U.S. patent application number 12/158705 was filed with the patent office on 2009-10-29 for exhaust emission control device.
This patent application is currently assigned to HINO MOTORS, LTD.. Invention is credited to Yoshihide Takenaka.
Application Number | 20090266061 12/158705 |
Document ID | / |
Family ID | 38228170 |
Filed Date | 2009-10-29 |
United States Patent
Application |
20090266061 |
Kind Code |
A1 |
Takenaka; Yoshihide |
October 29, 2009 |
EXHAUST EMISSION CONTROL DEVICE
Abstract
An exhaust emission control device is provided which can
effectively regenerate a NO.sub.x absorption reduction catalyst
even in a relatively low temperature region to improve NO.sub.x
reduction ratio while minimizing deterioration of fuel economy.
Incorporated in an exhaust pipe 4 through which exhaust gas 3
discharged from a diesel engine 1 via an exhaust manifold 2 flows
is a reformer 8 having a fuel adding device 5, a heater 6 and a
reforming catalyst 7. Arranged downstream of the reformer is a
NO.sub.x absorption reduction catalyst 9.
Inventors: |
Takenaka; Yoshihide; (Tokyo,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, L.L.P.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
HINO MOTORS, LTD.
Hino-shi
JP
|
Family ID: |
38228170 |
Appl. No.: |
12/158705 |
Filed: |
December 26, 2006 |
PCT Filed: |
December 26, 2006 |
PCT NO: |
PCT/JP2006/325874 |
371 Date: |
June 23, 2008 |
Current U.S.
Class: |
60/295 ; 60/297;
60/299 |
Current CPC
Class: |
F01N 3/0814 20130101;
B01D 2255/91 20130101; F01N 13/009 20140601; F01N 3/0807 20130101;
F01N 2610/03 20130101; F01N 2240/30 20130101; F01N 3/281 20130101;
B01D 53/9431 20130101; F01N 3/28 20130101; Y02T 10/24 20130101;
F01N 13/0097 20140603; Y02T 10/12 20130101 |
Class at
Publication: |
60/295 ; 60/297;
60/299 |
International
Class: |
F01N 3/023 20060101
F01N003/023; F01N 3/035 20060101 F01N003/035; F01N 3/10 20060101
F01N003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 2005 |
JP |
2005-375719 |
Claims
1. An exhaust emission control device comprising a reformer
incorporated in an exhaust pipe through which exhaust gas from an
engine flows, said reformer having a fuel adding device, a heater
and a reforming catalyst, and a NO.sub.x-absorption reduction
catalyst arranged downstream of the reformer.
2. An exhaust emission control device as claimed in claim 1,
wherein the heater in the reformer is constituted by an anterior
oxidation catalyst unit with oxidation catalyst having heating
function being evenly arranged.
3. An exhaust emission control device as claimed in claim 2,
wherein the anterior oxidation catalyst unit is a membrane metal
heater comprising a strip-like metal membrane coated with oxidation
catalyst and capable of temperature raising through application of
current so as to serve as oxidation catalyst with heating function
and an insulating alumina tape as oxidation catalyst, the metal
membrane and the insulating tape being wound together spirally in
an overlapping manner.
4. An exhaust emission control device as claimed in claim 2,
wherein the anterior oxidation catalyst unit is a wire mesh heater
comprising wire sheets coated with oxidation catalyst and capable
of temperature raising through application of current so as to
serve as oxidation catalyst with heating function and insulating
alumina meshes as oxidation catalyst, the wire sheet and the
insulating mesh being laminated alternately and plurally in a
direction of flow of the exhaust gas.
5. An exhaust emission control device as claimed in claim 1,
wherein the heater in the reformer comprises an anterior oxidation
catalyst unit with centrally arranged oxidation catalyst with
heating function, a mixer being arranged between said anterior
oxidation catalyst unit and the reforming catalyst.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust emission control
device.
BACKGROUND ART
[0002] Exhaust gas from a diesel engine has heretofore been
purified by a catalyst incorporated in an exhaust pipe through
which the exhaust gas flows. Known as this kind of catalyst is a
NO.sub.x-absorption reduction catalyst which has a property of
oxidizing NO.sub.x in the exhaust gas to temporarily absorb the
same in the form of nitrate when an air/fuel ratio of the exhaust
gas is lean, and conducting decomposition into NO.sub.x for
reduction and purification thereof with the assistance of unburned
HC and CO when the oxygen concentration in the exhaust gas is
lowered.
[0003] Known as this kind of NO.sub.x-absorption reduction catalyst
having the above-mentioned property is, for example, a catalyst
made from alumina and carrying platinum and barium or a catalyst
made from alumina and carrying platinum and potassium.
[0004] Since no further NO.sub.x can be absorbed once an absorbed
NO.sub.x amount increases into saturation in the
NO.sub.x-absorption reduction catalyst, it is periodically required
to lower the O.sub.2 concentration in the exhaust gas flowing to
the NO.sub.x-absorption reduction catalyst to decompose and
discharge NO.sub.x.
[0005] For example, in application to a gasoline engine, lowering
the operational air/fuel ratio in the engine (operating the engine
with rich air/fuel ratio) can lower the O.sub.2 concentration and
increase the reduction components such as unburned HC and CO in the
exhaust gas for facilitation of decomposition and discharge of
NO.sub.x. However, in use of a NO.sub.x-absorption reduction
catalyst in an exhaust emission control device for a diesel engine,
it is difficult to operate the engine with rich air/fuel ratio.
[0006] Thus, it has been necessary that fuel (HC) is added to the
exhaust gas upstream of a NO.sub.x-absorption reduction catalyst,
the added fuel being reacted as reducing agent with O.sub.2 on the
reduction catalyst so as to lower the O.sub.2 concentration in the
exhaust gas (see, for example, Reference 1).
[0007] [Reference 1] JP 2000-356127A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0008] However, in such fuel addition upstream of a
NO.sub.x-absorption reduction catalyst, part of HC produced due to
evaporation of the added fuel reacts with O.sub.2 (combustion) in
the exhaust gas on the NO.sub.x-absorption reduction catalyst, and
decomposition and discharge of NO.sub.x are started after the
O.sub.2 concentration becomes substantially zero in an ambient
atmosphere around the NO.sub.x-absorption reduction catalyst. Thus,
in a driving condition that a combustion temperature (about
220-250.degree. C.) necessary for reaction of HC with O.sub.2
(combustion) cannot be obtained on the NO.sub.x-absorption
reduction catalyst (for example, in driving at reduced speed on
city roads often congested with traffic), NO.sub.x cannot be
efficiently decomposed and discharged from the reduction catalyst
and the regeneration of the reduction catalyst does not efficiently
progress, disadvantageously resulting in decrease of recovery ratio
of NO.sub.x-absorption sites occupied in volume of the catalyst to
deteriorate absorption capacity.
[0009] Temperature raise control to the engine and/or increase in
amount of fuel to be added so as to overcome the problem will,
however, bring about substantial deterioration of fuel economy,
resulting in difficulty in practical application.
[0010] The invention was made in view of the above and has its
object to provide an exhaust emission control device which can
effectively regenerate a NO.sub.x-absorption reduction catalyst
even in a relatively low temperature region to improve NO.sub.x
reduction ratio while minimizing deterioration of fuel economy.
Means or Measures for Solving the Problems
[0011] The invention is directed to an exhaust gas emission control
device comprising a reformer incorporated in a gas pipe through
which exhaust gas from an engine flows, said reformer having a fuel
adding device, a heater and a reforming catalyst, and a
NO.sub.x-absorption reduction catalyst arranged downstream of the
reformer.
[0012] The above-mentioned means can obtain the following workings
or operations.
[0013] With the exhaust gas from the engine being delivered via the
exhaust pipe to the reformer, fuel is added as reducing agent by
the fuel adding device on an entry side of the heater. Thus, the
fuel is heated by the heater to produce concentrated HC gas with
the exhaust gas being raised to a temperature required for action
of the reforming catalyst. The HC gas is guided together with the
exhaust gas to the reforming catalyst. After it reacts with O.sub.2
coexisting in the ambient atmosphere to raise the ambient
temperature and O.sub.2 is consumed, the HC gas is decomposed into
highly reactive H.sub.2 and CO which are guided to a posterior
NO.sub.x-absorption reduction catalyst and, on a surface of the
NO.sub.x-absorption reduction catalyst, NO.sub.x is effectively
reduced into N.sub.2 even at a temperature lower than a
conventional combustion temperature in fuel addition.
[0014] As a result, even in a driving condition that a reaction
temperature necessary for reaction of HC with O.sub.2 (combustion)
cannot be obtained on the NO.sub.x-absorption reduction catalyst
(for example, in driving at reduced speed on city roads often
congested with traffic), by operating the reformer with a minimum
level of electricity and without temperature raise control to the
engine nor increase in amount of fuel to be added, NO.sub.x can be
efficiently decomposed and discharged from the NO.sub.x-absorption
reduction catalyst, so that regeneration of the NO.sub.x-absorption
reduction catalyst effectively progresses, resulting in increase of
recovery ratio of NO.sub.x-absorption sites occupied in volume of
the catalyst to prevent deterioration of absorption capacity and of
fuel economy, leading to attainment of practical application.
[0015] In the exhaust emission control device, the heater in the
reformer may be constituted by an anterior oxidation catalyst unit
with oxidation catalyst having heating function being evenly
arranged.
[0016] The anterior oxidation catalyst unit may be a membrane metal
heater comprising a strip-like metal membrane coated with oxidation
catalyst and capable of temperature raising through application of
current so as to serve as oxidation catalyst with heating function
and an insulating alumina tape as oxidation catalyst, the metal
membrane and the insulating tape being wound together spirally in
an overlapping manner.
[0017] Alternatively, the anterior oxidation catalyst unit may be a
wire mesh heater comprising wire sheets coated with oxidation
catalyst and capable of temperature raising through application of
current so as to serve as oxidation catalyst with heating function
and insulating alumina meshes as oxidation catalyst, the wire sheet
and the insulating mesh being laminated alternately and plurally in
a direction of flow of the exhaust gas.
[0018] In the exhaust emission control device, the heater in the
reformer may comprise an anterior oxidation catalyst unit with a
centrally arranged oxidation catalyst with heating function, a
mixer being arranged between the anterior oxidation catalyst unit
and the reforming catalyst.
Effects of the Invention
[0019] An exhaust emission control device according to the
invention has excellent effects that a NO.sub.x-absorption
reduction catalyst can be effectively regenerated even in a
relatively low temperature region to improve NO.sub.x reduction
ratio while minimizing the deterioration of fuel economy.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic view showing an embodiment of the
invention;
[0021] FIG. 2 is a perspective view showing a membrane metal heater
as heater in the embodiment of the invention;
[0022] FIG. 3 is a perspective view showing a wire mesh heater as
heater in the embodiment of the invention;
[0023] FIG. 4 is a schematic view showing a further embodiment of
the invention; and
[0024] FIG. 5 is a front view showing a mixer in the further
embodiment of the invention.
EXPLANATION OF THE REFERENCE NUMERALS
[0025] 1 diesel engine (engine)
[0026] 3 exhaust gas
[0027] 4 exhaust pipe
[0028] 5 fuel adding device
[0029] 6 heater
[0030] 7 reforming catalyst
[0031] 8 reformer
[0032] 9 NO.sub.x-absorption reduction catalyst
[0033] 15 fuel
[0034] 16 metal membrane
[0035] 17 insulating alumina tape
[0036] 18 membrane metal heater
[0037] 19 wire sheet
[0038] 19' insulating alumina mesh
[0039] 20 wire mesh heater
[0040] 32 oxidation catalyst with heating function
[0041] 33 anterior oxidation catalyst unit
[0042] 34 mixer
BEST MODE FOR CARRYING OUT THE INVENTION
[0043] Next, embodiments of the invention will be described in
conjunction with the drawings.
[0044] FIG. 1 shows an embodiment of the invention. Incorporated in
an exhaust pipe 4 through which exhaust gas 3 discharged from a
diesel engine 1 via an exhaust manifold 2 flows is a reformer 8
having a fuel adding device 5, a heater 6 and a reforming catalyst
7. A NO.sub.x-absorption reduction catalyst 9 is arranged
downstream of the reformer.
[0045] The fuel adding device 5 in the reformer 8 comprises an
injection nozzle 10 arranged on the entry side of the heater 6 and
connected via a fuel supply pipe 12 to a fuel tank 11. Fuel 15 such
as light oil may be added as reducing agent to the entry side of
the heater 6 via the injection nozzle 10 by driving a supply pump
13, which is incorporated in the fuel supply pipe 12, and opening
an addition valve 14.
[0046] The heater 6 in the reformer 8 is constituted by an anterior
oxidation catalyst unit with evenly arranged oxidation catalyst
with heating function. The heater 6 may be, for example, a membrane
metal heater 18 as shown in FIG. 2 which comprises a strip-like
metal membrane 16 coated with oxidation catalyst and capable of
temperature raising through application of current so as to serve
as oxidation catalyst with heating function and an insulating
alumina tape 17 as oxidation catalyst, the metal membrane and the
insulating tape being wound together spirally in an overlapping
manner. Alternatively, it may be a wire mesh heater 20 as shown in
FIG. 3 which comprises wire sheets 19 coated with oxidation
catalyst and capable of temperature raising through application of
current so as to serve as oxidation catalysts with heating function
and insulating alumina meshes 19' as oxidation catalysts, the wire
sheet and the insulating alumina mesh being laminated alternately
and plurally in a direction of flow of the exhaust gas 3.
[0047] The reforming catalyst 7 in the reformer 8 serves to
decompose the HC component, which is produced due to fuel addition
by the fuel adding device 5, into H.sub.2 and CO in the exhaust gas
3. This kind of reforming catalyst 7 may comprise, for example, an
oxide such as alumina or silica or a complex oxide such as zeolite
as a carrier carrying for example Pd, Pt or Rh as active metal.
[0048] In a controller 22 serving as engine control computer (ECU:
Electronic Control Unit), current driving conditions are determined
by a revolution speed signal 23a from a revolution speed sensor 23
which detects revolution speed of the diesel engine 1, a load
signal 24a from an accelerator sensor 24 which detects a step-in
angle of an accelerator pedal and a temperature signal 25a from a
temperature sensor 25 which detects temperature of the exhaust gas
3 having passed through the reformer 8 and NO.sub.x-absorption
reduction catalyst 9. On the basis of the current driving
conditions thus determined, an amount of fuel 15 to be added by the
fuel adding device 5, time of current application to the heater 6
and the like are determined so that the controller 22 outputs a
drive command signal 13a to the supply pump 13, an opening/closing
command signal 14a to the addition valve 14 and a current
application command signal 6a to the heater 6. Thus, the fuel 15 is
injected via the injection nozzle 10 in the fuel adding device 5
and is passed through the heater 6 to produce concentrated HC gas
and raise the exhaust gas 3 to a temperature (about 300.degree. C.)
required for action of the reforming catalyst 7. Then, the HC gas
is guided together with the exhaust gas 3 to the reforming catalyst
7 and reacts with O.sub.2 coexisting in the ambient atmosphere to
raise the ambient temperature and consumes O.sub.2; thereafter, the
HC gas is decomposed into highly reactive H.sub.2 and CO which are
introduced into the posterior NO.sub.x-absorption reduction
catalyst 9 for regeneration of the same.
[0049] In FIG. 1, reference numeral 26 denotes a suction pipe for
the diesel engine 1 having an air cleaner 27 at its upstream end.
Incorporated in the suction pipe 26 downstream thereof is a
compressor 29 driven by a turbine 28 which in turn is incorporated
in the exhaust pipe 4 on a discharge side of the exhaust manifold
2. The turbine 28 and the compressor 29 constitutes a turbocharger
30. Incorporated in the suction pipe 26 downstream of the
compressor 29 is an intercooler 31.
[0050] Next, mode of working or operation of the above embodiment
will be described.
[0051] With the exhaust gas 3 from the diesel engine 1 being
delivered via the exhaust pipe 4 to the reformer 8, the fuel 15 is
added as reducing agent via the injection nozzle 10 of the fuel
adding device 5 to the entry side of the heater 6 such as the
membrane metal heater 18 (see FIG. 2) or the wire mesh heater 20
(see FIG. 3) with oxidation catalyst floor temperature being raised
through application of current so that the fuel 15 is heated by the
heater 6 to produce concentrated HC gas while the exhaust gas 3 is
raised to a temperature (about 300.degree. C.) required for the
action of the reforming catalyst 7; the HC gas is guided together
with the exhaust gas 3 to the reforming catalyst 7 and reacts with
O.sub.2 coexisting in the ambient atmosphere. Thus, after the
ambient temperature is raised and O.sub.2 is consumed, the HC gas
is decomposed into high reactive H.sub.2 and CO which are guide to
the posterior NO.sub.x-absorption reduction catalyst 9 and on the
surface of the reduction catalyst 9 NO.sub.x is efficiently reduced
into N.sub.2 even at a temperature lower than a conventional
combustion temperature in fuel addition.
[0052] If the heater 6 were constituted by the anterior oxidation
catalyst unit solely with oxidation catalysts having heating
function, the whole of the anterior oxidation catalyst unit must be
raised to a temperature required for action thereof, which would
require greater electricity. In view of the fact that a percentage
of the fuel 15 required to be oxidized by the anterior oxidation
catalyst unit is about 40% or less, in the embodiment, the heater 6
is constituted by an anterior oxidation catalyst unit with the
evenly arranged oxidation catalyst or catalysts with heating
function such as the membrane metal heater 18 (see FIG. 2) or the
wire mesh heater 20 (see FIG. 3), so that by applying electricity
on the evenly arranged oxidation catalyst or catalysts with heating
function, temperature required for starting of oxidizing the fuel
15 can be maintained on the oxidation catalysts with heating
function by means of less electric power, thereby attaining
effective regeneration of the NO.sub.x-absorption reduction
catalyst 9 with less application of current to the heater 6.
Depending upon the percentage of the fuel 15 to be oxidized by the
anterior oxidation catalyst unit, the membrane metal heater 18 may
be formed by spirally winding the single strip-like metal membrane
16 and plural insulating alumina tapes 17 in an overlapping manner;
or the wire mesh heater 20 may be formed by laminating the single
wire sheet 19 and the plural insulating alumina meshes 19'
alternately and plurally.
[0053] The reason why the reforming catalyst 7 is made to have no
heating function is that if the reforming catalyst 7 were of
heating function, then the temperature on the entry side of the
reforming catalyst 7 might not be sufficiently raised and would
bring abut wasteful portions as catalyst. In the embodiment, the
anterior oxidation catalyst unit is arranged upstream of the
reforming catalyst 7, so that the whole including the entry side of
the reforming catalyst 7 can be increased in temperature and bring
about no wasteful portions.
[0054] As a result, even in a driving condition at lower load
region that a combustion temperature (about 220-250.degree. C.)
necessary for reaction of HC with O.sub.2 (combustion) cannot be
obtained on the NO.sub.x-absorption reduction catalyst 9 (for
example, in driving at reduced speed on city roads often congested
with traffic), by operating the reformer 8 with a minimum level of
electricity and without temperature raise control to the diesel
engine 1 nor increase in amount of fuel to be added, NO.sub.x can
be efficiently decomposed and discharged from the
NO.sub.x-absorption reduction catalyst 9, so that regeneration of
the NO.sub.x-absorption reduction catalyst 9 effectively
progresses, resulting in increase of recovery ratio of
NO.sub.x-absorption sites occupied in volume of the catalyst to
prevent deterioration of absorption capacity and of fuel economy,
leading to attainment of practical application.
[0055] Thus, while minimizing the deterioration of fuel economy,
regeneration of the NO.sub.x absorption reduction catalyst can be
efficiently conducted even in a relatively low temperature region
to improve NO.sub.x reduction ratio.
[0056] FIG. 4 shows a further embodiment of the invention in which
parts similar to those in FIG. 1 are represented by the same
reference numerals. With a fundamental structure being the same as
that in FIG. 1, it is characterized in that, as shown in FIG. 4, a
heater 6 in a reformer 8 is constituted by an anterior oxidation
catalyst unit 33 having centrally arranged oxidation catalyst 32
with heating function, a mixer 34 being arranged between the
anterior oxidation catalyst unit 33 and a reforming catalyst 7.
[0057] The mixer 34 is constituted, for example, by a plurality of
disks 36 arranged in a direction of flow of the exhaust gas 3, each
disk being partly cut out and having a number of through holes 35
with different diameters as shown in FIG. 5.
[0058] In the embodiment shown in FIGS. 4 and 5, with exhaust gas 3
from a diesel engine 1 being delivered via an exhaust pipe 4 to the
reformer 8, fuel 15 is added as reducing agent via an injection
nozzle 10 of a fuel adding device 10 on an entry side of the heater
6 which is constituted by the anterior oxidation catalyst 33 with
the centrally arranged oxidation catalyst 32 with heating function
with oxidation catalyst floor temperature being locally raised by
through application of current. Then, the fuel 15 is locally heated
by the oxidation catalyst 32 with heating function to produce
concentrated HC gas and is stirred for mixing by the mixer 34. As a
result, just like the FIG. 1 embodiment, the exhaust gas 3 is
raised to a temperature (about 300.degree. C.) required for action
of the reforming catalyst 7 and the HC gas is guided together with
the exhaust gas 3 to the reforming catalyst 7 and reacts with
O.sub.2 coexisting with the ambient atmosphere. After the ambient
temperature is raised and O.sub.2 is consumed, the HC gas is
decomposed into highly reactive H.sub.2 and CO which are guided to
a posterior NO.sub.x absorption reduction catalyst 9 and, on the
surface of the NO.sub.x-absorption reduction catalyst 9, NO.sub.x
is effectively reduced into N.sub.2 even at a temperature lower
than a conventional combustion temperature in fuel addition.
[0059] In the embodiment shown in FIG. 4, the heater 6 is
constituted by the anterior oxidation catalyst unit 33 with the
centrally arranged oxidation catalyst 32 with heating function, so
that by centralizing the electricity to the centrally arranged
oxidation catalyst 32 with heating function, the temperature enough
for starting the oxidization of the fuel 15 can be maintained on
the oxidation catalyst 32 with heating function by electricity less
than that of the FIG. 1 embodiment, so that the NO.sub.x-absorption
reduction catalyst 9 can be efficiently regenerated through a
minimum level of current application to the heater 6.
[0060] As a result, just like the embodiment shown in FIG. 1, even
in a driving condition in a lower load region that a combustion
temperature (about 220-250.degree. C.) necessary for reaction of HC
with O.sub.2 (combustion) cannot be obtained on the
NO.sub.x-absorption reduction catalyst 9 (for example, in driving
at reduced speed on city roads often congested with traffic), by
operating the reformer 8 with a minimum level of electricity and
without temperature raise control to the diesel engine 1 nor
increase in amount of fuel to be added, NO.sub.x can be efficiently
decomposed and discharged from the NO.sub.x-absorption reduction
catalyst 9, so that regeneration of the NO.sub.x absorption
reduction catalyst 9 effectively progresses, resulting in increase
of recovery ratio of NO.sub.x absorption sites occupied in volume
of the catalyst to prevent deterioration of absorption capacity and
of fuel economy, leading to attainment of practical
application.
[0061] Thus, also in the embodiment shown in FIG. 4, just like the
embodiment shown in FIG. 1, the NO.sub.x-absorption reduction
catalyst can be efficiently regenerated even in a relatively low
temperature region to improve the NO.sub.x reduction ratio while
minimizing the deterioration of fuel economy.
[0062] It is to be understood that an exhaust emission control
device according to the invention is not limited to the above
embodiments and that various changes and modifications may be made
without departing from the scope of the invention.
* * * * *