U.S. patent application number 12/185409 was filed with the patent office on 2008-12-04 for exhaust gas purifying apparatus for international combustion.
This patent application is currently assigned to Honda Motor Co., Ltd.. Invention is credited to Tomoko MORITA, Norio Suzuki, Katsuji Wada.
Application Number | 20080295498 12/185409 |
Document ID | / |
Family ID | 35695807 |
Filed Date | 2008-12-04 |
United States Patent
Application |
20080295498 |
Kind Code |
A1 |
MORITA; Tomoko ; et
al. |
December 4, 2008 |
EXHAUST GAS PURIFYING APPARATUS FOR INTERNATIONAL COMBUSTION
Abstract
An exhaust gas purifying apparatus for an internal combustion
engine including an ammonia generating device and a NOx removing
device. The ammonia generating device is provided in an exhaust
system of the engine, and generates ammonia by a reaction of NOx
and reducing components in exhaust gases when the exhaust gases are
in a reducing state. The NOx removing device is provided downstream
of the ammonia generating device, and adsorbs NOx in the exhaust
gases when the exhaust gases are in an oxidizing state. The NOx
removing device reduces the adsorbed NOx to generate ammonia and
retains the generated ammonia when the exhaust gases are in the
reducing state.
Inventors: |
MORITA; Tomoko; (Wako-shi,
JP) ; Suzuki; Norio; (Wako-shi, JP) ; Wada;
Katsuji; (Wako-shi, JP) |
Correspondence
Address: |
ARENT FOX LLP
1050 CONNECTICUT AVENUE, N.W., SUITE 400
WASHINGTON
DC
20036
US
|
Assignee: |
Honda Motor Co., Ltd.
Tokyo
JP
|
Family ID: |
35695807 |
Appl. No.: |
12/185409 |
Filed: |
August 4, 2008 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11311264 |
Dec 20, 2005 |
|
|
|
12185409 |
|
|
|
|
Current U.S.
Class: |
60/286 ;
60/301 |
Current CPC
Class: |
F01N 2570/18 20130101;
F01N 13/009 20140601; F02D 2250/36 20130101; B01D 2251/2062
20130101; F01N 3/0842 20130101; F01N 2370/04 20130101; F01N 3/0814
20130101; B01D 53/9409 20130101; F01N 2510/063 20130101; F01N
2430/06 20130101 |
Class at
Publication: |
60/286 ;
60/301 |
International
Class: |
F01N 3/10 20060101
F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2004 |
JP |
2004-375164 |
Claims
1. An exhaust gas purifying apparatus for an internal combustion
engine having fuel injection means for injecting fuel into at least
one cylinder of said engine, said exhaust gas purifying apparatus
comprising: ammonia generating means, provided in an exhaust system
of said engine, for generating ammonia by a reaction of NOx and
reducing components in exhaust gases when the exhaust gases are in
a reducing state; NOx removing means, provided downstream of said
ammonia-generating means, for adsorbing NOx in the exhaust gases
when the exhaust gases are in an oxidizing state, said NOx removing
means reducing the adsorbed NOx to generate ammonia and retaining
the generated ammonia when the exhaust gases are in the reducing
state: and reducing components supply means for supplying reducing
components to an upstream side of said ammonia generating means by
executing at least one post injection after a main injection
through said fuel injection means.
2. The exhaust gas purifying apparatus according to claim 1,
wherein said ammonia generating means comprises a heat-resistant
porous carrier and one or more of precious metals selected from the
group of consisting of palladium (Pd), platinum (Pt), rhodium (Rh),
ruthenium (Ru), and iridium (Ir) carried by said carrier.
3. An exhaust gas purifying apparatus for an internal combustion
engine having at least one fuel injection valve for injection fuel
into at least one cylinder of said engine, said exhaust gas
purifying apparatus comprising: ammonia generating device, provided
in an exhaust system of said engine, for generating ammonia by a
reaction of NOx and reducing components in exhaust gases when the
exhaust gases are in a reducing state; and NOx removing device,
provided downstream of said ammonia-generating device, for
adsorbing NOx in the exhaust gases when the exhaust gases are in an
oxidizing state, said NOx removing device reducing the adsorbed NOx
to generate ammonia and retaining the generated ammonia when the
exhaust gases are in the reducing state; and reducing components
supply device for supplying reducing components to an upstream side
of said ammonia generating device by executing at least one post
injection after a main injection through said at lest one fuel
injection valve.
4. The exhaust gas purifying apparatus according to claim 3,
wherein said ammonia generating device comprises a heat-resistant
porous carrier and one or more of precious metals selected from the
group of consisting of palladium (Pd), platinum (Pt), rhodium (Rh),
ruthenium (Ru), and iridium (Ir) carried by said carrier.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an exhaust gas purifying
apparatus for an internal combustion engine, and particularly, to
an exhaust gas purifying apparatus including a NOx removing device
for removing NOx from the exhaust gases.
[0003] 2. Description of the Related Art
[0004] A lean NOx catalyst absorbs NOx in exhaust gases when the
exhaust gases are in an oxidizing state. In an oxidizing state, the
concentration of oxygen in the exhaust gases is relatively high
compared with the concentration of reducing components (HC, CO).
The lean NOx catalyst also reduces absorbed NOx when the exhaust
gases are in a reducing state. In a reducing state, the
concentration of reducing components in the exhaust gases is
relatively high compared with the concentration of oxygen.
[0005] Japanese Patent Laid-open No. 2001-140630 discloses an
exhaust gas purifying apparatus, including an ammonia generating
catalyst and a NOx removing catalyst. The ammonia generating
catalyst generates ammonia when the exhaust gases are in the
reducing state. The NOx removing catalyst reduces NOx using the
ammonia generated by the ammonia generating catalyst: as a reducing
agent. The above-described lean NOx catalyst is an example of the
NOx removing catalyst in the exhaust gas purifying apparatus. In
the exhaust gas purifying apparatus of Japanese Patent Laid-open
No. 2001-140630, the stoichiometric-rich operation and the lean
operation are performed alternately to increase the time period in
which ammonia and NOx coexist, thereby removing NOx. In the
stoichiometric-rich operation, the air-fuel ratio is set to a value
on the rich side with respect to the stoichiometric ratio or a
value equal to the stoichiometric ratio. In the lean burn
operation, the air-fuel ratio is set to a value on the lean side
with respect to the stoichiometric ratio.
[0006] In the above-described conventional exhaust gas purifying
apparatus, the time period of the stoichiometric-rich operation
becomes relatively large in order to generate a sufficient amount
of ammonia for reducing NOx, resulting in increased fuel
consumption.
SUMMARY OF THE INVENTION
[0007] The present invention provides an exhaust gas purifying
apparatus which reduces the time period in which exhaust gases are
in the reducing state by effectively performing ammonia generation
and NOx reduction to suppress deterioration of the fuel consumption
rate.
[0008] The present invention is achieved by providing an exhaust
gas purifying apparatus for an internal combustion engine,
including an ammonia generating device provided in an exhaust
system of the engine and a NOx removing device provided downstream
of the ammonia generating device. The ammonia generating device
generates ammonia by a reaction of NOx and reducing components in
exhaust gases when the exhaust gases are in a reducing state. The
NOx removing device adsorbs NOx in the exhaust gases when the
exhaust gases are in an oxidizing state, reduces the adsorbed NOx
to generate ammonia, and retains the generated ammonia when the
exhaust gases are in the reducing state.
[0009] With this configuration, NOx in the exhaust gases is
adsorbed by the NOx removing device when the exhaust gases are in
the oxidizing state. When the exhaust gases are in the reducing
state, the ammonia generated by the ammonia generating device and
the NOx removing device reduces NO), adsorbed by the NOx removing
device, and a part of the generated ammonia is retained by the NOx
removing device. Further, the retained ammonia is used to reduce
NOx when the exhaust gases enter the oxidizing state. Therefore,
the present invention eliminates the need to alternately perform a
lean burn operation, wherein the exhaust gases are in the oxidizing
state, and a rich operation wherein the exhaust gases are in the
reducing state, such as in a conventional system. NOx removal
capability can be maintained by continuing the lean burn operation
until the amount of exhausted NOx exceeds the maximum amount of NOx
that the NOx removing device can adsorb, and, thereafter,
performing the rich operation or supplying reducing components to
the exhaust system for a short period of time. That is, the ammonia
generating capacity of the ammonia generating device and the
ammonia-retaining capacity of the NOx removing device are fully
used. As such, the generation of ammonia and the reduction of NOx
can be performed efficiently, suppressing deterioration of the fuel
consumption rate.
[0010] In the ammonia generating device, the ammonia generating
capacity is high when the temperature thereof is comparatively
high. In the NOx removing device, the ammonia-retaining capacity is
high when the temperature thereof is comparatively low. Therefore,
arranging the NOx removing device downstream of the ammonia
generating device effectively contributes to efficiently generating
and retaining ammonia. Consequently, the reduction of NOx by
ammonia can be promoted.
[0011] In one embodiment of the present invention, the exhaust gas
purifying apparatus further includes a reducing components supply
device for supplying reducing components to an upstream side of the
ammonia generating device. With this configuration, reducing
components are supplied to the ammonia generating device, thereby
promoting reduction of NOx and generation of ammonia.
[0012] In an embodiment of the present invention, the reducing
components supply device supplies reducing components by enriching
an air-fuel ratio of an air-fuel mixture in a combustion chamber of
the engine.
[0013] In an embodiment of the present invention, the ammonia
generating device comprises a heat-resistant porous carrier and one
or more of precious metals such as palladium (Pd), platinum (Pt),
rhodium (Rh), ruthenium (Ru), and iridium (Ir) carried by the
carrier.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a diagram illustrating a configuration of an
internal combustion engine and an exhaust gas purifying apparatus
therefor according to one embodiment of the present invention;
[0015] FIGS. 2A-2C illustrate the NOx removing device illustrated
in FIG. 1;
[0016] FIG. 3 is a graph illustrating an effect of disposing an
ammonia-generating catalyst upstream of the NOx removing device;
and
[0017] FIG. 4 is a graph illustrating another effect of disposing
an ammonia-generating catalyst upstream of the NOx removing
device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0018] Preferred embodiments of the present invention will now be
described with reference to the drawings.
[0019] FIG. 1 is a diagram illustrating a configuration of an
internal combustion engine (hereinafter referred to as "engine")
and an exhaust gas purifying apparatus of the engine according to
one embodiment of the present invention. The engine 1 can be a
diesel engine in which fuel is directly injected into cylinders,
and each cylinder is provided with a fuel injection valve 6. The
fuel injection valve 6 is electrically connected to an electronic
control unit 7 (hereinafter referred to as "ECU"). A valve opening
timing and a valve opening period of the fuel injection valve 6 are
controlled by the ECU 7.
[0020] An exhaust pipe 2 of the engine 1 is provided with a NOx
removing device 4. An ammonia generating catalyst 3 is provided
upstream of the NOx removing device 4. The ammonia generating
catalyst 3 reduces nitrogen dioxide (NO.sub.2) to generate nitrogen
(N.sub.2), hydrogen (H.sub.2), and ammonia (NH.sub.3) by the
chemical reaction expressed by the following chemical equations (1)
and (2), when the exhaust gases are in the reducing state,
2NO.sub.2+4H.sub.2.fwdarw.N.sub.2+4H.sub.2O (1)
2NO.sub.2+7H.sub.2.fwdarw.2NH.sub.3+4H.sub.2O (2)
[0021] The ammonia generating catalyst 3 comprises a heat-resistant
porous carrier and one or more of precious metals such as palladium
(Pd), platinum (Pt), rhodium (Rh), ruthenium (Ru), and iridium (Ir)
carried by the carrier.
[0022] The NOx removing device 4 includes platinum (Pt) as a
catalyst, ceria having NOx adsorbing capacity, and zeolite for
retaining ammonia (NH.sub.3) in the exhaust gases as ammonium ion
(NH.sub.4.sup.+). The platinum is carried by an alumina
(Al.sub.2O.sub.3) carrier.
[0023] When the amount of NOx adsorbed by the NOx removing device 4
reaches the limit of its NOx adsorbing capacity, i.e., the maximum
NOx adsorbing amount, the NOx removing device 4 cannot adsorb
additional NOx. Accordingly, to timely reduce the adsorbed NOx,
reducing components are supplied to the NOx removing device 4. In
this embodiment, reducing components can be supplied by setting an
air-fuel ratio of an air-fuel mixture in the combustion chamber on
a rich side with respect to the stoichiometric ratio, in increments
of an amount of fuel injected from the fuel injection valve 6, and
reducing an intake air amount using a throttle valve (not shown).
That is, reducing components can be supplied by enriching the
air-fuel ratio. By enriching the air-fuel ratio, a concentration of
reducing components in the exhaust gases which flow into the NOx
removing device 4 becomes higher than a concentration of oxygen,
and reducing components can be supplied to the NOx removing device
4.
[0024] FIGS. 2A-2C illustrate the NOx removal in the NOx removing
device 4. First, in the initial condition, when the air-fuel ratio
of the air-fuel mixture that burns in the engine 1 is set to a
value on the lean side with respect to the stoichiometric ratio,
(i.e., when the lean burn operation is performed), the
concentration of reducing components in the exhaust gases that flow
into the NOx removing device 4 becomes lower than the concentration
of oxygen. That is, the exhaust gases enter the oxidizing state. In
this state, nitric oxide (NO) and oxygen (O.sub.2) in the exhaust
gases react by the action of the catalyst to be adsorbed by the
ceria as nitrogen dioxide (NO.sub.2), as shown in FIG. 2A. Further,
the nitric oxide, which has not reacted with oxygen, is also
adsorbed by the ceria.
[0025] Next, when the concentration of reducing components in the
exhaust gases is made higher than the concentration of oxygen by
enriching the air-fuel ratio, the exhaust gases enter the reducing
state. Then, hydrogen and carbon monoxide are generated by the
steam reforming reaction shown by the following equation (3).
Further, carbon dioxide and hydrogen are generated from carbon
monoxide and water by the water gas reaction expressed by the
following equation (4).
C.sub.nH.sub.m+nH.sub.2O.fwdarw.nCO+(n+m/2)H.sub.2 (3)
CO+H.sub.2O.fwdarw.CO.sub.2+H.sub.2 (4)
[0026] Further, as shown in FIG. 2B, NOx contained in the exhaust
gases and NOx (NO, NO.sub.2) adsorbed by the ceria and platinum
react, by the action of the catalyst, with the hydrogen generated
in the reforming catalyst 3 and the hydrogen generated in the NOx
removing device 4 to generate ammonia (NH.sub.3) and water. These
reactions are expressed by the following chemical equations (5) and
(6).
2NO.sub.2+7H.sub.2.fwdarw.2NH.sub.3+4H.sub.2O (5)
2NO+5H.sub.2.fwdarw.2NH.sub.3+2H.sub.2O (6)
[0027] The generated ammonia is adsorbed by the zeolite in the form
of an ammonium ion (NH.sub.4.sup.+).
[0028] Next, when the air-fuel ratio is set to a value on the lean
side with respect to the stoichiometric ratio to perform the lean
burn operation, and the concentration of reducing components in the
exhaust gases which flow into the NOx removing device 4 is set to a
value on the lower side of the concentration of oxygen, the exhaust
gases enter the oxidizing state. Then, NOx is adsorbed by the ceria
as shown in FIG. 2C, similar to FIG. 2A. Further, when ammonium
ions are adsorbed by the zeolite, NOx and oxygen in the exhaust
gases react with ammonia to generate nitrogen (N.sub.2) as
expressed by the following equations (7) and (8).
4NH.sub.3+4NO+O.sub.2.fwdarw.4N.sub.2+6H.sub.2O (7)
2NH.sub.3+NO+NO.sub.2.fwdarw.2N.sub.2+3H.sub.2O (8)
[0029] As described above, in the NOx removing device 4, the
ammonia generated when supplying reducing components is adsorbed by
the zeolite, and the adsorbed ammonia reacts with NOx during the
lean burn operation. Accordingly, NOx can be efficiently
removed.
[0030] An accelerator sensor 11 for detecting an operation amount
AP of an accelerator pedal of the vehicle driven by the engine 1
(hereinafter referred to as "accelerator operation amount AP") and
an engine rotational speed sensor 12 for detecting an engine
rotational speed NE are connected to the ECU 7. The detection
signals of these sensors are supplied to the ECU 7.
[0031] The ECU 7 calculates a fuel injection period, which is a
valve opening period of the fuel injection valve 6, and an
execution timing of the fuel injection according to the detection
signals of these sensors. Further, the ECU 7 performs a drive
control of the fuel injection valve 6 according to the calculation
result. Specifically, an amount of NOx adsorbed by the NOx removing
device 4 is estimated, and enrichment of the air-fuel ratio for
making the exhaust gases enter the reducing state is performed when
the estimated amount of adsorbed NOx reaches a predetermined
threshold value.
[0032] FIG. 3 is a time graph illustrating the relationship between
the air-fuel ratio control, a reducing-component amount QRED, and a
NOx amount QNOx in exhaust gases. In FIG. 3, the solid line
corresponds to this embodiment, and the dashed line corresponds to
an example where the ammonia generating catalyst 3 is not provided.
Further, the reducing-component amount QRED indicates an amount of
reducing components emitted from the engine 1, for example, an
amount of reducing components which flow into the ammonia
generating catalyst 3. The NOx amount QNOx indicates an amount of
NOx emitted to the downstream side of the NOx removing device 4,
specifically, a NOx amount after the amount of NOx adsorbed in the
NOx removing device 4 has become saturated.
[0033] Normally, the air-fuel ratio is set to a value on the lean
side with respect to the stoichiometric ratio to perform the lean
burn operation. An enrichment of the air-fuel ratio is started from
the time t1 when the estimated amount of adsorbed NOx reaches a
predetermined threshold value. The enrichment ends at time t2. At
this time, the reducing-component amount QRED rapidly increases and
the exhaust gases enter the reducing state. In this embodiment,
since ammonia is generated by the ammonia generating catalyst 3 and
supplied to the NOx removing device 4, the degree of the enrichment
can be made smaller to reduce the reducing-component amount QRED,
compared with an exhaust gas purifying apparatus where the ammonia
generating catalyst 3 is not provided. Further, the amount of
ammonia retained by the NOx removing device 4 in the reducing state
is increased by the ammonia generated by the ammonia generating
catalyst 3, and the amount of NOx reduced during the lean burn
operation increases. Therefore, the time the amount of NOx adsorbed
by the NOx removing device 4 has become saturated is delayed from
time t3 to time t4, thereby making it possible to lower the
execution frequency of enrichment of the air-fuel ratio for
reducing NOx.
[0034] In FIG. 4, the curve L1 shows a relationship between a
temperature T4 of the NOx removing device 4 and an amount QNH3A of
adsorbed ammonia. The curve L2 shows a relationship between a
temperature T3 of the ammonia-generating catalyst 3 and an amount
QNH3G of generated ammonia. As shown in this figure, while
adsorption of ammonia in the NOx removing device 4 is promoted in a
low-temperature region, where temperatures are equal to or less
than 230 degrees C., generation of ammonia in the ammonia
generating catalyst 3 is promoted in a high-temperature region
where temperatures are equal to or higher than 270 degrees C.
[0035] Accordingly, by providing the ammonia generating catalyst 3
upstream of the NOx removing device 4, the temperature T3 of the
ammonia generating catalyst 3 can be made comparatively high and
the temperature T4 of the NOx removing device 4 can be made
comparatively low. Therefore, by taking advantage of both
characteristics of the ammonia generating catalyst 3 and the NOx
removing device 4, efficient generation and adsorption (storage) of
ammonia can be performed. More preferably, the ammonia generating
catalyst 3 may be disposed at a position where the temperature T3
is 300 degrees C. or more, and the NOx removing device 4 may be
disposed at a position where the temperature T4 is 200 degrees C.
or more.
[0036] As described above, since the ammonia generating catalyst 3
is disposed upstream of the NOx removing device 4, which has
ammonia-retaining capacity, ammonia is supplied from the ammonia
generating catalyst 3 to the NOx removing device 4. As a result,
the amount of ammonia retained in the NOx removing device 4 is
increased when the exhaust gases are in the reducing state.
[0037] At the same time, a degree of the air-fuel ratio enrichment
can be made smaller compared with the conventional apparatus.
Further, since the amount of generated and retained ammonia
increases, the amount of NOx reduced by ammonia during the lean
burn operation increases, thereby reducing execution frequency of
the air-fuel ratio enrichment for reducing NOx adsorbed by the NOx
removing device 4. Consequently, the fuel consumption rate can be
improved compared with the conventional apparatus.
[0038] In one embodiment of the present invention, the NOx removing
device 4 corresponds to the NOx removing means, and the ammonia
generating catalyst 3 corresponds to the ammonia generating means.
Further, the fuel injection valve 6 and the ECU 7 comprise the
reducing components supply means. Specifically, increasing the fuel
injection amount by the air-fuel ratio enrichment corresponds to
supplying reducing components.
[0039] The present invention is not limited to the above-described
embodiment, and various modifications may be made. For example, in
the above-described embodiment, the supply of reducing components
is performed by increasing an amount of the main fuel injection,
wherein one main injection per cylinder is performed by the fuel
injection valve 6. Alternatively, the supply of reducing components
may be performed by executing one or more post injections, wherein
a supplemental fuel injection is executed after the main injection.
Alternatively, a mechanism for directly supplying fuel to the
exhaust pipe 2 may be provided as the reducing components supply
means.
[0040] Further, in the above-described embodiment, ceria can be
used as a NOx adsorbent. Alternatively, other materials which
adsorb or absorb NOx may be used instead of ceria.
[0041] Further, in the above-described embodiment, there is shown
an example where the present invention is applied to the exhaust
gas purification of the diesel internal combustion engine. The
present invention may be applied to the exhaust gas purification of
a gasoline internal combustion engine. Further, the present
invention can also be applied to the exhaust gas purification of a
watercraft propulsion engine, such as an outboard engine having a
vertically extending crankshaft.
[0042] The present invention may be embodied in other specific
forms without departing from the spirit or essential
characteristics thereof. The presently disclosed embodiments are
therefore to be considered in all respects as illustrative and not
restrictive, the scope of the invention being indicated by the
appended claims, rather than the foregoing description, and all
changes which come within the meaning and range of equivalency of
the claims are, therefore, to be embraced therein.
* * * * *