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.SOLUTION: In order to prioritize suppression of emission amounts of NOx and N2O after regeneration treatment of an SCR catalyst 18, an excess air ratio λ is set to a range of 1<λ≤1.1, and an appropriate air amount and an appropriate NOx amount are supplied to the SCR catalyst 18 by compensating for an insufficient air amount (oxygen concentration) by the introduction of outside air by the drive of a blower 30. Decomposing ammonia and nitrogen oxide into nitrogen and water by chemical reaction under the SCR catalyst 18 has made it possible to achieve a configuration in which air (oxygen) is forcedly fed to the SCR catalyst 18 as means to prevent emission of ammonia and nitrogen oxide, which can hardly be achieved by a conventional technique. By this configuration, an amount of oxygen and an amount of nitrogen oxide required for the reaction of the adsorption catalyst can be independently controlled.SELECTED DRAWING: Figure 4

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 an internal combustion engine such as an engine using a catalyst are known. In addition, 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 into 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] Patent Document 1 describes, 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 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 when the temperature of the selective reduction catalyst acquired by the temperature acquisition unit exceeds the activation temperature of the selective reduction catalyst.

[0005] Patent Document 2 describes an exhaust gas purification device for an internal combustion engine that obtains driving force by the combustion of ammonia, comprising a catalyst having a three-way catalytic function and an ammonia adsorption function, provided in the main flow path through which exhaust gas from the internal combustion engine flows, and a control unit that changes the exhaust gas mixing ratio upstream of the catalyst from stoichiometric to dilute according to information relating to at least one of the desorption of ammonia from the catalyst and the activation temperature of the catalyst. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2019-167823 [Patent Document 2] Japanese Patent Publication No. 2019-167822 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, prior art, including Patent Documents 1 and 2, has shown that 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). However, when exhaust gas containing ammonia is passed through a catalyst with a three-way catalytic function in a dilute state, there are concerns about the generation of nitrogen oxides (NOx) and nitrous oxide (N2O).

[0008] Furthermore, for example, Patent Documents 1 and 2 do not specify the degree of dilution.

[0009] 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, respectively, necessary for decomposing ammonia into nitrogen and water to regenerate the adsorption catalyst, thereby preventing the release of ammonia and nitrogen oxides. [Means for solving the problem]

[0010] 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 achieve a predetermined fuel-air ratio with excess air, and comprises a catalyst device provided in the exhaust gas passage through which the exhaust gas after combustion flows, and consisting of an oxidation-reduction catalyst having an oxidation-reduction function and an adsorption catalyst having an ammonia adsorption function; a gas supply unit that supplies an oxygen-containing gas to the adsorption catalyst; and a control unit that, when it is determined that the adsorption catalyst is in an active state, controls the gas supply unit to supply the gas to the adsorption catalyst and performs a regeneration process for the adsorption catalyst. The control unit, in synchronization with the start of supplying the gas from the gas supply unit, adjusts the amount of nitrogen oxides in the exhaust gas to a predetermined amount corresponding to the amount of oxygen contained in the gas by making the excess air ratio thinner than the predetermined excess air ratio. It is characterized by the following.

[0011] According to the present invention, a catalytic device for purifying exhaust gas when a fuel containing ammonia is burned after being mixed with air to achieve a predetermined fuel-air ratio of excess air 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.

[0012] When the control unit determines that the adsorption catalyst is in an active state, it controls the gas supply unit to supply gas to the adsorption catalyst and performs a regeneration process for the adsorption catalyst.

[0013] 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, thereby preventing the release of ammonia and nitrogen oxides. By supplying gas from the gas supply unit to secure the necessary amount of oxygen, and by diluting the excess air ratio to adjust the amount of nitrogen oxides in the exhaust gas to a predetermined amount, the amount of oxygen and nitrogen oxides necessary for the regeneration treatment of the adsorption catalyst (restoration of adsorption function) can be secured.

[0014] The present invention further includes an air excess rate sensor provided upstream of the catalytic converter with respect to the direction in which the exhaust gas flows in the exhaust gas passage, which detects the air excess rate of the exhaust gas flowing through the exhaust gas passage, and the control unit provides feedback control of the fuel-air ratio based on the air excess rate detected by the air excess rate sensor.

[0015] Based on the air excess ratio detected by the air excess ratio sensor, the fuel-air ratio is feedback-controlled. Thereby, a desired (e.g., stoichiometric, lean, etc.) fuel-air ratio can be maintained.

[0016] In the present invention, the control unit determines the active state based on the measured or estimated temperature of the adsorption catalyst, and sets the time point when the temperature reaches a predetermined temperature as the start timing of the regeneration process.

[0017] Based on the temperature of the adsorption catalyst, the start timing of the regeneration process can be set.

[0020] In the present invention, the air excess ratio λr when lean is set in the range of 1 < λ ≤ 1.1.

[0021] By setting the air excess ratio λr when lean in the range of 1 < λ ≤ 1.1, nitrogen oxides sufficient for the regeneration process of the adsorption catalyst can be obtained.

[0022] In the present invention, provided on the downstream side of the adsorption catalyst with respect to the flow direction of the exhaust gas in the exhaust gas passage, and equipped with a NOx concentration sensor for detecting NOx in the exhaust gas flowing through the exhaust gas passage, the control unit determines that the output value of the NOx concentration sensor reaches a predetermined value If the above occurs as the end timing of the regeneration process of the adsorption catalyst, terminates the supply of the gas by the gas supply unit, and returns the air excess ratio when lean to the predetermined air excess ratio.

[0023] The end timing of the regeneration process can be determined by the NOx sensor.

[0024] The present invention An exhaust gas purification device for purifying exhaust gas produced when a fuel containing ammonia is burned after being mixed with air to achieve a predetermined fuel-air ratio of excess air, comprising: a catalytic device installed in the exhaust gas passage through which the exhaust gas after combustion flows, comprising a redox catalyst having a redox function and an adsorption catalyst having an ammonia adsorption function; a gas supply unit for supplying an oxygen-containing gas to the adsorption catalyst; and a control unit that, when the adsorption catalyst is determined to be in an active state, controls the gas supply unit to supply the gas to the adsorption catalyst and performs a regeneration process for the adsorption catalyst. wherein the adsorption catalyst When the oxidizing ability is stronger than the selective reducing ability in which the control unit supplies the gas from the gas supply unit, and the air excess ratio maintains a predetermined air excess ratio.

[0025] It only supplies gas from the gas supply unit to secure the required amount of oxygen, and can secure the amount of oxygen and the amount of nitrogen oxides necessary for the regeneration treatment (restoration of the adsorption function) of the adsorption catalyst.

[0026] In the present invention, when a predetermined time has elapsed since the start of the regeneration treatment, point it determines the end time of the regeneration treatment of the adsorption catalyst, and is characterized by ending the supply of gas by the gas supply unit.

[0027] It is possible to determine the end time of an appropriate regeneration treatment.

[0028] The exhaust gas purification method according to the present invention mixes a fuel containing ammonia with air so as to have a fuel-air ratio with a predetermined air excess ratio and burns it, guides the exhaust gas after combustion to an exhaust gas passage, and passes it through a redox catalyst having a redox function and an adsorption catalyst having an ammonia adsorption function, thereby purifying the exhaust gas. When it is determined that the adsorption catalyst is in an active state, a gas containing oxygen is supplied to the adsorption catalyst, and at the same time as the start of the supply of the gas, the execution of a regeneration treatment for diluting the air excess ratio is started, and when the NOx of the exhaust gas flowing through the downstream side of the adsorption catalyst in the exhaust gas passage reaches a predetermined value At the point when the above is reached it determines the end time of the regeneration treatment, returns the air excess ratio to the predetermined air excess ratio, and ends the supply of the gas.

[0029] According to this exhaust gas purification method, appropriate amounts of oxygen and nitrogen compounds necessary for the regeneration treatment can be supplied respectively.

[0030] The exhaust gas purification method according to the present invention mixes a fuel containing ammonia with air so as to have a fuel-air ratio with a predetermined air excess ratio and burns it, guides the exhaust gas after combustion to an exhaust gas passage, and has a redox function An exhaust gas purification method for purifying exhaust gas by passing it through an adsorption catalyst having a stronger oxidizing ability than its selective reducing ability, characterized in that when it is determined that the adsorption catalyst is in an active state, a regeneration process is started in which an oxygen-containing gas is supplied to the adsorption catalyst, and when a predetermined time has elapsed from the start of the regeneration process, it is determined that the regeneration process has ended, and the supply of the gas is terminated.

[0031] According to this exhaust gas purification method, the adsorption catalyst is effective when the strength of its oxidizing ability exceeds a predetermined value relative to the strength of its selective reducing ability.

[0032] The exhaust gas purification program according to the present invention is characterized by operating a computer as a control device for the exhaust gas purification device described above. [Effects of the Invention]

[0033] As described above, the present invention can supply appropriate amounts of oxygen and nitrogen oxides, which are necessary for decomposing ammonia into nitrogen and water to regenerate the adsorption catalyst, and can prevent the release of ammonia and nitrogen oxides. [Brief explanation of the drawing]

[0034] [Figure 1] This is a schematic diagram of the engine system according to this embodiment. [Figure 2] This is a characteristic diagram showing the excess air ratio and various component concentrations in an internal combustion engine (ammonia engine) according to this embodiment. [Figure 3] In this embodiment, the N2O concentration downstream of the three-way catalyst and the O2 concentration ratio to NOx are characteristic diagrams that serve as the basis for setting the upper limit of λ. [Figure 4] 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 5] This characteristic diagram compares the amount of NOx reduction in the exhaust gas purification treatment during the regeneration process of the SCR catalyst according to this embodiment with that of a comparative example. [Figure 6] This is a control flowchart showing the flow of exhaust gas purification treatment during regeneration, in the case of a modified example where an adsorption catalyst with strong oxidizing ability is used. [Modes for carrying out the invention]

[0035] Figure 1 is a schematic diagram of an engine system 10 as one embodiment of the present invention.

[0036] 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."

[0037] 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.

[0038] 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 the vehicle's electronic control unit (ECU, "Electronic Control Unit," not shown).

[0039] 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.

[0040] 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.

[0041] As will be explained in more detail later, one of the objectives of this embodiment is to increase the amount of air (oxygen) compared to the mixture ratio of the fuel-air mixture burned in the internal combustion engine 12. Therefore, the following explanation will use the air excess ratio λ.

[0042] 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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] (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.

[0052] The control unit 20 controls the fuel injection amount based on the detection signal from the λ sensor 24 so that it becomes a target λ (for example, λ=1) as a predetermined excess air ratio.

[0053] The three-way catalyst 16 is located at the uppermost upstream end 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] (Regeneration treatment of SCR catalyst 18) By the way, 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, and other incomplete combustion components such as unburned ammonia, hydrogen, and nitrogen oxides, as well as 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 to have a predetermined excess air ratio (for example, λ=1), thereby completely purifying harmful exhaust gas components such as ammonia and nitrogen oxides.

[0058] In other words, before the three-way catalyst reaches its activation temperature, unpurified ammonia and nitrogen oxides will flow into the SCR catalyst 18.

[0059] Of these, ammonia is adsorbed by the SCR catalyst 18 and is therefore not released into the environment.

[0060] However, when the SCR catalyst 18 reaches its desorption temperature, ammonia adsorbed during cold conditions (below the desorption 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.

[0061] 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).

[0062]

number

[0063] In this comparative example (for example, Patent Document 1), the excess air ratio λ in an internal combustion engine (with a configuration equivalent to the internal combustion engine 12 of this embodiment) is adjusted from stoichiometric (λ=1) to lean (λ>1) to supply nitrogen oxides and air to the SCR catalyst 18, but neither is in the appropriate amount. For example, if the amount of oxygen is adjusted to the appropriate amount, the amount of nitrogen oxides becomes excessive, and if the amount of nitrogen oxides is adjusted to the appropriate amount, the amount of oxygen becomes insufficient. The excess NOx cannot be consumed by the SCR reaction. Furthermore, since N2O hardly reacts in the SCR catalyst 18, it is released into the environment.

[0064] Therefore, the exhaust gas purification device 14 according to this embodiment is equipped with a blower 30. The blower 30 is responsible for introducing air from one end of the air inlet pipe 32 and sending it between the three-way catalyst 16 and the SCR catalyst 18.

[0065] In other words, by introducing 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.

[0066] Figure 2 shows the concentration characteristics of the component gases (NH3, O2, NOx, N2O) contained in the exhaust gas downstream of the three-way catalyst 16, with the excess air ratio λ on the horizontal axis.

[0067] 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.

[0068] In order to prioritize the reduction of NOx and N2O emissions after regeneration, in this embodiment, the excess air ratio λ was set to the range of 1 < λ ≤ 1.1 based on the N2O concentration downstream of the three-way catalyst and the characteristic diagram of the O2 concentration ratio to NOx shown in Figure 3. That is, as shown in Figure 3, when λ exceeds 1.1, the slope of the N2O concentration changes in the direction of increasing sharpness, so the upper limit of λ was set to 1.1 or less.

[0069] On the other hand, with such an excess air ratio λ (1 < λ ≤ 1.1), it can be understood that the amount of air (oxygen concentration) is low, and the regeneration reaction does not proceed.

[0070] In this embodiment, 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.

[0071] Furthermore, the roles of the λ sensor 24, temperature detection unit 26, and NOx concentration sensor 28 described above, which are specifically designed for ammonia decomposition treatment (chemical changes in equations (1) to (4)) by the SCR catalyst 18, are as follows.

[0072] The λ sensor 24 is responsible for detecting the air excess ratio λ of the exhaust gas emitted from the internal combustion engine 12 in order to control the air excess ratio λ during adjustment to be within a predetermined range of 1 < λ ≤ 1.1.

[0073] The temperature detection unit 26 is responsible for detecting the temperature that triggers the start of adjustment of the exhaust gas air excess ratio λ and the start of operation of the blower 30.

[0074] The NOx concentration sensor 28 is responsible for detecting the NOx concentration that triggers the completion of adjustment of the exhaust gas air excess ratio λ and the termination of operation of the blower 30.

[0075] The operation of this embodiment will be explained below in accordance with the flowchart in Figure 4.

[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 operation of the blower 30 is started, then the process moves to step 104, where the excess air ratio λ is set to a predetermined excess air ratio λa (in the range of 1 < λa ≤ 1.1), and the process moves to step 106.

[0078] When the blower 30 starts operating, air is introduced from one end of the air intake pipe 32 into the exhaust gas pipe 22 between the three-way catalyst 16 and the SCR catalyst 18.

[0079] Therefore, since the necessary amount of air (oxygen) is secured, the exhaust gas can be kept to an air excess ratio λ (in the range of 1 < λa ≤ 1.1) that corresponds to the necessary amount of nitrogen oxides.

[0080] In step 106, the concentration of NOx detected downstream of the SCR catalyst 18 (RNOx) is compared with a predetermined concentration of NOx at the end of the regeneration process of the SCR catalyst 18 (RNOx_end).

[0081] If the comparison in step 106 determines that RNOx ≥ RNOx_end, it is determined that the regeneration process of the SCR catalyst 18 is complete, and the process moves to step 108, where the excess air ratio λ is set to 1. Then, the process moves to step 110, where the operation of the blower 30 is terminated, and this routine ends. Therefore, air is supplied to the SCR catalyst by the blower 30 from the time the temperature Tc of the SCR catalyst 18 reaches or exceeds the activation temperature Ta until the regeneration process of the SCR catalyst 18 is complete.

[0082] Figure 5 is a characteristic diagram showing a comparison of NOx and N2O emissions from exhaust gas discharged from the exhaust pipe 22 (exhaust gas discharged downstream of the SCR catalyst 18) in two cases: when outside air is forcibly introduced by driving the blower 30, as in the engine system 10 of this embodiment, and in a configuration without forced outside air introduction (for example, Patent Document 1).

[0083] As can be seen from Figure 5, in this embodiment, NOx emissions are reduced to more than 1 / 10 of the NOx emissions in the comparative example.

[0084] As shown in Figure 3, increasing the excess air ratio λ increases N2O. This is a result of N2O being produced in the three-way catalyst 16 upstream of the exhaust gas purification device 14. With the present invention, by setting the excess air ratio λ to 1.1 or less, a reduction in N2O can also be achieved.

[0085] According to this embodiment, in the SCR catalyst 18, a mixing ratio such that λ = 1.1 or higher is preferable for the amount of NOx required for the chemical reaction to purify NOx. However, in order to prioritize the suppression of NOx and N2O emissions after the regeneration treatment of the SCR catalyst 18, the excess air ratio λ is set in the range of 1 < λ ≤ 1.1, and the insufficient amount of air (oxygen concentration) is supplemented 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.

[0086] In other words, in the SCR catalyst 18, by chemically decomposing ammonia and nitrogen oxides into nitrogen and water, and as a means of preventing the release of ammonia and nitrogen oxides, a configuration that could not be easily conceived from conventional technology is adopted in which air (oxygen) is forcibly injected into the SCR catalyst 18, thereby allowing the amount of oxygen and nitrogen oxides required for the reaction of the adsorption catalyst to be controlled separately.

[0087] [Differentiation] In this embodiment, a catalyst with stronger oxidizing ability compared to the SCR catalyst 18 was used as the adsorption catalyst. As long as this catalyst has ammonia adsorption properties, catalysts other than the SCR catalyst 18 can also be used.

[0088] For example, as an adsorption catalyst, a catalyst can be used in which ceramics or titanium dioxide are used as a support, and zeolite is supported as the active catalytic component.

[0089] This section describes the case where the oxidizing ability of the adsorption catalyst is strong compared to its selective reducing ability (for example, when a noble metal is supported on a zeolite along with copper). In the case of such an adsorption catalyst, some of the adsorbed ammonia is converted to NO as it is oxidized on the noble metal.

[0090] Because this NO allows for a selective reduction catalytic reaction, there is no need to supply nitrogen oxides to the adsorption catalyst.

[0091] Therefore, during the regeneration process, only the forced introduction of air by the blower 30 is initiated, and control is maintained to keep the exhaust gas air excess ratio λ at 1.

[0092] Furthermore, the system can recognize when a predetermined regeneration time has been reached based on the catalyst temperature and air supply rate, and then stop the air supply.

[0093] Figure 6 is a control flowchart showing the flow of exhaust gas purification treatment during regeneration, relating to a modified example, when an adsorption catalyst with strong oxidizing ability, such as zeolite, is used. Steps that are the same as those in Figure 4 are denoted with the letter "A" at the end of the same step number.

[0094] In step 100A, the temperature Tc of a catalyst with strong oxidizing ability to replace the SCR catalyst 18 is compared with the activation temperature Ta of the catalyst. If it is determined that Tc ≥ Ta (positive determination), the process proceeds to step 102.

[0095] In step 102A, the operation of blower 30 is started.

[0096] When the blower 30 starts operating, air is introduced from one end of the air intake pipe 32 into the exhaust gas pipe 22 between the three-way catalyst 16 and the SCR catalyst 18.

[0097] This ensures that the necessary amount of air (oxygen) is secured, and in the case of the modified adsorption catalyst, some of the ammonia is converted to NO as it oxidizes on the noble metal, and the NOx exhaust gas during the regeneration process is suppressed by a chemical reaction between the ammonia and air (oxygen) and NO.

[0098] In the next step, 105, it is determined whether the regeneration time has been reached based on the temperature of the adsorption catalyst or the amount of air supplied.

[0099] If the comparison in step 105 results in a positive determination, it is determined that the regeneration process of the SCR catalyst 18 is complete, and the process proceeds to step 110A, where the operation of the blower 30 ends, and this routine is completed. Therefore, air is supplied to the SCR catalyst by the blower 30 from the time the temperature Tc of the SCR catalyst 18 reaches or exceeds the activation temperature Ta until the time required for the regeneration process of the SCR catalyst 18 has elapsed.

[0100] (Embodiment) The present invention may constitute embodiments of the dependent relationships shown in the following appendix.

[0101] [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 gas supply unit that supplies an oxygen-containing gas to the adsorption catalyst, When the adsorption catalyst is determined to be in an active state, the control unit controls the gas supply unit to supply the gas to the adsorption catalyst and performs a regeneration process for the adsorption catalyst. An exhaust gas purification device having the following features.

[0102] [Note 2] 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 exhaust gas purification device according to Appendix 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.

[0103] [Note 3] The exhaust gas purification apparatus according to Appendix 1 or Appendix 2, wherein the control unit determines the active state based on the temperature of the adsorption catalyst measured or estimated, and sets the time when the temperature reaches a predetermined level as the start time for the regeneration process.

[0104] [Note 4] The exhaust gas purification device according to any one of the appendices 1 to 3, wherein the control unit synchronizes with the start of supplying the gas from the gas supply unit to reduce the excess air ratio to a lower than the predetermined excess air ratio, thereby adjusting the amount of nitrogen oxides in the exhaust gas to a predetermined amount corresponding to the amount of oxygen contained in the gas.

[0105] [Note 5] The exhaust gas purification device described in Appendix 4, wherein the excess air ratio λr when the mixture is lean is set in the range of 1 < λ ≤ 1.1.

[0106] [Note 6] The exhaust gas passage is provided with respect to the flow direction of the exhaust gas, and includes a NOx concentration sensor that detects NOx in the exhaust gas flowing through the exhaust gas passage. The exhaust gas purification device according to any one of the appendices 1 to 5, wherein the control unit determines that the regeneration process of the adsorption catalyst is complete when the output value of the NOx concentration sensor exceeds a predetermined value, terminates the supply of gas by the gas supply unit, and returns the dilute air excess ratio to the predetermined air excess ratio.

[0107] [Note 7] When the oxidizing ability of the adsorption catalyst exceeds a predetermined value relative to its selective reducing ability, The exhaust gas purification device according to any one of the appendices 1 to 3, wherein the control unit supplies the gas from the gas supply unit and maintains the excess air ratio at the predetermined excess air ratio.

[0108] "Note 8" The control unit, The exhaust gas purification device according to Appendix 7, wherein when a predetermined time has elapsed since the start of the regeneration process, or when the output value of a NOx concentration sensor that detects NOx in the exhaust gas flowing downstream of the adsorption catalyst with respect to the flow direction of the exhaust gas in the exhaust gas passage falls below a predetermined value, it is determined that the regeneration process of the adsorption catalyst has ended, and the supply of gas by the gas supply unit is terminated.

[0109] [Note 9] An exhaust gas purification method for purifying exhaust gas by burning a fuel containing ammonia 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, When it is determined that the adsorption catalyst is in an active state, an oxygen-containing gas is supplied to the adsorption catalyst, and a regeneration process to dilute the excess air ratio is started in synchronization with the start of the gas supply. The time when the NOx in the exhaust gas flowing downstream of the adsorption catalyst in the exhaust gas passage exceeds a predetermined value is determined to be the end of the regeneration process, the excess air ratio is returned to the predetermined excess air ratio, and the supply of the gas is terminated. Exhaust gas purification methods.

[0110] [Note 10] An exhaust gas purification method for purifying exhaust gas by burning a fuel containing ammonia 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, When it is determined that the adsorption catalyst is in an active state, the regeneration process of supplying an oxygen-containing gas to the adsorption catalyst is initiated. When a predetermined time has elapsed since the start of the regeneration process, or when the NOx in the exhaust gas flowing downstream of the adsorption catalyst in the exhaust gas passage falls below a predetermined value, the end of the regeneration process is determined, and the supply of the gas is terminated. Exhaust gas purification methods.

[0111] [Note 11] Computers, An exhaust gas purification program that operates as the control unit for the exhaust gas purification device described in any one of the appendices 1 to 7. [Explanation of Symbols]

[0112] 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 30 Blower (gas supply unit) 32 Air intake pipe

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 gas supply unit that supplies an oxygen-containing gas to the adsorption catalyst, The system includes a control unit that, when the adsorption catalyst is determined to be in an active state, controls the gas supply unit to supply the gas to the adsorption catalyst and performs a regeneration process for the adsorption catalyst, The control unit synchronizes with the start of supplying the gas from the gas supply unit to reduce the excess air ratio to a lower than the predetermined excess air ratio, thereby adjusting the amount of nitrogen oxides in the exhaust gas to a predetermined amount corresponding to the amount of oxygen contained in the gas. Exhaust gas purification device.

2. The exhaust gas purification device according to claim 1, wherein the excess air ratio λr when the gas is diluted is set in the range of 1 < λ ≤ 1.

1.

3. The exhaust gas passage is provided with respect to the flow direction of the exhaust gas, and includes a NOx concentration sensor that detects NOx in the exhaust gas flowing through the exhaust gas passage, The exhaust gas purification apparatus according to claim 1, wherein the control unit determines that the regeneration process of the adsorption catalyst is complete when the output value of the NOx concentration sensor exceeds a predetermined value, terminates the supply of gas by the gas supply unit, and returns the dilute air excess ratio to the predetermined air excess ratio.

4. An exhaust gas purification device for purifying exhaust gas when a fuel containing ammonia is mixed with air and burned to 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 gas supply unit that supplies an oxygen-containing gas to the adsorption catalyst, The system includes a control unit that, when the adsorption catalyst is determined to be in an active state, controls the gas supply unit to supply the gas to the adsorption catalyst and performs a regeneration process for the adsorption catalyst, When the adsorption catalyst has a stronger oxidizing ability than its selective reducing ability, The control unit supplies the gas from the gas supply unit and maintains the excess air ratio at a predetermined level, thereby providing an exhaust gas purification device.

5. The control unit is The exhaust gas purification device according to claim 4, wherein, when a predetermined time has elapsed from the start of the regeneration process, it is determined that the regeneration process of the adsorption catalyst has ended, and the supply of gas by the gas supply unit is terminated.

6. An exhaust gas purification method for purifying exhaust gas by mixing a fuel containing ammonia with air to achieve a predetermined fuel-air ratio with excess air, burning the fuel, 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, When it is determined that the adsorption catalyst is in an active state, an oxygen-containing gas is supplied to the adsorption catalyst, and a regeneration process to dilute the excess air ratio is started in synchronization with the start of the gas supply. The time when the NOx in the exhaust gas flowing downstream of the adsorption catalyst in the exhaust gas passage exceeds a predetermined value is determined to be the end of the regeneration process, the excess air ratio is returned to the predetermined excess air ratio, and the supply of the gas is terminated. Exhaust gas purification methods.

7. An exhaust gas purification method for purifying 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 and having an oxidizing ability stronger than selective reduction ability, When it is determined that the adsorption catalyst is in an active state, the regeneration process of supplying an oxygen-containing gas to the adsorption catalyst is initiated. The end of the regeneration process is determined when a predetermined time has elapsed since the start of the regeneration process, and the supply of the gas is terminated. Exhaust gas purification methods.

8. A computer, An exhaust gas purification program that operates as a control unit for an exhaust gas purification device according to any one of claims 1 to 5.

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