U.S. patent application number 12/342412 was filed with the patent office on 2009-08-27 for exhaust gas treatment system for an internalcombustion engine.
Invention is credited to Sakutaro Hoshi, Koji YOSHIDA.
Application Number | 20090211231 12/342412 |
Document ID | / |
Family ID | 40473629 |
Filed Date | 2009-08-27 |
United States Patent
Application |
20090211231 |
Kind Code |
A1 |
YOSHIDA; Koji ; et
al. |
August 27, 2009 |
EXHAUST GAS TREATMENT SYSTEM FOR AN INTERNALCOMBUSTION ENGINE
Abstract
An exhaust gas treatment system for an internal combustion
engine reduces the amount of NOx in exhaust gas flowing through an
exhaust passage of the engine. The system has a plasma generator
including two electrodes spaced away from each other in the exhaust
passage, a high-frequency power supply connected to one of the
electrodes, and a NOx absorber provided between the electrodes.
Inventors: |
YOSHIDA; Koji; (Kariya-shi,
JP) ; Hoshi; Sakutaro; (Kariya-shi, JP) |
Correspondence
Address: |
MORGAN & FINNEGAN Transition Team;C/O Locke Lord Bissell & Liddell
3 WORLD FINANCIAL CENTER
NEW YORK
NY
10281-2101
US
|
Family ID: |
40473629 |
Appl. No.: |
12/342412 |
Filed: |
December 23, 2008 |
Current U.S.
Class: |
60/275 ;
60/311 |
Current CPC
Class: |
F01N 2240/28 20130101;
F01N 3/0814 20130101 |
Class at
Publication: |
60/275 ;
60/311 |
International
Class: |
F01N 3/00 20060101
F01N003/00; F01N 3/02 20060101 F01N003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2007 |
JP |
2007-339322 |
Claims
1. An exhaust gas treatment system for an internal combustion
engine, the system for reducing the amount of NOx in exhaust gas
flowing through an exhaust passage of the engine, comprising: a
plasma generator including; two electrodes spaced away from each
other in the exhaust passage; a high-frequency power supply
connected to one of the electrodes; and a NOx absorber provided
between the electrodes.
2. The exhaust gas treatment system according to claim 1, wherein a
plurality of plasma generators is provided in series in the exhaust
passage, and the plasma generators are operated at different
timings from each other.
3. The exhaust gas treatment system according to claim 2, further
comprising a controller that monitors engine load and changes the
number of plasma generators to be operated depending on the engine
load.
4. The exhaust gas treatment system according to claim 1, wherein
the energy for discharge between the electrodes is set in a range
of 642 to 942 kJ/mol.
5. The exhaust gas treatment system according to claim 1, wherein
the NOx absorber contains a material that allows physisorprtion of
NOx thereon.
6. The exhaust gas treatment system according to claim 5, wherein
the material is selected from the group consisting of: alkali
metals; alkali earth metals; lanthanoids; oxides of the alkali
metals, the alkali earth metals or the lanthanoids; compounds of
either the alkali metals, the alkali earth metals or the
lanthanoids with elements other than the alkali metals, the alkali
earth metals and the lanthanoids; and oxides of the compounds.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an exhaust gas treatment
system for an internal combustion engine.
[0002] In boilers and internal combustion engines, exhaust gas is
produced as a result of the combustion of fuel and discharged into
the atmosphere. The exhaust gas contains various substances such as
particulate matter (PM) including carbide particles, hydrocarbons
(HC), sulfur oxides (SOx: SO, SO.sub.2), nitrogen oxides (NOx: NO,
NO.sub.2, N.sub.2O), and carbon oxides (COx: CO, CO.sub.2). Recent
emission standards are very strict because of various environmental
issues such as global warming, and therefore establishment of
technologies for exhaust gas purification is required. Particularly
in transportations like automobile, there are many constraints such
as size, weight, cost, efficiency and ease of maintenance, but a
demand for such technologies is expected to increase rapidly in the
future. Therefore, development of an exhaust gas treatment system
with high efficiency is an urgent need.
[0003] In automotive gasoline engines, a catalytic converter with a
catalyst such as platinum (a three-way catalytic converter) is
commonly used to reduce the amount of PM, HC and NOx in exhaust gas
by means of oxidizing and reducing reactions. The engines are
generally controlled so as to operate on a stoichiometric air fuel
ratio by using oxygen sensors. In diesel engines having high fuel
economy, emission of COx such as CO.sub.2 is 20% to 30% less than
that of the gasoline engines, but reducing catalysts are difficult
to be used in diesel engines because of the presence of excess
oxygen in exhaust gas. Therefore, various methods for reducing NOx
emission are used practically. One of the methods is recirculating
a part of exhaust gas back to engine cylinders (an exhaust gas
recirculation: EGR) and then using a diesel particulate filter
(DPF) to collect PM generated in large amounts due to the EGR.
Other methods include injecting urea into exhaust gas (a urea
selective catalytic reduction: urea SCR), and storing NOx
temporarily and then reducing the stored NOx at a proper timing by
injection of fuel (a diesel particulate-NOx reduction system:
DPNR).
[0004] However, the combination of EGR and DPF not only reduce NOx
emission insufficiently, but also adversely affects the drivability
and performance of the automobiles. The urea SCR requires
installation of an additional urea tank and periodic replenishment
of urea, The DPNR requires periodic injection of extra fuel,
thereby lowering fuel economy, Furthermore, implementation of the
above methods need to be controlled precisely depending on
combustion condition of the engine, and therefore engine control
becomes complex. Such complex engine control results in enlargement
of engine development and period thereof, thereby increasing a cost
of the engine development. Furthermore, any of the methods needs a
precious metal catalyst such as platinum, which is not preferable
from the viewpoint of cost and procurement of catalyst
material.
[0005] In a known engine disclosed in Japanese Unexamined Patent
Application Publication No. 61-31615, exhaust gas is introduced
through an exhaust pipe into a dissociation cylinder (reformer)
having corona discharge needles at the outer surface thereof. NOx
in the exhaust gas is decomposed into oxygen atom (oxygen radical)
and nitrogen atom (nitrogen radical) by the discharge in the
dissociation cylinder. The oxygen atom is reacted with carbon
monoxide contained in large amounts in the exhaust gas to produce
carbon dioxide, and the nitrogen atom is reacted with the other
nitrogen atom to produce nitrogen (N.sub.2). As a result, the
amount of NOx in the exhaust gas is reduced.
[0006] However, NOx concentration in the exhaust gas is low, and
therefore discharge decomposition of low concentrated NOx in the
exhaust gas is not efficient.
[0007] The present invention is directed to an exhaust gas
treatment system that reduces the amount of NOx in exhaust gas more
efficiently.
SUMMARY OF THE INVENTION
[0008] In accordance with an aspect of the present invention, an
exhaust gas treatment system for an internal combustion engine
reduces the amount of NOx in exhaust gas flowing through an exhaust
passage of the engine. The system has a plasma generator including
two electrodes spaced away from each other in the exhaust passage,
a high-frequency power supply connected to one of the electrodes,
and a NOx absorber provided between the electrodes.
[0009] Other aspects and advantages of the invention will become
apparent from the following description, taken in conjunction with
the accompanying drawings, illustrating by way of example the
principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] The features of the present invention that are believed to
be novel are set forth with particularity in the appended claims.
The invention together with objects and advantages thereof, may
best be understood by reference to the following description of the
presently preferred-embodiments together with the accompanying
drawings in which:
[0011] FIG. 1 is a schematic view of a diesel engine having an
exhaust gas treatment system according to a first embodiment of the
present invention; and
[0012] FIG. 2 is a schematic view of a diesel engine having an
exhaust gas treatment system according to a second embodiment of
the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0013] The following will describe the first embodiment of the
present invention with reference to FIG. 1. A diesel engine 1
includes a cylinder block 2, an intake manifold 3 and an exhaust
manifold 4. The cylinder block 2 is formed with four combustion
chambers 2A, 2B, 2C and 2D defined in respective cylinders (not
shown in the drawings). The intake manifold 3 introduces air from
an intake pipe 5 into the combustion chambers 2A to 2D, and the
exhaust manifold 4 collects exhaust gas from the combustion
chambers 2A to 2D into an exhaust pipe 6. In the exhaust pipe 6 as
an exhaust passage, two plasma generators 12 and 22 are disposed in
series. The diesel engine 1 further includes an electronic control
unit (ECU) 10 as a controller.
[0014] The plasma generator 12 includes a high-frequency power
supply 16 electrically connected to the ECU 10, two plate-shaped
electrodes 13 and 14 spaced away from each other in the exhaust
pipe 6, and a NOx absorber 15 provided between the electrodes 13
and 14. The electrodes 13 and 14 are disposed parallel to each
other. The electrode 13 is electrically connected to the
high-frequency power supply 16, and the electrode 14 is grounded.
The electrodes 13 and 14 are covered with a dielectric material.
The NOx absorber 15 is of a porous body made of electrically
conductive Al.sub.2O.sub.3 and supporting NOx-storage particles
made of BaO. As with the plasma generator 12, the plasma generator
22 includes two electrodes 23 and 24, a high-frequency power supply
26, and a NOx absorber 25 provided between the electrodes 23 and
24.
[0015] The following will describe the operation of the exhaust gas
treatment system according to the first embodiment, When the diesel
engine 1 is started, air in the intake pipe 5 is introduced through
the intake manifold 3 into the combustion chambers 2A to 2D, and
compressed by pistons (not shown in the drawings). Diesel fuel
injected from injection nozzles (not shown in the drawings) into
the compressed air is ignited spontaneously for combustion, and
exhaust gas is discharged from the combustion chambers 2A to 2D
into the exhaust manifold 4.
[0016] The exhaust gas then flows in the exhaust pipe 6 and passes
through the NOx absorber 15 of the plasma generator 12, so that NOx
in the exhaust gas is stored on the NOx-storage particles of the
NOx absorber 15. The plasma generator 12 thus reduces NOx
concentration of the exhaust gas passing therethrough. When the
amount of NOx on the NOx absorber 15 reaches a predetermined limit,
the plasma generator 12 cannot reduce the NOx concentration of the
exhaust gas any more. In such a case, the exhaust gas passes
through the NOx absorber 25 of the other plasma generator 22, so
that NOx in the exhaust gas is stored on the NOx-storage particles
of the NOx absorber 25. The plasma generator 22 thus reduces NOx
concentration of the exhaust gas passing therethrough, as with the
plasma generator 12.
[0017] When the amount of NOx on the NOx absorber 15 reaches a
predetermined level, the ECU 10 drives the high-frequency power
supply 16 so that discharge occurs (that is, plasma is generated)
between the electrodes 13 and 14. The discharge energy is set in a
range of 642 to 942 kJ/mol. This energy range is higher than a
range wherein NOx can be decomposed into nitrogen and oxygen atoms
(N, O), but lower than a range wherein nitrogen (N.sub.2) can be
decomposed into nitrogen atoms. Therefore, NOx on the NOx absorber
15 is decomposed into N.sub.2 and O.sub.2 at a given rate, thereby
being released from the NOx absorber 15. If NOx is newly produced
from the nitrogen and oxygen atoms, the NOx is stored on the NOx
absorbers 15 or 25 again, and finally all NOx on the NOx absorber
15 is decomposed. Since the above discharge energy is lower than
the energy for decomposition of N.sub.2, the newly produced N.sub.2
is prevented from being decomposed to produce NOx again. While the
discharge occurs in the plasma generator 12, the plasma generator
22 stores NOx in the exhaust gas on the NOx absorber 25.
[0018] In the meantime, the amount of NOx on the NOx absorber 25 of
the plasma generator 22 reaches a predetermined limit, However, the
previously stored NOx on the NOx absorber 15 of the plasma
generator 12 is decomposed into N.sub.2 and O.sub.2 by the
discharge between the electrodes 13 and 14 to be released from the
NOx absorber 15. Therefore, exhaust gas passing through the NOx
absorber 15, NOx in the exhaust gas is stored on the NOx-storage
particles of the NOx absorber 15 again. While the NOx is stored on
the NOx absorber 15, plasma is generated between the electrodes 23
and 24 in the plasma generator 22, as in the case of the plasma
generator 12. As a result, the NOx on the NOx absorber 25 is
decomposed into N.sub.2 and O.sub.2: to be released from the NOx
absorber 25.
[0019] The above-described operations of the plasma generators 12
and 22 are repeated alternately, so that NOx concentration of the
exhaust gas is reduced. In the first embodiment, the plasma is
generated alternately by the plasma generators 12 and 22, but may
be generated intermittently at a predetermined time interval by
each plasma generator. Alternatively, the plasma may be generated
by each plasma generator at any time depending on the exhaust gas
amount determined by the ECU 10, based on the engine operating
condition such as engine speed.
[0020] The exhaust gas treatment system according to the first
embodiment has two plasma generators 12 and 22. The plasma
generator 12 has the electrodes 13 and 14 spaced in the exhaust
pipe 6, the high-frequency power supply 16 connected to the
electrode 13, and the NOx absorber 15 provided between the
electrodes 13 and 14. The plasma generator 22 which is of
substantially the same structure as the plasma generator 12 is
provided in series with the plasma generator 12 in the exhaust pipe
6. Therefore, while NOx is newly being stored and concentrated on a
NOx absorber in one of the two plasma generators, concentrated NOx
on a NOx absorber can be decomposed by the plasma between the two
electrodes in the other of the two plasma generators. As a result,
the amount of NOx in exhaust gas is reduced more efficiently. In
addition, plasma decomposition of highly concentrated NOx on a NOx
absorber reduces the amount of NOx in exhaust gas more efficiently,
as compared to plasma decomposition of low concentrated NOx in
exhaust gas without using a NOx absorber.
[0021] Though two plasma generators are provided in the exhaust
pipe in the first embodiment, three or more plasma generators may
be used to achieve the same effect. In the first embodiment, the
discharge energy is set in the range of 642 to 942 kJ/mol for each
plasma generator, but not limited to this range. If the discharge
energy is higher than 942 kJ/mol, N.sub.2 produced from NOx on a
NOx absorber may be decomposed to produce NOx again. However, since
N.sub.2 is decomposed within a NOx absorber, NOx newly produced
from the N.sub.2 is stored on the NOx-storage particles of the NOx
absorber again without being released from the NOx absorber.
Accordingly, the discharge energy may be set at least in a range of
642 kJ/mol or more.
[0022] In the first embodiment, the NOx absorber 15 is of a porous
body made of electrically conductive Al.sub.2O.sub.3 and supporting
the NOx-storage particles made of BaO, but the present invention is
not limited to this structure. According to the invention, the NOx
absorber 15 may contain at least a material that allows
physisorption of NOx thereon. The material includes, for example,
alkali metals such as Na, K, Li, alkali earth metals such as Ba,
Mg, Ca, lanthanoids such as La, Ce, and oxides of the alkali
metals, the alkali earth metals or the lanthanoids such as MgO. The
material further includes, for example, compounds of either the
alkali metals, the alkali earth metals or the lanthanoids with
elements other than the alkali metals, the alkali earth metals and
the lanthanoids such as NaCl, and oxides of the compounds such as
BaSO.sub.4.
[0023] The following will describe the second embodiment of the
present invention with reference to FIG. 2. The second embodiment
differs from the first embodiment in that the number of plasma
generators is increased, but the other components and structures
are substantially the same as those of the first embodiment.
Therefore, the following description will use same reference
numbers for the common elements or components in both embodiments,
and the description of such elements or components for the second
embodiment will be omitted.
[0024] FIG. 2 shows a diesel engine 31 having an exhaust gas
treatment system according to the second embodiment. The system has
the two plasma generators 12 and 22 of the first embodiment and
further four plasma generators 32, 42, 52 and 62. The six plasma
generators 12, 22, 32, 42, 52 and 62 are provided in series in the
exhaust pipe 6 and electrically connected to the ECU 10. As with
the plasma generators 12 and 22, the plasma generator 32 includes
two electrodes 33 and 34, a NOx absorber 35 provided between the
electrodes 33 and 34, and a high-frequency power supply 36.
Similarly, the plasma generator 42 includes two electrodes 43 and
44, a NOx absorber 45 and a high-frequency power supply 46. The
plasma generator 52 includes two electrodes 53 and 54, a NOx
absorber 55 and a high-frequency power supply 56. The plasma
generator 62 includes two electrodes 63 and 64, a NOx absorber 65
and a high-frequency power supply 66.
[0025] The following will describe the operation of the exhaust gas
treatment system according to the second embodiment. While the
diesel engine 31 is in operation, the ECU 10 monitors the operating
condition (e.g. engine load) of the diesel engine 31. When the ECU
10 detects that the diesel engine 31 is operating under low engine
load, the ECU 10 drives the high-frequency power supplies 16 and 26
alternately, as described with reference to the first embodiment.
Therefore, while NOx is newly stored and concentrated on a NOx
absorber in one of the two plasma generators, concentrated NOx on a
NOx absorber in the other of the two plasma generators is
decomposed by the plasma between the two electrodes. As a result,
the amount of NOx in exhaust gas is reduced efficiently.
[0026] When the engine load is increased, the ECU 10 drives
alternately the four power supplies 16, 26, 36 and 46. When the
engine load is further increased, the ECU 10 drives alternately the
six power supplies 16, 26, 36, 46, 56 and 66. Since the amount of
NOx in exhaust gas is increased with an increase in the engine load
of the diesel engine 31, the number of plasma generators to be
operated is increased in the second embodiment. That is, in the
second embodiment, the number of plasma generators to be operated
is changed depending on the varying engine load of the diesel
engine 31. As a result, the plural plasma generators are operated
property depending on the variation in the amount of NOx in exhaust
gas, and the amount of NOx in exhaust gas is reduced more
efficiently.
[0027] In the second embodiment, operation timing of each power
supply is not described specifically, but any one or more of the
power supplies may be operated at a different timing from the other
power supplies. For example, the power supplies 16, 26, 36, 46, 56
and 66 may be operated one by one in this order. For example, the
power supplies 16, 36 (and 56) may be operated concurrently, while
the power supplies 26, 46 (and 66) may be operated
concurrently.
[0028] In the first and second embodiments, the exhaust gas
treatment system has a plurality of plasma generators, but may have
only one plasma generator. If the system has only one plasma
generator 12, the amount of NOx in exhaust gas cannot be reduced
during the plasma decomposition of NOx on the NOx absorber 15, but
highly concentrated NOx on the NOx absorber 15 is decomposed
surely. Therefore, the amount of NOx in exhaust gas is reduced more
efficiently, as compared to the case of discharge decomposition of
low concentrated NOx in exhaust gas.
[0029] In the first and second embodiments, the exhaust gas
treatment system is used for the diesel engine, but may be used for
boilers or other internal combustion engines such as a gasoline
engine.
[0030] Therefore, the present examples and embodiments are to be
considered as illustrative and not restrictive, and the invention
is not to be limited to the details given herein but may be
modified within the scope of the appended claims.
* * * * *