U.S. patent application number 12/552179 was filed with the patent office on 2010-12-16 for reduced backpressure combustion purifier.
Invention is credited to Lincoln Evans-Beauchamp.
Application Number | 20100314089 12/552179 |
Document ID | / |
Family ID | 43649928 |
Filed Date | 2010-12-16 |
United States Patent
Application |
20100314089 |
Kind Code |
A1 |
Evans-Beauchamp; Lincoln |
December 16, 2010 |
Reduced Backpressure Combustion Purifier
Abstract
Reverse flow heat exchangers including one or more pairs of
contiguous ducts are provided. An intake duct conveys particle
laden air, such as engine exhaust, to a combustion chamber and an
exit duct conveys the purified air away from the combustion
chamber. The exit duct is shaped such that the cross sectional area
thereof varies as function of the length thereof, for example, the
cross sectional area can increase as a function of distance from
the combustion chamber. The intake duct can also be shaped to have
a varying cross sectional area. A combustion purifier is formed by
the combination of the combustion chamber with the reverse flow
heat exchanger. When used in combination with an engine, the shapes
of the ducts can serve to increase the power or efficiency of the
engine by further reducing backpressure, as compared to a reverse
flow heat exchanger without the shaped ducts.
Inventors: |
Evans-Beauchamp; Lincoln;
(Palo Alto, CA) |
Correspondence
Address: |
PETERS VERNY , L.L.P.
425 SHERMAN AVENUE, SUITE 230
PALO ALTO
CA
94306
US
|
Family ID: |
43649928 |
Appl. No.: |
12/552179 |
Filed: |
September 1, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12202186 |
Aug 29, 2008 |
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12552179 |
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11800110 |
May 3, 2007 |
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12202186 |
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11787851 |
Apr 17, 2007 |
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11800110 |
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11404424 |
Apr 14, 2006 |
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11787851 |
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11412289 |
Apr 26, 2006 |
7566423 |
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11404424 |
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11412481 |
Apr 26, 2006 |
7500359 |
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11412289 |
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Current U.S.
Class: |
165/172 |
Current CPC
Class: |
F01N 2240/02 20130101;
F01N 3/2889 20130101; F01N 3/10 20130101; F01N 3/028 20130101; F01N
2570/10 20130101; F01N 3/28 20130101; F01N 2240/06 20130101 |
Class at
Publication: |
165/172 |
International
Class: |
F28F 1/10 20060101
F28F001/10 |
Claims
1. A system comprising: a combustion chamber; and a reverse flow
heat exchanger including a first duct having a first end, and a
second end opening into the combustion chamber; and a second duct,
contiguous with the first duct, and having a first end opening into
the combustion chamber, a second end, and a cross sectional area
that increases between the first end and the second end.
2. The system of claim 1 wherein the first duct has a cross
sectional area that decreases between the first end and the second
end thereof.
3. The system of claim 1 wherein a width of the second duct
increases linearly as a function of a length thereof.
4. The system of claim 1 wherein the first and second ducts are
spiral-wound around the combustion chamber.
5. The system of claim 1 wherein the combustion chamber defines a
first longitudinal axis and the reverse flow heat exchanger defines
a second longitudinal axis approximately perpendicular to the first
longitudinal axis.
6. A vehicle comprising: an engine having an exhaust pipe; and a
combustion purifier including a combustion chamber, and a reverse
flow heat exchanger having a first duct having a first end in fluid
communication with the exhaust pipe, and a second end opening into
the combustion chamber; and a second duct, contiguous with the
first duct, and having a first end opening into the combustion
chamber, a second end, and a cross sectional area that increases
between the first end and the second end.
7. The vehicle of claim 6 wherein the first duct has a cross
sectional area that decreases between the first end and the second
end thereof.
8. The vehicle of claim 6 wherein a width of the second duct
increases linearly as a function of a length thereof.
9. The vehicle of claim 6 wherein the first and second ducts are
spiral-wound around the combustion chamber.
10. The vehicle of claim 6 wherein the combustion chamber defines a
first longitudinal axis and the reverse flow heat exchanger defines
a second longitudinal axis approximately perpendicular to the first
longitudinal axis.
11. The vehicle of claim 6 further comprising a turbo charger, the
turbo charger including an impeller and a turbine, and the second
end of the second duct being in fluid communication with the
turbine of the turbo charger.
12. A system comprising: a combustion chamber; and a reverse flow
heat exchanger including a first duct having a first end, and a
second end opening into the combustion chamber; and a second duct,
contiguous with the first duct, and having a first end opening into
the combustion chamber, a second end, and a cross sectional area
that decreases between the first end and the second end.
13. The system of claim 12 wherein the first duct has a cross
sectional area that increases between the first end and the second
end thereof.
14. A vehicle comprising: an engine having an exhaust pipe; and a
combustion purifier including a combustion chamber, and a reverse
flow heat exchanger having a first duct having a first end in fluid
communication with the exhaust pipe, and a second end opening into
the combustion chamber; and a second duct, contiguous with the
first duct, and having a first end opening into the combustion
chamber, a second end, and a cross sectional area that decreases
between the first end and the second end.
15. The vehicle of claim 14 wherein the first duct has a cross
sectional area that decreases between the first end and the second
end thereof.
16. The vehicle of claim 14 further comprising a turbo charger, the
turbo charger including an impeller and a turbine, and the second
end of the second duct being in fluid communication with the
turbine of the turbo charger.
17. An electricity generating system comprising: a burner having an
exhaust; and a combustion purifier including a combustion chamber,
and a reverse flow heat exchanger having a first duct having a
first end in fluid communication with the exhaust, and a second end
opening into the combustion chamber; and a second duct, contiguous
with the first duct, and having a first end opening into the
combustion chamber, a second end, and a cross sectional area that
varies between the first end and the second end.
18. The electricity generating system of claim 17 wherein the cross
sectional area of the second duct increases between the first end
and the second end.
19. The electricity generating system of claim 17 wherein the cross
sectional area of the second duct decreases between the first end
and the second end.
20. The electricity generating system of claim 17 further
comprising a turbo charger, the turbo charger including an impeller
and a turbine, and the second end of the second duct being in fluid
communication with the turbine of the turbo charger.
21. A ramjet comprising: an intake duct; a combustion chamber in
fluid communication with the intake duct; a nozzle in fluid
communication with the combustion chamber; and a reverse flow heat
exchanger for regenerating heat from the nozzle to the intake duct,
the reverse flow heat exchanger including a contiguous interface
between the nozzle and the intake chamber, where the ramjet does
not include moving parts.
22. The ramjet of claim 21 wherein the intake duct and nozzle are
spiral-wound around the combustion chamber.
23. The ramjet of claim 21 wherein the intake duct is symmetric
around a longitudinal axis.
24. The ramjet of claim 21 wherein the intake duct has a cross
sectional area that decreases between a first end and a second end
thereof, where the second end of the intake duct opens into the
combustion chamber.
25. The ramjet of claim 21 wherein the nozzle is characterized by a
plurality of expansion regions separated by non-expansion
regions.
26. A method comprising: receiving an airflow in an intake duct;
receiving the airflow in a combustion chamber in fluid
communication with the intake duct; maintaining a continuous
combustion in the combustion chamber to heat the airflow; expanding
the heated airflow through a nozzle in fluid communication with the
combustion chamber; and regenerating heat from the nozzle to the
intake duct.
27. The method of claim 26 wherein maintaining the continuous
combustion in the combustion chamber includes combusting particles
in the airflow.
28. The method of claim 26 wherein regenerating heat from the
nozzle to the intake duct includes conducting heat through a
contiguous interface between the nozzle and the intake duct.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 12/202,186 filed Aug. 29, 2008 and entitled
"Temperature Ladder and Applications Thereof," which is a
continuation-in-part of U.S. patent application Ser. No. 11/800,110
filed May 3, 2007 and entitled "Particle Burner disposed between an
Engine and a Turbo Charger," which is a continuation-in-part of
U.S. patent application Ser. No. 11/787,851 filed Apr. 17, 2007 and
titled "Particle Burner including a Catalyst Booster for Exhaust
Systems," which is a continuation-in-part of U.S. patent
application Ser. No. 11/404,424 filed Apr. 14, 2006 and titled
"Particle Burning in an Exhaust System," a continuation-in-part of
U.S. patent application Ser. No. 11/412,289 filed Apr. 26, 2006 and
titled "Air Purification System Employing Particle Burning," now
U.S. Pat. No. 7,566,423 issued Jul. 28, 2009, and also a
continuation-in-part of U.S. patent application Ser. No. 11/412,481
filed Apr. 26, 2006 and titled "Reverse Flow Heat Exchanger for
Exhaust Systems," now U.S. Pat. No. 7,500,359 issued Mar. 10, 2009.
The disclosures of all of the above U.S. patent applications are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to exhaust cleaning systems
and air cleaning systems.
[0004] 2. Description of the Prior Art
[0005] When a fuel burns incompletely, pollutants such as particles
and hydrocarbons are released into the atmosphere. The United
States Environmental Protection Agency has passed regulations that
limit the amount of pollutants that, for example, diesel trucks,
power plants, generators, engines, automobiles, and off-road
vehicles can release into the atmosphere.
[0006] Currently, industries attempt to follow these regulations by
adding scrubbers, catalytic converters and particle traps to their
exhaust systems. However, these solutions increase the amount of
back pressure exerted on the engine or combustion system,
decreasing system performance. In addition, the scrubbers,
catalytic converters and particle traps themselves become clogged
by particles and require periodic cleaning to minimize back
pressure.
[0007] Radiation sources and heaters have been used in exhaust
systems, for example, to periodically clean the particle traps or
filter beds. Others solutions have included injecting fuel into the
filter beds or exhaust streams as the exhaust enters the filter
beds to combust the particles therein. However, the filter beds can
be sensitive to high temperatures and the radiation sources and
heaters must be turned off periodically.
[0008] Air purification systems currently use one of two methods to
remove particles such as dust, biological toxins, pet dander, dust,
and the like from the air in a room. One type of system uses an
ionizer to provide a surface charge to the air-borne particles so
that they adhere to a surface. However, ionizers emit ozone, a
respiratory irritant, into the air. Another type of system uses a
filter, such as a HEPA filter, to trap particles as the air flows
through the filter. However, filters need to be replaced or cleaned
periodically. Both methods typically require a fan to efficiently
circulate the air, which requires electricity and can be loud.
[0009] Catalyst systems reduce a toxicity of emissions from an
internal combustion engine by providing an environment for a
chemical reaction wherein toxic combustion by-products are
converted to less-toxic substances. Some of the reactions may
include oxidizing carbon monoxide to carbon dioxide, oxidizing
unburnt hydrocarbons to carbon dioxide and water, and reducing
nitrogen oxides to nitrogen and oxygen. These reactions have a net
exothermic effect. Conventional catalysts system dump heat
generated from the exothermic reaction into the environment.
[0010] It is known to capture heat energy from an exhaust stream
using a recuperator. A recuperator is used to transfer some of the
heat energy from the exhaust stream to cool fresh air before the
cool fresh air enters a turbine. This cools the exhaust stream and
heats the cool fresh air and, thus, recoups some of the heat
energy.
SUMMARY OF THE INVENTION
[0011] Various embodiments of the invention include a temperature
ladder configured for the destruction of particles or other
reactions. The temperature ladder comprises a reverse flow heat
exchanger and an energy source disposed at an intermediate point
within the heat exchanger. As is described further elsewhere
herein, the addition of energy at an intermediate point within the
reverse flow heat exchanger results in a feedback effect that
causes the region in which energy is introduced to reach a high
temperature.
[0012] Some embodiments include an exhaust system comprising a
combustion chamber and an energy source. The combustion chamber is
elevated to a high temperature using the temperature ladder. The
energy source is arranged with respect to the combustion chamber,
either inside or outside of the chamber, so as to be able to add
energy to gasses within the combustion chamber. The energy source
can comprise a resistive heating element, a coherent or incoherent
infrared emitter, or a microwave emitter, a flame, an inductive
coil, or the like. For example, a microwave emitter can be tuned to
a particular molecular bond. Where the energy source is disposed
outside of the combustion chamber, the energy source can either
heat the chamber walls to reradiate into the chamber; else the
combustion chamber can include a radiation transparent window.
[0013] Particles in an exhaust stream passing through the
combustion chamber are heated by the energy source to their
combustion temperature and are consequently removed from the
exhaust by burning. Microwave radiation tuned to excite a molecular
bond found in the particles can be particularly effective for
heating the particles rapidly. Additional air or fuel can be added
to the combustion chamber, as needed, to promote better combustion.
Once a combustion front is established in the combustion chamber,
the combustion reaction can become self-sustaining so that further
energy from the energy source is no longer required. Exhaust
entering the reverse flow heat exchanger is heated as it travels
toward the combustion changer, and exhaust having passed through
the combustion chamber is used to heat the pre-combustion chamber
gas.
[0014] In various embodiments, the combustion chamber has a
circular or non-circular cross-section in a plane perpendicular to
a longitudinal axis of the chamber. In some of these embodiments,
the cross-section is at least partially parabolic to focus heat
from the burning particles back into a hot zone within the
combustion chamber where the particle burning preferentially
occurs. The combustion chamber can be thermally insulated to better
retain heat in order to maintain the combustion reaction. The
exhaust system can also comprise a thermally insulated exhaust pipe
leading to the combustion chamber to further reduce the loss of
heat from the exhaust stream before particle burning can occur. In
some embodiments, a reverse flow heat exchanger is placed in fluid
communication with the combustion chamber so that heat is
transferred to the incoming exhaust stream from the combusted
exhaust stream exiting the combustion chamber. In certain
embodiments, the reverse flow heat exchanger is also thermally
insulated.
[0015] Various embodiments of the present invention are configured
to eliminate particles without the use of an obstructing particle
filter or trap. The absence of a particle filter or trap within the
combustion chamber allows for a non-restrictive flow path and
reduces backpressure relative to systems that employ a filter or
trap. In other embodiments, a particle filter or trap is disposed
after the combustion chamber. In these embodiments most (e.g.,
greater than 80, 90, 95 or 99%) of the particles are burned prior
to reaching the particle filter or trap. The particle filter or
trap therefore needs to be cleaned or replaced much less often. For
example, a particle filter may be configured to pass nano-sized ash
that is the product of combustion but block larger particles.
[0016] In some embodiments, a vehicle comprising an internal
combustion engine and the exhaust system described above is also
provided. The exhaust system optionally serves as either or both of
a muffler and a catalytic converter. Thus, the combustion chamber
and/or reverse flow heat exchanger can also include a catalyst. In
some embodiments, the combustion chamber and/or the reverse flow
heat exchanger can be sized to act as a resonating chamber to serve
as a muffler. For example, the combustion chamber can have a
diameter greater than a diameter of the exhaust pipe leading into
the combustion chamber. The vehicle can also comprise a controller
configured to control the energy source.
[0017] The systems described herein can be implemented in a variety
of settings where particles are present in a gas stream for the
combustion of these particles. Various embodiments include gasoline
engine exhaust systems, diesel exhaust systems, power plant
emission systems, fireplace chimneys, air cleaning devices, ship
propulsion systems, aircraft, generators, vehicle exhaust systems,
air purification systems, dust reduction systems, or other sources
of particle laden air.
[0018] The systems described herein may also be implemented in
settings wherein a catalyst is used to remove undesirable compounds
from a gas stream. For example, the systems may be used to elevate
a catalyst and/or gas stream to a working temperature. Likewise,
the systems may be used to maintain the catalyst and/or gas stream
at the working temperature. Some embodiments are configured for
both combustion of particles and operation of a catalyst. In these
embodiments, the particles are optionally combusted prior to
passing of the gas stream through the catalyst. If interaction of
the exhaust with the catalyst is exothermic, the catalyst may
function as the energy source or a part thereof.
[0019] Some embodiments include an air purification system. This
system optionally comprises a spiral reverse flow heat exchanger,
including two ducts, spiral-wound around or above a combustion
chamber. The reverse flow heat exchanger receives particle-laden
air into the combustion chamber. In the combustion chamber, the
particles are burned, which heats the air. The exiting air,
substantially particle-free, exits the combustion chamber at an
elevated temperature. The reverse flow heat exchanger transfers the
heat from the exiting air to preheat the particle-laden air
entering the combustion chamber. Air circulation may be
accomplished using a fan or through the rising of the heated
air.
[0020] In some embodiments, an exhaust system comprises a reverse
flow heat exchanger including a plate defining a surface and
separating an exit chamber and an intake chamber. Each chamber of
the heat exchanger has an inlet and an outlet located at opposing
ends to allow flow therethrough. The exhaust system also comprises
a first manifold coupled to the reverse flow heat exchanger and in
fluid communication with the intake chamber inlet.
[0021] A vane is optionally disposed within the first manifold is
situated relative to the intake chamber inlet so as to reduce
resistance to fluid flow near the intake chamber inlet. The exhaust
system can also comprise a heating manifold that receives exhaust
from the intake chamber, heats the exhaust, and returns the exhaust
to the exit chamber. In some embodiments, the heating manifold
includes a combustion chamber for burning particles in the exhaust.
In these embodiments the exhaust system can also comprise an energy
source for heating the particles to at least a combustion
temperature.
[0022] Another exemplary exhaust system comprises a first manifold
and a reverse flow heat exchanger coupled to the first manifold.
Here, the reverse flow heat exchanger defines a transverse plane
and includes a plurality of parallel plates in a stacked geometry
separating a number of chambers, each chamber having an inlet and
an outlet. These chambers comprise a set of intake chambers
alternating with a set of exit chambers, where the inlets of the
intake chambers being in fluid communication with the first
manifold and the outlets of the intake chambers being in fluid
communication with the inlets of the exit chambers. The exhaust
system can further comprise a heating manifold coupled to the
reverse flow heat exchanger to provide the fluid communication
between the outlets of the intake chambers and the inlets of the
exit chambers.
[0023] In some embodiments an exhaust cleaner comprises a reverse
flow heat exchanger and a gas permeable catalyst. The reverse flow
heat exchanger includes a first duct interleaved with a second
duct, where each duct is spiral-wound around a central volume. The
first and second ducts are also in fluid communication with each
other across the central volume. The gas permeable catalyst is
optionally disposed within the central volume and separates the
central volume into first and second regions. The first duct of the
reverse flow heat exchanger opens into the first region, and the
second duct of the reverse flow heat exchanger opens into the
second region. In some embodiments, the catalyst comprises a
substrate and a catalytic material. Additionally, the central
volume can further comprise a heating element or other energy
source.
[0024] An exemplary vehicle comprises an internal combustion engine
and an exhaust system configured to receive exhaust from the
internal combustion engine. The exhaust system includes an exhaust
cleaner comprising a reverse flow heat exchanger and a gas
permeable catalyst. The reverse flow heat exchanger includes a
first duct interleaved with a second duct, where each duct is
optionally spiral-wound around a central volume. The first and
second ducts are also in fluid communication with each other across
the central volume. The gas permeable catalyst is disposed within
or near by the central volume and optionally separates the central
volume into first and second regions. The first duct of the reverse
flow heat exchanger opens into the first region, and the second
duct of the reverse flow heat exchanger opens into the second
region. In some of these embodiments, the exhaust cleaner further
comprises an inlet chamber and an outlet chamber, wherein the inlet
chamber is in fluid communication with the first duct and the
outlet chamber is in fluid communication with the second duct. The
inlet chamber can include vanes that protrude into the inlet
chamber, and the outlet chamber can include vanes extending
outward.
[0025] An exemplary method for cleaning vehicle or other exhaust is
also provided. The method comprises heating exhaust from an
internal combustion engine in a first duct of a reverse flow heat
exchanger, passing the exhaust from the first duct, through a gas
permeable catalyst, and into a second duct of the reverse flow heat
exchanger, where catalysis of incomplete combustion products at the
catalyst heats the catalyst and further heats the exhaust, and
cooling the exhaust within the second duct by transferring heat to
the first duct. Here, the ducts of the reverse flow heat exchanger
can be interleaved and/or spiral-wound. The method can also
comprise monitoring a temperature of the catalyst. In some of these
embodiments, the method further comprises employing a heating means
to heat the exhaust whenever the temperature of the catalyst is
below a threshold.
[0026] Yet another exemplary embodiment of the invention comprises
an engine, a turbo charger including an impeller and a turbine, and
a particle burner disposed between the engine and the turbine and
configured to receive exhaust from the engine. The system can
comprise a vehicle or a stationary system such as a power plant or
generator, for example. The engine can be a diesel engine, an
aircraft engine, or a gasoline engine, in various embodiments.
[0027] Yet another exemplary method comprises burning fuel in an
engine to produce an exhaust including particles, using the exhaust
to drive a turbine of a turbo charger, and heating the exhaust to a
combustion temperature of the particles before using the exhaust to
drive the turbine. In some embodiments, heating the exhaust
includes generating heat by catalyzing the further combustion of
gaseous products of incomplete combustion. Heating the exhaust can
also include passing the exhaust through a reverse flow heat
exchanger. The reverse flow heat exchanger can comprise two
interleaved ducts, and in some instances the ducts are
spiral-wound.
[0028] The present invention also provides systems comprising a
combustion chamber in combination with a reverse flow heat
exchanger. Such systems can be used as stand-alone air purifiers or
as combustion purifiers when configured to receive the exhaust from
a burner or an engine, for example. In an exemplary system, a
reverse flow heat exchanger includes first and second contiguous
ducts also referred to herein as an intake duct and an exit duct.
The first duct has a first and second ends, and the second end
opens into the combustion chamber. The second duct also has first
and second ends, with the first end opening into the combustion
chamber. In some of these embodiments, a cross sectional area of
the second duct increases between the first end and the second
end.
[0029] In further embodiments, the first duct has a cross sectional
area that decreases between the first end and the second end. In
various embodiments, a width of the second duct increases linearly
as a function of a length thereof. The ducts are spiral-wound
around the combustion chamber, in some embodiments, whereas in
other embodiments the combustion chamber defines a first
longitudinal axis and the reverse flow heat exchanger defines a
second longitudinal axis perpendicular or approximately
perpendicular to the first longitudinal axis.
[0030] In other embodiments of the system, a cross sectional area
of the second duct decreases between the first end and the second
end, rather than increasing. In some of these embodiments, the
first duct has a cross sectional area that increases between the
first end and the second end. The first and second ducts in some of
these embodiments are spiral-wound around the combustion chamber,
in some embodiments, whereas in other embodiments the combustion
chamber defines a first longitudinal axis and the reverse flow heat
exchanger defines a second longitudinal axis approximately
perpendicular to the first longitudinal axis.
[0031] Embodiments of the system where the cross sectional area of
the second duct either increases or decreases between the first end
and the second end can be used as a combustion purifier in fluid
communication with an exhaust pipe of an engine in a vehicle. In
some embodiments the vehicle further comprises a turbo charger
including an impeller and a turbine, and in these embodiments the
second end of the second duct is in fluid communication with the
turbine of the turbo charger.
[0032] Embodiments of the system where the cross sectional area of
the second duct varies between the first end and the second end can
also be used as a combustion purifier in fluid communication with
an exhaust of a burner used in an electricity generating system
such as a diesel generator or a coal-fired power plant. Here, too,
the generating system can further comprise a turbo charger
including an impeller and a turbine, where the second end of the
second duct is in fluid communication with the turbine of the turbo
charger.
BRIEF DESCRIPTION OF THE FIGURES
[0033] FIG. 1 depicts a system for burning particles in an exhaust
system in accordance with various embodiments of the invention.
[0034] FIG. 2 depicts a system for burning particles in an exhaust
system in accordance with various embodiments of the invention.
[0035] FIG. 3 depicts a system for burning particles in an exhaust
system in accordance with various embodiments of the invention.
[0036] FIG. 4 depicts a system for burning particles in an exhaust
system in accordance with various embodiments of the invention.
[0037] FIG. 5A depicts a cross sectional view of the system for
burning particles further comprising a reverse flow heat exchanger
in accordance with various embodiments of the invention.
[0038] FIG. 5B illustrates temperature as a function of position in
the system of FIG. 5A at various times according to various
embodiments of the invention.
[0039] FIG. 6 depicts a schematic representation of a vehicle
comprising an internal combustion engine and an exhaust system in
accordance with various embodiments of the invention.
[0040] FIG. 7 depicts a cross sectional view taken perpendicular to
a vertical axis of an exemplary spiral reverse flow heat exchanger
and combustion chamber in an air purification system in accordance
with various embodiments of the invention.
[0041] FIG. 8 depicts a cross sectional view along a vertical axis
of the air purification system in accordance with various
embodiments of the invention.
[0042] FIG. 9 is a flow chart depicting a method for purifying air
in accordance with various embodiments of the invention.
[0043] FIGS. 10 and 11 depict top and front views, respectively, of
an exemplary system for burning particles in an exhaust system in
accordance with various embodiments of the invention.
[0044] FIGS. 12 and 13 depict cross sections of the intake chamber
and exit chamber, respectively, of the system shown in FIGS. 10 and
11 in accordance with various embodiments of the invention.
[0045] FIG. 14 depicts a cross section taken along the line 14-14
of FIG. 11 in accordance with various embodiments of the
invention.
[0046] FIG. 15 depicts a cross section taken along the line 15-15
of FIG. 11 in accordance with various embodiments of the
invention.
[0047] FIG. 16 depicts a cross section taken along the line 16-16
of FIG. 10 in accordance with various embodiments of the
invention.
[0048] FIGS. 17 and 18 depict top and front views, respectively, of
an exemplary system for burning particles in an exhaust system in
accordance with various embodiments of the invention.
[0049] FIGS. 19 and 20 depict cross sections of the intake chamber
and exit chamber, respectively, of the system shown in FIGS. 17 and
18 in accordance with various embodiments of the invention.
[0050] FIG. 21 depicts a cross section taken along the line 21-21
of FIG. 17 with several alternative implementations of a vane in
accordance with various embodiments of the invention.
[0051] FIG. 22 depicts a cross section taken along the line 22-22
of FIG. 17 in accordance with various embodiments of the
invention.
[0052] FIG. 23 depicts a cross sectional view taken perpendicular
to a vertical axis of an exemplary reverse flow heat exchanger and
catalyst in an exhaust system in accordance with various
embodiments of the invention.
[0053] FIGS. 24 and 25 show top and side views, respectively, of an
exemplary exhaust system in accordance with various embodiments of
the invention.
[0054] FIG. 26 depicts a cross section of an exhaust system taken
along line 26-26 of FIG. 25 in accordance with various embodiments
of the invention.
[0055] FIG. 27 depicts a schematic representation of a particle
burner disposed between an engine and a turbo charger according to
various embodiments of the invention.
[0056] FIG. 28 depicts a cross sectional view of a reverse flow
heat exchanger disposed in a spiral configuration around a
combustion chamber according to various embodiments of the
invention.
[0057] FIG. 29 depicts a cross sectional view of another reverse
flow heat exchanger disposed in a spiral configuration around a
combustion chamber according to various embodiments of the
invention.
[0058] FIG. 30 depicts a cross sectional view of a reverse flow
heat exchanger connected to a combustion chamber according to
various embodiments of the invention.
[0059] FIG. 31 depicts a cross sectional view of another reverse
flow heat exchanger connected to a combustion chamber according to
various embodiments of the invention.
[0060] FIG. 32 is a chart showing exhaust temperature of a diesel
engine run with and without an exemplary exhaust cleaner as a
function of several different test conditions.
[0061] FIG. 33 is a chart showing exhaust backpressure of a diesel
engine run with and without an exemplary exhaust cleaner as a
function of the several different test conditions used in the chart
of FIG. 32.
[0062] FIG. 34 depicts a schematic representation of a catalytic
converter disposed between an engine and a turbo charger according
to various embodiments of the invention.
[0063] FIG. 35 depicts a cross sectional view of an exemplary
ramjet according to various embodiments of the invention.
[0064] FIG. 36 depicts a cross sectional view of another exemplary
ramjet, with exemplary temperature profiles, according to various
embodiments of the invention.
[0065] FIG. 37 is a flow chart depicting a method for operating a
ramjet in accordance with various embodiments of the invention.
DETAILED DESCRIPTION
[0066] An exhaust system comprises a combustion chamber and an
energy source to facilitate the combustion of particles within the
chamber. Once ignited, the combustion can continue and may be
self-sustaining so long as the concentration of combustible
particles in the exhaust entering the chamber remains sufficiently
high. In some embodiments, the disclosed device can replace both
the muffler and the catalytic converter in a vehicle exhaust system
and offers reduced back pressure for better fuel economy and lower
maintenance costs. The device requires little to no maintenance and
is self-cleaning.
[0067] FIG. 1 depicts an exhaust system 100 comprising a combustion
chamber 110 and an energy source 120. The combustion chamber 110
can be constructed using any suitable material capable of
withstanding the exhaust gases at the combustion temperature of the
particles. Suitable materials include stainless steel, titanium,
and ceramics, for example. In one embodiment, the combustion
chamber 110 has a non-circular cross-section 130 perpendicular to a
longitudinal axis of the combustion chamber 110. At least a portion
of the cross-section 130 can be parabolic, circular or otherwise
shaped in order to focus radiation from the combustion reaction
into a hot zone within the combustion chamber 110. It will be
appreciated that the combustion chamber 110, in some embodiments,
can be proportioned to serve as a resonating chamber so that the
combustion chamber 110 also performs as a muffler. In alternative
embodiments, energy source 120 may include other energy providing
devices discussed herein.
[0068] One advantage of various embodiments of the present
invention is the absence of an obstructing particle filter or trap
within the combustion chamber 110. A particle trap or filter is
obstructing if it permanently traps un-combusted particles and,
thus, as more and more un-combusted particles are trapped, reduces
gas throughput through combustion chamber 110 over time. By not
restricting the flow of exhaust gas through the combustion chamber
110, some embodiments of the invention serve to avoid an increase
back-pressure over time as compared with prior art systems.
[0069] Energy source 120, in the illustrated embodiment, comprises
a resistive heating element wrapped around the outside of the
combustion chamber 110. In another embodiment, the energy source
120 is placed externally along the longitudinal length of the
combustion chamber 110. In some embodiments, a controller (not
shown) for the energy source 120 is provided to control the power
to the energy source 120 and to turn off the energy source 120 when
not needed, such as when no exhaust is flowing. Alternative
embodiments of energy source 120 are discussed elsewhere
herein.
[0070] In various embodiments, energy source 120 may be an internal
or external energy source. For example, an internal energy source
may include a catalytic converter that generates energy through
reactions with exhaust gasses. An external energy source is an
energy source that receives energy from an external source and
provides it to combustion chamber 110. For example, a resistive
heater is an external energy sources that receives energy form a
battery or generator and provides this energy to combustion chamber
110. Energy source 120 may be continuous or periodic. A periodic
energy source is on that provides energy to combustion chamber 110
on a single pulse basis. For example, merely to initiate a
reaction. A non-continuous spark and a single induction pulse are
examples of periodic energy sources. A continuous energy source is
one that provides energy to combustion chamber 110 in a more
continuous manner. For example, a continuous energy source is one
that can be used to maintain combustion that would otherwise not be
self sustaining. Examples of continuous energy sources include
microwaves, a resistive electrical heater, a continuous electrical
discharge (arc), or a continuously powered (e.g., more than one
pulse) induction coil.
[0071] In operation, an exhaust gas containing particles, such as
carbonaceous particles like soot, flows through the combustion
chamber 110. An exhaust gas is a gas that has been at least
partially depleted of oxygen or some other oxidizer through a
combustion process. The energy source 120 heats the wall of the
combustion chamber 110 which re-radiates infrared (IR) radiation
into the interior of the combustion chamber 110. Some of the IR
radiation is absorbed by the particles in the exhaust gas as they
traverse the combustion chamber 110. When the particles reach a
temperature at which they ignite, about 800.degree. F. for
carbonaceous particles, the particles may burn completely, leaving
no residue. Accordingly, essentially particle-free exhaust leaves
the combustion chamber 110.
[0072] The heat produced by the combustion of the particles can
make the continuing reaction self-sustaining so that the energy
source 120 is no longer necessary. A thermocouple (not shown) can
be placed on or in the combustion chamber 110 in order to monitor
the temperature of the combustion reaction to provide feedback to a
controller (not shown) for controlling the power to the energy
source 120. As noted above, the combustion chamber 110 can be
shaped to focus IR radiation from the combustion reaction onto a
focal point or line within the combustion chamber 110 to create a
hot zone that helps to sustain the continuing reaction in the
absence of external heating.
[0073] In other embodiments, a flame is used to burn the particles
in the combustion chamber while in use and/or to initiate the
combustion process. Accordingly, the combustion chamber can include
a fuel inlet and an igniter to light the flame. A flame can also be
used in combination with the energy source or as a part thereof.
The fuel may include gasoline, diesel fuel, natural gas, hydrogen,
ethanol, propane, butane, or the like.
[0074] FIG. 2 depicts alternative embodiments of exhaust system 100
comprising combustion chamber 110 and energy source 120. In these
embodiments, the energy source 120 is disposed within the
combustion chamber 110. The energy source 120, as shown, comprises
a coiled resistive heating element. As above, the energy source 120
can take other shapes and, for example, can be longitudinally
disposed internally along the length of the combustion chamber 110.
In those embodiments in which the energy source 120 is disposed
within the combustion chamber 110, energy from the energy source
120 can directly heat the particles in the exhaust as well as heat
the walls of the combustion chamber 110 as in the embodiment of
FIG. 1.
[0075] FIG. 3 depicts a cross-section of alternative embodiments of
exhaust system 100 comprising combustion chamber 110 having an
inlet 320 and an outlet 330, optional thermal insulation 340, an
energy source 120, and a radiation transparent window 360 into the
combustion chamber 110. In the illustrated embodiment, a diameter
of the combustion chamber 110 is greater than a diameter of the
inlet 320. This arrangement slows the exhaust gas as it enters the
combustion chamber 110 and can create a muffling effect.
Alternatively, the diameter of outlet 330 may be greater than the
diameter of combustion chamber 110. In some embodiments, the
diameters of inlet 320, combustion chamber 110 and outlet 330 are
similar.
[0076] In some embodiments, the inlet 320 and/or the combustion
chamber 110 are thermally insulated by the thermal insulation 340
to retain as much heat as possible in the exhaust gas as the gas
enters the combustion chamber 110. It will be appreciated that
insulation 340 can be similarly applied to the other embodiments
disclosed herein. For example, a blanket of insulation 340 can be
wrapped around the energy source 120 and combustion chamber 110 of
FIG. 1.
[0077] In the embodiments illustrated by FIG. 3, energy source 120
can be, for example, a coherent or incoherent IR emitter or
microwave emitter, such as a Klystron tube, or the like. Energy
source 120 can be configured to emit radiation directionally and/or
within a desired range of wavelengths. Accordingly, radiation
transparent window 360 is provided to allow radiation to pass
directly into the combustion chamber 110. In some embodiments, the
radiation transparent window 360 extends completely around the
circumference of the combustion chamber 110.
[0078] As noted, energy source 120 can be tuned to produce
radiation within a desired range of wavelengths. Thus, the
radiation can be tuned to excite specific molecular bonds that are
known to be present in the particles of the exhaust stream. For
example, microwave radiation can be tuned to excite carbon-hydrogen
bonds or carbon-carbon bonds where the particles in the exhaust are
known to include such bonds. Tuning the radiation in this manner
can heat particles to their ignition temperature more quickly and
with less energy.
[0079] The radiation transparent window 360 is constructed using a
material that can withstand the heated exhaust gases within the
combustion chamber 110. In some embodiments, radiation transparent
window 360 is a microwave transparent window constructed using
fiberglass, plastic, polycarbonate, quartz, porcelain, or the like.
In other embodiments, the radiation transparent window 360 is an IR
transparent window constructed using, for instance, sapphire.
[0080] Surfaces within inlet 320 and/or combustion chamber 110 are
optionally textured so as to create improved flow properties
therein. For example, a textured surface may result in more
efficient heat exchange or a thicker boundary layer between flowing
gasses and the surface. Texturing may include mere roughening of
the surface or may include the addition of projections from the
surface into the gas flow.
[0081] FIG. 4 depicts an alternative embodiment of exhaust system
100 to illustrate other optional components that can be employed in
conjunction with any of the preceding embodiments. In these
embodiments, exhaust system 100 comprises a combustion chamber 110
having an inlet 420 and an outlet 430, energy source 120, an air
inlet 450, a fuel intake 460, and a catalyst 470. As in the
previous example, the combustion chamber 110 can have a greater
diameter than the inlet 420 and the outlet 430. Alternatively, the
outlet 430 can have the same diameter as combustion chamber 110.
The energy source 120, as shown, is a resistive heating element
disposed within the combustion chamber 410, but can alternatively
be disposed externally and can alternatively be an IR or microwave
emitter, or other instance of energy source 120.
[0082] The combustion chamber 410 may comprise air intake 450
and/or fuel intake 460. In some embodiments, air intake 450 is
configured to introduce oxygen to the combustion chamber to aid the
combustion reaction in the event that there is not enough oxygen
present in the exhaust as it enters the combustion chamber 410. In
some embodiments, fuel intake 460 introduces fuel into the
combustion chamber to burn and, thus, heat the exhaust as it enters
through inlet 420. It will be appreciated that adding fuel with or
without air can, in some instances, replace the need for the energy
source 120. In such embodiments, a spark generator or other
ignition source can be employed to ignite the combustion reaction
with the added fuel.
[0083] In certain embodiments, the combustion chamber 410
additionally comprises at least one catalyst 470 to catalyze
oxidation and/or reduction reactions in the exhaust stream. The
catalyst 470 can include platinum, rhodium, palladium, and/or the
like deposited on a honeycomb substrate or ceramic beads. In these
embodiments, the combustion chamber 410 is configured to
additionally function as a catalytic converter in the exhaust
system 100. It will be understood that heating the exhaust gas in
the presence of the catalyst 470 can advantageously improve the
completeness of the reaction being catalyzed. The catalyst 470 may
be 2-way or 3-way, and may be configured to operate at temperatures
between roughly 750 and 900.degree. C.
[0084] FIG. 5A depicts an alternative embodiment of exhaust system
100 comprising an inlet 505, a reverse flow heat exchanger 510,
combustion chamber 110, and an outlet 520. The heat exchanger 510
serves to pre-heat the exhaust before the exhaust enters the
combustion chamber 110. The heat exchanger 510 can also serve as a
muffler, in some embodiments. Heat exchanger 510 is separated into
two or more sections by at least one wall 525. Exhaust enters the
exhaust system 100 via the inlet 505 and is directed into one
section of the heat exchanger 510. Heated gases exiting the
combustion chamber 110 through another section of the heat
exchanger 510 transfer heat to the incoming gases through the wall
525. In some embodiments, the heat exchanger 510 and/or the
combustion chamber 110 are insulated by thermal insulation 530. As
in other embodiments described herein, the inlet 505 can also be
thermally insulated.
[0085] In some embodiments, the combustion chamber 110 has a
circular, parabolic or partially parabolic cross-section 535
perpendicular to a longitudinal axis to create a hot zone. The
combustion chamber 110 also comprises energy source 120. In some
embodiments, a radiation transparent window separates the energy
source 120 from the combustion chamber 110.
[0086] In some embodiments, the exhaust system 100 further
comprises at least one catalyst 545 configured to catalyze
oxidation and/or reduction reactions of undesirable gases in the
exhaust stream such as NO.sub.x compounds. In those embodiments
where the heat exchanger 510 is configured to act as a muffler, and
the combustion chamber 110 comprises catalyst 545, it will be
appreciated that the exhaust system 100 can replace both the
muffler and the catalytic converter in a conventional vehicle
exhaust system. Advantageously, because the combustion chamber 110
burns the particles present in the exhaust stream, it will be
further appreciated that the exhaust system 100 can additionally
replace a particle trap in a conventional exhaust system.
[0087] Catalyst 545 may be placed in combustion chamber 110, at an
exit of combustion chamber 110 or in the region of heat exchanger
510 following the combustion chamber 110. By placing catalyst 545
in one or more of these positions particles are burned in
combustion chamber 110 before they have a chance to reach catalyst
545. As such, catalyst 545 has a reduced chance of becoming fouled
or contaminated. Catalyst 545 may be placed following combustion
chamber 110 if a preferred operating temperature of catalyst 545 is
lower than the operating temperature of combustion chamber 110. For
example, in various embodiments, the temperature within combustion
chamber 110 is greater than approximately 537, 600 or 650.degree.
C., while the temperature at catalyst 545 may be less than these
values.
[0088] In various embodiments, the change in temperature between
the exhaust at inlet 505 and combustion chamber 110 is at least
100, 200, 350, 500 or 600 degrees C. In some embodiments, it is
desirable to have a minimal pressure differential between inlet 505
and outlet 520. For example, to maintain the efficiency of an
engine it is sometimes preferable to restrict exhaust flow as
little as possible. The pressure differential between inlet 505 and
outlet 520 is less than 3, 2, 1.5, 1.0, 0.5, 0.25 or 0.1 atm. The
pressure within combustion chamber may vary according to the
application. For example, if exhaust system 100 is used to process
the exhaust of a diesel truck, the pressure may be on the order of
2 atm. If exhaust system 100 is used to process the exhaust of a
diesel engine in a typical locomotive or ship the pressure may be
closer to 8 atm.
[0089] It should be noted that in some embodiments the catalyst 545
comprises a substrate, such as a grating, with a surface coating of
a catalytic material that is placed over an opening 550 of the heat
exchanger 510 or within heat exchanger 510. While such a catalyst
545 may at least partially restrict the flow of exhaust gas through
the combustion chamber 110, the catalyst is not considered a
particle trap or filter. Specifically, openings in the catalyst
substrate are too large to trap or filter the remaining nano-sized
ash particles in the exhaust following combustion. Additionally,
such a catalyst 545 tends not to collect particles for at least two
reasons. First, particles are mostly eliminated from the exhaust by
combustion before the exhaust reaches the catalyst 545. Second,
even if a group of particles survives the combustion reaction and
adheres to the catalyst 545, the restriction around the particles
would cause a local increase in temperature which would cause the
particles to burn and not be retained thereon.
[0090] Likewise, some embodiments that employ a microwave emitter
as the energy source 120 include a microwave-blocking grating (not
shown) either across the opening 550 or further downstream along
the exhaust path to prevent microwaves from propagating out of the
exhaust system 100. For essentially the reasons discussed above,
although such a microwave-blocking grating may at least partially
restrict the flow of exhaust gas through the combustion chamber
110, the microwave-blocking grating is not a particle trap or
filter. Specifically, the openings of the grating are too large to
trap or filter particles in the exhaust, particles are eliminated
from the exhaust before the exhaust reaches the microwave-blocking
grating, and any particles that survive and adhere to the
microwave-blocking grating simply burn off.
[0091] FIG. 5B illustrates temperature as a function of position in
the system of FIG. 5A at various times. These positions are along a
gas flow path between inlet 505 and outlet 520. At startup (Time 0)
energy source 120 provides a change in temperature of .DELTA.T at
combustion chamber 110. Other areas of combustion chamber 110 are
at ambient temperature. At a Time 1 gasses that have received the
temperature increase of .DELTA.T travel into the reverse flow heat
exchanger 510 toward outlet 520. Heat from these gasses traverse
through wall 525 and heat gas that has yet to enter combustion
chamber 110. The gas now entering the combustion chamber 110 is now
preheated. When this preheated gas receives energy from energy
source 120 it is again heated by approximately .DELTA.T. However,
because the gas was preheated the absolute temperature reached is
now higher than at Time 0. The reverse flow heat exchanger thereby
produces a feedback effect wherein an energy input can be used to
increase the temperature at an intermediate point within the heat
exchanger. Through this process the temperature in the combustion
chamber 110 is elevated until a steady state is reached at a Time
2. Gas leaving through outlet 520 is slightly hotter than gas
entering inlet 505. This temperature difference is a function of
the efficiency of the reverse flow heat exchanger 510. This process
of raising temperature within the combustion chamber and the
systems used to perform this process are referred to herein as a
temperature ladder. A temperature ladder can increase both the
temperature which gases reach and the amount of time they are at an
elevated temperature.
[0092] In some embodiments, a steady state is reached when the
energy provided by energy source 120 is equal to the energy
difference between gas entering inlet 505 and gas exiting outlet
520 plus energy lost through walls of exhaust system 100. In some
embodiments, a steady state is reached when the temperature within
combustion chamber 110 is the same as a temperature of energy
source 120. Under these conditions energy source 120 no longer adds
energy to the gases within combustion chamber 110. In some
embodiments, a steady state is reached because the temperature rise
achieved per unit of energy added to the exhaust gasses declines as
the absolute temperature increases. As a result the temperature
rise (.DELTA.T) in the combustion chamber at Time 0 may be greater
than the temperature rise achieved at steady state at Time 2.
[0093] Different types of energy source 120 may result in different
types of steady states. For example if energy source 120 includes a
flame then the maximum temperature of combustion chamber 110 is the
temperature of this flame. If energy source 120 includes a
microwave source, then energy source 120 may provide energy to
gasses within combustion chamber 110 irrespective of temperature
over a wide temperature range.
[0094] The presence of reverse flow heat exchanger 510 and
combustion chamber 110 result in any particles in the exhaust gas
being raised to a higher temperature and heated for a longer time
than would be achieved by combustion chamber 110 alone. In various
embodiments, the combustion chamber 110 operates at least 100, 200,
300, 400 degrees C. greater than the temperature of gasses entering
the reverse flow heat exchanger 510. When the combustion of
particle is exothermic, energy released by the combustion is added
to the system. For example, burning some carbon containing
particles may release energy. This energy supplements the energy
provided by energy source 120 and under some conditions is
sufficient to maintain combustion after energy source 120 is turned
off or turned down. The burning of particles may occur at a
combustion front at which the gas temperature reaches the particle
combustion temperature. This combustion front may be within
combustion chamber 110 or may travel into the reverse flow heat
exchanger toward inlet 505. Combustion may increase both the
temperature and pressure of the exhaust gasses.
[0095] FIG. 6 shows a schematic representation of a vehicle 600
comprising an internal combustion engine 605 such as a diesel
engine. The vehicle 600 also comprises an exhaust system 100 that
includes an exhaust pipe 615 from the engine 605 to reverse flow
heat exchanger 510, a combustion chamber 110, and energy source
120. The vehicle 600 further comprises a controller 635 for
controlling the power to the energy source. The controller 635 can
be coupled to the engine 605 so as to control the amount of energy
provided by energy source 120 when the engine is not operating, for
example. The controller 635 can also control the energy source 120
in a manner that is responsive to engine 605 operating conditions.
Further, the controller 635 can also control the energy source 120
according to conditions in the combustion chamber 110. For
instance, the controller 635 can monitor a thermocouple in the
combustion chamber 110 so that no power goes to the energy source
120 when the temperature within the combustion chamber 110 is
sufficiently high to maintain a self-sustaining combustion
reaction.
[0096] An alternative embodiment of the invention comprises an air
purifier such as for a hospital room, a clean room, a factory, an
office, a residence, or the like. An exemplary air purification
system comprises a combustion chamber and a means for heating
particles to at least an ignition temperature of particles within
the chamber. A reverse flow heat exchanger is wrapped around or
adjacent to the combustion chamber to recycle excess heat from the
exiting air to the entering air. The means for heating can be
energy source 120 or the like.
[0097] Unlike the exhaust systems described previously herein,
these embodiments are designed for environments in which the
concentration of particles in the incoming air is low. Therefore,
in embodiments that employ an energy source, the energy source is
typically run constantly to maintain the combustion of the
particles. Additionally, or alternatively, a fuel can be supplied
to the combustion chamber to compensate for the lower concentration
of particles. Like the exhaust systems discussed elsewhere herein,
this further air purifier requires little to no maintenance and is
self-cleaning. Advantageously, some embodiments of the air purifier
do not require a continuous energy source and/or a fan to maintain
air movement.
[0098] FIG. 7 depicts a cross sectional view of an air purification
system 700. The cross section depicted is taken perpendicular to a
vertical axis of the air purification system 700. A reverse flow
heat exchanger 710 comprises two ducts, an incoming duct 720 and an
outgoing duct 730 coiled around a combustion chamber 740.
Combustion chamber 740 is an alternative embodiment of combustion
chamber 110 and reverse flow heat exchanger 710 is an alternative
embodiment of reverse flow heat exchanger 510. The air purification
system 700 also comprises an inlet 750 and an outlet 760 shown in
dashed lines to represent that these components are optionally out
of the plane of the drawing. The inlet 750 is an opening through
which particle-laden air enters the incoming duct 720 of the
reverse flow heat exchanger 710. The outlet 760 is an opening
through which substantially particle-free air leaves the outgoing
duct 730 of the reverse flow heat exchanger 710. Typically, the
reverse flow heat exchanger 710 and the combustion chamber 740 are
constructed using stainless steel, but other suitable materials
will be familiar to those skilled in the art.
[0099] The reverse flow heat exchanger 710 transfers heat from the
air exiting the combustion chamber 740 to the particle-laden air
entering the combustion chamber 740. After the particle-laden air
enters the combustion chamber 740, the particles are burned and the
air exits the combustion chamber 740 substantially particle-free.
As particles, including dust, biological toxins, pollen, other
examples provided herein, and the like, typically combust before or
at about 800.degree. F., the air exiting the combustion chamber 740
may be significantly warmer than room temperature. This excess heat
is transferred from the air exiting the combustion chamber 740
through the walls of the reverse flow heat exchanger 710 to preheat
the incoming particle-laden air. In some embodiments, the heat
exchanger 710 acts as insulation for the combustion chamber 740,
making the air purification system 700 safer and more energy
efficient.
[0100] In some embodiments, an optional fan (not shown), can be
placed at the inlet 750 and/or the outlet 760 to improve air flow
through the air purification system 700. At the outlet 760, for
instance, the fan draws air out from the air purification system
700. The fan can be run continuously, periodically, or when the air
purification system 700 is first activated. The fan can be
connected to a control circuit and/or temperature sensor described
elsewhere herein.
[0101] Combustion chamber 740 is optionally coupled to incoming
duct 720 and outgoing duct 730 by vents 770. Vents 770 may be open
along the entire length of combustion chamber 740, or as
illustrated in FIG. 8, may be disposed at specific parts of
combustion chamber 740.
[0102] FIG. 8 depicts a cross sectional view of the air
purification system 700 along a line 8-8 as noted in FIG. 7. The
reverse flow heat exchanger 710 includes an inlet 750 and an outlet
760. An incoming duct 720 is depicted using an arrow pointing into
the page. An outgoing duct 730 is depicted using an arrow pointing
out of the page. The inlet 750 and the outlet 760 are optionally
located at opposite ends of the air purification system 700. When
the system is operated in a vertical orientation, outlet 760 is
optionally above inlet 750.
[0103] In some embodiments, the air purification system 700 has a
height dimension approximately equal to the height of a room in
which the air purification system 700 will be installed.
Accordingly, the inlet 750 can be near the floor while the outlet
760 can be near the ceiling, or vice-versa. This height ensures
that most of the air in the room circulates through the air
purification system 700. Other dimensions, including the number of
windings, the spacings between the walls, and the like can be
determined by one skilled in the art. For example, in various
embodiments, air purification system 700 has a height between 2-3
feet, between 2.5 to 4.5 feet, or greater than 4 feet.
[0104] The air purification system 700 also includes energy source
120. Energy source 120 can be disposed near the bottom or top of
the combustion chamber 740 or in another location, such as at an
intermediate position within the combustion chamber 740. Energy
source 120 heats air within combustion chamber. This causes the air
to rise through convection. The rising air draws further air in to
combustion chamber 740 from the incoming ducts 720 via the lower of
vents 770 and pushes air out of combustion chamber into one of
outgoing ducts 730 via the higher of vents 770. As this process
continues, the incoming air is preheated by the outgoing air and
the temperature within the combustion chamber increases as
described elsewhere herein. Eventually, the temperature within the
combustion chamber 740 reaches the combustion temperature particles
within the incoming air. Burning these particles cleans the air and
may add additional energy to combustion chamber 740. For example,
the combustion of particles from a relatively clean burning engine
may add 1.6.degree. C. while combustion of particles from a
relatively dirty engine may add 28.degree. C. to the temperature of
the exhaust.
[0105] The air purification system 700 may additionally include a
control circuit 830 to monitor and control the combustion and flow
rate through the air purification system 700. For example, control
circuit 830 may control operation of energy source 120 by
controlling current to a heater, power to a microwave source, fuel
flow through a fuel inlet 820, or the like. In some embodiments,
control circuit 830 is configured to monitor the temperature within
combustion chamber 740, e.g. using a thermal couple, and to control
the operation of energy source 120 responsive to this temperature.
In some embodiments, control circuit 830 is configured to maintain
combustion chamber 740 at a target temperature. For example,
control circuit 830 may be configured to reduce or eliminate the
energy supplied to combustion chamber 740 via energy source 120 if
the air received by combustion chamber 740 includes enough
particles to provide energy via combustion. A control circuit
similar to control circuit 830 may be included in other embodiments
of the invention disclosed herein.
[0106] The air turnover rate in a room can be varied as needed. An
appropriate rate will depend on factors such as the size of the
room, air cleanliness requirements for the room, energy efficiency,
and the like. For example, in a hospital room or an industrial
clean room, where very clean air is required, the air turnover rate
can be set significantly higher than in an office where energy
efficiency can be more important. The turnover rate can be
increased by increasing the flow rate through the air purifier, for
example, by increasing the rate at which energy is provided using
energy source 120.
[0107] In some embodiments air purification system 700 includes a
fan to help facilitate the flow if air through the system. This fan
is typically disposed near the entrance of inlet 750 or the exit of
outlet 760. The fan is optionally controlled by control circuit
830. The spacing and/or sizes of incoming ducts 720, outgoing ducts
730 and combustion chamber 740 are optionally configured to muffle
any noise produced by the fan.
[0108] FIG. 9 is a flowchart depicting a method for purifying air.
In a step 910, particle-laden air is drawn into a combustion
chamber, e.g. combustion chamber 740. In some embodiments, the
particle-laden air is drawn in behind the heated rising air in the
combustion chamber 740 or by, for example, a fan. In other
embodiments, the particle-laden air is drawn in by the process of
convection as air is headed by energy source 120. In step 920, the
particles in the combustion chamber 740 are combusted to provide
particle-free air. The combustion reaction is caused by radiation
or heat energy within the combustion chamber 740. This energy is
provided by energy source 120. For example, in some embodiments, a
fuel source, such as a propane or butane source can be in fluid
communication with the fuel inlet 820. As the fuel mixed with the
particle-laden air combusts, the reaction creates heat, further
heating other particles to a combustion point. In other
embodiments, energy source 120 comprises an electric heater under
the control of control circuit 830. After the combustion reaction,
the air is substantially particle-free.
[0109] In step 930 the particle-free air is vented from the
combustion chamber 740. As the heated particle-free air rises by
convection and expands, it establishes a circulation through the
air purification system 700 which forces the particle-free air out
of the combustion chamber 740 and through the outgoing duct 730,
venting the air. Additionally, a fan can assist the venting of the
air.
[0110] In step 940, heat from the now particle-free air is
transferred to the particle-laden air being drawn into the
combustion chamber 740. This step can be performed using, e.g. heat
exchanger 710. By transferring heat from the particle-free air to
the particle-laden air, the particle-laden air is pre-heated prior
to combustion which results in greater overall energy efficiency
and a temperature ladder.
[0111] Another embodiment of the invention is directed to an
exhaust system having a stacked geometry. This exhaust system
comprises a reverse flow heat exchanger coupled to a means for
heating the exhaust gas, such as a combustion chamber for burning
particles carried by the exhaust gas. The reverse flow heat
exchanger recovers heat from the exhaust gas after passing through
the heating means and transfers the heat to the exhaust gas
entering the heating means. The heat recovery increases the energy
efficiency of the exhaust system and provides further advantages as
described elsewhere herein.
[0112] FIGS. 10 and 11 show top and front views, respectively, of
an exemplary exhaust system 1000. The exhaust system 1000 is
generally applicable and can be included, for example, as part of a
vehicle, a power plant, a fireplace, or other sources of particle
laden air discussed herein. Exhaust system 100 and the components
thereof represent alternative embodiments of exhaust system 100 and
components thereof, respectively. The embodiment depicted in FIGS.
10 and 11 comprises a reverse flow heat exchanger 1010 including
two chambers separated by a plate 1020 (shown in dashed lines to
indicate that the plate is internal to the heat exchanger 1010).
One chamber of the heat exchanger 1010 is in fluid communication
between a first manifold 1120 and a combustion chamber 1030. A
second chamber of the heat exchanger 1010 is in fluid communication
between the combustion chamber 1030 and a second manifold 1130. The
chambers within the heat exchanger 1010 are described in greater
detail below and comprise illustrative embodiments of the systems
illustrated in FIGS. 1-6. The heat exchanger 1010 including the
plate 1020, the combustion chamber 1030, and the manifolds 1120,
1130 can be constructed using any suitable material capable of
withstanding the exhaust gases at the operating temperature of the
exhaust system 1000. Suitable materials include stainless steel,
titanium, and ceramics, for example. The plate 1020 should be
constructed of a material with high thermal conductivity, such as a
metal, to provide good heat transfer between the chambers.
[0113] In operation, exhaust gas 1110 from a particle laden source
such as a diesel engine enter the manifold 1120 and are directed
through the heat exchanger 1010 to the combustion chamber 1030. In
the illustrated embodiment, particles within the exhaust are burned
in the combustion chamber 1030, increasing the temperature of the
exhaust gas. Combustion of the particles is facilitated by energy
source 120 attached to the combustion chamber 1030.
[0114] The heated exhaust gas 1140 exits the combustion chamber
1030, passes back through the heat exchanger 1010, and leaves the
exhaust system 1000 through the manifold 1130. In the heat
exchanger 1010, heat from the hot gas 1140 exiting the combustion
chamber 1030 is transferred to the incoming exhaust gas 1110 from
the manifold 1120 through the plate 1020. By using the residual
heat of the combustion of the particles to heat the incoming
exhaust gas 1110, the exhaust system 1000 utilizes less energy.
Other advantages of the heat exchanger 1010 are discussed elsewhere
herein.
[0115] It will be appreciated that although the illustrated
embodiment in FIGS. 10 and 11 includes a combustion chamber 1030,
the present invention is not limited to exhaust systems including a
discrete combustion chamber. While the heat exchanger 1010 is
typically coupled to some heating source to raise the temperature
of the exhaust gas, the combustion chamber 1030 is merely one
example. The combustion chamber 1030 can be replaced, for example,
with a catalytic converter comprising a catalytic material
supported on a substrate that is heated by a resistive heating
element. The region in which combustion takes place (combustion
chamber 1030) may be indistinguishable from other parts of heat
exchanger 1010. In general terms, the combustion chamber 1030 is an
example of a heating manifold that heats the exhaust gas from the
intake chamber 1210 of the heat exchanger 1010 and returns it to
the exit chamber 1310 of the heat exchanger 1010.
[0116] FIG. 12 and FIG. 13 are cross sections of the exhaust system
1000. In FIG. 12, a cross section 1200 is taken along section 12-12
in FIG. 10 through an intake chamber 1210. The intake chamber 1210
is formed between the plate 1020, an exterior wall of the heat
exchanger 1010 (not visible in this perspective), and two spacers
1220 that maintain a proper spacing between the exterior wall and
the plate 1020. Openings between the spacers 1220 form an inlet
1230 and an outlet 1240 of the intake chamber 1210. The inlet 1230
and the outlet 1240 provide fluid communication between the intake
chamber 1210 and the manifold 1120 and the combustion chamber 1030,
respectively.
[0117] The cross section 1200 is characterized by a transverse
surface 1250, seen edge on in FIG. 12, which bisects the heat
exchanger 1010 along a longitudinal axis thereof. In this
embodiment, the inlet 1230 is below the transverse surface 1250 and
the outlet 1240 is above the transverse surface 1250. Placing the
inlet 1230 and outlet 1240 on opposite sides of the transverse
surface 1250 causes the exhaust gas to traverse a diagonal of the
intake chamber 1210.
[0118] In FIG. 13, a cross section 1300 is taken along section
13-13 in FIG. 10 through an exit chamber 1310. The exit chamber
1310 is formed between the plate 1020 (not visible in this
perspective), another exterior wall of the heat exchanger 1010, and
two spacers 1220'. As above, openings between the spacers 1220'
form an inlet 1320 and an outlet 1330 that provide fluid
communication with the combustion chamber 1030 and the manifold
1130, respectively. In various embodiments, manifolds 1120 and 1130
consist of a continuous tube separated by a baffle 1340, generally
aligned with the transverse surface 1250, configured to prevent
fluid communication between manifolds 1120 and 1130. In these
embodiments, the manifolds 1120 and 1130 share a common
longitudinal axis that is approximately parallel to a plane defined
by the plate 1020 and perpendicular to the transverse surface
1250.
[0119] In the illustrated embodiment, the inlet 1320 is below the
transverse surface 1250 and the outlet 1330 is above the transverse
surface 1250. As with the intake chamber 1210, the inlet 1320 and
outlet 1330 are on opposite sides of the transverse surface 1250 so
that the fluid flow is diagonal across the exit chamber 1310.
Arranging the fluid flows along the diagonals of the two chambers
1210, 1310 provides the exhaust gases 1110 and 1140 greater
opportunity to transfer heat therebetween.
[0120] Some embodiments of the heat exchanger 1010 include multiple
plates 1020 to form multiple alternating intake and exit chambers
1210, 1310 to provide even greater heat transfer. Exhaust gasses
may flow between the plates in serial or in parallel. FIGS. 10 and
11 are also representative of these embodiments. FIG. 14 shows a
cross section 1400 taken along the section 14-14 in FIG. 11 of an
exhaust system 1000 including multiple plates 1020. Cross section
1400 shows the multiple plates 1020 forming alternating intake
chambers 1410 and exit chambers 1420 where the intake chambers 1410
are open to receive exhaust from the manifold 1120. Similar to the
above chambers 1210, 1310, each of the chambers 1410, 1420 are
formed by two plates 1020 separated by spacers 1220 with openings
therebetween to provide inlets and outlets. It will be appreciated
that in these embodiments, as well as in the embodiments with only
a single set of chambers 1210, 1310, the external walls of the heat
exchanger 1010 can also be plates 1020. One method of forming the
heat exchanger 1010 is to assemble a stack of alternating plates
1020 and spacers 1220 and to weld or bolt the assembly together in
a stacked geometry.
[0121] The manifold 1120 can also include one or more vanes
disposed relative to an intake chamber inlet 1230 to reduce
resistance to fluid flow near that intake chamber inlet 1230. For
example, vanes 1430 extend from the plates 1020 in FIG. 14. The
vanes 1430 effectively increase the orifice size of the inlets 1230
to reduce fluid frictions. In, various embodiments, vanes 1430 can
be joined to the ends of the plates 1020. In other embodiments, the
vanes 1430 are integral with the plates 1020 and can be formed by
bending the ends of the plates 1020 before assembling the heat
exchanger 1010.
[0122] FIG. 15 shows a cross section 1500 taken along section 15-15
in FIG. 11 of the exhaust system 1000. Cross section 1500 shows
multiple plates 1020 forming alternating intake chambers 1410 and
exit chambers 1420 where the exit chambers 1420 are open to vent
exhaust to the manifold 1120. The manifold 1130 can also include
one or more vanes 1430 disposed relative to the exit chamber
outlets 1330 in order to reduce resistance to fluid flow near the
exit chamber outlets 1330. For example, a vane 1430 extends from
the plate 1020 as shown in FIG. 15. In various embodiments, vanes
1430 also extend from the ends of the plates 1020 at the intake
chamber outlets 1240 and the exit chamber inlets 1320 that
communicate with the combustion chamber 1030.
[0123] FIG. 16 shows a cross section 1600 taken along the section
16-16 of exhaust system 1000 of FIG. 10. Cross section 1600 shows
an end-on view of multiple plates 1020, including the vanes 1430,
and multiple spacers 1220 forming alternating intake chambers
inlets 1230 and exit chambers outlets 1330. Also depicted in FIG.
16 is the baffle 1340 configured to prevent fluid communication
between manifolds 1120 and 1130. In this configuration exhaust
flows between plates in parallel, e.g., one time back and forth.
However, in alternative embodiments, the exhaust may traverse back
and for the between some of the plates more than once in
series.
[0124] FIGS. 17 and 18 show top and front views, respectively, of
another exemplary exhaust system 1700. The exhaust system 1700 is
generally similar to the exhaust system 1000 but differs with
respect to the orientation of the heat exchanger 1010.
Specifically, the heat exchanger is rotated relative to the
manifolds 1120, 1130 and/or the combustion chamber 1030 such that
the transverse plane 1430 of the heat exchanger 1010 is aligned
vertically rather than horizontally. Accordingly, the baffle 1340
is also rotated from horizontal to vertical.
[0125] Some embodiments of the exhaust system 1000, 1700 include
insulation 1810 around the heat exchanger 1010 and the combustion
chamber 1030, as shown in FIG. 18. The use of insulation reduces
the amount of energy required to heat the exhaust gas within the
combustion chamber 1030. More generally, it will be appreciated
that insulation 1810 can be applied individually to any of the heat
exchanger 1010, the combustion chamber 1030, and the manifold 1120,
or to any combination of these components.
[0126] FIGS. 19 and 20 are cross sections of exhaust system 1700.
In FIG. 19, a cross section 1900 is taken along section 19-19 in
FIG. 18 through an intake chamber 1210, and in FIG. 20 a cross
section 2000 is taken along the line 20-20 in FIG. 18 through an
exit chamber 1310. As before, the intake chamber 1210 and the exit
chamber 1310 are formed between the plate 1020, an exterior wall of
the heat exchanger 1010, and spacers 1220. Openings between the
spacers 1220 form the inlets 1230, 1320 and outlets 1240, 1330. The
intake chamber 1210 is in fluid communication between the manifold
1120 and the combustion chamber 1030. The exit chamber 1310 is in
fluid communication between the combustion chamber 1030 and the
manifold 1130. In various embodiments, manifolds 1120 and 1130
consist of a continuous tube separated by a vertical baffle
1340.
[0127] The heat exchanger 1010 is again characterized by a
transverse plane 1910 with the inlet 1230 below the transverse
plane 1910 and the outlet 1240 above the transverse plane 1910.
Likewise, the inlet 1320 is below the transverse plane 1910 and the
outlet 1330 is above the transverse plane 1910. The inlets 1230,
1320 and outlets 1240, 1330 are on opposite sides of the transverse
plane 1910 so that fluid flows diagonally through the chambers
1210, 1310.
[0128] FIG. 21 shows a cross section 2100 taken along the section
21-21 within manifold 1120 of exhaust system 1700. Cross section
2100 shows multiple plates 1020 forming alternating intake chambers
1410 and exit chambers 1420. As above, each chamber 1410, 1420 is
formed between two plates 1020 and spacers 1220. FIG. 21 shows a
number of alternative concepts for vanes 1430 that can extend from
the ends of the plates 1020. In some embodiments, vanes 2110 are
disposed on both sides of an opening. In other embodiments, vanes
2120 can be spherically shaped, vanes 2130 can be of different
lengths, and vanes 2140 can be aerodynamically shaped. When vanes
1430 on successive openings increasingly extend into a manifold, as
in FIGS. 14 and 15, or as the succession of vanes 2120, 2130, and
2140, the vanes 1430 are said to be "feathered." Feathering further
helps to direct flow within the respective manifold to reduce flow
friction loses.
[0129] FIG. 22 shows a cross section 2200 taken along section 22-22
of exhaust system 1700. Cross section 2200 shows multiple plates
1020, including vanes 1430, and multiple spacers 1220 forming
alternating intake chambers inlets 1230 and exit chambers outlets
1330. Also depicted is baffle 1340 configured to prevent fluid
communication between manifolds 1120 and 1130. It will be
appreciated that in these embodiments the manifolds 1120 and 1130
define separate but parallel longitudinal axes. These axes are
approximately perpendicular to a plane defined by the plate 1020
and parallel to the transverse surface 1250.
[0130] Several further advantages of reverse flow heat exchangers
1010 should be noted. For example, these heat exchangers are
self-cleaning. It will be appreciated that should a deposit form on
an internal surface of one of the plates 1020, the restriction to
the flow of exhaust gas around the deposit will tend to cause a
local increase in the temperature at the restriction. Eventually,
the local temperature increase will reach an ignition temperature
of the deposit material, causing the deposit to burn away. Another
advantage of the heat exchangers 1010 is that the heated internal
surfaces of the chambers 1210, 1310 reduce the resistance to fluid
flow through the chambers 1210, 1310 thereby lowering head loss
through the exhaust system 1000. Further, it will be appreciated
that the heat exchangers 1010 can serve to muffle sound due to the
expansions and contractions that the exhaust gas goes through as it
passes through successive openings. The muffling effect can be
further enhanced by tuning the dimensions of the chambers to behave
as resonating chambers. Accordingly, heat exchangers 1010 can
replace mufflers on vehicles or dampen the sounds of fans.
[0131] FIG. 23 depicts a cross sectional view of still another
embodiment 2300 of the invention comprising a particle burner
including a catalyst booster. Embodiment 2300 is an alternative
embodiment of the exhaust systems illustrated elsewhere herein. The
system illustrated in FIG. 23 is an alternative embodiment of the
systems illustrated in prior figures. The cross section depicted is
taken perpendicular to a vertical axis of the embodiment 2300.
Specifically, the embodiment 2300 comprises a reverse flow heat
exchanger 2310 and a gas permeable catalyst 2340. The heat
exchanger 2310 comprises two interleaved ducts, an incoming duct
2320 and an outgoing duct 2330. Each duct 2320 and 2330 is
spiral-wound around a central volume that optionally includes the
catalyst 2340. The ducts 2320 and 2330 are in fluid communication
with each other across the central volume and through the catalyst
2340. The incoming duct 2320 comprises an inlet 2350 and the
outgoing duct 2330 comprises an outlet 2380. The catalyst 2340
separates the central volume into first and second regions 2360 and
2370. The incoming duct 2320 opens into the first region 2360 and
the outgoing duct 2330 opens into the second region 2370. In
alternative embodiments, all or part of the catalyst 2340 is
disposed in outgoing duct 2330.
[0132] The inlet 2350 is an opening through which exhaust enters
the incoming duct 2320 of the heat exchanger 2310. The exhaust
flows through the incoming duct 2320 to the central volume. The
exhaust then exits the central volume, travels through the outgoing
duct 2330, and leaves the heat exchanger 2310 via the outlet
2380.
[0133] As the exhaust traverses the central volume or before the
central volume, particles within the exhaust are heated to an
ignition temperature and therefore combust. Additionally, gases
within the exhaust that result from incomplete fuel combustion are
oxidized as they pass through the catalyst 2340. Catalyst 2340 is
optionally disposed in other locations within the embodiment 2300.
For example, the catalyst 2340 may be disposed within the exit duct
2330.
[0134] The combustion of the particles and the oxidation of these
gases at the catalyst 2340 both give off heat which heats the
catalyst 2340 and the exhaust within the central volume. In various
embodiments, the heat generated from these exothermic reactions is
sufficient to maintain the catalyst 2340 at an operating
temperature of approximately 900-1000, 1000-1000 or greater than
1100.degree. F. The ability to operate at high operating
temperatures, those above the ignition temperature of the
particles, alleviates the need for a particle trap in the exhaust
system.
[0135] As noted, the exiting exhaust is hotter than the entering
exhaust, and as the exhaust travels through outgoing duct 2330,
heat is transferred through the duct walls to warm the exhaust in
the incoming duct 2320. Recovery of heat in this manner boosts the
energy efficiency of the embodiment 2300. It should also be noted
that the heat exchanger 2310 acts as insulation for the catalyst
2340, thus making the embodiment 2300 safer.
[0136] The catalyst 2340 can comprise a substrate supporting a
catalytic material, for example. In various embodiments, the
catalytic material is added to a washcoat and applied to the
substrate. The washcoat provides increased surface area for the
catalytic material. Exemplary substrates comprise a mesh of
stainless steel or a porous ceramic, but other suitable materials
will be familiar to those skilled in the art. Suitable catalytic
materials include platinum, palladium, and rhodium, but other
suitable materials will be familiar to those skilled in the art. An
exemplary washcoat comprises a mixture of silicon and aluminum, but
other suitable materials familiar to those skilled in the art can
be employed. Alternatively, the catalyst 2340 can comprise a simple
mesh of the catalytic material without a substrate, or a catalytic
material deposited directly onto a substrate.
[0137] FIGS. 24 and 25 show top and side views, respectively, of an
exemplary exhaust cleaner 2400 in accordance with an embodiment of
the invention. FIG. 26 depicts a cross section 2600 of the exhaust
cleaner 2400 taken along section 26-26 of FIG. 25. The exhaust
cleaner 2400 is generally applicable and can be used, for example,
in conjunction with any of the sources of particle laden air
discussed elsewhere herein. In these applications, the exhaust
cleaner 2400 can replace the catalytic converter, particle trap,
and/or the muffler.
[0138] The exhaust cleaner 2400 comprises a reverse flow heat
exchanger 2310, a catalyst 2340, an inlet chamber 2410, an outlet
chamber 2420, and an enclosure 2430. The inlet chamber 2410
includes a portal 2520 (see FIG. 26) and the outlet chamber 2420
includes a portal 2530 (FIG. 26). The portals 2520 and 2530 allow
the inlet chamber 2410 and the outlet chamber 2420, respectively,
to be in fluid communication with the heat exchanger 2310. The
enclosure 2430 is disposed around the reverse flow heat exchanger
2310 and the inlet and outlet chambers 2410, 2420. For use with a
tractor truck, the exhaust cleaner 2400 is generally approximately
seven feet long. Dimensions of the exhaust cleaner 2400 may be
designed to allow for easy substitution for the mufflers of
existing exhaust systems. The generally oblong cross-section of
exhaust cleaner 2400, as illustrated in FIG. 26, may provide
aerodynamic advantages in vehicle use.
[0139] As shown in FIG. 25, exhaust from an internal combustion
engine initially enters from one end of the inlet chamber 2410. The
exhaust leaves the inlet chamber 2410 through the portal 2520 and
enters the heat exchanger 2310. The exhaust spirals in through the
heat exchanger 2310, passes through the catalyst 2340, and then
spirals out again through the heat exchanger 2310. The exhaust then
exits the heat exchanger 2310 through portal 2530 to the outlet
chamber 2420 and out of the exhaust cleaner 2400.
[0140] In some embodiments, inlet chamber 2410 comprises vanes 2610
that protrude into the inlet chamber 2410 at the portal 2520.
Likewise, outlet chamber 2420 can comprise vanes 2620 extending
outward at the portal 2530. Vanes and their advantages are
discussed elsewhere herein. In some embodiments, the ducts,
portals, inlets and outlets may be feathered as also discussed
elsewhere herein.
[0141] The exhaust cleaner 2400 can also include a means (not
shown) for pre-heating the exhaust before the exhaust reaches the
catalyst 2340 to permit catalysis to occur at a desired operating
temperature, such as 900.degree. C. This may be necessary for a
short period of time after a cold engine, for instance. The means
for pre-heating may be disposed near the inlet chamber 2410 or
anywhere within the flow path between the inlet chamber 2410 and
the catalyst 2340. The means for pre-heating can be, for example,
an instance of energy source 120, or any means for heating
discussed elsewhere herein. The exhaust cleaner 2400 can also
include a control circuit (not shown) to monitor the catalyst 2340
and to control the means for pre-heating.
[0142] Typically, the enclosure 2430, the heat exchanger 2310, and
the inlet and outlet chambers 2410 and 2420 are made from stainless
steel, titanium, and/or ceramics, but other suitable materials will
be familiar to those skilled in the art. Typically, the walls
separating the ducts 2320, 2330 are constructed of a material with
a high thermal conductivity, such as a metal (e.g., copper, steal,
or nickel), to provide good heat transfer from the outgoing duct
2330 to the incoming duct 2320.
[0143] An exemplary method for manufacturing the exhaust cleaner
2400 comprises attaching opposite sides of the catalyst 2340 to the
ends of two metal sheets. The metal sheets are then wrapped around
the catalyst 2340 to form the ducts 2320, 2330 of the reverse flow
heat exchanger 2310. A spacer placed at either side of one of the
two sheets can be used to maintain the proper spacing between the
ducts 2320, 2330. After the sheets have been wrapped around
catalyst 2340, the inlet and outlet chambers 2410 and 2420 can be
attached to the reverse flow heat exchanger 2310. An enclosure can
then be wrapped around the entire assembly, or further metal sheets
can be attached to span between the chambers 2410, 2420 and the
reverse flow heat exchanger 2310 to fully enclose the flow path of
the exhaust. Lastly, end caps can be attached to the assembly to
scal the ends. In some embodiments, one or more of these end caps
are removable for easy replacement of the catalyst. For example,
one of the end caps could be threaded or tack welded. The catalyst
is mounted on a support structure that can be removed when one of
the end caps are removed. The exhaust cleaner 2400 may include
slots, tracks, guides, or the like to receive the catalyst support
structure.
[0144] FIG. 27 depicts a schematic representation of a particle
burner 2700 disposed between an engine 2710 and a turbine 2720 of a
turbo charger 2730 in accordance with an embodiment of the
invention. In various embodiments, the particle burner 2700
comprises the exhaust cleaner 2400 (FIG. 24) or other exhaust
systems illustrated herein As shown in FIG. 27, air enters the
turbo charger 2730 and is compressed by an impeller 2740 of the
turbo charger 2730 before entering the engine 2710. Exhaust from
the engine 2710 passes through the particle burner 2700 before
returning to the turbo charger 2730 where the exhaust powers the
turbine 2720.
[0145] Since the turbine 2720 operates at a relatively high
pressure, i.e., between about two and ten atmospheres, the pressure
within the particle burner 2700 is also elevated relative to the
ambient air pressure. A higher pressure within the particle burner
2700 is beneficial because a catalyst within the particle burner
2700, such as catalyst 2340 (FIG. 23), oxidizes the gaseous
products of incomplete combustion more efficiently. Thus, the
catalyst can employ less catalytic material to achieve similar
results as a catalyst that operates at a lower pressure. In some
embodiments, the weight of catalytic material in the catalyst
(e.g., catalyst 2340) is about 50% or less of the weight of
catalytic material in a catalyst disposed in an exhaust system of
the prior art. For example, an automotive catalytic converter of
the prior art may include between 3 and 7 grams of platinum while
various embodiments of the invention (e.g., illustrated in FIGS.
5A-27) may achieve better catalysis with less than 3.0, 2.5, 2.0 or
1.5 grams.
[0146] It should be noted that placing the particle burner 2700
between the engine 2710 and the turbo charger 2730 creates a longer
air path between these two components. This longer air path can
create an increased lag which may reduce the efficiency of the
turbo charger 2730. In various embodiments, a feedback system can
compensate for the reduced efficiency of the turbo charger 2730. In
some embodiments, the control system is also coordinated with a
bypass system (not shown) of the turbo charger 2730 that allows
excess exhaust to bypass the turbo charger 2730. In some
embodiments, combustion of particles may heat the gas and increase
its pressure, thus increasing efficiency of the turbo charger
2730.
[0147] The present invention also provides reverse flow heat
exchangers characterized by one or more pairs of contiguous ducts
where the shape of at least one of the ducts varies such that the
cross sectional area of the duct either increases or decreases over
a length thereof. An intake duct conveys particle laden air, such
as engine exhaust, to a combustion chamber and an exit duct conveys
the cleaned air away from the combustion chamber. Heat from the
heated air in the exit duct is conducted across the contiguous
boundary to pre-heat the incoming particle laden air in the intake
duct.
[0148] For example, in some embodiments the exit duct leading away
from the combustion chamber is shaped such that the cross sectional
area of the exit duct varies as function of the length thereof. The
intake duct can also be shaped to have a varying cross sectional
area, in some embodiments. Shaping the cross sections of the ducts
serves to affect the flow therethrough, such as to provide a
nozzle, for example. When used in combination with an engine, the
shapes of the ducts can serve to increase the power or efficiency
of the engine by further reducing backpressure, as compared to a
reverse flow heat exchanger without the shaped ducts.
[0149] FIG. 28 depicts an embodiment of a system 2800 of the
present invention comprising a combustion chamber 2810 and a
reverse flow heat exchanger 2820. The perspective shown in FIG. 28
provides a cross-section through the system 2800 taken
perpendicular to a longitudinal axis (extending perpendicular to
the plane of the drawing) defined by the combustion chamber 2810.
The combustion chamber 2810 is generally cylindrical around the
longitudinal axis. As described elsewhere herein, an energy source
(not shown) is arranged with respect to the combustion chamber
2810, either inside or outside of the combustion chamber 2810, so
as to be able to provide energy within the combustion chamber 2810
to heat particles to above a combustion temperature. As also
described elsewhere herein, a catalyst can be disposed within the
combustion chamber 2810.
[0150] The reverse flow heat exchanger 2820 comprises an intake
duct 2830 and an exit duct 2840 that are contiguous in that they
share a common wall. In the illustrated embodiment, the intake duct
2830 and the exit duct 2840 are spiral-wound around the combustion
chamber.
[0151] The intake duct 2830 includes two ends. Particle laden air,
such as from an internal combustion engine, is drawn into the
reverse flow heat exchanger 2820 at one end of the intake duct 2830
and flows from the other end of the intake duct 2830 into the
combustion chamber 2810, as shown. The second end of the intake
duct 2830 opens into the combustion chamber 2810 through an opening
in a sidewall of the combustion chamber 2810.
[0152] After the particles are burned in the combustion chamber
2810, the cleaned air is vented from the combustion chamber 2810
through the exit duct 2840. The exit duct 2840 also includes two
ends, where one end of the exit duct 2840 opens into the combustion
chamber 2810 through a second opening through the sidewall of the
combustion chamber 2810. The cleaned air is expelled from the exit
duct 2840 through the second end thereof.
[0153] The openings into the combustion chamber 2810 through which
the air enters and exits are set opposite one another and are
offset from one another along the height of the combustion chamber
2810. Thus, only the opening into the combustion chamber 2810 shown
in FIG. 28 is the intake chamber 2830, while a cross section taken,
for example, above the one shown in FIG. 28 would show only the
opening into the exit duct 2840 and not the opening into the intake
duct 2830.
[0154] Accordingly, the flow from the intake duct 2830 into the
combustion chamber 2810 goes from being tangential within the
intake duct 2830 to being radial through the opening to parallel
the longitudinal axis of the combustion chamber 2810 within the
combustion chamber 2810. The flow then turns to exit through the
opening into the exit duct 2840 and turns again to resume
tangential flow within the exit duct 2840. Advantageously, the
vortical flow around the longitudinal axis through the combustion
chamber 2810 causes particles within the flow to move towards the
center of the combustion chamber 2810 where the temperature is
highest.
[0155] In the embodiment shown in FIG. 28, a cross sectional area
of the exit duct 2840 increases between the first end and the
second end as the exit duct 2840 widens. The cross sectional area
of the exit duct 2840 is measured perpendicular to a centerline
2850 of the exit duct 2840. In those embodiments where the top and
bottom sides of the exit duct 2840 are flat and parallel, the cross
sectional area of the exit duct 2840 increases as a function of the
width, w, of the exit duct 2840 measured perpendicular to the
centerline 2850. It should be noted that although the width of the
exit duct 2840 increases uniformly over the entire length thereof,
the shape of the exit duct 2840 is not so limited, and in other
embodiments an exit duct can include a segment, for example, where
the width remains constant over some length.
[0156] The intake duct 2830 also defines a centerline (not shown)
and can include a shape that varies as a function of the centerline
analogously to the exit duct 2840. In the embodiment illustrated by
FIG. 28, the intake duct 2830 decreases in cross sectional area
towards the combustion chamber 2810 while the exit duct 2840
increases in cross sectional area from the combustion chamber 2810.
The exit duct 2840 serves as a nozzle, and as in a ramjet, heated
expanding air within this nozzle accelerates through the expanding
exit duct 2840. This, in turn, creates a suction that helps draw
more air in through the intake duct 2830.
[0157] FIG. 29 shows another embodiment of a system 2900 comprising
a combustion chamber 2910 and a reverse flow heat exchanger 2920
including contiguous intake and exit ducts 2930, 2940 spiral-wound
around the combustion chamber 2910. In this embodiment, the cross
sectional area of the exit duct 2940 decreases away from the
combustion chamber 2910 and the cross-sectional area of the intake
duct 2930 increases towards the combustion chamber 2910.
[0158] FIG. 30 depicts an embodiment of a system 3000 of the
present invention comprising a combustion chamber 3010 and a
reverse flow heat exchanger 3020. The perspective shown in FIG. 30
is the same as in FIG. 5A. As described elsewhere herein, an energy
source (not shown) is arranged with respect to the combustion
chamber 3010, either inside or outside of the combustion chamber
3010, so as to be able to provide energy within the combustion
chamber 3010 to heat particles to above a combustion temperature.
As also described elsewhere herein, a catalyst can be disposed
within the combustion chamber 3010.
[0159] The reverse flow heat exchanger 3020 comprises an intake
duct 3030 and an exit duct 3040 that are contiguous in that they
share a common wall 3050. In the illustrated embodiment, the
combustion chamber 3010 defines a first longitudinal axis 3060 and
the reverse flow heat exchanger 3020 defines a second longitudinal
axis 3070 approximately perpendicular to the first longitudinal
axis 3060.
[0160] As in the embodiment illustrated with respect to FIG. 28,
the intake duct 3030 includes two ends. Particle laden air, such as
from an internal combustion engine, is drawn into the reverse flow
heat exchanger 3020 at one end of the intake duct 3030 and flows
from the other end of the intake duct 3030 into the combustion
chamber 3010, as shown. The second end of the intake duct 3030
opens into the combustion chamber 3010 through an opening in a
sidewall of the combustion chamber 3010. The exit duct 3040 also
includes two ends, where one end of the exit duct 3040 opens into
the combustion chamber 3010 through a second opening through the
sidewall of the combustion chamber 3010. The cleaned air is
expelled from the exit duct 3040 through the second end
thereof.
[0161] In the embodiment shown in FIG. 30, a cross sectional area
of the exit duct 3040 increases between the first end and the
second end as the exit duct 3040 widens. The cross sectional area
of the exit duct 3040 is measured perpendicular to a centerline
3080 of the exit duct 3040. In those embodiments where the opposing
sides of the exit duct 3040 arc flat and parallel, the cross
sectional area of the exit duct 3040 increases as a function of the
height, h, of the exit duct 3040 measured perpendicular to the
centerline 3080. In this embodiment, the height of the exit duct
3040, and hence the cross sectional area, increases linearly as a
function of a length of the exit duct 3040. It should be noted that
although the height of the exit duct 3040 increases uniformly over
the entire length thereof, the shape of the exit duct 3040 is not
so limited, and in other embodiments an exit duct can include a
segment, for example, where the height remains constant over some
length. In other embodiments, the opposing top and bottom surfaces
of the exit duct 3040 are flat and parallel such that the height is
constant and instead the width of the exit duct 3040 varies.
[0162] The intake duct 3030 also defines a centerline (not shown)
and can also include a shape that varies as a function of the
centerline analogously to the exit duct 3040. In the embodiment
illustrated by FIG. 30, the intake duct 3030 decreases in cross
sectional area towards the combustion chamber 3010 while the exit
duct 3040 increases in cross sectional area from the combustion
chamber 3010. As in the embodiment of FIG. 28, the exit duct 3040
serves as a nozzle, and the accelerating gases therein create a
suction that helps draw more air in through the intake duct
3030.
[0163] Still other embodiments are also possible. FIG. 31
illustrates another system 3100, similar to system 3000 (FIG. 30),
but differing in that the cross sectional area of the intake duct
3110 is constant rather than decreasing towards the combustion
chamber 3010, as in system 3000. Other embodiments of both the
spiral and flat reverse flow heat exchangers can be made so that
the cross sectional area of the intake duct increases towards the
combustion chamber and the cross sectional area of the exit duct
continues to increase away from the combustion chamber. Still other
embodiments will be readily apparent.
[0164] The systems in FIGS. 28-31 can be used, for example, as an
exhaust cleaner in conjunction with an engine of a vehicle,
essentially as illustrated by FIG. 6. In these embodiments the
engine includes an exhaust pipe that is in fluid communication with
the intake duct. The exit duct, in some embodiments, vents to the
atmosphere. In some other embodiments, the vehicle further
comprises a turbo charger including an impeller and a turbine, and
the second end of the exit duct is in fluid communication with the
turbine of the turbo charger, as in FIG. 27.
[0165] Exemplary results are provided in FIGS. 32 and 33. Both
charts represent data obtained from a heavy-duty Detroit Diesel,
60-series, 400 horsepower engine including a turbocharger operated
under a series of test modes performed with two different setups.
In a first setup the engine was operated with an attached muffler
but without a catalyst, and in the second setup the engine was
operated with an exemplary exhaust cleaner of the invention
disposed in line between the engine and the turbocharger as
generally illustrated by FIG. 27. The measurements were performed
by an independent laboratory recognized by the Environmental
Protection Agency (EPA) and certified by the California Air
Resources Board (CARB) in accordance with the testing procedures
established by 40 C.F.R. Part 86, Appendix 1.
[0166] The exemplary exhaust cleaner used for these tests comprised
a reverse flow heat exchanger 2920 in which the cross sectional
area of the exit duct 2940 decreased leaving the combustion chamber
2910 and the cross-sectional area of the intake duct 2930 increased
towards the combustion chamber 2910 as generally illustrated by
FIG. 29. A catalyst was disposed within the combustion chamber
2910. In this exemplary exhaust cleaner, the cross-sectional area
of the intake duct 2930 expanded by about 1.5:1 over the length
thereof. The exit duct 2940 reversed these values for a 1:1.5
compression.
[0167] As noted elsewhere herein, systems of the invention can
include an energy source to facilitate the initial combustion of
particles within the combustion chamber, but once ignited,
self-sustaining combustion can be maintained. Test results shown in
FIGS. 32 and 33 were obtained under such self-sustained combustion
without the addition of further energy. The 8 test modes varied
parameters of load, RPM, and torque. Test modes 1-3 held the load
and RMP constant at 15% and 1800 RPM, respectively, and decreased
torque from 1250.0 ft-lbs to 937.5 ft-lbs to 625.0 ft-lbs. Test
mode 4 was also obtained at 1800 RPM, but used a 10% load and a
torque of 125.0 ft-lbs. Test modes 5-7 perform a similar series to
test modes 1-3 with a constant 10% load, a constant 1350 RPM, and
decreasing torque from 1250.0 ft-lbs to 975.0 ft-lbs to 650.0
ft-lbs. Test mode 8 employed a load of 15%, 600 RPM, and no
torque.
[0168] It can be seen from FIG. 32 that catalysis and combustion
within the combustion chamber 2910 resulted in higher exhaust
temperatures for all test modes. For all test modes, carbon
monoxide concentrations in the exhaust were reduced to less than
half of their concentrations without the exhaust cleaner.
Similarly, hydrocarbons were reduced by at least a third, and
reductions were also observed in non-methane hydrocarbons and
NO.sub.x gases. Particle measurements were cumulative over all
tests modes for each setup.
[0169] FIG. 33 compares the measured backpressures with and without
the exhaust cleaner disposed between the engine and the muffler. In
7 of the 8 test modes the reduction in backpressure was
unexpectedly large, exceeding two thirds. In five of these test
modes the reduction in backpressure was greater than 90%, and
better than 95% in three of the five. Generally, each additional
flow-through device placed in line between an engine and the
ambient environment further increases backpressure. Here, the
exhaust cleaner demonstrated an unexpected ability to reduce
backpressure substantially.
[0170] FIG. 34 illustrates still another embodiment of the
invention. In this embodiment a catalytic converter 3400 is
disposed between an engine 2710 and a turbine 2720 of a turbo
charger 2730. The catalytic converter 3400 includes a catalyst
3410. The catalytic converter 3400 can be, but is not required to
be, a combustion chamber as described herein. The exhaust is
conducted from the engine 2710 to the catalytic converter 3400
through a first exhaust system 3420, and from the catalytic
converter 3400 to the turbine 2720 of the turbo charger 2730
through a second exhaust system 3430. The first and second exhaust
systems 3420 and 3430 can comprise, but are not required to
comprise, a reverse flow heat exchanger as described herein.
[0171] The first and second exhaust systems 3420 and 3430 in FIG.
34 are not drawn to any particular scale but merely schematically
represent that between the engine 2710 and the catalytic converter
3400 the exhaust is allowed to expand and then is compressed before
entering the catalytic converter 3400. Similarly, the exhaust
leaving the catalytic converter 3400 is allowed to expand and then
is compressed before entering the turbine 2720. The expansions and
compressions occur due to variations in the cross sectional areas
of the first and second exhaust systems 3420 and 3430, where
increasing cross sectional areas permit expansion and decreasing
cross sectional areas create compression.
[0172] FIG. 35 illustrates an exemplary ramjet 3500 according to
another embodiment of the present invention. The ramjet 3500
comprises an intake duct 3510, a combustion chamber 3520 in fluid
communication with the intake duct 3510, and a nozzle 3530 in fluid
communication with the combustion chamber 3520. The ramjet 3500
additionally comprises a reverse flow heat exchanger 3540 for
regenerating heat from the nozzle 3530 to the intake duct 3510. The
reverse flow heat exchanger 3540 includes a contiguous interface
3550 between the nozzle 3530 and the intake chamber 3510. It is
noted that the ramjet 3500 does not include moving parts such as
turbine blades and rotating shafts, unlike some other devices that
commonly include an intake, a nozzle, and a combustion chamber.
Also, as used herein, a nozzle is defined as a duct characterized
by a cross sectional area that increases between a first end that
opens into the combustion chamber 3520 and a second opposite end.
The cross sectional area of the nozzle 3530 can increase
continuously as shown in FIG. 35 or step-wise, as discussed further
with respect to FIG. 36, below.
[0173] As provided in previously described embodiments, in the
reverse flow heat exchanger 3540, heat is conducted across the
contiguous interface 3550 from the hot gas traversing the nozzle
3530 away from the combustion chamber 3520 and to the cool gas
traversing the intake duct 3510 towards the combustion chamber
3520. Because the nozzle 3530 is characterized by an increasing
cross sectional area, hot gas traversing the nozzle 3530 expands,
drops in pressure, and releases heat. The contiguous interface 3550
can be, for example, a shared wall between the nozzle 3530 and the
intake duct 3510 made from a material like stainless steel that is
characterized by good heat conduction and sufficient strength and
chemical inertness at the highest temperatures seen in the ramjet
3500.
[0174] It will be appreciated that in the illustrated ramjet 3500
the reverse flow heat exchanger 3540 comprises the entire intake
duct 3510, the entire nozzle 3530, and the contiguous interface
3550 therebetween, however, in other embodiments the intake duct
3510 and the nozzle 3530 are only partially joined by the
contiguous interface 3550 and either or both may extend beyond the
reverse flow heat exchanger 3540. In short, the reverse flow heat
exchanger 3540 comprises at least those segments of each of the
intake duct 3510 and the nozzle 3530 that share the contiguous
interface 3550, and the reverse flow heat exchanger 3540 may
comprise all of either of the intake duct 3510 and the nozzle 3530.
In some embodiments, the reverse flow heat exchanger 3540 comprises
at least the segments of each of the intake duct 3510 and the
nozzle 3530 that share the contiguous interface 3550, and these
segments are spiral-wound around the combustion chamber 3520 in the
manner illustrated by FIG. 28, for example.
[0175] In some embodiments, the intake duct 3510 is symmetric
around a longitudinal axis 3560. In these embodiments, flow through
the intake duct 3510 follows a linear path. In some of these
embodiments, the cross sectional area of the intake duct 3510
remains constant between the ends thereof, as shown in FIG. 35. In
other embodiments, the intake duct 3510 has a cross sectional area
that decreases between a first end and a second end thereof, where
the second end of the intake duct 3510 opens into the combustion
chamber 3520.
[0176] FIG. 36 illustrates an exemplary ramjet 3600 according to
another embodiment of the present invention. In this embodiment, a
nozzle 3610 includes a plurality of expansion regions 3620
separated by non-expansion regions 3630. The expansion regions 3620
are characterized by increasing cross sectional areas, while the
non-expansion regions 3630 are characterized by constant cross
sectional areas. Also shown in FIG. 36 is an exemplary temperature
profile 3640 for the nozzle 3610. It can be seen from the
temperature profile 3640 that the heated airflow increases in
temperature as it traverses the expansion regions 3620.
[0177] In both ramjets 3500 and 3600 the intake duct 3510 is
illustrated as having a constant cross-section. It will be
understood, however, that like the embodiment shown in FIG. 30, the
intake ducts in ramjets 3500 and 3600 can alternatively decrease in
cross sectional area towards the combustion chamber 3520.
[0178] FIG. 37 is a flow chart depicting a method 3700 for
operating a ramjet in accordance with various embodiments of the
invention. The method 3700 comprises a step 3710 of receiving an
airflow in an intake duct, a step 3720 of receiving the airflow in
a combustion chamber in fluid communication with the intake duct, a
step 3730 of maintaining a continuous combustion in the combustion
chamber to heat the airflow, a step 3740 of expanding the heated
airflow through a nozzle in fluid communication with the combustion
chamber, and a step 3750 of regenerating heat from the nozzle to
the intake duct.
[0179] The step 3710 of receiving the airflow in the intake duct
can comprise receiving exhaust from a diesel engine, for example.
Diesel exhaust can be received at a pressure of between about 2
atmospheres (atm) and about 4 atm. Receiving the airflow at about 2
atm or greater may not require further compression and can employ
an intake duct having a constant cross sectional area, such as in
FIGS. 35 and 36. On the other hand, where step 3710 comprises
receiving the airflow at a lower pressure, below about 2 atm, the
cross sectional area of the intake duct can narrow towards the
combustion chamber, as in FIG. 30, to boost the pressure of the
airflow, for instance, to within the range of about 2 atm to about
4 atm.
[0180] The step 3730 of maintaining a continuous combustion in the
combustion chamber to heat the airflow received in the combustion
chamber in step 3720 can include, for example, combusting particles
in the airflow such as soot particles. Maintaining the continuous
combustion optionally comprises heating the airflow with an energy
source and/or adding a fuel to the combustion chamber.
[0181] The step 3740 of expanding the heated airflow through the
nozzle can comprise expanding the heated airflow continuously, as
through nozzle 3530, or step-wise, as through nozzle 3610. As
previously noted, expanding the heated airflow drops the pressure
of the airflow and releases further heat. In step 3750 heat from
the nozzle is regenerated to the intake duct. Step 3750 can
therefore comprise the use of a reverse flow heat exchanger and can
comprise conducting heat across a contiguous boundary between the
nozzle and the intake duct, in some embodiments.
[0182] Several embodiments are specifically illustrated and/or
described herein. However, it will be appreciated that
modifications and variations are covered by the above teachings and
within the scope of the appended claims without departing from the
spirit and intended scope thereof. For example, while the
specification discusses separate parts of the reverse flow heat
exchanger and a combustion chamber, there may not be distinct
boundaries between these elements. Further, non-combustible
particle such as ash are optionally separated and captured
following the combustion chamber 110 using a centrifugal particle
separator. Such separators are known in the art, see for example
U.S. Pat. No. 7,258,713. Exhaust systems discussed herein, such as
exhaust system 100 are optionally disposed in parallel arrays or
clusters.
[0183] The embodiments discussed herein are illustrative of the
present invention. As these embodiments of the present invention
are described with reference to illustrations, various
modifications or adaptations of the methods and or specific
structures described may become apparent to those skilled in the
art. All such modifications, adaptations, or variations that rely
upon the teachings of the present invention, and through which
these teachings have advanced the art, are considered to be within
the spirit and scope of the present invention. Hence, these
descriptions and drawings should not be considered in a limiting
sense, as it is understood that the present invention is in no way
limited to only the embodiments illustrated.
* * * * *