JP2020041428A - Post-exhaust treatment device - Google Patents

Abstract

To provide a post-exhaust treatment device capable of suppressing nitrogen oxide slip right after engine start.SOLUTION: To solve the problem, the post-exhaust treatment device includes: a first urea SCR 102 installed in an exhaust pipe 112 of an engine 101, an exhaust emission control catalyst 103 arranged on the exhaust downstream side of the first urea SCR 102; a second urea SCR 105 arranged on the exhaust downstream side of the exhaust emission control catalyst 103; a first urea water injector 106 arranged on the exhaust upstream side of the first urea SCR 102; a first exhaust temperature detector 107 arranged between the first urea SCR 102 and the exhaust emission control catalyst 103; a second urea water injector 108 arranged between the exhaust emission control catalyst 103 and the second urea SCR 105; and a second exhaust temperature detector 109 arranged between the exhaust emission control catalyst 103 and the second urea SCR 105.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an exhaust aftertreatment device for purifying exhaust of an engine.

  Exhaust aftertreatment devices comprising urea SCR or LNT are known.

  The exhaust aftertreatment device provided with the urea SCR estimates or detects the nitrogen oxide emission of the engine, supplies urea water to the urea SCR according to the nitrogen oxide emission, and hydrolyzes the urea water to ammonia with the exhaust heat. To reduce nitrogen oxides with ammonia.

  In an exhaust after-treatment device provided with a urea SCR, it is common to execute ammonia storage control. In the ammonia storage control, the nitrogen oxide purification rate when the exhaust gas temperature is low can be increased by storing ammonia in the urea SCR.

  An exhaust aftertreatment device equipped with an LNT stores nitrogen oxides during lean operation and reduces nitrogen oxides during rich operation.

  In particular, with the recent tightening of exhaust regulations, exhaust aftertreatment devices have been developed that can purify nitrogen oxides when the exhaust temperature is high or low by using urea SCR and LNT together.

JP 2011-220115 A JP 2013-117191 A

  However, even in an exhaust aftertreatment device using both urea SCR and LNT, immediately after the engine is started, the amount of nitrogen oxide stored in the LNT is limited, and a nitrogen oxide slip occurs until the urea SCR reaches the activation temperature. There is a fear.

  Although it is conceivable to execute the engine warm-up control or to heat the urea SCR with an electric heater or a burner, any of these is a trade-off between fuel efficiency and cost.

  In view of the above circumstances, an object of the present invention is to provide an exhaust after-treatment device capable of suppressing a nitrogen oxide slip immediately after starting an engine.

  In an exhaust aftertreatment device for purifying the exhaust of an engine, a first urea SCR installed in an exhaust pipe of the engine and an exhaust downstream side of the first urea SCR installed in the exhaust pipe are provided. An exhaust purification catalyst, a second urea SCR installed in the exhaust pipe and disposed downstream of the exhaust purification catalyst, and a second urea SCR installed in the exhaust pipe and exhaust upstream of the first urea SCR. A first urea water injector disposed therein, a first exhaust temperature detector disposed on the exhaust pipe, disposed between the first urea SCR and the exhaust purification catalyst, A second urea water injector disposed between the exhaust purification catalyst and the second urea SCR; and a second urea water injector disposed in the exhaust pipe, the second urea water injector being disposed between the exhaust purification catalyst and the second urea SCR. A second exhaust gas temperature sensor disposed therebetween. Providing post-processing apparatus.

  When the exhaust gas temperature detected by the first exhaust gas temperature detector is equal to or lower than a first threshold exhaust gas temperature, the first urea water injector supplies urea water to the first urea SCR; When the exhaust gas temperature detected by the second exhaust gas temperature detector is equal to or lower than a second threshold exhaust gas temperature higher than the first threshold exhaust gas temperature, the first urea water injector supplies the first urea water injector with the first urea water. When the engine performs post-injection while supplying to the urea SCR, and the exhaust temperature detected by the second exhaust temperature detector is equal to or lower than a third threshold exhaust temperature higher than the second threshold exhaust temperature. The urea water is supplied to the first urea SCR by the first urea water injector, and the urea water is supplied to the second urea water injector by the second urea water injector while the engine performs post-injection. May be further equipped with a control device for supplying the urea SCR Masui.

  A hydrocarbon injector disposed in the exhaust pipe and disposed between the first urea SCR and the exhaust gas purification catalyst, wherein the exhaust gas temperature detected by the first exhaust gas temperature detector is equal to the first exhaust gas temperature. Urea water is supplied to the first urea SCR by the first urea water injector when the exhaust gas temperature detected by the second exhaust temperature detector is lower than the first exhaust gas temperature. When the temperature is equal to or lower than a second threshold exhaust temperature higher than the threshold exhaust temperature, the urea water is supplied to the first urea SCR by the first urea water injector, and the hydrocarbon is injected by the hydrocarbon injector into the first urea SCR. The first urea water injection is performed when the exhaust gas is supplied to an exhaust purification catalyst and the exhaust temperature detected by the second exhaust temperature detector is equal to or lower than a third threshold exhaust temperature higher than the second threshold exhaust temperature. Urea water is supplied to the first urea SCR by the While the hydrocarbons in the hydrocarbon injector is supplied to the exhaust gas purifying catalyst, it is desirable to further comprise a control device for supplying urea water to the second urea SCR in the second urea water injector.

  It is desirable that the first urea SCR and the second urea SCR include zeolite.

The exhaust gas purifying catalyst, it is desirable to provide one or both of the oxidation catalyst and _the NO _X storage reduction catalyst.

  It is possible to provide an exhaust after-treatment device capable of suppressing a nitrogen oxide slip immediately after starting the engine.

It is a figure explaining the structure of the exhaust after-treatment device concerning an embodiment. It is a figure explaining operation of an exhaust after-treatment device concerning an embodiment. It is a figure explaining the effect of the exhaust aftertreatment device concerning an embodiment.

  Hereinafter, embodiments will be described with reference to the accompanying drawings.

As shown in FIG. 1, the exhaust post-treatment device 100 according to the embodiment, the engine (e.g., diesel engines) An apparatus for purifying the exhaust 101, the first of the NO _X selective reduction catalyst (S elective C atalytic R eduction: follows) 102 of "urea SCR", and the exhaust gas purifying catalyst 103, particulate collection filter (C atalyzed S oot F ilter: follows) 104 called "CSF", and the second urea SCR105, first Urea water injector 106, a first exhaust gas temperature detector 107, a second urea water injector 108, a second exhaust gas temperature detector 109, a hydrocarbon injector 110, a control device 111, Is provided. The control unit 111 is composed of, for example, a ECU (E ngine C ontrol U nit ) and DCU (D osing C ontrol U nit ) and the like.

  The first urea SCR 102 is installed in an exhaust pipe 112 of the engine 101. The first urea SCR 102 contains zeolite. The zeolite generates heat (adsorbs heat of adsorption) when adsorbing water. Therefore, the first urea SCR 102 raises the exhaust gas temperature by using the water contained in the exhaust gas. The first urea SCR 102 is specialized in water adsorption efficiency (heat generation efficiency) and has a heat generation function as a main function.

The exhaust purification catalyst 103 is provided in the exhaust pipe 112 and is disposed downstream of the first urea SCR 102 in exhaust gas. In the exhaust gas purification catalyst 103, zeolite is carried on a part of the exhaust gas upstream side, and similarly to the first urea SCR 102, the temperature of the exhaust gas is raised by using water contained in the exhaust gas. Exhaust gas purifying catalyst 103, an oxidation catalyst (D iesel O xidation C atalyst: hereinafter "DOC") and _the NO _X storage reduction catalyst: also comprising one (L ean N O _X T rap hereinafter referred to as "LNT") Yes, it can have both DOC and LNT. When both the DOC and the LNT are provided, the DOC is arranged on the exhaust upstream side, and the LNT is arranged on the exhaust downstream side. DOC oxidizes carbon monoxide to carbon dioxide and reduces hydrocarbons to carbon dioxide and water. The LNT oxidizes nitrogen monoxide to nitrogen dioxide and occludes nitrogen dioxide during lean operation, releases nitrogen dioxide during rich operation, and reduces nitrogen dioxide to nitrogen, water and carbon dioxide. The exhaust purification catalyst 103 generates heat when oxidizing hydrocarbons and carbon monoxide (generates heat of oxidation). Therefore, the exhaust gas temperature can be increased by supplying hydrocarbons and carbon monoxide to the exhaust gas purifying catalyst 103.

  The CSF 104 collects soot contained in the exhaust gas. By arranging the DOC upstream of the exhaust of the CSF 104, nitrogen dioxide and heat can be efficiently supplied to the CSF 104, so that the combustion of soot can be promoted.

  The second urea SCR 105 is provided in the exhaust pipe 112 and is arranged on the exhaust gas downstream side of the exhaust purification catalyst 103. The second urea SCR 105 contains zeolite, like the first urea SCR 102. The second urea SCR 105 has a larger volume than the first urea SCR 102. The second urea SCR 105 reduces nitric oxide and nitrogen dioxide with ammonia to nitrogen and water. Unlike the first urea SCR 102, the second urea SCR 105 is specialized in exhaust purification efficiency and has an exhaust purification function as a main function.

  The first urea water injector 106 is installed in the exhaust pipe 112 and is arranged on the exhaust upstream side of the first urea SCR 102. The first urea water injector 106 supplies urea water to the first urea SCR 102. The first urea water injector 106 is controlled by the control device 111.

  The first exhaust gas temperature detector 107 is installed in the exhaust pipe 112 and is disposed between the first urea SCR 102 and the exhaust gas purification catalyst 103. The first exhaust gas temperature detector 107 detects an exhaust gas temperature between the first urea SCR 102 and the exhaust gas purifying catalyst 103. The exhaust gas temperature detected by the first exhaust gas temperature detector 107 is input to the control device 111.

  The second urea water injector 108 is provided in the exhaust pipe 112 and is disposed between the exhaust purification catalyst 103 and the second urea SCR 105. The second urea water injector 108 supplies urea water to the second urea SCR 105 according to the amount of nitrogen oxide discharged. The nitrogen oxide emission amount is estimated based on the engine speed and the fuel supply amount, or detected by a nitrogen oxide concentration detector. The urea water supplied to the second urea SCR 105 is hydrolyzed to ammonia by exhaust heat. The second urea water injector 108 is controlled by the control device 111.

  The second exhaust gas temperature detector 109 is installed in the exhaust pipe 112 and is disposed between the exhaust gas purifying catalyst 103 and the second urea SCR 105. The second exhaust gas temperature detector 109 detects an exhaust gas temperature between the exhaust gas purifying catalyst 103 and the second urea SCR 105. The exhaust gas temperature detected by the second exhaust gas temperature detector 109 is input to the control device 111.

  The hydrocarbon injector 110 is provided in the exhaust pipe 112 and is disposed between the first urea SCR 102 and the exhaust purification catalyst 103. The hydrocarbon injector 110 supplies a hydrocarbon (unburned fuel) to the exhaust purification catalyst 103. The hydrocarbon injector 110 is controlled by the control device 111.

  When the exhaust gas temperature detected by the first exhaust gas temperature detector 107 is equal to or lower than a first threshold exhaust gas temperature (for example, 150 ° C.), the control device 111 controls the first urea water injector 106 to remove urea water. One urea SCR 102 is supplied. By supplying the urea water to the first urea SCR 102, the water contained in the urea water can be adsorbed on the first urea SCR 102, so that the exhaust gas temperature can be raised. When supplying urea water to the first SCR 102, for example, the amount of water contained in the exhaust gas (the amount of water adsorbed by the first SCR 102) is estimated based on the engine speed and the amount of fuel supply, and the urea water is supplied in accordance with the amount of water. The calorific value of the first SCR 102 is estimated, and the urea water supply amount is adjusted to maximize the calorific value. In addition, the amount of water contained in the exhaust gas can be estimated with high accuracy by estimating the standard water amount contained in the exhaust gas based on the engine speed and the fuel supply amount and correcting the standard water amount with the outside air temperature and the outside air humidity. .

  When the exhaust gas temperature detected by the second exhaust gas temperature detector 109 is equal to or lower than a second threshold exhaust gas temperature (for example, 180 ° C.) higher than the first threshold exhaust gas temperature, the controller 111 While the urea water is supplied to the first urea SCR 102 by the water injector 106, the post-injection is executed by (the fuel injector of) the engine 101. By executing the post injection, hydrocarbons and carbon monoxide can be supplied to the exhaust purification catalyst 103 and the hydrocarbons and carbon monoxide can be oxidized by the exhaust purification catalyst 103, so that the exhaust temperature can be increased. Become.

  When the exhaust gas temperature detected by the second exhaust gas temperature detector 109 is equal to or lower than the second threshold exhaust gas temperature, the control device 111 replaces or adds to post-injection and uses the hydrocarbon injector 110 to remove hydrocarbons from the exhaust purification catalyst. 103 can be supplied. By supplying hydrocarbons to the exhaust purification catalyst 103, the hydrocarbons can be oxidized by the exhaust purification catalyst 103, so that the exhaust gas temperature can be raised. When supplying hydrocarbons to the exhaust purification catalyst 103, for example, the amount of hydrocarbons contained in exhaust gas (the amount of hydrocarbons supplied to the exhaust purification catalyst 103) is estimated based on the engine speed and the amount of fuel supplied, and The amount of heat generated by oxidation of the exhaust purification catalyst 103 is estimated according to the amount of hydrocarbons, and the amount of hydrocarbon supplied is adjusted so as to maximize the amount of heat generated by oxidation.

  When the exhaust gas temperature detected by the second exhaust gas temperature detector 109 is equal to or lower than a third threshold exhaust gas temperature (for example, 200 ° C.) higher than the second threshold exhaust gas temperature, the control device 111 While the urea water is supplied to the first urea SCR 102 by the water injector 106, post injection is performed by the engine 101, and / or the hydrocarbon is supplied to the exhaust purification catalyst 103 by the hydrocarbon injector 110, The urea water is supplied to the second urea SCR 105 by the urea water injector 108. The third threshold exhaust temperature means the activation temperature of the second urea SCR 105. By supplying the urea water to the second urea SCR 105, the water contained in the urea water can be adsorbed on the second urea SCR 105, so that the exhaust gas temperature can be raised.

  When the exhaust gas temperature detected by the second exhaust gas temperature detector 109 is higher than the third threshold exhaust gas temperature, the control device 111 stops the execution of post-injection and the supply of hydrocarbons, and performs the normal (conventional) operation. Execute exhaust gas purification control. In the exhaust gas purification control, urea water is supplied to the second urea SCR 105 according to the nitrogen oxide emission amount so that a specified exhaust gas purification rate is achieved.

  In summary, the control device 111 executes the following control immediately after starting the engine.

As shown in FIG. 2, in step S101, the exhaust temperatures T ₁ detected by the first exhaust temperature sensor 107 determines whether the first threshold exhaust temperature T _THRESHOLD1 less, the exhaust temperatures T ₁ second when: 1 threshold exhaust temperature T _THRESHOLD1, the process proceeds to step S102, if the exhaust gas temperature T _{1 THRESHOLD1} than the first threshold exhaust temperature T, the processing flow advances to step S103.

In step S102, urea water is supplied to the first urea SCR 102 by the first urea water injector 106 to increase the exhaust gas temperature T1 ( _first temperature increase control).

In step S103, it is determined whether the exhaust gas temperature T ₂ detected by the second exhaust gas temperature detector 109 is equal to or lower than a second threshold exhaust gas temperature T _THRESHOLD2 , and the exhaust gas temperature T ₂ is set to the second threshold exhaust gas temperature T _THRESHOLD2. in the following cases, the process proceeds to step S104, if the exhaust temperature T _{2 THRESHOLD2} than the second threshold exhaust temperature T, the processing flow advances to step S105.

In step S104, in order to raise the exhaust gas temperature T _2, while supplying the urea water in the first urea water injector 106 to the first urea SCR 102, whether to perform the post injection in the engine 101, and / or hydrocarbon Hydrocarbon is supplied to the exhaust purification catalyst 103 by the injector 110 (second temperature raising control).

In step S105, the exhaust temperature T ₂ detected by the second exhaust temperature detector 109 determines whether the third threshold exhaust temperature T _THRESHOLD3 below, the exhaust temperature T ₂ is the third threshold exhaust temperature T _THRESHOLD3 in the following cases, the process proceeds to step S106, if the exhaust temperature T ₂ of the third threshold exhaust temperature T _THRESHOLD3 greater, the process proceeds to step S107.

In step S106, in order to raise the exhaust gas temperature T _2, together to supply urea water to the first urea water injector 106 first urea SCR 102, to execute the post injection in the engine 101, and / or hydrocarbon injection The urea water is supplied to the second urea SCR 105 by the second urea water injector 108 while the hydrocarbon is supplied to the exhaust purification catalyst 103 by the heater 110 (third temperature increase control).

  In step S107, the above-described temperature increase control is stopped, and the exhaust gas purification control is executed.

Accordingly, as shown in FIG. 3, since the exhaust temperatures T ₁ and T ₂ can be quickly raised after the engine is started, and the exhaust temperature can be set to be higher than the activation temperature of the second urea SCR 105, it is possible to quickly start the operation after the engine is started. At this stage, nitrogen oxides can be purified by the second urea SCR 105, and nitrogen oxide slip immediately after engine start can be suppressed. In particular, the exhaust temperatures T ₁ is originally but to remain as shown in broken line in FIG. 3, it is quickly heated than the original by the addition of hydrocarbons.

Reference Signs List 100 exhaust aftertreatment device 101 engine 102 first urea SCR
103 Exhaust purification catalyst 104 CSF
105 Second urea SCR
106 first urea water injector 107 first exhaust temperature detector 108 second urea water injector 109 second exhaust temperature detector 110 hydrocarbon injector 111 controller 112 exhaust pipe

Claims (5)

In the exhaust aftertreatment device that purifies the exhaust of the engine,
A first urea SCR installed in an exhaust pipe of the engine;
An exhaust gas purification catalyst installed in the exhaust pipe and arranged on the exhaust gas downstream side of the first urea SCR;
A second urea SCR installed in the exhaust pipe and arranged on the exhaust gas downstream side of the exhaust purification catalyst;
A first urea water injector installed in the exhaust pipe and arranged on the exhaust upstream side of the first urea SCR;
A first exhaust gas temperature detector installed in the exhaust pipe and disposed between the first urea SCR and the exhaust gas purification catalyst;
A second urea water injector disposed in the exhaust pipe and disposed between the exhaust purification catalyst and the second urea SCR;
A second exhaust gas temperature sensor installed in the exhaust pipe and disposed between the exhaust gas purification catalyst and the second urea SCR;
An exhaust aftertreatment device characterized by comprising: When the exhaust gas temperature detected by the first exhaust gas temperature detector is equal to or lower than a first threshold exhaust gas temperature, the first urea water injector supplies urea water to the first urea SCR; When the exhaust gas temperature detected by the second exhaust gas temperature detector is equal to or lower than a second threshold exhaust gas temperature higher than the first threshold exhaust gas temperature, the first urea water injector supplies the first urea water injector with the first urea water. When the engine performs post-injection while supplying to the urea SCR, and the exhaust temperature detected by the second exhaust temperature detector is equal to or lower than a third threshold exhaust temperature higher than the second threshold exhaust temperature. The urea water is supplied to the first urea SCR by the first urea water injector, and the urea water is supplied to the second urea water injector by the second urea water injector while the engine performs post-injection. And a control device for supplying the urea SCR to the urea SCR. Item 7. An exhaust aftertreatment device according to Item 1. A hydrocarbon injector disposed on the exhaust pipe and disposed between the first urea SCR and the exhaust gas purification catalyst;
When the exhaust gas temperature detected by the first exhaust gas temperature detector is equal to or lower than a first threshold exhaust gas temperature, the first urea water injector supplies urea water to the first urea SCR; When the exhaust gas temperature detected by the second exhaust gas temperature detector is equal to or lower than a second threshold exhaust gas temperature higher than the first threshold exhaust gas temperature, the first urea water injector supplies the first urea water injector with the first urea water. The hydrocarbon is supplied to the exhaust gas purification catalyst by the hydrocarbon injector while the urea SCR is supplied, and the exhaust gas temperature detected by the second exhaust gas temperature detector is higher than the second threshold exhaust gas temperature. When the temperature is equal to or lower than the threshold exhaust temperature of 3, the urea water is supplied to the first urea SCR by the first urea water injector, and the hydrocarbon is supplied to the exhaust purification catalyst by the hydrocarbon injector. Urea water is supplied to the second urine using the second urea water injector. Exhaust post-treatment device according to claim 1, further comprising a control device for supplying to the SCR. The exhaust aftertreatment device according to any one of claims 1 to 3, wherein the first urea SCR and the second urea SCR include zeolite. The exhaust gas purifying catalyst, an exhaust aftertreatment device according to any one of claims 1 to 4 comprising one or both of the oxidation catalyst and _the NO _X storage reduction catalyst.

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