CN111788372A

CN111788372A - Exhaust gas purification system for internal combustion engine and exhaust gas purification method for internal combustion engine

Info

Publication number: CN111788372A
Application number: CN201980014018.8A
Authority: CN
Inventors: 阿野田洋
Original assignee: Isuzu Motors Ltd
Current assignee: Isuzu Motors Ltd
Priority date: 2018-02-19
Filing date: 2019-02-13
Publication date: 2020-10-16
Also published as: JP2019143513A; WO2019159932A1; JP6969423B2

Abstract

A control device provided in an exhaust gas purification system of an internal combustion engine determines whether or not an estimated amount of adsorbed reducing agent at the start of regeneration in a selective reduction type catalyst device is equal to or greater than a predetermined target amount at the start of filter regeneration for removing PM from a filter device by combustion. When the estimated reductant adsorption amount is equal to or greater than the target amount, control is performed to reduce the adsorbed reductant in the selective reduction catalyst device so that the estimated reductant adsorption amount in the selective reduction catalyst device is less than the target amount.

Description

Exhaust gas purification system for internal combustion engine and exhaust gas purification method for internal combustion engine

Technical Field

The present disclosure relates to an exhaust gas purification system and an exhaust gas purification method for purifying exhaust gas discharged from an internal combustion engine.

Background

In internal combustion engines such as diesel engines and lean burn gasoline engines, the following exhaust gas purification systems are the mainstream: in order to reduce NOx, NOx Reduction is attempted in a wide operating region from a low load to a high load by combining an NOx absorption Reduction catalyst (LNT catalyst, LNT: Lean NOx Trap) and a Selective Catalytic Reduction catalyst (SCR catalyst, SCR: Selective Catalytic Reduction) and further adding a Filter (for example, DPF: Diesel Particulate Filter) that traps exhaust particulates (PM: Particulate Matter) (for example, see patent document 1).

Prior art documents

Patent document

Patent document 1: japanese national Japanese patent application publication No. 2006-512529

Disclosure of Invention

Problems to be solved by the invention

However, in such an exhaust gas purification system, since the SCR catalyst is used, NH adsorbed to the SCR catalyst is generated by a rapid temperature rise of the exhaust gas during regeneration control of the filter₃(ammonia) is desorbed and ammonia slip may occur. Thus, NH from the SCR catalyst₃The filter regeneration control is started in a state where the adsorption amount is reduced to a certain extent.

In particular, when the LNT device carrying the LNT catalyst is disposed at the front stage of the SCR device carrying the SCR catalyst, NOx is absorbed by the LNT catalyst of the LNT device, and NH in the SCR device₃Reduction of consumption is less efficient, so to NH₃The waiting time until the adsorption amount is reduced becomes long, and the time until the filter regeneration is started may become long. If the time until the start of filter regeneration becomes long, there is an amount of NOx dischargedIncreasing the fear.

An object of the present disclosure is to provide an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine, which can solve the problem that the time until the filter regeneration is started becomes long and the accompanying increase in the amount of NOx emission, while avoiding the reducing agent adsorbed by the SCR catalyst of the SCR device being desorbed and released and flowing out to the downstream side of the SCR device at the time of the filter regeneration.

Means for solving the problems

An exhaust gas purification system for an internal combustion engine according to an aspect of the present disclosure includes, in an exhaust passage of the internal combustion engine, an NOx adsorption-reduction catalyst device that adsorbs NOx in an exhaust gas and a selective reduction catalyst device that reduces NOx in the exhaust gas with a reducing agent in this order from an upstream side, and includes a filter device that traps particulate matter in the exhaust gas in the exhaust passage, and includes a control device including a calculation unit that calculates an estimated reducing agent adsorption amount that is an estimated value of a reducing agent adsorption amount in the selective reduction catalyst device, and a determination unit that determines whether or not the estimated reducing agent adsorption amount at the time of regeneration start calculated by the calculation unit is equal to or greater than a preset target amount at the time of start of filter regeneration in which particulate matter in the filter device is burned and removed, when the determination unit determines that the estimated adsorbed amount of the reducing agent calculated by the calculation unit is equal to or greater than the target amount, the consumption unit performs adsorbed reducing agent consumption control for reducing the adsorbed reducing agent in the selective reduction catalyst device so that the estimated adsorbed amount of the reducing agent calculated by the calculation unit becomes less than the target amount.

Further, an exhaust gas purification method for an internal combustion engine according to the present disclosure includes, in an exhaust passage of the internal combustion engine, an NOx adsorption-reduction catalyst device that adsorbs NOx in exhaust gas and a selective reduction catalyst device that reduces NOx in exhaust gas with a reducing agent in this order from an upstream side, includes a filter device that traps particulate matter in exhaust gas in the exhaust passage, calculates an estimated reducing agent adsorption amount that is an estimated value of a reducing agent adsorption amount in the selective reduction catalyst device, determines whether or not the calculated estimated reducing agent adsorption amount at the start of regeneration of a filter that burns and removes particulate matter in the filter device is equal to or greater than a predetermined target amount at the start of regeneration, and performs adsorbed reducing agent consumption control that reduces the adsorbed reducing agent in the selective reduction catalyst device when the estimated reducing agent adsorption amount is equal to or greater than the target amount, so that the calculated estimated reducing agent adsorption amount is less than the target amount.

Effects of the invention

According to the exhaust gas purification system for an internal combustion engine and the exhaust gas purification method for an internal combustion engine of the present disclosure, it is possible to avoid the reducing agent adsorbed by the SCR catalyst of the SCR device from being desorbed and released and flowing out to the downstream side of the SCR device at the time of filter regeneration, and to solve the problem that the time until filter regeneration is started becomes long.

Drawings

Fig. 1 is a diagram schematically showing the configuration of an exhaust gas purification system for an internal combustion engine according to an embodiment of the present disclosure.

Fig. 2 is a diagram schematically showing the configuration of a control device of an exhaust gas purification system for an internal combustion engine according to an embodiment of the present disclosure.

Fig. 3 is a diagram showing an example of a control flow for implementing the exhaust gas purification method of the internal combustion engine according to the embodiment of the present disclosure.

Fig. 4 is a graph illustrating a relationship between the engine outlet temperature and the NOx purification rate in the LNT catalyst and the SCR catalyst.

Detailed Description

Hereinafter, an exhaust gas purification system for an internal combustion engine and an exhaust gas purification method for an internal combustion engine according to one embodiment will be described with reference to the drawings.

As shown in fig. 1, an exhaust gas purification system 1 of an internal combustion engine (hereinafter, referred to as an exhaust gas purification system) according to an embodiment is configured to be supplied from an engine main body (E: an internal combustion engine main body)

The exhaust passage 11 through which the exhaust gas G discharged from the exhaust gas generator 10 passes includes, in order from the upstream side: an LNT device (NOx catalyst device) 21 having a NOx absorbing function; a CSF device (filter device with catalyst) 22 that traps PM (particulate matter) in the exhaust gas G; an aqueous urea solution supply device 23 for supplying aqueous urea solution (strictly speaking, for generating NH)₃(ammonia: reductant) reductant-producing material, but will be referred to herein as reductant for simplicity of description); an SCR device (e.g., urea SCR catalyst device: selective reduction catalyst device) 24 that passes NH generated from urea water₃To reduce and purify NOx; and a DOC device (DOC: Diesel Oxidation Catalyst) 25 that converts NH flowing out from the SCR device 24₃Oxidized and purified and referred to as ASC (Ammonia Slip Catalyst).

The urea solution supply device 23 is further provided with a control device 40 for controlling an injection amount U1 of the urea solution U injected from the urea solution supply device 23. The control device 40 is usually incorporated in a so-called engine control unit control device that controls the entire engine main body 10, but may be a separate control device.

That is, the exhaust gas purification system 1 is configured to include, in the exhaust passage 11 of the internal combustion engine, an LNT device 21 that absorbs NOx in the exhaust gas G and an SCR catalyst device 24 that reduces NOx in the exhaust gas G by a reducing agent in this order from the upstream side, and to include, in the exhaust passage 11, a CSF device 22 that traps PM in the exhaust gas G. In addition, a control device 40 for controlling the exhaust gas purification system 1 is included.

Note that, although the NOx occlusion reduction catalyst device is exemplified as the LNT device 21 that adsorbs NOx, the present disclosure is not limited to this NOx occlusion reduction catalyst device as long as it is a catalyst that adsorbs NOx and purifies NOx in the exhaust gas. Further, as a filter device for collecting PM (particulate matter), a CSF device, which is one type of filter device carrying a catalyst, is exemplified, but the present disclosure is not limited to this CSF as long as it is a filter device requiring filter regeneration.

Further, the exhaust gas purification system shown in fig. 1 is an example, and the present disclosure is not limited to the exhaust gas purification system in which a selective reduction catalyst device that reduces NOx in the exhaust gas by a reducing agent is disposed downstream of a NOx adsorption reduction catalyst device that adsorbs NOx in the exhaust gas, and a filter device that requires filter regeneration is disposed in a certain position in an exhaust passage.

Further, as the LNT device 21, a device carrying a NOx occlusion reduction catalyst or the like is exemplified. The NOx occlusion reduction catalyst is composed of a molded body or the like, and an NOx occluding material composed of a noble metal catalyst such as platinum and an alkaline earth metal such as barium is supported on a catalyst carrier. In addition, in the lean combustion state, NOx in the exhaust gas is temporarily absorbed in the NOx absorbent, and the exhaust gas is made rich by NOx purification control before the NOx absorption amount is saturated, whereby NOx absorbed in the NOx absorbent is released and reduced by the three-way function of the noble metal catalyst.

The CSF device (filter device with catalyst) 22 is formed of cordierite material, silicon carbide (SiC) material or the like, and thin walls of ceramic are used as a filter by alternately plugging both ends of cells of honeycomb ceramic. The particulate collection filter is excellent in heat resistance, and therefore, when the filter is regenerated, the collected PM can be burned and removed by heating, and the collection performance can be maintained by the filter regeneration treatment. In addition, an oxidation catalyst is supported to more easily cause combustion of PM.

The aqueous urea solution supply device 23 is an injection device for supplying the aqueous urea solution U supplied from the aqueous urea solution tank 23a through the aqueous urea solution supply pipe 23b to the SCR device 24, and the control device 40 performs adjustment control of the presence or absence of injection of the aqueous urea solution U and the injection amount U1 thereof.

The SCR device 24 is configured to carry, for example, a urea selective reduction catalyst that uses NH generated by using urea water as a reducing agent U₃Reacts with NOx in the exhaust gas G to generate nitrogen and water. Examples of the urea selective reduction catalyst include iron ion-exchange aluminosilicates and copper ion-exchange aluminosilicatesStone catalyst, etc. having adsorbed NH₃And passing the adsorbed NH₃To reduce the function of purifying NOx. By using this selective reduction catalyst device 24, NH is not directly used₃Instead, aqueous urea solution is injected into the exhaust gas G to hydrolyze NH generated from the aqueous urea solution₃React with NOx to make NOx harmless.

Further, regarding the NOx sensors arranged in the sensor group of the exhaust passage 11, the 1 st NOx sensor 31 is provided on the inlet side of the LNT device 21, and this 1 st NOx sensor 31 is used to detect the 1 st NOx concentration Cn1 which is the NOx concentration in the exhaust gas G flowing into the LNT device 21. Further, a2 nd NOx sensor 32 is provided on the inlet side of the SCR device 24, and this 2 nd NOx sensor 32 is used to detect a2 nd NOx concentration Cn2 which is the NOx concentration in the exhaust gas G flowing into the SCR device 24. Further, a 3 rd NOx sensor 33 is provided on the outlet side of the DOC device 25, and this 3 rd NOx sensor 33 is used to detect a 3 rd NOx concentration Cn3, which is the NOx concentration in the exhaust gas G flowing out from the DOC device 25.

Further, as for the lambda sensor (air-fuel ratio sensor: oxygen concentration sensor), the 1 st lambda sensor 34 is provided on the inlet side of the LNT device 21, and this 1 st lambda sensor 34 is used to detect the 1 st air-fuel ratio Ca1, which is the air-fuel ratio (lambda) of the exhaust gas G flowing into the LNT device 21. Further, a2 nd λ sensor 35 is provided on the inlet side of the CSF device 22, and this 2 nd λ sensor 35 is used to detect a2 nd air-fuel ratio Ca2, which is the air-fuel ratio (λ) of the exhaust gas G flowing into the CSF device 22.

Further, as for the exhaust gas temperature sensor, a1 st exhaust gas temperature sensor (1 st temperature detecting means) 36 for detecting a1 st exhaust gas temperature Tg1, which is the temperature of the exhaust gas G flowing into the LNT device 21, is provided on the inlet side of the LNT device 21. Further, a2 nd exhaust gas temperature sensor (2 nd temperature detecting means) 37 for detecting a2 nd exhaust gas temperature Tg2, which is the temperature of the exhaust gas G flowing into the SCR device 24, is provided on the inlet side of the SCR device 24. Further, a 3 rd exhaust gas temperature sensor 38 is provided on the inlet side of the CSF device 22, and the 3 rd exhaust gas temperature sensor 38 detects a 3 rd exhaust gas temperature Tg3, which is the temperature of the exhaust gas G flowing into the CSF device 22.

That is, the present invention is configured to include: a1 st exhaust gas temperature sensor 36 that measures a1 st exhaust gas temperature Tg1 that is the temperature of the exhaust gas G flowing into the LNT device 21; and a2 nd exhaust gas temperature sensor 37 that measures a2 nd exhaust gas temperature Tg2 that is the temperature of the exhaust gas G flowing into the SCR device 24.

The detection values of these various sensors 31 to 38 are input to the control device 40, and the control device 40 performs various calculations based on these input data and outputs a control command to the engine main body 10. At the same time, a control command is also output to the aqueous urea solution supply device 23, and the injection amount U1 of the reducing agent U injected from the aqueous urea solution supply device 23 is adjusted and controlled.

Further, the exhaust gas purification system 1 performs filter regeneration control for oxidizing and removing PM trapped in the CSF device 22 by raising the exhaust gas temperature in accordance with the control command of the control device 40, performs NOx purification control (NOx regeneration control) for releasing absorbed NOx in the LNT device 21 by raising the exhaust gas temperature and making the air-fuel ratio of the exhaust gas G rich, and performs reduction purification of the released NOx by the three-way catalyst carried on the LNT device 21, and performs sulfur purification control for removing sulfur components absorbed in the LNT device 21 by raising the exhaust gas temperature to a temperature higher than the temperature of the NOx regeneration control.

As shown in fig. 2, the control device 40 includes a filter regeneration control unit 41 for performing the above-described filter regeneration control, an NOx purification control unit 42 for performing the NOx purification control, a sulfur purification control unit 43 for performing the sulfur purification control, and an aqueous urea solution supply control unit 44, and is configured to further include an estimated NH₃Adsorption amount calculation unit (calculation unit) 51, NH₃Adsorption amount determination unit (determination unit 52), and adsorbed NH₃A consuming unit (consuming unit) 53.

The estimated NH₃The adsorption amount calculation unit 51 calculates NH in the SCR device 24₃Estimated NH that is an estimated value of the amount of (reducing agent) adsorption₃A member for adsorbing Se. In addition, NH₃The adsorption amount determination unit 52 is the following member: at the start of filter regeneration for removing PM by combustion in the CSF device 22, it is determined that NH is estimated₃The estimated NH at the start of filter regeneration calculated by the adsorption amount calculation unit 51₃Whether the adsorption amount Se is a preset target NH₃An adsorption amount St or more.

In addition, NH is adsorbed₃The consuming part 53 is the following: at NH₃In the adsorption amount determination section 52, the NH is estimated₃Estimated NH calculated by the adsorption amount calculation part 51₃The adsorption amount Se is the target NH₃When the adsorption amount St is equal to or more than the adsorption amount St, NH is adsorbed in the SCR device 24₃Reduced adsorbed NH₃Consumption control so that NH is estimated₃Estimated NH calculated by the adsorption amount calculation part 51₃The adsorption amount Se becomes less than the target NH₃The adsorption amount St.

The adsorbed NH₃The consumption unit 53 is configured to perform adsorption reductant consumption control for raising or maintaining the temperature of the exhaust gas G so that the 1 st exhaust gas temperature Tg1 detected by the 1 st exhaust gas temperature sensor 36 becomes equal to or higher than the 1 st set temperature Tgc1 that is set in advance based on the NOx emission temperature in the LNT device 21. The 1 st set temperature Tgcl is set to a temperature at which the NOx purification rate of the LNT device 21 decreases, in other words, a temperature at which the NOx absorbing capacity decreases, for example, 400 ℃ or higher, so that the relationship between the NOx purification rate and the engine outlet temperature illustrated in fig. 4 shows a temperature at which the NOx purification rate of the LNT decreases.

By the temperature rise of the NOx occlusion reduction catalyst of the LNT device 21 due to the temperature rise of the exhaust gas G, NOx occluded in the LNT device 21 is released before the filter regeneration is started at the time of filter regeneration, and the released NOx flows into the SCR device 24 on the downstream side. By the inflow of NOx and NH adsorbed by the SCR device 24₃NOx is reduced and purified by the reaction, and NH can be adsorbed in the SCR device 24₃And (4) reducing.

In this case, it is preferable that the air-fuel ratio (λ) in the exhaust gas G be lean, unlike the NOx purification control. This is because if the air-fuel ratio is brought into a rich state, the catalyst is released from the NOx absorption reduction type catalystSince the discharged NOx is reduced and purified by the three-way catalyst, the NOx flowing into the SCR device 24 is reduced, and NH adsorbed in the SCR device 24₃The reduction effect of (a) is reduced.

Further, NH is adsorbed₃The consumption unit 53 is preferably configured to raise or maintain the 2 nd exhaust gas temperature Tg2 so as to adsorb NH₃In the consumption control, the 2 nd exhaust gas temperature Tg2 detected by the 2 nd exhaust gas temperature sensor 37 is based on NH in the SCR device 24₃A2 nd set temperature Tgc2 or higher predetermined based on the consumption rate and based on NH in the SCR device 24₃The discharge temperature is not higher than the preset 3 rd set temperature Tgc 3. The 2 nd set temperature Tgc2 is set to be high in NOx purification rate and absorb NH₃The consumption rate of (b) is increased, for example, around 300 ℃, so that in the relationship between the NOx purification rate and the engine outlet temperature illustrated in fig. 4, there is a temperature at which the NOx purification rate in the SCR is increased.

By the temperature rise of the SCR catalyst of the SCR device 24 due to the temperature rise of the exhaust gas G, NH adsorbed to the SCR device 24 is caused to flow before the start of filter regeneration at the time of filter regeneration₃Reacts with NOx. Due to the efficiency of the NOx reduction reaction, i.e., NH₃The consumption efficiency is increased when the 2 nd exhaust gas temperature Tg2 is equal to or higher than the set 2 nd set temperature Tgc2, so that NH can be absorbed in the SCR device 24 in a short time₃And (4) reducing.

In addition, if the SCR catalyst temperature of the SCR device 24 becomes too high, the NOx purification rate in the SCR device 24 decreases, so the 2 nd exhaust gas temperature Tg2 is suppressed to the 3 rd set temperature Tgc3 or lower set as described above. The 3 rd set temperature Tgc3 is set to have a low NOx purification rate and to absorb NH₃The consumption rate of (2) is decreased, for example, about 400 ℃, so that the relationship between the NOx purification rate and the engine outlet temperature illustrated in fig. 4 has a temperature at which the NOx purification rate in the SCR is decreased. That is, according to the relationship between the NOx purification rate and the engine outlet temperature illustrated in fig. 4, the 2 nd exhaust gas temperature Tg2 is raised or maintained within a temperature range corresponding to the temperature range Ra in which the NOx purification rate in the SCR is raised.

Also, embodiments of the present disclosureThe exhaust gas purification method of the internal combustion engine of the formula (hereinafter, referred to as exhaust gas purification method) is a method of: the exhaust passage 11 of the internal combustion engine includes, in order from the upstream side, an LNT device 21 that absorbs NOx in the exhaust gas G and a NOx passing NH₃The SCR device 24 that reduces NOx in the exhaust gas G, and the CSF device 22 that traps PM in the exhaust gas G is included in the exhaust passage 11, as a method described below.

In the exhaust gas purification method, NH in the SCR device 24 is calculated₃Estimated value of adsorbed amount, i.e., estimated NH₃The adsorption Se is determined at the beginning of filter regeneration for burning and removing PM of CSF device 22 by calculating estimated NH at the beginning of regeneration₃Whether the adsorption amount Se is a preset target NH₃At least the adsorption amount St, in estimating NH₃The adsorption amount Se is the target NH₃When the adsorption amount St is equal to or more than the adsorption amount St, NH is adsorbed in the SCR device 24₃Reduced adsorbed NH₃Consumption control so that the calculated estimated NH₃The adsorption amount Se becomes less than the target NH₃The adsorption amount St.

This control can be implemented by a control flow of one example as shown in fig. 3. The control flow of fig. 3 shows: when the internal combustion engine starts to operate, the control flow is called from the higher-level control flow, is executed in parallel with the operation control flow of the other exhaust gas purification system 1, is interrupted when the operation of the internal combustion engine is completed, returns to the higher-level control flow, and is completed together with the higher-level control flow.

If the control flow of fig. 3 is called from the higher-level control flow and started, then "there is a reproduction request? "is used to determine whether or not there is a filter regeneration request (hereinafter referred to as regeneration request) that requests filter regeneration control (hereinafter referred to as regeneration control) in the CSF device 22. In this determination, when there is no reproduction request, the control flow returns to the higher-level control flow, and after a predetermined time has elapsed, the control flow is called again by the higher-level control flow and started, and the flow is repeated.

"there is a regeneration request" at step S11? If there is a regeneration request for the determination of "yes", the process proceeds to "stop of NOx purification control" in step S12. In the "stop of the NOx purification control" in step S12, the NOx purification control of the NOx occlusion reduction catalyst is stopped, and the NOx reduction control (DeNOx control) of the NOx occlusion reduction catalyst is stopped. That is, the NOx purification control is stopped.

In the next step S13 "input of SCR inlet temperature", the 2 nd exhaust gas temperature Tg2 detected by the 2 nd exhaust gas temperature sensor 37, that is, the SCR inlet temperature is input. And, at "target NH₃In the setting of the adsorption amount St, "NH that can be adsorbed in the SCR device 24 is used₃Since the adsorption amount Smax is greatly influenced by the temperature of the SCR catalyst, the target NH at the time of filter regeneration (hereinafter referred to as regeneration) is set based on the 2 nd exhaust gas temperature Tg2₃The adsorption amount St. Since the flow rate of the exhaust gas is small during regeneration and the temperature of the exhaust gas rapidly increases, ammonia slip is likely to occur, the target NH is not limited to the target NH during regeneration₃The target NH at the time of regeneration is smaller than the adsorption amount St0₃The adsorption amount St is set to a value smaller than St 0.

Further, in the case of "estimating NH₃In the calculation of the adsorption amount Se', NH in the SCR device 24 is calculated₃Estimated value of adsorbed amount, i.e., estimated NH₃The amount of Se adsorbed. The estimated NH₃The adsorption Se is from NH supply₃Amount minus NH consumed₃Amount, further minus NH₃Value obtained by leakage amount (estimated NH)₃Adsorbed amount Se being previously estimated NH₃Adsorption amount + supply of NH₃Amount-consumption of NH₃Amount of-NH₃Amount of leakage).

The supply of NH₃The amount being NH produced by hydrolysis from the urea water U₃The supply amount of (4) is calculated based on the injection amount U1 of the urea water U supplied from the urea water supply device 23, and the like₃Amount of the compound (A).

Consumption of NH₃The amount is NH used when reducing the amount of NOx generated from the engine main body 10₃Amount of the compound (A). Based on the amount of NOx flowing into the SCR device 24 and the temperature of the SCR catalyst (e.g., replaced with a2 nd exhaust gas temperature Tg 2), exhaust gas GFlow rate, NO and NO₂Ratio of (1) and NH at the time of reaction₃The amount of adsorption and the like were calculated to calculate the NH consumed₃Amount of the compound (A). The NOx amount flowing into the SCR device 24 can be estimated from the NOx amount per unit time obtained from the 2 nd NOx concentration Cn2 on the outlet side of the LNT device 21 and the flow rate of the exhaust gas G.

The NOx amount flowing into the SCR device 24 (SCR inlet NOx amount) is a value obtained by subtracting the NOx absorption/desorption amount of the LNT device 21 and the NOx reduction amount of the LNT device 21 from the engine outlet NOx amount (SCR inlet NOx amount — NOx absorption/desorption amount of LNT device — NOx reduction amount of LNT device).

The amount of NOx at the engine outlet may be estimated from the engine operating state or calculated from the NOx sensor at the inlet side of the LNT device 21 and the exhaust gas flow rate. The NOx adsorption/desorption amount of the LNT device 21 may be calculated from the LNT temperature, the exhaust gas flow rate, and the NOx adsorption amount. The NOx reduction amount of the LNT device 21 may be calculated from the LNT temperature, the exhaust gas flow rate, the NOx absorption amount, and the air-fuel ratio.

In addition, NH₃The amount of slip is based on NH in the SCR device 24₃The adsorption amount, the temperature, the flow rate of the exhaust gas G, and the like.

Then, in the determination of "Se ≧ St" at S14 in the next step, the estimated NH is determined₃Whether the adsorption amount Se is larger than the target NH₃The adsorption amount St. In the determination of "Se ≧ St" in step S14, NH is estimated₃The adsorption amount Se is the target NH₃If the adsorption amount St is equal to or greater than the adsorption amount St (yes), the process proceeds to "adsorb NH" in step S15₃Consumption control ", after a predetermined time has elapsed, the process returns to step S13 to estimate a new estimated NH that has changed within the predetermined time₃Adsorption Se and new target NH₃The adsorption amounts St are compared.

In the adsorption of NH₃During the consumption control, adsorption of NH into the SCR device 24 is performed₃Control of reduction so that the calculated estimated NH is₃The adsorption amount Se becomes less than the target NH₃The adsorption amount St or the 2 nd exhaust gas temperature Tg2 is set to the 2 nd set temperature Tgc2 and a 3 rd set temperature Tgc 3. Specifically, NH is adsorbed in the catalyst₃In the consumption control, the temperature of the exhaust gas G is raised or maintained so that the 1 st exhaust gas temperature Tg1 becomes the 1 st set temperature Tgc1 or higher. As the temperature increase of the exhaust gas G, the following method is adopted: the fuel injection amount in the engine main body 10 is increased, or the unburned fuel supplied to the exhaust passage 11 by the after injection or the in-exhaust pipe fuel injection is oxidized in the LNT device 21 to generate heat, or the like.

In the determination of "Se ≧ St" in step S14, NH is estimated₃The adsorption amount Se is less than the target NH₃In the case of the adsorption amount St, "regeneration condition is satisfied? ". "regeneration condition is satisfied" in step S16? "yes", it is determined whether or not the start condition of regeneration control in the CSF device 22 is satisfied, and if the start condition of regeneration control is not satisfied (no), the process returns to step S13 after a predetermined time has elapsed.

On the other hand, "regeneration condition is satisfied? If the start condition of the regeneration control is satisfied (yes), "the process proceeds to" regeneration control "in step S17, the regeneration control in the CSF device 22 is performed, and after the regeneration control is completed, the process proceeds to return to the higher-level control flow, and after a predetermined time has elapsed, the process is called again from the higher-level control flow and started, and the flow is repeated.

In the middle of the control flow of fig. 3, if the operation of the internal combustion engine is finished, the control is terminated by interruption, and after the termination process of the control, which is not shown but is necessary, the control flow returns to the higher-level control flow and is terminated together with the higher-level control flow.

Further, the 1 st exhaust gas temperature Tg1 is used instead of the catalyst temperature of the LNT device 21, but the 3 rd exhaust gas temperature Tg3 may be used, and when a more accurate catalyst temperature is estimated, the 1 st exhaust gas temperature Tg1 and the 3 rd exhaust gas temperature Tg3 may be used, and a simple average or a weighted average may be used as the catalyst temperature of the LNT device 21.

Further, the 2 nd exhaust gas temperature Tg2 is used instead of the catalyst temperature of the SCR device 24, but a 4 th exhaust gas temperature sensor may be provided in the exhaust passage 11 between the SCR device 24 and the DOC device 25, and the 4 th exhaust gas temperature Tg4 detected by the 4 th exhaust gas temperature sensor may be used, and when a more accurate catalyst temperature is estimated, the 2 nd exhaust gas temperature Tg2 and the 4 th exhaust gas temperature Tg4 may be used, and a simple average or a weighted average may be used as the catalyst temperature of the SCR device 24.

As described above, 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 embodiment, NH adsorbed by the SCR catalyst of the SCR device 24 is prevented from being adsorbed at the time of filter regeneration₃Is released and discharged to flow out to the downstream side of the SCR device 24, and can solve the problem that the time until the filter regeneration is started becomes long.

Particularly, when the LNT device 21 carrying the LNT catalyst is disposed in the front stage of the SCR device 24 carrying the SCR catalyst, NOx is absorbed by the LNT catalyst of the LNT device 21, and NH in the SCR device 24 is absorbed by the LNT catalyst of the LNT device 21₃Reduction of consumption is less efficient, so to NH₃The waiting time until the adsorption amount is reduced becomes long, and the time until the filter regeneration is started becomes long, but this problem can be solved more effectively.

That is, NH within the SCR device 24₃When the adsorption amount is large and the NOx adsorption amount of the LNT device 21 is small, it is necessary to saturate the NOx adsorption amount of the LNT device 21 and consume the adsorbed NH of the SCR device 24₃Time is required. In response to such a situation, the temperature is raised to a temperature at which the NOx absorption efficiency of the LNT device 21 is lowered, whereby the adsorbed NH in the SCR device 24 by the released NOx from the LNT device 21 is obtained₃Consumption is performed, saturation of NOx absorption in the LNT device 21 becomes unnecessary, and reaction efficiency is improved by a temperature rise of the SCR catalyst of the SCR device 24 (═ NH₃Improvement in consumption efficiency), the time until the start of filter regeneration can be shortened. This can reduce the NOx emission amount and also suppress excessive PM accumulation in the CSF device 22.

The present application is based on the japanese patent application filed on 19/2/2018 (japanese application 2018-027008) and the content thereof is hereby incorporated by reference.

Industrial applicability

The exhaust gas purification system and the exhaust gas purification method according to the present disclosure are useful in that, at the time of filter regeneration, the reducing agent adsorbed by the SCR catalyst of the SCR device is prevented from being desorbed and released and flows out to the downstream side of the SCR device, and the problem that the time until filter regeneration is started becomes long and the concern that the NOx emission amount increases as a result thereof is solved.

Description of the reference numerals

1 exhaust gas purification system for internal combustion engine

10 Engine main body

11 exhaust passage

21 LNT device (absorption reduction type catalyst device)

22 CSF device (Filter device with catalyst)

23 Urea water supply device (reducing agent supply device)

24 SCR device (selective reduction type catalyst device)

25 DOC device (ASC: oxidation catalyst device)

31 st NOx sensor

32 nd NOx sensor

33 rd NOx sensor

34 1 st lambda sensor

35 nd 2 lambda sensor

36 st 1 exhaust gas temperature sensor (1 st temperature detector)

37 nd 2 nd exhaust gas temperature sensor (2 nd temperature detecting device)

38 rd exhaust gas temperature sensor

40 control device

41 Filter regeneration control section

42 NOx purification control section

43 Sulfur purification control section

44 urea water supply control unit

51 presumption of NH₃Absorption amount calculating part (calculating part)

52 NH₃Adsorption amount determination part (determination part)

53 absorption of NH₃Consumption part (consumption part)

G exhaust gas

U Urea water (reducing agent)

Claims

1. An exhaust gas purification system of an internal combustion engine,

in an exhaust passage of the internal combustion engine including, in order from an upstream side, an NOx absorption reduction catalyst device that absorbs NOx in exhaust gas and a selective reduction catalyst device that reduces NOx in exhaust gas by a reducing agent, and in the exhaust passage including a filter device that traps particulate matter in exhaust gas, the exhaust gas purification system being characterized in that,

comprises a control device having a calculation unit, a determination unit, and a consumption unit,

the calculation unit calculates an estimated reductant adsorption amount that is an estimated value of the reductant adsorption amount in the selective reduction catalyst device,

the determination unit determines whether or not the estimated amount of adsorption of the reducing agent at the time of start of regeneration calculated by the calculation unit is equal to or greater than a preset target amount at the time of start of regeneration of the filter device for removing particulate matter by combustion,

when the determination unit determines that the estimated adsorbed amount of the reducing agent calculated by the calculation unit is equal to or greater than the target amount, the consumption unit performs adsorbed reducing agent consumption control for reducing the adsorbed reducing agent in the selective reduction catalyst device so that the estimated adsorbed amount of the reducing agent calculated by the calculation unit becomes less than the target amount.

2. The exhaust gas purification system according to claim 1,

comprising a1 st temperature detection means for measuring the temperature of the exhaust gas flowing into the NOx absorption-reduction catalyst device,

the consumable unit is configured to: in the adsorbed reductant consumption control, the exhaust gas temperature is raised or maintained so that the 1 st exhaust gas temperature detected by the 1 st temperature detection device becomes equal to or higher than the 1 st set temperature that is set in advance based on the NOx emission temperature in the adsorption-reduction catalyst device.

3. The exhaust gas purification system according to claim 1 or 2,

comprising a2 nd temperature detection means for measuring the temperature of the exhaust gas flowing into the selective reduction catalyst device,

the consumable unit is configured to: in the adsorbed reductant consumption control, the exhaust gas temperature is raised or maintained so that the 2 nd exhaust gas temperature detected by the 2 nd temperature detection device becomes equal to or higher than the 2 nd set temperature that is set in advance based on the reductant consumption efficiency in the selective reduction catalyst device and equal to or lower than the 3 rd set temperature that is set in advance based on the reductant release temperature in the selective reduction catalyst device.

4. An exhaust gas purification method of an internal combustion engine,

in an exhaust passage of the internal combustion engine including, in order from an upstream side, an NOx absorption reduction catalyst device that absorbs NOx in exhaust gas and a selective reduction catalyst device that reduces NOx in exhaust gas by a reducing agent, and in the exhaust passage including a filter device that traps particulate matter in exhaust gas, the exhaust gas purification method is characterized in that,

calculating an estimated reductant adsorption amount which is an estimated value of the reductant adsorption amount in the selective reduction catalyst device,

determining whether or not the calculated estimated amount of adsorption of the reducing agent at the start of regeneration is equal to or greater than a preset target amount at the start of regeneration of the filter for burning and removing particulate matter in the filter device,

when the estimated reductant adsorption amount is equal to or greater than the target amount, adsorbed reductant consumption control is performed to reduce the adsorbed reductant in the selective reduction catalyst device so that the calculated estimated reductant adsorption amount is less than the target amount.