JP2019120144A - Engine system - Google Patents

Abstract

To provide an engine system which enables reduction of harmful substances discharged to the outside.SOLUTION: An engine system 10 has an engine 12, an exhaust emission control device 14 and a controller 16. The exhaust emission control device 14 includes: a first oxidation-reduction catalyst 18; a selector valve 20 for switching an exhaust passage to a basic passage or a bypass passage; a second oxidation-reduction catalyst 22 provided on the basic passage; an adsorber 34 provided on the bypass passage; a heat exchanger 24 provided between the selector valve 20 and the adsorber 34 in the bypass passage; and first and second temperature sensors 30, 32 which detect temperatures of the first and second oxidation-reduction catalysts 18, 22. The controller switches the selector valve 20 according to detection temperatures detected by the first and second temperature sensors 30, 32.SELECTED DRAWING: Figure 1

Description

  The present specification discloses an engine system having an engine and an exhaust gas purification device for purifying exhaust gas output from the engine.

  2. Description of the Related Art Conventionally, an exhaust gas purification device for purifying exhaust gas output from an engine has been widely known. Generally, such an exhaust gas purification apparatus is provided with a redox catalyst that purifies and reduces harmful substances contained in the exhaust gas.

  Such a redox catalyst does not activate at low temperatures and can not exert sufficient purification capability. Therefore, there has been a problem that exhaust gas can not be sufficiently purified when the oxidation-reduction catalyst is at a low temperature, such as at the beginning of engine operation. Therefore, in some cases, it has been proposed to provide the exhaust gas purification apparatus with a first oxidation-reduction catalyst, an adsorber for adsorbing harmful substances, and a second oxidation-reduction catalyst. According to this technique, before activating the first redox catalyst, harmful substances are adsorbed by the adsorber, and after activating the first redox catalyst, the harmful substances are cleaned by the first redox catalyst. The harmful substance desorbed from the adsorber can be purified with a second oxidation reduction catalyst provided downstream of the adsorber.

  For example, Patent Document 1 discloses an exhaust system in which a first catalyst zone, an adsorption zone, and a second catalyst zone are arranged in order from the upstream side. In this patent document 1, a heat exchanger is provided to exchange heat between the exhaust flowing from the first catalyst zone to the adsorption zone and the exhaust flowing from the adsorption zone to the second catalyst zone. By providing such a heat exchanger, the arrival time to the desorption start temperature at which desorption of harmful substances is started in the adsorption zone can be delayed, and the time until the second catalyst zone is activated can be shortened.

Patent No. 3435652

  However, in Patent Document 1, exhaust continues to flow in the adsorption zone even after the first catalyst zone is activated. Although the exhaust flowing into the adsorption zone is somewhat removed by heat exchange with the exhaust flowing into the second catalytic zone, it is sufficiently higher than the outside air. As the exhaust gas continues to flow into the adsorption zone, the adsorption zone may reach the desorption start temperature before the second catalyst zone is activated. In this case, there is a problem that the harmful substance is discharged to the outside without being removed. This is a particularly serious problem when the harmful substance is a substance having a strong odor such as ammonia.

  Thus, the present specification discloses an engine system capable of further reducing harmful substances discharged to the outside.

  An engine system disclosed in the present specification is an engine system including an engine, an exhaust gas purification device for purifying exhaust gas output from the engine, and a control unit for controlling driving of the engine and the exhaust gas purification device. The exhaust gas purification apparatus is provided with a first oxidation-reduction catalyst for purifying harmful substances contained in the exhaust gas, and a path of exhaust gas provided downstream of the first oxidation-reduction catalyst and output from the first oxidation-reduction catalyst A switching valve for switching between the basic path and a bypass path whose downstream end reaches the basic path, and a second oxidation valve provided on the basic path for purifying the harmful substance contained in the exhaust gas An adsorption that is provided on a reduction catalyst and on the bypass path, adsorbs the harmful substance contained in the exhaust gas, and releases the adsorbed harmful substance as the temperature rises. And a heat exchanger provided between the switching valve and the adsorber in the bypass path, for heat exchange between the exhaust input to the adsorber and the exhaust output from the adsorber. A heat exchanger for removing heat from the exhaust gas input to the adsorber and heating the exhaust gas output from the adsorber before sending it to the second oxidation reduction catalyst; and purifying the first redox catalyst A first capability detector for detecting the capability and a second capability detector for detecting the purification capability of the second redox catalyst, wherein the control unit comprises the first capability detector and the second capability detector. The switching valve is switched according to the detected purification capacity.

  In this case, the first ability detector is a first temperature sensor that detects the temperature of the first redox catalyst, and the second ability detector is a second temperature that detects the temperature of the second redox catalyst. It may be a sensor.

  In addition, when the purification capacity of the first redox catalyst is less than a prescribed activity threshold, the control unit causes the exhaust gas to pass through the bypass path, and the purification capacity of the first redox catalyst is active. When the purification capacity of the second oxidation reduction catalyst is equal to or higher than the threshold value and less than the activation threshold, the purification capacity of the second oxidation reduction catalyst is activated so that the exhaust gas passes through the basic path without passing through the bypass. When it is above the threshold value, the switching valve may be switched so that the exhaust passes through the bypass path.

  Furthermore, the desorption device further includes a desorption detector for detecting completion of desorption of the harmful substance in the adsorber, and the control unit is configured to perform the desorption after the purification capacity of the second oxidation reduction catalyst becomes equal to or more than the activity threshold. When the separation completion is detected by the separation detector, the switching valve may be switched so that the exhaust gas passes through the basic path without passing through the bypass.

  In this case, the desorption detector may be a third temperature sensor that detects the temperature of the adsorber. As another mode, the desorption detector is based on the absolute value of the difference between the air-fuel ratio of the exhaust flowing into the first redox catalyst and the air-fuel ratio of the exhaust flowing into the second oxidation reduction catalyst. The removal of the harmful substance may be detected.

  Further, the control unit may continue driving of the engine until completion of desorption of the harmful substance in the adsorber is detected.

  Further, a first air-fuel ratio sensor that detects an air-fuel ratio of the exhaust flowing into the first oxidation reduction catalyst as a first air-fuel ratio, and an air-fuel ratio of the exhaust flowing into the second oxidation reduction catalyst as a second air-fuel ratio A second air-fuel ratio sensor to be detected, and the control unit is configured to supply the engine to the engine based on the second air-fuel ratio during a period in which desorption of the harmful substance occurs in the adsorber. The air-fuel ratio of the gas may be determined, and the air-fuel ratio may be determined based on the first air-fuel ratio during another period.

  In this case, the control unit may determine whether desorption of the harmful substance has occurred based on the difference between the first air fuel ratio and the second air fuel ratio.

  The engine may be an ammonia engine, and the harmful substance may include ammonia.

  According to the engine system disclosed herein, the switching valve switches between the basic path and the bypass path. Therefore, since the exhaust gas does not always flow to the adsorber, the temperature rise of the adsorber and hence the start of desorption of harmful substances can be controlled to some extent. As a result, harmful substances discharged to the outside can be further reduced.

It is a block diagram showing composition of an engine system. It is a figure which shows the change of the ammonia concentration of each part, and temperature. It is a flowchart which shows the flow of switching control of a switching valve. It is a flowchart which shows the flow of determination control of an air fuel ratio. It is a flowchart which shows the other example of the flow of determination control of an air fuel ratio.

  Hereinafter, the configuration of engine system 10 will be described with reference to the drawings. FIG. 1 is a block diagram showing the configuration of an engine system 10. The engine system 10 includes an engine 12, an exhaust purification device 14 that purifies exhaust gas from the engine 12, and a controller 16 that controls driving of the engine 12 and the exhaust purification device 14.

  The engine 12 is an ammonia engine driven using ammonia as a fuel. The exhaust from the engine 12 contains nitrogen, water vapor, ammonia, nitrogen oxides and hydrogen. Also, the exhaust from the engine 12 is usually at a high temperature.

The exhaust gas discharged from the engine 12 is discharged to the exhaust gas purification device 14. The exhaust gas purification device 14 is a device that purifies or removes harmful substances contained in the exhaust gas and discharges it out of the vehicle. The exhaust purification device 14 includes a first oxidation reduction catalyst 18. The first redox catalyst 18 detoxifies the harmful substances contained in the exhaust gas by redox. In the case of an ammonia engine, ammonia (NH ₃ ) and nitrogen oxides (NO _x ) become harmful substances. The first redox catalyst 18 for redoxing such ammonia and nitrogen oxides uses, for example, ceramics or titanium oxide as a support, and also base metal oxides such as vanadium, molybdenum and tungsten, or zeolites and noble metals Is used as an active catalyst component. In the first redox catalyst 18, ammonia (NH ₃ ), hydrogen (H ₂ ) and nitrogen oxides (NO _x ) are reduced to nitrogen (N ₂ ) and water vapor (H ₂ O).

  By the way, such an oxidation-reduction reaction does not occur sufficiently if the first oxidation-reduction catalyst 18 is less than the prescribed first activation temperature Ta1. The first activation temperature Ta1 is usually sufficiently higher than the normal temperature and sufficiently lower than the temperature of the exhaust gas discharged from the engine 12. Therefore, when the first redox catalyst 18 is lower than the first activation temperature Ta1 such as at the start of operation of the engine 12, the first redox catalyst 18 can not purify harmful substances, and the first redox catalyst 18 is harmful. Exhaust gas containing substance will be output. On the other hand, when the operation of the engine 12 continues to a certain extent, the temperature of the first redox catalyst 18 rises due to the high temperature exhaust gas, and becomes equal to or higher than the first activation temperature Ta1. In this state, the above-mentioned oxidation-reduction reaction occurs in the first oxidation-reduction catalyst 18, and purification of harmful substances is performed. In this case, the first redox catalyst 18 outputs exhaust gas from which harmful substances have been removed.

  The first oxidation / reduction catalyst 18 is provided with a first temperature sensor 30 for detecting the temperature of the first oxidation / reduction catalyst 18 as a first catalyst temperature T1. The first catalyst temperature T1 detected by the first temperature sensor 30 is output to the controller 16. The first temperature sensor 30 functions as a first capability detector that detects the purification capability of the first redox catalyst 18. In addition, as long as the purification capacity of the first redox catalyst 18 can be detected, another sensor may be used instead of the temperature sensor. For example, a concentration sensor for detecting the concentration of harmful substances contained in the output exhaust gas from the first redox catalyst 18 may be provided instead of or in addition to the temperature sensor.

  A switching valve 20 is provided downstream of the first redox catalyst 18. The switching valve 20 is a three-way valve that switches the path of the exhaust to either the basic path or the bypass path. The bypass path is a path toward the second oxidation reduction catalyst 22 through the heat exchanger 24, the adsorber 26 and the heat exchanger 24 which will be described later. The basic route is a route toward the second oxidation reduction catalyst 22 without passing through the heat exchanger 24 and the adsorber 26. The switching of the switching valve 20 is controlled by the controller 16, which will be described later.

  The basic route is provided with a second oxidation reduction catalyst 22. Like the first redox catalyst 18, the second redox catalyst 22 detoxifies harmful substances (ammonia, nitrogen oxides) contained in the exhaust gas by redox. If the second oxidation reduction catalyst 22 is also below the specified second activation temperature Ta2, the redox reaction does not occur sufficiently, and therefore the harmful substance can not be purified. The second activation temperature Ta2 may be the same as or different from the first activation temperature Ta1. In the following, it is assumed that Ta1 = Ta2.

  Further, the second oxidation reduction catalyst 22 is also provided with a second temperature sensor 32 that detects the temperature of the second oxidation reduction catalyst 22 as a second catalyst temperature T2. The second catalyst temperature T 2 detected by the second temperature sensor 32 is output to the controller 16. The second temperature sensor 32 functions as a second ability detector that detects the purification ability of the second reduction catalyst 22.

  A heat exchanger 24 and an adsorber 26 are provided on the bypass path. The adsorber 26 adsorbs and holds harmful substances, particularly ammonia. The adsorber 26 includes, for example, a substance having an acid point that easily adsorbs ammonia, such as zeolite, as an adsorptive substance. In such an adsorber 26, generally, the lower the temperature, the higher the adsorption amount of harmful substances. On the other hand, since the adsorber 26 can not adsorb the harmful substance as the temperature rises, desorption of the adsorbed substance occurs. The desorption start temperature Tds at which desorption of the substance adsorbed by the adsorber 26 starts is often comparable to the first activation temperature Ta1 and the second activation temperature Ta2 under normal pressure environment. In addition, when the adsorber 26 reaches the desorption completion temperature Tde higher than the desorption start temperature Tds, it can be considered that all harmful substances have been desorbed from the adsorber 26. The desorption completion temperature Tde is usually higher than the first activation temperature Ta1 and the second activation temperature Ta2.

  The adsorber 26 is also provided with a third temperature sensor 34 that detects the temperature of the adsorber 26 as the adsorber temperature T3. The adsorber temperature T3 detected by the third temperature sensor 34 is output to the controller 16. The third temperature sensor 34 functions as a desorption detector for detecting completion of desorption of harmful substances in the adsorber 26. Alternatively, the third temperature sensor 34 may be eliminated, and the desorption completion may be detected based on the difference between the first air-fuel ratio λ1 and the second air-fuel ratio λ2 described later.

  A heat exchanger 24 is provided between the switching valve 20 and the adsorber 26. The heat exchanger 24 is a heat exchanger 24 that exchanges heat between the exhaust gas input to the adsorber 26 and the exhaust gas output from the adsorber 26. That is, the exhaust gas input to the adsorber 26 is at a higher temperature than the exhaust gas output from the adsorber 26. By bringing the exhaust gas having this temperature difference into close proximity in the heat exchanger 24 and exchanging heat, the exhaust gas inputted to the adsorber 26 is removed. On the other hand, the exhaust gas output from the adsorber 26 is heated and the temperature rises. This warmed exhaust is sent to the basic pathway (i.e., the second oxidation reduction catalyst 22) as apparent from FIG. And when this heat exchanger 24 is provided, while temperature rise of the adsorber 26 is suppressed compared with the case where there is no heat exchanger 24, temperature rise of the 2nd oxidation reduction catalyst 22 is promoted. In other words, it can be said that the time until the desorption start of harmful substances by the adsorber 26 is prolonged, and the time until the activation of the second reduction catalyst 22 is shortened.

  A first air-fuel ratio sensor 36 is provided between the engine 12 and the first oxidation-reduction catalyst 18 to detect the concentration of oxygen contained in the exhaust gas as a first air-fuel ratio λ1. The second air-fuel ratio sensor 38 detects the concentration of oxygen contained in the exhaust as the second air-fuel ratio λ2 immediately upstream of the second oxidation reduction catalyst 22 (downstream from the junction of the bypass route and the basic route). It is provided. The air-fuel ratios λ1 and λ2 detected by the first air-fuel ratio sensor 36 and the second air-fuel ratio sensor 38 are output to the controller 16.

  The controller 16 controls the drive of the engine 12 and the exhaust gas purification device 14 described above. The controller 16 includes, for example, a CPU that performs various operations, and a storage device that stores various data, programs, and the like. The controller 16 controls switching of the switching valve 20 based on the first catalyst temperature T1, the second catalyst temperature T2, and the adsorber temperature T3. Further, the controller 16 determines the air-fuel ratio of the mixed gas supplied to the engine 12 based on the first air-fuel ratio λ1 and the second air-fuel ratio λ2. The switching control of the switching valve 20 and the determination control of the air-fuel ratio will be described in detail later. The determined air-fuel ratio is input to the fuel injection device 28. The fuel injection device 28 injects an amount of fuel according to the instructed air-fuel ratio. The injected fuel is introduced into the engine 12 as a mixed gas mixed with air.

  Next, exhaust gas purification processing in the engine system 10 will be described. In the engine system 10 disclosed herein, the harmful substance is adsorbed by the adsorber 26 until the first redox catalyst 18 is activated, and after the first redox catalyst 18 is activated, the first redox catalyst 18 is activated. The redox catalyst 18 purifies harmful substances. Further, the harmful substance desorbed from the adsorber 26 after being adsorbed by the adsorber 26 is purified by the second reduction catalyst 22. Hereinafter, such exhaust purification processing will be described in detail.

  First, when the first catalyst temperature T1 is less than the first activation temperature Ta1 as in the initial operation of the engine 12, etc., that is, the first redox catalyst 18 is not sufficiently activated and harmful substances The case where purification is impossible will be described. In this case, the controller 16 switches the switching valve 20 so that the exhaust passes through the bypass path.

  In this case, the exhaust gas discharged from the engine 12 is first input to the first redox catalyst 18. However, since the first redox catalyst 18 is not activated, many harmful substances (ammonia, nitrogen oxides) are released downstream as they are without redox. On the other hand, when the high temperature exhaust gas flows in, the temperature of the first redox catalyst 18 gradually rises.

  The exhaust gas output from the first redox catalyst 18 passes through the switching valve 20 and flows to the bypass path. The exhaust gas flowing into the bypass path is first removed in the heat exchanger 24 by heat exchange of the exhaust gas output from the adsorber 26. As a result, the exhaust going from the heat exchanger 24 to the adsorber 26 has a lower temperature than the exhaust going from the switching valve 20 to the heat exchanger 24.

  The heat removed exhaust flows into the adsorber 26. Here, as described above, since the purification by the first redox catalyst 18 is not performed, the exhaust gas flowing into the adsorber 26 contains harmful substances. Further, at the initial stage of operation of the engine 12 or the like, the adsorber temperature T3 is sufficiently smaller than the desorption start temperature Tds. Therefore, the harmful substance contained in the exhaust gas is adsorbed and held by the adsorber 26. As a result, the adsorber 26 outputs an exhaust gas from which harmful substances have been sufficiently removed. Although the exhaust gas flowing into the adsorber 26 is removed by the heat exchanger 24, the temperature is sufficiently high compared to the outside air. Therefore, as the exhaust gas continues to flow into the adsorber 26, the temperature of the adsorber 26 gradually rises and approaches the desorption start temperature Tds.

  The exhaust gas output from the adsorber 26 flows into the heat exchanger 24 and exchanges heat with the exhaust gas input to the adsorber 26. Then, the exhaust gas heated by this heat exchange is input to the second oxidation reduction catalyst 22. At this time, the second catalyst temperature T2 is lower than the second activation temperature Ta2. However, when the heated exhaust gas is input, the second catalyst temperature T2 gradually increases. Note that if T2 <Ta2, purification of harmful substances by the second reduction catalyst 22 can not be performed, but at this point of time, exhaust gas input to the second reduction catalyst 22 has harmful substances removed by the adsorber 26. ,no problem.

[When T1TTa1 and T2 <Ta2]
Next, as a result of the high temperature exhaust from the engine 12 being continuously output, the first catalyst temperature T1 becomes equal to or higher than the first activation temperature Ta1, but the second catalyst temperature T2 is lower than the second activation temperature Ta2. explain. In this case, although the first redox catalyst 18 can purify the harmful substance, the second redox catalyst 22 can not clean the harmful substance. In this state, the controller 16 switches the switching valve 20 so that the exhaust passes through the basic path.

  In this case, the exhaust gas input from the engine 12 to the first redox catalyst 18 is purified of harmful substances by the first redox catalyst 18. As a result, the first redox catalyst 18 outputs an exhaust that is sufficiently purified of harmful substances. This exhaust flows into the basic path. That is, the exhaust gas output from the first redox catalyst 18 is directly input to the second oxidation reduction catalyst 22 without passing through the bypass path. As described above, when not passing through the bypass path, the temperature of the exhaust reaching the second reduction catalyst 22 is higher than when passing through the bypass path. As a result, by selecting the basic route, the rise of the second catalyst temperature T2 is promoted, and the time until the second catalyst temperature T2 reaches the second activation temperature Ta2 can be shortened. In addition, when the basic route is selected, the exhaust does not flow to the adsorber 26. As a result, the temperature rise of the adsorber temperature T3 is suppressed, and the time until the adsorber temperature T3 reaches the desorption start temperature Tds can be prolonged.

  Next, the case where the second catalyst temperature T2 rises to the second activation temperature Ta2 or more due to the heat of exhaust while the adsorber temperature T3 is less than the desorption completion temperature Tde will be described. In this case, the controller 16 switches the switching valve 20 so that the exhaust passes through the bypass path.

  Also in this case, harmful substances contained in the exhaust from the engine 12 are purified by the first redox catalyst 18. Therefore, the first redox catalyst 18 outputs exhaust gas in which harmful substances are sufficiently purified. The exhaust flows into the adsorber 26 through the heat exchanger 24. Although the exhaust gas is removed by the heat exchanger 24, it is sufficiently hot as compared to the outside air. Therefore, the temperature of the adsorber 26 gradually increases due to the exhaust. Then, when the adsorber temperature T3 becomes equal to or higher than the desorption start temperature Tds, desorption of harmful substances from the adsorber 26 is started. In this case, the adsorber 26 discharges exhaust gas containing harmful substances. The exhaust gas flows into the second reduction catalyst 22 through the heat exchanger 24.

  The second redox catalyst 22 is fully activated. Therefore, the NO 2 reduction catalyst 22 purifies harmful substances contained in the exhaust gas discharged from the adsorber 26, that is, harmful substances desorbed from the adsorber 26. And, from the second reduction catalyst 22, exhaust gas in which harmful substances are sufficiently purified is discharged. Then, after the second oxidation reduction catalyst 22 is thus activated (after T2 ≧ Ta2), the exhaust gas is allowed to flow through the bypass path, thereby promoting the temperature rise of the adsorber 26 and causing harmful effects from the adsorber 26. It accelerates the detachment of the substance.

  Next, the case where the adsorber temperature T3 is equal to or higher than the desorption completion temperature Tde due to the heat of exhaust will be described. When the adsorber temperature T3 reaches the desorption completion temperature Tde, the adsorption amount of harmful substances in the adsorber 26 can be considered to be almost zero. In this state, the controller 16 switches the switching valve 20 so that the exhaust passes through the basic path. When the desorption of the adsorber 26 is completed as described above, the reason for switching to the basic path is to prevent the thermal deterioration of the adsorber 26. That is, at this point, the adsorption amount of harmful substances in the adsorber 26 is almost zero. There is no advantage to keep the exhaust gas flowing to the adsorber 26, but rather the disadvantage is the deterioration of the adsorber 26 due to the heat of the exhaust. Therefore, when the adsorber temperature T3 reaches the desorption completion temperature Tde, the operation is switched to the basic path, and the inflow of the exhaust gas to the adsorber 26 is stopped.

  As apparent from the above description, according to the engine system 10 disclosed in the present specification, according to the purification ability of the first redox catalyst 18 and the second oxidation reduction catalyst 22, exhaust paths can be divided into basic paths and bypass paths. Switch to one of the. This makes it possible to shorten the time to the activation of the catalytic converter, in particular, the second reduction catalyst 22, and to prolong the time to the start of the desorption of harmful substances from the adsorber 26. As a result, harmful substances can be effectively prevented from being discharged outside without being purified. Further, in the present embodiment, the exhaust flowing into the adsorber 26 is removed by the heat exchanger 24, and the exhaust directed from the adsorber 26 to the second reduction catalyst 22 is warmed. Therefore, the time to the activation of the second redox catalyst 22 can be further shortened, and the time to the desorption start of harmful substances from the adsorber 26 can be further prolonged.

  Next, the relationship between the temperature of each part and the ammonia concentration of each part in the engine system 10 will be described with reference to FIG. In FIG. 2, a to e are graphs showing the ammonia concentration in each part. Specifically, a is the engine outlet, b is the outlet of the first redox catalyst, c is the interior of the adsorber 26, d is the outlet of the adsorber 26, and e is the outlet of the second redox catalyst. It shows the ammonia concentration. Moreover, f of FIG. 2 is a graph which shows the change of temperature T1-T3.

  In the illustrated example, the engine 12 is started at time 0. At time t0, the controller 16 switches the switching valve 20 so that the exhaust gas passes through the bypass path. Further, all of the first redox catalyst 18, the second redox catalyst 22, and the adsorber 26 are at normal temperature.

  When the engine 12 starts up, exhaust gas containing harmful substances such as ammonia is discharged from the engine 12. In particular, immediately after the start of the engine 12, the ammonia concentration of the exhaust gas is high because the engine 12 is not warmed up. The first redox catalyst 18 can not purify such ammonia because it is low temperature and not activated. On the other hand, since the adsorber 26 is lower than the desorption start temperature Tds, harmful substances such as ammonia can be adsorbed.

  As a result, at the initial stage of operation of the engine 12 (time 0 to t1), at the engine outlet (a) and the first redox catalyst outlet (b), the ammonia concentration becomes high. Further, since the adsorber 26 adsorbs harmful substances such as ammonia, the concentration of ammonia in the interior (c) of the adsorber 26 is also increased. On the other hand, most of the ammonia is adsorbed by the adsorber 26, so the ammonia concentration becomes almost zero at the outlet (d) of the adsorber 26 and at the outlet (e) of the second oxidation reduction catalyst.

  The temperature of each of the first redox catalyst 18, the second oxidation reduction catalyst 22, and the adsorber 26 gradually increases due to the heat of the exhaust gas. However, since the adsorber 26 is located downstream of the first redox catalyst 18 and the inflow exhaust gas is removed by the heat exchanger 24, the temperature rise rate of the adsorber 26 is the Lower than the first redox catalyst 18. As a result, before the adsorber 26 reaches the desorption start temperature Tds, the first redox catalyst 18 reaches the first activation temperature Ta1.

  At time t1, when the first redox catalyst 18 reaches the first activation temperature Ta1, the controller 16 switches the switching valve 20 so that the exhaust gas passes through the basic path without passing through the bypass path. At this time, since the first redox catalyst 18 exerts a sufficient purification capability, the ammonia concentration at the first redox catalyst outlet (b) becomes almost zero.

  At this time, the basic route is selected, and the exhaust flows to the second reduction catalyst 22 without flowing to the adsorber 26. Therefore, while the temperature rise of the adsorber 26 becomes slow, the temperature rise rate of the second oxidation reduction catalyst 22 improves. As a result, before the adsorber temperature T3 reaches the desorption start temperature Tds, the second catalyst temperature T2 reaches the second activation temperature Ta2.

  At time t2, when the second catalyst temperature T2 reaches the second activation temperature Ta2, the controller 16 switches the switching valve 20 so that the exhaust gas passes through the bypass path. In this case, since the exhaust gas also flows to the adsorber 26, the temperature of the adsorber 26 gradually rises.

  Then, at time t3, when the adsorber temperature T3 reaches the desorption start temperature Tds, ammonia is gradually released from the adsorber 26. As a result, the ammonia concentration in the adsorber (c) decreases, and the ammonia concentration in the adsorber outlet (d) increases. Then, when the adsorber temperature T3 further rises and approaches the desorption completion temperature Tde, the amount of ammonia released from the adsorber 26 decreases, so the ammonia concentration at the adsorber outlet (d) decreases gradually . During this time, the ammonia released from the adsorber 26 is purified by the activated second oxidation reduction catalyst 22. As a result, the ammonia concentration at the second redox catalyst outlet (e) is kept at zero.

  Finally, at time t4, when the adsorber temperature T3 reaches the desorption completion temperature Tde, the ammonia concentration at the inside and at the outlet of the adsorber 26 becomes substantially zero. In this state, the controller 16 switches the switching valve 20 so that the exhaust gas flows into the basic path without passing through the bypass path. As a result, since the exhaust gas does not flow to the adsorber 26, it is possible to suppress the deterioration of the adsorber 26 caused by the heat of the exhaust gas.

  Next, the flow of the switching control of the switching valve 20 will be described with reference to FIG. FIG. 3 is a flowchart showing the flow of the switching control of the switching valve 20 by the controller 16. As shown in FIG. 3, when the engine 12 is started, the controller 16 first sets a parameter J indicating the adsorption state of the adsorber 26 to 0 (S10). Subsequently, it is determined whether the first catalyst temperature T1 is equal to or higher than the first activation temperature Ta1 (S12). As a result of the determination, if the first catalyst temperature T1 is less than the first activation temperature Ta1, the controller 16 sets the switching valve 20 in the bypass path (S14). While the bypass path is selected, the controller 16 determines whether the adsorber temperature T3 is equal to or higher than the desorption completion temperature Tde (S16). As a result of the determination, when T3 ≧ Tde, that is, when the desorption in the adsorber 26 is completed, 1 is set to the parameter J, and the process returns to step S12 (S18). On the other hand, if T3 <Tde, the process returns to step S12 while maintaining J = 0.

  If it is determined in step S12 that T1 ≧ Ta1, then it is determined whether or not the parameter J is 1 (S20). As a result of the determination, if J = 1, that is, if the adsorber 26 has been desorbed, the controller 16 subsequently determines whether the operation of the engine 12 has stopped (S26). As a result of the determination, if the operation of the engine 12 is stopped, the process ends. On the other hand, if the engine 12 continues the operation, the controller 16 sets the switching valve 20 to the basic path (S24), and then returns to step S12.

  On the other hand, if T1 ≧ Ta1 and J = 0 (No in S20), the controller 16 subsequently determines whether the second catalyst temperature T2 is equal to or higher than the second activation temperature Ta2 (S22). If T2 ≧ Ta2 as a result of the determination, the controller 16 proceeds to step S24 and sets the switching valve 20 in the bypass path (S14). On the other hand, if T1 ≧ Ta1 and J = 0 and T2 <Ta2, the process proceeds to step S24 and the switching valve 20 is set to the basic path.

  As apparent from the above description, the controller 16 controls the switching of the switching valve 20 based on the first catalyst temperature T1, the second catalyst temperature T2, and the adsorber temperature T3. The temperatures T1, T2 and T3 can be said to be parameters indicating the purification capacity of the catalyst and the adsorption / desorption state of the adsorber 26, respectively. Therefore, in the present embodiment, it can be said that the controller 16 performs switching control of the switching valve 20 in accordance with the purification capacity of the catalyst and the adsorption / desorption state of the adsorber 26.

  It is desirable that the engine 12 be continuously operated until desorption from the adsorber 26 is completed in order to ensure adsorption of harmful substances by the adsorber 26 also at the time of starting the engine next time. That is, the controller 16 continues the operation of the engine 12 until T3 ≧ Tde is reached. Thus, for example, even if the user instructs to stop the engine before T3 ≧ Tde, the controller 16 causes the operation of the engine 12 to continue. At this time, it is desirable to announce to the user that the engine 12 can not be stopped for exhaust gas purification. In addition, when it is desired to terminate the desorption of harmful substances early by the adsorber 26 as described above, the combustion of the engine 12 may be adjusted so that the exhaust gas temperature becomes particularly high. For example, it is known that exhaust temperature rises when combustion timing of mixed gas in the engine 12 is delayed.

  Next, determination control of the air-fuel ratio of the mixed gas supplied to the engine 12 will be described. The controller 16 is based on the first air-fuel ratio λ1 which is the air-fuel ratio (oxygen concentration) of the exhaust at the engine outlet and the second air-fuel ratio λ2 which is the air-fuel ratio (oxygen concentration) of the exhaust at the inlet of the second oxidation reduction catalyst. , Determine the air-fuel ratio of the mixed gas.

  More specifically, since ammonia has a strong pungent odor, it is desirable to avoid the release to the outside as much as possible. Therefore, in the engine system 10 using an ammonia engine, it is desirable that the ammonia contained in the exhaust gas be oxidized reliably.

  Here, in a situation where desorption of ammonia in the adsorber 26 does not occur, the amount of ammonia to be oxidized and purified is only the amount of ammonia contained in the exhaust gas discharged from the engine 12. Therefore, in this case, ammonia can be oxidized and purified by adjusting the air-fuel ratio of the mixed gas supplied to the engine 12 so that the first air-fuel ratio λ1 at the engine outlet becomes the stoichiometric ratio.

  On the other hand, when desorption of ammonia occurs in the adsorber 26, the amount of ammonia to be oxidized and purified is added to the amount of ammonia contained in the exhaust gas discharged from the engine 12 and the amount of ammonia desorbed from the adsorber 26 There is also. As described above, in the situation where desorption of ammonia occurs, if the air-fuel ratio of the mixed gas is adjusted based on the first air-fuel ratio λ1 at the engine outlet, oxygen necessary for oxidation of ammonia runs short and ammonia can not be purified There is a fear. Therefore, when desorption of ammonia occurs, the air-fuel ratio of the mixed gas supplied to the engine 12 is adjusted so that the second air-fuel ratio λ2 at the inlet of the second oxidation reduction catalyst 22 becomes the stoichiometric ratio.

  FIG. 4 is a flow chart showing the flow of determination control of the air-fuel ratio of the mixed gas. As shown in FIG. 4, the controller 16 first determines whether a basic route is currently selected (S30). As apparent from the above description, since desorption of ammonia does not occur during the period when the basic route is selected, when the basic route is selected, the controller 16 mixes the mixed gas based on the first air-fuel ratio λ1. The air-fuel ratio of is determined (S32).

  On the other hand, when the bypass route is selected, the controller 16 subsequently determines whether the second catalyst temperature T2 is equal to or higher than the second activation temperature Ta2 (S34). When T2 <Ta, desorption of ammonia does not occur, so the controller 16 determines the air-fuel ratio of the mixed gas based on the first air-fuel ratio λ1 (S32). On the other hand, when T2 ≧ Ta, desorption of ammonia may occur. Therefore, in this case, the controller 16 determines whether the absolute value of the difference between the first air-fuel ratio λ1 and the second air-fuel ratio λ2 is equal to or greater than a prescribed reference value λJ (S36). In the case of | λ1−λ2 | <λJ, that is, when the first air fuel ratio λ1 and the second air fuel ratio λ2 are substantially equal, it can be determined that desorption of ammonia has not occurred. Therefore, in this case, the controller 16 determines the air-fuel ratio of the mixed gas based on the first air-fuel ratio λ1 (S32).

  On the other hand, when | λ1−λ2 | ≧ λJ, it can be determined that the ammonia desorbed from the adsorber 26 is flowing into the second oxidation reduction catalyst 22. In this case, oxygen is further required to oxidize the desorbed ammonia. Therefore, in this case, the controller 16 determines the air-fuel ratio of the mixed gas based on the second air-fuel ratio λ2 (S38).

  As apparent from the above description, according to the present embodiment, when desorption of ammonia is occurring, mixing is performed based on the second air-fuel ratio λ2 at the inlet of the second reduction catalyst 22 downstream of the adsorber 26. The air fuel ratio of the gas is determined. As a result, ammonia can be reliably oxidized (purified).

  The difference between the first air-fuel ratio λ1 and the second air-fuel ratio λ2 extends not only when the desorption of ammonia occurs, but also when the adsorption of ammonia by the adsorber 26 occurs. Therefore, if only | λ1−λ2 | is monitored, there is a possibility that the adsorption state may be mistaken as the desorption state. In the flowchart shown in FIG. 4, the reason for monitoring not only | λ1−λ2 | but also the second catalyst temperature T2 and the state of the switching valve 20 (steps S30 and S34) is to prevent such erroneous recognition. Therefore, steps S30 and S34 may be omitted as long as there is a step that can prevent misidentification between the adsorption state and the desorption state. For example, after the first redox catalyst 18 is activated, it is considered that adsorption of ammonia by the adsorber 26 does not occur. Therefore, as shown in FIG. 5, first, it may be determined whether the first catalyst temperature T1 is equal to or higher than the first activation temperature Ta1 (S40). When T1 <Ta1 (before the first oxidation reduction catalyst 18 is activated), the air-fuel ratio of the mixed gas is adjusted at the first air-fuel ratio λ1 (S32). In the case of T1TTa1 (after the first redox catalyst 18 is activated), it is further confirmed whether or not | λ1−λ2 | ≧ λJ is satisfied (S36). As a result of confirmation, in the case of | λ1−λ2 | ≧ λJ, it is judged that desorption of ammonia has occurred, and the air fuel ratio of the mixed gas is adjusted based on the second air fuel ratio λ2 (S38). On the other hand, if λ1−λ2 | <λJ, the air-fuel ratio of the mixed gas is adjusted based on the first air-fuel ratio λ1 (S32).

  As another mode, desorption of ammonia may be determined based on the adsorber temperature T3. That is, the desorption start temperature Tds at which the desorption of ammonia starts and the desorption completion temperature Tde at which the desorption of ammonia is completed are known. Therefore, when the adsorber temperature T3 is in the range between the desorption start temperature Tds and the desorption completion temperature Tde, it is determined that desorption of ammonia is occurring, and the second air-fuel ratio λ2 is used. The air-fuel ratio of the mixed gas may be determined.

  In any case, when desorption of ammonia from the adsorber 26 occurs, the ammonia is purified by determining the air-fuel ratio of the mixed gas based on the second air-fuel ratio λ2 at the inlet of the second oxidation reduction catalyst 22 It can be reliably prevented from being released outside without being

  The configuration described above is an example, and a bypass path having the heat exchanger 24 and the adsorber 26, a basic path to the second reduction catalyst 22 without passing through the heat exchanger 24 and the adsorber 26, and If the switching valve 20 for switching between the bypass path and the basic path is switched according to the purification ability of the first redox catalyst 18 and the second oxidation reduction catalyst 22, the other configuration is appropriately changed. May be Therefore, in the above-mentioned example, although the purification capacity of the first redox catalyst 18 is determined based on the first catalyst temperature T1, the purification capacity may be determined using, for example, a concentration sensor or the like. Further, in the above description, completion of desorption of ammonia by the adsorber 26 is determined based on the adsorber temperature T3 (see step S16), but not at the adsorber temperature T3 but at the first air-fuel ratio λ1 and the first air-fuel ratio λ1. The desorption completion may be determined based on the difference between the two air-fuel ratios λ2.

  Also, so far, the activation temperatures Ta1 and Ta2 and the desorption completion temperature Tde have been described as constant values, but these values are also regarded as fluctuation values that fluctuate depending on the deterioration of the catalyst and the adsorption substance. Good. For example, it is known that the redox catalyst has a high activation temperature as it deteriorates. Therefore, the activation temperatures Ta1 and Ta2 may be increased according to the deterioration of the redox catalyst.

  Also, although the engine 12 is an ammonia engine in the above description, the engine 12 may be another type of engine, for example, an engine that burns fossil fuel. In this case, unburned fuel and hydrocarbons contained in the exhaust gas correspond to harmful substances. Therefore, in this case, if the first oxidation reduction catalyst 18 and the second oxidation reduction catalyst 22 are for purifying unburned fuel and hydrocarbons, and the adsorber 26 adsorbs the unburned fuel and hydrocarbons. Good.

DESCRIPTION OF SYMBOLS 10 engine system, 12 engine, 14 exhaust purification apparatus, 16 controller, 18 1st oxidation reduction catalyst, 20 switching valve, 22 2nd oxidation reduction catalyst, 24 heat exchanger, 26 adsorber, 28 fuel injection device, 30 1st temperature Sensor, 32 second temperature sensor, 34 third temperature sensor, 36 first air-fuel ratio sensor, 38 second air-fuel ratio sensor.

Claims (10)

With the engine,
An exhaust gas purification device for purifying exhaust gas output from the engine;
A control unit that controls driving of the engine and the exhaust purification device;
An engine system having
The exhaust gas purification device
A first redox catalyst that purifies harmful substances contained in the exhaust;
A switch is provided downstream of the first redox catalyst, and switches the path of the exhaust gas output from the first redox catalyst to either the basic path or the bypass path whose downstream end reaches the basic path With the valve,
A second oxidation reduction catalyst provided on the basic route and purifying the harmful substance contained in the exhaust;
An adsorber provided on the bypass path to adsorb the harmful substance contained in the exhaust gas and release the adsorbed harmful substance as the temperature rises.
It is provided between the switching valve and the adsorber in the bypass path,
A heat exchanger for exchanging heat between the exhaust gas input to the adsorber and the exhaust gas output from the adsorber, which removes heat from the exhaust gas input to the adsorber, and from the adsorber A heat exchanger for warming the exhaust gas to be output and sending it to the second oxidation reduction catalyst;
A first capability detector for detecting the purification capability of the first redox catalyst;
A second ability detector for detecting the purification ability of the second redox catalyst;
And the control unit switches the switching valve in accordance with the purification ability detected by the first ability detector and the second ability detector.
An engine system characterized by The engine system according to claim 1,
The first capability detector is a first temperature sensor that detects the temperature of the first redox catalyst,
The second capability detector is a second temperature sensor that detects the temperature of the second reduction catalyst.
An engine system characterized by The engine system according to claim 1 or 2,
The control unit is configured such that the exhaust gas passes through the bypass path when the purification capacity of the first redox catalyst is less than a prescribed activity threshold, and the purification capacity of the first redox catalyst is greater than or equal to the activity threshold And, if the purification capacity of the second oxidation reduction catalyst is less than the activation threshold, the exhaust gas passes through the basic path without passing through the bypass, and the purification capacity of the oxidation reduction catalyst is greater than the activation threshold An engine system according to claim 1, wherein the switching valve is switched such that the exhaust gas passes through the bypass path. The engine system according to claim 3, further comprising:
A desorption detector for detecting completion of desorption of the harmful substance in the adsorber;
The control unit controls the exhaust gas without the exhaust gas passing through the bypass when the desorption detector detects completion of desorption after the purification capacity of the second oxidation reduction catalyst becomes equal to or higher than the active threshold. An engine system characterized by switching the switching valve so as to pass through a basic path. The engine system according to claim 4,
The engine system, wherein the desorption detector is a third temperature sensor that detects the temperature of the adsorber. The engine system according to claim 4,
The desorption detector removes the harmful substance based on the absolute value of the difference between the air-fuel ratio of the exhaust flowing into the first oxidation reduction catalyst and the air-fuel ratio of the exhaust flowing into the second oxidation reduction catalyst. An engine system characterized by detecting release completion. The engine system according to any one of claims 3 to 6, wherein
The control system continues driving of the engine until completion of desorption of the harmful substance in the adsorber is detected. The engine system according to any one of claims 1 to 7, further comprising:
A first air-fuel ratio sensor that detects, as a first air-fuel ratio, an air-fuel ratio of exhaust flowing into the first oxidation-reduction catalyst;
A second air-fuel ratio sensor that detects an air-fuel ratio of the exhaust flowing into the second oxidation reduction catalyst as a second air-fuel ratio;
Equipped with
The control unit determines an air-fuel ratio of the mixed gas to be supplied to the engine based on the second air-fuel ratio during a period in which desorption of the harmful substance occurs in the adsorber, and during another period Determines the air-fuel ratio based on the first air-fuel ratio,
An engine system characterized by The engine system according to claim 8, wherein
An engine system, wherein the control unit determines whether desorption of the harmful substance has occurred based on a difference between the first air fuel ratio and the second air fuel ratio. The engine system according to any one of claims 1 to 9, wherein
The engine is an ammonia engine,
The harmful substances include ammonia,
An engine system characterized by

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