JP7298575B2 - Exhaust purification system for internal combustion engine - Google Patents

Description

The present invention relates to an exhaust purification system for an internal combustion engine.

As an exhaust gas purification system for purifying NOx in the exhaust gas of diesel engines mounted on vehicles such as trucks and buses, a selective reduction catalyst that reduces NOx to nitrogen and water using urea water etc. as a reducing agent. (SCR: Selective Catalytic Reduction) systems have been developed and implemented. An exhaust gas purification system using SCR is disclosed in Patent Document 1, for example.

An exhaust purification system using an SCR supplies urea water stored in a urea water tank to an exhaust pipe upstream of the SCR. is set to be returned. An appropriate amount of urea water is injected by, for example, a urea water injector provided in an exhaust pipe forming an exhaust passage.

Also, there is known a technique of supplying ammonia into an exhaust pipe instead of urea water (see, for example, Patent Document 2).

SCR has an optimum temperature at which the catalytic reaction is activated (hereinafter referred to as "activation temperature"). The activation temperature is, for example, about 200° C., depending on the type of catalyst.

Here, when the exhaust temperature drops, it becomes lower than the activation temperature of the SCR, and the reaction efficiency of the catalyst drops. The same is true when a NOx storage catalyst such as LNT (Lean NOx Trap) is used as the catalyst, and the reaction efficiency of the catalyst decreases when the temperature is lower than the activation temperature of the LNT.

In consideration of this, there is a technique for preventing the reaction efficiency of the catalyst from decreasing by increasing the temperature inside the exhaust pipe, as disclosed in Patent Document 3, for example. In Patent Document 3, unburned fuel is supplied to an oxidation catalyst (DOC: Diesel Oxidation Catalyst) provided upstream of the LNT, and the heat generated by oxidation of the unburned fuel by DOC raises the temperature of the exhaust gas. , a configuration is disclosed that enhances the catalysis of downstream LNTs.

JP 2012-7557 A JP 2013-124569 A JP 2013-194702 A

However, if the temperature of the exhaust gas is raised by directly injecting unburned fuel into the exhaust pipe or by post-injecting it into the engine, there is a drawback that CO2 is generated.

The present invention has been made in consideration of the above points, and provides an exhaust gas purification system capable of increasing the exhaust gas temperature to the activation temperature of the catalyst to improve the exhaust gas purification efficiency while suppressing the generation of CO2. offer.

One aspect of the exhaust gas purification system for an internal combustion engine of the present invention includes:
An exhaust purification system for purifying exhaust gas from an internal combustion engine,
a NOx reduction catalyst or NOx storage catalyst disposed in an exhaust pipe of the internal combustion engine;
an oxidation catalyst arranged in the exhaust pipe upstream of the NOx reduction catalyst or the NOx storage catalyst;
an ammonia supply device for supplying ammonia to the oxidation catalyst;
a control unit that controls supply of ammonia to the oxidation catalyst by the ammonia supply device based on an exhaust temperature increase request;
Prepare.

According to the present invention, it is possible to increase the exhaust gas temperature to the activation temperature of the catalyst while suppressing the generation of CO2, thereby improving the exhaust purification efficiency.

The figure which showed the principal part structure of the exhaust gas purification system of Embodiment 1. Flowchart for explaining temperature increase control according to Embodiment 1 The figure which showed the principal part structure of the exhaust gas purification system of Embodiment 2. Flowchart for explaining temperature increase control according to Embodiment 2

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described with reference to the drawings.

<1> Embodiment 1
<1-1> Configuration of Exhaust Purification System FIG. 1 is a diagram showing the configuration of a main part of an exhaust purification system according to the present embodiment. In this embodiment, a mode in which the present invention is applied to an exhaust purification system 100 for a diesel engine 10 will be described. However, the exhaust gas purification system according to the present embodiment is applicable not only to the exhaust gas purification system 100 for the diesel engine 10, but also to an exhaust gas purification system for a gasoline engine.

The exhaust purification system 100 is mounted on a vehicle such as a truck, for example, and purifies NOx in the exhaust gas of the engine 10 .

The engine 10 includes, for example, a combustion chamber, a fuel injection device that injects fuel into the combustion chamber, and an engine ECU (not shown) that controls the fuel injection device. Engine 10 combusts and expands a mixture of fuel and air in a combustion chamber to generate power. The engine 10 is connected to an intake pipe 20 that introduces air into the combustion chamber and an exhaust pipe 30 that discharges post-combustion exhaust gas from the combustion chamber to the outside of the vehicle.

The exhaust purification system 100 has a DOC (Diesel Oxidation Catalyst) 101 , a DPF (Diesel Particulate Filter) 102 and an SCR (Selective Catalytic Reduction) 103 . The exhaust purification system 100 may have a LNT (Lean NOx Trap) or the like as a catalyst in addition to the SCR 103 or instead of the SCR.

The DOC 101 is formed by supporting rhodium, cerium oxide, platinum, aluminum oxide, or the like on a carrier made of aluminum oxide, metal, or the like. The DOC 101 oxidizes and removes unburned components (hydrocarbons HC and carbon monoxide CO) in the exhaust gas, heats the exhaust gas with the heat of reaction at this time, and oxidizes NO in the exhaust gas to NO2.

The DPF 102 consists of a filter with a catalyst, collects particulate matter (PM) contained in the exhaust gas, and burns and removes the collected PM.

The SCR 103 has, for example, a cylindrical honeycomb support made of ceramic. The honeycomb walls are supported or coated with a catalyst such as zeolite or vanadium. The SCR 103 stores ammonia and selectively reduces and purifies NOx from the exhaust gas by the stored ammonia.

The exhaust purification system 100 has an ammonia supply device 110 that supplies ammonia into the exhaust pipe 30 . The ammonia supply device 110 has an ammonia tank 111 that stores liquefied ammonia (liquefied NH3), a shutoff valve 112, a pressure reducing valve 113, flow control valves 114 and 115, and ammonia injection ports 116 and 117.

The exhaust purification system 100 also has an unburned fuel supply device 120 that supplies unburned fuel into the exhaust pipe on the upstream side of the DOC 101 . The unburned fuel supply device 120 includes a fuel tank 121 that stores fuel for the diesel engine 10, and an unburned fuel injector 122 that injects the fuel in the fuel tank 121 into the exhaust pipe 30 on the upstream side of the DOC 101. have.

Furthermore, the exhaust purification system 100 has an ECU (Electronic Control Unit) 130 . ECU 130 controls the operation of exhaust purification system 100 .

The ECU 130 includes, for example, a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an input port, an output port, and the like. Functions of the ECU 130, which will be described later, are realized, for example, by the CPU referring to control programs and various data stored in ROM, RAM, or the like. However, the function is not limited to processing by software, and can of course be realized by a dedicated hardware circuit.

The ECU 130 communicates with an engine ECU (not shown) of the engine 10 and the like to control them and acquire their states.

The ECU 130 functions as a control unit that controls the supply of ammonia to the DOC 101 by the ammonia supply device 110 . The ECU 130 also controls supply of unburned fuel to the exhaust pipe 30 on the upstream side of the DOC 101 by the unburned fuel supply device 120 .

Specifically, the ECU 130 inputs temperature information detected by a temperature sensor 141 provided at the entrance of the SCR 103 and a temperature sensor 142 provided at the entrance of the DOC 101, and based on the temperature information, the shutoff valve 112, By controlling the opening degrees of the flow control valves 114 and 115, the amount of ammonia injected from the ammonia injection ports 116 and 117 is controlled. Similarly, ECU 130 receives temperature information detected by temperature sensors 141 and 142, and controls the injection amount of unburned fuel from unburned fuel injector 122 based on the temperature information.

<1-2> Temperature Increase Control Next, temperature increase control according to the present embodiment will be described.

FIG. 2 is a flow chart for explaining temperature increase control according to the present embodiment. The flowchart of FIG. 2 is executed by the ECU 130. FIG.

When the temperature increase control is started, the ECU 130 acquires exhaust temperature information by inputting temperature information detected by the temperature sensor 141 in step S11.

In the subsequent step S12, the ECU 130 determines whether or not there is an exhaust temperature increase request. Specifically, the ECU 130 determines that there is an exhaust temperature increase request if the exhaust temperature is less than the SCR activation temperature (for example, 200° C.), and that there is no exhaust temperature increase request if the exhaust temperature is equal to or higher than the SCR activation temperature. I judge. The threshold value (SCR activation temperature) used in step S12 is, of course, preferably set appropriately according to the type and structure of the SCR catalyst used.

When the ECU 130 obtains a negative result in step S12 (step S12; NO), it ends the temperature increase control.

On the other hand, when a positive result is obtained in step S12 (step S12; YES), the ECU 130 proceeds to step S13. The ECU 130 determines whether or not the exhaust temperature detected by the temperature sensor 142 is lower than the ammonia combustion temperature of the DOC 101 in step S13.

When a positive result is obtained in step S13 (step S13; YES), the ECU 130 proceeds to step S14 and supplies the DOC 101 with unburned fuel. Specifically, the ECU 130 causes the unburned fuel injector 122 to inject unburned fuel in step S14.

On the other hand, when a negative result is obtained in step S13 (step S13; NO), the ECU 130 proceeds to step S15 and supplies the DOC 101 with ammonia. Specifically, the ECU 130 causes the ammonia injection port 117 to inject ammonia by controlling the shutoff valve 112 and the flow rate adjustment valve 115 to be open in step S15.

After performing the process of step S14 or step S15, or while performing the process of step S14 or step S15, the ECU 130 returns to step S11.

The threshold (the ammonia combustion temperature of the DOC 101) used in step S13 is, of course, preferably set appropriately according to the type and structure of the DOC used.

In short, in the control of the present embodiment, when the exhaust gas temperature is less than the predetermined threshold, if ammonia is supplied to the DOC 101, the ammonia is not sufficiently burned (oxidized) by the DOC 101, resulting in a temperature raising effect. Since it becomes lower, first, unburned fuel is supplied to the DOC 101 to raise the exhaust gas temperature to a predetermined threshold value. Then, when the exhaust temperature reaches a predetermined threshold value, ammonia is supplied to the DOC 101 to raise the temperature using ammonia.

As a result, the generation of CO2 can be suppressed as compared with the case where the exhaust gas temperature is raised only with unburned fuel.

Here, the control shown in FIG. 2 is based on the premise that the combustible temperature of the DOC 101 is lower for unburned fuel than for ammonia.

When the DOC 101 burns ammonia and the exhaust gas temperature rises to the SCR activation temperature, the ECU 130 controls the flow control valve 114 to open to supply ammonia to the SCR 103 . At this time, the ECU 130 may control the flow regulating valve 115 to be closed or may be controlled to remain open.

According to the above configuration, the SCR 103 arranged in the exhaust pipe 30 of the internal combustion engine, the DOC 101 arranged in the exhaust pipe 30 on the upstream side of the SCR 103, the ammonia supply device 110 that supplies ammonia to the DOC 101, By providing a control unit (ECU 130) that controls the supply of ammonia to the DOC 101 by the ammonia supply device 110 based on the temperature request, the exhaust temperature can be adjusted to the activation temperature of the catalyst while suppressing the generation of CO2. Exhaust purification efficiency can be improved by raising the temperature.

Here, the combustion of ammonia in DOC 101 produces N2 and H2O, which are harmless and have no greenhouse effect. Some of the ammonia becomes NOx, but it is purified to N2 and H2O in the downstream SCR 103, so there is no impact on the environment.

Further, according to the present embodiment, since the ammonia supply device 110 is shared by the DOC 101 and the SCR 103, it is possible to suppress an increase in the size of the exhaust purification system. However, the SCR 103 may be configured to supply urea water instead of ammonia.

Note that the preliminary temperature rise of the SCR 103 by unburned fuel in step S14 may be performed only by injecting unburned fuel from the unburned fuel injector 122 into the exhaust pipe 30 as described above. The injection of unburned fuel from 122 into the exhaust pipe 30 and the temperature rise of the exhaust gas by the engine may be combined. Since the oxidation reaction of the DOC 101 slows down at low temperatures, it is preferable to combine the injection of unburned fuel from the unburned fuel injector 122 into the exhaust pipe 30 and the temperature rise of the exhaust gas by the engine 10 .

Further, by combining the injection of unburned fuel from the unburned fuel injector 122 into the exhaust pipe 30 and the temperature rise of the exhaust gas by an electric heater (not shown) provided inside the exhaust pipe 30, Preliminary temperature rise may be performed.

In the present embodiment, the case where the present invention is applied to the exhaust gas purification system 100 using the SCR 103 as a catalyst for purifying NOx has been described, but the present invention is not limited to this. It can be widely applied when using temperature dependent NOx reduction type catalysts or NOx storage catalysts. That is, the control unit (ECU 130) determines whether or not there is an exhaust temperature increase request based on the relationship between the activation temperature of the NOx reduction catalyst or NOx storage catalyst and the exhaust temperature, and determines that there is an exhaust temperature increase request. In this case, ammonia should be supplied to the DOC 101 .

<2> Embodiment 2
<2-1> Configuration of Exhaust Purification System FIG. 3, in which parts corresponding to those in FIG. The exhaust purification system 200 of the present embodiment is provided with an ignition device 150 in the vicinity of the ammonia injection port 117 as compared with the exhaust purification system 100 of FIG. Ignition device 150 is, for example, a spark plug or a glow plug. Ignition of ignition device 150 is controlled by ECU 130 . Further, compared with the exhaust gas purification system 100, the exhaust gas purification system 200 does not include the unburned fuel supply device 120. As shown in FIG.

FIG. 4, in which parts corresponding to those in FIG. 2 are denoted by the same reference numerals, is a flowchart for explaining the temperature increase control according to the present embodiment. Only steps different from the control in FIG. 2 will be described below.

When a positive result is obtained in step S13 (step S13; YES), the ECU 130 proceeds to step S21 and controls the cutoff valve 112 and the flow rate adjustment valve 115 to open to inject ammonia from the ammonia injection port 117. At the same time, the ignition device 150 is ignited. As a result, the ignition device 150 burns ammonia to raise the temperature of the exhaust gas.

On the other hand, when a negative result is obtained in step S13 (step S13; NO), the ECU 130 proceeds to step S22 and controls the cutoff valve 112 and the flow rate adjustment valve 115 to open, thereby opening the ammonia injection port 117. Ammonia is supplied to the DOC 101 by injecting ammonia from the . In step S22, the ECU 130 does not cause the ignition device 150 to ignite.

After performing the process of step S21 or step S22, or while performing the process of step S21 or step S22, the ECU 130 returns to step S11.

As described above, according to the present embodiment, the heating unit (igniter 150) arranged near the ammonia injection port (ammonia injection port 117) of the ammonia supply device 110 is provided, and the control unit (ECU 130) When an exhaust temperature increase request occurs and (i) when the exhaust temperature is lower than the ammonia combustion temperature in the DOC 101, the ammonia supplied from the ammonia supply device 110 is heated by the heating unit (ignition device 150) and burned. (ii) when the exhaust temperature is equal to or higher than the ammonia combustion temperature in the DOC 101, ammonia is supplied to the DOC 101 and burned in the DOC 101 to raise the exhaust temperature.

As a result, compared with the first embodiment, it is not necessary to raise the temperature using unburned fuel, so the generation of CO2 can be further suppressed.

In this embodiment, the case where the ignition device 150 for burning ammonia is provided as the heating unit has been described, but the heating unit is not limited to this. The point is that the heating unit should be able to raise the temperature of the exhaust gas to the ammonia combustion temperature of the DOC 101 . For example, the heating unit may be an electric heater or the like.

The above-described embodiments are merely examples of specific implementations of the present invention, and the technical scope of the present invention should not be construed to be limited by these. That is, the present invention can be embodied in various forms without departing from its spirit or essential characteristics.

In the above-described embodiment, the flow control valves 114, 115 and the ammonia injection ports 116, 117 are shown separately, but the flow control valve 114 and the ammonia injection port 116, the flow control valve 115 and the ammonia injection port 117 are Each may be configured integrally.

The present invention has the effect of increasing the exhaust gas temperature to the activation temperature of the catalyst while suppressing the generation of CO2, thereby improving the exhaust purification efficiency. ) Widely applicable to exhaust purification systems using catalysts.

10 diesel engine (engine)
20 intake pipe 30 exhaust pipe 100, 200 exhaust purification system 101 DOC (oxidation catalyst)
102 DPF (Diesel Particulate Filter)
103 SCR (selective reduction catalyst)
110 ammonia supply device 111 ammonia tank 112 cutoff valve 113 pressure reducing valve 114, 115 flow control valve 116, 117 ammonia injection port 120 unburned fuel supply device 121 fuel tank 122 unburned fuel injector 130 ECU (control unit)
141, 142 temperature sensor 150 ignition device

Claims (5)

An exhaust purification system for purifying exhaust gas from an internal combustion engine,
a NOx reduction catalyst or NOx storage catalyst disposed in an exhaust pipe of the internal combustion engine;
an oxidation catalyst arranged in the exhaust pipe upstream of the NOx reduction catalyst or the NOx storage catalyst;
an ammonia supply device for supplying ammonia to the oxidation catalyst;
a control unit that controls supply of ammonia to the oxidation catalyst by the ammonia supply device based on an exhaust temperature increase request;
an unburned fuel supply device for supplying unburned fuel to the oxidation catalyst;
with
The control unit supplies the unburned fuel to the oxidation catalyst when the exhaust temperature increase request is generated and (i) the exhaust temperature is lower than the ammonia combustion temperature in the oxidation catalyst. (ii) if the exhaust gas temperature is equal to or higher than the ammonia combustion temperature in the oxidation catalyst, the ammonia is supplied to the oxidation catalyst to raise the exhaust gas temperature;
Exhaust purification system. The control unit performs the control (ii) after performing the control (i).
The exhaust purification system according to claim 1 . An exhaust purification system for purifying exhaust gas from an internal combustion engine,
a NOx reduction catalyst or NOx storage catalyst disposed in an exhaust pipe of the internal combustion engine;
an oxidation catalyst arranged in the exhaust pipe upstream of the NOx reduction catalyst or the NOx storage catalyst;
an ammonia supply device for supplying ammonia to the oxidation catalyst;
a control unit that controls supply of ammonia to the oxidation catalyst by the ammonia supply device based on an exhaust temperature increase request;
a heating unit arranged in the exhaust pipe on the upstream side of the oxidation catalyst ;
with
When the exhaust temperature increase request is generated, the control unit (i) causes the heating unit to increase the exhaust temperature when the exhaust temperature is lower than the ammonia combustion temperature in the oxidation catalyst, and (ii) when the exhaust temperature is equal to or higher than the combustion temperature of ammonia in the oxidation catalyst, increasing the exhaust temperature by supplying the ammonia to the oxidation catalyst;
Exhaust purification system. The heating unit is an ignition device capable of burning ammonia,
The exhaust purification system according to claim 3 . The NOx reduction type catalyst or the NOx storage catalyst has a catalytic reaction that depends on the temperature,
The control unit determines whether or not there is an exhaust temperature increase request based on the relationship between the activation temperature of the NOx reduction catalyst or the NOx storage catalyst and the exhaust temperature.
The exhaust purification system according to any one of claims 1 to 4 .

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