JP2022054625A - 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; a first temperature sensor detecting a temperature of exhaust gas flowing into the oxidation catalyst; a second 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 temperatures detected by the first and second temperature sensors.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 reduces NOx in the exhaust gas to nitrogen (N2) by the action of a catalyst, thereby reducing NOx. To. Before the DPF regeneration, the ammonia in the SCR is purified (purged).

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,
A first temperature sensor that detects the temperature of the exhaust gas flowing into the oxidation catalyst, and
A second 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 temperature detected by the first and second temperature sensors.
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 so-called continuously regenerating type catalytic filter, which collects particulate matter (PM: Particulate Matter) contained in the exhaust gas and continuously burns and removes the collected and deposited 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 temperature sensor 141 is provided near the entrance of the DOC 101. Further, a temperature sensor 142 is provided near the entrance of the DPF 102. The temperature sensor 141 detects the temperature of the exhaust gas flowing into the DOC 101. The temperature sensor 142 detects the temperature of the exhaust gas flowing into the DPF 102.

The ECU 130 inputs the temperature information detected by the temperature sensors 141 and 142, and controls the opening degree of the isolation valve 112 and the flow control valve 115 based on the temperature information, thereby injecting the ammonia from the ammonia injection port 117. 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 this ammonia is burned by the DOC 101 to promote DPF regeneration, thereby generating CO2. It can be reduced.

The DPF regeneration by supplying ammonia in this 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.

Here, there are the following two reactions for removing PM (soot) deposited on DPF102.

(1) PM combustion by O2 in an environment with a high exhaust temperature (for example, 500 ° C or higher)

(2) PM combustion due to the reaction of 2NO2 + 2C → 2CO2 + N2 at an appropriate exhaust temperature (for example, around 300 ° C)

The conventional DPF regeneration by fuel combustion mainly relies on the reaction of (1). On the other hand, the DPF regeneration by supplying ammonia in the present embodiment mainly promotes the reaction of (2).

When ammonia is supplied to DOC101 under the condition that ammonia is oxidizable in DOC101, a reaction of 4NH3 + 7O2 → 4NO2 + 6H2O occurs in DOC101, and NO2 is generated. This NO2 is used for the PM combustion reaction of (2) above in DPF102.

Here, in general, NO2 is generated by DOC101 from NO contained in the exhaust gas from the engine, and this is used for the PM combustion reaction of (2) above. In the present embodiment, by supplying ammonia to DOC101, more NO2 can be given to DPF102, and as a result, the reaction of (2) above is further promoted.

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.

When the ECU 130 starts DPF regeneration, in step S11, the temperature of the temperature sensor 141 determines whether or not the temperature at which ammonia can be oxidized in the DOC 101. This temperature is, for example, about 250 ° C.

When the ECU 130 obtains an affirmative result in step S11 (step S11; YES), the ECU 130 proceeds to step S12. In step S12, the ECU 130 determines whether or not the temperature of the temperature sensor 142 is in a temperature range suitable for burning the deposited particles in the DPF 102. This temperature range is, for example, 300 ° C to 350 ° C.

When the ECU 130 obtains an affirmative result in step S12 (step S12; YES), the ECU 130 proceeds to step S13. The ECU 130 supplies ammonia to the DOC 101 in step S13. Specifically, the ECU 130 supplies ammonia to the DOC 101 by injecting ammonia from the ammonia injection port 117 by controlling the isolation valve 112 and the flow rate adjusting valve 115 to be in the open state.

Next, in step S14, 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 S14; YES), ends the DPF regeneration control and targets. If the value is not exceeded (step S14; NO), the process returns to step S11.

If a negative result is obtained in step S11 or step S12, the ECU 130 moves to step S15 and requests temperature adjustment. For example, the ECU 130 requires the engine ECU (not shown) to raise the temperature of the exhaust gas by the engine. Further, for example, when an electric heater for raising the temperature of the exhaust pipe 30 is provided, the temperature may be adjusted by the electric heater. In short, the temperature is adjusted so that a positive result can be obtained in steps S11 and S12 by some means.

Here, when affirmative results are obtained in steps S11 and S12 and ammonia is supplied to DOC101 in step S13, as described above, a reaction of 4NH3 + 7O2 → 4NO2 + 6H2O occurs in DOC101, and 2NO2 + 2C → 2CO2 + N2 in DPF102. PM combustion by the reaction is performed.

As a result, 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 exhaust gas into the exhaust pipe 30 upstream of the oxidation catalyst, a first temperature sensor 141 that detects the temperature of the exhaust gas flowing into the oxidation catalyst, and particles. Based on the temperature detected by the second temperature sensor 142 that detects the temperature of the exhaust gas flowing into the collection filter and the first and second temperature sensors 141 and 142, into the exhaust pipe 30 by the ammonia supply device 110. By providing a control unit (ECU 130) for controlling the supply of the exhaust gas, 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 addition to the configuration of the above-described embodiment, an acquisition unit for acquiring the amount of NOx contained in the exhaust gas on the upstream side of the DOC101 is provided, and the ECU 130 supplies ammonia based on the amount of NOx acquired by the acquisition unit. May be controlled. For example, the ECU 130 may be controlled to supply ammonia when a positive result is obtained in steps S11 and S12 and the amount of NOx acquired by the acquisition unit is less than the threshold value. By doing so, by supplying ammonia when the NO2 is likely to be insufficient in the DPF102, the NO2 generated by the combustion of ammonia in the DOC101 can be sent to the DPF102, and as a result, the DPF regeneration can be promoted. ..

Here, the acquisition unit for acquiring the amount of NOx may be the NOx sensor 160 as shown in FIG. 1, or may be an estimation means for estimating the amount of NOx by calculation based on the operating state of the internal combustion engine. ..

Further, the amount of ammonia supplied to the DOC 101 may be controlled based on the O2 concentration in the exhaust gas. For example, ammonia may be supplied only when the O2 concentration in the exhaust is sufficient for ammonia combustion (NH3 oxidation) in DOC101.

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, 142 Temperature sensor 160 NOx sensor

Claims (4)

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,
A first temperature sensor that detects the temperature of the exhaust gas flowing into the oxidation catalyst, and
A second 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 temperature detected by the first and second temperature sensors.
Exhaust purification system equipped with. The control unit
The temperature of the first temperature sensor is a temperature at which ammonia can be oxidized in the oxidation catalyst, and the temperature of the second temperature sensor is a temperature range suitable for combustion of deposited particles in the particle collection filter. When the temperature is high, the ammonia supply device controls to supply ammonia.
The exhaust purification system according to claim 1. Further, an acquisition unit for acquiring the amount of NOx contained in the exhaust gas on the upstream side of the oxidation catalyst is provided.
The control unit
The temperature of the first temperature sensor is a temperature at which ammonia can be oxidized in the oxidation catalyst, and the temperature of the second temperature sensor is a temperature range suitable for combustion of deposited particles in the particle collection filter. And when the amount of the NOx acquired by the acquisition unit is less than the threshold value, the ammonia supply device controls to supply ammonia.
The exhaust purification system according to claim 1. 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 3.

Images