JP2022054626A - Exhaust emission control system for internal combustion engine - Google Patents

Abstract

To provide an exhaust emission control system capable of effectively regenerating a DPF while suppressing generation of CO2.SOLUTION: An exhaust emission control system includes: an oxidation catalyst connected to an exhaust pipe of an internal combustion engine; a particulate collection filter connected to the exhaust pipe on the downstream side of the oxidation catalyst; an ammonia supply device supplying ammonia into the exhaust pipe on the upstream side of the oxidation catalyst; an oxygen concentration acquisition section acquiring an oxygen concentration in the exhaust pipe supplied with ammonia; a temperature sensor detecting a temperature of exhaust gas flowing into the particulate collection filter; and a control section controlling supply of ammonia into the exhaust pipe by using the ammonia supply device on the basis of the oxygen concentration acquired by the oxygen concentration acquisition section and the temperature detected by the temperature sensor.SELECTED DRAWING: Figure 1

Description

The present invention relates to a DPF regeneration technique in an exhaust purification system of an internal combustion engine.

Conventionally, as an exhaust purification device for an internal combustion engine such as a diesel engine, an oxidation catalyst (DOC: Diesel Oxidation Catalyst), a diesel particulate filter (DPF: Diesel Particulate Filter), and a selective reduction catalyst (SCR: Selective Catalystic Reduction) are provided. Is known (see, for example, Patent Document 1).

DOC oxidizes most of the organic components contained in the soot in the exhaust gas and purifies HC and CO. In the following, soot may be referred to as particulate matter (PM: Particulate Matter).

The DPF is provided after the DOC and collects PM in the exhaust gas. The collected PM is deposited on the DPF. When the amount of PM deposited is equal to or greater than a predetermined value, DPF regeneration is performed. The DPF regeneration is performed, for example, by injecting fuel to the exhaust upstream side of the DOC and burning it in the DOC to raise the temperature of the exhaust gas and burning the PM deposited in the DPF.

The SCR is provided after the DPF. In SCR, ammonia generated by hydrolyzing urea water injected into the exhaust pipe with the heat of the exhaust is reduced by reducing NOx in the exhaust to nitrogen (N2) by the action of a catalyst. To.

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

Special Table 2010-591459 Gazette Japanese Unexamined Patent Publication No. 2013-124569

By the way, since the temperature rise of the exhaust gas for the conventional DPF regeneration is performed by direct injection of unburned fuel into the exhaust pipe or post-injection into the engine as described above, there is a drawback that a large amount of CO2 is generated. be.

The present invention has been made in consideration of the above points, and provides an exhaust gas purification system capable of effectively performing DPF regeneration while suppressing the generation of CO2.

One aspect of the exhaust gas purification system for an internal combustion engine of the present invention is:
An exhaust purification system that purifies the exhaust gas of an internal combustion engine.
An oxidation catalyst connected to the exhaust pipe of the internal combustion engine and
A particle collection filter connected to the exhaust pipe on the downstream side of the oxidation catalyst,
An ammonia supply device that supplies ammonia into the exhaust pipe on the upstream side of the oxidation catalyst,
An oxygen concentration acquisition unit that acquires the oxygen concentration in the exhaust pipe to which the ammonia is supplied, and an oxygen concentration acquisition unit.
A temperature sensor that detects the temperature of the exhaust gas flowing into the particle collection filter, and
A control unit that controls the supply of ammonia into the exhaust pipe by the ammonia supply device based on the oxygen concentration acquired by the oxygen concentration acquisition unit and the temperature detected by the temperature sensor.
To prepare for.

According to the present invention, DPF regeneration can be effectively performed while suppressing the generation of CO2.

The figure which showed the main part structure of the exhaust gas purification system of embodiment A flowchart used to explain the DPF regeneration control according to the embodiment.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

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

The exhaust purification system 100 is mounted on a vehicle such as a truck, 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 in the combustion chamber, an engine ECU that controls the fuel injection device, and the like (not shown). The engine 10 generates power by burning and expanding a mixture of fuel and air in a combustion chamber. The engine 10 is connected to an intake pipe 20 that introduces air into the combustion chamber and an exhaust pipe 30 that discharges the exhaust gas after combustion discharged from the combustion chamber to the outside of the vehicle.

The exhaust purification system 100 includes an oxidation catalyst (DOC: Diesel Oxidation Catalyst) 101, a particle particulate filter (DPF: Diesel Particulate Filter) 102, and a selective catalytic reduction (SCR: Selective Catalytic Reduction) 103. The exhaust gas purification system 100 may have LNT (Lean NOx Trap) or the like as a catalyst in addition to SCR103 or in place of SCR.

DOC101 is formed by supporting rhodium, platinum or the like on a carrier made of aluminum oxide, metal or the like. DOC101 oxidizes and removes unburned components (hydrocarbon HC and carbon monoxide CO) in the exhaust, heats and raises the exhaust gas with the reaction heat at this time, and oxidizes NO in the exhaust to NO2.

The DPF 102 is composed of a filter with a catalyst, and collects particulate matter (PM: Particulate Matter) contained in the exhaust gas, and burns and removes the collected and accumulated PM.

The SCR 103 has, for example, a cylindrical shape and has a honeycomb carrier made of ceramic. A catalyst such as zeolite or vanadium is supported or coated on the wall surface of the honeycomb. The SCR 103 occludes ammonia and selectively reduces and purifies NOx from the exhaust gas by the occluded ammonia.

The exhaust purification system 100 includes an ammonia supply device 110 that supplies ammonia into the exhaust pipe 30. The ammonia supply device 110 includes an ammonia tank 111 for storing liquefied ammonia (liquefied NH3), a shutoff valve 112, a pressure reducing valve 113, a flow rate adjusting valves 114 and 115, and an ammonia injection port 116 and 117.

Further, the exhaust gas purification system 100 has an ECU (Electronic Control Unit) 130. The ECU 130 controls the operation of the exhaust gas 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. The functions described later in the ECU 130 are realized, for example, by the CPU referring to a control program and various data stored in a ROM, RAM, or the like. However, the function is not limited to processing by software, and of course, it can be realized by a dedicated hardware circuit.

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

The ECU 130 functions as a control unit that controls the supply of ammonia into the exhaust pipe 30 by the ammonia supply device 110.

A lambda sensor 150 as an oxygen sensor is provided in the exhaust pipe 30 on the upstream side of the DOC 101 and on the upstream side of the ammonia injection port 117. The lambda sensor 150 detects the oxygen concentration in the exhaust pipe 30.

A temperature sensor 141 is provided near the entrance of the DPF 102. The temperature sensor 141 detects the temperature of the exhaust gas flowing into the DPF 102.

The ECU 130 is injected from the ammonia injection port 117 by controlling the opening degrees of the isolation valve 112 and the flow rate control valve 115 based on the oxygen concentration detected by the lambda sensor 150 and the temperature detected by the temperature sensor 141. Control the amount of ammonia.

<2> DPF regeneration control Next, the DPF regeneration control according to the present embodiment will be described.

First, before giving a detailed explanation, the principle of DPF regeneration according to the present embodiment will be described.

When soot is deposited on the DPF 102, the exhaust pressure rises and causes problems such as deterioration of fuel efficiency. Therefore, DPF regeneration is performed in which the soot is burned so as not to exceed the accumulated amount determined in advance in an experiment or the like. Conventionally, when the exhaust temperature to the DPF does not reach, for example, 500 ° C or higher, which enables combustion of soot, unburned fuel is supplied to the DOC, and the exhaust temperature is raised by oxidation and heat generation (combustion). Is generally done, but CO2 is generated.

In consideration of this, in the present embodiment, ammonia is supplied into the exhaust pipe 30 on the upstream side of the DOC 101, and the ammonia is burned by the DOC 101 to promote DPF regeneration. This makes it possible to reduce the generation of CO2.

The DPF regeneration by supplying ammonia in the present embodiment can be used in combination with the conventional DPF regeneration by fuel combustion. For example, the exhaust temperature is raised by conventional fuel combustion until the exhaust temperature at which ammonia can be burned in the DOC 101, and then the DPF regeneration by supplying ammonia is switched. As a result, CO2 generated during DPF regeneration can be reduced.

FIG. 2 is a flowchart provided for explaining the DPF regeneration control according to the present embodiment. The flowchart of FIG. 2 is executed by the ECU 130. The flowchart of FIG. 2 is performed under the condition that the temperature of the exhaust gas flowing into the DOC 101 at the start of the process is a temperature at which ammonia can be oxidized in the DOC 101 (for example, 250 ° C. or higher). Until this condition is met, it is necessary to raise the temperature with conventional fuel.

In step S11, the ECU 130 determines whether or not the oxygen concentration detected by the lambda sensor 150 is equal to or higher than a predetermined threshold value, and if it is equal to or higher than the threshold value (step S11; YES), the process proceeds to step S12.

The ECU 130 adjusts the ammonia supply amount based on the temperature detected by the temperature sensor 141 and the oxygen concentration detected by the lambda sensor 150 in step S12. Specifically, the ECU 130 adjusts the amount of ammonia supplied from the ammonia injection port 117 by adjusting the opening degree of the flow rate adjusting valve 115.

At this time, first, the ECU 130 adjusts the supply amount of ammonia so that the temperature detected by the temperature sensor 141 becomes the combustible temperature of soot in the DPF 102 (for example, 550 to 600 ° C.). For example, when the temperature detected by the temperature sensor 141 is lower than the combustion temperature, the flow rate adjusting valve 115 is controlled so as to increase the amount of ammonia supplied. In other words, the ECU 130 adjusts the amount of ammonia supplied by the ammonia supply device 110 so that the temperature of the exhaust gas detected by the temperature sensor 141 becomes equal to or higher than a predetermined threshold value.

Secondly, the ECU 130 supplies ammonia based on the oxygen concentration detected by the lambda sensor 150, the oxygen required for combustion of ammonia in DOC101, and the oxygen required for combustion of soot in DPF102. The amount of ammonia supplied by the device 110 is adjusted. In other words, if the amount of ammonia supplied is too large with respect to the amount of oxygen in the exhaust, a large amount of oxygen will be used for the combustion of ammonia in the DOC102, and the oxygen will be insufficient in the combustion of soot in the DPF102. Occurs. Taking this into consideration, do not supply more ammonia than necessary. That is, the supply amount of ammonia may be an amount such that the temperature of the temperature sensor 141 becomes the combustible temperature of soot in DPF 102 (for example, 550 to 600 ° C.), and in order to avoid oxygen shortage in DPF 102. It is preferable to control so as not to supply more unnecessary ammonia.

Here, since the combustion of ammonia in DOC101 is represented by 4NH3 + 7O2 → 4NO2 + 6H2O or NH3 + O2 → N2 + H2O (coefficients are ignored), CO2 for raising the temperature is not generated.

Next, in step S13, the ECU 130 determines whether or not the PM removal amount in the DPF 102 exceeds the target amount, and if it exceeds the target amount (step S13; YES), ends the DPF regeneration control and targets. If the value is not exceeded (step S13; NO), the process returns to step S11.

In this way, efficient DPF regeneration can be performed while suppressing the generation of CO2.

<3> Summary As described above, according to the present embodiment, the oxidation catalyst (DOC101) connected to the exhaust pipe 30 of the internal combustion engine and the particles connected to the exhaust pipe 30 on the downstream side of the oxidation catalyst. A collection filter (DPF102), an ammonia supply device 110 that supplies ammonia into the exhaust pipe 30 upstream of the oxidation catalyst, and an oxygen sensor (lambda sensor) that detects the oxygen concentration in the exhaust pipe 30 to which ammonia is supplied. 150), an exhaust pipe by the ammonia supply device 110 based on the temperature sensor 141 that detects the temperature of the exhaust gas flowing into the particle collection filter, the oxygen concentration detected by the oxygen sensor, and the temperature detected by the temperature sensor 141. By providing a control unit (ECU 130) for controlling the supply of ammonia into the 30, it is possible to realize an exhaust gas purification system 100 capable of effectively performing DPF regeneration while suppressing the generation of CO2.

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 gas purification system. However, the SCR 103 may be configured to supply urea water instead of ammonia.

The above-described embodiment is merely an example of the embodiment of the present invention, and the technical scope of the present invention should not be construed in a limited manner by these. That is, the present invention can be implemented in various forms without departing from its gist or its main features.

In the above-described embodiment, the case where an oxygen sensor (lambda sensor 150) is provided as an oxygen concentration acquisition unit for acquiring the oxygen concentration in the exhaust pipe 30 to which ammonia is supplied has been described, but the oxygen concentration acquisition unit is this. Not limited to. For example, the oxygen concentration may be obtained by estimation from the intake flow rate sensor of the engine and the fuel injection amount.

The present invention can be widely used as a DPF regeneration technique for an exhaust purification system.

10 Diesel engine (engine)
20 Intake pipe 30 Exhaust pipe 100 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 Isolation valve 113 Pressure reducing valve 114, 115 Flow control valve 116, 117 Ammonia injection port 130 ECU (control unit)
141 Temperature sensor 150 Lambda sensor

Claims (7)

An exhaust purification system that purifies the exhaust gas of an internal combustion engine.
An oxidation catalyst connected to the exhaust pipe of the internal combustion engine and
A particle collection filter connected to the exhaust pipe on the downstream side of the oxidation catalyst,
An ammonia supply device that supplies ammonia into the exhaust pipe on the upstream side of the oxidation catalyst,
An oxygen concentration acquisition unit that acquires the oxygen concentration in the exhaust pipe to which the ammonia is supplied, and an oxygen concentration acquisition unit.
A temperature sensor that detects the temperature of the exhaust gas flowing into the particle collection filter, and
A control unit that controls the supply of ammonia into the exhaust pipe by the ammonia supply device based on the oxygen concentration detected by the oxygen concentration acquisition unit and the temperature detected by the temperature sensor.
Exhaust purification system equipped with. The control unit
When the oxygen concentration acquired by the oxygen concentration acquisition unit is equal to or higher than a predetermined threshold value, ammonia is supplied into the exhaust pipe by the ammonia supply device.
The exhaust purification system according to claim 1. The control unit
The amount of ammonia supplied by the ammonia supply device is adjusted based on the temperature of the exhaust gas detected by the temperature sensor.
The exhaust purification system according to claim 1 or 2. The control unit
The amount of ammonia supplied by the ammonia supply device is adjusted so that the temperature of the exhaust gas detected by the temperature sensor becomes equal to or higher than a predetermined threshold value.
The exhaust purification system according to claim 3. The predetermined threshold value is the combustible temperature of the soot of the particle collection filter.
The exhaust purification system according to claim 4. The control unit
The ammonia supply is based on the oxygen concentration acquired by the oxygen concentration acquisition unit, the oxygen required for combustion of ammonia in the oxidation catalyst, and the oxygen required for combustion of soot in the particle collection filter. Adjust the amount of ammonia supplied by the device,
The exhaust gas purification system according to any one of claims 1 to 5. A selective reduction catalyst is connected to the exhaust pipe on the downstream side of the particle collection filter.
The ammonia supply device supplies ammonia to the selective reduction catalyst in addition to the inside of the exhaust pipe on the upstream side of the oxidation catalyst.
The exhaust gas purification system according to any one of claims 1 to 6.

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