U.S. patent application number 12/338250 was filed with the patent office on 2009-07-02 for exhaust gas treatment system for an internal combustion engine.
Invention is credited to Sakutaro HOSHI, Atsushi Kidokoro, Toru Sasatani, Koji Yoshida.
Application Number | 20090165439 12/338250 |
Document ID | / |
Family ID | 40459840 |
Filed Date | 2009-07-02 |
United States Patent
Application |
20090165439 |
Kind Code |
A1 |
HOSHI; Sakutaro ; et
al. |
July 2, 2009 |
EXHAUST GAS TREATMENT SYSTEM FOR AN INTERNAL COMBUSTION ENGINE
Abstract
An exhaust gas treatment system for an internal combustion
engine includes an exhaust pipe and an energy applying device.
Exhaust gas discharged from the internal combustion engine flows
into the exhaust pipe. The energy applying device applies energy to
the exhaust gas flowing through the exhaust pipe. The energy
applied to the exhaust gas is greater than the energy for
decomposing nitrogen monoxide (NO) and less than the energy for
decomposing nitrogen (N.sub.2).
Inventors: |
HOSHI; Sakutaro;
(Kariya-shi, JP) ; Yoshida; Koji; (Kariya-shi,
JP) ; Kidokoro; Atsushi; (Kariya-shi, JP) ;
Sasatani; Toru; (Kariya-shi, JP) |
Correspondence
Address: |
Locke Lord Bissell & Liddell LLP;Attn: IP Docketing
Three World Financial Center
New York
NY
10281-2101
US
|
Family ID: |
40459840 |
Appl. No.: |
12/338250 |
Filed: |
December 18, 2008 |
Current U.S.
Class: |
60/275 ;
60/276 |
Current CPC
Class: |
F01N 2240/28 20130101;
B01D 2259/818 20130101; B01D 2257/702 20130101; Y02C 20/10
20130101; B01D 2257/402 20130101; Y02A 50/20 20180101; B01D 53/925
20130101; B01D 2258/014 20130101; B01D 2257/502 20130101; B01D
2257/404 20130101; B01D 2259/804 20130101; F01N 3/0892 20130101;
B01D 53/323 20130101; B01D 2258/012 20130101; F01N 2570/14
20130101; Y02A 50/2344 20180101 |
Class at
Publication: |
60/275 ;
60/276 |
International
Class: |
F01N 3/00 20060101
F01N003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 25, 2007 |
JP |
P2007-332319 |
Claims
1. An exhaust gas treatment system for an internal combustion
engine comprising: an exhaust pipe into which exhaust gas
discharged from the internal combustion engine flows; and an energy
applying device for applying energy to the exhaust gas flowing
through the exhaust pipe, wherein the energy applied to the exhaust
gas is greater than the energy for decomposing nitrogen monoxide
(NO) and less than the energy for decomposing nitrogen
(N.sub.2).
2. The exhaust gas treatment system according to claim 1, wherein
the applying energy by the energy applying device is set in a range
from 642 to 942 kJ/mol.
3. The exhaust gas treatment system according to claim 1, wherein
the applying energy by the energy applying device is adjustable
according to amount of the exhaust gas.
4. The exhaust gas treatment system according to claim 3, wherein
the applying energy by the energy applying device is adjustable
according to temperature of the exhaust gas.
5. The exhaust gas treatment system according to claim 1, the
exhaust gas treatment system further comprising a NOx detector for
detecting NOx concentration, wherein the operation of the energy
applying device is controlled based on NOx concentration in the
exhaust gas.
6. The exhaust gas treatment system according to claim 1, wherein
the energy applying device is a low-temperature plasma
generator.
7. The exhaust gas treatment system according to claim 6, wherein
the low-temperature plasma generator has a pair of electrode plates
arranged within the exhaust pipe and a high-frequency power source
connects to the electrode plates.
8. The exhaust gas treatment system according to claim 1, wherein
the energy applying device is an ultraviolet irradiating unit.
9. The exhaust gas treatment system according to claim 1, wherein
the exhaust gas treatment system has a plurality of the energy
applying devices.
10. The exhaust gas treatment system according to claim 9, wherein
the plurality of the energy applying devices is arranged in series
along the exhaust pipe.
11. The exhaust gas treatment system according to claim 9, wherein
the exhaust pipe is branched and the energy applying devices are
disposed in each branched exhaust pipe in parallel arrangement.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to an exhaust gas treatment
system for an internal combustion engine.
[0002] Combustion in an internal combustion engine, a boiler and
the like results in discharging to the atmosphere of such exhaust
gases as particulate matters (PM), hydrocarbons (HC), sulfur oxides
(SOx including SO, SO.sub.2), nitrogen oxides (NOx including NO,
NO.sub.2 and N.sub.2O) and carbon oxides (COx including CO,
CO.sub.2). Regulations on emissions of such exhaust gas components
have become more strict recently in consideration of environmental
issues such as global warming. Therefore, importance has been
attached to establishment of technologies for exhaust gas
purification. Though there are many restrictions in size, weight,
cost, working efficiency, maintenance and the like of exhaust gas
purification system for transportation device such as a vehicle,
demand for effective exhaust gas treatment system is expected to be
expanded rapidly. Therefore, development of such exhaust gas
treatment system with high efficiency is now an urgent need.
[0003] In a gasoline engine for vehicle, the engine operation is
controlled based on signals from an oxygen sensor or the like such
that a theoretical air-fuel ratio is obtained. This allows an
oxidation-reduction catalytic converter (three-way catalyst) using
platinum and the like to be used for removing PM, HC and NOx from
exhaust gas. On the other hand, a diesel engine has good fuel
efficiency, and emissions of carbon oxides such as CO.sub.2 and the
like from the diesel engine are about 20 to 30 percent lower than
that from the gasoline engine. However, exhaust gas from the diesel
engine contains a large amount of excess oxygen, so that the use of
a reduction catalyst in the diesel engine is difficult. Thus,
various methods for reducing NOx in the diesel engine have been put
into practice use. According to one method, exhaust gas is
recirculated for reducing NOx, which is called exhaust gas
recirculation (EGR), thereby generating excess PM, and then the
excess PM is captured by a filter or the like that is called diesel
particulate filter (DPF). According to another method, urea is
injected into exhaust gas for reducing NOx, which is called urea
selective catalytic reduction (Urea-SCR). According to still
another method, NOx is absorbed temporarily and then reduced by
fuel and the like at any appropriate time, which is called diesel
particulate matter-NOx reduction system (DPNR).
[0004] However, in the case of the combination of EGR and DPF, the
effect of reducing NOx emissions is relatively small and the
driving performance of the vehicle is restricted. The method of
Urea-SCR is disadvantageous in the installation of a urea tank and
the need of replenishing the tank with urea. In the method of DPNR,
periodical injection of surplus fuel is required, thereby
deteriorating the fuel consumption of the vehicle. These methods
for exhaust gas purification need to be performed in accordance
with conditions of engine combustion. Therefore, engine controlling
becomes complicated, so that engine development becomes enlarged,
with the result that the development period is extended and the
cost thereof increased accordingly. All the methods require a noble
metal such as platinum as a catalyst, which is a problem in view of
the cost and the need of conserving natural resources.
[0005] To solve the above problems, Japanese Patent Application
Publication 61-31615 discloses an engine which reforms NOx by means
of electric discharge. In this engine, a dissociation cylinder
(reformer) is directly connected to an exhaust pipe of the engine,
and corona discharge needles are arranged in the outer periphery of
the dissociation cylinder. NOx in exhaust gas is decomposed by
electric discharge in the dissociation cylinder, and the oxygen
atom (oxygen radical) of the decomposed NOx combines with carbon
oxide in exhaust gas thereby to form carbon dioxide. Meanwhile,
nitrogen atom in the decomposed NOx combines with the other
nitrogen atom in the decomposed NOx thereby to form nitrogen
(N.sub.2). As a result, NOx in exhaust gas is reduced. However, it
is hard to reduce NOx efficiently unless the following conditions
are satisfied. A first condition is that the amount of carbon
monoxide in exhaust gas is sufficiently greater than the amount of
oxygen radical produced by the electric discharge. A second
condition is that the chemical reactivity of nitrogen (nitrogen
radical) separated from nitrogen oxides (NOx) is low enough to
inhibit the production of NOx.
[0006] When the diesel engine is being operated under a lean burn
condition or combustion with excess air (oxygen), exhaust gas
contains therein a large amount of oxygen. This approach will not
be expected to be satisfied with the first condition. Meanwhile, it
is well known that under complete combustion wherein combustion
takes place under a high temperature (oxidation reaction) and PM
and HC are decreased effectively, but NOx emissions are increased.
This approach will not be expected to be satisfied with the second
condition under engine operation at a high temperature such as
complete combustion or high power operation. Thus, when the
electric discharge merely occurs under a high temperature of
exhaust gas, it results that NOx is regenerated easily and, in some
cases, NOx is increased in exhaust gas.
[0007] The present invention is directed to provide an exhaust gas
treatment system for an internal combustion engine which can reduce
NOx reliably while preventing nitrogen generated by the
decomposition of NOx from being further decomposed to regenerate
NOx.
SUMMARY OF THE INVENTION
[0008] In accordance with the present invention, an exhaust gas
treatment system for an internal combustion engine includes an
exhaust pipe and an energy applying device. Exhaust gas discharged
from the internal combustion engine flows into the exhaust pipe.
The energy applying device applies energy to the exhaust gas
flowing through the exhaust pipe. The energy applied to the exhaust
gas is greater than the energy for decomposing nitrogen monoxide
(NO) and less than the energy for decomposing nitrogen (N.sub.2).
Thus, NOx is decomposed, but N.sub.2 is hardly decomposed, so that
N.sub.2 generated by decomposition of NOx is prevented from being
further decomposed to regenerate NOx. Thus, nitrogen atoms in
exhaust gas are gradually combined to form a stable nitrogen
molecule (N.sub.2). Therefore, NOx in exhaust gas can be reduced
reliably.
[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 of a preferred embodiment of the
present invention;
[0012] FIG. 2 is a graph explaining the operation of a
low-temperature plasma generator forming a part of the exhaust gas
treatment system according to the preferred embodiment of the
present invention; and
[0013] FIG. 3 is a schematic view of a diesel engine with the
exhaust gas treatment system according to an alternative embodiment
of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0014] The following will describe the preferred embodiment of the
present invention with reference to FIGS. 1 and 2. FIG. 1 shows a
diesel engine 1 which is equipped with an exhaust gas treatment
system according to the preferred embodiment of the present
invention. The diesel engine 1 includes a cylinder block 2 having
four cylinders defining therein combustion chambers 2A, 2B, 2C, 2D,
an intake manifold 3 and a exhaust manifold 4 both of which are
provided in communication with the respective combustion chambers
2A, 2B, 2C, 2D. The intake manifold 3 is connected to an intake
pipe 5 in which intake air flows. The exhaust manifold 4 is
connected to an exhaust pipe 6 in which exhaust gas discharged from
the combustion chambers 2A, 2B, 2C, 2D flows. A low-temperature
plasma generator 12 is disposed in the exhaust pipe 6. The diesel
engine 1 has an electric control unit (ECU) 10. The low-temperature
plasma generator 12 serves as an energy applying device.
[0015] The low-temperature plasma generator 12 includes a
high-frequency power source 21, and a pair of electrode plates 22,
23. The high-frequency power source 21 is electrically connected to
the ECU 10. The electrode plate 22 is disposed inside of the
exhaust pipe 6 and connected to the high-frequency power source 21.
The electrode plate 23 is disposed inside of the exhaust pipe 6 and
grounded. As shown in FIG. 1, the electrode plates 22, 23 are
disposed parallel and spaced apart to each other in the exhaust
pipe 6. The electrode plates 22, 23 are covered with a dielectric
material, respectively.
[0016] The following will describe the operation of the diesel
engine 1 with the exhaust gas treatment system according to this
preferred embodiment of the present invention with reference to
FIG. 1. In operation of the diesel engine 1, air flowing in the
intake pipe 5 flows into the combustion chambers 2A, 2B, 2C, 2D
through the intake manifold 3. In the respective combustion
chambers 2A, 2B, 2C, 2D, the intake air is compressed by pistons
(not shown), and then fuel injected into the compressed air from an
injection nozzle (not shown) is ignited for combustion. Combustion
gas is discharged from the combustion chambers 2A, 2B, 2C, 2D as
exhaust gas to the exhaust manifold 4.
[0017] When the exhaust gas flows from the exhaust manifold 4
through the exhaust pipe 6, the ECU 10 activates the high-frequency
power source 21 to cause a local electric discharge between a pair
of the electrode plates 22, 23 in accordance with the amount of
exhaust gas. By so doing, the ambient temperature of plasma is
prevented from increasing (or low-temperature plasma), so that
stable plasma reaction continues to achieve under a pressure near
the atmospheric pressure. As shown in FIG. 2, the electric
discharge occurs in a pulse manner that discharge (ON) and
non-discharge (OFF) are repeated alternately. The electric
discharge energy is controlled by adjusting the frequency and the
voltage in accordance with the amount of exhaust gas, thereby
making it possible to prevent nitrogen (N.sub.2) in the exhaust gas
from being decomposed. Exhaust gas flowing between the electrode
plates 22, 23 collides with electrons which are accelerated in the
electric field between the electrode plates 22, 23, thus NOx in
exhaust gas being decomposed thereby to produce nitrogen (N.sub.2),
oxygen (O.sub.2) and the other oxides. As a result, NOx in exhaust
gas is reduced. The electric discharge energy between the electrode
plates 22, 23 is set greater than energy for decomposing nitrogen
monoxide (NO) and less than energy for decomposing nitrogen
(N.sub.2), or it is set in the range from 642 to 942 kJ/mol. This
prevents the nitrogen (N.sub.2) produced by decomposing NOx from
being decomposed to regenerate NOx.
[0018] Allowing exhaust gas to pass through the low-temperature
plasma generator 12, NOx in the exhaust gas is decomposed to
produce N.sub.2, O.sub.2 and the other oxide, which are then
emitted into the atmosphere.
[0019] The low-temperature plasma generator 12 provides exhaust gas
with an electric discharge energy that is larger than energy
capable of decomposing nitrogen monoxide (NO), but less than energy
capable of decomposing nitrogen (N.sub.2). Thus, NOx in exhaust gas
is decomposed to produce N.sub.2, O.sub.2 and the other oxygen, but
the produced N.sub.2 is hardly decomposed to regenerate NOx at all.
Thus, N.sub.2 produced by decomposition of NOx is prevented from
being decomposed into NOx. Therefore, almost all nitrogen atoms in
exhaust gas are consequently combined to form a stable nitrogen
molecule (N.sub.2), with the result that NOx in exhaust gas is
reduced reliably.
[0020] The low-temperature plasma generator 12 is advantageous in
that it has a compact structure in which a pair of the electrode
plates 22, 23 is arranged within the exhaust pipe 6 and the
high-frequency power source 21 is arranged outside the exhaust pipe
6. Thus, the low-temperature plasma generator 12 may be mounted
even to a narrow exhaust pipe. Furthermore, energy consumption may
be reduced in comparison with a system using a thermal plasma
generator.
[0021] In this preferred embodiment, the applying energy is
adjustable according to the amount of exhaust gas, however, the
present invention is not limited. Alternatively, the applying
energy may be adjustable according to the exhaust gas temperature,
as well.
[0022] In this preferred embodiment, there is provided only single
low-temperature plasma generator. Alternatively, the energy
applying device may be composed of a plurality of low-temperature
plasma generators. The use of a plurality of low-temperature plasma
generators expands the area where the energy is applied to the
exhaust gas, so that more amount of NOx may be decomposed. The
plural low-temperature plasma generators may be arranged in series
along the exhaust pipe 6. Alternatively, the exhaust pipe may be
branched and a low-temperature plasma generator may be disposed in
each branched pipe so that the plural low-temperature plasma
generators are provided in parallel arrangement. The energy
applying device of the present invention is not limited to the
low-temperature plasma generator. Alternatively, any device that is
operable to apply energy of a predetermined range to exhaust gas,
for example, an ultraviolet irradiating unit is usable. Therefore,
the present invention does not limit the applying energy to plasma.
Alternatively, various other kinds of means are usable for applying
energy to exhaust gas.
[0023] In the preferred embodiment, the ECU 10 controls the
operation of the high-frequency power source 21 based on the amount
of exhaust gas. Alternatively, a NOx detector 11 may be provided
for detecting the NOx concentration in exhaust gas, as shown in
FIG. 3, and the operation of high-frequency power source 21 may be
controlled in accordance with the detected value of the NOx
detector 11. NOx concentration can be estimated based on the
relation between a specific operating condition of the diesel
engine 1 and its corresponding preliminarily measured NOx, and
plasma may be generated in accordance with such estimated NOx
concentration. This effectively reduces the NOx concentration to an
appropriately low level. Controlling the plasma appropriately, PM,
HC, and COx can be removed effectively. By generating, for example,
oxygen radical (active oxygen) and ozone (O.sub.3), PM can be
changed to CO and CO.sub.2, HC to H.sub.2O, CO and CO.sub.2, and CO
to CO.sub.2, respectively.
[0024] In the above-described preferred embodiment, the exhaust gas
treatment system is applied to the diesel engine 1 as an internal
combustion engine, but it is applicable to other apparatuses than
the diesel engine 1. Alternatively, the exhaust gas system of the
present invention is applicable to a gasoline engine, a boiler, and
the like.
[0025] 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.
* * * * *