JP3147193B2 - Exhaust gas purification system for diesel engine - Google Patents

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 a diesel engine.

[0002]

2. Description of the Related Art Corona discharge is performed in an exhaust gas stream containing nitrogen oxides (NO _x ) to activate NO _x , and this gas is brought into contact with an adsorbent catalyst such as activated alumina to remove NO _x . For example, Japanese Unexamined Patent Publication No. Sho 51-6171
No. 6,086,045.

[0003]

In the case of a diesel engine, the concentration of oxygen (O ₂ ) in the exhaust gas is higher than that of a gasoline engine.
With O _X is activated, O ₂ is also activated, and reacted with N ₂ molecules becomes a NO or NO _2, a phenomenon that NO _X is increased from the beginning occurs. Therefore, according to the present invention, as a result of various experiments, when hydrocarbon (HC) is added to the exhaust gas stream of a diesel engine having a high O ₂ concentration and corona discharge is applied to the gas stream, HC is converted to CO _2. An intermediate product is produced beforehand, and it is confirmed that the intermediate product reacts with NO _X to be reduced to N ₂ , and an exhaust gas purifying apparatus for a diesel engine utilizing this phenomenon is provided. The temperature of the exhaust gas of the diesel engine is lower than the exhaust gas temperature of the gasoline engine, and the efficiency of the purifying device based on the above-described principle is good for low-temperature exhaust gas. However, for a high-temperature exhaust gas, a single catalyst without corona discharge can achieve higher efficiency. Therefore, in the present invention, these two
NO in all operating ranges by combining different types of catalysts
It is intended to provide an apparatus for achieving purification of _X.

[0004]

The exhaust gas purifying system of a diesel engine according to the present invention has, as basic means, a first purifying unit and a second purifying unit connected to an exhaust pipe of a diesel engine. A muffler, a high voltage generator for applying corona discharge to the first purification unit, a valve provided in a pipe for adding light oil into an exhaust pipe on the upstream side of the muffler, and an input from a sensor provided in a diesel engine and an exhaust pipe. And a control unit for sending an output signal to the high voltage generator and the valve based on the signal.

[0005]

[Action] NO _X control unit, when exhaust gas temperature of the diesel engine is in a state below the set value, and a function of adding the oil to open the valve with operating the high voltage generator. When the exhaust gas temperature is low, the first purification unit mainly performs the purifying operation, and when the exhaust gas temperature is high, the second purification unit mainly functions.

[0006]

FIG. 3 is an explanatory view showing the principle of the present invention. A plate electrode 60 is attached to the cylindrical reaction tube 10, and the catalyst 20 is filled on the plate electrode 60. Flat plate electrode 60
Is, for example, a conductive material formed in a mesh shape, through which the exhaust gas G can freely pass. The plate electrode 60 is grounded via a line 62. Catalyst 2
0 is, for example, activated alumina (γ-alumina) or SiO ₂
And Al ₂ O ₃ combined zeolitic catalyst from example mordenite (H-ZSM5) is obtained by the pellets. It is known that these catalysts are effective in reducing and removing nitrogen oxides. A plate electrode 70 is disposed above the catalyst 20 in the reaction tube 10, and a hydrocarbon HC supply device 30 is provided further upstream of the plate electrode 70 .

The flat electrode 70 is connected to the high voltage generator 40 via a line 42. The high voltage generator 40 is
For example, a high voltage waveform is generated by a rotary gap method, and a high voltage pulse waveform as shown in FIG. 5 is generated. The waveform has a peak value of, for example, 10 to 20 KV and is about 500 Hz. The pulse voltage plate electrode 70 that received waveform to generate a corona discharge electrostatic. Flowing a simulated gas G corresponding to the exhaust gas of the diesel engine to the reaction tube 10, by generating corona discharge in the gas stream with added hydrocarbon HC, it was studied removed state of the NO _X in the gas stream.

FIG. 7 shows discharge energy on the horizontal axis and N on the vertical axis.
A graph in which took purification rate of O _X, NO _X although the exhaust gas temperature difference is found to be able to efficiently removed. The waveform of the high voltage that generates the corona discharge may be an AC voltage shown in FIG. As the AC voltage, for example, an AC waveform of 10 to 20 kHz is obtained using an inverter. Corona discharge using a pulse voltage or an AC voltage has an effect that stability is higher than that of a conventional DC discharge. FIG. 4 shows a first embodiment of an exhaust gas purifying apparatus for a diesel engine created based on the above principle. The exhaust gas purifying apparatus generally denoted by reference numeral 100A has a cylindrical casing 110, a honeycomb-shaped carrier catalyst 120 is inserted into the casing 110, and the downstream side of the gas G is supported by the flat electrode 130. . The plate electrode 130 is, for example, a wire mesh and is grounded via a line 132. The honeycomb carrier catalyst 120 is formed by molding a ceramic material such as cordierite into a honeycomb structure and coating the same with activated alumina. On the upstream side of the honeycomb carrier catalyst 120 in the casing 110, a plate electrode 170 is provided.
And connected to the rotary spark gap 152 of the high voltage generator 150 via the line 172 . The hydrocarbon supply device 160 is connected to a tank such as light oil or gasoline, and injects a required amount of hydrocarbon into the flow of the exhaust gas G. The exhaust gas mixed with hydrocarbons is activated in the corona discharge, and the reaction is promoted by the catalyst to be purified.

FIG. 8 shows an embodiment having a more specific structure of an exhaust gas purifying apparatus utilizing this principle. The exhaust gas purifying apparatus generally denoted by reference numeral 200 has a cylindrical casing 210, and an outer cylinder 220 on the inlet side serving as an inlet for the exhaust gas G and an outer cylinder 230 on the outlet side are connected. Immediately after the outer cylinder 220 on the inlet side of the casing 210, a first plate electrode 250 supported by a ring-shaped first insulating member 240 is provided. The first insulating member 240 is made of, for example, an insulator, and a concave portion is provided in a ring-shaped outer peripheral portion. As the plate electrode 250, for example, a stainless steel wire net is used. The first insulating member is fixed to the inside of the casing 210 using a pin-shaped insulating member 260 inserted into a hole provided in a casing made of a conductive material and a bolt / nut 270.

The first plate electrode 250 is connected to a bolt / nut 270 which is a conductive member.
0 to the high voltage generator 500. A second flat plate electrode 320 is fixed to the center of the casing 210 by bolts and nuts 330.
0 is connected to ground via line 340. Between the first insulating member 240 and the second plate electrode 320, a first honeycomb carrier catalyst 300 provided with a buffer material 310 on the outer periphery is inserted. In the vicinity of the outlet side of the casing 210, the third plate electrode 360 is connected to the second insulating member 350.
Installed by The third plate electrode 360 and the insulating member 350 have the same structure as the first plate electrode 250 and the insulating member, and are fixed at predetermined positions by a pin-shaped insulating member 370 and a bolt / nut 380. The third plate electrode 360 is connected to the high voltage generator 50 via a line 390.
Connected to 0.

Between the second plate electrode and the second insulating member 350, a second honeycomb carrier catalyst 400 provided with a buffer material 410 on the outer periphery is inserted. Outer cylinder 2 for exhaust gas G
On the upstream side of 20 is supplied devices arranged of the NO _X reducing agent (not shown), and supplies the required amount of hydrocarbon and gas oil. The first plate electrode 250 and the third plate electrode 360 supplied with a high voltage from the high voltage generator 500 are connected to the second plate electrode 32.
A pulse corona or an AC corona is discharged toward zero. Two honeycomb carrier catalysts 30 under corona discharge
0,400 effectively removing NO _X in the exhaust gas G of a diesel engine. Note that, by arranging three or more units of the electrode and the honeycomb carrier catalyst in series, a more effective exhaust gas purifying device can be configured.

FIG. 1 is an explanatory view showing an outline of an exhaust gas purifying system for a vehicle-mounted diesel engine provided with a purifying device in which a catalyst involving corona discharge described above and a honeycomb catalyst are combined. A diesel engine, generally designated by the reference numeral 600, is supplied with fuel by a fuel injection pump 610. The fuel injection pump 610 is provided with a rotation sensor 612 and a load sensor 614, and the rotation speed and load state of the engine detected by the sensors are transmitted to the control unit 700 as input information via a line. The exhaust gas of the diesel engine is sent to a particle trap 640 via an exhaust pipe 630, and particles in the gas are captured. The exhaust gas that has exited the particle trap 640 is sent to the muffler 800.
60 and an oxygen (O ₂ ) sensor 662 are provided, and a light oil supply pipe 655 is attached. A valve 650 is attached in the middle of the light oil supply pipe 655, and controls the opening of the supply pipe 655 in accordance with a command from the control unit 700. A first purification unit 200 and a second purification unit 900 are provided in a casing 810 of the muffler 800.
Are arranged in series.

The first purification unit 200 has the same configuration as that of the apparatus described with reference to FIG. 8, and is provided between the first plate electrode 250 and the second plate electrode 320, and between the second plate electrode 320 and the second plate electrode 320. Honeycomb carrier catalysts 300 and 400 are inserted between the three plate electrodes 360, respectively. As the catalyst, for example, activated alumina is used. First and third plate electrodes 250 and 36
0 is the high voltage generator 50 via lines 280, 390
0 is connected to the rotary gap 520. Second plate electrode 320 is grounded via line 340.
The first purification unit 200 is provided with a low-temperature exhaust gas G.
More effective against Therefore, the temperature sensor 660
Temperature of the exhaust gas G detected by the
If the temperature is equal to or lower than the set temperature, the control unit 700 opens the valve 650 to add light oil to the exhaust gas, activates the high-voltage generator 500, and causes the first purification unit 200 to function.

When the temperature of the exhaust gas G becomes equal to or higher than the set temperature, the control unit 700 closes the valve 650 to stop the addition of the light oil, and also stops the corona discharge. Therefore, the first purification unit functions as a simple honeycomb carrier catalyst. The second purification unit 900 disposed in series behind the first purification unit 200 is a honeycomb-type catalyst. For example, a ceramic carrier made of a ceramic material is coated with zeolite-based mordenite (H-ZSM5). It was done. This honeycomb carrier catalyst exerts a higher purification effect on the exhaust gas G having a high temperature.
Therefore, by operating the first purification unit 200 and the second purification unit 900, high purification efficiency can be obtained in the entire temperature range of the exhaust gas G. FIG. 2 shows the effect of the present invention. When the horizontal axis represents the engine speed ratio (percent) and the vertical axis represents the engine load factor (percent), the exhaust gas amount (NO) in the 13 operation mode is shown. ₆ is a graph showing a result of multiplying _X ) by a weighting factor. The first purification unit is operated in the region A where the engine speed is low and the load factor is low, and thus the exhaust gas temperature is low, and the second purification unit achieves effective purification in the region B where the exhaust gas temperature is high. I do.

[0015]

According to the present invention as described above, a purification system of exhaust gas of the diesel engine, the exhaust gas NO _X
Since the first purification unit and a honeycomb-supported catalyst for the reducing agent is added purify NO _X by giving the corona discharge in the presence of a catalyst have configured system combined in series, the total temperature of the exhaust gas High purification efficiency can be obtained in the region. Thus, by controlling the system according to the operating condition of the diesel engine, it is possible to achieve a cleaning effective NO _X in the entire operating range of the engine.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of a system according to the present invention.

FIG. 2 is a graph showing the effect of the present invention.

FIG. 3 is an explanatory view showing an example of a basic structure of the present invention.

FIG. 4 is an explanatory view showing a basic structure of a first purification unit.

FIG. 5 is an explanatory diagram showing a waveform of a pulse voltage.

FIG. 6 is an explanatory diagram showing a waveform of an AC voltage.

FIG. 7 is a graph showing an effect.

FIG. 8 is an explanatory diagram showing a specific structure of a first purification unit.

[Explanation of symbols]

10 reaction tube 20 catalyst pellets 30 hydrocarbon feed device 40 high voltage generating equipment 6 0 plate electrode 200 first purification unit 500 the high voltage generator 600 diesel engine 630 exhaust pipe 800 muffler 900 second purification unit

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁷ identification code FI F01N 3/24 F01N 3/24 J (58) Investigated field (Int.Cl. ⁷ , DB name) F01N 3/08 F01N 3 / 20 F01N 3/24

Claims (1)

(57) [Claims] 1. A muffler having a first purification unit and a second purification unit connected to an exhaust pipe of a diesel engine, a high voltage generator for applying corona discharge to the first purification unit, and an upstream side of the muffler The output signal to the valve provided in the pipe for adding light oil to the exhaust pipe of the diesel engine and the valve provided in the high voltage generator and the pipe for adding light oil based on the input signal from the sensor provided in the exhaust pipe The control unit is installed in the pipeline that activates the high-voltage generator and adds light oil when the exhaust gas temperature of the diesel engine is below the set value.
Diesel engine exhaust gas purification system comprising includes a an open function for adding light oil valve to be.