U.S. patent application number 13/264758 was filed with the patent office on 2012-02-09 for apparatus for treating diesel engine exhaust gas.
Invention is credited to Wataru Minami, Hikaru Yamamoto.
Application Number | 20120031083 13/264758 |
Document ID | / |
Family ID | 43356443 |
Filed Date | 2012-02-09 |
United States Patent
Application |
20120031083 |
Kind Code |
A1 |
Minami; Wataru ; et
al. |
February 9, 2012 |
APPARATUS FOR TREATING DIESEL ENGINE EXHAUST GAS
Abstract
An apparatus for treating Diesel engine exhaust gas includes a
filter unit which is located in the upstream side of a flow passage
in a Diesel engine exhaust duct, the filter unit being composed of
a plural number of filter chambers which are thermally insulated
from each other and selectively opened for admission of the exhaust
gas. Located in the downstream side is a nitrogen oxide treatment
section to induce reactions between nitrogen oxides and reductant
gas components of the exhaust gas. The exhaust gas is admitted into
one of the filter chambers in one time period to trap particulate
material on a filter in a filter chamber while letting reductant
gas components of the exhaust gas pass through toward the nitrogen
oxide treatment section which is located in the downstream side. In
the nitrogen oxide treatment section, reducing reactions are
induced between nitrogen oxides and reductant gas components of the
exhaust gas in the presence of a nitrogen oxide reduction catalyst.
Concurrently, in a filter chamber which is disconnected from an
exhaust gas inlet passage, a heater is turned on to burn off
particulate matter trapped on a filter in a filter chamber.
Inventors: |
Minami; Wataru; (Ibaraki,
JP) ; Yamamoto; Hikaru; (Ibaraki, JP) |
Family ID: |
43356443 |
Appl. No.: |
13/264758 |
Filed: |
June 16, 2010 |
PCT Filed: |
June 16, 2010 |
PCT NO: |
PCT/JP2010/060160 |
371 Date: |
October 17, 2011 |
Current U.S.
Class: |
60/297 |
Current CPC
Class: |
B01D 2255/1025 20130101;
B01D 2251/204 20130101; B01D 2258/012 20130101; F01N 2330/10
20130101; F01N 3/0212 20130101; F01N 2590/08 20130101; Y02T 10/12
20130101; B01D 53/9418 20130101; F01N 3/027 20130101; F01N 13/017
20140601; Y02T 10/24 20130101; B01D 2255/1028 20130101; F01N 3/0214
20130101; F01N 3/032 20130101; B01D 2251/208 20130101; F01N 13/009
20140601; F01N 2610/03 20130101; F01N 3/2066 20130101; B01D 53/9477
20130101 |
Class at
Publication: |
60/297 |
International
Class: |
F01N 3/035 20060101
F01N003/035 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2009 |
JP |
2009-144173 |
Claims
1. An apparatus for treating Diesel engine exhaust gas, into which
Diesel engine exhaust gas is introduced to get rid of particulate
matter and to reduce nitrogen oxides in said exhaust gas to
harmless nitrogen gas, characterized in that said apparatus
comprises: a filter unit located in an upstream side of a Diesel
engine exhaust gas duct and composed of a plural number of filter
chambers each encasing a permeable filter member capable of
trapping particulate matter in said exhaust gas while permitting
passage therethrough of reductant gas components in said exhaust
gas, and a nitrogen oxide treatment section located in a downstream
side of said Diesel engine exhaust gas duct and encasing a nitrogen
oxide reduction catalyst to induce reducing reactions between
nitrogen oxides and said reductant gas components in said exhaust
gas; said filter chambers of said filter unit being thermally
insulated from each other and each provided with a heater to burn
off trapped particulate matter; and a control means for the control
of exhaust gas feed to the respective filter chambers of said
filter unit, said control means being adapted to feed exhaust gas
successively to said filter chambers, making an exhaust gas feed to
one filter chamber in one time period while suspending an exhaust
gas feed to other filter chambers during that time period.
2. An apparatus for treating Diesel engine exhaust gas as set forth
in claim 1, wherein each one of said filter chambers of said filter
unit is packed with a permeable filter of ceramic fiber capable of
filtering out particulate matter in said exhaust gas while
permitting passage of reductant gas components including at least
carbon monoxide and hydrocarbons.
3. An apparatus for treating Diesel engine exhaust gas as set forth
in claim 2, wherein said filter is packed between tubular inner and
outer casings, of which said inner casing having an inlet opening
at one end of a closed porous tube, said heater being located
within said inner casing and extended forward toward said inlet
opening from a closed bottom end, and said outer casing being
formed of a heat insulating material.
4. An apparatus for treating Diesel engine exhaust gas as set forth
in claim 1, wherein said filter unit further comprises a shutter
for covering and uncovering inlet openings of the respective filter
chambers under control of said control means, in such a way as to
uncover an inlet opening of one of said filter chambers to let said
exhaust gas in, and turning on a heater in other filter chamber to
burn off trapped particulate matter on said filter while said inlet
opening is closed by said shutter.
5. An apparatus for treating Diesel engine exhaust gas as set forth
in claim 4, wherein said control means is adapted to turn on a
heater of a filter chamber in a phase of trapping particulate
material, and to heat said exhaust gas up to a temperature range
suitable for activation of said nitrogen oxide reduction catalyst
in said nitrogen oxide treatment section.
6. An apparatus for treating Diesel engine exhaust gas as set forth
in claim 1, wherein said filter chambers of said filter unit are
arranged in a circular formation and said shutter is in the form of
a rotary shutter adapted to uncover an inlet opening of one of said
filter chambers selectively in one time period and provided with a
communication passage for introduction of said exhaust gas through
the uncovered inlet opening.
7. An apparatus for treating Diesel engine exhaust gas as set forth
in claim 1, wherein said nitrogen oxide reduction catalyst is
constituted by an occlusion material of a honeycomb structure.
8. An apparatus for treating Diesel engine exhaust gas as set forth
in claim 7, wherein said occlusion material employs iridium or
rhodium as a nitrogen oxide reduction catalyst on a porous carrier
of silica.
Description
TECHNICAL FIELD
[0001] This invention relates to an apparatus for treating Diesel
engine exhaust, particularly suitable for use on a vehicle like a
construction machine which is driven from a Diesel engine, for the
purpose of cleaning its exhaust gas by removal of toxic particulate
substances and nitrogen oxides.
TECHNICAL BACKGROUND
[0002] As an internal combustion engine, Diesel engines excel
gasoline engines in heat efficiency and are at an advantage in fuel
cost or mileage and other aspects except for the need for taking an
ecological countermeasure or countermeasures to cope with emissions
of a large amount of black smoke of so-called PM (particulate
matter) in addition to nitrogen oxide (NOx). In this connection,
there have thus far been proposed various exhaust cleaning systems
which are adapted to remove NOx and PM from exhaust gas. NOx are
converted to N.sub.2 by a reducing reaction before release to the
atmosphere. On the other hand, PM is removed by the use of a
permeable filter which is capable of trapping PM while permitting
passage of gaseous components of exhaust gas.
[0003] NOx are converted to N.sub.2 gas by a reducing reaction in
the presence of a reducing agent or reductant. For example,
disclosed in Patent Literature 1 below is a NOx treatment system
which is incorporated into an exhaust gas duct for treatment of
nitrogen oxides. This treatment system is adapted to induce
reducing reactions between nitrogen oxides NOx and a reductant. In
order to induce reducing reactions in an efficient and effective
manner, this treatment system is arranged to treat exhaust gases by
reduction in the presence of a nitrogen oxide reduction catalyst.
In this regard, as a nitrogen oxide reduction catalyst, the system
of Patent Literature employs a metal such as iridium or rhodium in
combination with a carrier of silica. Further, as a preferred
reductant, a mention is made of hydrogen, carbon monoxide,
hydrocarbons, and oxygen-containing compounds.
[0004] A system for removal of PM in exhaust gas is disclosed, for
example, in Patent Literature 2 below. In Patent Literature 2, a
filter for separating PM components from other exhaust gas
components is made of ceramic fiber having sufficient heat
resistance along with air or gas permeability. This filter is put
in an exhaust gas flow to trap particulate matter in the exhaust
gas. The PM trapped on the filter, however, causes clogging of the
filter, increasing pressure losses in the exhaust gas flow and as a
result making it difficult to secure a sufficient flow rate of the
exhaust gas. To cope with this problem, the permeable filter is
provided with a heater thereby to heat and burn off trapped PM.
PRIOR ART LITERATURE(S)
[0005] Patent Literature 1: Japanese Patent Application Laid Open
under 2004-73921 [0006] Patent Literature 2 Japanese Patent
Application Published under 4,023,514
SUMMARY OF THE INVENTION
Problem(s) to be Solved by the Invention
[0007] In Patent Literature 1, as a preferred reducing agent or
reductant for use in detoxifying NOx in exhaust gas by conversion
to NO.sub.2, a mention is made of hydrogen, carbon monoxide,
hydrocarbons, oxygen-containing compounds. On the other hand, in
Patent Literature 2, trapped PM is burned off to prevent clogging
of a filter, causing oxidation to carbon monoxide and hydrocarbons
in the exhaust gas which is passed through the filter. That is to
say, although a reductant is necessitated in the NOx treating
system of Patent Literature 1, reductant components of exhaust gas,
including carbon monoxide and hydrocarbons, are consumed at the
time of burning off trapped PM in Patent Literature 2.
[0008] Therefore, in case the NOx treating technology of Patent
Literature 1 is combined with the PM stripping technology of Patent
Literature 2, it becomes difficult to utilize carbon monoxide and
hydrocarbons which exist in the exhaust gas as a reductant useful
in the treatment of NOx. That is to say, in order to detoxify NOx
and eliminate PM in Diesel engine exhaust gas on the basis of
disclosures of Patent Literatures 1 and 2, it becomes a requisite
to provide an additional feed path for a reductant which induces
reducing reactions in the treatment of NOx. In this regard, it is
conceivable to feed exhaust gas to a NOx treating system in a stage
anterior to removal of PM. However, in that case, one will face a
problem of contamination of a nitrogen oxide reduction catalyst
with PM to such a degree as to lose its functions as a catalyst
prematurely in an early stage.
[0009] Thus, it is difficult to construct an all-round cleaning
system for Diesel engine exhaust gas, by simply combining the NOx
treating mechanism of Patent Literature 1 with the PM elimination
mechanism of Patent Literature 2.
[0010] In view of the foregoing situations, it is an object of the
present invention to provide an apparatus for treating Diesel
engine exhaust gas to effectively get rid of environmental
pollutants such as PM and NOx which are contained in a large amount
in Diesel engine exhaust gas.
Means for Solving Problem(S)
[0011] In order to achieve the above-stated objective, according to
the present invention, there is provided an apparatus for treating
Diesel engine exhaust gas, into which Diesel engine exhaust gas is
introduced to get rid of particulate matter and to reduce nitrogen
oxides in the exhaust gas to harmless nitrogen gas, characterized
in that the apparatus comprises: a filter unit located in an
upstream side of a Diesel engine exhaust gas duct and composed of a
plural number of filter chambers each encasing a permeable filter
member capable of trapping particulate matter in the exhaust gas
while permitting passage therethrough of reductant gas components
in the exhaust gas, and a nitrogen oxide treatment section located
in a downstream side of the exhaust gas duct and encasing a
nitrogen oxide reduction catalyst to induce reducing reactions
between nitrogen oxides and the reductant gas components in the
exhaust gas; the filter chambers of the filter unit being thermally
insulated from each other and each provided with a heater to burn
off trapped particulate matter; and a control means for the control
of exhaust gas feed to the respective filter chambers of the filter
unit, the control means being adapted to feed exhaust gas
successively to the filter chambers, making an exhaust gas feed to
one filter chamber in one time period while suspending an exhaust
gas feed to other filter chambers during that time period.
[0012] The filter in each one of the above-mentioned filter
chambers is a permeable filter which is capable of trapping solid
particulate matter (PM) like black smoke in the exhaust gas while
permitting passage therethrough of gaseous components of the
exhaust gas. Diesel engine exhaust gas generally contains reductant
gas components such as carbon monoxide and hydrocarbons. These
reductant gas components are allowed to flow out of a filter
chamber without being consumed there, and utilized as reducing
agents in the nitrogen oxide treatment section which is located
downstream of the filter chamber. More particularly, a permeable
filter of ceramic fiber filter of good heat resistance is employed
in each one of the filter chambers in conditions which will prevent
oxidation reactions of the exhaust gas when it is admitted
selectively into one of the filter chambers and brought into
contact with the filter, letting reductant gas components in the
exhaust gas pass through.
[0013] As the filter is used continuously and repeatedly for
trapping PM, it is inevitably clogged with trapped PM. The filter
unit is provided with a plural number of filter chambers, so that,
while one filter chamber is in a phase or stage of trapping PM,
filters in other filter chambers are regenerated by getting rid of
trapped PM. For this purpose, the respective filter chambers are
successively connected to an exhaust inlet passage one after
another by means of a shutter, which is operated to connect the
exhaust inlet passage selectively to one of the filter chambers in
one time period while disconnecting other filter chambers from the
exhaust inlet passage during that time period. A heater which is
provided in each one of the filter chambers is turned on to burn
off trapped PM when not in a PM trapping phase, thereby to restore
the filter performance. In this regard, it is preferred that each
one of the filter chambers be enshrouded in a heat insulating wall
to thermally insulate a filter chamber in a PM trapping phase from
a filter chamber or chambers which are in a heated state for
restoration of filter performance.
[0014] In addition to combustion of PM components, the heater which
is provided in each filter chamber can be utilized for exhaust gas
temperature control. That is, it is desirable to control the
exhaust gas temperature in such a range as would accelerate
nitrogen oxide reducing reactions at the time when NOx in the
exhaust gas are reacted with a reductant in the presence of a
nitrogen oxide reduction catalyst in the nitrogen oxide treatment
section which is located downstream of the filter unit. In the case
of an iridium base catalyst, it is activated to a maximum degree in
a temperature range of from 240.degree. C. to 300.degree. C.
Accordingly, in a filter chamber which is in the PM stripping
stage, it is desirable to control the heater in that chamber in
such a way to heat the exhaust gas up to a temperature range which
will contribute to acceleration of reducing reactions in the
succeeding nitrogen oxide treatment section.
[0015] After removal of PM in a filter chamber, the exhaust gas
which contains reductant gas components is introduced into the
nitrogen oxide treatment section which is located downstream of the
filter unit and packed with a nitrogen oxide reduction catalyst. In
this instance, various metal oxides can be used as a catalyst. More
specifically, iridium or rhodium can be suitably used in
combination with a carrier of porous silica. In the presence of a
catalyst of this sort, nitrogen oxides (NOx) in the exhaust gas are
converted to N.sub.2 gas and H.sub.2O by reactions with reductant
gas components in the exhaust gas including carbon monoxide and
hydrocarbons. Thus, the Diesel engine exhaust gas is cleaned by
removal or reductions in amount of PM and NOx components.
[0016] PM which is contained in a large amount in Diesel engine
exhaust gas is securely trapped on a filter in one of the filter
chambers under conditions which will not impair reductant gas
components, and the exhaust gas which still contains NOx is
introduced into the nitrogen oxide treatment section along with the
reductant gas components to get rid of environmental pollutants in
Diesel engine exhaust gas. Besides, while PM is removed in one
filter chamber, filters in other chambers are regenerated by
complete combustion of trapped PM.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a system diagram of an apparatus for treating
Diesel engine exhaust gas, according to the present invention.
[0018] FIG. 2 is a diagrammatic illustration explanatory of
structural makeup of a filter chamber.
DESCRIPTION OF PREFERRED EMBODIMENT(S)
[0019] Hereafter, the present invention is described by way of its
preferred embodiments. Shown in FIG. 1 is a system arrangement
adopted by the present invention. In that figure, indicated at 1 is
an exhaust duct for conduction of exhaust gas from a Diesel engine.
A filter unit 2 is fitted in this exhaust duct 1 at an upstream end
of the latter in the direction of exhaust gas flow, and a nitrogen
oxide treatment section 3 is located in a downstream side of the
exhaust duct 1.
[0020] The filter unit 2 is composed of a plural number of filter
chambers 10 each having a tubular outer casing 11 and a tubular
inner casing 12 which is located internally of the outer casing
tube 11 as shown in FIG. 2. In the upstream side of the exhaust
duct 1, each filter chamber is provided with a gas inlet plate 13
with an inlet opening 14 at a position radially inward of the inner
casing 12. The tubular inner casing 12 is formed of a porous plate
to permit permeative circulation of an influent gas. On the other
hand, the outer casing 11 is made up of heat insulating walls.
Further, an end closure plate 15 is fitted in the inner casing tube
12 at the downstream end of the filter unit 2. An annular outlet
opening 16 is formed between the outer and inner casings 11 and
12.
[0021] Engine exhaust gas is admitted into one of the filter
chambers 10 through the inlet opening 14 and allowed to flow into
the annular space between the outer and inner casings 11 and 12,
through the pores in the porous walls of the inner casing tube 12.
Exhaust gas is brought into contact with a filter 17 which is
packed in the annular space between the outer and inner casings 11
and 12 to trap particulate matter (PM) thereon. As a consequence,
PM is filtered out and separated from the exhaust gas before it
flows out through the outlet opening 16.
[0022] Trapped PM on the filter 17, including black smoke, is
rendered harmless by complete combustion. At the same time, the
filter 17 can be regenerated by complete combustion of trapped PM
on the filter 17. For this purpose, a heater 18 is provided
internally of the inner casing 12 of each filter chamber 10. The
heater 18 is fixedly supported on the end closure plate 15. Trapped
PM in the filter 17 can be burned off completely by turning on the
heater 18. Since the filter chamber 10 is heated to a high
temperature at this time, the filter 17 is made of ceramic fiber
with sufficient heat resistance.
[0023] In the case of the particular embodiment shown in FIG. 1,
the filter unit 2 is composed of four filter chambers 10. By means
of a rotary shutter 20, the inlet openings 14 to the respective
filter chambers 10 are selectively connected to an exhaust inflow
passage 1a which is connected to the exhaust duct 1. The rotary
shutter 20 is provided with a communication port 21, by way of
which the respective filter chambers 10 are successively connected
to the inflow passage 1a one after another by rotation of the
rotary shutter 20. That is to say, during a time period when one of
the filter chambers 10 is connected to the exhaust inflow passage
10, other filter chambers 10 are disconnected from the exhaust
inflow passage 1a.
[0024] The rotary shutter 20 is rotationally driven from a motor
22. The motor 22 as well as the heaters 18 are put in operation
under control of a control circuit 23. In the case of a Diesel
engine vehicle, for example, in the case of a construction machine
like hydraulic power shovel type excavator, a battery is mounted on
the vehicle. Such an onboard battery can be utilized as a power
source 24 for the motor 22 and heater 18.
[0025] The nitrogen oxide treatment section 3, which is located
downstream of the filter unit 2 in the exhaust duct 1, is
constituted by a reaction chamber 30 which is packed with a
nitrogen oxide reduction catalyst 31. The nitrogen oxide reduction
catalyst 31 is constituted, for example, by a honeycomb structure
of an occlusion material with good permeability. NOx is occluded in
the occlusion material along with the reduction catalyst to induce
a reducing reaction, and resulting N.sub.2 gas and H.sub.2O are
discharged through an outflow passage 1b. As a nitrogen oxide
reductant, for example, an iridium or rhodium metal on a porous
silica carrier with a small amount of alkaline metal content can be
suitably applied.
[0026] Further, as a reductant to be reacted with NOx, hydrogen,
carbon monoxide, hydrocarbons and oxygen-containing compounds can
be used for this purpose. Diesel engine exhaust gas contains large
amounts of reducing gas components including carbon monoxide and
hydrocarbons. Thus, the exhaust gas itself can be used as a
reductant. For this purpose, the exhaust gas is retained in a
non-oxidation state reactions until it is introduced into the
nitrogen oxide treatment section 3.
[0027] As described hereinabove, PM is trapped on the filters 17 in
the respective filter chambers 10 of the filter unit 2 which is
located upstream of the nitrogen oxide treatment section 3 in the
exhaust duct 1. Trapped PM is burned off in the filter chambers 10
by the heaters 18 to regenerate the respective filters. However, if
the exhaust gas is fed to a filter chamber 10 which is in a phase
of burning off trapped PM, the reducing gas components of the
exhaust gas will lose functions as a reductant.
[0028] Of a plural number of filter chambers 10 of the filter unit
2, regeneration of a filter 17 by complete combustion of PM is not
carried out in a filter chamber 10 which is in the phase of
separating and removing PM from the exhaust gas. That is to say,
regeneration of a filter 17 is not carried out as long as its
filter chamber 10 is connected to form part of a flow passage of
the exhaust gas through the exhaust duct 1. It is after the filter
chamber 10 has been disconnected from the exhaust gas flow passage
that the filter chamber 10 is heated to a temperature for complete
combustion of PM which has deposited on its filter 17. Therefore,
the respective filter chambers 10 of the filter unit 2 are
thermally insulated from each other.
[0029] By adoption of the arrangements as described above, it
becomes possible to separate and remove toxic particulate matter
(PM) which occurs in Diesel engine emissions, while converting NOx
into a harmless form. Diesel engine exhaust gas in the exhaust duct
1 flows from the inflow passage 1a toward the outflow passage 1b,
but a heater 18 of a filter chamber 10 is not turned on when the
filter chamber 10 is connected to the inflow passage 1a for removal
of PM from the influent exhaust gas. Accordingly, while PM in the
exhaust gas is removed and trapped on a filter 17 within a filter
chamber 10, there is no possibility of oxidization of reductants
like carbon monoxide and hydrocarbons which are contained in the
exhaust gas. That is to say, after separation of PM, the exhaust
gas flowing out of each filter chamber 10 contains NOx along with
non-oxidized reductant gas components.
[0030] In this manner, while PM is trapped in one of the filter
chambers 10 by its filtering function, heaters 18 in other filter
chambers 10 are turned on one after another to heat the respective
filter chambers up to a temperature at which trapped PM is burned
off and removed by complete combustion for regeneration of the
filters 17. While PM is filtered out in one of the four filter
chambers 10, there is no need for concurrently burning off PM in
all of the remaining three filter chambers 10. That is to say, it
is possible to turn on and off the heaters 18 in relation with
intermittent 90 degrees revolutions of the rotary shutter 20,
turning off a heater 18 of a filter chamber 10 which will come to a
PM filtering position next time, cooling off that filter chamber 10
before starting a PM filtering operation. On-off of the respective
heaters 17 is controlled by a control circuit 23. In this regard,
arrangements may be made to revolve the rotary shutter 20
intermittently at predetermined time intervals, or upon detection
of a pressure loss in a filter chamber 10 in a PM filtering phase,
revolving the rotary shutter 20 when pressure in a filter chamber
10 exceeds a predetermined value.
[0031] After removal of PM, the exhaust gas which contains NOx
along with reductant gas components is admitted into a reaction
chamber 30 of the nitrogen oxide treatment section 3. In the
reaction chamber 30, the exhaust gas is brought into contact with a
nitrogen oxide reduction catalyst 31. As a consequence, NOx are
occluded in the nitrogen oxide reduction catalyst 31 along with
reductants such as carbon monoxide and hydrocarbons, and converted
to harmless N.sub.2 gas by reducing reactions in the presence of
the reductants just mentioned. Thus, after removal of PM components
and following detoxification of NOx components, cleaned exhaust gas
is allowed to flow into the outflow passage 1b of the exhaust duct
1 to prevent or suppress environmental pollutions which would
otherwise be caused by Diesel engine emissions.
[0032] In this instance, in inducing reducing reactions between NOx
and reductants such as carbon monoxide and hydrocarbons which are
occluded in the nitrogen oxide reduction catalyst 31, the reductive
reactions in the reaction chamber 30 can be accelerated by
activating the nitrogen oxide reduction catalyst 31. For instance,
an iridium type catalyst can be activated to a maximum degree in a
temperature range between 240.degree. C. and 300.degree. C.
Accordingly, the control circuit 23 at the control of the heaters
18 may be arranged not only to turn on those heaters 18 in filter
chambers 10 which are not in a PM stripping phase while turning off
a heater 18 in a filter chamber which is in a PM filtering phase,
but to turn on a filter 18 in a filter chamber 10 in a PM filtering
phase to heat the exhaust gas up to such a temperature as will
contribute to activation of the nitrogen oxide reduction catalyst
31 upon introduction into the reaction chamber 31.
TABLE-US-00001 DESCRIPTION OF REFERENCE NUMERALS 1: Exhaust duct
1a: Inflow passage 1b: Outflow passage 2: Filter unit 3: Nitrogen
oxide treatment section 10: Filter chamber 11: Tubular outer casing
12: Tubular inner casing 16: Outlet opening 17: Filter 18: Heater
20: Rotary shutter 21: Communication passage 30: Reaction chamber
31: Nitrogen oxide reduction catalyst
* * * * *