JP6733383B2 - Exhaust gas purification system for internal combustion engine and exhaust gas purification method for internal combustion engine - Google Patents

Description

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

The exhaust passage of a diesel engine may be equipped with an ammonia slip catalyst device (ASC) in order to prevent release of ammonia flowing into the exhaust passage downstream of the selective reduction catalyst device (SCR) to the atmosphere. ..

This ammonia slip catalyst device is a device that carries a noble metal catalyst such as platinum (Pt) and chemically changes ammonia into harmless nitrogen (N ₂ ) by the function of this noble metal catalyst. However, when the temperature of the catalyst is high, ammonia may not be chemically changed to only nitrogen but may be chemically changed to nitrogen oxide (NOx) or nitrous oxide (N ₂ O). In this case, the exhaust gas purification system There was a possibility that the NOx purification performance as a whole would deteriorate.

In addition, a front NOx catalyst and a rear NOx catalyst are provided in this order from the upstream side in the exhaust passage, and in order to prevent desorption and release of adsorbed ammonia due to a temperature rise of the rear NOx catalyst, the exhaust passage is arranged in parallel with the exhaust passage. An exhaust gas purification device for an internal combustion engine has been proposed in which a bypass passage that bypasses the latter-stage NOx catalyst is provided, and when the temperature of the latter-stage NOx catalyst is higher than a temperature threshold value, exhaust gas is caused to flow through the bypass passage. ..

JP, 2010-209737, A

By the way, in the above exhaust gas purification apparatus for an internal combustion engine, the exhaust gas is caused to flow in the bypass passage when the post-stage NOx catalyst (ammonia slip catalyst device) is at a high temperature. When the temperature rises to 1, there is a concern that a large amount of ammonia adsorbed on the front NOx catalyst (selective reduction type catalyst device) will be desorbed and this desorbed ammonia will be released to the atmosphere via the bypass passage.

An object of the present invention is to provide an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine capable of achieving both suppression of the amount of NOx produced by an ammonia slip catalyst device and suppression of the amount of ammonia slip to the atmosphere. To provide.

An exhaust gas purifying system for an internal combustion engine of the present invention to achieve the above object is configured by including an urea water supply device, a selective reduction catalyst device, and an ammonia slip catalyst device in the exhaust passage of the internal combustion engine in order from the upstream side. In an exhaust gas purification system for an internal combustion engine, a bypass passage that bypasses the ammonia slip catalyst device is provided in parallel with the exhaust passage, and a flow passage switching that switches the flow of exhaust gas between the exhaust passage and the bypass passage. In addition to a device, a control device for controlling the exhaust gas purification system is equipped with a temperature detection device in the exhaust passage upstream of the selective reduction catalyst device, and the detection value of the temperature detection device is preset. When the temperature is equal to or higher than the set temperature threshold value, the flow path switching device is controlled to switch the flow of exhaust gas from the exhaust passage to the bypass passage, and further, the fluctuation when the detection value of the temperature detection device rises. When the amount is equal to or greater than a preset variation amount threshold value, the urea water supply amount from the urea water supply device is set in advance from a set supply amount set based on the operating state of the internal combustion engine. It is configured to perform control for reducing the amount by the amount of reduction.

Further, an exhaust gas purification method for an internal combustion engine of the present invention to achieve the above object, in order from the upstream side in the exhaust passage of the internal combustion engine, a urea water supply device, a selective reduction catalyst device, an ammonia slip catalyst device An internal combustion engine configured to include a bypass passage that bypasses the ammonia slip catalyst device in parallel with the exhaust passage, and a passage switching device that switches a flow of exhaust gas between the exhaust passage and the bypass passage. In the exhaust gas purification method, when the temperature of the exhaust gas flowing into the selective reduction catalyst device is equal to or higher than a preset temperature threshold value, the flow path switching device is controlled to change the flow of the exhaust gas to the exhaust gas. While switching from the passage to the bypass passage, when the variation amount when the temperature of the exhaust gas flowing into the selective reduction catalyst device rises is equal to or more than a preset variation amount threshold value, the urea water supply The method is characterized in that control is performed to reduce the supply amount of urea water from the device by a preset decrease amount set from a set supply amount set based on the operating state of the internal combustion engine.

According to the exhaust gas purifying system for an internal combustion engine and the exhaust gas purifying method for an internal combustion engine of the present invention, an ammonia slip catalyst device downstream of the selective reduction catalyst device when the exhaust gas flowing into the selective reduction catalyst device is at a high temperature When the temperature of NOx becomes high soon and NOx may be generated in the ammonia slip catalyst device, the amount of NOx generated in the ammonia slip catalyst device can be suppressed by flowing the exhaust gas into the bypass passage. it can.

Furthermore, when the exhaust gas is flowing through the bypass passage, the temperature of the exhaust gas flowing into the selective reduction catalyst device rises sharply, and when ammonia stored in the selective reduction catalyst device may be desorbed, By reducing the amount of urea water supplied from the urea water supply device, the amount of ammonia produced by hydrolyzing urea water is reduced, so that the amount of ammonia slip to the atmosphere can be suppressed.

That is, it is possible to achieve both suppression of the amount of NOx generated by the ammonia slip catalyst device and suppression of the amount of ammonia slip to the atmosphere.

It is a figure which shows the structure of the exhaust gas purification system of the internal combustion engine of this invention. It is a figure which shows the control flow of the exhaust gas purification method of the internal combustion engine of this invention. It is a figure which shows the structure of the exhaust gas purification system of the internal combustion engine of a prior art. It is a figure which shows the relationship of the temperature of the ammonia slip catalyst apparatus in oxygen atmosphere, and the density|concentration of each gas component contained in exhaust gas.

Hereinafter, an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine according to embodiments of the present invention will be described with reference to the drawings.

As shown in FIG. 1, an exhaust gas purification system 1 of the present invention includes an oxidation catalyst device (DOC) in an exhaust passage (exhaust pipe) 11 of an engine (internal combustion engine) (not shown) in order from an upstream side (engine side). ) 12, a particulate collection device 13, a urea water supply device 20, a selective reduction catalyst device (SCR) 14, and an ammonia slip catalyst device (ASC) 15.

The oxidation catalyst device 12 is configured such that a base material forming a honeycomb structure carries a precious metal catalyst (oxidation catalyst) that oxidizes hydrocarbon (HC), carbon monoxide (CO), and the like of the exhaust gas G. As the noble metal catalyst, a platinum (Pt)-based catalyst that oxidizes hydrocarbon into water and carbon dioxide and carbon monoxide into carbon dioxide is preferable.

Since the oxidation reaction of hydrocarbons and carbon monoxide by this noble metal catalyst is an exothermic reaction, the heat of the exhaust gas G rises due to this heat generation. By utilizing this, when a high temperature exhaust gas G is required, such as during forced PM regeneration control of the particulate matter collection device 13, it is included in the exhaust gas G passing through the exhaust passage 11 on the upstream side of the oxidation catalyst device 12. The exhaust gas G is heated to a high temperature by temporarily increasing the amount of hydrocarbons and oxidizing the increased amount of hydrocarbons by the oxidation catalyst device 12.

As a method of temporarily increasing the amount of hydrocarbons, for example, a method of performing post-injection of fuel in a cylinder (not shown) of the engine, or an exhaust passage 11 upstream of the oxidation catalyst device 12 is used. There is a method of injecting fuel from this fuel injection device by providing a fuel injection device (not shown).

The particulate matter collection device 13 is configured to include a filter therein to collect particulate matter (PM) in the exhaust gas G. This filter is composed of a monolith honeycomb type wall flow type filter in which inlets and outlets of cells (channels) of a porous ceramic honeycomb are alternately sealed.

Exhaust gas G flows in from the inlet of the unplugged cell of the particulate collection device 13 and, after passing through the PM trapping wall formed at the boundary with the unplugged cell at the adjacent outlet. , The outlet flows out from the outlet of an unsealed cell. The PM contained in the exhaust gas G is collected by the PM collection wall, but the collection amount is limited. Therefore, before the amount of collected PM reaches the limit value, the high temperature exhaust gas G is passed through the inside of the particulate collection device 13, and the heat of the exhaust gas G collects inside the particulate collection device 13. The forced PM regeneration control for burning and removing the generated PM is regularly performed.

The selective reduction catalyst device 14 produces ammonia (NH ₃ ) produced by hydrolyzing the urea water U injected from the urea water supply device 20 provided in the exhaust passage 11 on the upstream side thereof with the heat of the exhaust gas G. This is a device that purifies nitrogen oxides (NOx) contained in the exhaust gas G into nitrogen (N ₂ ) as a reducing agent.

It should be noted that ammonia that is not used for purifying NOx contained in the exhaust gas G is stored inside the selective reduction catalyst device 14 or flows out (slip) to the exhaust passage 11 on the downstream side of the selective reduction catalyst device 14. ) Do. Further, the ammonia storage capacity (upper limit amount of ammonia that can be stored) of the selective reduction catalyst device 14 decreases as the temperature of the selective reduction catalyst device 14 increases.

The ammonia slip catalyst device 15 has the same structure as that of the oxidation catalyst device 11 and carries a noble metal catalyst such as platinum (Pt), and the function of this noble metal catalyst causes the exhaust passage 11 on the downstream side of the selective reduction catalyst device 14. It is a device that chemically changes the ammonia that has flowed out into harmless nitrogen (N ₂ ). However, in this ammonia slip catalyst device 15, as shown in FIG. 4, when the temperature of the catalyst is high, ammonia is not chemically changed into only nitrogen but nitrogen oxides (NOx) and nitrous oxide (N ₂ O). There is a risk of chemical changes.

Further, the urea water supply device 20 is supplied with the urea water U stored in the urea water tank 22 by the urea water supply pump 21. The supply amount (injection amount) of the urea water U to the exhaust passage 11 is controlled by adjusting and controlling the output of the urea water supply pump 21 by a urea water supply control unit (DCU) 40 described later. The supply amount of the urea water U may be controlled by adjusting the valve opening degree of the urea water supply device 20.

Further, an upstream NOx concentration sensor 23 is provided in the exhaust passage 11 between the urea water supply device 20 and the particulate collection device 13 on the upstream side of the selective reduction catalyst device 14, and the urea water supply device 20 and the selective reduction catalyst device are provided. A temperature sensor (temperature detection device) 24 is provided in the exhaust passage 11 (exhaust passage 11 upstream of the selective reduction catalyst device 14) between the two. Further, a downstream NOx concentration sensor 25 is provided in the exhaust passage 11 on the downstream side of the selective reduction catalyst device 14.

Further, a urea water supply control device (DCU, control device) 40 that controls the exhaust gas purification system 1 of the internal combustion engine of the present invention is provided. The urea water supply control device 40 receives data relating to the operating state of the engine, such as the intake air flow rate to the engine, from the engine control device (ECU) 41 that controls the operating state of the engine, and the upstream NOx concentration sensor 23, The data of the detection values of the temperature sensor 24 and the downstream NOx concentration sensor 25 are received, and the output of the urea water supply pump 21 is adjusted and controlled based on the received data, and the urea from the urea water supply device 20 is adjusted. This is a device for controlling the supply amount of water U.

As described above, in the ammonia slip catalyst device 15, when the temperature of the catalyst is high, there is a possibility that ammonia may be chemically changed to nitrogen oxides or nitrous oxide instead of being chemically changed to only nitrogen. The NOx purification performance may be reduced.

To cope with this, the exhaust gas purification system 1 of the present invention is provided with a bypass passage 31 that bypasses the ammonia slip catalyst device 15 in parallel with the exhaust passage 11 as shown in FIG. The system is provided with a three-way valve (flow path switching device) 32 that switches between the exhaust passage 11 and the bypass passage 31. This point is different from the exhaust gas purification system 1X of the internal combustion engine as the comparative example of the conventional technique shown in FIG.

Then, when the detected value Ta of the temperature sensor 24 is equal to or higher than the set temperature threshold value T1, the urea water supply control device 40 controls the three-way valve 32 to cause the flow of the exhaust gas G from the exhaust passage 11 to the bypass passage 31. Control to switch. The set temperature threshold value T1 is a threshold value set in advance by experiments or the like as a value at which ammonia may chemically change to nitrogen oxides or nitrous oxide in the ammonia slip catalyst device 15 when the threshold temperature T1 is equal to or higher than the threshold value. In FIG. 1, the exhaust gas passing through the exhaust passage 11 is represented by Ga, and the exhaust gas passing through the bypass passage 31 is represented by Gb.

According to this configuration, when the exhaust gas G flowing into the selective reduction catalyst device 14 is at a high temperature, the temperature of the ammonia slip catalyst device 15 on the downstream side of the selective reduction catalyst device 14 soon becomes high, and the ammonia slip catalyst device When there is a possibility that NOx will be generated in 15, the amount of NOx generated in the ammonia slip catalyst device 15 can be suppressed by causing the exhaust gas G to flow in the bypass passage 31.

However, only by the control for switching the flow of the exhaust gas G from the exhaust passage 11 to the bypass passage 31, when the operating state of the engine suddenly becomes a high load and the exhaust gas G rapidly rises in temperature, the selective reduction type is selected. A large amount of ammonia adsorbed in the catalyst device 14 is desorbed, and this desorbed ammonia may be released to the atmosphere via the bypass passage 31.

Therefore, in the exhaust gas purification system 1 of the present invention, when the urea water supply control device 40 is switching the flow of the exhaust gas G from the exhaust passage 11 to the bypass passage 31, the detected value T of the temperature sensor 24 is further increased. When the variation amount ΔT when increasing is equal to or greater than the set variation amount threshold value ΔT1, the supply amount S of the urea water U from the urea water supply device 20 is set to a preset supply amount S1 that is preset based on the operating state of the engine. Control is performed to reduce the set reduction amount S2. This set fluctuation amount threshold value ΔT1 is a threshold value set in advance by experiments or the like as a value at which the amount of ammonia desorbed from the selective reduction catalyst device 14 becomes excessive when the threshold value ΔT1 is equal to or more than this threshold value. Further, the variation amount ΔT is a value obtained by subtracting the previously transmitted data Tb from the latest data Ta transmitted from the temperature sensor 24 to the urea water supply control device 40 (ΔT=Ta−Tb).

According to this configuration, when the exhaust gas G is flowing in the bypass passage 31, the temperature of the exhaust gas G flowing into the selective reduction catalyst device 14 suddenly rises, and the ammonia stored in the selective reduction catalyst device 14 is discharged. When there is a risk of desorption, the amount of urea water U supplied from the urea water supply device 20 is reduced to reduce the amount of ammonia generated by hydrolyzing the urea water U. Therefore, ammonia slip to the atmosphere The amount can be suppressed.

Regarding the above-mentioned set reduction amount S2, if the urea water supply control device 40 performs control to set the set reduction amount S2 based on the amount of ammonia stored in the selective reduction catalyst device 14, the selective reduction will be performed. The amount of ammonia flowing from the selective reduction catalyst device 14 to the bypass passage 31 can be reliably suppressed while maintaining the NOx purification performance of the catalyst device 14.

Although a three-way valve is used as the flow path switching device 32 in FIG. 1, a flow rate adjusting valve (flow rate adjusting device) 32 having not only a flow path switching function but also a flow rate adjusting function may be provided instead. In this case, the exhaust gas G is not passed through either the exhaust passage 11 or the bypass passage 31 like the three-way valve 32, but the exhaust gas G is passed through either the exhaust passage 11 or the bypass passage 31 or both. It can be distributed.

Next, a control flow of the exhaust gas purification method for an internal combustion engine of the present invention based on the exhaust gas purification system 1 for an internal combustion engine will be described with reference to FIG. The control flow of FIG. 2 is a control flow that is called by a higher-level control flow and starts at every control time preset by experiments or the like while the engine is operating.

When the control flow of FIG. 2 starts, in step S10, the temperature Ta of the exhaust gas G flowing into the selective reduction catalyst device 14 is detected and stored by the temperature sensor (temperature detection device) 24, and the previous main control is performed. At the time of control by the flow, the temperature Tb detected and stored by the temperature sensor 24 is recalled. When the control according to this control flow is the first time after the engine operation is started, the temperature Tb is set to zero. After performing the control of step S10, the process proceeds to step S20.

In step S20, it is determined whether the temperature Ta detected in step S10 is equal to or higher than the set temperature threshold T1. This set temperature threshold T1 is set to an optimum value in advance by experiments or the like. If the temperature Ta is lower than the set temperature threshold T1 (NO), the process proceeds to step S90, and in step S90, the flow of the exhaust gas G is switched to the bypass passage (branch passage) 31 at the time of the control by the previous main control flow. In this case, the flow of the exhaust gas G is switched from the bypass passage 31 to the exhaust passage 11. After performing the control of step S90, the process proceeds to return and the present control flow ends.

On the other hand, if the temperature Ta is equal to or higher than the set temperature threshold T1 in step S20 (YES), the process proceeds to step S30, and in step S30, the flow of the exhaust gas G is changed from the exhaust passage 11 to the bypass passage (branch passage) 31. Switch to. After performing the control of step S30, the process proceeds to step S40.

In step S40, it is determined whether or not the temperature Ta of the exhaust gas G flowing into the selective reduction catalyst apparatus 14 of this time detected in step S10 is higher than the temperature Tb of the exhaust gas Ga flowing into the selective reduction catalyst apparatus of the previous time. judge. When the temperature Ta is equal to or lower than the temperature Tb in step S40 (NO), the process proceeds to step S80, and in step S80, the supply amount S of the urea water U from the urea water supply device 20 is changed to the operating state of the engine. The set supply amount (normal supply amount) S1 set based on the above is set. After performing the control of step S80, the process proceeds to return and the present control flow ends.

On the other hand, if the temperature Ta is higher than the temperature Tb in step S40 (YES), the process proceeds to step S50, and in step S50, the difference between the temperature Ta and the temperature Tb, that is, the selective reduction catalyst device 14 flows. The variation amount ΔT (=Ta−Tb) when the temperature of the exhaust gas G increases is calculated. After performing the control of step S50, the process proceeds to step S60.

In step S60, it is determined whether or not the variation amount ΔT calculated in step S50 is equal to or greater than the set variation amount threshold ΔT1. This set variation threshold ΔT1 is set to an optimum value obtained in advance by experiments or the like. If the fluctuation amount ΔT is less than the set fluctuation amount threshold ΔT1 (NO), the process proceeds to step S80, and in step S80, the supply amount S of the urea water U from the urea water supply device 20 is determined based on the operating state of the engine. It is set to the set supply amount (normal supply amount) S1 set by the above. After performing the control of step S80, the process proceeds to return and the present control flow ends.

On the other hand, in step S60, when the variation amount ΔT is equal to or greater than the set variation amount threshold ΔT1 (YES), the process proceeds to step S70, and in step S70, the supply amount S of the urea water U from the urea water supply device 20 is changed. The set supply amount S1 set based on the operating state of the internal combustion engine is set to an amount reduced by the set reduction amount S2. This set reduction amount S2 is set in advance based on the amount of ammonia stored in the selective reduction catalyst device 14. After performing the control of step S70, the process proceeds to return and the control flow ends.

As described above, the exhaust gas purification method for an internal combustion engine according to the present invention, which is based on the exhaust gas purification system 1 for an internal combustion engine according to the present invention, selects the urea water supply device 20 and the urea water supply device 20 in order from the upstream side in the exhaust passage 11 of the internal combustion engine. A reduction catalyst device 14 and an ammonia slip catalyst device 15 are provided, and a bypass passage 31 that bypasses the ammonia slip catalyst device 15 is provided in parallel with the exhaust passage 11, and a flow of the exhaust gas G is provided between the exhaust passage 11 and the bypass passage 31. In the exhaust gas purifying method for an internal combustion engine, which is configured to include the flow path switching device 32 that switches with the above, when the temperature Ta of the exhaust gas G flowing into the selective reduction catalyst device 14 is equal to or higher than a preset temperature threshold value T1. In addition, when the flow path switching device 32 is controlled to switch the flow of the exhaust gas G from the exhaust passage 11 to the bypass passage 31 and the temperature of the exhaust gas G flowing into the selective reduction catalyst device 14 further rises. When the variation amount ΔT (=Ta−Tb) is equal to or greater than the preset variation amount threshold value ΔT1, the supply amount S of the urea water U from the urea water supply device 20 is set based on the operating state of the internal combustion engine. The method is characterized in that control is performed to reduce the preset supply amount S1 by a preset decrease amount S2.

According to the exhaust gas purification system 1 for an internal combustion engine and the exhaust gas purification method for an internal combustion engine of the present invention, it is possible to achieve both suppression of the amount of NOx generated in the ammonia slip catalyst device 15 and suppression of the amount of ammonia slip to the atmosphere. be able to.

In the control of the present invention, the flow path switching device 32 is controlled to switch the flow of the exhaust gas G between the exhaust passage 11 and the bypass passage 31, and when the passage has already been switched to the side to be switched, There is no need to newly operate the flow path switching device 32.

1, 1X Exhaust Gas Purification System for Internal Combustion Engine 11 Exhaust Passage 14 Selective Reduction Catalyst (SCR)
15 Ammonia slip catalyst system (ASC)
20 Urea Water Supply Device 24 Temperature Sensor (Temperature Detection Device)
31 Bypass passage (branch passage)
32 Three-way valve, flow control valve (flow path switching device)
40 Urea water supply control device (control device)
G Exhaust gas Ga Exhaust gas passing through the exhaust passage Gb Exhaust gas passing through the branch passage Ta Temperature sensor detected value T1 Set temperature threshold ΔT Variation amount when temperature sensor detected value ΔT1 Set variation threshold S urea water Amount of urea water supplied from the supply device S1 Set supply amount S2 Set decrease amount

Claims (3)

In an exhaust gas purifying system for an internal combustion engine, which comprises an urea water supply device, a selective reduction catalyst device, and an ammonia slip catalyst device in order from the upstream side to an exhaust passage of the internal combustion engine
A bypass passage that bypasses the ammonia slip catalyst device is provided in parallel with the exhaust passage, and a flow passage switching device that switches the flow of exhaust gas between the exhaust passage and the bypass passage is provided.
A temperature detection device is provided in the exhaust passage on the upstream side of the selective reduction catalyst device,
A control device for controlling the exhaust gas purification system,
When the detected value of the temperature detection device is equal to or higher than a preset temperature threshold value, by controlling the flow passage switching device, while switching the flow of exhaust gas from the exhaust passage to the bypass passage,
Furthermore, when the fluctuation amount when the detection value of the temperature detection device increases is equal to or greater than a preset fluctuation amount threshold value, the urea water supply amount from the urea water supply device is changed to the operating state of the internal combustion engine. An exhaust gas purification system for an internal combustion engine configured to perform control to reduce a preset supply amount that is set based on the above, by a preset decrease amount. The control device is
The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the set reduction amount is configured to be set based on the amount of ammonia stored in the selective reduction catalyst device. The exhaust passage of the internal combustion engine is provided with a urea water supply device, a selective reduction catalyst device, and an ammonia slip catalyst device in this order from the upstream side, and a bypass passage that bypasses the ammonia slip catalyst device is provided in parallel with the exhaust passage. In an exhaust gas purification method for an internal combustion engine configured to include a flow path switching device that switches a flow of gas between the exhaust passage and the bypass passage,
When the temperature of the exhaust gas flowing into the selective reduction catalyst device is equal to or higher than a preset temperature threshold value, the flow passage switching device is controlled so that the exhaust gas flows from the exhaust passage to the bypass passage. With switching
Furthermore, when the variation amount when the temperature of the exhaust gas flowing into the selective reduction catalyst device rises is equal to or more than a preset variation amount threshold value, the urea water supply amount from the urea water supply device is changed. An exhaust gas purification method for an internal combustion engine, comprising performing control to reduce a preset supply amount set based on an operating state of the internal combustion engine by a preset decrease amount.

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