JPH07208150A - Feeding device of reducer for exhaust gas catalyst - Google Patents

Abstract

PURPOSE:To provide a feeding device of reducer for exhaust gas catalyst which can avoid the blocking of a spit hole by a carbide when HC as a reducer is fed to an exhaust system. CONSTITUTION:To the exhaust pipe 3 of a diesel engine 1, a lean NOx catalyst 9 is provided. The case 11 of a reducer feeding device 10 is fixed to the lower surface of the exhaust pipe 3. A gas feeding passage 17 whose lower end is opened to a space 12, and its upper end is opened to the exhaust pipe 3, is formed to the case 11. An ECU 21 drives an electric fuel pump 19 to feed a light oil to the space 12, and by heating the heating part of a heater 14 so as to heat the light oil, an HC having few carbon number in the molecule is produced, which is fed to the upstream side of the lean NOx catalyst 9 in the exhaust pipe 3 through the gas feeding passage 17. In this case, the case 11 is made at a high temperature by the heater 14, and the front end opening of the gas feeding passage 17 provided to the part of the case 11 is also maintained at a high temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reducing agent supply device for an exhaust catalyst, and more specifically, to a lean NO _x catalyst arranged in an exhaust system of a diesel engine, for example, as a reducing agent.
The present invention relates to a reducing agent supply device for an exhaust catalyst which supplies C.

[0002]

2. Description of the Related Art In the exhaust gas regulations of diesel engines, it is required to reduce NO _x by post-treatment. A catalyst capable of reducing NO _x even in an oxygen atmosphere is being developed. An exhaust emission control device using a lean NO _x catalyst that reduces NO _x in the presence of HC in this oxidizing atmosphere is disclosed in Japanese Patent Application Laid-Open No. HEI 4-hei.
It is disclosed in Japanese Patent Laid-Open No. 175417 and Japanese Patent Laid-Open No. 4-214918. Further, in Japanese Patent Application Laid-Open No. 4-214918, a low melting point HC is generated from fuel by heating or the like, and this low melting point HC is supplied to the catalyst upstream of the exhaust pipe of the engine so that the NO _x purification rate of the lean NO _x catalyst is increased. I am trying to increase.

[0003]

However, low melting point HC
The generator and the exhaust pipe of the engine are connected by an HC supply pipe, and some of the HC generated by the low melting point HC generator is H
C is carbonized at the outlet of the C supply pipe, and HC is generated by the carbonized deposit.
There was a risk of blocking the outlet of the supply pipe. In particular,
When the exhaust gas temperature is 400 ° C. or lower, it is significantly carbonized.

Therefore, an object of the present invention is to provide a reducing agent supply device for an exhaust catalyst capable of avoiding clogging of a blow-out port due to a carbide when supplying HC as a reducing agent to an exhaust system.

[0005]

The invention of claim 1 is provided in an exhaust system of a combustor, and is N in the presence of HC in an oxidizing atmosphere.
A reducing agent supply device for a lean NO _x catalyst for reducing O _x, comprising a low carbon number HC producing means for producing HC having a small number of carbon atoms in a molecule by heating a fuel,
Said HC generated in the low carbon number HC generation means at a high temperature, the exhaust gas catalyst for the reducing agent supply apparatus that supplies to the upstream side of said lean NO _x catalyst in the exhaust system and the gist thereof.

The invention of claim 2 has as its gist the reducing agent supply device for an exhaust gas catalyst, wherein the combustor of the invention of claim 1 is an internal combustion engine. According to a third aspect of the present invention, an exhaust catalyst reduction is provided in which the tip of an HC supply pipe for supplying the HC generated by the HC generating means in the first aspect to the exhaust system is arranged at the most upstream part of the exhaust system of the combustor. The agent supply device is the gist.

[0007]

According to the first and second aspects of the invention, the low carbon number HC producing means produces the HC having a small number of carbon atoms in the molecule by heating the fuel. Then, HC generated in the low carbon number HC generation means at a high temperature, combustor (e.g., an internal combustion engine) is supplied to the upstream side of the lean NO _x catalyst in an exhaust system of an. At this time, since the HC produced by the low carbon number HC producing means is supplied in a high temperature state, carbonization of the HC due to the lowering of the temperature at the air outlet is suppressed, and the obstruction of the air outlet by the carbonized deposit of HC is avoided. It

According to a third aspect of the invention, in addition to the operation of the first aspect of the invention, the tip of the HC supply pipe for supplying the HC produced by the HC producing means to the exhaust system of the combustor is located at the end of the exhaust system of the combustor. It is located in the upstream part. Therefore, the tip portion of the HC supply pipe is exposed to the exhaust gas having a high temperature, the tip portion of the HC supply pipe becomes a high temperature, and the carbonization of HC due to the lowering of the temperature at the blowout port is suppressed. Blockage of the outlet is avoided.

[0009]

【Example】

(First Embodiment) A first embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a reducing agent supply device for an exhaust gas catalyst of this embodiment. A diesel engine 1 as a combustor is mounted on a vehicle. An intake pipe 2 and an exhaust pipe 3 are connected to the diesel engine 1. A piston 5 is arranged inside a cylinder 4 of the diesel engine 1, and a combustion chamber 6 is formed above the piston 5. The combustion chamber 6 communicates with the intake pipe 2 via an intake valve 7, and also communicates with the exhaust pipe 3 via an exhaust valve 8.

The exhaust pipe 3 is made of transition metal or noble metal.
Supported zeolite type or silicalite type
Or made of alumina, in an oxygen atmosphere in the presence of HC
NO _xTo reduce the so-called lean NO_xCatalyst 9
It is placed.

The case 11 of the reducing agent supply device 10 has a cylindrical shape and is made of iron. This iron material is a heat resistant material. The upper surface of the cylindrical case 11 is the exhaust pipe 3
Bottom surface (lower surface) of the lean NO _x catalyst 9 at the upstream side
It is fixed by welding. In addition, a cylindrical space 12 is formed in the case 11, and a screw hole 13 extending downward from the space 12 is formed. And
The heat generating portion 15 of the heat generating element 14 is disposed in the space 12 by screwing the screw portion of the heat generating element 14 into the screw hole 13. In this embodiment, a ceramic glow plug used as an electric preheater of a diesel engine is used as the heating element 14, and a rod-shaped heating portion of the ceramic glow plug is arranged in the space 12. . Then, by supplying electric power to the heating element 14 by duty control, the heating section 15 generates heat. In addition, the heating portion 15 of the heating element 14 in the space portion 12
A heating space is formed around the.

A fuel supply passage 16 extending horizontally is formed in the case 11 of the reducing agent supply device 10. One end of the fuel supply passage 16 is open to the bottom of the space 12 and the other end is the outer peripheral surface of the case 11. It is open to. A gas supply passage 17 extending in the vertical direction is formed in the case 11 of the reducing agent supply device 10. One end of the gas supply passage 17 is opened to the upper surface of the space 12 and the other end is opened to the inside of the exhaust pipe 3. ing.

One end of a fuel supply pipe 18 is connected to the fuel supply passage 16 of the case 11, and the other end of the fuel supply pipe 18 is connected to a fuel tank 20 via an electric fuel pump 19. Then, when the electric fuel pump 19 is driven, the light oil that is the fuel in the fuel tank 20 is changed to the fuel supply pipe 18
And the space 1 through the fuel supply passage 16 of the case 11.
2 is supplied.

Electronic control unit (hereinafter referred to as ECU)
Reference numeral 21 is mainly composed of a microcomputer.
A power supply circuit 22 is connected to the ECU 21, and the power supply circuit 22
Applies a battery voltage (12 volts) to the heating element 14 at a desired duty ratio in response to a command signal from the ECU 21. An electric fuel pump 19 is connected to the ECU 21, and the ECU 21 drives and controls the electric fuel pump 19. Further, an accelerator position sensor, a crank angle sensor and the like (not shown) are connected to the ECU 21 to input an accelerator position signal, a crank angle signal and the like. Then, the ECU 21 detects the operating conditions of the diesel engine 1 based on the engine speed based on the crank angle signal and the accelerator opening based on the accelerator position signal, and controls the electric fuel pump 19 and the heating element 14 according to the operating conditions.

Here, the effect of heating the fuel (light oil) by the heating element 14 in the reducing agent supply device 10 will be described. According to the experiments conducted by the present inventors, it has been found that hydrocarbons that efficiently purify NO _x with the lean NO _x catalyst 9 have 10 or less carbon atoms in the molecule, as shown in FIG. On the other hand, light oil, which is a fuel, has an average carbon number of about 15, and as shown in FIG. 3, the light oil can be decomposed by heating it to 800 ° C. or higher, and as shown in FIG. It was found that the NO _x purification rate is improved.
Further, as shown in FIG. 3, the decomposition of light oil starts at 600 ° C. or higher, but it is preferably 800 ± 50 ° C. In the present embodiment, the heating temperature of light oil is 800 ° C.

In order to generate HC having a small number of carbon atoms in the molecule from the fuel (light oil) in this way, in this embodiment, a space 1 is formed by using a ceramic glow plug as the heating element 14.
The atmosphere of 2 (heating space) was kept at 800 ° C. or higher.

Next, the supply control of the decomposition gas (HC gas having 10 or less carbon atoms) which acts as a reducing agent for NO _x will be described. In the lean NO _x catalyst 9, as shown in FIG.
The temperature range of the catalyst for purifying NO _x is limited. That is, the lower limit temperature of use is a temperature at which NO _x is purified, or a temperature at which deterioration due to low temperature poisoning of the catalyst does not occur. The upper limit temperature for use is a temperature at which NO _x is no longer purified, or a use temperature determined by the heat resistance of the catalyst. Then, the temperature range is a temperature range between the lower limit temperature of use and the upper limit temperature of use. This temperature window depends on the type of catalyst. As described above, in order to supply the cracked gas (HC gas having 10 or less carbon atoms) within the temperature window of the catalyst, the catalyst temperature may be directly measured, but in the present embodiment, the catalyst temperature is set to diesel. It is estimated from the operating state of the engine 1. That is, in a diesel engine with a small amount of HC and CO in the exhaust gas, the temperature rise due to the exothermic reaction in the catalyst is small, so the exhaust gas temperature may be regarded as the catalyst temperature,
This exhaust gas temperature can be estimated from the operating state of the diesel engine.

Therefore, regardless of the mounting position of the lean NO _x catalyst 9, as shown in FIG. 6, the region within the temperature window in the relationship between the engine speed and the accelerator opening (HC gas supply region indicated by the hatched portion). ) Is measured in advance, and the HC fuel gas is supplied by driving the electric fuel pump 19 and the heating element 14 during engine operation in this region.

In the present embodiment, the case 11, the heating element 14 and the electric fuel pump 19 heat the fuel to generate HC having a small number of carbon atoms in the molecule and thus a low carbon number H.
C generating means is configured.

Next, the operation of the reducing agent supply device thus constructed will be described. The ECU 21 detects the engine speed and the accelerator opening degree and determines from the map of FIG. 6 whether or not the vehicle is in the HC gas supply region. That is, it is determined whether or not it is within the temperature window of FIG. Then, in the HC gas supply region, the ECU 21 calculates the fuel supply amount according to the engine speed using the map of FIG. 7, and the heating element according to the engine speed using the map of FIG. The duty ratio of power supply to 14 (ceramics / glow plug) is calculated. The ECU 21 drives and controls the electric fuel pump 19 and the heating element 14 so that the fuel supply amount and the power supply duty ratio thus obtained are obtained.

As a result, the electric fuel pump 19 is controlled according to the operating conditions of the diesel engine 1, and an appropriate amount of fuel (light oil) is supplied from the fuel tank 20 to the space 12 of the case 11. In addition, a command signal is output to the power supply circuit 22 according to the operating conditions of the diesel engine 1, and electric power sufficient to raise the fuel sent to the space 12 by the electric fuel pump 19 to the decomposition temperature of 800 ° C. is generated. Body 1
4 (ceramics glow plug). As a result, in the space 12 of the case 11, fuel (light oil)
H of which the number of carbon atoms in the molecule is "10" or less
C gas is produced.

The fuel thus decomposed is introduced into the exhaust pipe 3 through the gas supply passage 17 as decomposed gas.
In the exhaust pipe 3, it is mixed with the exhaust gas and sent to the lean NO _x catalyst 9. In the lean NO _x catalyst 9, the decomposed gas acts as a reducing agent for NO _{x in} the exhaust gas and purifies NO _x .

When the decomposed gas is supplied into the exhaust pipe 3, the case 11 is also heated to a high temperature by the heating element 14 (ceramic glow plug), and the gas supply passage 17 is provided.
The carbonization of HC is avoided at the outlet of the.

As described above, in this embodiment, the case 11 of the reducing agent supply device 10 is directly fixed to the exhaust pipe 3, and the case 11 and the heating element 14 (ceramics / glow plug) are integrally formed. Since it is done, case 11
Is heated to a high temperature by the heating element 14 (ceramics / glow plug), and the gas supply passage 17 is provided in a part of the case 11.
The tip opening is also kept hot. In this way, while the generated HC is at a high temperature, the lean N in the exhaust pipe 3 is
Since then supplied to the upstream side of the O _x catalyst 9, HC outlet obstruction of the HC outlet due to carbonization of HC due to be cooled can be prevented. That is, in the conventional method (type in which HC is supplied by the gas supply pipe), HC may be carbonized, and the carbonized deposit may block the outlet of the HC supply pipe. Such a thing is prevented beforehand, and HC having a small number of carbon atoms in the molecule can be stably supplied into the exhaust pipe 3. In this way, it is possible to avoid the clogging of the air outlet due to the carbide when supplying HC as the reducing agent to the exhaust system of the diesel engine 1.

Further, since the HC outlet of the gas supply passage 17 faces upward, the HC comes into contact with the exhaust gas and is cooled to H
Even if the C gas returns to the liquid state, it only drops downward and does not block the HC outlet of the gas supply passage 17. In other words, when the HC outlet of the gas supply passage 17 faces downward, liquid HC is accumulated in the HC outlet of the gas supply passage 17 due to the surface tension, and the HC outlet of the gas supply passage 17 is blocked and HC gas is discharged. Of the gas supply passage 17 may be obstructed, but this is avoided by directing the HC outlet of the gas supply passage 17 upward. (Second Embodiment) Next, the second embodiment will be described focusing on the differences from the first embodiment.

In this embodiment, the thermal decomposition section in the case 11 is as shown in FIG. Exothermic part 15 of exothermic body 14
A Pt, Pd-based catalyst 23 is supported on the surface or the heat generating portion 15
The particles are scattered in the form of particles and are held by a wire mesh 24 in order to prevent the catalyst 23 from being scattered. The light oil decomposition effect at this time can lower the decomposition temperature as shown in FIG.

Further, as a modification of this embodiment, as shown in FIG. 11, radiating fins 25 are arranged on the surface of the heating portion 15 of the heating element 14 so that the heat of the heating element 14 can be efficiently transmitted to the catalyst 23. You may (Third Embodiment) Next, the third embodiment will be described focusing on the differences from the first embodiment.

In the present embodiment, the electric fuel pump 1
Instead of No. 9, a distributed fuel injection pump of a diesel engine is used, and the feed fuel pressure from the feed pump of the distributed fuel injection pump is used.

As shown in FIG. 12, the distribution type fuel injection pump 26 has a built-in feed pump (for example, a vane type). The feed pump has a drive shaft, and the drive shaft is drivingly connected to the crankshaft of the engine. The rotor is rotated by the rotation of the drive shaft to suck up the fuel in the fuel tank and send it to the pump chamber in the distributed fuel injection pump 26. The discharge port of the feed pump of the distributed fuel injection pump 26 is connected to the fuel supply passage 16 of the case 11 of the reducing agent supply device 10 through the throttle 27 and the electromagnetic safety valve 28. Then, a part of the fuel discharged from the feed pump of the distribution type fuel injection pump 26 is supplied into the case 11 of the reducing agent supply device 10.

With such a structure, the configuration shown in FIG.
As shown in, the HC concentration in the exhaust pipe 3 can be made constant regardless of the engine speed. This is because the supply amount of light oil increased in proportion to the pump feed pressure which increased in proportion to the increase in engine speed.

The electromagnetic safety valve 28 shown in FIG.
1, the ECU 21 closes the electromagnetic safety valve 28 when the ignition switch is turned off and when an abnormality is detected by the self-diagnosis of the ECU 21. (Fourth Embodiment) Next, the fourth embodiment will be described focusing on the differences from the first embodiment.

As shown in FIG. 14, the electric fuel pump 1
9 is a reducing agent supply device 10 through an electromagnetic flow control valve 29.
It is connected to the fuel supply passage 16 of the case 11. As a method of controlling the heating element 14 (ceramics / glow plug), as shown in FIG. Synchronize the operation (heat generation or stop). That is, the drive duty of the flow control valve 29 and the drive duty of the heating element 14 are synchronized. By doing so, it is possible to make the power (glow power) to the heating element 14 (ceramics glow plug) and the amount of decomposition of the fuel proportional. As a result, without using the map for calculating the fuel supply amount shown in FIG.
The fuel supply amount can be controlled using the map for calculating the power supply duty ratio shown in. (Fifth Embodiment) Next, the fifth embodiment will be described focusing on the differences from the first embodiment.

As shown in FIG. 16, two signal lines are provided between the ECU 21 and the power supply circuit 22 so that the ECU 21 outputs the operation signal shown in FIG. In this case, the current detection signal shown in FIG. 17 is output. In this way, the ECU 2
1, the operating signal (voltage signal;
V) is output and the current detection signal (I) is input, the resistance value R of the heating element 14 (ceramics glow plug) can be detected (R = I / V).

Further, as shown in FIG. 18, the surface temperature of the heating element 14 (ceramics / glow plug) and the heating element 14
The relationship of the resistance values of is measured in advance and is mapped. The ECU 21 stores the map in advance.

The ECU 21 calculates the resistance value R of the heating element 14 (ceramics / glow plug) from the operation signal (voltage signal) and the current detection signal to the power supply circuit 22, and the surface of the heating element 14 is calculated from the map of FIG. Estimate the temperature. And
As shown in FIG. 17, the surface temperature of the heating element 14 is controlled to reach the target temperature. (Sixth Embodiment) Next, a sixth embodiment will be described focusing on the differences from the first embodiment.

As shown in FIG. 19, the case 11 of the reducing agent supply device 10 is attached to the cylinder head 30 of the diesel engine 1 at a position close to the exhaust port 31.
Further, an HC supply pipe 32 is attached to the gas supply passage 17 of the case 11, and its tip (blowout port) is extended to a position near the exhaust valve 8.

In this way, the tip of the HC supply pipe 32 (HC
Since the gas outlet) is located near the exhaust valve 8, H
The tip of the C supply pipe 32 is exposed to the exhaust gas having the highest temperature after combustion in the combustion chamber 6, and the tip of the HC supply pipe 32 can be heated to a high temperature.

As described above, in this embodiment, the tip of the HC supply pipe 32 for supplying HC to the exhaust system is arranged at the most upstream part of the intake system of the Tiesel engine 1, that is, immediately downstream of the exhaust valve 8. The tip of the HC supply pipe 32 is exposed to exhaust gas having a high temperature, and the tip of the HC supply pipe 32 can be heated to a high temperature. Therefore, carbonization of the HC due to the temperature lowering at the outlet of the HC is suppressed, and blockage of the outlet due to the carbonized deposits of the HC is avoided.

The present invention is not limited to the above-mentioned embodiments, and the diesel engine was used as the combustor in the above-mentioned embodiments, but the invention is not limited to this.
For example, another internal combustion engine such as a gasoline engine, an external combustion engine such as a Stirling engine, a gas turbine, or
It may be embodied in a boiler or the like. In addition to light oil, liquid fuel such as kerosene, kerosene and heavy oil, and solid fuel such as coal are used as fuel. Furthermore, in the above-mentioned embodiment, although HC having a small number of carbon atoms in the molecule was produced from the fuel by thermal decomposition, HC having a small number of carbon atoms in the molecule may be produced from the fuel by fractional distillation.

[0041]

As described above in detail, according to the present invention,
It has an excellent effect that it is possible to avoid clogging of the air outlet due to carbide when supplying HC as a reducing agent to the exhaust system.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of a reducing agent supply device for an exhaust catalyst according to a first embodiment.

FIG. 2 is a characteristic diagram showing the relationship between the carbon number of hydrocarbon molecules and the NO _x purification rate.

FIG. 3 is a characteristic diagram showing a relationship between a heating temperature and a ratio of hydrocarbons having 10 or less carbon numbers.

FIG. 4 is a characteristic diagram showing a relationship between a heating temperature and a NO _x purification rate.

FIG. 5 is a characteristic diagram showing the relationship between catalyst temperature and NO _x purification rate.

FIG. 6 is a map for explaining an HC gas supply region.

FIG. 7 is a map showing a relationship between an engine speed and a fuel supply amount.

FIG. 8 is a map showing a relationship between an engine speed and a power supply duty ratio.

FIG. 9 is a main part configuration diagram of a reducing agent supply device for an exhaust catalyst according to a second embodiment.

FIG. 10 is a characteristic diagram showing a relationship between a heating temperature and a ratio of hydrocarbons having 10 or less carbon atoms.

FIG. 11 is a configuration diagram of a main part of a reducing agent supply device for an exhaust catalyst in an application example of the second embodiment.

FIG. 12 is a main part configuration diagram of a reducing agent supply device for an exhaust catalyst according to a third embodiment.

FIG. 13 is a characteristic diagram showing the relationship between the engine speed, the HC concentration in the exhaust pipe, and the feed pump pressure.

FIG. 14 is a main part configuration diagram of a reducing agent supply device for an exhaust gas catalyst according to a fourth embodiment.

FIG. 15 is a waveform diagram showing drive signals for a flow rate control valve and a heating element.

FIG. 16 is a main part configuration diagram of a reducing agent supply device for an exhaust catalyst according to a fifth embodiment.

FIG. 17 is a time chart showing various waveforms, temperature changes, and resistance value changes.

FIG. 18 is a map showing the relationship between the surface temperature of the heating element and the resistance value.

FIG. 19 is a configuration diagram of main parts of a reducing agent supply device for an exhaust gas catalyst according to a sixth embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Diesel engine as a combustor 9 Lean NO _x catalyst 11 Case constituting low carbon number HC generating means 14 Heating element constituting low carbon number HC generating means 19 Electric fuel pump constituting low carbon number HC generating means 21 ECU 32 HC supply pipe

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kiyonori Sekiguchi 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Japan Auto Parts Research Institute (72) Inventor Yoshimichi Ito 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Stock Association Company Japan Auto Parts Research Institute (72) Inventor Shinya Hirota 1 Toyota-cho, Toyota-shi, Aichi Toyota Automobile Co., Ltd.

Claims (3)

[Claims] 1. A reducing agent supply device for a lean NO _x catalyst that is provided in an exhaust system of a combustor and reduces NO _x in the presence of HC in an oxidizing atmosphere. HC with low carbon number
And a low carbon number HC generating means for generating HC, and the HC generated by the low carbon number HC generating means is supplied to the upstream side of the lean NO _x catalyst in the exhaust system in a high temperature state. Exhaust catalyst reducing agent supply device. 2. The reducing agent supply device for an exhaust catalyst according to claim 1, wherein the combustor is an internal combustion engine. 3. The exhaust gas according to claim 1, wherein a tip end of an HC supply pipe for supplying the HC generated by the HC generating means to an exhaust system is arranged at a most upstream portion of the exhaust system of the combustor. Reductant supply device for catalyst.