JPH08270433A - Exhaust emission control method for diesel engine and device therefor - Google Patents

Abstract

PURPOSE: To accelerate the atomization and vaporization of fuel and improve the reduction efficiency of NOx by injecting catalyst fuel into each cylinder in the exhaust stroke of a diesel engine, operated by main fuel, separately from the main fuel, and leading the vaporized catalyst fuel to an NOx purifying catalyst device, along with exhaust gas. CONSTITUTION: A diesel engine 1 is provided with an accumulator type fuel injection device 2 provided with an injector 4, an accumulator 6 for accumulating fuel, force-fed from a high pressure pump 5, so as to supply the fuel to the injector 4, and a pump control valve for regulating the injection quantity of the high pressure pump 5. When the diesel engine 1 is operated with main fuel, catalyst fuel formed of light oil is injected into each cylinder in the exhaust stroke of the engine 1. separately from the main fuel. At this time, the catalyst temperature judging means 19 of a control device 9 judges the injection time of the catalyst fuel when the exhaust gas temperature is within a set range, and an addition quantity collating means 20 determines the optimum addition quantity in correspondence with the rotating speed and load of the engine 1 to inject the catalyst fuel.

Description

Detailed Description of the Invention

[0001]

The present invention relates to N contained in exhaust gas.
The O _X an exhaust gas purification method and apparatus for a diesel engine to remove.

[0002]

In general, NO _X in the exhaust gas of a diesel engine, which is removed by the NO _X purification catalyst device interposed in an exhaust passage of a diesel engine, The exhaust gas for removing NO _X The HC component is insufficient.
Therefore, in the NO _x purification catalyst device, fuel (light oil) containing an HC component is added as a reducing agent to remove NO _x contained in the exhaust gas of a diesel engine. An exhaust emission control device for such a diesel engine is known, for example, as shown in Japanese Utility Model Laid-Open No. 5-87218 (illustrated in FIG. 7).

In the figure, an exhaust passage 102 is provided in a diesel engine 101, and NO is provided in the exhaust passage 102.
_{An X} purification catalyst device 103 is provided. Exhaust passage 1
02, a light oil supply device 104 is arranged on the upstream side of the NO _x purification catalyst device 103.
_The gasification and mixing promoting means 10 is provided between the _X purification catalyst devices 103.
5 is installed. The gasification and mixing promoting means 105 promotes the gasification of light oil and the mixing of light oil and exhaust gas.

[0004] Then, in the NO _X purification catalyst device 103, light oil in the exhaust gas NO _X is reduced by acting as a reducing agent, NO _X contained in the exhaust gas is adapted to be removed.

[0005]

[SUMMARY OF THE INVENTION However, since In the exhaust purification system of conventional diesel engines, even with gasification mixing acceleration means 105, it is difficult to atomization and vaporization of the light oil, NO _X There was a problem that the reduction efficiency was low.

Further, there is a problem that it is necessary to additionally install the light oil supply device 104 and the gasification mixing promoting means 105 in order to atomize or vaporize the light oil. The present invention has been made to solve the above-mentioned problems, and an object thereof is to promote atomization and vaporization of fuel, increase NO _x reduction efficiency, and provide a device for gas oil addition. An object of the present invention is to provide an unnecessary exhaust gas purification method for a diesel engine and an apparatus therefor.

[0007]

According to the first aspect of the present invention,
In the exhaust stroke of a diesel engine that operates on main fuel, a catalyst fuel is injected into the cylinder separately from the main fuel, so that the catalyst fuel vaporized and the exhaust gas are intercalated in an exhaust passage for NO _X purification catalyst. It is characterized by leading to a device.

According to the second aspect of the present invention, the catalyst fuel is supplied from the diesel engine and the injectors mounted in each cylinder of the diesel engine, separately from the main fuel for operating the diesel engine, in the exhaust stroke of the diesel engine. A pressure accumulation type fuel injection device for injecting into the cylinder,
An exhaust passage provided in the diesel engine, a NO _x purification catalytic device interposed in the exhaust passage, a catalyst temperature sensor mounted inside or at the inlet of the NO _x purification catalytic device, a rotational speed of the diesel engine, A rotation sensor for detecting a crank angle, a load sensor for detecting a load of a diesel engine, a catalyst temperature sensor, a rotation sensor, and a load sensor are connected to an input side, and a control device is connected to an injector on an output side. The control device is preset in accordance with the catalyst temperature determining means for determining that the fuel for the catalyst is to be injected when the temperature of the exhaust gas or the catalyst is within the set range, and the fluctuating rotational speed and load of the diesel engine. The optimum addition amount is determined by comparing the detected rotation speed and load on the addition amount map, and the injection amount according to the addition amount is set to the injector. It is characterized by having an addition amount collating means for outputting.

[0009]

According to the first aspect of the present invention, the catalyst fuel is injected into the cylinder separately from the main fuel during the exhaust stroke of the diesel engine operating with the main fuel. The catalyst fuel injected into the cylinder during the exhaust stroke is sufficiently vaporized by the high temperature exhaust gas.

Then, the vaporized catalyst fuel is introduced together with the exhaust gas into the NO _x purification catalyst device provided in the exhaust passage. In the middle of the exhaust passage from the diesel engine to the NO _X purification catalyst device, the vaporized catalyst fuel sufficiently mixes with the exhaust gas and reaches the NO _X purification catalyst device.
In the NO _X purification catalyst device, NO _X in the exhaust gas is reduced via the catalyst fuel.

According to the second aspect of the invention, the main fuel is injected into each cylinder of the diesel engine from the injector of the pressure-accumulation type fuel injection device to operate the diesel engine. Fuel for the catalyst is injected into the cylinder during the exhaust stroke of the engine. Then, the injection amount of the catalyst fuel is determined as follows.

First, the temperature of the exhaust gas or the catalyst inside or at the inlet of the NO _X purification catalyst device is detected by the catalyst temperature sensor, a signal thereof is sent to the control device, and the temperature of the exhaust gas is detected by the catalyst temperature determination means of the control device. When it is within the set range, it is determined that the catalyst fuel should be injected. If it is decided that fuel for the catalyst should be injected, then
In the addition amount comparison means, the optimum addition amount is determined by comparing the detected rotation number and load in the addition amount map set in advance corresponding to the fluctuating rotation number and load of the diesel engine, and the addition amount is determined. The injection quantity corresponding to the quantity data is output to the injector.

In this manner, the catalyst fuel injected into the cylinder produces the same effect as that of the first aspect of the invention.

[0014]

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

1 to 6, a method and an apparatus for purifying exhaust gas of a diesel engine according to an embodiment of claims 1 and 2 will be described. 1 and 2, reference numeral 1 is a diesel engine of in-line 4-cylinder, and this diesel engine 1 is equipped with a fuel injection device 2 of a pressure accumulation type. The pressure-accumulation type fuel injection device 2 is different in structure from the normally used column type fuel injection device, and will be described with reference to FIGS. 1, 2 and 4.

The pressure-accumulation type fuel injection device 2 is equipped with injectors 4, 4, 4, 4 which are mounted in the cylinders 3, 3, 3, 3 of the diesel engine 1 (only one is shown in FIG. 1).
(Only one is shown in FIG. 1), the high-pressure pump 5 that operates with the driving force of the diesel engine 1, the fuel that is pumped from the high-pressure pump 5 is stored, and the fuel is supplied to the injectors 4, 4, 4, and 4, respectively. A pressure accumulator chamber 6, a three-way valve 7, 7, 7, 7 for adjusting the injection amount of each injector 4, and a pump control valve 8 for adjusting the injection amount of the high-pressure pump 5 are provided. The injection amount is given as a pressure feed time of the catalyst fuel from the high-pressure pump 5 according to a command from the control device 9 described later, and is proportional to the pressure feed time. In the figure,
Reference numeral 5A indicates a fuel tank.

The injector 4 is a needle (not shown).
And a valve seat (not shown) on which the needle is seated, and the valve seat is opened and closed by the raising and lowering of the needle to inject fuel. That is, the injector 4 injects fuel from the pressure accumulating chamber 6 when the 3-way valve 7 is turned on and no back pressure is applied to the needle. On the other hand, when the 3-way valve 7 is turned off, the injector 4 is discharged from the pressure accumulating chamber 6. When a back pressure is applied to the needle, the needle sits on the valve seat and stops the fuel injection.

A control device 9 controls the three-way valve 7 of the injector 4 and the pump control valve 8 of the high-pressure pump 5, and has a load sensor 10 for detecting the load of the diesel engine 1 on its input side and a diesel engine. A rotation sensor 11 for detecting the number of rotations of 1 and a crank angle and a pressure sensor 12 for detecting the internal pressure of the pressure accumulating chamber 6 are connected.

When a plunger pump is adopted as the high pressure pump 5 and the pump control valve 8 is opened,
The lowering of the plunger 13 draws fuel into the upper chamber 14 of the plunger 13 in the drawing. If the pump control valve 8 closes when the cam 15 rotates and rises, the chamber 1
The fuel in 4 is pressurized by the plunger 13 and the check valve 16
The pressure is supplied to the pressure accumulating chamber 6 via.

The control device 9 controls the pump based on the detection signal of the pressure sensor 12 to open and close the pump control valve 8 so that the internal pressure of the pressure accumulating chamber 6 becomes a high pressure within a certain range, and the 3-way valve of the injector 4 is controlled. 7, a control signal is output based on the detection signals of the load sensor 10 and the rotation sensor 11 to maintain the injection timing of the main fuel of light oil and its injection amount appropriately.

Then, as shown in FIG. 3, the diesel engine 1 is operated by the main fuel, and the catalyst fuel, which is made of light oil, is supplied to the cylinders 3, 3, 3, 3 separately from the main fuel in the exhaust stroke of the diesel engine 1. It is designed to be injected into each. Here, the exhaust stroke excludes the end of the combustion stroke.
That is, the beginning of the exhaust stroke does not include the end of the combustion stroke.
1 and 2, an exhaust passage 17 is provided in the diesel engine 1. A NO _X purification catalyst device 18 is provided in the exhaust passage 17, and a catalyst temperature sensor 19A for detecting the temperature of exhaust gas is attached to an inlet of the NO _X purification catalyst device 18 in the exhaust passage 17.

The catalyst fuel is supplied to each cylinder 3, 3, 3,
In order to inject into the inside of 3, the control device 9 has a catalyst temperature judgment means 19 and an addition amount comparison means 20. The catalyst temperature determination means 19 determines to inject the catalyst fuel when the temperature of the exhaust gas is within the set range. The addition amount collating means 20 collates the addition amount map (shown in FIG. 6) preset corresponding to the fluctuating rotation number and load of the diesel engine 1 with the detected rotation number and load to determine the optimum addition amount. The injection amount corresponding to the determined addition amount data is output to the injector 4. The addition amount map of FIG. 6 is provided with a large number of addresses for partitioning the operating region where the addition of the catalyst fuel catalyst (reducing agent) is effective, and the optimum addition amount is set for each of these addresses. Here, the addition amount is set to 0 in the operation area having no address.

Therefore, in this embodiment, the detection signals of the load sensor 10 and the rotation sensor 11 are sent to the control device 9. Based on a command from the control device 9, the injector 4
A control signal for appropriately maintaining the injection timing of the main fuel and the injection amount of the main fuel is output to the injector 4 of the pressure-accumulation type fuel injection device 2 with respect to the 3-way valve 7. Injector 4
The main fuel is from each cylinder 3, 3 of the diesel engine 1.
The diesel engine 1 is injected into 3 and 3, respectively, and operates by repeating each of four strokes of intake, compression, combustion (explosion, expansion) and exhaust.

In addition to the main fuel, the catalyst fuel is injected from the injector 4 into the cylinders 3, 3, 3, 3 in the exhaust stroke of the diesel engine 1. In such a state, the exhaust purification device of the diesel engine purifies NO _x as described below. This will be described according to the procedure shown in the flowchart of FIG.

First, in step S1, the catalyst temperature sensor 19A detects the temperature of the exhaust gas by the catalyst temperature sensor 19A at the inlet of the NO _X purification catalyst device 18, and the signal is sent to the control device 9. In step S2, the catalyst temperature determination means 19 of the control device 9 determines whether the temperature of the exhaust gas is within the set range. When the temperature of the exhaust gas is within the set range (YES),
It is determined that the catalyst fuel should be injected, and the process proceeds to step S3. When the temperature of the exhaust gas is lower than the set range (N
O), since the activity of the catalyst is insufficient, it is not judged that the fuel for the catalyst should be injected. Further, when the temperature of the exhaust gas is higher than the set range (NO), the catalyst may be deteriorated, and it is not determined that the catalyst fuel should be injected.

In step S3, the rotation speed and crank angle of the diesel engine 1 detected by the rotation sensor 11 are read by the control device 9. In step S4, the load of the diesel engine 1 detected by the load sensor 10 is read by the control device 9. Step S
5, the addition amount matching means 20 of the control device 9
The optimum addition amount of the catalyst fuel is determined by collating the detected rotation number and load in the addition amount map preset corresponding to the fluctuating rotation number of the diesel engine 1 and the load.

In step S6, the pressure feed time of the catalyst fuel from the high-pressure pump 5 is determined according to the data of the addition amount. Then, the catalyst fuel is injected from the injector 4 for the pressure feed time of the catalyst fuel from the high-pressure pump 5, and the catalyst fuel is used in the exhaust stroke of the diesel engine 1 that operates on the main fuel separately from the main fuel. 3,3,3
Is injected into. The timing of injection of the catalyst fuel is set on the basis of the top dead center at the rotation speed and crank angle of the diesel engine 1.

The catalyst fuel injected into each cylinder 3, 3, 3, 3 in the exhaust stroke is sufficiently vaporized by the high temperature exhaust gas in each cylinder 3, 3, 3, 3. Then, the vaporized catalyst fuel is guided to the NO _X purification catalyst device 18 provided in the exhaust passage 17 together with the exhaust gas. In the middle of the exhaust passage 17 from the diesel engine 1 to the NO _X purifying catalytic device 18, the vaporized catalytic fuel sufficiently mixes with the exhaust gas and reaches the NO _X purifying catalytic device 18.

In the NO _X purification catalyst device 18, NO _X in the exhaust gas is reduced by using the catalyst fuel as a reducing agent. According to the above configuration, the catalyst fuel is injected in the exhaust stroke of the diesel engine 1, so that the catalyst fuel reaches the NO _X purification catalyst device 18 in a vaporized state.

Therefore, NO_XSmell in purification catalyst device 18
The catalyst fuel functions as a reducing agent (HC species), and NO
_XPromoting the reaction on the catalyst of the purification catalyst device 18,
NO _XNO in the purification catalyst device 18_XIncrease the efficiency of reduction
Can be In addition, the addition amount matching means 20
Touch the diesel engine in response to varying engine speed and load.
Determine the optimum amount of the medium fuel and select the amount of addition.
Injection into each cylinder 3, 3, 3, 3 of the diesel engine 1
So no_XCan be optimally purified. Immediately
If there is too little HC, NO_XWill be insufficiently purified
However, this can be prevented. Also, if too much HC is present, the catalyst
Fuel for fuel will be discharged as it is without reacting,
This can be prevented.

Further, the exhaust purification system of the diesel engine controls the catalyst temperature judgment means 19 and the addition amount comparison means 20 of the control device 9 to inject the main fuel by using the pressure accumulation type fuel injection device 2. Since it is possible to perform the two-stage injection of the fuel for the catalyst and the injection of the fuel for the catalyst, it is sufficient to change the software in the control device 9, and a new device for fuel addition is not required. Therefore, it is not necessary to use the conventional light oil supply device or the gasification mixing promoting means.

The catalyst fuel is used for each cylinder 3, 3, 3,
Since the high-temperature combustion gas in 3 is sufficiently vaporized, the catalyst fuel can be prevented from adhering to the exhaust passage 17. In the present embodiment, in addition to the main injection for operating the diesel engine 1, the exhaust stroke of the diesel engine 1 from the injectors 4 mounted on the cylinders 3, 3, 3, 3 of the diesel engine 1 is separately performed. The catalyst fuel is injected into each of the cylinders 3, 3, 3, 3 but only one or more of the cylinders 3, 3, 3, 3 can be used as the catalyst fuel. It is also possible to inject, and even in that case, an optimal amount of catalyst fuel can be injected by the addition amount map.

Further, in this embodiment, a catalyst temperature sensor 18A is attached to the inlet of the NO _X purification catalyst device 18,
Although the temperature of the exhaust gas is detected, the catalyst temperature sensor 18A may be mounted inside the NO _X purification catalyst device 18 to detect the temperature of the exhaust gas or the catalyst. Further, in the present embodiment, the case where the diesel engine is an in-line 4-cylinder has been described as an example, but the present invention is not limited to this. For example, an in-line 6-cylinder diesel engine other than the in-line 4-cylinder, a V-type diesel engine is used. It can also be applied to engines.

[0034]

According to the invention described in claim 1, since the catalyst fuel is injected in the exhaust stroke of the diesel engine,
The catalytic fuel reaches the NO _X purifying catalytic device in a vaporized state. Accordingly, the NO _X purification catalyst device, the catalyst for the fuel acts as HC species as a reducing agent, NO _X
To promote the reaction on a catalyst purifying catalyst device, NO _X
This has the effect of increasing the NO _x reduction efficiency in the purification catalyst device.

According to the second aspect of the present invention, in addition to the effect of the first aspect of the present invention, since the fuel for the catalyst is injected, the addition amount matching means is used to cope with the changing rotational speed and load of the diesel engine. Thus, the optimum injection amount is determined, and the injection amount can be injected into the diesel engine, so that the NO _x can be optimally purified. Further, the exhaust emission control system of the diesel engine controls the catalyst temperature determination means and the addition amount comparison means of the control device to control the injection of the main fuel and the injection of the catalyst fuel by using the pressure accumulation type fuel injection device. Since two-stage injection can be carried out, only a change in software in the control device is required and no new device for fuel addition is required.
Therefore, it is not necessary to use the conventional light oil supply device or the gasification mixing promoting means.

[Brief description of drawings]

FIG. 1 is a configuration diagram of an exhaust emission control device for a diesel engine according to an embodiment of the present invention.

FIG. 2 is an explanatory view of the diesel engine.

FIG. 3 is an explanatory diagram of a fuel injection timing of the pressure-accumulation fuel injection device of the diesel engine.

FIG. 4 is an explanatory diagram of a pressure-accumulation type fuel injection device of the diesel engine.

FIG. 5 is a flowchart of the exhaust emission control device for the diesel engine.

FIG. 6 is an explanatory diagram showing an addition amount map.

FIG. 7 is an explanatory diagram of a conventional exhaust emission control device for a diesel engine.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Diesel engine 2 Accumulation type fuel injection device 3 Cylinder 4 Injector 9 Control device 10 Load sensor 11 Rotation sensor 17 Exhaust passage 18 NO _X purification catalyst device 19 Catalyst temperature determination means 19A Catalyst temperature sensor 20 Addition amount comparison means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Takayuki Tsuchiya 1-chome Ichichome, Ageo-shi, Saitama Nissan Diesel Industry Co., Ltd.

Claims (2)

[Claims] 1. In the exhaust stroke of a diesel engine operating with main fuel, a catalyst fuel is injected into a cylinder separately from the main fuel, so that the vaporized catalyst fuel is interposed in an exhaust passage together with exhaust gas. A method for purifying exhaust gas of a diesel engine, characterized by leading to a catalyst device for purifying NO _x . 2. Accumulated pressure for injecting catalyst fuel into a cylinder in a diesel engine exhaust stroke from a diesel engine and an injector mounted in each cylinder of the diesel engine separately from a main fuel for operating the diesel engine. Type fuel injection device, an exhaust passage provided in a diesel engine, a NO _x purification catalyst device provided in the exhaust passage, and a catalyst temperature sensor mounted inside or at the inlet of the NO _x purification catalyst device , A rotation sensor for detecting the rotation speed and crank angle of the diesel engine, a load sensor for detecting the load of the diesel engine, a catalyst temperature sensor, a rotation sensor, and a load sensor on the input side, and an injector on the output side. Control device, and the control device determines that the temperature of the exhaust gas or the catalyst is within the set range. Optimum by comparing the catalyst temperature judgment means to judge that the fuel for the catalyst is to be injected with the rotating speed and load detected in a preset addition amount map corresponding to the changing rotating speed and load of the diesel engine. An exhaust emission control device for a diesel engine, comprising: an addition amount comparison means for determining an addition amount and outputting an injection amount corresponding to the addition amount to an injector.