U.S. patent application number 12/259533 was filed with the patent office on 2009-05-14 for exhaust gas purifying system.
Invention is credited to Yoshifumi Kato.
Application Number | 20090120075 12/259533 |
Document ID | / |
Family ID | 39971112 |
Filed Date | 2009-05-14 |
United States Patent
Application |
20090120075 |
Kind Code |
A1 |
Kato; Yoshifumi |
May 14, 2009 |
EXHAUST GAS PURIFYING SYSTEM
Abstract
An exhaust gas purifying system removes particulate matter from
exhaust gas from an engine through an exhaust passage. The system
includes a filter, a reforming catalyst, an injector, and a heat
transfer member. The filter is provided in the exhaust passage and
collects the particulate matter in the exhaust gas. The reforming
catalyst is provided in the exhaust passage and generates the heat
of reaction by reforming fuel. The injector supplies the fuel to
the reforming catalyst. The heat transfer member is in directly
contact with the filter and the reforming catalyst to transfer the
heat therebetween.
Inventors: |
Kato; Yoshifumi;
(Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN, L.L.P.
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Family ID: |
39971112 |
Appl. No.: |
12/259533 |
Filed: |
October 28, 2008 |
Current U.S.
Class: |
60/297 |
Current CPC
Class: |
F01N 2240/30 20130101;
F01N 13/145 20130101; F01N 13/017 20140601; F01N 3/0814 20130101;
F01N 3/2073 20130101; F01N 3/0234 20130101; F01N 3/0821
20130101 |
Class at
Publication: |
60/297 |
International
Class: |
F01N 3/035 20060101
F01N003/035 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 9, 2007 |
JP |
2007-292343 |
Claims
1. An exhaust gas purifying system for removing particulate matter
from exhaust gas from an engine through an exhaust passage,
comprising: a filter provided in the exhaust passage and collecting
the particulate matter in the exhaust gas; a reforming catalyst
provided in the exhaust passage and generating the heat of reaction
by reforming fuel; an injector supplying the fuel to the reforming
catalyst; and a heat transfer member being in directly contact with
the filter and the reforming catalyst to transfer the heat
therebetween.
2. An exhaust gas purifying system for removing particulate matter
from exhaust gas from an engine through an exhaust passage,
comprising: a filter provided in the exhaust passage and collecting
the particulate matter in the exhaust gas; a reforming catalyst
provided in the exhaust passage and being in directly contact with
the filter, the reforming catalyst generating the heat of reaction
by reforming fuel; and an injector supplying the fuel to the
reforming catalyst.
3. The exhaust gas purifying system according to claim 1, wherein
the reforming catalyst circumferentially surrounds the filter.
4. The exhaust gas purifying system according to claim 1, further
comprising a heating member provided upstream of the filter and
allowing the exhaust gas to flow downstream therethrough, the
heating member receiving the heat of reaction generated at the
reforming catalyst.
5. The exhaust gas purifying system according to claim 1, wherein
the heat transfer member is in surface contact with the reforming
catalyst and the filter.
6. The exhaust gas purifying system according to claim 1, wherein
the heat transfer member has a hollow cylindrical shape, the
reforming catalyst is disposed outside of the heat transfer member,
and the filter is disposed inside the heat transfer member.
7. The exhaust gas purifying system according to claim 1, wherein
the heat transfer member is a partition wall to separate the filter
and the reforming catalyst.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an exhaust gas purifying
system, and more particularly to a system for removing particulate
matter from exhaust gas of a diesel engine.
[0002] In a conventional exhaust gas purifying system, a filter is
provided in an exhaust pipe to collect particulate matter in
exhaust gas of a diesel engine. In order to prevent particulate
matter accumulation on the filter and thereby to prevent an
increase in the flow resistance of the filter, particulate matter
needs to be removed from the filter so that the filter is
regenerated. In a known system, for example, disclosed in Japanese
Unexamined Patent Application Publication No. 59-155523,
hydrocarbon is supplied to a filter that contains oxidation
catalysts. The hydrocarbons are oxidized or burned off on the
filter, thereby removing particulate matter on the filter. The
system has a fuel injection unit at an exhaust pipe disposed
upstream of the filter with respect to the flow of exhaust gas. The
fuel injection unit is connected through a fuel passage to a diesel
fuel tank. The fuel passage has a reformer that contains reforming
catalysts. The reformer produces hydrocarbons highly reactive with
the oxidation catalysts of the filter by reforming diesel fuel. The
reformer is connected to a bypass passage branching from the
exhaust pipe. Exhaust gas flowing in the exhaust pipe is introduced
through the branch passage into the reformer to preheat the
reforming catalysts, thereby accelerating the reforming reaction of
the diesel fuel in the reforming catalysts.
[0003] The system disclosed in the reference No. 59-155523,
however, requires two catalytic reactions for removal of
particulate matter on the filter. Specifically, the system requires
reforming of diesel fuel in the reforming catalyst and oxidation of
hydrocarbons in the oxidation catalysts of the filter, which
prevents efficient removal of particulate matter from the
filter.
[0004] The present invention is directed to an exhaust gas
purifying system that efficiently removes particulate matter from a
filter.
SUMMARY OF THE INVENTION
[0005] In accordance with an aspect of the present invention, an
exhaust gas purifying system removes particulate matter from
exhaust gas from an engine through an exhaust passage. The system
includes a filter, a reforming catalyst, an injector, and a heat
transfer member. The filter is provided in the exhaust passage and
collects the particulate matter in the exhaust gas. The reforming
catalyst is provided in the exhaust passage and generates the heat
of reaction by reforming fuel. The injector supplies the fuel to
the reforming catalyst. The heat transfer member is in directly
contact with the filter and the reforming catalyst to transfer the
heat therebetween.
[0006] In accordance with another aspect of the present invention,
an exhaust gas purifying system removes particulate matter from
exhaust gas from an engine through an exhaust passage. The system
includes a filter, a reforming catalyst and an injector. The filter
is provided in the exhaust passage and collects the particulate
matter in the exhaust gas. The reforming catalyst is provided in
the exhaust passage and is in directly contact with the filter. The
reforming catalyst generates the heat of reaction by reforming
fuel. The injector supplies the fuel to the reforming catalyst.
[0007] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
The invention together with objects and advantages thereof, may
best be understood by reference to the following description of the
presently preferred embodiments together with the accompanying
drawings in which:
[0009] FIG. 1 is a schematic view of an exhaust gas purifying
system according to a first embodiment of the present
invention;
[0010] FIG. 2 is a longitudinal cross-sectional view of a reformer
of the exhaust gas purifying system of FIG. 1;
[0011] FIG. 3 is a cross-sectional view taken along the line
III-III in FIG. 2;
[0012] FIG. 4 is a longitudinal cross-sectional view of a reformer
according to a second embodiment of the present invention;
[0013] FIG. 5 is a longitudinal cross-sectional view of a reformer
according to a third embodiment of the present invention; and
[0014] FIG. 6 is a cross-sectional view taken along the line VI-VI
in FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0015] The following will describe the first embodiment of the
present invention with reference to FIGS. 1 through 3. FIG. 1 shows
an exhaust gas purifying system according to the first embodiment.
A diesel engine 1 includes a cylinder head 1A connected to an
intake manifold 2 and an exhaust manifold 3. The intake manifold 2
introduces air into the diesel engine 1, and the exhaust manifold 3
emits exhaust gas out of the diesel engine 1. The exhaust manifold
3 is connected to an exhaust pipe 4 as an exhaust passage. Exhaust
gas of the diesel engine 1 flows through the exhaust manifold 3 and
the exhaust pipe 4, as indicated by arrow A in FIG. 1. The exhaust
pipe 4 is connected to a reformer 7 accommodating therein a filter
5 and a reforming catalyst 6 and supplied with diesel fuel from an
injector 8. The filter 5 collects particulate matter in exhaust gas
(diesel particulate, hereinafter referred to as PM). The reforming
catalyst 6 reforms diesel fuel used as a fuel of the diesel engine
1. The injector 8 is connected to a diesel fuel tank (not shown in
drawings) through a fuel passage 9 and extends into the reformer 7,
thereby injecting diesel fuel into the reformer 7.
[0016] As shown in FIG. 2, the reformer 7 is a hollow cylindrical
case made of a metal and having tapered longitudinal ends connected
to the exhaust pipe 4. The reformer 7 has therein a partition wall
7A as a heat transfer member. The partition wall 7A is a hollow
cylindrical member made of a metal such as stainless steel and
accommodates therein the cylindrical filter 5 so that an outer
peripheral surface 5A of the filter 5 is in contact with an inner
peripheral surface 7B of the partition wall 7A. That is, the
partition wall 7A is in surface contact with the filter 5. The
filter 5 is a wall-flow filter having a honeycomb structure formed
of a porous ceramic such as cordierite and removes PM from exhaust
gas flowing downstream therethrough. The filter 5, the reforming
catalyst 6, the reformer 7, the partition wall 7A and the injector
8 are components of the exhaust gas purifying system.
[0017] The reforming catalyst 6 has a hollow cylindrical shape and
disposed outside the partition wall 7A in the reformer 7. An inner
peripheral surface 6A of the reforming catalyst 6 is in contact
with an outer peripheral surface 7C of the partition wall 7A, and
an outer peripheral surface 6B of the reforming catalyst 6 is in
contact with an inner peripheral surface 7D of the reformer 7. That
is, the partition wall 7A is in surface contact with the reforming
catalyst 6. The injector 8 extends into the reformer 7 through an
outer peripheral surface 7G and the inner peripheral surface 7D of
the reformer 7. The injector 8 is disposed at such a position that
allows diesel fuel to be injected upstream of the reforming
catalyst 6 in the reformer 7. The reforming catalyst 6 is, for
example, a rhodium (Rh) containing catalyst, where diesel fuel is
reacted with oxygen (O.sub.2) and water vapor (H.sub.2O) in exhaust
gas, thereby reforming the diesel fuel so as to produce carbon
monoxide (CO), hydrogen (H.sub.2), and hydrocarbon (HC). This
reforming of diesel fuel in the reforming catalyst 6 occurs through
exothermic reaction at a temperature of about 700 to 800 degrees
Celsius. That is, the reforming catalyst 6 produces the heat of
reaction at a temperature of about 700 to 800 degrees Celsius by
reforming diesel fuel. The filter 5 is disposed inside the
reforming catalyst 6. That is, the filter 5 is surrounded along the
entire circumference thereof by the reforming catalyst 6, and the
partition wall 7A is in directly contact with the filter 5 and the
reforming catalyst 6, as shown in FIG. 3. Therefore, the heat of
reaction generated when the reforming catalyst 6 reforms diesel
fuel is transferred efficiently to the filter 5 via the partition
wall 7A.
[0018] As shown in FIG. 2, the partition wall 7A has at the
upstream end thereof an opening 7E formed between the outer
peripheral surface 7C and the inner peripheral surface 7D and
extending circumferentially. The partition wall 7A also has at the
downstream end an opening 7F formed between the outer peripheral
surface 7C and the inner peripheral surface 7D and extending
circumferentially. The exhaust gas introduced from the exhaust pipe
4 into the reformer 7 flows mostly in the space surrounded by the
partition wall 7A and passes through the filter 5 out of the
reformer 7. The rest of the exhaust gas flows through the opening
7E into the space formed between the outer peripheral surface 7C
and the inner peripheral surface 7D, passes through the reforming
catalyst 6, and then flows through the opening 7F out of the
reformer 7 while joining the exhaust gas passing through the filter
5.
[0019] As described above, the filter 5 and the reforming catalyst
6 are disposed parallel to each other, and the partition wall 7A is
in directly contact with the filter 5 and the reforming catalyst 6
to transfer the heat therebetween in the reformer 7. That is, the
filter 5 and the reforming catalyst 6 are in indirectly contact
with each other, and are in physically contact with each other.
Since the thermal conductivity of a solid or the partition wall 7A
is larger than that of a gas, the heat of reaction generated at the
reforming catalyst 6 is efficiently transferred to the filter 5 via
the partition wall 7A. In addition, a part of the exhaust gas
introduced into the reformer 7 is branched through the opening 7E
and passes through the reforming catalyst 6 provided at the space
between the outer peripheral surface 7C and the inner peripheral
surface 7D in the reformer 7.
[0020] Referring to FIG. 1, the reformer 7 is connected at the
downstream side thereof to a NOx storage reduction (NSR) catalyst
10, and the NOx storage reduction catalyst 10 is connected at the
downstream side thereof to a selective catalytic reduction (SCR)
catalyst 11. The NSR catalyst 10 contains therein alkaline earth
metals like barium (Ba) as a storage material. In lean exhaust gas,
that is, in an oxidizing atmosphere with high oxygen concentration
wherein the injector 8 injects no diesel fuel, the NSR catalyst 10
temporarily stores nitrogen oxides (hereinafter referred to as NOx)
in the exhaust gas. In rich exhaust gas, that is, in a reducing
atmosphere with low oxygen concentration wherein the injector 8
injects diesel fuel, the NSR catalyst 10 releases the stored NOx
for reduction to nitrogen (N.sub.2) and produces ammonia
(NH.sub.3). Specifically, NSR catalyst 10 reduces the stored NOx to
nitrogen by using carbon monoxide, hydrogen, and hydrocarbon
produced by the reforming catalyst 6 as the reducing agent. In the
SCR catalyst 11, the remaining NOx in the exhaust gas is reacted
with ammonia produced by the NSR catalyst 10, thereby being reduced
to nitrogen.
[0021] The following will describe the operation of the exhaust gas
purifying system according to the first embodiment in a lean
condition wherein the injector 8 injects no diesel fuel into the
reformer 7. As shown in FIG. 1, exhaust gas of the diesel engine 1
flows through the exhaust manifold 3 and the exhaust pipe 4 into
the reformer 7. The exhaust gas flows mostly in the space
surrounded by the partition wall 7A (see FIG. 2) and passes through
the filter 5 out of the reformer 7, so that PM in the exhaust gas
is collected by the filter 5. The rest of the exhaust gas flows
through the opening 7E into the space between the outer peripheral
surface 7C and the inner peripheral surface 7D. The exhaust gas
then passes through the reforming catalyst 6, but reforming
reaction in the reforming catalyst 6 does not occur because the
injector 8 injects no diesel fuel into the reformer 7. After
passing through the reforming catalyst 6, the exhaust gas flows
through the opening 7F out of the reformer 7.
[0022] The exhaust gas emitted from the reformer 7 passes through
the NSR catalyst 10 and the SCR catalyst 11. Since the injector 8
injects no diesel fuel into the reformer 7, the exhaust gas from
the reformer 7 is in the oxidizing atmosphere. Therefore, the NSR
catalyst 10 stores NOx in the exhaust gas but produces no ammonia,
and no reaction occurs in the SCR catalyst 11. As described above,
in the lean condition, PM in exhaust gas is collected by the filter
5, and NOx in the exhaust gas is stored on the NSR catalyst 10.
Therefore, exhaust gas emitted out of the system contains neither
PM nor NOx.
[0023] The following will describe the operation of the exhaust gas
purifying system according to the first embodiment in a rich
condition wherein the injector 8 injects diesel fuel into the
reformer 7. When the amount of PM accumulated on the filter 5
becomes a predetermined level, the injector 8 injects diesel fuel
into the reformer 7 thereby to supply diesel fuel to the reforming
catalyst 6. In the reforming catalyst 6, the diesel fuel is reacted
with oxygen in exhaust gas introduced through the opening 7E into
the space between the outer peripheral surface 7C and the inner
peripheral surface 7D, thereby being reformed so as to produce
carbon monoxide. This reforming of diesel fuel in the reforming
catalyst 6 occurs through exothermic reaction at a temperature of
about 700 to 800 degrees Celsius. Since the partition wall 7A is in
directly contact with the filter 5 and the reforming catalyst 6,
the heat of reaction generated at the reforming catalyst 6 is
efficiently transferred to the filter 5 through the contact,
thereby heating the filter 5. When the filter 5 is heated to the PM
combustion temperature, the accumulated PM on the filter 5 is
burned off, and the filter 5 is regenerated. That is, the heat of
reaction generated at the reforming catalyst 6 is used for heating
the PM on the filter 5.
[0024] The exhaust gas introduced into the space between the outer
peripheral surface 7C and the inner peripheral surface 7D flows
through the opening 7F out of the reformer 7 along with carbon
monoxide, hydrogen, and hydrocarbon produced by the reforming
catalyst 6. The exhaust gas from the reformer 7 then passes through
the NSR catalyst 10. The NSR catalyst 10 releases the NOx
previously stored in the oxidizing atmosphere for reduction to
nitrogen and produces ammonia. Specifically, NSR catalyst 10
reduces the stored NOx to nitrogen by using carbon monoxide,
hydrogen, and hydrocarbon serving as reducing agent produced by the
reforming catalyst 6, and produces ammonia. In the SCR catalyst 11,
NOx remaining in the exhaust gas that is not reduced in the NSR
catalyst 10 is reacted with ammonia produced by the NSR catalyst
10, thereby being reduced to nitrogen.
[0025] According to the first embodiment, since the partition wall
7A being in directly contact with the filter 5 and the reforming
catalyst 6 is provided in the reformer 7, the heat of reaction
generated at the reforming catalyst 6 is efficiently transferred to
the filter 5 via the partition wall 7A. Therefore, the filter 5 is
heated to the PM combustion temperature without using any heating
means other than the heat of reaction at the reforming catalyst 6,
and the accumulated PM is efficiently removed from the filter 5.
Additionally, the heat of reaction at the reforming catalyst 6 is
efficiently transferred to the filter 5 because the filter 5 is
surrounded along the entire circumference thereof by the reforming
catalyst 6. Therefore, the filter 5 is heated to the PM combustion
temperature, and the accumulated PM is removed from the filter 5
more efficiently than heretofore.
[0026] The following will describe an exhaust gas purifying system
according to the second embodiment of the present invention. In the
second embodiment, the filter is in directly contact with the
reforming catalyst without providing a partition wall therebetween
as a heat transfer member, but the other components and structures
are substantially the same as those of the first embodiment.
Therefore, the following description will use the same reference
numbers for the common elements or components in both embodiments,
and the description of such elements or components in FIGS. 1
through 3 for the second embodiment will be omitted. FIG. 4 shows a
reformer 17 according to the second embodiment. As with the
reformer 7 of the first embodiment, the reformer 17 is provided by
a hollow cylindrical case made of a metal. The reformer 17
accommodates therein a hollow cylindrical partition wall 17A so
that a downstream end 17B of the partition wall 17A is disposed at
a middle position as viewed in longitudinal direction of the
reformer 17, thereby being divided radially into two spaces.
[0027] A cylindrical filter 15 is provided downstream of the
partition wall 17A so that an upstream end 15A of the filter 15 is
in contact with the downstream end 17B of the partition wall 17A.
As with the filter 5 of the first embodiment, the filter 15 is a
wall-flow filter and removes PM from exhaust gas flowing downstream
therethrough. A hollow cylindrical reforming catalyst 16 is
disposed in the space formed between an outer peripheral surface
15B of the filter 15 and an inner peripheral surface 17C of the
reformer 17. An inner peripheral surface 16A of the reforming
catalyst 16 is in contact with the outer peripheral surface 15B,
and an outer peripheral surface 16B of the reforming catalyst 16 is
in contact with the inner peripheral surface 17C. That is, the
reforming catalyst 16 is in surface contact with the filter 15. In
the reforming catalyst 16, as with the reforming catalyst 6 of the
first embodiment, diesel fuel is reacted with oxygen and water
vapor in the exhaust gas so as to produce carbon monoxide,
hydrogen, and hydrocarbon, thereby reforming the diesel fuel. This
reforming of diesel fuel in the reforming catalyst 16 occurs
through exothermic reaction at a temperature of about 700 to 800
degrees Celsius. That is, the reforming catalyst 16 produces the
heat of reaction at a temperature of about 700 to 800 degrees
Celsius by reforming diesel fuel. The heat of reaction generated at
the reforming catalyst 16 is directly transferred to the filter 15
in close contact therewith.
[0028] The partition wall 17A has at the upstream end thereof an
opening 17E formed between an outer peripheral surface 17D of the
partition wall 17A and the inner peripheral surface 17C and
extending circumferentially. The exhaust gas introduced from the
exhaust pipe 4 into the reformer 17 flows mostly in the space
surrounded by the partition wall 17A and passes through the filter
15 out of the reformer 17. The rest flows through the opening 17E
into the space formed between the inner peripheral surface 17C and
the outer peripheral surface 17D, passes through the reforming
catalyst 16, and then flows out of the reformer 17. According to
the second embodiment, since the filter 15 is in directly contact
with the reforming catalyst 16, the heat of reaction generated at
the reforming catalyst 16 is directly transferred to the filter 15.
That is, the heat of reaction generated at the reforming catalyst
16 is used for heating the PM on the filter 15. Therefore, the
filter 15 is heated to the PM combustion temperature without using
any heating means other than the heat of reaction at the reforming
catalyst 16, and the accumulated PM is efficiently removed from the
filter 15, as with the first embodiment.
[0029] The following will describe an exhaust gas purifying system
according to the third embodiment of the present invention. FIG. 5
shows a reformer 27 according to the third embodiment. The reformer
27 has a heating member 21 made of a metal such as stainless steel.
The heating member 21 is a component of the exhaust gas purifying
system. The heating member 21 is composed of a hollow cylindrical
frame 21A and a mesh body 21C disposed inside the frame 21A. The
heating member 21 is disposed upstream of the filter 5 in the space
inside the partition wall 7A so that an outer peripheral surface 21
B of the frame 21A is in contact with the inner peripheral surface
7B of the partition wall 7A. As shown in FIG. 5, the mesh body 21C
has therein a plurality of passages extending in longitudinal
direction of the reformer 17 to allow the exhaust gas to flow
downstream therethrough. Therefore, the exhaust gas introduced into
the space of the partition wall 7A passes through the filter 5
after passing through the mesh body 21C. The partition wall 7A is
in directly contact with the reforming catalyst 6 and the heating
member 21.
[0030] According to the third embodiment, the heating member 21
allowing the exhaust gas to flow therethrough is disposed upstream
of the filter 5 in the space of the partition wall 7A so that the
partition wall 7A is in directly contact with the reforming
catalyst 6 and the heating member 21. Therefore, the heating member
21 is heated by the heat of reaction generated at the reforming
catalyst 6, thereby increasing the temperature of the exhaust gas
passing through the mesh body 21C of heating member 21. That is,
the filter 5 disposed downstream of the heating member 21 is heated
by the exhaust gas passing through the mesh body 21, as well as by
the heat of reaction transferred from the reforming catalyst 6 via
the partition wall 7A. Therefore, the filter 5 is heated more
efficiently to the PM combustion temperature, and the accumulated
PM is removed more efficiently from the filter 5.
[0031] The above embodiments may be modified in various ways as
exemplified below.
[0032] In the above embodiments, the reformer is divided radially
into the two spaces by the partition wall. Alternatively,
cylindrical partition walls having different diameters may be
concentrically disposed in the reformer so that the filters and the
reforming catalysts are disposed alternately, thereby constituting
a multilayer structure.
[0033] In the embodiments, the opening is formed at the partition
wall of the reformer, and a part of exhaust gas constantly flows
through the upstream opening into the space formed between the
outer peripheral surface of the partition wall and the inner
peripheral surface of the reformer. Alternatively, the reformer may
have a valve operable to open the upstream opening to allow the
exhaust gas to flow through the opening only when diesel fuel needs
to be reformed.
[0034] In the first and second embodiments, the filter is
surrounded along the entire circumference thereof by the reforming
catalyst. Alternatively, the filter may be surrounded along only
the partial circumference thereof by the reforming catalyst.
[0035] Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein but may be
modified within the scope of the appended claims.
* * * * *