Exhaust gas purification device, exhaust gas purification method, exhaust gas purification program

Abstract

To prevent emission of ammonia and nitrogen oxide by supplying oxygen and nitrogen oxide in an appropriate amount respectively required for decomposing ammonia into nitrogen and water, and causing an adsorption catalyst to perform regeneration treatment under monitoring by an NOx concentration sensor.SOLUTION: When compared to a threshold set as a limit of pure NOx concentration, an output value of an NOx concentration sensor 28 reaches the threshold sooner than an acceptable range of an appropriate regeneration treatment completion timing, and the regeneration treatment is finished in a state of imperfect regeneration treatment. Therefore, when the regeneration treatment of an SCR catalyst 18 is started, an output value of concentration detected by the NOx concentration sensor 28 is stored as ammonia concentration ΔNH3, and hereafter, a result of subtracting ΔNH3 from the output value of the concentration detected by the NOx concentration sensor 28 is compared to the threshold.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification device using a catalyst, an exhaust gas purification method, and an exhaust gas purification program in an internal combustion engine.

Background Art

[0002] Techniques for purifying harmful substances such as nitrogen oxides (NOx) such as nitrogen monoxide and nitrogen dioxide contained in the exhaust gas of internal combustion engines such as engines using a catalyst are known. Further, as an internal combustion engine, an ammonia engine using ammonia as fuel has been studied. Since ammonia does not contain carbon atoms, there is an advantage that carbon dioxide is not generated by combustion in an ammonia engine.

[0003] When ammonia is completely burned, all ammonia is converted to nitrogen and water. However, when ammonia is actually burned in an ammonia engine, there are incomplete combustion components, and for example, exhaust gas containing unreacted ammonia, nitrogen oxides, etc. is discharged. Therefore, it is desirable to purify unreacted ammonia, nitrogen oxides, etc. contained in the exhaust gas using a catalyst or the like.

[0004] In Patent Document 1, as an exhaust gas purification device for an internal combustion engine that obtains driving force by burning ammonia, a redox catalyst having an oxidation action and a reduction action provided in a main flow path through which exhaust gas from the internal combustion engine flows, a selective reduction catalyst provided in the main flow path, a temperature acquisition unit that acquires the temperature of the selective reduction catalyst, and when the temperature of the selective reduction catalyst acquired by the temperature acquisition unit exceeds the activation temperature of the selective reduction catalyst, a control unit that changes the mixing ratio of the exhaust gas upstream of the redox catalyst and the selective reduction catalyst from stoichiometric to lean is described.

[0005] In Patent Document 2, in order to measure the ammonia concentration in exhaust gas, it is described that two sensors, a zirconia NOx concentration sensor and a constant potential electrolytic sensor, are provided, and the ammonia concentration is calculated based on the difference between their measured values.

[0006] In the prior art, including Patent Document 1, when it is determined that the regeneration treatment conditions for the adsorption catalyst are met, the exhaust gas mixing ratio is changed from stoichiometric (excess air ratio λ=1) to dilute (excess air ratio λ>1), and the dilute state is terminated by comparing the detected value near the outlet of the adsorption catalyst, which is detected by a NOx concentration sensor that detects the concentration of nitrogen oxides, with a predetermined threshold. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2019-167823 [Patent Document 2] Japanese Patent Publication No. 2022-067790 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, conventional technology does not take into account the ammonia concentration that affects the NOx concentration sensor. In other words, when detecting nitrogen oxide concentration with the NOx concentration sensor, the ammonia concentration emitted from the adsorption catalyst before the end of the regeneration process is added to the detected value in the NOx concentration sensor. As a result, the threshold is reached earlier than the intended end time of the dilution state, and the dilution state ends prematurely.

[0009] As described in Patent Document 2, a constant potential electrolytic sensor can be used to detect only the concentration of nitrogen oxides. However, constant potential electrolytic sensors are not widely used, and maintenance is complicated, making their application to mass-produced power equipment and the like impractical. Therefore, it is preferable to use a NOx concentration sensor that is easy to maintain, inexpensive, and highly versatile.

[0010] The present invention aims to provide an exhaust gas purification device, an exhaust gas purification method, and an exhaust gas purification program that can supply appropriate amounts of oxygen and nitrogen oxides, which are necessary for decomposing ammonia into nitrogen and water to regenerate the adsorption catalyst, under the monitoring of a NOx concentration sensor, thereby preventing the release of ammonia and nitrogen oxides. [Means for solving the problem]

[0011] The exhaust gas purification device according to the present invention is an exhaust gas purification device for purifying exhaust gas produced when a fuel containing ammonia is burned after being mixed with air to a predetermined fuel-air ratio with an excess air content, and comprises a catalytic device provided in the exhaust gas passage through which the exhaust gas after combustion flows, and composed of an oxidation-reduction catalyst having an oxidation-reduction function and an adsorption catalyst having an ammonia adsorption function, a NOx concentration sensor capable of detecting the concentration of at least nitrogen oxides discharged from the adsorption catalyst, and when the adsorption catalyst is determined to be in an active state, a regeneration process is started in which nitrogen oxides and oxygen are supplied to the adsorption catalyst at a dilute ratio lower than the predetermined excess air content to oxidize the ammonia adsorbed on the adsorption catalyst, At the time it is determined that the adsorption catalyst is in an active state The NOx concentration sensor detected above The initial output value was considered as the ammonia concentration, and detected by the NOx concentration sensor. From the output value The value obtained by subtracting the aforementioned initial output value is used as the correction value, The system includes a control unit that terminates the playback process when the correction value reaches a predetermined threshold.

[0012] According to the present invention, a catalytic device for purifying exhaust gas when a fuel containing ammonia is mixed with a fuel-air ratio that results in a predetermined excess air ratio and burned comprises an oxidation-reduction catalyst having an oxidation-reduction function and provided in the exhaust gas passage through which the exhaust gas after combustion flows, and an adsorption catalyst having an ammonia adsorption function.

[0013] A predetermined excess air ratio is, for example, a stoichiometric value where the excess air ratio λ is 1 (λ=1), and it is preferable to provide feedback control to this stoichiometric value based on an excess air ratio sensor.

[0014] When the control unit determines that the adsorption catalyst is in an active state, it supplies at least nitrogen oxides and oxygen to the adsorption catalyst at a dilute ratio lower than a predetermined excess air ratio (λ>1) and starts a regeneration process to oxidize the ammonia adsorbed on the adsorption catalyst.

[0015] Furthermore, the output value detected by the NOx concentration sensor is compared with a predetermined threshold, and the point at which this threshold is reached is defined as the end of regeneration.

[0016] Here, the NOx concentration sensor can detect the concentration of at least nitrogen oxides emitted from the adsorption catalyst, but it also reacts to the concentration of ammonia.

[0017] Therefore, the control unit terminates the regeneration process when the correction value obtained by subtracting the ammonia concentration that reacts with the NOx concentration sensor from the output value detected by the NOx concentration sensor reaches a predetermined threshold.

[0018] This allows for the supply of appropriate amounts of oxygen and nitrogen oxides, which are necessary for decomposing ammonia into nitrogen and water to regenerate the adsorption catalyst, under the monitoring of a NOx concentration sensor, thereby preventing the release of ammonia and nitrogen oxides.

[0020] When it is determined that the adsorption catalyst is in an active state, the initial output value detected by the NOx concentration sensor can be considered as the concentration of ammonia, and the value obtained by subtracting the initial output value from the output value detected by the NOx concentration sensor can be used as the correction value.

[0021] In the present invention, The control unit, The system is characterized by calculating the rate of change of the output value detected by the NOx concentration sensor, and using the calculated conversion rate as the correction value.

[0022] The rate of change of the output value detected by the NOx concentration sensor may be calculated, and the calculated conversion rate may be used as the correction value. Since the rate of change of nitrogen oxides is greater than the rate of change of ammonia, the difference can be used to offset the ammonia concentration.

[0023] In the present invention, when determining the end of the regeneration process using the change rate of the nitrogen oxides, a predetermined period from the start of the regeneration process is set as a masking period during which the determination is not performed.

[0024] When determining the end of the regeneration process using the change rate of the nitrogen oxides, it is preferable to set a predetermined period from the start of the regeneration process as a masking period during which the determination is not performed.

[0025] In the present invention, an air excess ratio sensor is further provided upstream of the catalyst device in the direction in which the exhaust gas flows in the exhaust gas passage, for detecting the air excess ratio of the exhaust gas flowing in the exhaust gas passage. The supply of the nitrogen oxides and the oxygen for the regeneration process by the control unit is a combustion operation that is leaner than a predetermined air excess state, and the control unit performs feedback control of the fuel-air ratio based on the air excess ratio detected by the air excess ratio sensor.

[0026] The predetermined air excess ratio is, for example, the stoichiometry where the air excess ratio λ is 1 (λ = 1), and feedback control is performed based on the stoichiometry using the air excess ratio sensor.

[0027] When the control unit determines that the adsorption catalyst is in an active state, the regeneration process is started by supplying at least nitrogen oxides and oxygen to the adsorption catalyst in a lean state (λ > 1) compared to a predetermined air excess state, and oxidizing the ammonia adsorbed on the adsorption catalyst.

[0028] In the present invention, the control unit measures or estimates the temperature of the adsorption catalyst, and determines the active state of the adsorption catalyst based on the measured or estimated temperature of the adsorption catalyst.

[0029] The start timing of the regeneration process can be determined by measuring or estimating the temperature of the adsorption catalyst and determining the active state of the adsorption catalyst based on the measured or estimated temperature of the adsorption catalyst.

[0030] The exhaust gas purification method according to the present invention is an exhaust gas purification method comprising a control unit that purifies exhaust gas by burning a fuel containing ammonia mixed with air at a predetermined fuel-air ratio with excess air, guiding the exhaust gas after combustion into an exhaust gas passage and passing it through a redox catalyst having an oxidation-reduction function and an adsorption catalyst having an ammonia adsorption function, wherein when the control unit determines that the adsorption catalyst is in an active state, it starts a regeneration process to oxidize the ammonia adsorbed on the adsorption catalyst by supplying nitrogen oxides and oxygen to the adsorption catalyst at a dilute ratio lower than the predetermined excess air ratio, When it is determined that the adsorption catalyst is in an active state The concentration of at least nitrogen oxides emitted from the adsorption catalyst was detected by a NOx concentration sensor capable of detecting this concentration. The initial output value at the start of the regeneration process is considered to represent the ammonia concentration, and the value obtained by subtracting the initial output value from the output value detected by the NOx concentration sensor is used as the correction value. A key feature is that the playback process terminates when the correction value reaches a predetermined threshold.

[0031] The exhaust gas purification program according to the present invention is characterized in that a computer is operated as the control unit of the exhaust gas purification device described above. [Effects of the Invention]

[0032] As described above, in the present invention, oxygen and nitrogen oxides, which are necessary for decomposing ammonia into nitrogen and water to regenerate the adsorption catalyst, can be supplied in appropriate amounts under the monitoring of a NOx concentration sensor, thereby preventing the release of ammonia and nitrogen oxides. [Brief explanation of the drawing]

[0033] [Figure 1] This is a schematic diagram of the engine system according to this embodiment. [Figure 2] This is a characteristic diagram of the components (nitrogen oxides, ammonia) near the outlet of the adsorption catalyst according to this embodiment. [Figure 3] This is a control flowchart showing the flow of the exhaust gas purification process during the regeneration process of the SCR catalyst, which is executed by the control unit according to this embodiment. [Figure 4] This is a characteristic diagram of the rate of change of components (nitrogen oxides, ammonia) near the outlet of the modified adsorption catalyst. [Figure 5] This is a schematic diagram of the engine system in a modified form. [Modes for carrying out the invention]

[0034] Figure 1 is a schematic diagram of an engine system 10 as one embodiment of the present invention.

[0035] The engine system 10 includes an internal combustion engine 12. The internal combustion engine 12 is an ammonia engine that obtains driving force by burning ammonia gas. Hereafter, ammonia gas will be simply referred to as "ammonia."

[0036] The engine system 10 includes an exhaust gas purification device 14 that purifies harmful substances, such as ammonia (NH3) and nitrogen oxides (NOx), in the exhaust gas from the internal combustion engine 12.

[0037] The internal combustion engine 12 is supplied with air at a flow rate adjusted by the throttle, and with a fuel supply valve adjusted by the fuel supply valve, as controlled by the control unit 20. The control unit 20 is implemented, for example, by an electronic control unit (ECU, "Electronic Control Unit," not shown).

[0038] The control unit 20 controls the mass ratio (mixture ratio) of air to fuel in the exhaust gas discharged from the internal combustion engine 12 to rich, stoichiometric, and lean states. When the mixture ratio is defined as "Φ = stoichiometric air-fuel ratio / actual air-fuel ratio of the mixture", the rich state means a mixture ratio where Φ > 1, the stoichiometric state means a mixture ratio where Φ = 1, and the lean state means a mixture ratio where Φ < 1.

[0039] Here, Φ is the equivalent ratio, and its reciprocal is the air excess ratio λ, which is the unit used to express an excess of air. For example, an air excess ratio λ > 1 corresponds to a dilute state.

[0040] As will be explained in more detail later, one of the objectives of this embodiment is to increase the amount of air (oxygen) beyond the target mixing ratio. Therefore, the following explanation will use the air excess ratio λ.

[0041] The exhaust gas purification device 14 of this embodiment purifies harmful substances in exhaust gas by utilizing oxidation-reduction and adsorption functions. In the following description, a three-way catalyst 16 is given as an example of a catalyst with oxidation-reduction function, and a selective catalytic reduction catalyst 18 is given as an example of a catalyst with adsorption function.

[0042] Furthermore, as a catalyst with redox function, catalysts other than the three-way catalyst 16 can also be used, as long as they possess both oxidizing and reducing properties. For example, as a redox catalyst, a catalyst can be used that uses ceramics or titanium oxide as a support and supports precious metals such as platinum, rhodium, or palladium as the active catalyst component.

[0043] Similarly, as a catalyst with adsorption capabilities, catalysts other than SCR catalyst 18 can be used, as long as they are catalysts that have an ammonia adsorption effect. For example, for adsorption, catalysts can be used that use ceramics or titanium oxide as a support and support zeolite as the active catalyst component.

[0044] As shown in Figure 1, the exhaust gas purification device 14 mainly consists of a three-way catalyst 16 and an SCR catalyst 18, which are attached in order from the upstream side to the exhaust gas pipe 22 extending from the internal combustion engine 12. That is, the exhaust gas from the internal combustion engine 12 passes through the flow path in the exhaust gas pipe 22, through the three-way catalyst 16 and the SCR catalyst 18, and is released into the outside air.

[0045] Furthermore, in the exhaust gas pipe 22, an excess air ratio sensor 24 (hereinafter referred to as λ sensor 24) is provided between the internal combustion engine 12 and the three-way catalytic converter 16 to detect the excess air ratio λ of the gas flowing through the exhaust gas pipe 22.

[0046] Furthermore, the exhaust gas pipe 22 is equipped with a temperature detection unit 26 for detecting the temperature of the gas flowing through the exhaust gas pipe 22 and a NOx concentration sensor 28 for detecting the NOx concentration, located downstream of the SCR catalyst 18.

[0047] The detection signals detected by the λ sensor 24, the temperature detection unit 26, and the NOx concentration sensor 28 are sent to the control unit 20.

[0048] Furthermore, the λ sensor 24 may not directly detect the excess air ratio λ, but rather detect information that allows for the acquisition of the excess air ratio λ as a result of analysis by the control unit 20.

[0049] The control unit 20 adjusts the exhaust gas mixture ratio upstream of the three-way catalyst 16 and the SCR catalyst 18 by switching the mixture ratio of the internal combustion engine 12 using the acquired detection values.

[0050] (Details of each part of the exhaust gas purification device 14) The λ sensor 24 acquires the oxygen (O2) concentration (i.e., the mixture ratio) of the exhaust gas from the internal combustion engine 12 upstream of the three-way catalyst 16.

[0051] The control unit 20 is configured to feedback control the fuel injection amount to achieve the target λ based on the detection signal from the λ sensor 24.

[0052] The three-way catalyst 16 is located at the upstream end of the flow path of the exhaust gas pipe 22, in other words, upstream of the SCR catalyst 18. The three-way catalyst 16 can purify ammonia, nitrogen oxides (NOx), and hydrogen (H2) in the exhaust gas, but it has the characteristic that its purification performance decreases when the mixing ratio falls outside a predetermined range near stoichiometry.

[0053] The SCR catalyst 18 is located at the downstream end of the main flow path, in other words, downstream of the three-way catalyst 16. The SCR catalyst 18 can purify nitrogen oxides (NOx) in the exhaust gas using ammonia as a reducing agent.

[0054] The temperature detection unit 26 is a sensor that measures the temperature near the outlet of the SCR catalyst 18. The control unit 20 estimates the temperature Tc of the SCR catalyst 18 from the value detected by the temperature detection unit 26. The temperature detection unit 26 may also be a sensor that measures the temperature near the inlet of the SCR catalyst 18, and in this case as well, the control unit 20 estimates the temperature Tc of the SCR catalyst 18 from the value detected by the temperature detection unit 26. Alternatively, the temperature detection unit 26 may directly measure the temperature inside the catalyst of the SCR catalyst 18 (so-called floor temperature), and the measured value may be used as the temperature Tc of the SCR catalyst 18.

[0055] The temperature detection unit 26 is responsible for determining when to start the regeneration process of the SCR catalyst 18, which will be described later.

[0056] In other words, the output value (SCR catalyst temperature tc) detected by the temperature detection unit 26 is compared with a predetermined threshold (SCR catalyst activity temperature ta), and when it exceeds the threshold, the regeneration process of the SCR catalyst 18 is started.

[0057] The NOx concentration sensor 28 is a sensor that detects the NOx concentration in the gas flowing through the exhaust gas pipe 22 near the inlet and outlet of the SCR catalyst 18.

[0058] The NOx concentration sensor 28 plays a role in determining when the regeneration process of the SCR catalyst 18, which will be described later, is complete.

[0059] In other words, after the regeneration process of the SCR catalyst 18 begins, the output value detected by the NOx concentration sensor 28 is compared with a predetermined threshold value, and when it exceeds that threshold value, the regeneration process of the SCR catalyst 18 is terminated.

[0060] Furthermore, the output value detected by the NOx concentration sensor 28 includes the NOx concentration plus, if ammonia is emitted from the SCR catalyst 18, the concentration of that ammonia component. Therefore, it is necessary to exclude the ammonia component concentration from the output value used to determine the completion of the regeneration process of the SCR catalyst 18 (details below).

[0061] (Regeneration treatment of SCR catalyst 18) Incidentally, the ammonia engine, which is the internal combustion engine 12 in this embodiment, is started at a predetermined throttle opening and fuel injection period. The exhaust gas contains water vapor, nitrogen, as well as unburned ammonia, hydrogen, nitrogen oxides, and other incomplete combustion components and harmful exhaust gas components. However, after the three-way catalyst 16 is heated by the high-temperature combustion gas and exceeds its activation temperature, the exhaust gas is controlled so that the excess air ratio λ becomes 1, thereby completely purifying harmful exhaust gas components such as ammonia and nitrogen oxides.

[0062] In other words, before the three-way catalyst reaches its activation temperature, unpurified ammonia and nitrogen oxides will flow into the SCR catalyst 18.

[0063] Of these, ammonia is adsorbed by the SCR catalyst 18, and therefore, theoretically, is not released into the environment.

[0064] However, when the SCR catalyst 18 reaches its desorption temperature, ammonia adsorbed during cold conditions (below the oxidation temperature) may be released. Therefore, following the start of the internal combustion engine 12 (ammonia engine), it is necessary to detoxify the ammonia adsorbed on the SCR catalyst 18.

[0065] In the SCR catalyst 18, ammonia is converted to nitrogen and water through a chemical reaction between nitrogen oxides and oxygen (air) via the CSR reaction shown in equations (1) to (3) and the oxidation reaction in equation (4), thereby rendering the ammonia harmless. When the adsorbed ammonia is consumed by the above chemical reaction, the adsorption capacity of the SCR catalyst 18 is restored (regeneration treatment of the SCR catalyst 18).

[0066]

number

[0067] Therefore, in this embodiment, the air excess ratio λ in the internal combustion engine 12 is adjusted from stoichiometric (λ=1) to lean (λ>1), thereby performing a regeneration process in which nitrogen oxides and air are supplied to the SCR catalyst 18.

[0068] The start time for the regeneration process is determined when the output value (SCR catalyst temperature tc) detected by the temperature detection unit 26 is compared with a predetermined threshold (SCR catalyst activity temperature ta) and exceeds that threshold.

[0069] Furthermore, the end of the regeneration process is determined when the output value detected by the NOx concentration sensor 28, after the start of the regeneration process of the SCR catalyst 18, is compared with a predetermined threshold value and exceeds that threshold value.

[0070] (Avoiding ammonia spills) Due to the operation of the internal combustion engine 12, there is a short period (within acceptable limits) during which ammonia is released without being adsorbed by the SCR catalyst 18 before the regeneration process begins.

[0071] On the other hand, when the regeneration process is started, the NOx concentration sensor 28 reacts not only to nitrogen oxides (NOx) but also to the concentration of ammonia (NH3). Since the reaction ratio is NOx:NH3=1:1, the output value of the concentration detected by the NOx concentration sensor 28 is the sum of the concentrations of nitrogen oxides and ammonia.

[0072] Therefore, when compared to the threshold value set as the limit of pure NOx concentration, the output value of the NOx concentration sensor 28 (see thin solid line A in Figure 2) reaches the threshold earlier than the acceptable range for the proper completion of the regeneration process (see range B in Figure 2) (see point C in Figure 2), resulting in the regeneration process ending in an incomplete state (a state with a large amount of residual ammonia).

[0073] Therefore, in this embodiment, when the regeneration process of the SCR catalyst 18 is started, the output value of the concentration detected by the NOx concentration sensor 28 is stored as the ammonia concentration ΔNH3, and thereafter, the result of subtracting ΔNH3 from the output value of the concentration detected by the NOx concentration sensor 28 is compared with a threshold value (see thick solid line D in Figure 2).

[0074] As a result, the output value -ΔNH3 of the NOx concentration sensor 28 (see thick solid line D in Figure 2) reaches a threshold (see point E in Figure 2) within the acceptable range for the appropriate regeneration process completion time (see range B in Figure 2), and the regeneration process can be terminated when the regeneration process is in an appropriate state (ammonia level within the acceptable range).

[0075] The operation of this embodiment will be explained below with reference to the flowchart in Figure 3.

[0076] In step 100, the temperature Tc of the SCR catalyst 18, which is estimated from the temperature detection unit 26 or directly measured by the temperature detection unit 26, is compared with the activity temperature Ta of the SCR catalyst 18. If it is determined that Tc ≥ Ta (affirmative determination), the process proceeds to step 102.

[0077] In step 102, the output value detected by the NOx concentration sensor 28 is stored as the ammonia concentration ΔNH3 (initial value), and the process proceeds to step 104.

[0078] In step 104, the excess air ratio λ is set to a predetermined excess air ratio λr (1 < λr), and the process proceeds to step 106.

[0079] In step 106, the output value (RNOx) of the NOx concentration detected downstream of the SCR catalyst 18 is read, then the process moves to step 108, where the ammonia concentration ΔNH3 stored in step 102 is read, and the process moves to step 110.

[0080] In step 110, the value obtained by subtracting the ammonia concentration ΔNH3 from the output value RNOx is set as the new true output value RNOx (RNOx ← RNOx - ΔNH3), and the process proceeds to step 112.

[0081] In step 112, the calculated value RNOx in step 110 is compared with the NOx concentration (threshold value RNOx_end) at the end of the regeneration process of the predetermined SCR catalyst 18.

[0082] As a result of the comparison in this step 106, if it is determined that RNOx < RNOx_end, the process returns to step 106, and the above steps (steps 106, 108, 110) are repeated.

[0083] It is also determined that the regeneration process of the SCR catalyst 18 has ended. The process proceeds to step 114, where the air excess ratio λ is set to 1, and this routine ends.

[0084] As described above, in the present embodiment, when the regeneration process of the SCR catalyst 18 is started, the output value of the concentration detected by the NOx concentration sensor 28 is stored as the ammonia concentration ΔNH3. Thereafter, the result obtained by subtracting ΔNH3 from the output value of the concentration detected by the NOx concentration sensor 28 is compared with the threshold value. Therefore, the output value of the NOx concentration sensor 28 - ΔNH3 reaches the threshold value within the allowable range of the appropriate regeneration process end timing, and the regeneration process can be ended in an appropriate regeneration process state.

[0085] In the above embodiment, ΔNH3 is subtracted from the output value of the concentration detected by the NOx concentration sensor 28 and compared with the threshold value. However, ΔNH3 may be added to the threshold value.

[0086] [Modification Example 1] In the present embodiment, the end timing of the regeneration process of the SCR catalyst 18 is determined by comparing the NOx concentration value RNOx with the threshold value RNOx_end.

[0087] In this case, the new true output value RNOx (RNOx←RNOx-ΔNH3) must be obtained by subtracting the ammonia concentration ΔNH3 detected at the start of the regeneration process from the output value RNOx of the NOx concentration sensor 28.

[0088] In Modification 1, the rate of change of the output value RNOx of the NOx concentration sensor 28 is calculated, and this rate of change is compared with a predetermined threshold value for the rate of change.

[0089] As shown in Figure 4, by comparing the rate of change, the influence of ammonia, which originally has a small rate of change, can be eliminated, and it is simply a matter of comparing the rate of change of the output value RNOx of the NOx concentration sensor 28 with the threshold value for the rate of change.

[0090] Furthermore, since the rate of change of the output value RNOx of the NOx concentration sensor 28 at the start of the regeneration process fluctuates greatly (hunting may occur), it is preferable to set a predetermined period from the start of the regeneration process as the judgment masking period.

[0091] [Differentiation 2]

[0092] In this embodiment (including Modification 1), the lean air excess ratio λ of the internal combustion engine is adjusted to be lean, and a regeneration process is performed in which nitrogen oxides and air are supplied to the SCR catalyst 18. However, the air may be supplied separately.

[0093] As shown in Figure 5, the exhaust gas purification device 14A according to the modified example 2 is equipped with a blower 30. The blower 30 is responsible for introducing air from one end of the air inlet pipe 32 and supplying it between the three-way catalyst 16 and the SCR catalyst 18.

[0094] In other words, by introducing outside air through the operation of the blower 30, the required amount of air in the exhaust gas can be kept to an excess air ratio λ that corresponds to the required amount of nitrogen oxides.

[0095] In the SCR catalyst 18, the amount of NOx required for the reactions in equations (1) to (4) above is preferably determined by a mixing ratio such that λ = 1.1 or higher. However, in order to suppress the emission of NOx and N2O after the regeneration treatment of the SCR catalyst 18, it is desirable to bring λ closer to stoichiometric values ​​(λ = 1) as early as possible.

[0096] To prioritize the reduction of NOx and N2O emissions after regeneration, the excess air ratio λ was set to a range of 1 < λ ≤ 1.1 based on the N2O concentration downstream of the three-way catalyst and the O2 concentration ratio characteristics to NOx.

[0097] On the other hand, it has been found that with such an excess air ratio λ (1 < λ < 1.1), the amount of air (oxygen concentration) is low, making it difficult for the regeneration reaction to proceed.

[0098] In the modified example 2, the insufficient amount of air (oxygen concentration) is compensated for by introducing outside air by driving the blower 30, thereby supplying the appropriate amount of air and the appropriate amount of NOx to the SCR catalyst 18.

[0099] In the modified example 2, the λ sensor 24 has the role of detecting the air excess ratio λ of the exhaust gas discharged from the internal combustion engine 12 in order to control the air excess ratio λ during adjustment to one of the predetermined ranges of 1 < λ < 1.1.

[0100] Furthermore, in the modified example 2, the temperature detection unit 26 has the role of detecting a temperature that triggers the start of the regeneration process, as well as the start of the blower 30's operation.

[0101] Furthermore, in the modified example 2, the NOx concentration sensor 28 has the role of detecting the NOx concentration that triggers the termination of the regeneration process, as well as the termination of the blower 30's operation.

[0102] (Embodiment) The present invention may constitute embodiments of the dependent relationships shown in the following appendix.

[0103] [Note 1] An exhaust gas purification device for purifying exhaust gas when a fuel containing ammonia is burned after being mixed with air to achieve a predetermined fuel-air ratio with excess air, A catalytic converter is provided in the exhaust gas passage through which the exhaust gas after combustion flows, and comprises an oxidation-reduction catalyst having an oxidation-reduction function and an adsorption catalyst having an ammonia adsorption function. A NOx concentration sensor capable of detecting the concentration of at least nitrogen oxides emitted from the adsorption catalyst, When the adsorption catalyst is determined to be in an active state, the control unit supplies nitrogen oxides and oxygen to the adsorption catalyst at a dilute ratio lower than the predetermined excess air ratio to start a regeneration process to oxidize the ammonia adsorbed on the adsorption catalyst, and terminates the regeneration process when a correction value obtained by excluding the ammonia concentration that reacts with the NOx concentration sensor from the output value detected by the NOx concentration sensor reaches a predetermined threshold value. An exhaust gas purification device having the following features.

[0104] [Note 2] The control unit, The exhaust gas purification device according to Appendix 1, wherein, at the point in time when it is determined that the adsorption catalyst is in an active state, the initial output value detected by the NOx concentration sensor is considered to be the concentration of ammonia, and the value obtained by subtracting the initial output value from the output value detected by the NOx concentration sensor is used as the correction value.

[0105] [Note 3] The control unit, An exhaust gas purification device according to Appendix 1 or Appendix 2, which calculates the rate of change of the output value detected by the NOx concentration sensor and uses the calculated conversion rate as the correction value.

[0106] [Note 4] The exhaust gas purification device described in Appendix 3, wherein, when determining the completion of the regeneration process using the rate of change of nitrogen oxides, a predetermined period from the start of the regeneration process is defined as a masking period during which no determination is made.

[0107] [Note 5] The system further includes an air excess rate sensor, which is provided upstream of the catalytic converter with respect to the direction in which the exhaust gas flows in the exhaust gas passage, and which detects the air excess rate of the exhaust gas flowing through the exhaust gas passage. The supply of nitrogen oxides and oxygen for the regeneration process by the control unit is a combustion operation that is leaner than a predetermined excess air state. The exhaust gas purification device according to any one of the appendices 1 to 4, wherein the control unit provides feedback control of the fuel-air ratio based on the excess air ratio detected by the excess air ratio sensor.

[0108] [Note 6] The control unit, An exhaust gas purification device according to any one of the appendices 1 to 5, comprising measuring or estimating the temperature of the adsorption catalyst, and determining the activity state of the adsorption catalyst based on the measured or estimated temperature of the adsorption catalyst.

[0109] [Note 7] An exhaust gas purification method comprising a control unit that purifies exhaust gas by burning a fuel containing ammonia mixed with air at a predetermined fuel-air ratio with excess air, guiding the exhaust gas after combustion into an exhaust gas passage, and passing it through an oxidation-reduction catalyst having oxidation-reduction function and an adsorption catalyst having ammonia adsorption function, The control unit, When the adsorption catalyst is determined to be in an active state, a regeneration process is initiated to oxidize the ammonia adsorbed on the adsorption catalyst by supplying nitrogen oxides and oxygen to the adsorption catalyst at a dilute ratio lower than the predetermined excess air ratio. The regeneration process is terminated when a correction value obtained by subtracting the concentration of ammonia that reacts with the NOx concentration sensor from the output value detected by a NOx concentration sensor capable of detecting the concentration of at least nitrogen oxides emitted from the adsorption catalyst reaches a predetermined threshold. Exhaust gas purification methods.

[0110] [Note 8] Computers, An exhaust gas purification program that operates as the control unit of the exhaust gas purification device according to any one of claims 1 to 6. [Explanation of Symbols]

[0111] 10 Engine System 12 Internal Combustion Engines 14. Exhaust gas purification system 16. Three-way catalyst (oxidation-reduction catalyst) 18 SCR catalyst (adsorption catalyst) 20 Control Unit 22 Exhaust pipe 24. Air Excess Rate Sensor (λ Sensor) 26 Temperature detection unit 28 NOx concentration sensor

Claims

1. An exhaust gas purification device for purifying exhaust gas when a fuel containing ammonia is burned after being mixed with air to achieve a predetermined fuel-air ratio with excess air, A catalytic converter is provided in the exhaust gas passage through which the exhaust gas after combustion flows, and comprises an oxidation-reduction catalyst having an oxidation-reduction function and an adsorption catalyst having an ammonia adsorption function. A NOx concentration sensor capable of detecting the concentration of at least nitrogen oxides discharged from the adsorption catalyst, When the adsorption catalyst is determined to be in an active state, the control unit supplies nitrogen oxides and oxygen to the adsorption catalyst at a dilute ratio lower than the predetermined excess air ratio to start a regeneration process to oxidize the ammonia adsorbed on the adsorption catalyst. At the same time, when the adsorption catalyst is determined to be in an active state, the control unit considers the initial output value detected by the NOx concentration sensor as the ammonia concentration, subtracts the initial output value from the output value detected by the NOx concentration sensor as a correction value, and terminates the regeneration process when the correction value reaches a predetermined threshold. An exhaust gas purification device having the following features.

2. The control unit, The exhaust gas purification device according to claim 1, wherein the rate of change of the output value detected by the NOx concentration sensor is calculated, and the calculated conversion rate is used as the correction value.

3. The exhaust gas purification device according to Claim 2, wherein when determining the completion of the regeneration process using the rate of change of nitrogen oxides, a predetermined period from the start of the regeneration process is set as a masking period during which no determination is made.

4. The exhaust gas passage further comprises an air excess rate sensor provided on the upstream side of the catalyst device with respect to the direction in which the exhaust gas flows, for detecting the air excess rate of the exhaust gas flowing in the exhaust gas passage, The supply of nitrogen oxides and oxygen for the regeneration process by the control unit is a combustion operation that is leaner than a predetermined excess air state. The exhaust gas purification device according to claim 1, wherein the control unit provides feedback control of the fuel-air ratio based on the excess air ratio detected by the excess air ratio sensor.

5. The control unit, The exhaust gas purification device according to claim 1, comprising measuring or estimating the temperature of the adsorption catalyst, and determining the activity state of the adsorption catalyst based on the measured or estimated temperature of the adsorption catalyst.

6. An exhaust gas purification method comprising a control unit that burns a fuel containing ammonia mixed with air to achieve a predetermined fuel-air ratio with excess air, guides the exhaust gas after combustion into an exhaust gas passage, and purifies the exhaust gas by passing it through an oxidation-reduction catalyst having an oxidation-reduction function and an adsorption catalyst having an ammonia adsorption function, The control unit, When the adsorption catalyst is determined to be in an active state, a regeneration process is initiated to oxidize the ammonia adsorbed on the adsorption catalyst by supplying nitrogen oxides and oxygen to the adsorption catalyst at a dilute ratio lower than the predetermined excess air ratio. When it is determined that the adsorption catalyst is in an active state, the initial output value detected by a NOx concentration sensor capable of detecting the concentration of at least nitrogen oxides discharged from the adsorption catalyst at the start of the regeneration process is considered to be the ammonia concentration. A correction value is obtained by subtracting the initial output value from the output value detected by the NOx concentration sensor, and the regeneration process is terminated when this correction value reaches a predetermined threshold. Exhaust gas purification methods.

7. A computer, An exhaust gas purification program that operates as the control unit of the exhaust gas purification device according to any one of claims 1 to 5.

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