JPH1150835A - Exhaust emission control device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To add an HC component to an NOx emission control catalyst to improve emission control performance without lowering fuel economy. SOLUTION: A catalyst converter is provided in an engine exhaust system, and an NOx emission control catalyst, composed of zeolite carrying active metal, is provided on the catalyst converter. A normal injection controlling means, for injecting fuel in the last period in a compression stroke, and an injection controlling means in a suction stroke are provided on an ECU for controlling fuel injection. The fuel is injected by an injector by the injection controlling means in the suction stroke in the first period in the suction stroke (a crank angle is between A-B); and the injected fuel is dispersed in the whole combustion chamber, and then is burnt concurrently with the fuel injection in the last period in the compression stroke. An HC component is included much in the combustion gas to improve the emission control performance of the NOx emission control catalyst.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an exhaust gas purifying apparatus for an engine, and more particularly to an exhaust gas purifying apparatus for a diesel engine having a NOx purifying catalyst in an exhaust system.

[0002]

2. Description of the Related Art Conventionally, in an engine of an automobile or the like, a catalyst is provided in an exhaust system to purify exhaust gas after combustion. As such a catalyst for purifying exhaust gas, a three-way catalyst is often used. The three-way catalyst is composed of three harmful components contained in the exhaust gas, which particularly affect the environment, namely, carbon monoxide (CO),
It exhibits excellent purification characteristics for hydrocarbons (HC) and nitrogen oxides (NOx).

However, in a diesel engine,
Since combustion is performed in an oxygen excess state more than the stoichiometric air-fuel ratio (air / fuel = 14.7), reflecting the air-fuel ratio at the time of combustion,
The composition of the exhaust gas after combustion is also in an oxygen-excess state. However, the conventional three-way catalyst has a problem that the NOx purification performance is extremely reduced under an oxygen-excess atmosphere (lean atmosphere), so that NOx cannot be removed effectively. For this reason, for a diesel engine, a catalyst exhibiting excellent NOx purification characteristics even in a lean atmosphere (hereinafter referred to as a NOx purification catalyst), such as a metal-supported zeolite that decomposes and purifies NOx into N ₂ by NOx and HC, is used. Came to be used.

[0004] In recent years, it has been known that the NOx purification rate of this type of NOx purification catalyst is improved by adding an HC component. Attempts have been made to improve the characteristics of the NOx purification catalyst by adding and supplying fuel to the exhaust gas by utilizing this characteristic.

For example, in Japanese Utility Model Laid-Open No. 3-68516, a zeolite catalyst is provided in an exhaust system, and a fuel component (H) is added to the exhaust gas after combustion by using an injector for supplying fuel.
(C component) is disclosed.

[0006]

However, in the above-mentioned diesel engine, the fuel added to the NOx purification catalyst does not contribute to combustion at all. For this reason, some fuels are wasted without extracting combustion energy,
As a result, fuel economy has been reduced. In other words, it was difficult to say that the fuel was being used efficiently enough.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an exhaust gas in which an HC component is added to a NOx purification catalyst to improve its purification performance without reducing fuel consumption. It is to provide a purification device.

[0008]

Means for Solving the Problems In order to achieve the above object, the present inventors focused on the following points.

That is, as a means for adding the HC component to the NOx purification catalyst, the waste gas is exhausted by supplying the combustion gas containing a large amount of the HC component instead of directly supplying the unburned fuel to the NOx purification catalyst. Fuel can be eliminated. In other words, by performing combustion that includes a large amount of HC components after combustion, the fuel plays two roles of generating torque by combustion and improving the purification performance of the NOx purification catalyst, thereby suppressing a decrease in fuel efficiency. We devised that.

[0010] Based on such a viewpoint, the present invention, apart from the normal injection for generating torque at the end of the compression stroke,
Fuel injection is performed in the intake stroke for the purpose of generating combustion gas containing a large amount of HC components.

More specifically, the invention according to claim 1 is an exhaust gas purifying apparatus for a diesel engine comprising a fuel injection means for injecting fuel into a combustion chamber and a NOx purifying catalyst provided in an exhaust system. A normal injection means for causing the fuel injection means to perform fuel injection at the end of the compression stroke to cause combustion in the combustion chamber; and an intake stroke injection means for performing fuel injection to the fuel injection means during an intake stroke. It is what you have decided.

[0012] According to the above-described aspects of the invention, the fuel injected during the intake stroke mixes well with the intake air and is widely dispersed throughout the combustion chamber. Then, combustion is performed in the combustion chamber by the normal injection performed at the end of the compression stroke, and the fuel injected in the intake stroke becomes a combustion gas containing a large amount of HC components. As a result, the combustion gas discharged from the combustion chamber is H
As a result, a large amount of the C component is contained, and the purification performance of the NOx purification catalyst is improved. Therefore, the amount of generated NOx can be reduced without lowering the fuel efficiency.

According to a second aspect of the present invention, there is provided the exhaust gas purifying apparatus for a diesel engine according to the first aspect, wherein
The Ox purification catalyst is a catalyst that adsorbs hydrocarbons in exhaust gas and purifies nitrogen oxides using the hydrocarbons as a reducing agent.

According to the above-mentioned invention specific matter, H in the exhaust gas
The C component is adsorbed by the catalyst, and the HC component purifies NOx with the help of the NOx purifying catalyst.

According to a third aspect of the present invention, there is provided the exhaust gas purifying apparatus for a diesel engine according to the second aspect.
The Ox purification catalyst is a zeolite-based catalyst supporting an active metal.

According to the above-mentioned specific features of the invention, a NOx purification catalyst can be obtained with a specific configuration.

According to a fourth aspect of the present invention, in the exhaust gas purifying apparatus for a diesel engine according to the first aspect, the intake stroke injection means executes the fuel injection in the first half of the intake stroke.

According to the above-mentioned invention, the fuel injected in the intake stroke is easily dispersed by the intake air, and is easily spread in the combustion chamber. Therefore, the combustion gas contains more HC components, and the purification performance of the NOx purification catalyst is further improved.

According to a fifth aspect of the present invention, in the exhaust gas purifying apparatus for a diesel engine according to the first aspect, the intake stroke injection means injects fuel toward the top of the piston.

According to the above aspect of the invention, the fuel injected during the intake stroke collides with the top of the piston, is atomized, and easily spreads throughout the combustion chamber. As a result, the combustion gas contains more HC components, and the purification performance of the NOx purification catalyst is further improved.

[0021]

Embodiments of the present invention will be described below with reference to the drawings.

First, the overall configuration of the engine 1 according to the present embodiment will be described. Engine 1 is a diesel engine. As shown in FIG. 1, four cylinders 5 are arranged in a row on an engine body 2 of the engine 1. These cylinders 5 are respectively connected to four independent intake pipes 4 branched from the surge tank 3, and are configured so that fresh air is introduced through these intake pipes 4.

A so-called common rail 6 is provided for the engine body 2. The common rail 6 is a type of fuel injection device that stores high-pressure fuel and supplies fuel to the combustion chamber of each cylinder 5 based on a control signal from a control unit (ECU) 40.

Each cylinder 5 is provided with an injector 7 for injecting fuel by operating a needle valve by a solenoid according to a control signal. These injectors 7 serving as fuel injection means are connected to the common rail 6.

The common rail 6 is connected to a fuel pump 9 via a fuel passage 8, and the pump 9 is connected to a fuel tank (not shown). Therefore, the fuel pumped from the fuel pump 9 is supplied to each injector 7 via the common rail 6. A pressure regulating valve 10 is provided in the fuel passage 8. This pressure regulating valve 10
Is a pressure adjusting means for adjusting the pressure of fuel sent to the common rail 6 to adjust the injection pressure of the injector 7. Therefore, the injection pressure is adjusted by operating the pressure regulating valve 10 according to the control signal. A pressure sensor 11 is provided on the common rail 6, and the pressure sensor 11 detects an injection pressure.

The exhaust system of the engine 1 has an exhaust manifold 12 for collecting exhaust gas discharged from each cylinder 5.
And an exhaust pipe 13 connected to the exhaust manifold 12.

In the middle of the exhaust pipe 13, a catalytic converter 14 having a NOx purification catalyst made of metal-supported zeolite is installed. As the metal-supporting zeolite, for example, a zeolite such as Y-type, β-type, mesopore, MFI, or the like, on which a noble metal such as Pt, Rh, or Ir, or an active metal such as a transition metal Cu is used is used.

Next, a specific configuration of the engine 1 will be described. As shown in FIG. 2 and FIG.
A piston 23 is vertically slidably inserted into the cylinder formed by the above. The lower surface of the cylinder head 24 attached to the upper portion of the cylinder block 21 and the inner peripheral surface of the cylinder block 21 (the wall surface of the cylinder)
And the upper surface of the piston 23, a combustion chamber 25 is defined.

The cylinder head 24 is provided with two air supply ports 26 communicating with the combustion chamber 25 from one side, respectively.
Two exhaust ports 27 are respectively provided from the other side to the combustion chamber 25. As shown in FIG. 3, the openings 26 of these ports 26 and 27 to the combustion chamber 25 are formed.
a, 27a are arranged in a square shape on the lower surface of the cylinder head. On / off valves 28 and 29 are provided in these ports 26 and 27, respectively. That is, an intake valve 28 that opens and closes an opening 26 a of each air supply port 26 and an exhaust valve 29 that opens and closes an opening 27 a of each exhaust port 27 are provided. The valve stems 28a, 29a of the intake valve 28 and the exhaust valve 29 penetrate the cylinder head 24 and protrude upward. The umbrella portions 28b, 29b connected to the respective valve shaft portions 28a, 29a are connected to the respective ports 26, 27.
The openings 26a and 27a are closely attached to and separated from the valve seat 30 respectively.

The cylinder head 24 has a combustion chamber 2
Step-shaped injector insertion hole 3 opening at the center of 5
1 are provided vertically. The injector 7 is attached to the injector insertion hole 31. In other words, the injector 7 is inserted into the injector insertion hole 31 in a state where the fuel injection portion 7a at the tip thereof is exposed in the combustion chamber 25.
Has been inserted. In other words, the fuel injection section 7a is provided at a position facing the upper surface of the piston 23. Then, the two mounting bolts 32 penetrate through the fixed plate 33 supported on the upper surface of the flange portion 7b at the intermediate portion of the injector 7, and are screwed into the cylinder head 24,
The injector 7 and the cylinder head 24 are integrated.

As shown in FIG. 4, the injector body 10
A nozzle 102 having a fuel injection section 7a swelling downward is provided integrally with a lower portion of the nozzle 1. This fuel injection unit 7
As shown in FIG.
Four injection holes 106 opening to 5 are arranged in a cross shape in a plan view. An oil chamber 10 for temporarily storing fuel is provided around a needle valve 103 slidably inserted in the nozzle 102.
4 are provided. A fuel supply pipe 15 is provided at a flange portion 7b provided at an intermediate portion of the injector body 101.
A fuel inlet 107 for introducing fuel supplied through the fuel inlet 107 is provided, and the fuel introduced from the fuel inlet 107 is supplied to the oil chamber 104 through the fuel supply passage 108. A plunger (not shown) organically coupled to the needle valve 103 is slidably inserted in an intermediate portion of the injector main body 101. The plunger is operated based on a control signal from the ECU 40 described later. The opening and closing of the needle valve 103 is controlled by moving up and down.

As shown in FIG. 1, the engine 1 is provided with a control unit (ECU) 40. The ECU 40 includes a signal from a crank angle sensor 41 for detecting an engine crank angle, a signal from an engine load sensor 42 for detecting an engine load, and a signal from an accelerator opening sensor 49 for detecting an amount of depression of an accelerator pedal. A signal from a water temperature sensor 43 for detecting an engine water temperature, a signal from an intake air temperature sensor 49b for detecting an intake air temperature, and a combustion chamber 25 installed in the exhaust manifold 12.
A signal from the first exhaust gas temperature sensor 44 for detecting the temperature of the exhaust gas immediately after being discharged from the fuel cell, and a second exhaust gas temperature sensor 45 for detecting the temperature of the exhaust gas immediately upstream of the catalytic converter 14
And a signal from a third exhaust gas temperature sensor 46 that detects the temperature of the exhaust gas immediately downstream of the catalytic converter 14.
Catalyst temperature sensor 4 for detecting the temperature of catalytic converter 14
7 by controlling the operation of the fuel pump 9, the pressure regulating valve 10, and the injector 7 based on these signals, so that the main injection is performed near the compression top dead center of each cylinder 5. The normal injection to be performed and the intake stroke injection for injecting fuel in the intake stroke of each cylinder are performed. Note that the normal injection is a fuel injection performed for the main purpose of generating torque by burning the injected fuel. On the other hand, the intake stroke injection is a fuel injection mainly performed to generate a combustion gas containing a large amount of HC components.

As shown in FIG. 6, the ECU 40 is provided with a normal injection control means 51 and an intake stroke injection control means 52 as an exhaust gas purification system 50.

Next, the fuel injection control by the exhaust gas purification system 50 will be described.

As shown in FIG. 7, from the position where the piston 23 is at the top dead center, that is, the position where the crank angle is 0 °, the intake valve 28 opens and air (fresh air) starts to be introduced into the combustion chamber 25. The first crank angle belongs to the first half of the intake stroke.
When the predetermined angle A is reached, the solenoid of the injector 7 is energized by the intake stroke injection control means 52, and fuel is injected from the fuel injection section 7a. Thereafter, the injection is continued until the crank angle reaches a second predetermined angle B belonging to the first half of the intake stroke, and when the crank angle exceeds the second predetermined angle B, the injection is stopped. That is, intake stroke injection for injecting fuel is performed within a predetermined period of the first half of the intake stroke. Thereafter, the piston 23 continues to descend further, and air continues to be introduced through the air supply port 26 until the bottom dead center at which the crank angle reaches 180 °.
At that time, the fuel injected in the intake stroke injection is mixed with the introduced air and dispersed throughout the combustion chamber 25.

The piston 23 that has reached the bottom dead center changes from descending to rising, and the compression stroke starts. When the crank angle reaches a predetermined angle C belonging to the end of the compression stroke, fuel is injected from the injector 7 by the normal injection control means 51,
Normal injection is performed.

Each fuel injected in the intake stroke injection and the normal injection is burned in the combustion chamber 25, and a torque is generated in the expansion stroke. At this time, the gas after combustion contains not less than 10% of oxygen and also a large amount of HC components. The reason will be described below.

For example, as disclosed in page 83 of the preprints 963 (1996-5) of the Society of Automotive Engineers of Japan, generally, when the injection timing is advanced from the top dead center, the combustion gas The NOx component therein increases while the HC component decreases. However, when the injection timing is further advanced,
Conversely, the NOx component decreases while the HC component increases. This is considered to be due to the fact that the earlier the injection timing, the more easily the fuel spreads over the entire combustion chamber, the more easily the combustion occurs simultaneously over the entire combustion chamber, the lower the temperature of the combustion field, and the like. Therefore, the fuel injected by the intake stroke injection becomes a combustion gas containing a large amount of HC components after combustion.

Then, the operation shifts from the expansion stroke to the exhaust stroke.
The combustion gas containing a large amount of the C component is discharged from the combustion chamber 25. The exhaust gas flows through the catalytic converter 14 after passing through the exhaust manifold 12 and the exhaust pipe 13. And
The NOx component in the exhaust gas is
It is purified by the Ox purification catalyst. At this time, H in the exhaust gas
The C component is adsorbed on the NOx purification catalyst and improves the purification performance of the catalyst. That is, a portion of the HC component by partial oxidation of the active species CO ^-, and this CO ^- by reacting with NOx in the NOx purification catalyst help, NOx will be reduced N ₂ and CO _2.

Therefore, the purification performance of the NOx purification catalyst is improved, and the amount of NOx discharged outside the system is reduced.

As described above, according to the purification control system 50, the fuel injection is performed in the intake stroke separately from the normal injection performed at the end of the compression stroke, so that the HC component of the combustion gas can be increased. . Therefore, the HC component can be supplied to the NOx purification catalyst without discharging the unburned fuel to the exhaust system. Therefore, the combustion energy can be extracted from all the fuel injected into the combustion chamber, and the purification performance of the NOx purification catalyst can be improved. As a result, the amount of generated NOx can be further reduced without lowering fuel efficiency.

In particular, since the intake stroke injection is performed in the first half of the intake stroke, the injected fuel is easily mixed with the intake air and spread over the entire combustion chamber 25. Therefore, the HC component contained in the combustion gas increases, and the purification performance of the NOx purification catalyst can be further improved.

<Other Embodiments> Regarding the intake stroke injection, the following embodiment may be used in addition to the above embodiment.

The injection pressure in the intake stroke may be higher than the normal injection pressure. As a result, the fuel injected during the intake stroke is more easily dispersed, and as a result, the HC component contained in the combustion gas further increases.
Therefore, the purification performance of the NOx purification catalyst is further improved.

In the intake stroke injection, the fuel may be injected toward the upper surface of the piston so that the injected fuel is atomized. That is, the fuel injection section 7 a of the injector 7 may be configured so that the injected fuel is injected toward the top of the piston 23.

When the engine is at full load, since the combustion chamber 25 is relatively hot, the fuel injected in the intake stroke may burn before the end of the compression stroke. Therefore, when the load of the engine is equal to or more than the predetermined value, the intake stroke injection may be prohibited. This makes it possible to prevent abnormal combustion from occurring.

In the above embodiment, fuel is injected in the first half of the intake stroke. However, fuel may be injected in the second half of the intake stroke.

[0048]

As described above, according to the present invention, the following effects are exhibited.

According to the first aspect of the present invention, by injecting fuel in the intake stroke, the fuel is widely dispersed throughout the combustion chamber. Therefore, the combustion gas contains a large amount of the HC component, and the purification performance of the NOx purification catalyst is improved. That is, the fuel generates combustion energy and improves the purification performance of the NOx purification catalyst. Therefore, the amount of generated NOx can be reduced without lowering fuel efficiency.

According to the second and third aspects of the present invention, it is possible to obtain a catalyst capable of reducing the generation amount of NOx without lowering the fuel consumption with a specific structure.

According to the fourth aspect of the present invention, the fuel injected during the intake stroke can be easily dispersed in the combustion chamber, and the HC component contained in the combustion gas can be increased. Therefore, the purification performance of the NOx purification catalyst can be further improved.

According to the fifth aspect of the invention, the fuel injected during the intake stroke can be atomized, and the fuel can be more widely dispersed in the combustion chamber. Therefore, the HC component contained in the combustion gas can be further increased,
The purification performance of the NOx purification catalyst can be further improved.

[Brief description of the drawings]

FIG. 1 is an overall configuration diagram of a purification control system of an engine.

FIG. 2 is an enlarged sectional view of a part of the engine.

FIG. 3 is a sectional view taken along line AA of FIG. 2;

FIG. 4 is a partially cutaway longitudinal sectional view of the injector.

FIG. 5 is a sectional view taken along line BB of FIG. 4;

FIG. 6 is a block diagram of an exhaust gas purification system.

FIG. 7 is a time chart of fuel injection control.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 3 Surge tank 6 Common rail 7 Injector 9 Fuel pump 10 Pressure regulating valve 11 Pressure sensor 14 Catalytic converter 40 ECU 41 Crank angle sensor 50 Exhaust gas purification system 51 Normal injection control means 52 Exhaust stroke injection control means

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI F02M 61/14 310 B01D 53/36 101B (72) Inventor Mitsunori Kondo 3-1, Fuchu-cho Shinchi, Aki-gun, Hiroshima Mazda

Claims (5)

[Claims] An exhaust gas purifying apparatus for a diesel engine comprising a fuel injection means for injecting fuel into a combustion chamber and a NOx purification catalyst provided in an exhaust system, wherein fuel is injected into the fuel injection means at the end of a compression stroke. Exhaust gas of a diesel engine, comprising: a normal injection means for causing the fuel injection means to perform fuel injection during an intake stroke. Purification device. 2. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the NOx purifying catalyst is a catalyst that adsorbs hydrocarbons in the exhaust gas and purifies nitrogen oxides using the hydrocarbons as a reducing agent. An exhaust gas purifier for a diesel engine. 3. The exhaust gas purifying apparatus for a diesel engine according to claim 2, wherein the NOx purifying catalyst is a zeolite catalyst carrying an active metal. 4. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the intake stroke injection means executes fuel injection in a first half of the intake stroke. 5. The exhaust gas purifying apparatus for a diesel engine according to claim 1, wherein the intake stroke injection means injects fuel toward a top of the piston.