JPH06129231A - Particulate, method of processing particulate in trap - Google Patents

Abstract

PURPOSE:To provide a particulate processing method in a diesel engine which can burn and remove particulate sticking to a trap during running of a vehicle. CONSTITUTION:In a diesel engine incorporating a trap 26 for removing particulate trapped therein, the volume of intake-air into an engine cylinder 1 is decreased by a throttle valve 18, and an exhaust valve 10 is opened in the vicinity of the bottom dead center of the intake stroke of the engine so as to allow counter flow of exhaust gas into the engine cylinder. As a result, the temperature of the exhaust gas rises up. Accordingly, the temperature of the exhaust gas is raised, and accordingly particulate can be burnt and removed during running of a vehicle, without thermally damaging the trap for removing particulate. Thereby it is possible to reduce the manhours and the cost for removing particulate.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying exhaust gas of a diesel engine during traveling, and especially when traveling under a light load. The present invention relates to a treatment method of continuously removing particulate matter (PM) captured by a trap by increasing the temperature of exhaust gas.

[0002]

2. Description of the Related Art In a diesel engine, particulates containing carbon particles as a main component are generated in the exhaust gas one after another. Therefore, as one means for capturing the particulates, the exhaust gas is trapped by a ceramic (cordierite) trap. Captured the curate. The particulate matter thus trapped in the trap has a temperature of the exhaust gas of about 700 ° C. when the vehicle is under a high load when climbing a slope or traveling at a high speed. However, the temperature of the exhaust gas is about 300 ° C. and the particulate matter cannot be burned and removed during steady running of the vehicle. On the other hand, the trap used for diesel engines to remove particulates as described above is made of ceramic, so if fuel is added and burned at one time to remove a large amount of particulates, high temperature will be generated due to a large temperature change. Stress may occur and the trap may be thermally destroyed. This is the particulate matter. Traps are not generally popular 1
It was one cause.

[0003]

As described above, in the conventional removal of particulates by the method of adding fuel and burning at the same time, the ceramic trap is thermally destroyed due to a rapid rise in temperature, so that a small amount of particulates is removed. It has been desired that the successive burning removals be performed while the vehicle is being driven by a diesel engine.

By the way, the temperature of the exhaust gas of the diesel engine is 500 near the maximum running load as described above.
℃ -700 ℃, but under normal running load (1/1 of full load)
6 to 1/4) decreases to 200 to 300 ° C,
It was thought that continuous combustion and removal due to the temperature of the exhaust gas of particulates could not be performed while the vehicle was running.

The present invention has been made in view of the current state of the conventional removal of particulates by combustion.
The purpose is to remove the particulates adhering to the trap,
It is an object of the present invention to provide a method for treating particulates that can be continuously burned and removed by the temperature of exhaust gas while the vehicle is traveling.

[0006]

In the diesel engine, which is equipped with a trap for removing particulates and captures particulates in exhaust gas by the traps and removes the particulates, a trap for the particulates in the engine is provided. The amount of intake air is reduced by reducing the opening of the throttle valve to raise the temperature of the exhaust gas, and the exhaust valve is opened near the bottom dead center of the intake stroke of the engine and exhaust gas flows back into the cylinder through the exhaust valve. And further increase the back pressure of the exhaust gas of the engine at the exhaust port.

[0007]

In the structure of the present invention, in order to capture the particulates in the exhaust gas that are generated one after another by the trap and burn them one after another to remove them, in particular, the amount of intake air into the cylinder of the engine at a light load. The combustion temperature is raised by decreasing the throttle valve opening by decreasing the throttle valve opening degree, and the exhaust valve is opened near the bottom dead center of the intake stroke of the engine to allow exhaust gas to flow back into the cylinder through the exhaust valve. When EGR (exhaust gas recirculation) is performed, the air in the cylinder is adiabatically compressed. Therefore, the temperature rises due to compression and the temperature rises further due to the mixing of high-temperature exhaust gas. And the exhaust gas temperature rises, and the particulates become the exhaust gas temperature at which the particulates can be completely combusted even when the load is light while the vehicle is traveling.

Further, by taking a method of increasing the back pressure of the exhaust gas of the engine, for example, by increasing the back pressure by an exhaust throttle valve, or by using a turbocharger,
When the back pressure is increased, the reverse flow rate of the exhaust gas is increased, the air in the cylinder is further adiabatically compressed, and the gas temperature before the compression stroke is increased, so that the temperature of the exhaust gas is further increased.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. Here, FIG. 1 is an explanatory diagram showing a configuration of a main part of a diesel engine used in the exhaust gas purification method of the embodiment, FIG. 2 is a p-v diagram of the embodiment, and FIG. 3 is a reverse flow of exhaust gas in the embodiment. Explanatory diagram showing the state of air in the front and rear cylinders,
FIG. 4 is an explanatory diagram of the operation of the exhaust auxiliary cam in the embodiment.

First, the construction of a diesel engine used in the exhaust gas purification method of the embodiment will be described. This diesel engine is basically a four-cycle engine in which a piston 2 slides in a cylinder 1 and a crankshaft (not shown) is rotated by a connecting rod 3 as shown in FIG. Fuel injection valve 5
An intake valve 7 is installed at the intake port 6, and an exhaust valve 10 is installed at the exhaust port 9, and the valve spring 1 is installed at the end of the exhaust valve 10.
A tappet 15 that transmits the movement of a cam 14 having a spring receiver 12 and an auxiliary cam 13 that receives a force of 1 is installed.

The fuel injection valve 5 performs a fuel injection operation in synchronization with the crankshaft of the engine, and the intake valve 7 and the exhaust valve 10 are also opened and closed by a known valve opening / closing mechanism in synchronization with the crankshaft. Therefore, the opening / closing cycle is set in the same manner as in a normal engine.

A throttle valve 18 is provided at the intake port 6. Then, in the engine, a control device (not shown)
The control device is configured to control the fuel injection valve 5 and the throttle valve 18 so as to reduce the intake air and the fuel injection amount from the intake port 6 when the load is light. Auxiliary cam 13 near the bottom dead center of the stroke
As shown in FIG. 4, the exhaust valve 10 is opened and the exhaust gas is backflowed into the cylinder 1 whose atmospheric pressure is below atmospheric pressure by the throttle valve for a predetermined time near the bottom dead center of the intake stroke. It is configured to let. Further, at one end of the intake branch pipe 16 communicating with the intake port 6, the intake manifold 1
7 is installed and an intake passage is formed.

A throttle valve 18 is provided in the intake branch pipe 16 arranged in each cylinder of such a multi-cylinder engine.
Is installed, and its opening is determined in accordance with the required output of the engine, similarly to a known throttle valve. A ceramic (cordierite) trap 26 for removing particulates is provided downstream of the exhaust manifold 20 that communicates with the exhaust port 9 to detoxify exhaust gas discharged into the atmosphere. It is configured. For the purpose of increasing the back pressure of the exhaust gas, increasing the pressure of compression by the backflow gas in the cylinder 1, increasing the mixing amount of the exhaust gas, and increasing the gas temperature in the cylinder 1 before the compression stroke, it is not shown. Connect the turbocharger to the exhaust manifold, and connect the exhaust throttle valve 25 to the exhaust port 9.
Can be provided.

The diesel engine used in the examples is
During steady running (light load) by the control device described above,
Since the throttle valve opening is controlled so that the fuel injection amount and the intake air amount are reduced, the excess air is small and the combustion temperature rises, and the exhaust valve near the bottom dead center of the intake stroke is further increased. The exhaust gas temperature rises due to the valve opening.
The exhaust gas is guided to the trap 26, and the particulates in the exhaust gas are accumulated in the trap 26. However, in the embodiment, since the temperature of the exhaust gas rises to the temperature at which the particulates burn as described above, The particulates burn one after another and do not undergo a rapid temperature change, so the thermal stress generated is low, and the trap 26 is not thermally damaged,
The trapped particulates are burned and removed.

On the other hand, when the load is high, the throttle valve 18 is opened to the vicinity of full opening, and in the intake stroke of the engine in which the intake valve 7 is opened, the air in the intake port 6 and the cylinder 1 is close to atmospheric pressure and the air corresponding thereto. A certain amount of fuel is injected from the fuel injection valve 5, and the output is no different from that of a normal engine. Since the temperature of the exhaust gas reaches 500 ° C. to 700 ° C., the particulates trapped in the trap 26 are removed one after another without burning and causing thermal damage to the trap 26.

By the way, when the cooling water temperature and the load are low immediately after the engine is started, the opening of the throttle valve 18 is conventionally made small so as to limit the intake amount of air, and the pressure in the cylinder 1 is set as shown in FIG. It is known that the atmospheric pressure decreases from p7 to p1, but the air temperature in the cylinder at this time is the same as the atmospheric temperature. And a pressure p1 lower than atmospheric pressure
The intake stroke is started from, and the compression stroke is started from the same pressure p2 as p1, and the atmospheric pressure is obtained at the pressure p2a. Therefore, the intake air amount at the pressure p2a is given by a shown in FIG.

From this state, the air in the cylinder is compressed to the pressure p3, and is ignited at the position of the compression top dead center which is the pressure p3, and the pressure in the cylinder 1 is increased to the pressure p4 by the combustion and expanded from the pressure p4. The expansion stroke is completed at pressure p5, and the exhaust valve 10 is opened here. In this way, since the exhaust valve 10 is opened, the pressure in the cylinder 1 drops to the pressure p6 and close to the atmospheric pressure, and the exhaust stroke ends at the pressure p7.

However, neither the pressure p4 at the time of combustion nor the pressure p5 at the time of starting the exhaust gas reaches the desired exhaust gas temperature for burning the particulates.

On the other hand, in the embodiment, the intake stroke is started in the same manner as the conventional one, but at the pressure p2 in the intake stroke shown in FIG. 2, the air in the cylinder 1 is below atmospheric pressure as shown in FIG. 3 (b). Pressure P1. The exhaust valve 10 is opened by the auxiliary cam 13 at the pressure p2 at the intake bottom dead center, and the exhaust gas in the exhaust port 9 under the atmospheric pressure flows backward into the cylinder 1 which is a negative pressure. When this is shown in FIG. 3, as shown in FIG. 3B, the air in the cylinder 1 has a pressure P below atmospheric pressure.
1, the volume V1 is the displacement of the cylinder 1, and the temperature is t
However, due to the backflow of the exhaust gas, the air is adiabatically compressed to near atmospheric pressure as shown in (a), the volume decreases to V2, the pressure increases to P2, and the temperature rises to t2. . By the way, the temperature of the exhaust gas that flows back is about 300 ° C. at the time of low cooling water temperature immediately after the engine is started, and the compressed air mixes with this. When this state is shown in FIG. 2, the pressure becomes p8, and the temperature rises further than the temperature rise due to adiabatic compression. This mixed gas of air and exhaust gas is compressed from the pressure p8 in FIG.
The atmospheric pressure is reached at a, but the amount of the exhaust gas that has flowed back at this time is shown at b in FIG. As described above, in the example, the air in the cylinder is adiabatically compressed by the backflow of the exhaust gas, and as a result of the experiment, it was possible to raise the exhaust gas temperature to 500 ° C. or more immediately after the engine was started.

In the embodiment, the compression stroke is started from the high temperature and high pressure p8 shown in FIG. 2, and at the compression top dead center pressure p9, both the pressure and temperature are higher than the conventional pressure p3, and ignition and combustion are performed here. Therefore, the pressure in the cylinder 1 is pressure p10.
, The pressure is expanded from the pressure p10 and the expansion stroke is completed at the pressure p11. Even at the pressure p11 after expansion, the temperature is naturally higher than before.

In the embodiment, the reverse flow of the exhaust gas is caused by the negative pressure in the cylinder 1. Therefore, when the load is low and the exhaust temperature is low and the load is large, the amount of the exhaust gas is large and the temperature rise of the exhaust gas is large. The negative pressure in the cylinder 1 decreases as the load increases. For this reason, the reverse flow rate of exhaust gas also decreases, and when the throttle valve is fully opened at full load, the pressure in the cylinder 1 becomes almost atmospheric pressure, and the reverse flow of exhaust gas hardly occurs. Air can be inhaled and the same output can be achieved.

The diesel engine according to the embodiment aims at high speed output, and the intake valve 7 is still open even at the bottom dead center of the intake stroke, and at the same time, the exhaust valve 10 is opened by the auxiliary cam 13. On the other hand, in a configuration in which only one throttle valve is provided at one end of the intake manifold as in a known engine, part of the exhaust gas that flows backward from the exhaust port 9 passes through the inside of the cylinder 1 and passes through the intake pipe 16, It is sucked into the cylinder during another intake stroke. Then, it was confirmed that the exhaust gas passing through the intake pipe and the intake collecting pipe only lowers the temperature during the passage time or does not effectively compress the air in the cylinder 1 and reduces the effect of the embodiment. . On the other hand, in the configuration of the embodiment, it is more effective to dispose the throttle valve 18 in each intake pipe of the multi-cylinder engine in a part of the intake branch pipe 16. That is, as shown in FIG. 4, the intake and exhaust valves are simultaneously opened at the bottom dead center of intake air, so that exhaust gas is prevented from being sucked by another cylinder to prevent compression in the corresponding cylinder, and the inside of the intake port 6 is prevented. The backflow of exhaust gas to the upstream side of the throttle valve 18, which is at atmospheric pressure, is prevented from overflowing, and the compression of air due to the backflow of exhaust gas is further ensured in the cylinder 1.

Further, in the embodiment, a turbocharger is used to increase the back pressure of the exhaust gas passage at the time of low load to increase the EGR.
By increasing the amount, raising the supply pressure and temperature, and raising the temperature of the exhaust gas, the particulates trapped in the trap 26 can be burned and removed without causing thermal damage to the trap.

In the embodiment, the temperature of the exhaust gas flowing back is
The temperature is about 300 ° C, but it is possible to raise the temperature by more than 200 ° C by mixing with compressed air, and the exhaust gas temperature is
The temperature becomes 00 ° C or higher, and the particulates can be burned.

Further, the exhaust throttle valve 2 provided in the exhaust passage 9
When the exhaust pressure is increased by 5, the pressure at the start of compression becomes p13 in FIG. 2, the temperature further rises due to the corresponding adiabatic compression, and the mixing amount of the high-temperature exhaust gas also increases, further increasing the exhaust gas temperature. be able to.

[0026]

As described above, according to the present invention, in a diesel engine equipped with a trap for removing particulates, the particulates in the exhaust gas are captured and removed by the trap in the cylinder of the engine at a light load. The amount of intake air to the air is reduced by reducing the opening of the throttle valve, the temperature of the exhaust gas is raised, and the particulate removal trap is burned and removed while running without causing thermal damage to the particulate removal trap. Therefore, it is possible to reduce the man-hour and cost required for removing particulates.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a configuration of a main part of a diesel engine used in an embodiment of the present invention.

FIG. 2 is a p-v diagram of an embodiment of the present invention.

FIG. 3 is an explanatory diagram showing states of air in a cylinder before and after exhaust gas reverse flow in one embodiment of the present invention.

FIG. 4 is an explanatory diagram of an operation of the exhaust auxiliary cam in the embodiment of the present invention.

[Explanation of symbols]

 1 cylinder 2 piston 3 connecting rod 4 cylinder head 5 fuel injection valve 6 intake port 7 intake valve 9 exhaust port 10 exhaust valve 11 valve spring 13 auxiliary cam 14 cam 16 intake branch pipe 17 intake collecting pipe 18 throttle valve 25 exhaust throttle valve 26 trap

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[Procedure amendment]

[Submission date] November 5, 1992

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be amended] Claims

[Correction method] Change

[Correction content]

[Claims]

[Procedure Amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0006

[Correction method] Change

[Correction content]

[0006]

In the diesel engine, which is equipped with a trap for removing particulates and captures particulates in exhaust gas by the traps and removes the particulates, a trap for the particulates in the engine is provided. The intake air is decompressed by the throttle valve, and the exhaust valve is opened near the bottom dead center of the intake stroke of the engine to cause exhaust gas to flow back into the cylinder through the exhaust valve to raise the exhaust gas temperature and further This is achieved by increasing the back pressure of the exhaust gas.

Claims (2)

[Claims] 1. A diesel engine equipped with a trap for removing particulates, wherein particulates in exhaust gas are captured and removed by the trap, the intake air amount into the cylinder of the engine at light load is opened by opening a throttle valve. The temperature of the exhaust gas is raised by decreasing the temperature, and the exhaust valve is opened near the bottom dead center of the intake stroke of the engine to cause exhaust gas to flow back into the cylinder through the exhaust valve. Curate. How to treat particulates in the trap. 2. The particulate according to claim 1, wherein the back pressure of the exhaust gas at the exhaust port is further increased. How to treat particulates in the trap.