and optionally oxidizing gas to a capillary flow passage;
[0016] FIG. 6
shows a schematic of an arrangement for using
combustion heat to preheat the liquid fuel;
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[0017] FIG. 7 is a side view of another embodiment of a fuel-
vaporizing device employing a moveable rod to clean deposits from a
capillary flow passage;
[0018] FIG. 7A is a side view of the embodiment of FIG. 7 shown
with the moveable rod to clean deposits from a capillary flow passage fully
engaged within the capillary flow passage;
[0019] FIG. 8 is a schematic view of an apparatus for generating
power in accordance with the invention wherein a Stirling engine is used to
generate electricity in accordance with one embodiment of the invention;
[0020] FIG. 9 shows a partial cross-sectional schematic view of a
power-producing device in accordance with another embodiment of the
invention; and
[0021] FIG. 10 is a block diagram of a hybrid power system in
accordance with the present invention.
[0022] Reference is now made to the embodiments illustrated in
Figs. 1-10 wherein like numerals are used to designate like parts
throughout.
[0023] The present invention provides a power producing
apparatus which advantageously combusts a high energy density liquid
fuel. In a preferred embodiment, the apparatus includes at least one
capillary sized flow passage connected to the fuel supply, a heat source
arranged along the flow passage to heat liquid fuel in the flow passage
sufficiently to deliver a stream of vaporized fuel from an outlet of the flow
passage, a combustion chamber in which the vaporized fuel is combusted,
and a conversion device which converts heat produced by combustion in
the combustion chamber into mechanical and/or electrical power. The use
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of heated capillaries in connection with a combustion chamber and power
conversion device is disclosed in U.S. Patent No. 7,313,916, filed by
Pellizzari on May 10, 2002, entitled "Method and Apparatus for Generating
Power By Combustion of Vaporized Fuel".
[0024] The flow passage can be a capillary tube heated by a
resistance heater, a section of the tube heated by passing electrical
current therethrough. The capillary flow passage also is characterized
by having a low thermal inertia, so that the capillary passageway 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 capillary sized fluid passage is
preferably formed in a capillary body such as a single or multilayer
metal, ceramic or glass body. The passage has 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 can be a discrete layer or wire of resistance heating
material incorporated in or on the capillary body.
[0025] The fluid passage may be any shape comprising an
enclosed volume opening to an inlet and an outlet and through which a
fluid may pass. The fluid passage may have any desired cross-section
with a preferred cross-section being a circle of uniform diameter. Other
capillary fluid passage cross-sections include non-circular shapes such
as triangular, square, rectangular, oval or other shape and the cross
section of the fluid passage need not be uniform. The fluid passage can
extend rectilinearly or non-rectilinearly and may be a single fluid
passage or multi-path fluid passage.
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[0026] A
capillary-sized flow passage can be provided with a
hydraulic diameter that is preferably less than 2 mm, more preferably less
than 1 mm, and most preferably less than 0.5 mm. The "hydraulic
diameter" is a parameter used in calculating fluid flow characteristics
through a fluid carrying element and is defined as four times the flow area
of the fluid-carrying element divided by the perimeter of the solid boundary
in contact with the fluid (generally referred to as the "wetted" perimeter).
For a tube having a circular flow passage the hydraulic diameter and the
actual diameter are equivalent. In the case where the capillary passage is
defined by a metal capillary tube, the tube can have an inner diameter of
0.01 to 3 mm, preferably 0.1 to 1 mm, most preferably 0.15 to 0.5 mm.
Alternatively, the capillary passage can be defined by transverse cross
sectional area of the passage that can be 8 x 10-5 to 7 mm2, preferably 8 x
10-3 to 8 x 10-1 mm2 and more preferably 2 x 10-3 to 2 x 10-1 mm2. Many
combinations of a single or multiple capillaries, various pressures, various
capillary lengths, amounts of heat applied to the capillary, and different
shapes and/or cross-sectional areas will suit a given application.
[0027] The
conversion device can be a Stirling engine, micro-
turbine or other suitable device for converting heat to mechanical or
electrical power with an optional generator capable of producing up to
about 510 kg-m/sec (5,000 watts) of power. The liquid fuel can be any
type of hydrocarbon fuel such as jet fuel, gasoline, kerosene or diesel oil,
an oxygenate such as ethanol, methanol, methyl tertiary butyl ether, or
blends of any of these and the fuel is preferably supplied to the flow
passage at pressures of preferably less than 7.0 kg-m/sec (100 psig), more
preferably less than 3.5 kg-m/sec (50 psig), even more preferably less than
0.7 kg-m/sec (10 psig), and most preferably less than 0.35 kg-m/sec (5
psig). The vaporized fuel can be mixed with air to form an aerosol having
a mean droplet size of 25 pm or less, preferably 10 pm or less, thus
allowing clean and efficient ignition capabilities.
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[0028] According to a preferred embodiment of the invention, liquid
fuel is delivered via a heated capillary tube (e.g., a small diameter glass,
ceramic or metallic material such as stainless steel tube having an inner
diameter of 3 mm or less) to a combustion chamber in which the
vaporized fuel is mixed with preheated or unheated air. The vaporized fuel
can be mixed with air at ambient temperature, which is drawn into air
supply passages leading into the combustion chamber. Alternatively, the
vaporized fuel can be mixed with air that has been preheated such as by a
heat exchanger that preheats the air with heat of exhaust gases removed
from the combustion chamber. If desired, the air can be pressurized such
as by a blower prior to mixing with the vaporized fuel.
[0029] During
vaporization of liquid fuel in a heated capillary
passage, deposits of carbon and/or heavy hydrocarbons may accumulate
on the capillary walls and flow of the fuel can be severely restricted which
ultimately can lead to clogging of the capillary flow passage. The rate at
which these deposits accumulate is a function of capillary wall
temperature, the fuel flow rate and the fuel type. While it is thought that
fuel additives may be useful in reducing such deposits, should clogging
develop, the fuel vaporizing device of the present invention
advantageously provides a means for cleaning deposits formed during
operation.
[0030] In
accordance with the present invention, the air-fuel mixture
is combusted in a combustion chamber to produce heat that is converted
into mechanical or electrical power. The power-producing device provides
reliable liquid fuel delivery and atomization of vaporized fuel prior to
combustion.
[0031] The
heated capillary flow passage has the ability to form an
aerosol of small fuel droplets (e.g., 25 pm or less, preferably 10 pm or
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less) when the vaporized fuel mixes with air at ambient temperature,
operating at liquid fuel pressures below 7.0 kg-m/sec (100 psig), preferably
less than 3.5 kg-m/sec (50 psig), more preferably less than 0.7 kg-m/sec
(10 psig), and even more preferably less than 0.35 kg-m/sec (5 psig). The
present invention possesses the ability to combust fuel at low air supply
pressure (e.g., below 50.8 mm H20 (2 in H20)), starts rapidly, provides for
control of fouling, clogging and gumming, operates at reduced levels of
exhaust emissions and requires low ignition energy to ignite the fuel-air
mixture.
[0032] One advantage of the apparatus according to the invention
is its ignition energy requirement characteristics. Minimum ignition energy
is a term used to describe the ease with which an atomized fuel/air mixture
can be ignited, typically with an igniter such as a spark ignition source.
The device according to the invention can provide vaporized fuel and/or
aerosol with droplets having a Sauter Mean Diameter (SMD) of less than
25 pm, preferably less than 10 pm and more preferably less than 5 pm,
such fine aerosols being useful to improve the start-up characteristics and
flame stability in gas turbine applications. Additionally, very significant
reductions in minimum ignition energy can be achieved for fuels having
values of SMD at or below 25 pm. For example, as discussed in Lefebvre,
Gas Turbine Combustion (Hemisphere Publishing Corporation, 1983) at
page 252, Emin, a term that correlates the ease with which an atomized
fuel/air mixture may be ignited, is shown to sharply decrease as SMD
decreases. Minimum ignition energy is roughly proportional to the cube of
the Sauter Mean Diameter (SMD) of the fuel droplets in the aerosol. SMD
is the diameter of a droplet whose surface-to-volume ratio is equal to that
of the entire spray and relates to the mass transfer characteristics of the
spray. The relationship between Emin and SMD for various fuels is shown
in Lefebvre to be roughly approximated by the following relationship:
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log Emin = 4.5(log SMD) k; where Emin is measured in mJoules,
SMD is measured in pm, and
k is a constant related to fuel type.
[0033] According to Lefebvre, heavy fuel oil has a minimum ignition
energy of about 800 mJ at a SMD of 115 pm and a minimum ignition
energy of about 23 mJ at a SMD of 50 pm. Isooctane has a minimum
ignition energy of about 9 mJ at a SMD of 90 pm and a minimum ignition
energy of about 0.4 mJ at a SMD of 40 pm. For a diesel fuel, when SMD
is equal to 100 pm, Emin is about 100 mJ. A reduction in SMD to 30 pm
would yield a reduction in Emin to about 0.8 mJ. As may be appreciated,
ignition system requirements are substantially reduced for SMD values
below 25 pm.
[0034] The power conversion apparatus according to the present
invention has been found to exhibit highly desirable low ignition energy
requirements. A low ignition energy requirement improves the power
producing benefits of the present invention by reducing the weight of the
overall system and maximizing the power output through the reduction of
the parasitic power losses associated with the ignition system.
[0035] In view of the benefits hereinabove described, low energy
spark ignition devices are preferred for the igniter of the power producing
apparatus. Preferred are small piezo-electric ignition devices capable of
providing a spark energy in the range of about 5 to 7 millijoules (mJ).
Such devices are known to be simple, compact and present no parasitic
load issues. The ultra-fine fuel vaporization provided by the apparatus of
the invention cooperates to provide excellent ignition characteristics with
low energy piezo-electric ignition devices.
[0036] The emissions characteristics of liquid-fueled combustion
devices are known to be sensitive to the quality of the fuel droplet size
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distribution. High quality, fine sprays promote fuel evaporation and
enhance mixing, thereby reducing the need for fuel-rich combustion and
the often-attendant generation of smoke and soot. Small droplets follow
flow streamlines and are less prone to impact against burner walls.
Conversely, large droplets can impact burner walls and cause CO and
hydrocarbon emissions and carbon deposits. This problem is more
noticeable in devices where the flames are highly confined.
[0037] The heat produced during combustion of the vaporized fuel
can be converted to electrical or mechanical power. For instance, the heat
could be converted to any desired amount of electrical or mechanical
power, e.g., up to 510 kg-m/sec (5000 watts) of electrical power or
mechanical power. Compared to portable battery technology which can
only provide approximately 2.0 kg-m/sec (20 W) for a few hours or a noisy,
high emissions, internal combustion engine/generator producing above
102 kg-m/sec (1 kW), the apparatus according to one preferred
embodiment of the invention offers a quiet, clean power source in the few
hundred watt range.
[0038] Various technologies exist for conversion of heat produced
in the combustion chamber according to the invention into electrical or
mechanical power. For instance, in the 2.0 to 510 kg-m/sec (20 to 5000
watt) range, at least the following technologies are contemplated: Stirling
engines for conversion of heat into mechanical power which can be used
to drive a generator, micro-gas turbines which can be used to drive a
generator, thermoelectric for direct conversion of heat into electricity, and
thermophotovoltaics for direct conversion of radiant energy into electricity.
[0039] The thermoelectric devices offer advantages in terms of
being quiet and durable, and coupled with external combustion systems,
offer the potential for low emissions and flexibility as to fuel. Various
types
of thermoelectric generators, which can be used as the conversion device,
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include those disclosed in U.S. Patent Nos. 5,563,368; 5,793,119;
5,917,144; and 6,172,427.
[0040] The thermophotovoltaic devices offer advantages in terms
of being quiet, providing moderate power density, and coupled with
external combustion systems offer the potential for low emissions and
flexibility as to fuel. Various types of thermophotovoltaic devices, which
can be used as the conversion device, include those disclosed in U.S.
Patent Nos. 5,512,109; 5,753,050; 6,092,912; and 6,204,442. As shown
in U.S. Patent No. 6,204,442, a heat radiating body can be used to
absorb heat from combustion gases and heat radiated from the heat
radiating body is directed to a photocell for conversion to electricity, thus
protecting the photocell from direct exposure to the combustion gases.
[0041] Micro-gas turbines could be desirable in terms of high
specific power. Microturbine devices, which can be used as the conversion
device, include those disclosed in U.S. Patent Nos. 5,836,150; 5,874,798;
and 5,932,940.
[0042] Stirling engines offer advantages with respect to size,
quiet
operation, durability, and coupled with external combustion systems
offer the potential for low emissions and flexibility as to fuel. Stirling
engines that can be used as the conversion device will be apparent to
those skilled in the art.
[0043] Referring now to FIG. 1, a fuel-vaporizing device for
use in
the apparatus of the present invention is shown. Fuel vaporizing device 10,
for vaporizing a liquid fuel drawn from a source of liquid fuel, includes a
capillary flow passage 12, having an inlet end 14 and an outlet end 16. A
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fluid control valve 18 is provided for placing inlet end 14 of capillary flow
passage 12 in fluid communication with a liquid fuel source F and
introducing the liquid fuel in a substantially liquid state into capillary
flow
passage 12. As is preferred, fluid control valve 18 may be operated by a
solenoid. A heat source 20 is arranged along capillary flow passage 12.
As is most preferred, heat source 20 is provided by forming capillary flow
passage 12 from a tube of electrically resistive material, a portion of
capillary flow passage 12 forming a heater element when a source of
electrical current is connected to the tube at connections 22 and 24 for
delivering current therethrough. Heat source 20, as may be appreciated,
is then operable to heat the liquid fuel in capillary flow passage 12 to a
level sufficient to change at least a portion thereof from the liquid state to
a
vapor state and deliver a stream of substantially vaporized fuel from outlet
end 16 of capillary flow passage 20. By substantially vaporized is meant
that at least 50% of the liquid fuel is vaporized by the heat source,
preferably at least 70%, and more preferably at least 80% of the liquid fuel
is vaporized.
[0044] Fuel vaporizing device 10 also includes means for cleaning
deposits formed during the operation of the apparatus of the present
invention. The means for cleaning deposits shown in FIG. 1 includes fluid
control valve 18, heat source 20 and an oxidizer control valve 26 for
placing capillary flow passage 12 in fluid communication with a source of
oxidizer C. As may be appreciated, the oxidizer control valve can be
located at or near either end of capillary flow passage 12 or configured to
be in fluid communication with either end of capillary flow passage 12. If
the oxidizer control valve is located at or near the outlet end 16 of
capillary
flow passage 12, it then serves to place the source of oxidizer C in fluid
communication with the outlet end 16 of capillary flow passage 12. In
operation, heat source 20 is used to heat the oxidizer C in capillary flow
passage 12 to a level sufficient to oxidize deposits formed during the
heating of the liquid fuel F. In one embodiment, to switch from a fueling
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mode to a cleaning mode, the oxidizer control valve 26 is operable to
alternate between the introduction of liquid fuel F and the introduction of
oxidizer C into capillary flow passage 12 and enables the in-situ cleaning
of capillary flow passage when the oxidizer is introduced into the at least
one capillary flow passage.
[0045] One
technique for oxidizing deposits includes passing air or
steam through the capillary flow passage. As indicated, the capillary flow
passage is preferably heated during the cleaning operation so that the
oxidation process is initiated and nurtured until the deposits are
consumed. To enhance this cleaning operation, a catalytic substance may
be employed, either as a coating on, or as a component of, the capillary
wall to reduce the temperature and/or time required for accomplishing the
cleaning. For continuous operation of the fuel vaporizing device, more
than one capillary flow passage can be used such that when a clogged
condition is detected, such as by the use of a sensor, fuel flow can be
diverted to another capillary flow passage and oxidant flow initiated
through the clogged capillary flow passage to be cleaned. As an example,
a capillary body can include a plurality of capillary flow passages therein
and a valving arrangement can be provided to selectively supply liquid fuel
or air to each flow passage.
[0046]
Alternatively, fuel flow can be diverted from a capillary flow
passage and oxidant flow initiated at preset intervals. Fuel delivery to a
capillary flow passage can be effected by a controller. For example, the
controller can activate fuel delivery for a preset time period and deactivate
fuel delivery after the preset amount of time. The controller may also
effect adjustment of the pressure of the liquid fuel and/or the amount of
heat supplied to the capillary flow passage based on one or more sensed
conditions. The sensed conditions may include inter alia: the fuel
pressure, the capillary temperature or the air-fuel ratio. The controller may
also control one or more capillary flow passages to clean deposits.
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[0047] The cleaning technique may be applied to combustion
devices having a single flow passage. However, if the combustion device
is intermittently shut down during the cleaning operation, the energy
supplied to the flow passage during cleaning would preferably be
electrical. The time period between cleanings may either be fixed based
upon experimentally determined clogging characteristics, or a sensing and
control device may be employed to detect clogging and initiate the
cleaning process as required. For example, a control device could detect
the degree of clogging by sensing the fuel supply pressure to the capillary
flow passage.
[0048] As indicated, the oxidation cleaning technique may also be
applied to fuel vaporizing devices that are required to operate
continuously. In this case, multiple capillary flow passages are employed.
An exemplary multiple capillary flow passage fuel-vaporizing device for
use in the present invention is illustrated in FIGS. 2 and 3. FIG. 2 presents
a schematic view of a multiple capillary tube arrangement, integrated into
a single assembly 94. FIG. 3 presents an end view of the assembly 94.
As shown, the assembly can include the three capillary tubes 82A, 82B,
82C and a positive electrode 92 which can include a solid stainless steel
rod. The tubes and the rod can be supported in a body 96 of electrically
insulating material and power can be supplied to the rod and capillary
tubes via fittings 98. For example, direct current can be supplied to
upstream ends of one or more of the capillary tubes and a connection 95
at the downstream ends thereof can form a return path for the current
through rod 92.
[0049]
Reference is made now to FIG. 4, wherein a multiple
capillary tube vaporizing system 80 for use in the practice of the present
invention is shown. The system includes capillary tubes 82A through C,
fuel supply lines 84A through C, oxidizer supply lines 86A through C,
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oxidizer control valves 88A through C, power input lines 90A-C and
common ground 91. The system 80 allows cleaning of one or more
capillary tubes while fuel delivery continues with one or more other
capillary tubes. For example, combustion of fuel via capillary flow
passages 82B and 82C can be carried out during cleaning of capillary flow
passage 82A. Cleaning of capillary flow passage 82A can be
accomplished by shutting off the supply of fuel to capillary tube 82A,
supplying air to capillary flow passage 82A with sufficient heating to
oxidize deposits in the capillary flow passage. Thus, the cleaning of one
or several capillaries can be carried out while continuously delivering fuel.
The one or more capillary flow passages being cleaned are preferably
heated during the cleaning process by an electrical resistance heater or
thermal feedback from the application. Again, the time period between
cleanings for any given capillary flow passage may either be fixed based
upon known clogging characteristics, determined experimentally, or a
sensing and control system may be employed to detect deposit buildup
and initiate the cleaning process as required.
[0050] FIG. 5
shows an exemplary schematic of a control system to
operate an apparatus in accordance with the present invention, the
apparatus incorporating an oxidizing gas supply for cleaning clogged
capillary passages. The control system includes a controller 100 operably
connected to a fuel supply 102 that supplies fuel and optionally air to a
flow passage such as a capillary flow passage 104. The controller is also
operably connected to a power supply 106 that delivers power to a
resistance heater or directly to a metal capillary flow passage 104 for
heating the tube sufficiently to vaporize the fuel. If
desired, the
combustion system can include multiple flow passages and heaters
operably connected to the controller 100. The controller 100 can be
operably connected to one or more signal sending devices such as an on-
off switch, thermocouple, fuel flow rate sensor, air flow rate sensor, power
output sensor, battery charge sensor, etc. whereby the controller 100 can
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be programmed to automatically control operation of the combustion
system in response to the signal(s) outputted to the controller by the signal
sending devices 108.
[0051] In operation, the fuel vaporizing device of the apparatus
according to the present invention can be configured to feed back heat
produced during combustion such that the liquid fuel is heated sufficiently
to substantially vaporize the liquid fuel as it passes through the capillary
reducing or eliminating or supplementing the need to electrically or
otherwise heat the capillary flow passage. For example, the capillary tube
can be made longer to increase the surface area thereof for greater heat
transfer, the capillary tube can be configured to pass through the
combusting fuel or a heat exchanger can be arranged to use exhaust gas
from the combustion reaction to preheat the fuel.
[0052] FIG. 6 shows, in simplified form, how a capillary flow
passage 64 can be arranged so that liquid fuel traveling therethrough can
be heated to an elevated temperature to reduce the power requirements of
the fuel-vaporizing heater. As shown, a portion 66 of a tube comprising
the capillary flow passage passes through the flame 68 of the combusted
fuel. For initial start up, a resistance heater comprising a section of the
tube or separate resistance heater heated by electrical leads 70, 72
connected to a power source such as a battery 74 can be used to initially
vaporize the liquid fuel. After ignition of the vaporized fuel by a suitable
ignition arrangement, the portion 66 of the tube can be preheated by the
heat of combustion to reduce the power otherwise needed for continued
vaporization of the fuel by the resistance heater. Thus, by preheating the
tube, the fuel in the tube can be vaporized without using the resistance
heater whereby power can be conserved.
[0053] As will be appreciated, the fuel vaporizing device and
attendant system depicted in FIGS. 1 through 6 may also be used in
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connection with another embodiment of the present invention. Referring
again to FIG. 1, the means for cleaning deposits includes fluid control
valve 18, a solvent control valve 26 for placing capillary flow passage 12 in
fluid communication with a solvent, solvent control valve 26 disposed at
one end of capillary flow passage 12. In one embodiment of the apparatus
employing solvent cleaning, the solvent control valve is operable to
alternate between the introduction of liquid fuel and the introduction of
solvent into capillary flow passage 12, enabling the in-situ cleaning of
capillary flow passage 12 when the solvent is introduced into capillary flow
passage 12. While a wide variety of solvents have utility, the solvent may
comprise liquid fuel from the liquid fuel source. When this is the case, no
solvent control valve is required, as there is no need to alternate between
fuel and solvent, and the heat source should be phased-out or deactivated
during the cleaning of capillary flow passage 12.
[0054] FIG. 7 presents another exemplary embodiment of the
present invention. A fuel-vaporizing device 200 for use in the apparatus of
the present invention has a heated capillary flow passage 212 for
delivering liquid fuel F. Heat is provided by heat source 220, which is
arranged along capillary flow passage 212. As is most preferred, heat
source 220 is provided by forming capillary flow passage 212 from a tube
of electrically resistive material, a portion of capillary flow passage 212
forming a heater element when a source of electrical current is connected
to the tube at connections 222 and 224 for delivering current thereth rough.
[0055] In order to clean deposits formed during operation of fuel
vaporizing device 200, an axially moveable rod 232 is positioned through
opening 236 of end cap 234 of device body 230 so as to be in axial
alignment with the opening of inlet end 214 of capillary flow passage 212.
Packing material 238 is provided within the interior volume of end cap 234
for sealing. Referring now to FIG. 7A, axial moveable rod 232 is shown
fully extended within capillary flow passage 212. As may be appreciated,
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selecting the diameter of axial moveable rod 232 for minimal wall
clearance within the interior of capillary flow passage 212 produces a
combination capable of removing substantially all of the deposits built up
along the interior surface of capillary flow passage 212 during the
operation of fuel vaporizing device 200.
[0056] FIG. 8 shows a schematic of an apparatus in accordance
with the invention which includes a free-piston Stirling engine 30, a
combustion chamber 34 wherein heat at 550-750 C is converted into
mechanical power by a reciprocating piston which drives an alternator
32 to produce electrical power. The assembly also includes a capillary
flow passage/heater assembly 36, a controller 38, a rectifier/regulator
40, a battery 42, a fuel supply 44, a recuperator 46, a combustion
blower 48, a cooler 50, and a cooler/blower 52. In operation, the
controller 38 is operable to control delivery of fuel to the capillary 36
and to control combustion of the fuel in the chamber 34 such that the
heat of combustion drives a piston in the Stirling engine such that the
engine outputs electricity from the alternator 32. If desired, the Stirling
engine/alternator can be replaced with a kinematic Stirling engine
which outputs mechanical power. Examples of combustion chambers
and air preheating arrangements can be found in U.S. Patent Nos.
4,277,942, 4,352,269, 4,384,457 and 4,392,350.
[0057] FIG. 9 presents a partial cross-sectional schematic view of a
power-producing device in accordance with another embodiment of the
invention, which can form part of a heat conversion device such as a
Stirling engine assembly. As shown in FIG. 9, air delivered to an air inlet
by an air blower enters the combustion chamber 34 and mixes with
vaporized fuel delivered to the chamber by the capillary/heater
arrangement 36. Heat of combustion in the chamber 34 heats the end
of the Stirling engine 30 and a sliding piston reciprocates within an
alternator in a manner that generates electricity. The chamber 34 can
be designed
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to allow the exhaust gases to preheat incoming air and thus lower the
energy requirements for combusting the fuel. For instance, the housing
can include a multiwall arrangement, which allows the incoming air to
circulate in a plenum, which is heated by exhaust gases circulating in an
exhaust passage. Inlet air (indicated by arrow 55) can be caused to swirl in
the combustion chamber by passing the air through swirler vanes 56
around the combustion chamber 34. The combusted air-fuel mixture heats
the heat conversion device (Stirling engine) 30 and exhaust gases
(indicated by arrows 57) are removed from the combustion chamber.
[0058] In general, the power conversion apparatus could include a
liquid fuel source, at least one flow passage (e.g., one or more heated
capillary tubes) through which fuel from the fuel supply is vaporized and
delivered to a combustion chamber wherein the vaporized fuel is
combusted, and heat produced in the combustion chamber is used to drive
a Stirling engine or other heat conversion device. A heat exchanger can
be used to preheat air as the air travels through air passages in the heat
exchanger thereby maximizing efficiency of the device, i.e., by preheating
the air mixed with the vaporized fuel to support combustion in the
chamber, less fuel is needed to maintain the Stirling engine at a desired
operating temperature. The exhaust gas can travel through exhaust ducts
in the heat exchanger whereby heat from the exhaust gas can be
transferred to the air being delivered to the combustion chamber.
[0059] The combustion chamber can incorporate any suitable
arrangement wherein air is mixed with the vaporized fuel and/or an air-fuel
mixture is combusted. For example, the fuel can be mixed with air in a
venturi to provide an air-fuel mixture and the air-fuel mixture can be
combusted in a heat-generating zone downstream from the venturi. In
order to initiate combustion, the air-fuel mixture can be confined in an
ignition zone in which an igniter such as a spark generator ignites the
mixture. The igniter can be any device capable of igniting the fuel such as
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a mechanical spark generator, an electrical spark generator, resistance
heated ignition wire or the like. The electrical spark generator 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-mechanically due to
compression 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.
[0060] Some of the electrical power generated by the conversion
device can be stored in 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 and/or the electrical current can
be supplied to an igniter for initiating combustion of the fuel-air mixture
delivered to the combustion chamber.
[0061] If desired, the heat generated by combusting the fuel could
be used to operate any types of devices that rely on mechanical or
electrical power. For instance, a heat conversion source could be used to
generate electricity 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 heat conversion device could also be used to supply
power to non-portable devices or to locations where access to an electrical
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power grid is not available, inconvenient or unreliable. Such
locations and/or non-portable devices include remote living quarters
and military encampments, vending machines, marine equipment, etc.
[0062] Contemplated photovoltaic arrays for use in the hybrid
power generating systems of the present invention include a wide variety
of photovoltaic cells. Examples of preferred types known to be available
can provide 20-25% conversion efficiency and may include several
conversion layers. For example, a blue-responsive layer on an
outermost surface, then a green-red responsive layer, and then an
infrared layer. Other types are made with gallium rather than silicon.
Nevertheless, in certain circumstances, it may be more economic to use
a relatively inefficient (10-18%) cell, wherein the semi-conducting
surface of a cell is preferably provided with an adequate amount (in
terms of cross-sectional area) of conductive metallic strips so that the
generated current, which may be several times greater than that
envisaged by its manufacturers, does not cause overheating of the
semiconductor or even melting of metal conductors.
[0063] Alternatively, dedicated designs of solar cells may comprise
an amorphous type comprising layered amorphous silicon constructed on a
planar or non-planar surface, as those skilled in the art will understand.
Developments in the construction of these cells can allow cell material to
be evaporated or sprayed onto any surface to form a conforming coating.
[0064] A variety of methods for producing photovoltaic cells and
photovoltaic arrays are known, as evidenced by U.S. Patent
Nos. 4,152,824; 4,239,555; 4,451,969; 4,595,790; 4,851,308;
6,077,722; 6,111,189; 6,368,892; 6,423,565; and 6,465,724.
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[0065] As is
common in the art of power generation using
photovoltaic cells, means to balance out loading may be provided if, for
example, a part of the array is in a relatively poorly illuminated position. A
useful operating voltage is at least 12 volts, with higher voltages providing
enhanced utility from the standpoint of minimizing transmission losses and
semiconductor losses, particularly when the sunlight is weak and the
actual voltage drops. A step-up converter may be provided as is known in
the art, to maintain a constant output voltage though at varying currents.
Typically, an array used in combination with this invention may produce in
the range of 51 to 204 kg-m/sec (500 watts to 2 kilowatts) or more of
electricity.
[0066]
Referring now to FIG. 10, a block diagram of a hybrid power
system 300 in accordance with a preferred form is shown. As shown, a
power unit 310 is provided which includes a liquid fuel source, one or more
heated capillary tubes through which fuel from a fuel supply is vaporized
and delivered to a combustion chamber wherein the vaporized fuel is
combusted, and heat produced during combustion chamber is used to
drive a Stirling engine or other heat conversion device, as previously
described. The heat conversion device may be advantageously attached
to an alternator, such as a linear alternator for the production of electrical
power and sent to storage battery 340 that feeds power electronics
module 350, which, in turn, is connected to a load.
[0067]
Photovoltaic array 320, which may be selected from the
types previously described, is also electrically connected to storage battery
340 and may be sized to provide the total requirements of the load during
periods of peak solar radiation or may be designed for supplementation by
power unit 310. With respect to the sizing of the power unit 310, a unit
having an engine with a 35.7 kg-m/sec (350-watt) capacity would provide a
similar power output over 12 hours per day as a 102 kg-m/sec (1-kilowatt)
photovoltaic array provides on a sunny day. As such, the capacity of the
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power unit can be considerably lower than that of the PV array and still
provide dispatch capability and power reliability enhancement. As may be
appreciated multiple power units could be used simultaneously to address
larger applications.
[0068] As is
particularly preferred, photovoltaic array 320 provides
about 90% of delivered electricity, yielding a hybrid strategy that requires
about 300 to 800 hours annually of engine operation. The hybrid
architecture of the present invention can reduce the need for photovoltaic
panel and battery storage capacity by 25% to 50% and can reduce capital
and ownership costs as compared to photovoltaic arrays. Additionally, the
hybrid architecture contemplated reduces stress on the battery subsystem
(reduced levels of discharge, etc.) with resultant increases in replacement
schedules of a factor of two or more.
[0069] 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.
