U.S. patent application number 10/571535 was filed with the patent office on 2007-02-08 for exhaust gas-purifying device.
This patent application is currently assigned to HINO MOTORS LTD.. Invention is credited to Tatsuki Igarashi.
Application Number | 20070028603 10/571535 |
Document ID | / |
Family ID | 34308586 |
Filed Date | 2007-02-08 |
United States Patent
Application |
20070028603 |
Kind Code |
A1 |
Igarashi; Tatsuki |
February 8, 2007 |
Exhaust gas-purifying device
Abstract
Provided is a plasma assisted exhaust emission control device
with less electric power consumption and with no harmful gas
discharged into atmosphere. A filter body 7 is constituted by
porous members through which exhaust gas 2 passes for capturing of
particulates in the exhaust gas 2 and is provided with rod-like and
cylindrical electrodes 9 and 10 so as to generate plasma in the
filter body 7, thereby providing a plasma regenerative particulate
filter 11. The particulate filter 11 is accommodated in a filter
casing within an exhaust pipe 3. Oxidation catalysts 16 and are
arranged respectively upstream and downstream of adjacent to the
particular filter 11 in the filter casing 12 so as to obtain heat
insulation effect to the particulate filter 11.
Inventors: |
Igarashi; Tatsuki; (Tokyo,
JP) |
Correspondence
Address: |
C. IRVIN MCCLELLAND;OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
HINO MOTORS LTD.
Hino-shi
JP
|
Family ID: |
34308586 |
Appl. No.: |
10/571535 |
Filed: |
September 10, 2004 |
PCT Filed: |
September 10, 2004 |
PCT NO: |
PCT/JP04/13225 |
371 Date: |
March 10, 2006 |
Current U.S.
Class: |
60/295 ; 60/275;
60/297 |
Current CPC
Class: |
F01N 3/035 20130101;
B03C 3/155 20130101; B03C 2201/12 20130101; F01N 3/0275 20130101;
F01N 2240/28 20130101; B03C 3/41 20130101; F01N 13/0097 20140603;
B03C 3/025 20130101; B03C 3/49 20130101; B03C 2201/30 20130101;
F01N 13/017 20140601; F01N 3/103 20130101; B03C 3/06 20130101 |
Class at
Publication: |
060/295 ;
060/275; 060/297 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 11, 2003 |
JP |
2003-319850 |
Claims
1. An exhaust emission control device comprising a filter body
constituted by porous members through which exhaust gas passes for
capture of particulates entrained in the exhaust gas and electrodes
for generating plasma in said filter body, thereby providing a
plasma regenerative particulate filter, said particulate filter
being incorporated in a filter casing within an exhaust pipe,
oxidation catalysts being arranged respectively upstream and
downstream of and adjacent to the particulate filter in the filter
casing so as to obtain heat insulation effect to the particulate
filter.
2. The exhaust emission control device according to claim 1,
wherein the plasma regenerative particulate filter is divided into
a plurality of smaller units which are arranged in parallel with
each other within the filter casing, voltage for electric discharge
being separately applicable to the respective smaller units.
3. The exhaust emission control device according to claim 1 or 2,
wherein the filter body is constituted by porous members integrally
carrying oxidation catalyst.
4. The exhaust emission control device according to claim 1 or 2,
wherein the filter body is employed which comprises a number of
passages in the form of honeycomb through which exhaust gas passes,
inlet and outlet ends of the respective passages being alternately
plugged.
5. The exhaust emission control device according to claim 3,
wherein the filter body is employed which comprises a number of
passages in the form of honeycomb through which exhaust gas passes,
inlet and outlet ends of the respective passages being alternately
plugged.
6. The exhaust emission control device according to claim 4,
wherein the filter body has a rod-like electrode inserted at an
axis of the filter body and a cylindrical electrode fitted over an
outer periphery of the filter body.
7. The exhaust emission control device according to claim 5,
wherein the filter body has a rod-like electrode inserted at an
axis of the filter body and a cylindrical electrode fitted over an
outer periphery of the filter body.
Description
TECHNICAL FIELD
[0001] The present invention relates to an exhaust emission control
device for removing particulates in exhaust gas from an internal
combustion engine such as diesel engine.
BACKGROUND ART
[0002] Particulates or particulate matter discharged from a diesel
engine is mainly constituted by carbonic soot and a soluble organic
fraction (SOF) of high-boiling hydrocarbon and contains a trace of
sulfate (misty sulfuric acid fraction). In order to suppress such
kind of particulates from being discharged into atmosphere, it has
been envisaged as shown in FIG. 1 that a particulate filter 4 is
incorporated in an exhaust pipe 3 through which exhaust gas 2 from
a diesel engine 1 flows.
[0003] As detailedly shown in FIG. 2, the particulate filter 4
comprises a filter body 7 in the form of a porous honeycomb made of
ceramics such as cordierite. The filter body 7 has passages 5 or
grid-like compartments with inlets alternately plugged by plugs 8,
the passages 5 with the unplugged inlets being plugged by the plugs
8 at their outlets; only the exhaust gas 2 passing through porous
thin walls 6, which compartmentalize the passages 5, is discharged
downstream and the walls 6 capture the particulates at their inner
surfaces.
[0004] The particulates in the exhaust gas 2 are thus captured by
and accumulated on the inner surfaces of the walls 6 and
spontaneously ignite to be burned off upon shifting to a region of
operation with increased exhaust temperature. However, when an
operation or driving with temperature at or above a predetermined
temperature requisite tends not to continue for a long time, for
example, in a vehicle such as a shuttle-bus running mainly on
congested city roads, there may be a fear that an accumulated
particulate amount exceeds a treated amount, disadvantageously
resulting in clogging of the particulate filter 4.
[0005] Thus, development of a plasma assisted exhaust emission
control device has been promoted so as to satisfactorily burn off
the particulates even in a region of operation with lower exhaust
temperature. In the kind of plasma assisted exhaust emission
control device, electric discharge to the exhaust gas 2 to thereby
generate plasma excites the exhaust gas 2 to convert oxygen into
ozone and NO into NO.sub.2. Because of these excited exhaust gas
components being activated, the particulates can be satisfactorily
burned off even in a region of operation with lower exhaust
temperature.
[0006] Prior publications on plasma assisted exhaust emission
control devices are recited in, for example, the following
Reference 1. [0007] [Reference 1] JP 2002-501813A
SUMMARY OF THE INVENTION
Problems to be Solved by the Invention
[0008] However, in such conventional plasma assisted exhaust
emission control devices, much electric power consumption is
required for regeneration of the particulate filter 4 so that power
source is needed which has larger capacity to an extent that cannot
be afforded by any existing vehicle buttery. Moreover, charging is
required which matches the consumed electric power, resulting in
deterioration of fuel mileage.
[0009] Since the particulates are burned off at relatively low
temperature upon regeneration of the particulate filter 4, there
may be also a fear that harmful gas such as highly concentrated CO
or HC is generated and discharged into atmosphere.
[0010] The invention was made in view of the above and has its
object to provide a plasma assisted exhaust emission control device
with less electric power consumption and with no harmful gas
discharged into atmosphere.
Means or Measure for Solving the Problems
[0011] The invention is directed to an exhaust emission control
device comprising a filter body constituted by porous members
through which exhaust gas passes for capture of particulates
entrained in the exhaust gas and electrodes for generating plasma
in said filter body, thereby providing a plasma regenerative
particulate filter, said particulate filter being incorporated in a
filter casing within an exhaust pipe, oxidation catalysts being
arranged upstream and downstream of and adjacent to the particulate
filter in the filter casing so as to obtain heat insulation effect
to the particulate filter.
[0012] Thus, when the exhaust gas having flown into the filter
casing passes through the upstream oxidation catalyst, NO occupying
majority of NO.sub.x, in the exhaust gas is converted into highly
reactive NO.sub.2, which substantially accelerates an oxidization
reaction of the particulates to bring about satisfactory burn-off
of the particulates in a condition of operation with exhaust
temperature over about 250.degree. C.
[0013] However, when a condition of light-load operation with
exhaust temperature greatly falling below 250.degree. C. continues
for a long time, for example, during running or driving on
congested city roads, satisfactory burn-off of the particulates
cannot be expected; then, at a right moment when an accumulated
particulate amount is estimated to exceed a predetermined amount
(estimation may be based on, for example, pressure difference
between the entering and discharge sides of the filter body or
operational time period), voltage is applied across the electrodes
of the filter body to discharge electricity in the filter body.
[0014] When voltage is thus applied across the electrodes of the
filter body to discharge electricity in the filter body, inner gas
is excited to convert oxygen into ozone and NO into NO.sub.2, these
excited gas components which are being activated accelerate the
oxidation reaction of the particulates captured by the filter body.
As a result, the particulates are satisfactorily burned off even in
a condition of operation with lower exhaust temperature.
[0015] The plasma regenerative particulate filter is sandwiched and
heat insulated by the upstream and downstream oxidation catalysts
in one and the same filter casing, so that the filter body is
rapidly elevated in, temperature when the oxidization reaction of
the captured particulates begins. As a result, the particulates
have tendency of being more readily burned off and can be burned
off with a shorter electric discharge time than they could
conventionally and thus required electric power consumption is less
than that required conventionally.
[0016] The harmful gas such as highly concentrated CO or HC
generated due to combustion of the particulates with relatively low
temperature by the aid of the plasma is oxidized into harmless
CO.sub.2 or H.sub.2O when it passes through the downstream
oxidation catalyst and is discharged.
[0017] It is preferable in the invention that the plasma
regenerative particulate filter is divided into a plurality of
smaller units which are arranged in parallel with each other in the
filter casing, voltage for electric discharge being separately
applied to the respective smaller units.
[0018] Thus, the smaller units of the plasma regenerative
particulate filter can be separately regenerated, with an
advantageous result that power source with relatively small
capacity will suffice. Division into the smaller units improves
combustibility of the particulates per unit, so that regeneration
of the filter through plasma can be attained during stoppage of an
engine for example in a vehicle with an idle stopper.
[0019] In the invention, it is preferable that the porous members
constituting the filter body integrally carry oxidation catalysts,
which accelerates the oxidation reaction of the particulates
captured by the filter body to lower ignition temperature. As a
result, combustibility of the particulates in a condition of
operation with lower exhaust temperature is further enhanced to
attain further satisfactory burn-off of the particulates.
[0020] Upon carrying out the invention more concretely, employable
is a filter body having a plurality of passages in the form of
honeycomb through which exhaust gas passes, inlet and outlet ends
of the passages being alternately plugged. When such filter body is
employed, the filter body may have a rod-like electrode inserted at
its axis and a cylindrical electrode fitted over an outer periphery
of the filter body.
Effects of the Invention
[0021] According to an exhaust emission control device of the
invention, various meritorious effects can be obtained as follows.
[0022] (I) Even in a condition of operation with lower exhaust
temperature such as light-load operation, the particulates captured
by the filter body can be effectively burned off by the aid of
plasma. Moreover, due to the heat insulation effect by the upstream
and downstream oxidation catalysts, the filter body can be rapidly
elevated in temperature into environment for ready burn-off of the
particulates, so that the particulates can be burned off with a
shorter electric discharge time than they could conventionally,
whereby electric power consumption can be substantially reduced.
[0023] (II) The harmful gas such as highly concentrated CO or HC
generated due to combustion of the particulate with relatively low
temperature by the aid of plasma can be oxidized into harmless
CO.sub.2 or H.sub.2O when it passes through the downstream
oxidation catalyst and is discharged. Thus, the harmful gas is
prevented from remaining in the exhaust gas finally discharged into
the atmosphere. [0024] (III) NO occupying majority of NOx in the
exhaust gas can be converted into highly reactive NO.sub.2 when the
exhaust gas passed through the upstream oxidation catalyst, which
can substantially accelerate the oxidation reaction of the
particulates under a condition of operation with relatively high
exhaust temperature. This promotes spontaneous combustion of the
particulates by no aid of plasma to obtain sufficient burn-off.
[0025] (IV) When the plasma regenerative particulate filter is
divided into a plurality of smaller units which are arranged in
parallel with each other in the filter casing, voltage for electric
discharge being separately applied to the respective smaller units,
even a power source with relatively small capacity will suffice.
Regeneration of the filter through plasma can be also attained
during stoppage of an engine for example in a vehicle with an idle
stopper. [0026] (V) When employed are porous members constituting
the filter body and integrally carrying oxidation catalysts, the
oxidation reaction of the particulates captured by the filter body
can be accelerated by the oxidation catalysts,, so that the
particulates can be further reliably burned off in a region of
operation with lower exhaust temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 A schematic view showing arrangement of a
conventional particulate filter.
[0028] FIG. 2 A sectional view showing particulars of the
particulate filter shown in FIG. 1.
[0029] FIG. 3 A sectional view showing an embodiment of the
invention.
[0030] FIG. 4 A sectional view looking in the direction of arrows
II in FIG. 3.
EXPLANATION OF THE REFERENCE NUMERALS
[0031] 2 exhaust gas [0032] 3 exhaust pipe [0033] 4 particulate
filter [0034] 5 passage [0035] 7 filter body [0036] 9 rod-like
electrode (electrode) [0037] 10 cylindrical electrode (electrode)
[0038] 11 plasma regenerative particulate filter [0039] 11A, 11B,
11C and 11D smaller unit [0040] 12 filter casing [0041] 16 upstream
oxidation catalyst [0042] 17 downstream oxidation catalyst
Best Mode for Carrying Out the Invention
[0043] An embodiment of the invention will be described in
conjunction with the drawings.
[0044] FIGS. 3 and 4 show an embodiment of the invention in which
parts similar to those in FIGS. 1 and 2 are represented by the same
reference numerals.
[0045] As shown in FIGS. 3 and 4, used in an exhaust emission
control device of the invention is a plasma regenerative
particulate filter 11 comprising a filter body 7 similar to that
shown in FIG. 2 above and rod-like and cylindrical electrodes 9 and
10 so as to generate plasma in the filter body 7. Shown is an
example of the plasma regenerative particulate filter 11 divided
into a plurality of (four in the figure shown) smaller units 11A,
11B, 11C and 11D which are arranged in parallel with each other
within the filter casing 12.
[0046] The filter body 7 in each of the smaller units 11A, 11B, 11C
and 11D has the rod-like electrode 9 inserted into an axis of the
filter body 7 and the cylindrical electrode 10 fitted over the
outer periphery of the filter body 7. The rod-like electrodes 9 of
the smaller units 11A, 11B, 11C and 11D are connected to an anode
of a power source or buttery 14 through change-over relays 13a,
13b, 13c and 13d, respectively. The cylindrical electrodes 10 of
the smaller units 11A, 11B, 11C and 11D are connected to a cathode
of the power source 14 through an electrically conductive support
member 15 and the filter casing 12 so that voltage for electric
discharge may be separately applied to the respective smaller units
11A, 11B, 11C and 11D.
[0047] The support member 15 serves for support of the smaller
units 11A, 11B, 11C and 11D of the particulate filter 11 in the
filter casing 12 and also serves as partition or filler for gap
between the smaller units 11A, 11B, 11C and 11D.
[0048] The above-mentioned particulate filter 11 divided into the
plural smaller units 11A, 11B, 11C and 11D is accommodated in the
filter casing 12 within the exhaust pipe 3. Arranged upstream and
downstream of and adjacent to the particulate filter 11 in the
filter casing 12 are oxidation catalysts 16 and 17, respectively,
so as to obtain heat insulation effect to the particulate filter
11.
[0049] Each of the upstream and downstream oxidation catalysts 16
and 17 is of flow-through type and comprises a carrier with a
honeycomb structure made of ceramics such as cordierite, said
carrier carrying an appropriate amount of platinum. The upstream
catalyst 17 may have its capacity and platinum-carrying amount less
than those of the downstream catalyst 16.
[0050] The porous members constituting the filter body 7 of each of
the above-mentioned smaller units 11A, 11B, 11C and 11D may carry
oxidation catalysts so as to promote the oxidation reaction of the
particulates captured by the filter body 7.
[0051] In the exhaust emission control device thus constructed,
when the exhaust gas 2 having flown into the filter casing 12
passes through the upstream oxidation catalyst 16, NO occupying
majority of NO.sub.x. in the exhaust gas 2 is converted into highly
reactive NO.sub.2, so that oxidation reaction of the particulates
is substantially accelerated into satisfactory burn-off of the
particulates under a condition of operation with exhaust
temperature over about 250.degree. C.
[0052] However, when a condition of light-load operation with
exhaust temperature greatly falling below 250.degree. C. continues
for a long time, for example, during running or driving on
congested city roads, satisfactory burn-off of the particulates
cannot be expected; for this reason, at a right moment when an
accumulated particulate amount is estimated to exceed a
predetermined amount (estimation may be based on, for example,
pressure difference between the entering and discharge sides of the
filter body or operational time period), voltage for electric
discharge is applied separately to the smaller units 11A, 11B, 11C
and 11D to discharge electricity across the respective rod-like
electrodes 9 and cylindrical electrodes 10, thereby generating
plasma in the inner gas of the filter body 7.
[0053] Thus, the inner gas of the filter body 7 is excited to
convert oxygen into ozone and NO into NO.sub.2. These excited
exhaust gas components are being activated so that oxidization
reaction of the particulates captured by the filter body 7 is
accelerated by the excited exhaust gas components, whereby the
particulates are satisfactorily burned off even in a condition of
operation with lower exhaust temperature.
[0054] In this case, the plasma regenerative particulate filter 11
is sandwiched and heat insulated by the upstream and downstream
oxidation catalysts 16 and 17 in one and the same filter casing 12,
so that when the oxidation reaction of the captured particulates
begins, the filter body 7 is rapidly elevated in temperature. As a
result, the particulates have tendency of being more readily burned
off and can be burned off with a shorter electric discharge time
than they could conventionally and thus required electric power
consumption is less than that required conventionally.
[0055] Since voltage is applied across each of the smaller units
11A, 11B, 11C and 11D in the particulate filter 11 so as to
discharge electricity, the power source 14 with relatively small
capacity will suffice. Division into the smaller units 11A, 11B,
11C and 11D improves combustibility of the particulates per unit,
so that regeneration of the filter through plasma can be attained
during stoppage of an engine for example in a vehicle with an idle
stopper.
[0056] The harmful gas such as highly concentrated CO or HC
generated due to combustion of the particulates with relatively low
temperature by the aid of plasma is oxidized into harmless CO.sub.2
or H.sub.2O when it passes through the downstream oxidation
catalyst 17 and is discharged.
[0057] Thus, according to the above embodiment, even in a condition
of operation with lower exhaust temperature such as light-load
operation, the particulates captured by the filter body 7 can be
efficiently burned off by the aid of plasma; the filter body 7 can
be rapidly elevated in temperature due to heat insulation effect by
the upstream and downstream oxidation catalysts 16 and 17 into
environment for ready burn-off the particulates, so that the
particulates can be burned off with a shorter electric discharge
time than they could conventionally, whereby electric power
consumption can be substantially reduced.
[0058] The harmful gas such as highly concentrated CO or HC
generated due to combustion of the particulates with relatively low
temperature by the aid of plasma is oxidized into harmless CO.sub.2
or H.sub.2O when it passes through the downstream oxidation
catalyst 17 and is discharged. As a result, the harmful gas is
prevented from remaining in the exhaust gas 2 finally discharged
into the atmosphere.
[0059] NO occupying majority of NO.sub.x in the exhaust gas 2 can
be converted into highly reactive NO.sub.2 when the exhaust gas
passes through the upstream oxidation catalyst 16, which
substantially accelerates the oxidation reaction of the
particulates under a condition of operation with relatively high
exhaust temperature, whereby spontaneous combustion of the
particulates is promoted by no aid of plasma, thereby providing
satisfactory burn-off of the particulates.
[0060] As especially shown in the embodiment, when the particulate
filter 11 is divided into the plural smaller units 11A, 11B, 11C
and 11D which are arranged in parallel with each other within the
filter casing 12, voltage for electric discharge being separately
applicable to the respective smaller units 11A, 11B, 11C and 11D,
even the power source 14 with relatively small capacity will
suffice; regeneration of the filter through plasma can be attained
during stoppage of an engine, for example, in a vehicle with an
idle stopper.
[0061] In a case where employed are the porous members constituting
the filter body 7 and integrally carrying oxidation catalysts, the
oxidation reaction of the particulates captured by the filter body
7 can be accelerated by the oxidation catalysts, so that further
reliable burn-off of the particulates can be attained in a region
of operation with lower exhaust temperature.
[0062] It is to be understood that an exhaust emission control
device of the invention is not limited to the above-mentioned
embodiment and that various changed and modifications may be made
without leaving the gist of the invention. For example, the plasma
regenerative particulate filter may be constituted by a single
unit. The filter body may or may not carry oxidation catalysts.
Shapes and arrangement of the filter body and electrodes are not
limited to those shown.
* * * * *