JP2010185369A - Fuel supply device of engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve purification rate of nitrogen oxide in a selective catalytic reduction catalyst while avoiding complication of a system composition and suppressing rise in cost. <P>SOLUTION: In an exhaust emission control device, whether the present NO/NOx ratio is larger than 0.5 or not is determined (S2). If the NO/NOx ratio is larger than 0.5, a post injection amount is set based on engine rotation frequency NE and the NO/NOx ratio (S4) to execute post injection. The execution of the post injection raises temperature of exhaust gas exhausted from an engine and promotes oxidation reaction of an oxidation catalyst, and the NO/NOx ratio of the exhaust gas supplied to the SCR (selective catalytic reduction) catalyst is controlled to be 0.5. The NOx purification rate of the SCR catalyst can be improved thereby without complicating the system composition, which can suppress the rise in cost. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an engine exhaust gas purification apparatus including a selective reduction catalyst that selectively reduces and purifies nitrogen oxides in exhaust gas discharged from an engine.

  Conventionally, exhaust gases discharged from internal combustion engines such as diesel engines include pollutants such as HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide), and PM (particulate matter). Is included. Among these pollutants, NOx is difficult to purify with oxidation catalysts and three-way catalysts put to practical use in gasoline engine cars. Selective Catalytic Reduction (SCR) is a promising catalyst that can purify NOx. ) Catalyst development is underway.

  NOx discharged from the engine is mainly NO (nitrogen monoxide) and NO2 (nitrogen dioxide), and most is occupied by NO. The SCR catalyst is a catalyst that purifies NOx (NO and NO2) in the presence of a reducing agent such as ammonia, and decomposes NO and NO2 in the exhaust gas into water and nitrogen under the action of the reducing agent.

  As the reducing agent of the SCR catalyst, ammonia is often used, and urea water is added from the urea water tank to the exhaust system upstream of the SCR catalyst, and is hydrolyzed by the heat of the exhaust gas to generate ammonia. This ammonia acts as a reducing agent and reacts with NOx in the exhaust gas, thereby purifying NOx in the exhaust gas.

  Regarding the NOx purification reaction of the SCR catalyst, the NOx purification reaction is best when the ratio of NO to NO2 in the NOx in the exhaust gas is 1: 1 (NO / NOx = 0.5, where N0x = NO + NO2). It has been known. However, in actual vehicles, the NO / NOx ratio in the exhaust gas often deviates from 0.5 depending on the running state, and the maximum purification rate cannot always be obtained.

  Therefore, in Patent Document 1 (Japanese Patent Laid-Open No. 2005-23921), a bypass passage having a switching valve is provided on the upstream side of the oxidation catalyst, and the switching valve is controlled so that the NO / NOx ratio is 0.5, A technique for controlling the flow rate of exhaust gas flowing into an oxidation catalyst is disclosed.

Japanese Patent Laid-Open No. 2005-23921

  However, in the technique disclosed in Patent Document 1, not only a bypass passage needs to be provided separately, but also a drive mechanism for controlling the switching valve is required. For this reason, the system components increase, the control system becomes complicated, and the cost increases.

  The present invention has been made in view of the above circumstances, and is capable of improving the purification rate of nitrogen oxides in a selective catalytic reduction catalyst while avoiding a complicated system configuration and suppressing an increase in cost. The object is to provide a device.

  In order to achieve the above object, the present invention provides an exhaust gas purification apparatus for an engine comprising a selective reduction catalyst that selectively reduces and purifies nitrogen oxides in exhaust gas discharged from an engine. A calculation unit that calculates a composition ratio of the nitrogen oxide flowing in, a determination unit that determines a deviation state of the ratio from a predetermined threshold, and sets a fuel injection amount according to the deviation state, and the fuel injection amount And controlling the temperature of the exhaust gas so that the ratio becomes the threshold value.

  According to the present invention, the purification rate of nitrogen oxides in the selective catalytic reduction catalyst can be improved without complicating the system configuration, and the increase in cost can be suppressed.

1 is a configuration diagram of an engine system according to a first embodiment of the present invention. Same as above, block diagram related to exhaust gas purification system Same as above, characteristic diagram showing the relationship between post injection amount and engine speed Same as above, characteristic diagram showing the relationship between post-injection amount and NO / NOx ratio Same as above, flowchart of post injection amount setting routine A configuration diagram of an engine system according to a second embodiment of the present invention. Same as above, flowchart of exhaust pipe fuel injection amount setting routine

Embodiments of the present invention will be described below with reference to the drawings.
In the engine system shown in FIG. 1, reference numeral 1 denotes an engine, and in this embodiment, a diesel engine using a common rail fuel injection system. An intake port 2 and an exhaust port 3 are opened at the upper part of the combustion chamber of the engine 1, and an injector for injecting a common rail fuel for stocking high-pressure fuel pumped from a high-pressure pump (not shown) into the combustion chamber of each cylinder. 4 is faced. Reference numeral 5 denotes an intake valve, and reference numeral 6 denotes an exhaust valve.

  An intake passage 7 communicates with the upstream side of the intake port 2 and an intake chamber 8 is formed in the middle thereof. A throttle valve 9 is interposed upstream of the intake chamber 8, and an air cleaner 10 is attached to the air intake port of the intake passage 7. Further, an exhaust passage 11 communicates with the exhaust port 3 on the downstream side, and an exhaust gas aftertreatment system for purifying exhaust gas discharged from the engine is provided in the exhaust passage 11.

  Although not shown in FIG. 1, a turbocharger compressor is interposed on the upstream side of the throttle valve 9 in the intake passage 7. The turbocharger turbine is interposed upstream of the exhaust gas aftertreatment system in the exhaust passage 11.

  The exhaust gas aftertreatment system provided in the exhaust passage 11 includes, in order from the upstream side of the exhaust passage 11, a diesel oxidation catalyst (DOC) 12, a diesel particulate filter (Diesel Particulate Filter; DPF) 13, and selective reduction. A type (Selective Catalytic Reduction; SCR) catalyst 14 is provided.

  The DOC 12 mainly oxidizes HC (hydrocarbon) in the exhaust gas by a catalytic reaction, and also oxidizes NO in the exhaust gas to generate NO2. The DOC 12 is formed by supporting a noble metal such as platinum (Pt) and palladium (Pd) and a metal oxide such as alumina on the surface of a ceramic carrier made of, for example, a cordierite honeycomb structure.

  When the inlet temperature of the DOC 12 is highest, the ratio of the precious metal supported on the DOC 12 is 1: 1 (NOx = NO + NO2, NO / NOx = 0.5), that is, SCR. The catalyst 14 is set so as to have an oxidizing ability that gives the highest NOx purification rate. In particular, in this embodiment, the amount of platinum supported on the DOC 12 is such that the NO / NOx ratio is 0.5 when the maximum inlet temperature of the DOC 12 (for example, 300 ° C.) assumed under normal operating conditions. As such, the mass is set to 7 g.

  The DPF 13 is arranged on the downstream side of the DOC 12, and PM (Particulate) such as Soot (soot, carbon soot), SOF (Soluble Organic Fraction), SO4 (sulfate), etc. in the exhaust gas discharged from the DOC 12 is used. Matter (particulate matter) is collected. The DPF 13 is formed, for example, by forming heat-resistant ceramics such as cordierite into a honeycomb structure and sealing a large number of cells serving as gas flow paths so that the inlet side or the outlet side are staggered. When exhaust gas flows into the DPF 13, the exhaust gas flows downstream while passing through the porous partition walls of the DPF 13, and during that time, PM in the exhaust gas is collected by the DPF 13 and gradually accumulates.

  The SCR catalyst 14 reduces and purifies NOx in the exhaust gas using urea supplied in the exhaust gas as a reducing agent. The SCR catalyst 14 includes, for example, a metal-added zeolite, adds NH3 (ammonia) generated by decomposition of urea in urea water supplied into exhaust gas to NOx, and NOx is harmless to the human body. And decomposes into water.

  For this reason, a urea water injector 17 for injecting urea water supplied from the urea water tank 15 via the urea water pump 16 into the exhaust passage 11 is interposed between the DPF 13 and the SCR catalyst 14. Further, on the downstream side of the urea water injector 17, a mixer 18 for generating a swirling flow in the exhaust gas and atomizing the urea water injected from the urea water injector 17 is disposed. The urea water mixed with the exhaust gas by the mixer 18 is supplied to the SCR catalyst 14.

  On the other hand, reference numerals 50 and 100 denote electronic control units that control the engine system. The electronic control unit 50 is a urea water supply control unit (hereinafter referred to as “DCU”) that controls urea water supplied into the exhaust gas. Reference numeral 100 denotes an engine control unit (hereinafter referred to as “ECU”) that controls the operation of the engine 1. The DCU 50 and the ECU 100 are mainly configured by a microcomputer including a CPU, ROM, RAM, I / O interface, and the like, and include peripheral circuits such as an A / D converter, a timer, a counter, and various logic circuits. ing.

  Sensors such as a level sensor 20 for detecting the remaining amount of urea water in the urea water tank 15 and a temperature sensor 21 for detecting the temperature of urea water in the urea water tank 15 are connected to the input side of the DCU 50. Connected to the output side of the DCU 50 are actuators such as a urea water pump 16 for conveying urea water in the urea water tank 15 to the urea water injector 17 and a urea water injector 17 for injecting urea water into the exhaust passage 11. Has been.

  On the other hand, on the input side of the ECU 100, an intake air amount sensor 22 for detecting the intake air amount, a temperature sensor 23 for detecting the inlet temperature of the DPF 13 (temperature of exhaust gas supplied to the DPF 13), and the outlet temperature of the DPF 13 (directly connected to the DPF 13). A temperature sensor 24 that detects the temperature of the downstream exhaust gas), a differential pressure sensor 25 that detects the differential pressure between the inlet pressure and the outlet pressure of the DPF 13, and NO that detects the NO concentration of the exhaust gas flowing into the SCR catalyst 14. Sensors such as a sensor 26, a NOx sensor 27 for detecting the NOx concentration, a crank angle sensor 28 for detecting the crank position, and an accelerator opening sensor 29 for detecting the accelerator opening are connected. Further, on the output side of the ECU 50, an injector 4 that injects fuel into the combustion chamber of the engine 1 and an intake actuator 30 that controls opening and closing of the throttle valve 9 to adjust the throttle opening and control the intake amount (fresh air amount). Etc. are connected.

  The DCU 50 and the ECU 100 are connected via an in-vehicle network 200 based on a communication protocol such as CAN (Controller Area Network). The in-vehicle network 200 is connected to a plurality of other electronic control units (not shown) provided in the vehicle, such as a transmission control unit for controlling a transmission, a brake control unit for controlling a brake, and the like. Send and receive data to share various information.

  The DCU 50 calculates the drive amount of the urea water pump 16, the energization time of the urea water injector 17, and the like based on the engine operating state transmitted from the ECU 100 via the in-vehicle network 200, the output of each sensor, and the like. In addition, by injecting and supplying an appropriate amount of urea water into the exhaust passage 11 at an appropriate time, NOx reduction in the SCR catalyst 14 is effective even in an atmosphere having a high oxygen concentration such as exhaust gas of a diesel engine. To promote.

  On the other hand, the ECU 100 operates the engine 1 by calculating the fuel injection amount, the injection timing, and the like based on signals from various sensors for detecting the engine operating state and various control information input via the in-vehicle network 200. Control. In this engine control, during normal driving, the fuel injection amount and the injection timing are determined by referring to a map or the like according to the engine speed based on the signal from the crank angle sensor 28 and the load based on the signal from the accelerator opening sensor 29. For example, high-pressure fuel is injected from the injector 4 in a multi-stage injection pattern around the top dead center of the piston, which is a combination of pre-injection and main injection, for example, to stabilize combustion and reduce exhaust emissions.

  In addition, the ECU 100 executes regeneration control for regenerating the DPF 13 at a predetermined timing in parallel with normal engine control. The regeneration control of the DPF 13 intentionally exhausts the gas containing incomplete combustion components from the engine and burns (oxidizes) the DOC 12 to incinerate the PM trapped in the DPF 13 by the generated heat to filter the filter. This is the control to regenerate. In this DPF regeneration control, when the PM accumulation amount of the DPF 13 reaches a preset threshold value, a transition is made to a forced regeneration operation mode different from that during normal operation, and in multistage injection such as retarding the main injection before and after top dead center. By performing delayed injection, post injection near the bottom dead center of the piston, intake throttling via the intake actuator 30, etc., the temperature of the exhaust gas (regenerated gas) supplied to the DPF 13 is raised, and collected and deposited on the DPF 13 Incinerated PM is removed by incineration.

  Further, the ECU 100 monitors the NO / N0x ratio in the exhaust gas, and when this NO / N0x ratio is larger than the value (NO / N0x = 0.5) at which the NOx purification rate of the SCR catalyst 14 becomes maximum, post-injection. And the exhaust gas temperature is raised to promote the NO → NO 2 oxidation reaction in the DOC 12 so that the NO / NOx ratio becomes 0.5. This post injection control for improving the NOx purification rate is appropriately executed during normal operation, unlike the DPF regeneration control executed every predetermined cycle, and in parallel with the urea water supply control by the DCU 50. Executed.

  For this reason, as shown in FIG. 2, the ECU 100 has a NO / NOx ratio calculation unit 101, a NO / NOx ratio determination unit 102, and a NOx purification fuel injection control unit as control functions for improving the NOx purification rate of the SCR catalyst 14. 103.

  In this embodiment, the NO / NOx ratio calculation unit 101 uses the NO sensor 26 that detects the NO concentration of the exhaust gas flowing into the SCR catalyst 14 and the NOx sensor 27 that detects the NOx concentration, and outputs both of them. The NO / NOx ratio is calculated based on the value.

  In this case, the NO / NOx ratio may be obtained by estimating the NOx generation amount from the engine operating state without using the NO sensor 26 and the NOx sensor 27. For example, the NOx generation amount may be mapped according to the operating conditions, the NOx generation amount may be estimated using this map, and the NO / NOx ratio may be calculated. It is also possible to calculate the NOx generation amount by calculating the combustion temperature and the air-fuel mixture concentration from the oxygen concentration of the intake air and the combustion pressure in the cylinder, and calculate the NO / NOx ratio.

  The NO / NOx ratio determination unit 102 sets the NO / NOx ratio that maximizes the NOx purification rate of the SCR catalyst 14 as a threshold (NO / NOx = 0.5), and the NO of the exhaust gas supplied from the DOC 12 to the SCR catalyst 14. It is determined whether the / NOx ratio exceeds 0.5. And NO / NOx> O. When 5, the NOx purification fuel injection control unit 103 is instructed to perform post injection.

  The NOx purification fuel injection control unit 103 performs post-injection according to an instruction from the NO / NOx ratio determination unit 102 according to a deviation state from the threshold value of the NO / NOx ratio of the exhaust gas supplied from the DOC 12 to the SCR catalyst 14. Control. As described above, the DOC 12 has a precious metal loading amount so that the oxidation ability from NO to NO2 becomes maximum when the inlet temperature is maximum. Therefore, the NO / NOx ratio of the exhaust gas supplied to the SCR catalyst 14 becomes 0.5 by executing the post injection to raise the temperature of the exhaust gas supplied to the DOC 12 and promoting the oxidation reaction of the DOC 12. Can be controlled.

  In the present embodiment, the post-injection fuel injection amount is set according to the state of deviation of the current NO / NOx ratio from 0.5. The injection timing of the post injection is set to a predetermined constant injection timing. Specifically, based on the engine speed NE and the NO / NOx ratio, an optimal post-injection amount is determined and mapped in advance through experiments or simulations, and the post-injection amount PQ is set with reference to this map. To do.

  Then, the post injection amount PQ set from the map is injected into the cylinder through the injector 4 at a preset injection timing. That is, the post-injection is executed with the fuel amount based on the engine speed NE and the NO / NOx ratio, whereby the oxidation reaction of DOC 12 from NO to NO 2 due to the rise in the exhaust temperature is promoted and supplied to the SCR catalyst 14. The NO / NOx ratio of the exhaust gas is controlled to be 0.5.

  The characteristics of the post injection amount set by the map are set to characteristics as shown in FIGS. 3 and 4, for example. In this map characteristic, as shown in FIG. 3, when the engine speed NE is high when the engine speed NE is high, the post-injection amount PQ is slightly increased and the engine speed NE is The post-injection amount PQ is set to a constant value in the middle rotation range, and the post-injection amount PQ is set to be slightly reduced when the engine rotation speed NE is high in the high rotation range. Further, as a characteristic with respect to the NO / NOx ratio, as shown in FIG. 4, the post-injection amount PQ is increased as the NO / NOx ratio increases with the post-injection amount PQ = 0 when NO / NOx = 0.5. It is set to increase.

  When a deviation from NO / NOx = 0.5 occurs, the post injection amount PQ may be increased by a fixed amount regardless of the NO / NOx ratio.

  In addition to the fuel injection amount of post injection, the injection timing of post injection may be varied according to the deviation state from 0.5 of the NO / NOx ratio. Further, the post injection may be divided according to the deviation state of the NO / NOx ratio from 0.5, and the temperature rise effect of the exhaust gas can be further enhanced by this divided injection.

  Next, the program processing of the ECU 100 related to the improvement of the NOx purification rate of the SCR catalyst 14 will be described using the flowchart of the post injection amount setting routine shown in FIG.

  In the post injection amount setting routine of FIG. 5, first, in the first step S1, the current NO / NOx ratio calculated based on the outputs of the NO sensor 26 and the NOx sensor 27 is read. Next, it progresses to step S2 and it is determined whether the NO / NOx ratio exceeds 0.5.

  As a result, if NO / NOx> 0.5 in step S2, that is, if N0 in the exhaust gas supplied from the DOC 12 to the SCR catalyst 14 is greater than NO2, the temperature of the exhaust gas is raised by post injection. In order to promote the oxidation reaction of DOC12 from NO to NO2, the process proceeds from step S2 to step S3.

  In step S3, the engine speed NE is read. In step S4, a map (for example, the characteristic maps shown in FIGS. 3 and 4) is referred to based on the engine speed NE and the NO / NOx ratio, and the post injection amount PQ is determined. Set. In step S5, the post injection amount PQ is output to execute post injection, and the routine is exited. By executing this post-injection, the temperature of the exhaust gas discharged from the engine is raised, the NO → NO 2 oxidation reaction in the DOC 12 is promoted, and the NO / NOx ratio of the exhaust gas supplied to the SCR catalyst 14 is reduced to 0. It is controlled to be 5.

  On the other hand, if NO / NOx> 0.5 is not satisfied in step S2, the NO / NOx ratio in the exhaust gas is 0.5 due to execution of post-injection or the like, and the routine is exited from step S2. . As described above, in the present embodiment, when the inlet temperature of the DOC 12 becomes the highest in the normal operation state, the NO → NO2 oxidation ability of the DOC 12 is set to be the highest. Therefore, in a normal operation state, the NO / NOx ratio of the exhaust gas does not become less than 0.5.

  As described above, in the present embodiment, the fuel injection into the cylinder is controlled based on the NO / NOx ratio of the exhaust gas without changing the existing exhaust purification system using the DOC 12 and the SCR catalyst 14. Without complicating the configuration, the NO / NOx ratio of the exhaust gas supplied to the SCR catalyst 14 can be controlled to around 0.5 at which the purification rate becomes maximum, and an increase in cost can be suppressed.

  Moreover, since the NOx purification rate of the SCR catalyst 14 can be maintained near the maximum without being greatly influenced by the running state of the vehicle, the amount of urea water supplied into the exhaust gas can be reduced, and more Cost reduction effect can be enhanced.

  Further, since the exhaust temperature is raised by post injection and the oxidation reaction (NO → NO2) of the DOC 12 is promoted, torque shock does not occur as compared with other temperature raising processes of the exhaust temperature by the intake throttle, etc. There is no loss of drivability.

  Next, a second embodiment of the present invention will be described. In the second mode, fuel is injected into the exhaust system upstream of the DOC 12 in place of the post-injection into the cylinder in order to improve the NOx purification rate of the SCR catalyst 14 with respect to the first mode described above. .

  For this reason, the engine system of the second embodiment includes an exhaust pipe injector 40 for injecting fuel into the exhaust passage 11 upstream of the DOC 12 in addition to the injector 4 for injecting fuel into the cylinder, as shown in FIG. Yes. Other configurations are the same as those of the first embodiment.

  In the second embodiment, the function of the NOx purification fuel injection control unit 103 in the first embodiment is slightly changed, and the fuel injection amount to be injected from the exhaust pipe injector 40 is set based on the engine speed NE and the NO / NOx ratio. To do. Accordingly, a part of the program processing shown in the flowchart of FIG. 3 is changed to be the processing shown in the flowchart of FIG.

  That is, in steps S11 and S12 similar to the first embodiment, when the NO / NOx ratio exceeds 0.5, the engine speed NE is read in step S13, and the exhaust pipe fuel injection amount is set in step S14. The exhaust pipe fuel injection amount is almost the same as the post injection amount, and is set by referring to a map having the same characteristics as the post injection amount map based on the engine speed NE and the NO / NOx ratio.

  However, in the fuel injection into the exhaust pipe, there is almost no dilution of the fuel into the oil, and the heat loss is small compared with the case where the combustion gas is discharged from the cylinder through the exhaust port 3, It is possible to reduce the amount of fuel slightly compared to post injection.

  The injection timing of the exhaust pipe fuel injection is not particularly limited as compared with the injection timing of the post injection of the first embodiment, but the injection timing can be set in accordance with the pulsation of the crank exhaust pipe pressure. Further, as in the first embodiment, the injection timing of the exhaust pipe fuel injection may be varied or divided according to the deviation state of the NO / NOx ratio from 0.5.

  Then, after the exhaust pipe fuel injection amount is set, the routine proceeds from step 14 to step S15, where the exhaust pipe fuel injection amount is output, fuel is injected from the exhaust pipe injector 40 to the upstream side of the DOC 12, and this routine is exited. As a result, the fuel burns on the upstream side of the DOC 12, the inlet temperature of the DOC 12 rises, the NO → NO 2 oxidation reaction is promoted, and the NO / NOx ratio of the exhaust gas supplied to the SCR catalyst 14 becomes 0.5. It is controlled to become.

  Also in the second embodiment, as in the first embodiment, the NO / NOx ratio of the exhaust gas supplied to the SCR catalyst 14 can be controlled around 0.5 at which the purification rate is maximized without complicating the system configuration. And cost increase can be suppressed.

  In the engine exhaust gas purification apparatus of the present invention, it is desirable that the NO / NOx ratio be maintained at 0.5, but an advantageous effect can be obtained even if the NO / NOx ratio is changed within a predetermined range. .

1 Engine 4 Injector 12 DOC (Diesel oxidation catalyst)
14 SCR catalyst (selective reduction catalyst)
40 Exhaust Pipe Injector 100 Engine Control Unit 101 NO / NOx Ratio Calculation Unit 102 NO / NOx Ratio Determination Unit 103 Purification Fuel Injection Control Unit

Claims (5)

In an engine exhaust purification device equipped with a selective reduction catalyst that selectively reduces and purifies nitrogen oxides in exhaust gas discharged from an engine,
A calculation unit for calculating a composition ratio of the nitrogen oxide flowing into the selective catalytic reduction catalyst;
A determination unit for determining a deviation state of the ratio from a predetermined threshold;
A control unit configured to set a fuel injection amount according to the divergence state, and to control the temperature so that the ratio becomes the threshold value by raising the temperature of the exhaust gas by the fuel injection amount. apparatus.   2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the ratio is a constituent ratio of nitrogen monoxide and nitrogen dioxide in the exhaust gas, and the threshold value is 1: 1.   The control unit sets a fuel injection amount of post-injection injected into the cylinder based on the ratio and the engine speed, raises the exhaust gas by the fuel injection amount of the post-injection, and the ratio is the threshold value. The exhaust gas purifying device for an engine according to claim 1 or 2, wherein control is performed so that   The control unit sets a fuel injection amount to be injected into the exhaust system based on the ratio and the engine speed, and raises the exhaust gas by the fuel injection amount to the exhaust system so that the ratio becomes the threshold value. The engine exhaust gas purifying device according to claim 1 or 2, characterized by being controlled as described above. On the upstream side of the selective catalytic reduction catalyst, an oxidation catalyst carrying a noble metal is provided,
The amount of the noble metal supported is set so that the ratio of nitric oxide to nitric oxide in the exhaust gas in the operating state in which the inlet temperature of the oxidation catalyst is maximum is 1: 1. The engine exhaust gas purification apparatus according to any one of 1 to 4.

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