U.S. patent application number 11/806437 was filed with the patent office on 2008-12-04 for stoichiometric engine system utilizing reformed exhaust gas.
Invention is credited to Weidong Gong, Balamurugesh Thirunavukarasu, Martin Leo Willi.
Application Number | 20080295501 11/806437 |
Document ID | / |
Family ID | 39720661 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080295501 |
Kind Code |
A1 |
Gong; Weidong ; et
al. |
December 4, 2008 |
Stoichiometric engine system utilizing reformed exhaust gas
Abstract
A power system is provided having an engine configured to
combust a substantially stoichiometric air/fuel mixture and produce
a flow of exhaust. The power system also has an exhaust passageway
fluidly connected to the engine. In addition, the power system has
a catalytic device situated within the exhaust passageway.
Furthermore, the system has an exhaust gas recirculation loop
fluidly connected to the exhaust passageway. The system further has
a steam fuel reformer situated within the exhaust gas recirculation
loop.
Inventors: |
Gong; Weidong; (Dunlap,
IL) ; Willi; Martin Leo; (Dunlap, IL) ;
Thirunavukarasu; Balamurugesh; (Peoria, IL) |
Correspondence
Address: |
CATERPILLAR/FINNEGAN, HENDERSON, L.L.P.
901 New York Avenue, NW
WASHINGTON
DC
20001-4413
US
|
Family ID: |
39720661 |
Appl. No.: |
11/806437 |
Filed: |
May 31, 2007 |
Current U.S.
Class: |
60/299 |
Current CPC
Class: |
Y02T 10/12 20130101;
F02M 26/22 20160201; F02M 26/35 20160201; F02M 26/15 20160201; Y02T
10/121 20130101; F02M 26/36 20160201; F02M 26/28 20160201; F02M
25/12 20130101; F02M 26/27 20160201 |
Class at
Publication: |
60/299 |
International
Class: |
F01N 3/20 20060101
F01N003/20 |
Claims
1. A power system, comprising: an engine configured to combust a
substantially stoichiometric air/fuel mixture and produce a flow of
exhaust; an exhaust passageway fluidly connected to the engine; a
catalytic device situated within the exhaust passageway; an exhaust
gas recirculation loop fluidly connected to the exhaust passageway
downstream of the catalytic device; and a steam fuel reformer
situated within the exhaust gas recirculation loop.
2. The power system of claim 1, further including a fluid
passageway fluidly connected to the exhaust gas recirculation loop
upstream of the steam fuel reformer, the fluid passageway being
configured to direct at least a portion of the fuel to be combusted
by the engine through the steam fuel reformer.
3. The power system of claim 2, wherein the fluid passageway is
configured to direct all of the fuel to be combusted by the engine
through the steam fuel reformer.
4. The power system of claim 1, wherein the catalytic device
includes a 3-way catalyst.
5. The power system of claim 1, further including a heat exchanger
situated within the exhaust recirculation loop downstream of the
steam fuel reformer.
6. The power system of claim 1, wherein fuel in the air/fuel
mixture entering the engine is natural gas.
7. A power system, comprising: an engine configured to combust a
substantially stoichiometric air/fuel mixture and produce a flow of
exhaust; an exhaust passageway fluidly connected to the engine; a
catalytic device situated within the exhaust passageway; an exhaust
gas recirculation loop fluidly connected to the exhaust passageway
upstream of the catalytic device; and a steam fuel reformer
situated within the exhaust gas recirculation loop.
8. The power system of claim 7, further including a fluid
passageway fluidly connected to the exhaust gas recirculation loop
upstream of the steam fuel reformer, the fluid passageway being
configured to direct at least a portion of the fuel to be combusted
by the engine through the steam fuel reformer.
9. The power system of claim 8, wherein the fluid passageway is
configured to direct all of the fuel to be combusted by the engine
through the steam fuel reformer.
10. The power system of claim 7, wherein the catalytic device
includes a 3-way catalyst.
11. The power system of claim 7, further including a heat exchanger
situated within the exhaust recirculation loop downstream of the
steam fuel reformer.
12. A method for treating exhaust gas, comprising: combusting a
substantially stoichiometric air/fuel mixture; catalyzing an
exhaust gas generated by the combustion of the air/fuel mixture;
redirecting at least a portion of the exhaust gas so that the
redirected exhaust gas is combusted with the air/fuel mixture; and
enriching the redirected exhaust gas/fuel mixture.
13. The method of claim 12, further including catalyzing the
exhaust gas before redirecting at least a portion of the exhaust
gas.
14. The method of claim 12, further including catalyzing the
exhaust gas after a portion of the exhaust gas has been
redirected.
15. The method of claim 12, further including mixing at least a
portion of the fuel to be combusted with the redirected exhaust gas
before the redirected exhaust gas mixes with air.
16. The method of claim 12, directing the fuel to be combusted in
such a manner that all of the fuel to be combusted mixes with the
redirected exhaust gas before being mixed with air.
17. The method of claim 12, wherein enriching the redirected
exhaust gas includes increasing the amount of hydrogen and carbon
monoxide in the redirected exhaust gas.
18. The method of claim 17, wherein enriching the redirected
exhaust gas further includes decreasing the amount of water in the
redirected exhaust gas.
19. The method of claim 12, wherein catalyzing the exhaust gas
includes increasing the amount of carbon dioxide, water, and
nitrogen.
20. The method of claim 19, wherein catalyzing the exhaust gas
further includes decreasing the amount of hydrocarbons, carbon
monoxide, and nitrogen oxides.
Description
TECHNICAL FIELD
[0001] The present disclosure is directed to a stoichiometric
engine system, and more particularly, to a stoichiometric engine
system utilizing reformed exhaust gas.
BACKGROUND
[0002] Internal combustion engines, including diesel engines,
gasoline engines, natural gas engines, and other engines known in
the art exhaust a complex mixture of air pollutants. The air
pollutants are composed of solid particulate matter and gaseous
compounds including nitrous oxides (NOx) and carbon monoxide (CO).
In addition, some types of fuels such as, for example, diesel fuels
often contain sulfur that, at times, convert to potentially
corrosive and environmentally unfriendly byproducts. Due to
increased attention on the environment, exhaust emission standards
have become more stringent, and the amount of solid particulate
matter and gaseous compounds emitted to the atmosphere from an
engine is regulated depending on the type of engine, size of
engine, and/or class of engine.
[0003] U.S. Pat. No. 6,508,209 to Collier, Jr. ("the '209 patent")
discloses a natural gas powered engine system employing an
oxidation catalyst and exhaust gas recirculation (EGR) system to
reduce emissions in the engine exhaust. In the system, air and
natural gas fuel is combined and combusted in a plurality of
combustion chambers. Exhaust from some of the combustion chambers
is directed to the oxidation catalyst where carbon monoxide is
converted to carbon dioxide and released into the atmosphere.
Exhaust from the rest of the combustion chambers is mixed with
natural gas fuel and recirculated back to the intake of the engine.
By recirculating exhaust gas back to the engine, the peak
combustion temperature in the combustion chambers is lowered, which
reduces NOx production. In order to prevent engine misfires, which
can result from combusting an air/fuel mixture containing a
significant amount of recirculated exhaust, the exhaust/fuel
mixture is conditioned in a steam fuel reformer. In addition, any
water vapor remaining in the exhaust/fuel mixture may be removed by
condensation in a heat exchanger before the exhaust/fuel mixture is
combined with ambient air and combusted in the combustion
chambers.
[0004] Although the system in the '209 patent may reduce emissions
in the engine exhaust, it does not address the removal of
particulate matter and other hydrocarbon emissions from the exhaust
before the exhaust is released into the atmosphere. Many petroleum
based fuels generate particulate matter and other hydrocarbons when
combusted. Such particulate matter and other hydrocarbon emissions
are considered pollutants and are strictly regulated. By not
providing a means to reduce such emissions, the engine system might
not meet exhaust emissions standards.
[0005] The disclosed system is directed to overcoming one or more
of the problems set forth above.
SUMMARY OF THE INVENTION
[0006] In one aspect, the present disclosure is directed toward a
power system that includes an engine configured to combust a
substantially stoichiometric air/fuel mixture and produce a flow of
exhaust. The power system also includes an exhaust passageway
fluidly connected to the engine. In addition, the power system
includes a catalytic device situated within the exhaust passageway.
Furthermore, the system includes an exhaust gas recirculation loop
fluidly connected to the exhaust passageway. The system further
includes a steam fuel reformer situated within the exhaust gas
recirculation loop.
[0007] Consistent with another aspect of the disclosure, a method
is provided for treating exhaust gas. The method includes
combusting a substantially stoichiometric fuel/air mixture. The
method also includes catalyzing an exhaust gas generated by the
combustion of the air/fuel mixture. In addition, the method
includes redirecting at least a portion of the exhaust gas so that
it is combusted with the fuel/air mixture. The method further
includes enriching the redirected exhaust gas.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] FIG. 1 is a diagrammatic illustration of a power system
according to an exemplary disclosed embodiment of the present
disclosure; and
[0009] FIG. 2 is a diagrammatic illustration of a power system
according to another exemplary disclosed embodiment of the present
disclosure.
DETAILED DESCRIPTION
[0010] FIG. 1 illustrates an exemplary power system 10 having an
engine 12 that combusts a mixture of air and fuel to generate a
mechanical output and a flow of exhaust. For the purposes of this
disclosure, engine 12 is depicted and described as a natural gas
powered engine. One skilled in the art will recognize, however,
that engine 12 may be any other type of internal combustion engine
such as, for example, another gaseous fuel-powered engine, a
gasoline engine, a four-stroke diesel engine, or any engine capable
of being powered by a petroleum based or non-petroleum based fuel.
Engine 12 may include an engine block 14 defining a plurality of
cylinders 16, an air/fuel intake manifold 18 fluidly connecting
cylinders 16 to an air/fuel intake passageway 20, and an exhaust
manifold 22 fluidly connecting cylinders 16 to an exhaust
passageway 24. A piston (not shown) may be slidably disposed within
each cylinder 16 to reciprocate between a top-dead-center position
and a bottom-dead-center position, and a cylinder head (not shown)
may be associated with each cylinder 16.
[0011] Cylinder 16, the piston, and the cylinder head may form a
combustion chamber 26 fluidly connected to air/fuel intake manifold
18 and exhaust manifold 22 via fluid passageways 28 and 30,
respectively. In the illustrated embodiment, engine 12 includes six
such combustion chambers 26. However, it is contemplated that
engine 12 may include a greater or lesser number of combustion
chambers 26 and that combustion chambers 26 may be disposed in an
"in-line" configuration, a "V" configuration, or in any other
suitable configuration.
[0012] Power system 10 may also include an exhaust treatment system
32 for removing and/or reducing the amount of pollutants in the
exhaust produced by engine 12 and released into the atmosphere.
Exhaust treatment system 32 may include a catalyzed member 34
situated within exhaust passageway 24 and an exhaust gas
recirculating (EGR) loop 36 for directing a predetermined portion
of exhaust back to air/fuel intake 20 of engine 12.
[0013] Catalyzed member 34 may include a structure coated with or
otherwise containing a catalyst to reduce the by-products of
combustion. In one example, the structure may be coated with a
3-way catalyst that supports the reduction of particulate matter,
hydrocarbons, carbon monoxide (CO), and NOx. The catalyst may
include, for example, a base metal oxide, a molten salt, or a
precious metal that catalytically reacts with particulate matter,
CO, and NOx.
[0014] EGR loop 36 may include components that cooperate to
redirect a portion of the exhaust generated by engine 12 from
exhaust passageway 24 to air/fuel intake passageway 20.
Specifically, EGR loop 36 may include an inlet port 38, a
recirculation valve 40, a reformer 42, an EGR cooler 44, and a
discharge port 46. In addition, inlet port 38 may be fluidly
connected to reformer 42 via a fluid passageway 48, steam fuel
reformer 42 may be fluidly connected to EGR cooler 44 via a fluid
passageway 50, and discharge port 46 may be fluidly connected to
EGR cooler 44 via fluid passageway 52. Furthermore, recirculation
valve 40 may be disposed within fluid passageway 48, between inlet
port 38 and reformer 42. It is contemplated that inlet port 38 may
be located upstream or downstream of any turbochargers present (if
any) and/or additional emission control devices disposed within
exhaust passageway 24 (not shown) such as, for example, particulate
filters and catalytic devices.
[0015] Recirculation valve 40 may be located to regulate the flow
of exhaust through EGR loop 36. Recirculation valve 40 may be any
type of valve such as, for example, a butterfly valve, a diaphragm
valve, a gate valve, a ball valve, a globe valve, or any other
valve known in the art. In addition, recirculation valve 40 may be
solenoid-actuated, hydraulically-actuated, pneumatically-actuated
or actuated in any other manner to selectively restrict the flow of
exhaust through fluid passageway 48.
[0016] Reformer 42 may remove or reduce the amount of water vapor
in the exhaust gas flowing through EGR loop 36. In particular,
reformer 42 may facilitate a reaction between exhaust gas flowing
through reformer 42, and a fuel over a catalyst. The catalyst may
be any material that may promote a reforming reaction such as, for
example, nickel. In addition, the fuel may be any petroleum based
or non-petroleum based fuel or natural gas. The fuel may be
supplied from a source (not shown) such as, for example, a tank, a
pipeline, or any other source known in the art capable of supplying
fuel to EGR loop 36. Furthermore, the fuel may be directed to EGR
loop 36 via a fuel passageway 54 upstream of reformer 42. It is
contemplated that the source supplying fuel to EGR loop 36 may be
either the same source supplying fuel to air/fuel intake passageway
20 or a separate source. It is further contemplated that any
percentage including 100 percent of the fuel combusted by engine 12
may be supplied via fuel passageway 54.
[0017] The reaction mechanism between the exhaust gas and fuel may
be summarized in the following equations:
CH.sub.4+H.sub.2O.sup.vCO+3H.sub.2 (1)
CO+H.sub.2O.sup.vCO.sub.2+H.sub.2 (2)
[0018] As shown in equation 1, methane (CH.sub.4) in the fuel may
combine with water vapor (H.sub.2O) in the exhaust gas to produce
carbon monoxide (CO) and hydrogen (H.sub.2). The shift reaction
summarized by equation 2 may kinetically follow the reaction
summarized by equation 1. In particular, the water vapor (H.sub.2O)
remaining in the exhaust gas and fuel mixture after the first
reaction may combine with carbon monoxide (CO) also produced by the
first reaction to generate carbon dioxide (CO.sub.2) and hydrogen
(H.sub.2), thereby removing the remaining water vapor from the
exhaust gas and enriching the exhaust gas with hydrogen and carbon
monoxide.
[0019] Cooler 44 may be configured to cool the exhaust flowing
through EGR loop 36. Cooler 44 may include a liquid-to-air heat
exchanger, an air-to-air heat exchanger, or any other type of heat
exchanger known in the art for cooling an exhaust flow. It should
be understood that the size of cooler 44 may be reduced because the
reaction facilitated by reformer 42 may be an endothermic reaction.
The heat required for the reaction may be provided by thermal
energy contained within the recirculated exhaust gas, thereby
cooling the exhaust gas. Because of the cooling effect of the
endothermic chemical reaction facilitated by reformer 42, it is
contemplated that cooler 44 may be omitted, if desired.
[0020] FIG. 2 illustrates another exemplary embodiment of power
system 10 that positions catalyzed member 34 downstream of EGR loop
36. Positioning catalyzing member 34 downstream of EGR loop 36 may
decrease the size of reformer 42 and the amount of fuel needed to
remove or reduce water vapor from the recirculated exhaust gas.
This is because the reaction facilitated by catalyzing member 34
may generate water vapor and increase the amount of water vapor in
the exhaust. In configurations where catalyzing member 34 is
positioned upstream of EGR loop 36, exhaust gas being recirculated
back to engine 12 through EGR loop 36 may include the water vapor
generated by catalyzing member 34 in addition to water vapor that
may already be present in the exhaust gas. Therefore, more fuel and
a larger reformer 42 may be required to react with and remove the
additional amount of water vapor. However, in configurations where
catalyzing member 36 is positioned downstream of EGR loop 36, water
vapor may be generated in the portion of the exhaust gas that may
not be recirculated back to engine 12. In such a configuration,
reformer 42 may not need to handle the additional water vapor
generated by catalyzing member 34.
[0021] It should be understood that positioning catalyzing device
34 downstream of EGR loop 36 may require additional emission
control devices such as, for example, a particulate filter 56
located within exhaust passageway 24 upstream of EGR loop 36. Fuels
that are combusted by engine 12 may include particulate matter or
other elements that may corrode or foul the elements of EGR loop
36. It is contemplated that particulate filter 56 and/or other
emission control devices may alternatively be situated within fluid
passageway 48 of EGR loop 36, if desired.
INDUSTRIAL APPLICABILITY
[0022] The disclosed engine system may reliably and efficiently
remove or reduce emissions from exhaust that are released into the
atmosphere. In particular, the combination of a 3-way catalyst and
an EGR loop may effectively reduce or remove NOx, hydrocarbons, and
carbon monoxide from the engine exhaust. By utilizing a reformer,
water vapor may be removed from the recirculated exhaust gas, which
may increase the engine combustion flame speed. In addition, the
reformer may enrich the recirculated exhaust gas, which may also
increase the engine combustion flame speed. The increased flame
speed combined with the increased heat capacity of the recirculated
gas may ensure that the air/fuel mixture entering the engine may be
stably combusted at temperatures adverse to NOx formation.
[0023] By utilizing a 3-way catalytic device, particulate matter
and other hydrocarbon emissions may be removed or reduced from the
exhaust before it is released into the atmosphere. Therefore, the
system may be powered by various petroleum based or non-petroleum
based fuels and still meet stringent emissions standards.
[0024] It will be apparent to those skilled in the art that various
modifications and variations can be made in the disclosed system
without departing from the scope of the disclosure. Other
embodiments will be apparent to those skilled in the art from
consideration of the specification disclosed herein. It is intended
that the specification and examples be considered as exemplary
only, with a true scope being indicated by the following claims and
their equivalents.
* * * * *