JPH07247827A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

PURPOSE:To improve exhaust emission control performance of a diesel engine, particularly NOx emission control performance. CONSTITUTION:A diesel engine 10 has a corona discharge device 40 serially arranged on the way of an exhaust pipe 14 and a reduction catalyst device 80. The corona discharge device 40 is connected to a high voltage generation device 70. A nozzle 62 of a hydrocarbon supply device 60 is connected to the catalyst device 80. Data are input from an engine speed sensor 22, a load sensor 20, an exhaust temperature sensor 52, and an oxygen concentration sensor 54 to an ECU 30. When the exhaust temperature is low, the corona discharge device is operated for activating the exhaust gas by corona discharge, oxidizing NO to obtain NO2 which is fed to the catalyst. When the exhaust temperature is high, the corona discharge device is stopped. Reduction to N1 is conducted under addition of the hydrocarbon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying apparatus for an internal combustion engine, and more particularly to purifying nitrogen oxides.

[0002]

2. Description of the Related Art As a technique for purifying NOx (NO, NO ₂ ) in exhaust gas discharged from an internal combustion engine, particularly a diesel engine, an alumina or zeolite-based reduction catalyst is used in the presence of HC (reducing agent). (For example, Japanese Unexamined Patent Publication No. 63-283727), NOx for decomposing and removing NOx by subjecting exhaust gas to corona discharge treatment (for example, Japanese Unexamined Patent Publication No. 4-47110), or NOx It is known that the contained non-treated gas is subjected to corona discharge treatment and then contacted with a three-way catalyst or the like to remove NOx in the gas (JP-A-63-242323).

[0003]

However, the reduction and removal of NOx by the reduction catalyst described in the above-mentioned Japanese Patent Laid-Open No. 63-283727 obtains catalyst activity in an operating region where exhaust gas temperature is relatively low. Not used, the purification rate is still insufficient and HC used as a reducing agent
In most cases, diesel fuel, which is the fuel, is used, and the fuel consumption increases as a whole engine.

Further, in the decomposition and removal of NOx by corona discharge described in the above-mentioned Japanese Patent Application Laid-Open No. 4-47110, NOx molecules are activated by corona discharge in the exhaust gas and Nx molecules are activated.
It utilizes the property of dissociating into O and O and recombining with more stable molecules N ₂ and O ₂ , but when corona discharge is performed in the exhaust gas of a diesel engine with a high O ₂ concentration, N
The O ₂ molecule is also activated together with the Ox molecule and reacts with N ₂ and NO to generate NOx (particularly NO ₂ ) again, and as a result, almost no NOx purification effect can be obtained.

Further, the above-mentioned JP-A-63-24232 is also used.
The NOx removal method described in Japanese Patent Publication No. 3 shows a good NOx purification rate when the temperature of the gas to be treated is about room temperature.
It is still in the experimental stage, and when the exhaust gas temperature greatly changes depending on the operating state like an actual diesel engine, it is not possible to obtain a good NOx purification rate in the entire temperature range.

By the way, alumina-based catalysts and zeolite-based catalysts are effective as NOx reduction catalysts. FIG. 9 is a graph showing the characteristics of the alumina-based catalyst, and it has become clear from the study by the present inventors that the reducing property is higher for NO ₂ than NO. In addition, FIG. 10 shows the characteristics of the zeolite-based catalyst.
The present inventors have also found that in a relatively low temperature range up to around 0 ° C., the selective reduction property for NO ₂ is higher than that in NO, and in the high temperature region over 350 ° C., the reducing property for NO is also high. Research has revealed. On the other hand, as described above, when corona discharge is performed in the exhaust gas of a diesel engine, O ₂ molecules are activated together with NOx molecules and react with N ₂ and NO to generate NOx again. It has been confirmed that most of the produced NOx components are NO ₂ (NO oxidation effect by corona discharge). It was also confirmed that the exhaust gas temperature rises by about 100 to 200 ° C. due to the corona discharge. The present invention provides an exhaust gas purifying apparatus for an internal combustion engine that combines a corona discharge device and a reduction catalyst based on the above findings.

[0007]

The present invention is directed to a corona discharge treatment section for treating exhaust gas with corona discharge, a reduction catalyst layer provided downstream of the corona discharge treatment section, an exhaust gas temperature detecting means, and an exhaust gas temperature. Is a predetermined value or less, a control device for operating the corona discharge processing unit is provided as a basic means.

[0008]

The NOx purifying device of the present invention having the above structure is
When the temperature of the exhaust gas of the internal combustion engine is lower than a predetermined value, the corona discharge treatment unit is operated to convert most of NOx components in the exhaust gas into NO ₂ and the reduction catalyst provided in the downstream of the corona discharge treatment unit. Pour into layers. At this time, the corona discharge treatment not only increases the proportion of NO _{2 in} NOx but also raises the exhaust gas temperature itself, so that the reduction reaction in the reduction catalyst layer is favorably performed. When the temperature of the exhaust gas of the internal combustion engine exceeds a predetermined value, the exhaust gas is allowed to flow through the reduction catalyst layer as it is without operating the corona discharge treatment section. At this time, the exhaust gas temperature has reached a temperature at which the activity of the reduction catalyst layer is sufficiently obtained, so that the NOx reduction reaction is favorably performed.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is an explanatory view showing the outline of the apparatus of the present invention. The engine 10 has an intake pipe 12, an exhaust pipe 14, a piston 18, and the like, and is supplied with fuel from a fuel injection pump 16. The engine has a load sensor 20 and a rotation sensor 22.
Is provided and sends the load data Le and the rotation data Ne to the engine control unit (ECU) 30. On the downstream side of the exhaust pipe 14, the corona discharge device 40 and the catalyst device 80 are arranged in series. An oxygen sensor 54 is provided at the inlet of the catalyst device 80, and the oxygen concentration data Oe in the exhaust gas is sent to the ECU 3
Send to 0. The high voltage generator 70 receives a command from the ECU 30 and supplies a high frequency voltage to the anode side of the corona discharge device 40. The cathode side of the corona discharge device 40 is grounded. A hydrocarbon (HC) or light oil addition device 60 as an additive is connected to a nozzle 62 provided at the inlet of the catalyst device 80, and when a command from the ECU 30 is received, a predetermined amount of the additive is added to the inlet side of the catalyst device. Added to the exhaust gas of.

FIG. 2 is an explanatory view showing the structure of the corona discharge device. A corona discharge device indicated by reference numeral 40 in its entirety has an inlet-side casing 420 into which a substantially conical exhaust gas G is introduced.
And a cylindrical casing 410 sandwiched by the outlet side casing 430, and a corona discharge part fixed inside the casing 410 via a heat insulating material 412. The corona discharge part includes 20 reaction tubes 450 made of quartz glass.
Are fixed at both ends so that they are arranged in parallel with each other between the fixing plates 440 and 442 also made of quartz glass, and the fixing plate 440 is provided at the center of each reaction tube 450. The anode rod 452 is arranged so as to extend from the distribution plate 454 attached to, and the cathode plate 456 is wound around the outer periphery of each reaction tube 450. Also,
Lead wires (not shown) are connected to the distribution plate 454 and the cathode plate 452, respectively, and each lead wire has a lead wire outlet port 42 opened in the casings 420 and 430.
2, 432 is drawn out of the corona discharge treatment device, the anode side lead wire is connected to the high voltage generator 70, and the cathode side lead wire is grounded.

The anode side and the cathode side can be reversed. This corona discharge unit is, for example, 18 KV, 20
High-frequency voltage of about KHz, or 20 to 25 KV, 200
When applying a square wave pulse high voltage of ~ 300Hz,
When the diameter of the anode rod 452 is set to 2 to 3 mm and the inner diameter of the reaction tube 450 is set to about 14 to 20 mm, stable corona discharge is formed. The exhaust gas purifying apparatus of the present invention is
Optimal purification is achieved by properly using the corona discharge device 40 and the catalyst device 80 depending on the exhaust gas temperature. The control steps of the apparatus will be described below, but the ECU
30 stores various control maps in its storage device.

FIG. 3 shows the first control map M1. This map shows changes in exhaust temperature when the engine rotation speed ratio Ne is plotted on the horizontal axis and the engine load factor Le is plotted on the vertical axis. In this map M1, the exhaust temperature is 3
The region is divided into I and II at about 00 ° C. to control the operation of the corona discharge device and the operation of the hydrocarbon addition device. Region I
Is used to reduce NO to H
Together with the addition of C is a region reduced to N _2. Region I
I is a region where the exhaust temperature is low, and NO is once oxidized to NO ₂ by corona discharge, and then NO ₂ is reduced to N ₂ by a reduction catalyst.
It is a region to be reduced to.

FIG. 4 shows a second control map M2, which provides a map for calculating the NO concentration corresponding to the change in the load factor Le, with the horizontal axis representing the engine speed ratio Ne and the vertical axis representing the NO concentration. To do. FIG. 5 shows a third control map M3,
It shows how much the amount of HC added to the NO concentration should be set according to the O ₂ concentration in the exhaust gas. From the NO concentration obtained in the second control map M2 and the O ₂ concentration in the exhaust gas, the required amount of added HC can be calculated. Figure 6 shows HC
11 is a fourth control map M4 showing the relationship between the addition amount and the voltage Vo applied to the light oil injection pump equipped in the HC addition device 60. The pump provided in the HC addition device has a structure in which the discharge amount changes in proportion to the magnitude of the applied voltage. Therefore, when the addition amount of HC is given, the voltage of the pump that discharges the addition amount is set to the control map M.
You can know from 4.

FIG. 7 shows a fifth control map M5. This control map M5 is NO obtained in the second control map M2.
_{2 The} voltage applied to the corona discharge device is determined according to the concentration. The discharge voltage to be applied changes depending on the oxygen concentration in the exhaust gas. The ECU 30 calculates optimum purification conditions based on signal data from the engine and each sensor of the purification device, and controls each device. There are several means of implementing the control flow.

First Embodiment The exhaust temperature is determined by the first control map M1, the corona discharge device is operated in the low temperature region, and HC is added in the high temperature region. FIG. 8 shows a control flow of the first embodiment. Steps S1 to S from start to return
The processing up to 11 is as follows.

S1: Input of detection signals Ne, Le and Oe of the rotation speed sensor, the load sensor and the O ₂ sensor. S2: The operation area I or II is determined from the control map M1 based on the detection signals Ne and Le. S3: When it is determined in S2 that it is in the region I, the operation of the high voltage generator is stopped. S4: The NO concentration in the exhaust gas is read from the control map M2 based on the detection signals Ne and Le. S5: The amount of light oil (HC) added is read from the control map M3 from the NO concentration and the O ₂ concentration (Oe) detected in S1. S6: The drive voltage Vo of the light oil pump is determined from the control map M4 according to the amount of light oil added. S7: Send a control signal to the voltage regulator to apply the voltage Vo to the light oil pump. S8: When it is determined in S2 that the region is in the region II, the operation of the light oil pump is stopped. S9: The NO concentration in the exhaust gas is read from the control map M2 based on the detection signals Ne and Le. S10: The voltage (discharge voltage) Vh to be applied to the corona discharge portion is read by the control map M5 from the NO concentration and the O ₂ concentration (Oe) detected in S1. S11: Send a control signal to the high voltage generator so as to generate the discharge voltage Vh.

Second Embodiment In FIG. 1, a temperature sensor 52 is provided at the entrance of the corona discharge device 40, and the exhaust gas temperature data Te is sent to the ECU 30 to directly detect the exhaust gas temperature. It is operated and HC is added in a high temperature range. In FIG. 8, in step S21, an exhaust temperature sensor,
O ₂ sensor detection signal Te, Oe input. Thereafter, the process proceeds to step S2, and the same processing as in the first embodiment is performed.

Third Embodiment While the exhaust gas temperature is in the low temperature region, the corona discharge device is operated, HC is added to the exhaust gas passing through the corona discharge device, and only in the high temperature region, HC is added. In FIG. 8, after step S11, the process proceeds to step S4 and the following process is performed.

[0019]

As described above, the exhaust gas purifying apparatus of the present invention is provided with the control device for controlling the exhaust gas purifying apparatus by disposing the corona discharge device and the reduction catalyst device in series in the exhaust system of the engine. . The control device is
The corona discharge treatment section is operated to convert most of the NOx components in the exhaust gas into NO ₂ and flow it to the reduction catalyst device provided downstream of the corona discharge treatment section. At this time, not only the proportion of NO _{2 in} NOx is increased by the corona discharge treatment,
Since the temperature of the exhaust gas itself rises, the reduction reaction in the reduction catalyst device is favorably performed. When the temperature of the exhaust gas of the internal combustion engine is higher than a predetermined value, the exhaust gas is allowed to flow through the reduction catalyst device as it is without operating the corona discharge treatment section. At this time, since the exhaust gas temperature has reached a temperature at which the activity of the reduction catalyst device is sufficiently obtained,
The reduction reaction of Ox is performed well.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an apparatus according to an embodiment of the present invention.

FIG. 2 is a structural diagram of a corona discharge device.

FIG. 3 is a first control map included in the control device.

FIG. 4 is a second control map included in the control device.

FIG. 5 is a third control map included in the control device.

FIG. 6 is a fourth control map included in the control device.

FIG. 7 is a fifth control map included in the control device.

FIG. 8 is a flowchart of control processing.

FIG. 9 is a graph showing characteristics of a reduction catalyst.

FIG. 10 is a graph showing the characteristics of the reduction catalyst.

[Explanation of symbols]

 10 Engine 14 Exhaust Pipe 20 Load Sensor 22 Rotation Sensor 30 Control Device 40 Corona Discharge Device 52 Exhaust Temperature Sensor 54 Oxygen Concentration Sensor 60 Hydrocarbon Supply Device 70 High Voltage Generation Device 80 Reduction Catalyst Device

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B01D 53/86 ZAB 53/94 B01D 53/36 101 B

Claims (2)

[Claims] 1. A corona discharge device disposed in the middle of an exhaust pipe of an internal combustion engine for treating corona discharge of exhaust gas, a high voltage generator for supplying a high voltage to the corona discharge device, and a downstream side of the corona discharge device. Is provided with a reduction catalyst device, means for discriminating the temperature of exhaust gas, and a control device, and the control device issues a command to the high-voltage generation device to issue a corona discharge when the exhaust gas temperature is equal to or lower than a predetermined value. Exhaust gas purification device for internal combustion engine that operates the device. 2. A corona discharge device which is disposed in the middle of an exhaust pipe of an internal combustion engine and treats exhaust gas by corona discharge, a high voltage generator which supplies a high voltage to the corona discharge device, and a downstream side of the corona discharge device. Of the reduction catalyst device, a hydrocarbon supply device that supplies hydrocarbons as a reducing agent to the inlet side of the reduction catalyst device, a rotation sensor of the internal combustion engine, a load sensor of the internal combustion engine, and a reduction catalyst device of the reduction catalyst device. An oxygen sensor for detecting the oxygen concentration in the exhaust gas provided on the inlet side, and a control device are provided, and the control device determines the exhaust gas temperature based on the data from the rotation sensor and the load sensor of the internal combustion engine, and nitrogen oxides. Based on the data from the nitrogen oxide concentration and the oxygen sensor, the means to determine the amount of hydrocarbons to be added based on the nitrogen oxide concentration and the data from the oxygen sensor. An exhaust gas purifying apparatus for an internal combustion engine, comprising means for controlling a discharge voltage supplied to the corona discharge device, and issuing a command to the high voltage generator to operate the corona discharge device when the exhaust gas temperature is equal to or lower than a predetermined value.