JP2024044561A - exhaust control device - Google Patents

Abstract

To provide an exhaust control device capable of suppressing lowering of desulfurization speed while securing durability and safety of a turbine.SOLUTION: An exhaust control device is used in an exhaust system in which an NOx removal catalyst is provided downstream of a turbine of a turbocharger and an oxidation catalyst is not provided between the turbine and the NOx removal catalyst in an exhaust passage where exhaust gas from an engine flows. The exhaust control device includes: a control section that executes control for increasing a temperature of the NOx removal catalyst to a first set temperature or higher, maintaining a temperature of exhaust gas on an outlet side of the turbine at or below a second set temperature higher than the first set temperature and generating reduction gas contributing to desulfurization reaction in the NOx removal catalyst; and a determination section that determines which region out of a plurality of regions predetermined in accordance with engine speed and engine torque is corresponded to on the basis of the engine speed and the engine torque during an operation of the engine. On the basis of the determined region, the control section changes content of the control.SELECTED DRAWING: Figure 2

Description

The present disclosure relates to an exhaust control device.

Conventionally, as a device for purifying nitrogen oxides (NOx) contained in exhaust gas emitted from an engine, an SCR (Selective Catalytic Reduction) catalyst that uses urea water as a reducing agent has been known (for example, Patent Literature (see 1).

Also, in the past, a configuration has been known in which the SCR catalyst is placed downstream (e.g., directly below) the turbine of a turbocharger in order to heat the SCR catalyst as soon as possible after the engine is started. In this configuration, a configuration is also known in which an oxidation catalyst (e.g., DOC: Diesel Oxidation Catalyst) is not placed between the turbine and the SCR catalyst in order to achieve a faster temperature rise.

Japanese Patent No. 6270248

Exhaust from engines contains sulfur oxides (SOx) as well as nitrogen oxides. When these adhere to the surface of the SCR catalyst, the reducing effect decreases, so their removal (hereafter also referred to as desulfurization) is necessary.

In desulfurization, raising the temperature of the exhaust gas sufficiently is advantageous because it increases the rate of desulfurization. However, the upper limit temperature allowed for desulfurization is higher than the temperature that can ensure the durability and safety of the turbine. Therefore, if the temperature of the exhaust gas is raised to the upper limit temperature, the durability and safety of the turbine cannot be ensured.

For this reason, in the conventional configuration described above, the exhaust temperature was controlled so as not to exceed a temperature that could ensure the durability and safety of the turbine, and as a result, the desulfurization speed was reduced.

An object of one aspect of the present disclosure is to provide an exhaust control device that can suppress a decrease in desulfurization rate while ensuring durability and safety of a turbine.

In an exhaust control device according to an aspect of the present disclosure, a NOx purification catalyst is provided downstream of a turbine of a turbocharger in an exhaust passage through which exhaust gas from an engine flows, and an oxidation catalyst is provided between the turbine and the NOx purification catalyst. This is an exhaust control device used in an exhaust system not provided with an exhaust system, which raises the temperature of the NOx purification catalyst to a first set temperature or higher, and raises the temperature of the exhaust gas on the outlet side of the turbine to be lower than the first set temperature. a control unit that performs control to maintain a high second set temperature or lower and generate reducing gas that contributes to the desulfurization reaction in the NOx purification catalyst; a determination section that determines which region corresponds to one of a plurality of predetermined regions according to the engine rotation speed and the engine torque, and the control section is configured to perform a determination based on the determined region. Then, the content of the control is changed.

According to the present disclosure, it is possible to suppress the decrease in desulfurization rate while ensuring the durability and safety of the turbine.

A diagram schematically showing a configuration example of an engine according to an embodiment of the present disclosure A diagram schematically showing a configuration example of an exhaust control device according to an embodiment of the present disclosure FIG. 1 is a schematic diagram illustrating an example of a plurality of regions according to an embodiment of the present disclosure.

The following describes an embodiment of the present disclosure with reference to the drawings.

The configuration of the engine 1 of this embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram showing an example of the configuration of the engine 1 of this embodiment.

The engine 1 may be mounted on a moving body (e.g., an automobile, a ship, etc.) or may be stationary.

As shown in FIG. 1, the engine 1 includes, in addition to the engine body 2, an intake passage 10, an exhaust passage 20, a turbocharger 30, and an EGR (Exhaust Gas Recirculation) device 40. Note that each arrow illustrated in the intake passage 10 and the exhaust passage 20 indicates a flow of air (intake, exhaust).

The air drawn into the intake passage 10 is compressed by the compressor 31 of the turbocharger 30, cooled by the intercooler 11, and the flow rate is adjusted by the intake throttle valve 12 before being supplied to the engine body 2 via the intake manifold 13.

Although not shown in the figure, the engine body 2 is provided with a fuel injection device that injects fuel (e.g., main injection, after injection, etc.) into each cylinder. Note that in this embodiment, the engine body 2 is described as being a diesel engine, but is not limited to this.

The exhaust gas discharged from the engine body 2 is discharged from the exhaust manifold 21 into the exhaust passage 20. A portion of the exhaust gas discharged into the exhaust passage 20 flows into the EGR device 40 (specifically, the EGR upstream passage 41). In the following, the exhaust gas that flows into the EGR device 40 is referred to as "EGR gas."

The EGR device 40 includes an EGR upstream passage 41, an EGR cooler 42, an EGR downstream passage 43, and an EGR valve 44.

The EGR gas that has flowed into the upstream passage 41 is cooled by the EGR cooler 42, flows through the EGR downstream passage 43, has its flow rate adjusted by the EGR valve 44, and is returned to the intake passage 10. The EGR downstream passage 43 and the intake passage 10 communicate with each other on the downstream side of the intake throttle valve 12.

On the other hand, the exhaust gas that is not diverted to the EGR upstream passage 41 flows into the turbine 32 of the turbocharger 30, driving the turbine 32 to rotate.

Thereafter, the exhaust gas passes through an exhaust brake valve 23 provided on the downstream side of the turbine 32 and an SCR catalyst 50 (an example of a NOx purification catalyst) that purifies NOx in the exhaust gas, and is released into the atmosphere.

Although not shown, a urea water injector that injects urea water as a reducing agent into the exhaust passage 20 is provided downstream of the exhaust brake valve 23 and upstream of the SCR catalyst 50. Ammonia is generated from the urea water injected into the exhaust passage 20, and this ammonia is supplied to the SCR catalyst 50. As a result, NOx in the exhaust gas is reduced to nitrogen in the SCR catalyst 50.

Also, as shown in FIG. 1, in the exhaust passage 20 downstream of the turbine 32, no catalyst (e.g., DOC) is provided between the turbine 32 and the SCR catalyst 50.

Note that a catalyst (for example, an SCR catalyst), a filter (for example, a diesel particulate filter), etc. may be further provided downstream of the SCR catalyst 50.

The configuration of engine 1 has been explained above.

Next, the configuration of the exhaust control device 100 will be described with reference to FIG. 2. FIG. 2 is a schematic diagram showing an example of the configuration of the exhaust control device 100.

Although not shown, the exhaust control device 100 includes hardware such as a main storage device such as a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory), and stores computer programs. It has an auxiliary storage device such as a hard disk, flash memory, and a bus that connects them. The functions of the exhaust control device 100 described below are realized by the CPU loading a computer program read from the auxiliary storage device into the RAM of the main storage device and executing the program.

The exhaust control device 100 includes a determination section 110 and a control section 120.

The determination unit 110 acquires the engine speed and engine torque while the engine 1 is operating, and determines which of a number of predefined regions the engine 1 corresponds to based on the engine speed and torque.

The engine speed and engine torque acquired by the determination unit 110 may be values detected by a sensor (not shown), for example, or may be values calculated by other methods.

Here, a specific example of a plurality of predetermined areas will be described using FIG. 3. FIG. 3 is a diagram schematically showing an example of a plurality of areas. In FIG. 3, the vertical axis shows engine torque, and the horizontal axis shows engine rotation speed.

As shown in FIG. 3, areas A, B, and C are determined according to the engine speed and engine torque. Area A is an area where the engine torque is equal to or greater than the first threshold a, regardless of the engine speed (an example of the first area). Area B is an area where the engine torque is less than the first threshold a and the engine speed is less than the second threshold b (an example of the second area). Area C is an area where the engine torque is less than the first threshold a and the engine speed is equal to or greater than the second threshold b (an example of the third area).

Data indicating such areas A to C (eg, map data) is known to the determination unit 110.

Note that, hereinafter, the area determined by the determination unit 110 will be referred to as a "determination area."

The control unit 120 raises the temperature of the exhaust gas and generates reducing gas (e.g. , gases containing carbon monoxide).

Specifically, the control unit 120 raises the temperature of the SCR catalyst 50 to a first set temperature (e.g., 500 degrees) or higher, maintains the temperature of the exhaust gas on the outlet side of the turbine 32 at a second set temperature (e.g., 700 degrees) or lower that is higher than the first set temperature, and executes control to generate reducing gas that contributes to the desulfurization reaction in the SCR catalyst 50.

The second set temperature is, for example, the upper limit temperature at which the durability and safety of the turbine 32 are ensured (in other words, no malfunction occurs in the turbine 32).

Furthermore, the control unit 120 changes the content of the above-mentioned control based on the determination area.

For example, when the determination region is region A, the control unit 120 controls after injection, throttling of the intake throttle valve 12, retardation of the injection timing of main injection, and throttling of the EGR valve 44.

For example, when the judgment region is region B, the control unit 120 controls the after-injection, the throttling of the intake throttle valve 12, the retardation of the injection timing of the main injection, and the throttling of the exhaust brake valve 23.

For example, when the determination region is region C, the control unit 120 controls the after injection, the throttle of the intake throttle valve 12, and the retardation of the injection timing of the main injection.

Note that the control unit 120 reduces the opening degrees of the intake throttle valve 12, the exhaust brake valve 23, and the EGR valve 44 so that the engine torque does not decrease. Further, in retarding the injection timing of the main injection, the retard amount is determined based on a predetermined map (data in which the retard amount is determined according to the engine speed and engine torque).

The configuration of the exhaust control device 100 has been described above.

As described above, in the exhaust control device 100 of the present embodiment, the SCR catalyst 50 is provided downstream of the turbine 32 of the turbocharger 30 in the exhaust passage 20 through which exhaust from the engine main body 2 flows, and the SCR catalyst 50 is provided downstream of the turbine 32 of the turbocharger 30. This is an exhaust control device used in an exhaust system in which an oxidation catalyst is not provided between the SCR catalyst 50 and the SCR catalyst 50, which raises the temperature of the SCR catalyst 50 to a first set temperature or higher and controls the exhaust gas on the outlet side of the turbine 32. A control unit 120 that maintains the temperature below a second set temperature higher than the first set temperature and generates reducing gas that contributes to the desulfurization reaction in the SCR catalyst 50, and an engine rotation speed during operation of the engine body 2. and a determination section 110 that determines, based on the engine torque, which region corresponds to one of a plurality of regions predetermined according to the engine rotation speed and the engine torque, and the control section 120 includes: It is characterized by changing the content of control based on the determined area.

This feature makes it possible to both increase the temperature of the exhaust gas and generate reducing gas depending on the engine speed and engine torque. In other words, it is possible to suppress a decrease in the desulfurization rate while ensuring the durability and safety of the turbine.

Note that the present disclosure is not limited to the description of the embodiments described above, and various modifications can be made without departing from the spirit thereof.

The exhaust control device disclosed herein is useful for desulfurizing NOx purification catalysts.

REFERENCE SIGNS LIST 1 engine 2 engine body 10 intake passage 11 intercooler 12 intake throttle valve 13 intake manifold 20 intake passage 21 exhaust manifold 23 exhaust brake valve 30 turbocharger 31 compressor 32 turbine 40 EGR device 41 EGR upstream passage 42 EGR cooler 43 EGR downstream passage 44 EGR valve 50 SCR catalyst 100 exhaust control device 110 determination unit 120 control unit

Claims (6)

Exhaust control used in an exhaust system in which a NOx purification catalyst is provided downstream of a turbine of a turbocharger in an exhaust passage through which exhaust gas from an engine flows, and an oxidation catalyst is not provided between the turbine and the NOx purification catalyst. A device,
The temperature of the NOx purification catalyst is increased to a first set temperature or higher, the temperature of the exhaust gas on the outlet side of the turbine is maintained at a second set temperature or less higher than the first set temperature, and a desulfurization reaction occurs in the NOx purification catalyst. a control unit that executes control to generate reducing gas that contributes to;
a determination unit that determines, based on the engine rotation speed and engine torque during operation of the engine, which region corresponds to one of a plurality of predetermined regions according to the engine rotation speed and the engine torque; , has
The control unit includes:
changing the content of the control based on the determined area;
Exhaust control device. The plurality of regions include:
a first region in which the engine torque is equal to or greater than a first threshold value regardless of the engine speed;
a second region in which the engine torque is less than the first threshold value and the engine speed is less than a second threshold value;
a third region in which the engine torque is less than the first threshold value and the engine speed is equal to or greater than a second threshold value,
The control unit is
If the determined region is the first region,
It controls after-injection, intake throttle valve throttling, main injection timing retardation, and EGR (Exhaust Gas Recirculation) valve throttling.
If the determined region is the second region,
It controls after-injection, intake throttle valve throttling, main injection timing retardation, and exhaust brake valve throttling.
If the determined region is the third region,
Controls after-injection, intake throttle valve throttling, and retardation of main injection timing.
The exhaust control device according to claim 1. The control unit is
In throttling the intake throttle valve, the exhaust brake valve, and the EGR valve, the valve openings are reduced so that the engine torque does not decrease.
The exhaust control device according to claim 2. The second set temperature is
is the upper limit temperature at which the durability and safety of the turbine are ensured;
The exhaust control device according to claim 1. The reducing gas is
It is a gas containing carbon monoxide.
The exhaust control device according to claim 1. The NOx purification catalyst is
A selective catalytic reduction (SCR) catalyst.
The exhaust control device according to claim 1.

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