U.S. patent application number 12/869075 was filed with the patent office on 2011-03-31 for exhaust gas treatment apparatus.
This patent application is currently assigned to NGK Insulators, Ltd.. Invention is credited to Takashi Egami, Atsuo Kondo, Takeshi Sakuma, Masahiro TOKUDA.
Application Number | 20110072786 12/869075 |
Document ID | / |
Family ID | 43413635 |
Filed Date | 2011-03-31 |
United States Patent
Application |
20110072786 |
Kind Code |
A1 |
TOKUDA; Masahiro ; et
al. |
March 31, 2011 |
EXHAUST GAS TREATMENT APPARATUS
Abstract
There is provided an exhaust gas treatment apparatus 1a
including: a tubular body 10 and a discharge electrode 12 disposed
inside the tubular body. The tubular body 10 has a shape where an
inner diameter of the tubular body 10 is gradually reduced in a
predetermined range from a face 25 which contains a central point
24x of generation of corona discharge 24 generated by the discharge
electrode 12 and which is perpendicular to the flow passage toward
the downstream side 44 of the flow passage.
Inventors: |
TOKUDA; Masahiro;
(Nagoya-City, JP) ; Egami; Takashi;
(Tokoname-City, JP) ; Sakuma; Takeshi;
(Nagoya-City, JP) ; Kondo; Atsuo; (Okazaki-City,
JP) |
Assignee: |
NGK Insulators, Ltd.
Nagoya-City
JP
|
Family ID: |
43413635 |
Appl. No.: |
12/869075 |
Filed: |
August 26, 2010 |
Current U.S.
Class: |
60/275 |
Current CPC
Class: |
F01N 3/01 20130101; F01N
3/0275 20130101; B03C 3/70 20130101; B03C 3/41 20130101; B03C 3/06
20130101; B03C 3/49 20130101; B03C 2201/12 20130101; B03C 2201/30
20130101; B03C 2201/10 20130101 |
Class at
Publication: |
60/275 |
International
Class: |
F01N 3/01 20060101
F01N003/01 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 2009 |
JP |
2009-220042 |
Claims
1. An exhaust gas treatment apparatus comprising: a tubular body
functioning as a flow passage where exhaust gas passes, and a
discharge electrode disposed in an central portion in a cross
section perpendicular to a flow direction of the flow passage
inside the tubular body and causing corona discharge in the
vicinity thereof by applying a voltage; wherein the tubular body
has a shape where an inner diameter of the tubular body is
gradually reduced in a predetermined range from a face which
contains a central point of generation of corona discharge
generated by the discharge electrode and which is perpendicular to
the flow passage toward the downstream side of the flow passage,
and the number of particulates suspended in the exhaust gas is
decreased by charging the particulate matter contained in the
exhaust gas passing through the tubular body by corona discharge
caused by the discharge electrode, collecting the charged
particulate matter on an inner wall face of the tubular body by the
electric field generated from the discharge electrode toward the
inner wall face of the tubular body to agglomerate the plural
particulates, and allowing the agglomerated particulates to scatter
again.
2. The exhaust gas treatment apparatus according to claim 1,
wherein the discharge electrode has a disc-like electrode support
disposed perpendicularly to the flow direction of the flow passage
and a needle-like discharger disposed perpendicularly to the
electrode support and wherein the central point of generation of
corona discharge is the central point of a face which contains the
central point of generation of corona discharge of the tubular body
and which is perpendicular to the flow passage.
3. The exhaust gas treatment apparatus according to claim 2,
wherein the tubular body has a shape where the inner diameter of
the tubular body is reduced so that the distance from the central
point of generation of corona discharge to the inner wall face of
the tubular body in the predetermined range toward the downstream
side of the flow passage is in the range of .+-.10% of a length
from the central point of generation of corona discharge to the
inner wall face of the tubular body in the face which contains the
central point of generation of corona discharge of the tubular body
and which is perpendicular to the flow passage.
4. The exhaust gas treatment apparatus according to claim 3,
wherein the tubular body has a shape where a moving velocity of the
charged particulate matter proceeding in an exhaust gas flow
direction and a drift velocity when the particulate matter is drawn
to the inner wall face are taken into consideration.
5. The exhaust gas treatment apparatus according to claim 1,
wherein the length in the predetermined range where the inner
diameter of the tubular body is gradually reduced is 0.2 to 0.9
times the distance from the central point of generation of corona
discharge of the tubular body to the inner wall face of the tubular
body in the face perpendicular to the flow passage.
6. The exhaust gas treatment apparatus according to claim 2,
wherein the length in the predetermined range where the inner
diameter of the tubular body is gradually reduced is 0.2 to 0.9
times the distance from the central point of generation of corona
discharge of the tubular body to the inner wall face of the tubular
body in the face perpendicular to the flow passage.
7. The exhaust gas treatment apparatus according to claim 3,
wherein the length in the predetermined range where the inner
diameter of the tubular body is gradually reduced is 0.2 to 0.9
times the distance from the central point of generation of corona
discharge of the tubular body to the inner wall face of the tubular
body in the face perpendicular to the flow passage.
8. The exhaust gas treatment apparatus according to claim 4,
wherein the length in the predetermined range where the inner
diameter of the tubular body is gradually reduced is 0.2 to 0.9
times the distance from the central point of generation of corona
discharge of the tubular body to the inner wall face of the tubular
body in the face perpendicular to the flow passage.
9. The exhaust gas treatment apparatus according to claim 1,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
10. The exhaust gas treatment apparatus according to claim 2,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
11. The exhaust gas treatment apparatus according to claim 3,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
12. The exhaust gas treatment apparatus according to claim 4,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
13. The exhaust gas treatment apparatus according to claim 5,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
14. The exhaust gas treatment apparatus according to claim 6,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
15. The exhaust gas treatment apparatus according to claim 7,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
16. The exhaust gas treatment apparatus according to claim 8,
wherein the discharge electrode is supported in the central portion
of the flow passage by a porcelain bushing passing through the wall
face of the tubular body and extended up to the central portion in
a cross section perpendicular to the flow direction of the flow
passage.
17. The exhaust gas treatment apparatus according to claim 9,
wherein the porcelain in bushing has groove-shaped unevenness
formed on the surface thereof.
18. The exhaust gas treatment apparatus according to claim 10,
wherein the porcelain bushing has groove-shaped unevenness formed
on the surface thereof.
19. The exhaust gas treatment apparatus according to claim 11,
wherein the porcelain bushing has groove-shaped unevenness formed
on the surface thereof.
20. The exhaust gas treatment apparatus according to claim 1, which
is disposed in an exhaust system of a vehicle provided with a
gasoline engine as a drive mechanism.
Description
BACKGROUND OF THE INVENTION AND RELATED ART STATEMENT
[0001] The present invention relates to an exhaust gas treatment
apparatus. More specifically, the present invention relates to
exhaust gas treatment apparatus capable of decreasing the number of
the particulates present in exhaust gas by agglomerating the
particulate matter contained in the exhaust gas.
[0002] There is increased need to remove particulate matter and
harmful substances in exhaust gas discharged from internal
combustion engines such as automobile engines, construction machine
engines; industrial machine stationary engines and other combustion
burning appliances; and the like in consideration of influence on
the environment. In particular, in recent years, the regulations
regarding the removal of the particulate matter (hereinbelow
sometimes referred to as "PM") contained in exhaust gas have had a
tendency to be strengthened on a global basis.
[0003] As an exhaust gas treatment apparatus for treating exhaust
gas containing PM as described above, there is disclosed, for
example, an apparatus where PM is electrically collected by
adsorbing PM onto a positively electrified body with negatively
electrifying the PM by the electrified body after the PM is
agglomerated by allowing the PM to collide against a collision
guide member provided inside the flow passage where exhaust gas
passes (see, e.g., JP-A-2001-41024). The PM passed through the
positively electrified body is collected in the filter downstream
and incinerated and removed by applying current to the positively
electrified body to allow it to function as a heater.
[0004] Such an exhaust gas treatment apparatus has a defect of
increase in pressure loss because of complex flow passage
constitution, and manufacturing of the apparatus is not easy. In
addition, since sufficient agglomeration effect cannot be obtained,
the particulate matter passes through the apparatus and is released
without being agglomerated.
[0005] From such problems, there is disclosed an exhaust gas
treatment apparatus provided with an agglomerator which electrifies
particulate matter in exhaust gas by charge by corona discharge and
agglomerates the particulate matter in an electrode collecting the
charge by disposing two kinds of electrodes of charge emission and
charge collection communicating the charge by corona discharge due
to the application of a high voltage between them as an
agglomerator for agglomerating particulate matter (PM) in exhaust
gas in an exhaust gas passage which is formed by an exhaust pipe of
an internal combustion engine and where exhaust gas circulates in
the axial direction of the exhaust pipe in such a manner that a
charge communication portion of the first electrode is located in
almost the central portion in the diametrical direction of the
exhaust gas passage (see, e.g., JP-A-2005-320955).
[0006] In addition, as an agglomerator for exhaust gas treatment
apparatus used for an exhaust gas treatment apparatus as described
above and agglomerating the exhaust gas PM charged by corona
discharge by an agglomeration portion, there is disclosed an
agglomerator for an exhaust gas treatment apparatus provided with
the first conductive body disposed on the downstream side of the
exhaust gas stream of the electrified portion in the agglomeration
portion with applying a voltage to the first conductive body to
have a positive electric potential (see, e.g.,
JP-A-2005-324094).
[0007] Further, there is disclosed an exhaust gas purification
apparatus provided with a PM agglomeration means generating
particulate matter (agglomerated PM) having a large particle
diameter by agglomerating the particulate matter contained in
exhaust gas of an engine and PM trapping means disposed downstream
of the exhaust gas flow direction of the PM agglomeration means and
trapping the agglomerated PM agglomerated by the PM agglomeration
means (see, e.g., JP-A-2006-29267).
[0008] However, the aforementioned JP-A-2005-320955 discloses an
exhaust gas treatment apparatus where an electrode for collecting
charge is disposed on the downstream side of the flow passage. In
the case that the electrode is disposed in such a manner,
particulate matter charged by corona discharge is accelerated by
the electric field and passes through without being trapped by the
other electrode. Therefore, in the aforementioned constitution,
there is a problem that the effect in agglomerating the particulate
matter is small to be almost impossible to agglomerate the
particulate matter practically.
[0009] In addition, in the exhaust gas treatment apparatus
described in the JP-A-2005-320955, there is a description of
utilizing the electrode for collecting charge as an inner wall face
of the flow passage. In such a case, the particulate matter always
moving toward the downstream side on stream of exhaust gas easily
passes through the range of the electric field. Therefore, even in
such a case, there is a problem that the effect in agglomerating
the particulate matter is small to be almost impossible to
agglomerate the particulate matter practically. In particular, in a
case that the exhaust gas flow rate is high or that the number of
the particulates contained in exhaust gas is small, it is very
difficult to trap the particulate matter on the inner wall face of
the flow passage.
[0010] In addition, in the agglomerator for an exhaust gas
treatment apparatus described in the JP-A-2005-324094, a high
voltage is applied to the first conductive body constituting the
agglomeration portion to draw the electrified particulate matter.
It can shorten the moving distance of the electrified particulate
matter and has high agglomeration effect in comparison with the
exhaust gas treatment apparatus disposed in the JP-A-2005-320955.
However, there is a problem that constitution of the electrode (the
electrified portion and the agglomeration portion) is extremely
complex to make it difficult to use it for an automobile or the
like where large vibrations and the like are applied.
[0011] In addition, a PM agglomeration means used for the exhaust
gas purification apparatus described in the JP-A-2006-29267
accelerates the particulate matter in the exhaust gas flow
direction like the exhaust gas treatment apparatus described in the
JP-A-2005-320955. Therefore, there is a problem that the effect in
agglomerating the particulate matter is small to be almost
impossible to agglomerate the particulate matter practically.
[0012] Further, the exhaust gas treatment apparatuses described in
the aforementioned JP-A-2005-320955, JP-A-2005-324094, and
JP-A-2006-29267 have been developed in order to treat exhaust gas
containing a relatively large amount of particulate matter of a
diesel engine or the like. In the case of using them for a gasoline
engine or the like having a small number of the particulates in
exhaust gas in comparison with a diesel engine or the like, the
number of the particulates to be agglomerated is small, and the
particle diameters of the particulates are small. Therefore, the
effect in agglomerating the particulate matter is further
reduced.
[0013] In particular, a new standard by EURO 6 is supposed to be
applied as an exhaust gas regulation from 2012, and there is
desired the development of an exhaust gas treatment apparatus
capable of corresponding with a vehicle provided with a gasoline
engine as a driving mechanism. In particular, since a gasoline
engine has a low torque, if a filter increasing pressure loss of
exhaust gas is disposed in an exhaust system, knocking is easily
caused to cause an engine trouble or the like. Therefore, there is
desired the development of an exhaust gas treatment apparatus
provided with a mechanism which hardly charge a burden on an engine
or the like.
[0014] In addition, when a filter is disposed in an exhaust system
of a gasoline engine to run over a long distance, deposition of ash
derived from components contained in a gasoline of a fuel becomes a
serious problem. Since ash does not disappear even when
high-temperature regeneration (burning) is performed in a filter
unlike the PM, clogging is caused in the filter as a result to
cause the increase in pressure loss.
SUMMARY OF THE INVENTION
[0015] The present invention has been made in order to solve the
aforementioned problems of prior art and aims to provide an exhaust
gas treatment apparatus capable of decreasing the number of the
particulates contained in exhaust gas by agglomerating the
particulate matter contained in the exhaust gas.
[0016] As a result of earnest studies by the present inventors in
order to solve the aforementioned problems of prior art, they found
out that the problems can be solved by allowing the tubular body to
have an inner diameter gradually reduced in a predetermined range
from the central point generating corona discharge toward the down
stream side of the flow passage in an exhaust gas treatment
apparatus where a discharge electrode for causing corona discharge
is disposed in a tubular body functioning as a flow passage where
exhaust gas passes, particulate matter is charged by the corona
discharge caused by the electrode, the charged particulate matter
is trapped and agglomerated on the inner wall face of the tubular
body to be bloated, and then the bloated particulate matter is
scattered again; which led to the completion of the present
invention. More specifically, according to the present invention,
the following exhaust gas treatment apparatuses are provided.
[0017] [1] An exhaust gas treatment apparatus comprising: a tubular
body functioning as a flow passage where exhaust gas passes, and a
discharge electrode disposed in an central portion in a cross
section perpendicular to a flow direction of the flow passage
inside the tubular body and causing corona discharge in the
vicinity thereof by applying a voltage; wherein the tubular body
has a shape where an inner diameter of the tubular body is
gradually reduced in a predetermined range from a face which
contains a central point of generation of corona discharge
generated by the discharge electrode and which is perpendicular to
the flow passage toward the downstream side of the flow passage,
and the number of particulates suspended in the exhaust gas is
decreased by charging the particulate matter contained in the
exhaust gas passing through the tubular body by corona discharge
caused by the discharge electrode, collecting the charged
particulate matter on an inner wall face of the tubular body by the
electric field generated from the discharge electrode toward the
inner wall face of the tubular body to agglomerate plural
particulates, and allowing the agglomerated particulates to scatter
again.
[0018] [2] The exhaust gas treatment apparatus according to [1],
wherein the discharge electrode has a disc-like electrode support
disposed perpendicularly to the flow direction of the flow passage
and a needle-like discharger disposed perpendicularly to the
electrode support and wherein the central point of generation of
corona discharge is the central point of a face which contains the
central point of generation of corona discharge of the tubular body
and which is perpendicular to the flow passage.
[0019] [3] The exhaust gas treatment apparatus according to [2],
wherein the tubular body has a shape where the inner diameter of
the tubular body is reduced so that the distance from the central
point of generation of corona discharge to the inner wall face of
the tubular body in the predetermined range toward the downstream
side of the flow passage is in the range of .+-.10% of a length
from the central point of generation of corona discharge to the
inner wall face of the tubular body in the face which contains the
central point of generation of corona discharge of the tubular body
and which is perpendicular to the flow passage.
[0020] [4] The exhaust gas treatment apparatus according to [3],
wherein the tubular body has a shape where a moving velocity of the
charged particulate matter proceeding in an exhaust gas flow
direction and a drift velocity when the particulate matter is drawn
to the inner wall face are taken into consideration.
[0021] [5] The exhaust gas treatment apparatus according to any one
of [1] to [4], wherein the length in the predetermined range where
the inner diameter of the tubular body is gradually reduced is 0.2
to 0.9 times the distance from the central point of generation of
corona discharge of the tubular body to the inner wall face of the
tubular body in the face perpendicular to the flow passage.
[0022] [6] The exhaust gas treatment apparatus according to any one
of [1] to [5], wherein the discharge electrode is supported in the
central portion of the flow passage by a porcelain bushing passing
through the wall face of the tubular body and extended up to the
central portion in across section perpendicular to the flow
direction of the flow passage.
[0023] [7] The exhaust gas treatment apparatus according to [6],
wherein the porcelain bushing has groove-shaped unevenness formed
on the surface thereof.
[0024] [8] The exhaust gas treatment apparatus according to any one
of [1] to [7], which is disposed in an exhaust system of a vehicle
provided with a gasoline engine as a drive mechanism.
[0025] The exhaust gas treatment apparatus of the present invention
can decrease the number of the particulates present in exhaust gas
by agglomerating the particulate matter contained in exhaust gas.
In particular, since an exhaust gas treatment apparatus of the
present invention can decrease the number of the particulates even
without disposing a filter or the like causing increase in pressure
loss of the exhaust system, it can suitably be used as an exhaust
gas treatment apparatus for treating exhaust gas discharged from a
gasoline engine or the like where a harmful influence is caused by
disposing a filter or the like causing increase in pressure
loss.
BRIEF DESCRIPTION OF THE DRAWINGS
[0026] FIG. 1 is a side view schematically showing an embodiment of
an exhaust gas treatment apparatus of the present invention.
[0027] FIG. 2 is a plan view from the upstream side of the exhaust
gas treatment apparatus shown in FIG. 1.
[0028] FIG. 3 is a cross-sectional view showing the A-A' cross
section of the exhaust gas treatment apparatus shown in FIG. 2.
[0029] FIG. 4 is an explanatory view schematically explaining the
process of treating exhaust gas by one embodiment of an exhaust gas
treatment apparatus of the present invention.
[0030] FIG. 5 is a cross-sectional view schematically showing
another embodiment of an exhaust gas treatment apparatus of the
present invention.
[0031] FIG. 6 is an explanatory view schematically explaining the
process of treating exhaust gas by another embodiment of an exhaust
gas treatment apparatus of the present invention.
[0032] FIG. 7 is a front view schematically showing an example of a
discharge electrode used for an exhaust gas treatment apparatus of
the present invention.
[0033] FIG. 8 is a side view of the discharge electrode shown in
FIG. 7.
[0034] FIG. 9 is a side view schematically showing an example of a
porcelain bushing used for an exhaust gas treatment apparatus of
the present invention.
[0035] FIG. 10 is a top view of the porcelain bushing shown in FIG.
9.
[0036] FIG. 11 is a side view schematically showing another example
of a porcelain bushing used for an exhaust gas treatment apparatus
of the present invention.
[0037] FIG. 12 is a top view of the porcelain bushing shown in FIG.
11.
REFERENCE NUMERALS
[0038] 1a, 1b: exhaust gas treatment apparatus, 10: tubular body,
10a: inner wall face, 12: discharge electrode, 12a: electrode
support, 12b: discharger (needle-like discharger), 16: porcelain
bushing, 18, 19: voltage introduction portion, 20: exhaust gas, 22:
particulate matter, 22a: particulate matter (charged particulate
matter), 22b: particulate matter (agglomerated particulate matter),
24: corona discharge, 24x: central point of generation (central
point of generation of corona discharge), 25: face perpendicular to
the flow passage (face which contains central point of generation
of corona discharge and is perpendicular to the flow passage) 26:
electric field, 32: second discharge electrode, 34: unevenness, 42:
upstream side of the flow passage, 43: downstream side of flow
passage, D1: inner diameter before inner diameter of tubular body
is gradually reduced, D2: inner diameter after inner diameter of
tubular body is gradually reduced, L1: length of predetermined
range where inner diameter of tubular body is gradually reduced
(length of predetermined range), R1: distance from central point of
generation of corona discharge to inner wall face of tubular body
in face perpendicular to the flow passage (radius in cross section
of tubular body)
DETAILED DESCRIPTION OF THE INVENTION
[0039] Embodiments for carrying out the present invention will be
described with referring to drawings. However, the present
invention is by no means limited to these embodiments, and,
needless to say, various changes, modifications, and improvement
may be made on the basis of knowledge of a person of ordinary skill
in the art as long as they do not deviate from the scope of the
present invention.
[0040] [1] Exhaust Gas Treatment Apparatus:
[0041] FIG. 1 is a side view schematically showing an embodiment of
an exhaust gas treatment apparatus of the present invention, FIG. 2
is a plan view from the upstream side of the exhaust gas treatment
apparatus shown in FIG. 1, FIG. 3 is a cross-sectional view showing
the A-A' cross section of the exhaust gas treatment apparatus shown
in FIG. 2, and FIG. 4 is an explanatory view schematically
explaining the process of treating exhaust gas by one embodiment of
an exhaust gas treatment apparatus of the present invention.
Incidentally, FIG. 4 is a cross-sectional view showing an enlarged
portion of a cross-sectional view shown in FIG. 3.
[0042] As shown in FIGS. 1 to 4, the exhaust gas treatment
apparatus 1a of the present embodiment is provided with a tubular
body 10 functioning as a flow passage where exhaust gas 20 passes
and a discharge electrode 12 disposed in an central portion in a
cross section perpendicular to a flow direction of the flow passage
inside the tubular body 10.
[0043] The exhaust gas treatment apparatus 1a of the present
embodiment charges the particulate matter 22 contained in exhaust
gas 20 passing through the tubular body 10 by corona discharge 24
caused by the aforementioned discharge electrode 12, collects the
charged particulate matter 22a on the inner wall face 10a of the
tubular body 10 by the electric field 26 generated from the
discharge electrode 12 toward the inner wall face 10a of the
tubular body 10 to agglomerate plural particulates 22a, and allows
the agglomerated particulates 22b to scatter again, thereby
decreasing the number of the particulates 22 suspended in the
exhaust gas 20.
[0044] In the exhaust gas treatment apparatus 1a of the present
embodiment, the aforementioned tubular body 10 has a shape where an
inner diameter of the tubular body 10 is gradually reduced in a
predetermined range from the face 25 which contains the central
point 24x of generation of corona discharge 24 generated by the
discharge electrode 12 and which is perpendicular to the flow
passage toward the downstream side 43 of the flow passage.
Incidentally, in FIG. 4, the numeral 42 shows the upstream side of
the flow passage.
[0045] In the exhaust gas treatment apparatus 1a of the present
embodiment, the particulate matter 22a drawn to the inner wall face
10a of the tubular body 10 by the electric field 26 communicates
charge by being brought into contact with the tubular body 10 and
trapped (i.e., dust collection) on the inner wall face 10a of the
tubular body 10. In such a manner, the charged particulate matter
22a is drawn to the inner wall face 10a of the tubular body 10 in
sequence. The trapped plural particulates are agglomerated by the
Coulomb's force to form an aggregate of the plural particulates
22b. Then, the particulates 22b bloated by agglomeration up to a
certain size has increased mass and is unable to stay (i.e. to keep
being trapped) on the inner wall face 10a of the tubular body 10 to
be discharged toward the downstream side on stream of the exhaust
gas 20. Thus, the apparent number of the particulates 22 present in
the exhaust gas 20 is decreased.
[0046] Thus, the exhaust gas treatment apparatus of the present
embodiment traps the particulate matter contained in the exhaust
gas on the inner wall face of the tubular body by charging the
particulate matter to agglomerate plural particulates to be
bloated, followed by allowing the particulate matter to scatter
again, thereby decreasing the number (apparent number) of the
particulate matter in the exhaust gas. In particular, the exhaust
gas treatment apparatus of the present embodiment can decrease the
number of the particulates even without disposing a filter or the
like causing rise in pressure loss of the exhaust system and can
agglomerate the particulate matter in a good condition even in the
case that the number of the particulates of the exhaust gas is
small. For example, not only as the apparatus for treating exhaust
gas containing particulate matter in a relatively large amount such
as a diesel engine, but also as the apparatus for treating exhaust
gas discharged from a gasoline engine, it can suitably be used.
[0047] Incidentally, conventionally, there has been proposed an
exhaust gas treatment apparatus (see, e.g., the aforementioned
JP-A-2005-320955) where plural particulates are agglomerated. In
such an exhaust gas treatment apparatus, in the case that the
electrode for collecting charge is disposed on the downstream side
of the flow passage, particulate matter charged by corona discharge
is accelerated by the electric field and passes through without
being trapped by the electrode for collecting charge. Therefore, in
the aforementioned constitution, the effect in agglomerating the
particulate matter is small, and it is almost impossible to
agglomerate the particulate matter practically.
[0048] In addition, in the exhaust gas treatment apparatus
disclosed in JP-A-2005-320955, there has been described the usage
of the electrode for collecting charge as the inner wall face of
the flow passage. However, in such a case, the particulate matter
always moving toward the downstream side on stream of exhaust gas
easily passes through the range of the electric field before it
reaches the inner wall face of the flow passage. Therefore, also in
such a case, the effect in agglomerating the particulate matter is
small, and it is almost impossible to agglomerate the particulate
matter practically. In particular, in a case that the exhaust gas
flow rate is high or that the number of particulates contained in
exhaust gas is small, it is very difficult to trap the particulate
matter on the inner wall face of the flow passage.
[0049] That is, an electric field generated from the discharge
electrode toward the inner wall face of the tubular body spreads
from the central point (e.g., in the case of a needle-shaped
discharge electrode, the tip thereof) of generation of corona
discharge in a spherical surface shape (equipotential face), and
the electric field becomes weaker as the distance from the
aforementioned central point of generation increases. Therefore,
the electric field tends to be weaker toward outside of the tubular
body as it goes toward downstream side from the aforementioned
central point of generation, and the efficiency to trap the
particulate matter always moving on stream of exhaust gas becomes
extremely low.
[0050] In the exhaust gas treatment apparatus of the present
embodiment, since the tubular body has a shape where the inner
diameter is gradually reduced in a predetermined range from the
central point of generation of corona discharge toward the
downstream side of the flow passage, charged particulate matter can
be trapped in a good condition on the inner wall face of the
portion of the tubular body. In particular, by constituting the
inner wall face of the tubular body to have a shape close to that
of the electric field which spreads in an almost spherical surface
shape (equipotential face) with the central point of generation of
corona discharge as the base point, the charged particulate matter
can be trapped in a better condition.
[0051] Incidentally, in the discharge electrode of the exhaust gas
treatment apparatus of the present embodiment, it is preferable
that the central point of the generation of corona discharge
generated by discharge electrode is disposed in a position of the
central point of a face perpendicular to the flow passage of the
tubular body. This makes specifying of the central point of
generation of corona discharge easy. That is, the central point of
a face perpendicular to the flow passage of the tubular body is the
central point of generation of corona discharge (or electric
field). Incidentally, when the shape of the discharge electrode is
a symmetrical shape such as a rotational symmetric shape, by
disposing the central point of the discharge electrode to be
located in the central point of the face perpendicular to the flow
passage of the tubular body, the central point of generation of
corona discharge can coincide with the central point of the face
perpendicular to the flow passage of the tubular body.
[0052] Incidentally, by gradually reducing the inner diameter of
the tubular body, the efficiency of trapping particulate matter on
the inner wall face of the tubular body. However, on the other
hand, since the inner diameter of the flow passage is reduced, the
pressure loss of the exhaust system tends to be increased.
Therefore, as shown in FIG. 4, the "length L1 of the predetermined
range" where the inner diameter of the tubular body 10 is gradually
reduced is preferably 0.2 to 0.9 times, more preferably 0.4 to 0.7
times, particularly preferably 0.5 to 0.6 times the distance R1
from the central point 24x of generation of corona discharge 24 of
the tubular body 10 to the inner wall face of the tubular body in
the face perpendicular to the flow passage. Such a constitution
enables to improve the efficiency to trap the particulate matter in
a good condition with suppressing the increase in pressure loss to
the minimum.
[0053] Incidentally, the reduction rate of the inner diameter D2
after the inner diameter of the tubular body 10 is gradually
reduced (hereinbelow referred to as the "reduction rate of the
inner diameter of the tubular body") with respect to the inner
diameter D1 before the inner diameter of the tubular body 10 is
gradually reduced (i.e., inner diameter of the tubular body 10 on
the upstream side of the central point 24x of generation of corona
discharge 24) is preferably 0.6 to 48%, more preferably 5 to 23%,
particularly preferably 9 to 15%. Incidentally, the reduction rate
of the inner diameter of the tubular body can be obtained by the
following formula (1).
Reduction rate of inner diameter of tubular
body=(D1-D2)/D1.times.100 (1)
(wherein D1 is the inner diameter before the inner diameter of the
tubular body is gradually reduced, while D2 is the inner diameter
after the inner diameter of the tubular body is gradually
reduced)
[0054] In addition, a tubular body used for the exhaust gas
treatment apparatus of the present embodiment is preferably formed
so that the inner diameter is reduced to form in an almost
spherical surface shape where, in a predetermined range toward the
downstream side of the flow passage, the distance from the central
point of generation of corona discharge to the inner wall face of
the tubular body is within the range of .+-.10% of the length in a
face containing the aforementioned central point of generation of
corona discharge, and perpendicular to the flow passage (i.e.,
radius R1 in a cross section of the tubular body (see FIG. 4)). For
example, when the distance is outside the range of -10%, since the
inner diameter of the tubular body becomes narrow drastically, the
pressure loss of the exhaust system may increase by disposing an
exhaust gas treatment apparatus. On the other hand, when the
distance is outside the range of +10%, the rate of reduction the
tubular body (in other wards, rate of narrowing of the flow
passage) is too small, and the particulate matter moving on stream
of exhaust gas may easily exceed the effective electric field
range.
[0055] The charged particulate matter moving in the electric field
is moving at a speed balanced with the viscosity resistance of the
exhaust gas in a direction of the inner wall face of the tubular
body. Incidentally, the speed of the moving of the particulate
matter in the inner wall face direction of the tubular body is
sometimes referred to as a "drift velocity (w)".
[0056] The tubular body used for the exhaust gas treatment
apparatus of the present embodiment is preferably constituted to
have a shape in consideration of a moving velocity (v) of the
charged particulate matter in the exhaust gas flow direction and a
drift velocity (w) drawn to the inner wall face of the tubular body
in a predetermined range toward the downstream side of the flow
passage. That is, an inner face shape of the tubular body is not a
spherical shape in consideration of equipotential face simply, but
a shape in consideration of also a drift velocity (w) where the
particulate matter is drawn to the inner wall face of the tubular
body, thereby trapping the charged particulate matter in a good
condition.
[0057] Hereinbelow, a calculation method of the aforementioned
drift velocity (w) and a method for determining a shape of the
tubular body in consideration of the moving velocity (v) and the
drift velocity (w) of the particulate matter proceeding in the
exhaust gas flow direction will be described in more detail.
[0058] The drift velocity (w) can be obtained by the following
formula (2) with a charged amount (q) of the particulate matter,
charged electric field strength (E), gas (exhaust gas) viscosity
(.mu.), radius (a) of particulate matter, and Cunningham correction
coefficient (Cm).
[Formula 1]
w=3qE.times.Cm/6.pi..mu.a (2)
[0059] However, in an actual exhaust gas treatment apparatus, a
corona wind is present in a space where the charged particulate
matter (charged particulates) is trapped, and it is difficult to
obtain a field in consideration of space charge of the charged
particulates. Therefore, it is preferable that the "apparent drift
velocity (w.sub.d)" is calculated from the experimental value
(measurement value) of a dust collection efficiency (.eta.) for
trapping (collecting) the particulate matter to determine an ideal
shape for the tubular body by employing the "apparent drift
velocity (w.sub.d) as the actual drift velocity. Incidentally, the
experimental value (measurement value) of the dust collection
efficiency (.eta.) can be measured by a particle counter, for
example, the electrical low pressure impactor produced by Dekati
Ltd.
[0060] Incidentally, the aforementioned dust collection efficiency
(.eta..sub.1) is shown by the following formula (3) with the
concentration (Wi) of particulate matter on the inlet side and the
concentration (Wo) of particulate matter on the outlet side of the
exhaust gas treatment apparatus.
.eta.=1-Wo/Wi (3)
.eta.=1-exp(-w.sub.dA/Q) (4)
[0061] (In the formula (4), A denotes an area of a dust collection
electrode (i.e., area of the inner wall face of the tubular body),
and Q denotes a gas flow rate per unit time.)
[0062] An "apparent drift velocity (w.sub.d)" can be calculated by
the aforementioned formula (4) and the formula (5) with the
aforementioned actual experimental value (measurement value of dust
collection efficiency (.mu.)). Incidentally, for example, in an
area (A) of a dust collection electrode, the inner portion of the
tubular body has a circular columnar shape, the area is an area of
the inner wall face in a range from the tip of the discharge
electrode to 200 mm, and the gas flow rate (Q) per unit time is
15916 cm.sup.3/sec (0.955 m.sup.3/min.).
[0063] In addition, the moving velocity (v) of the charged
particulate matter in the exhaust gas flow direction can be
calculated from the aforementioned gas flow rate (Q) per unit
time.
[0064] As a method for determining the shape of the tubular body in
consideration of the moving velocity (v) in the exhaust gas flow
direction and the drift velocity (apparent drift velocity
(w.sub.d)), a tubular body shape in an about elliptic shape can be
determined by adding a drift moving distance in each position in
the exhaust gas flow direction with respect to the equipotential
face from the central point of generation of corona discharge. For
example, When the distance from the central point of generation of
corona discharge to the equipotential face is determined as R,
polar coordinates (x, y) of the point R' constituting the tubular
shape in consideration of the drift velocity can be shown by the
following formulae (5) and (6), and the tubular shape in
consideration of the drift velocity can be determined by suitably
determining the length of the predetermined range where the inner
diameter of the tubular body is gradually reduced with using the
aforementioned polar coordinates (x, y) of the point R'
constituting the tubular shape in consideration of the drift
velocity.
x=R cos .theta. (5)
y=R sin .theta.+R cos .theta.w.sub.d/v (6)
[0065] Incidentally, the tubular shape in consideration of the
drift velocity can be determined by stipulating the almost elliptic
shape where the moving distance (drift moving distance) of the
particulate matter due of the electric field is considered by
calculating the drift moving distance for every 0.05 mm in the pipe
direction.
[0066] In the case of determining the shape of the tubular body in
such a manner, it is preferable to use assumptions as described
below for simplifying the calculation.
(1) The inner wall area of the tubular body at 200 mm on the
downstream side from the tip of the discharge electrode is
determined as the electrode area (Incidentally, the tubular body is
assumed to be a straight pipe (having a fixed inner diameter of the
pipe)). (2) The gas flow rate (Q) per unit time and apparent drift
velocity (w.sub.d) are fixed regardless of the positions of the
particulates in the tubular body. (3) Even in the case that plural
tips of the discharge electrode are present, the apparent central
point of the electric field (central point of generation of corona
discharge) is a central point of a face perpendicular to the flow
passage. (4) Though electric field is generated also on the
upstream side of the discharge electrode, since the particulate
matter is trapped on the downstream side of the discharge
electrode, the tubular body is narrowed only on the downstream side
of the flow passage. Incidentally, the drift of the particulate
matter due to the electric field generated on the upstream side of
the discharge electrode is ignored.
[0067] As described above, the shape of the tubular body can be
made suitable for trapping the charged particulate matter,
agglomerating the trapped particulate matter, and scattering the
bloated particulate matter due to the agglomeration again. Further,
by the use of the aforementioned assumptions, the shape of the
tubular body can be determined more easily.
[0068] Incidentally, as a method for confirming the decrease in the
number of the particulates in exhaust gas by the exhaust gas
treatment apparatus of the present embodiment, a particle counter
is disposed on the downstream side of the exhaust gas treatment
apparatus to measure the number of the particulates in the exhaust
gas. An example of the aforementioned particle counter is the
Electrical Low Pressure Impactor (hereinbelow sometimes referred to
as "ELPI") produced by Dekati Ltd. According to such ELPI,
measurement (sampling) of the number of particulates having a
particle diameter of 0.007 to 10 .mu.m in the particulate matter is
possible. Incidentally, upon measurement, the particulates are
classified by the following particle diameters: 0.007 to 0.014,
0.014 to 0.0396, 0.0396 to 0.0718, 0.0718 to 0.119, 0.119 to 0.200,
0.200 to 0.315, 0.315 to 0.482, 0.482 to 0.760, 0.760 to 1.23, 1.23
to 1.95, 1.95 to 3.08, 3.08 to 6.27 (unit of .mu.m).
[0069] As a more specific measurement method, in the first place, a
particle counter is disposed on the downstream side of the exhaust
gas treatment apparatus, and the number of the particulates in the
exhaust gas is measured (sampled) in each of the case of applying a
voltage in each of the electrodes (upon applying a voltage) and the
case of applying no voltage (upon applying no voltage). Next, from
the sum of the measurement data by each particle diameter range,
the total number (total discharge number) of the particulates
discharged from the downstream side is calculated out. Next, from
the data of the total discharge number at each of the time of
applying a voltage and the time of applying no voltage, the ratio
of the number of the particulates reduced by the exhaust gas
treatment apparatus of the present embodiment can be obtained.
[0070] In the case of treating exhaust gas by the use of an exhaust
gas treatment apparatus of the present embodiment, there is no
particular limitation on the flow rate of the exhaust gas to be
treated, and the number of the particulates can be decreased in a
good condition with an exhaust gas flow rate of, for example, 200
m/second or less. Incidentally, since the exhaust gas flow rate
upon running of a general vehicle provided with a gasoline engine
as a drive mechanism is 150 m/second (in the case of 2 L engine,
6000 revolutions, and exhaust gas temperature of about 600.degree.
C.), even in such a vehicle, the treatment of exhaust gas can be
performed in a good condition by the use of the exhaust gas
treatment apparatus of the present embodiment.
[0071] Hereinbelow, the exhaust gas treatment apparatus of the
present embodiment will be described in more detail by each of the
constituents.
[0072] [1-1] Tubular Body:
[0073] The tubular body is connected to an exhaust system where
exhaust gas being discharged from an internal combustion engine or
the like and containing particulate matter passes to function as a
flow passage where exhaust gas passes. As described above, the
tubular body is constituted to have a shape where the inner
diameter is gradually reduced in a predetermined range from the
face containing the central point of generation of corona discharge
and perpendicular to the flow passage toward the downstream side of
the flow passage. Such a tubular body may be connected
independently to the exhaust pipe for discharging exhaust gas from
the internal engine, or apart of the exhaust pipe provided on the
internal combustion engine may be used as the tubular body in the
exhaust gas treatment apparatus of the present embodiment.
[0074] In the exhaust gas treatment apparatus of the present
embodiment, a discharge electrode and a dust collection electrode
are disposed inside the tubular body, and inside of the tubular
body is conducted a treatment where (1) the particulate matter is
charged by corona discharge, (2) the charged particulate matter is
trapped on the inner wall face of the tubular body by an electric
field, (3) plural trapped particulates are agglomerated, and (4)
the agglomerated particulates are scattered again.
[0075] Such a tubular body is used as not only a flow passage where
exhaust gas passes, but also the opposed electrode to generate an
electric field between the tubular body and the dust collection
electrode. Therefore, the tubular body is preferably constituted of
a conductive material. When the tubular body is used as the opposed
electrode of the dust collection electrode or the like, the tubular
body is preferably grounded.
[0076] As the tubular body, there can suitably be used a body made
of a conductive material such as stainless and iron used for an
exhaust pipe of an automobile.
[0077] There is no particular limitation on the length of the
tubular body as long as the tubular body has a length where the
discharge electrode is disposed inside thereof, the range having
the gradually reducing inner diameter of the tubular body is
provided as described above, and the exhaust gas treatment from the
charge of the particulate matter to the re-scattering of the
aforementioned particulate matter can be performed in the tubular
body.
[0078] In addition, the tubular body preferably has a circular
cylindrical shape having a straight central axis and is preferably
constituted so that the inner diameter is reduced in the
aforementioned range. Such a constitution can trap the charged
particulate matter in a good condition and inhibit excessive rise
in pressure loss.
[0079] [1-2] Discharge Electrode:
[0080] The discharge electrode is an electrode for generating
corona discharge which charges the particulate matter in exhaust
gas and disposed in the central portion in across section
perpendicular to the flow direction of the flow passage inside the
tubular body. In addition, the discharge electrode is used also as
an electrode for generating an electric field for trapping the
charged particulate matter with the inner wall face of the tubular
body functioning as a flow passage of a fluid as an opposed
electrode. This enabled the charged particulate matter to be
trapped on the inner wall face of a tubular body.
[0081] The discharge electrode is preferably constituted to be able
to generate corona discharge in a region up to the inner wall face
of the flow passage formed by the tubular body including the
vicinity of the discharge electrode in such a manner that more
particulate matter, preferably all the particular matter in the
exhaust gas passing through the tubular body passes through the
space where the corona discharge is generated.
[0082] In the exhaust gas treatment apparatus 1a shown in FIGS. 1
to 4, the discharge electrode 12 is supported in the central
portion of the flow passage by the porcelain bushing 16 passing
through the wall face of the tubular body 10 and extended to the
central portion in a cross section perpendicular to the flow
direction of the flow passage. Inside the porcelain bushing 16 is
disposed a voltage introduction portion 18 including a wire for
applying a voltage (high voltage) to the discharge electrode 12,
and the voltage introduction portion 18 and the discharge electrode
12 are electrically connected with each other in a state that
electrical insulation between the voltage introduction portion 18
and the tubular body 10 is secured.
[0083] Incidentally, FIGS. 1 and 4 show an example of a case where
a porcelain bushing 16 is disposed on the upstream side of the
central point 24x of generation of corona discharge 24 so as to
pass through the wall face of the tubular body 10. However, the
porcelain bushing 16 may be disposed so as to pass through the wall
face of the tubular body 10 on the downstream side of the central
point 24x of generation of corona discharge 24 as in the exhaust
gas purification apparatus 1b shown in FIGS. 5 and 6. In such a
case, the porcelain bushing 16 is disposed so as to pass through
the portion constituted to have a shape where the inner diameter of
the tubular body 10 is gradually reduced. Incidentally, the case
where the porcelain bushing 16 is disposed on the upstream side of
the central point 24x of generation of corona discharge 24 as shown
in FIGS. 1 to 4 has an advantage of easy installation of the
porcelain bushing 15 and the discharge electrode 12. Here, FIG. 5
is a cross-sectional view schematically showing another embodiment
of an exhaust gas treatment apparatus of the present invention.
FIG. 6 is an explanatory view schematically explaining the process
of treating exhaust gas by another embodiment of an exhaust gas
treatment apparatus of the present invention. Incidentally, FIG. 5
shows the same cross section as that shown in FIG. 3.
[0084] There is no particular limitation on the shape of the
discharge electrode as long as the discharge electrode has the tip
portion formed at a sharp angle and corona discharge generated
therein (more specifically, in the tip portion formed at a sharp
angle) by application of the high voltage between the discharge
electrode and the inner wall face of the tubular body. In the
exhaust gas treatment apparatus 1a shown in FIGS. 1 to 4, FIGS. 7
and 8 show an example of the case where the discharge electrode 12
has a disk-like electrode support 12a disposed perpendicularly to
the flow direction of the flow passage and a needle-like discharger
12b disposed perpendicularly to the electrode support 12a (i.e., in
parallel with the flow direction). By such a constitution, an
electric field concentrates in the tip portion of the needle-like
discharger 12b to cause corona discharge in a good condition. In
addition, by the needle-like discharger 12b, even if the tip
portion is worn away in some degree, corona discharge can be caused
by concentrating the electric field. Incidentally, "needle-like
discharger" means a discharger having a thin stick shape as the
entire shape besides a discharger having a sharp pointed tip
portion. Incidentally, in a discharge electrode 12 having such a
shape, the central portion of the electrode support 12a functions
as a portion where a voltage from the voltage introduction portion
18 (see FIG. 1) is introduced.
[0085] Here, FIG. 7 is a front view schematically showing an
example of the discharge electrode used for an exhaust gas
treatment apparatus of the present invention. FIG. 8 is a side view
of the discharge electrode shown in FIG. 7.
[0086] Incidentally, in FIGS. 7 and 8, 12 dischargers 12b are
disposed at regular intervals on the outside on each of the faces
of the electrode support 12a, and four dischargers 12b are further
disposed inside the positions of the 12 dischargers 12b. In
addition, the four discharger 12b disposed inside are longer than
the 12 discharger 12b disposed outside. Such a constitution can
cause corona discharge over a wider range inside the tubular body
to be able to charge the particulate matter in exhaust gas in a
good condition. In addition, assemblage and manufacturing of the
members are easy, and, since most of the particulate matter in
exhaust gas can be passed through in the vicinity of the discharge
portion, much particulate matter can be charged in a good
condition.
[0087] Incidentally, in the case that plural tips of the discharge
electrode are present, for example, as shown in FIGS. 7 and 8, even
in the case that the discharge electrode 12 has a disc-shaped
electrode support 12a disposed perpendicularly to the flow
direction of the flow passage and two or more needle-shaped
dischargers 12b disposed perpendicularly to the electrode support
12a, the central point of generation of corona discharge (in other
words, central point of generation of the electric field) can be
the central point of a face perpendicular to the flow passage.
[0088] Incidentally, the shape of the discharge electrode is not
limited to the aforementioned shape where needle-like dischargers
are disposed on the electrode support, and, for example, a
plurality of plate-like bodies each having at least one sharp blade
edge-like side may be disposed on the electrode support. In the
case of such a discharge electrode, the electric field concentrates
on the blade edge of each plate-like body to cause corona
discharge.
[0089] Regarding the material constituting the discharge electrode,
there can suitably be used the same material as that constituting
an electrode having conventionally been used for an exhaust gas
treatment apparatus performing agglomeration by charging the
particulate matter in exhaust gas. Examples of the material include
stainless steel, iron, nickel, kovar, platinum, copper, gold,
molybdenum, and tungsten.
[0090] In addition, the discharge electrode used for the exhaust
gas treatment apparatus of the present embodiment preferably has a
shape where more sharp portions are formed in a discharger portion
so that the electric field may concentrate. In addition, it is
preferable that dischargers are radially disposed from the center
of the cross section of the tubular body and that it has a shape
causing no decrease in pressure loss. In addition, as the
discharger 12b shown in FIGS. 7 and 8, it is preferably constituted
so that many practical discharge positions are present.
[0091] [1-3] Porcelain Bushing:
[0092] As described above, in the exhaust gas treatment apparatus
of the present embodiment, it is preferable that the discharge
electrode disposed inside the tubular body is supported in the
central portion of the flow passage by a porcelain bushing passing
through the wall face of the tubular body, being extended up to the
central portion in a cross section perpendicular to the flow
direction of the flow passage, and having electrical insulation.
Such a constitution can cause corona discharge in a good condition
by the discharge electrode and can generate an electric field for
trapping the particulate matter in a good condition.
[0093] Examples of the material for the porcelain bushing include
alumina, cordierite, mullite, and glass, and alumina or the like
excellent in insulation, thermal resistance, thermal shock
resistance, corrosion resistance, mechanical strength, and the
like, can be used more suitably.
[0094] Such a porcelain bushing preferably has a constitution where
a creeping discharge is not caused on the surface of the porcelain
bushing upon applying a voltage on each of the electrodes. For
example, as shown in FIGS. 9 and 10, as a porcelain bushing 16 used
for the exhaust gas treatment apparatus of the present embodiment,
one having a groove-like unevenness 34 formed on the surface
thereof can suitably be used. Here, FIG. 9 is a side view
schematically showing an example of a porcelain bushing used for an
exhaust gas treatment apparatus of the present invention, and FIG.
10 is a top view of the porcelain bushing shown in FIG. 9.
[0095] In addition, when particulate matter such as soot adheres to
the porcelain bushing, insulation breakdown may be caused between
the tubular body and the discharge electrode by the particulate
matter adhering to the porcelain bushing to hinder the generation
of the electric field for corona discharge or the dust collection.
Therefore, for example, it may have a constitution having a heater
disposed inside the porcelain bushing so that particulate matter
adheres to the surface of the porcelain bushing can be combusted
and removed by heating the heater.
[0096] In addition, it may have a constitution where a catalyst is
applied on the surface of the porcelain bushing exposed inside the
tubular body to be able to combust and remove adhering particulate
matter by the heat of exhaust gas from an engine or the like when
particulate matter adheres to the surface of the porcelain bushing.
For example, as such a catalyst, an oxidation catalyst used for
purification of exhaust gas discharged from an internal combustion
engine or the like can suitably be used. Suitable examples of the
oxidation catalyst include a conventionally known oxidation
catalyst containing platinum (Pt), rhodium (Rh), palladium (Pd), or
the like.
[0097] In addition, as shown in FIGS. 11 and 12, it may have a
shape where the side portion exposed inside the tubular body of the
porcelain bushing 16 protrudes toward the upstream side of the flow
passage. A porcelain bushing 16 thus constituted hardly hinders the
flow of exhaust gas to reduce resistance of exhaust gas against the
porcelain bushing 16, and the particulate matter hardly adheres to
the surface of the porcelain bushing 16. Here, FIG. 11 is a side
view schematically showing another example of a porcelain bushing
used for an exhaust gas treatment apparatus of the present
invention, and FIG. 12 is a top view of the porcelain bushing shown
in FIG. 11.
[0098] [1-4] Voltage Introduction Portion:
[0099] The voltage introduction portion is a member including a
wire or the like for applying a voltage to the discharge electrode
and connected to a power source (not illustrated) for causing
corona discharge and generating an electric field for trapping the
charged particulate matter. Incidentally, in the exhaust gas
treatment apparatus 1a of the present embodiment shown in FIGS. 1
to 4, it passes through the porcelain bushing 16 passing through
the wall face of the tubular body 10 from the outside of the
tubular body 10 and extended up to the central portion in a cross
section perpendicular to the flow direction of the flow passage to
be electrically connected to the discharge electrode 12 disposed
inside the tubular body 10.
[0100] [1-5] Power Source:
[0101] The powder source is for applying a voltage to the discharge
electrode, and, for example, a direct current power source (DC
power source), a pulse power source, or the like may suitably be
used. In particular, in the exhaust gas treatment apparatus of the
present embodiment, a direct current power source (DC power source)
is preferable.
[0102] Specific values of the voltage applied on the discharge
electrode and the electric power can suitably be determined so that
suitable discharge and electric field can be generated depending on
the size of the tubular body functioning as the flow passage; the
flow amount and flow rate of the exhaust gas passing through the
flow passage; the amount, size, number of the particulates
contained in the exhaust gas; and the like.
[0103] For example, though the voltage is not particularly limited,
in the case that the discharge electrode is electrically connected
with each other and that the exhaust gas treatment apparatus of the
present embodiment is used for treating exhaust gas discharged from
a gasoline engine, the voltage is preferably 6 to 10 kV, more
preferably 8 to 9 kV. In addition, the electric power is preferably
2 to 30 W, more preferably 4 to 15 W. Such a constitution enables
to perform the treatment of exhaust gas discharged from a gasoline
engine in a good condition.
Example
[0104] Hereinbelow, the present invention will be described more
specifically by Examples. However, the present invention is by no
means limited to these Examples.
Example 1
[0105] There was manufactured an exhaust gas treatment apparatus 1a
as shown in FIGS. 1 to 3. The tubular body 10 had a circular
cylindrical shape having a length of 300 mm in the exhaust gas flow
direction, an outer diameter of 60.5 mm, and an inner diameter of
53.5 mm, and the material of the tubular body was stainless
steel.
[0106] An alumina porcelain bushing 16 was disposed in the position
of 30 mm from the end face on the upstream side of the flow
direction of the tubular body 10 so that it passed through the
tubular body 10, and a voltage introduction portion 18 was disposed
inside the porcelain bushing 16. A discharge electrode 12 was
connected to the voltage introduction portion 18 to fix the
discharge electrode 12 inside the tubular body 10.
[0107] As shown in FIGS. 7 and 8, the discharge electrode 12 was
constituted by the disc-like electrode support 12a and the 16
dischargers 12b (12 dischargers at an angle of 30.degree. outside,
and 4 dischargers at an angle of 90.degree. inside) disposed on the
disc-like electric support 12a.
[0108] The disc-like electrode support had a shape where 1/4
circles having a radius of 7 mm was gouged out of the ring-shaped
support having the outer periphery of 20 mm so that a cross-shaped
support having a width of 3 mm remains in the central portion. In
addition, through-holes each having a diameter of 1.5 mm were
formed in portions where the dischargers were to be disposed, and
the dischargers were disposed in the through-holes. Incidentally,
the electrode support was formed of stainless steel.
[0109] Each of the dischargers had a diameter of 1.5 mm with a
sharp needle-like tip end and was formed of stainless steel. Each
of the 12 dischargers disposed on the outside had a length of
protruding by 10 mm from the surface of the electrode support, and
each of the 4 dischargers disposed on the inside had a length of
protruding by 20 mm from the surface of the electrode support.
[0110] In addition, the tubular body was formed to have a shape
where the inner diameter is gradually reduced in the range of 15 mm
from the face containing the central point of generation of corona
discharge toward the downstream side of the flow passage.
Incidentally, the shape of the tubular body was determined by a
method for determining the shape of the tubular body in
consideration of the aforementioned moving velocity in the exhaust
gas flow direction and apparent drift velocity.
[0111] As the measurement of the dust collection efficiency
(.eta.), exhaust gas discharged from an automobile engine was sent
in the exhaust gas treatment apparatus constituted in the same
manner as in the aforementioned exhaust gas treatment apparatus of
Example 1, and a constant voltage of 8 kV (electric current of 0.5
mA) was applied to the discharge electrode to measure the number of
the particulates on both the inlet and outlet sides of the exhaust
gas treatment apparatus. Incidentally, the dust collection
efficiency (.eta.) was 0.735.
[0112] The conditions for exhaust gas in the measurement of the
dust collection efficiency (.eta.) were as follows:
[0113] Engine rotational frequency: 2430 rpm,
[0114] Torque: 30 Nm,
[0115] Exhaust gas temperature: 339.degree. C.,
[0116] Temperature conversion air amount: 0.955 m.sup.3/min.
[0117] In addition, as the conditions for determining the shape of
the tubular body, the area (A) of an electrode for collecting dust
was the area (335.98 cm.sup.2) of the inner wall face in the range
from the tip of the discharge electrode to the position of 200 mm,
and the gas flow rate (Q) per unit time was 15916 cm.sup.3/sec
(0.955 m.sup.3/min).
[0118] The "apparent drift velocity (w.sub.d)" calculated from the
aforementioned formulae (4) and (5) was 63 cm/sec. In addition, the
"moving velocity (v) of the charged particulate matter proceeding
in the exhaust gas flow direction" calculated from the gas flow
rate (Q) per unit time is 708 cm/sec. From the above results, there
was determined the shape of the tubular body in consideration of
the moving velocity (v) in the exhaust gas flow direction and the
apparent drift velocity (w.sub.d).
[0119] The thus constituted exhaust gas treatment apparatus of
Example 1 was attached to a soot generator generating particulate
matter by a burner with light oil being used as the fuel, and test
exhaust gas (hereinbelow referred to as "exhaust gas" simply) at
about 195.degree. C. was introduced at a flow rate of 1.5
m.sup.3/min. In such a state, as shown in Table 1, a direct current
voltage of 8 kV with an electric power of 5 W was applied on the
discharge electrode of the exhaust gas treatment apparatus of
Example 1 to treat the exhaust gas. The mass (g/hour) of the
particulate matter on the inlet side of the exhaust gas treatment
apparatus during treating the exhaust gas, the number
(.times.10.sup.7 particulates/sec.), the mass (g/hour), and the
average particle diameter (.mu.m) of the particulates on the outlet
side were measured. The measurement results are shown in Table
2.
[0120] (Measurement of the Number of Particulates)
[0121] A particle counter (Electrical Low Pressure Impactor (ELPI)
produced by Dekati Ltd.) was equipped on the downstream side of the
discharge electrode to measure the number of the discharged
particulates by each particle diameter range on the downstream side
of each electrode in the case that a voltage was applied on the
discharge electrode (upon applying a voltage) and in the case that
no voltage was applied (upon applying no voltage). Then, from the
sum of the measurement data for each particle diameter range, the
total number (total discharge number) of the particulate matter
discharged from the downstream side was calculated out.
Incidentally, in the measurement, particles having the diameter of
0.007 to 10 .mu.m were measured and classified into the particulate
diameter regions of 0.007 to 0.014, 0.014 to 0.0396, 0.0396 to
0.0718, 0.0718 to 0.119, 0.119 to 0.200, 0.200 to 0.315, 0.315 to
0.482, 0.0482 to 0.760, 0.760 to 1.23, 1.23 to 1.95, 1.95 to 3.08,
3.08 to 6.27 (unit of .mu.m). Incidentally, for example, in the
case of the particle diameter of "0.07 to 0.014", particles having
a particle diameter of 0.007 .mu.m or more and below 0.014 .mu.m
are included.
[0122] (Measurement of Ratio of Reduced Particulate Matter)
[0123] From the data of the total discharge number (.times.10.sup.7
particulates/sec.) upon each of the application of a voltage and
the application of no voltage obtained by the aforementioned
measurement of the number of particulates, the ratio of the reduced
number of the discharged particle by the use of the exhaust gas
treatment apparatus was calculated by the following formula
(6).
(Total number upon applying no voltage-total
number upon applying a voltage)/total number upon
applying no voltage.times.100 (6)
[0124] (Measurement of Mass of Particulate Matter)
[0125] A bypass line from the exhaust gas flow passage was provided
on each of the upstream side and the downstream side of the
position where the exhaust gas treatment apparatus was disposed,
and a paper filter for sampling the particulate matter in the
exhaust gas passing through the bypass lines was disposed in each
of the bypass lines. The sampling time of the particulate matter by
the paper filter was three minutes, and the change in the paper
filter mass by the sampling was calculated from the paper filter
mass before sampling weighed in advance. By the mass change in the
mass of each of the paper filters disposed on the upstream side and
the downstream side, the mass (g/hour) of the particulate matter on
each of the inlet, side and the outlet side of the exhaust gas
treatment apparatus was calculated.
(Average Particle Diameter of Particulate Matter)
[0126] From the measurement data by particle diameter obtained by
the aforementioned measurement of the number of particulates, the
average particle diameter of the particulates contained in exhaust
gas was calculated by the following formula (7).
Average particle diameter=[.SIGMA.{(average particle
diameter in each sampling range).times.(number of
particulates sampled in each sampling range)]/total
discharge number (7)
[0127] (Pressure Loss .DELTA.p)
[0128] A socket was disposed as a slot for taking out exhaust gas
pressure on each of the upstream side and the downstream side on
the exhaust gas treatment apparatus mounted in the exhaust gas pipe
and connected with a meter (digital manometer produced by Cosmo
Instruments, Co., Ltd.) by means of a SUS tube and a teflon tube.
The pressure P1 on the upstream side of the exhaust gas treatment
apparatus and the pressure P2 on the downstream side of the exhaust
gas treatment apparatus were measured, and the pressure loss
(.DELTA.P(kPa)=P1-P2) was calculated.
TABLE-US-00001 TABLE 1 Distance where Inner diameter after inner
Inner diameter of inner diameter is body diameter of tubular
Discharge electrode tubular body gradually reduced is gradually
reduced Addition of drift Voltage Electric power (mm) (mm) (mm)
velocity (kV) (W) Example 1 53.5 15 47 Added 8 16 Example 2 53.5 20
39 Added 8 16 Example 3 53.5 25 23.4 Added 8 16 Example 4 53.5 15
44.3 Not added 8 16 Example 5 53.5 20 35.5 Not added 8 16 Comp. Ex.
1 53.5 Zero 53.5 None 8 16
TABLE-US-00002 TABLE 2 Particulate matter Particulate matter on
outlet side Ratio of reduced Condition of exhaust gas on inlet side
Average particle number of Flow rate Temperature Mass Mass Number
diameter particulates Pressure loss (m/sec.) (.degree. C.) (g/hour)
(g/hour) (.times.10.sup.7/sec.) (.mu.m) (%) .DELTA.P (kPa) Example
1 12 195 1.05 0.37 5.13 0.038 66 0.16 Example 2 12 195 1.07 0.37
4.82 0.038 68 0.4 Example 3 12 195 1.06 0.35 3.22 0.038 79 2.65
Example 4 12 195 1.06 0.37 5.03 0.038 67 0.21 Example 5 12 195 1.07
0.37 4.72 0.038 69 0.6 Comp. Ex. 1 12 195 1.08 0.39 6.03 0.038 60
0.03
Example 2
[0129] There was manufactured an exhaust gas treatment apparatus
constituted in the same manner as in Example 1 except that the
inner diameter of the tubular body was formed to be generally
reduced in the range from the face containing the central point of
generation of corona discharge to the position of 20 mm toward the
downstream side of the flow passage, and exhaust gas was treated in
the same manner as in Example 1. The measurement results of the
mass (g/hour) of particulate matter on the inlet side of the
exhaust gas treatment apparatus and the number (.times.10.sup.7
particulates/sec.), mass (g/hour), and average particle diameter
(.mu.m) of particulates on the outlet side during the exhaust gas
treatment are shown in Table 2.
Example 3
[0130] There was manufactured an exhaust gas treatment apparatus
constituted in the same manner as in Example 1 except that the
inner diameter of the tubular body was formed to be generally
reduced in the range from the face containing the central point of
generation of corona discharge to the position of 25 mm toward the
downstream side of the flow passage, and exhaust gas was treated in
the same manner as in Example 1.
Example 4
[0131] There was manufactured an exhaust gas treatment apparatus
constituted in the same manner as in Example 1 except that the
inner diameter of the tubular body was formed to be generally
reduced in a spherical surface shape along an equipotential face in
the range of 15 mm toward the downstream side of the flow passage
without adding the aforementioned apparent drift velocity, and
exhaust gas was treated in the same manner as in Example 1.
Example 5
[0132] There was manufactured an exhaust gas treatment apparatus
constituted in the same manner as in Example 4 except that the
inner diameter of the tubular body was formed to be generally
reduced in the range from the face containing the central point of
generation of corona discharge to the position of 20 mm toward the
downstream side of the flow passage, and exhaust gas was treated in
the same manner as in Example 1.
[0133] In the exhaust gas treatment apparatuses of Examples 2 to 5,
the measurement results of the mass (g/hour) of particulate matter
on the inlet side of the exhaust gas treatment apparatus and the
number (.times.10.sup.7 particulates/sec.), mass (g/hour, and
average particle diameter (.mu.m) of particulates on the outlet
side during the exhaust gas treatment in the same manner as in
Example 1 are shown in Table 2.
Comparative Example 1
[0134] There was manufactured an exhaust gas treatment apparatus
constituted in the same manner as in Example 1 except that the
tubular body had a circular cylindrical shape having a fixed size
of 53.5 mm from the inlet side to the outlet side of the apparatus,
and exhaust gas was treated in the same manner as in Example 1. The
measurement results of the mass (g/hour) of particulate matter on
the inlet side of the exhaust gas treatment apparatus and the
number (.times.10.sup.7 particulates/sec.), mass (g/hour, and
average particle diameter (.mu.m) of particulates on the outlet
side during the exhaust gas treatment are shown in Table 2.
DISCUSSION
[0135] Each of the exhaust gas treatment apparatuses of Example 1
to 5 had a high ratio of the reduced number of particulates in
comparison with the exhaust gas treatment apparatus of Comparative
Example 1, and the particulates could be agglomerated in a good
condition in exhaust gas. Incidentally, since each of the exhaust
gas treatment apparatuses of Examples 1 to 5 was constituted to
have a shape where the inner diameter of the tubular body was
reduced in the range from the central point of generation of corona
discharge to the position of 15 mm, 20 mm, or 25 mm, the pressure
loss was increased in comparison with the exhaust gas treatment
apparatus of Comparative Example 1. However, the increase was
small, and, even if it is installed in an exhaust system of a
vehicle provided with a gasoline engine, exhaust gas can be treated
in a good condition.
[0136] In addition, in the exhaust gas treatment apparatuses of
Examples 1 to 3, by the tubular body where a drift velocity was
added, a sufficient effect of reduction in the number could be
obtained though the increase in pressure loss was minute. That is,
by adding the drift velocity, the increase in pressure loss could
be suppressed to be very small with respect to the effect in
further reducing the number of particulates, and thereby high
purification performance and reduction of strain to an engine or
the like could be successfully combined further.
[0137] Incidentally, in the results shown in Table 2, the average
particle diameter of the particulates on the outlet side of
Examples 1 to 5 and Comparative Example 1 was 0.038 .mu.m. However,
from the results of measurement of the number for each particle
size using the aforementioned ELPI, in exhaust gas treatment
apparatuses of Examples 1 to 5, it was confirmed that the number of
particulates having a relatively large average particle diameter
among the particulates on the outlet side increased with the
passage of time. Here, Table 3 shows the change of the number of
the particulates for each particle diameter on the outlet side.
Table 3 shows results of measurement where the particles measured
on the outlet side of the exhaust gas treatment apparatus of
Example 1 were classified into three particle diameter ranges
(0.007 to 0.014 .mu.m, 0.014 to 1.23 .mu.m, and 1.23 to 6.27 .mu.m)
to measure the number of particulates contained in each particle
diameter range. Incidentally, Table 3 shows the measurement results
(before application) for 10 seconds before a voltage is applied and
the measurement results (7 minutes after application) for 10
seconds from when 7 minutes passed after a voltage is applied.
TABLE-US-00003 TABLE 3 Particle diameter (.mu.m) 0.007 to 0.014
0.014 to 1.23 1.23 to 6.27 Number of Before 5.43 .times. 10.sup.8
1.01 .times. 10.sup.9 2.86 .times. 10.sup.4 particulate application
matter 7 min, after 2.82 .times. 10.sup.8 5.69 .times. 10.sup.8
2.01 .times. 10.sup.5 application
[0138] As shown in Table 3, in the results of the measurement when
7 minutes passed after application, the number of the particulates
having small particle diameters in the range of 0.007 to 0.014
.mu.m was reduced, while the number of the particulates having
large particle diameters in the range of 1.23 to 6.27 .mu.m was
increased. By this, it was confirmed that, by the exhaust gas
treatment apparatus of Example 1, plurality of particulates in
exhaust gas, particularly, particulates having relatively small
particle diameters were agglomerated to be bloated as particulates
having larger particle diameters.
INDUSTRIAL APPLICABILITY
[0139] An exhaust gas treatment apparatus of the present invention
can be used as an exhaust gas treatment apparatus decreasing the
number of the particulates present in exhaust gas by agglomerating
and bloating the particulate matter in the exhaust gas discharged
from internal combustion engines such as automobile engines,
construction machine engines; industrial machine stationary engine
and other combustion burning appliances.
* * * * *