JP2007051594A - Exhaust emission control system and method for controlling same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control system having a selective contact reduction type catalyst device and an oxidation catalyst device arranged in an exhaust gas passage of an internal combustion engine in an order from an upstream side capable of preventing thermal deterioration of a selective contact reduction type catalyst while inhibiting discharge of ammonia to atmosphere, and a method for controlling the same. <P>SOLUTION: Supply quantity Qt of ammonia system water solution is calculated based on first supply quantity Q1 which can be consumed by the selective contact reduction type catalyst device 14 calculated from NOx emission quantity Won discharged from the internal combustion engine 11 and NOx conversion ratio ηnox of the selective contact reduction type catalyst device 14 and second supply quantity Q2 which can be consumed by the oxidation catalyst device 15 calculated from exhaust gas quantity Vg discharged from the internal combustion engine 11 and ammonia conversion efficiency ηnh3 of the oxidation catalyst device 15 when catalyst temperature of the selective contact reduction type catalyst device 14 gets high. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system control method and an exhaust gas purification system including a selective catalytic reduction catalyst device for purifying NOx in exhaust gas of an internal combustion engine such as a diesel engine.

  Many NOx purification catalysts that reduce NOx discharged from diesel internal combustion engines have been developed, and among them, exhaust gas purification equipped with a selective reduction catalyst device carrying a selective catalytic reduction catalyst called an SCR catalyst There is a system.

  In this exhaust gas purification system, as shown in FIG. 1, a selective catalytic reduction catalyst device (SCR catalyst device) 14 is disposed in an exhaust passage (exhaust pipe) 12 of a diesel internal combustion engine (engine) 11, There is an exhaust gas purification system 1 in which a diesel particulate filter device (DPF device) 13 is disposed upstream of the selective catalytic reduction catalyst device 14 and an oxidation catalyst device 15 is disposed downstream.

  In this exhaust gas purification system 1, PM (particulate matter) in the exhaust gas is collected by the upstream DPF device 13, and a reducing agent such as ammonia is used by the selective catalytic reduction catalyst device 14. NOx is reduced, and the oxidation catalyst device 15 purifies exhaust gas by oxidizing and removing unused reducing agent flowing out from the selective catalytic reduction catalyst device 14.

  In the selective catalytic reduction catalyst device 14 employing the urea selective catalytic reduction catalyst (urea SCR catalyst), urea water is used as a reducing agent. This urea water S is used as the selective catalytic reduction catalyst device 14. Is supplied into the exhaust gas from a urea water injection valve 21 as an aqueous solution supply device attached to the upstream exhaust passage 12. This urea water generates ammonia by hydrolysis. With this ammonia, NOx in the exhaust gas is reduced by the catalytic action of the selective catalytic reduction catalyst.

  The urea water S is adjusted in its supply amount and injected into the exhaust passage 12 from a urea water tank 22 by a urea water injection control device (control unit) 23 which is an aqueous solution supply amount adjusting means. The urea water injection control device 23 includes a supply amount adjusting device (ECU) 23A that calculates and adjusts the supply amount of the urea water S, and an injection valve control device that controls the urea water injection valve 21 to perform urea water injection ( DCU) 23B.

  The urea water injection control device 23 includes engine operation status data from a control device (engine control unit: ECU) 30 that controls the operation of the engine 11 and the exhaust gas temperature at the inlet / outlet of the selective catalytic reduction catalyst device 14. Data is input, and optimal urea water injection is performed based on these data.

On the other hand, regarding the DPF device 13, the PM soot component in the exhaust gas is easily combusted according to NO _2. Therefore, a selective catalytic reduction catalyst device is disposed upstream of the DPF device, and the NOx is upstream. If it purifies | cleans, the combustion efficiency of PM in a DPF device will fall. Since the frequency of performing the forced regeneration control for forcibly burning the PM increases due to the decrease in the PM combustion efficiency, the fuel consumption is deteriorated. Therefore, the DPF device 13 is disposed on the upstream side of the selective catalytic reduction catalyst device 14.

  In the forced regeneration of the DPF device 13, the exhaust temperature is generally increased by in-cylinder injection control of the engine 11 such as post injection. In order to suppress the deterioration of fuel consumption due to the post injection amount, it is required that the exhaust gas temperature at the inlet of the DPF device 13 is high. From this aspect as well, the DPF device 13 is disposed on the upstream side where the exhaust gas is less cooled. It is preferable to arrange.

  Further, the oxidation catalyst device 15 oxidizes ammonia flowing out from the selective catalytic reduction catalyst device 14 when the supply amount of the urea water S is larger than the amount consumed by the selective catalytic reduction catalyst device 14. Thus, it plays a role in reducing the amount of ammonia released into the atmosphere.

As an example of such an exhaust gas purification system, in order to improve the NOx purification rate and also prevent ammonia slip, a NOx catalyst (in the downstream of the particulate matter reduction device (DPF device) in the exhaust system) ( An exhaust gas purification device for a diesel engine that arranges an SCR catalyst, calculates the ratio of NO / NO ₂ based on the outlet temperature of the particulate matter reducing device, and controls the amount of urea supplied to the NOx catalyst based on the value Has been proposed (see, for example, Patent Document 1).

However, the exhaust gas purification system having this configuration has a problem of thermal degradation of the SCR catalyst accompanying the regeneration control of the PM combustion removal of the upstream DPF device.
That is, when the forced regeneration control is performed to burn and remove the PM collected and accumulated in the DPF device, the PM burns in the DPF device, so that high-temperature exhaust gas flows out downstream. Therefore, high-temperature exhaust gas flows into the SCR catalyst device on the downstream side, the SCR catalyst becomes high temperature, and thermal degradation proceeds. This thermal deterioration proceeds as the travel distance increases, and the NOx purification performance of the SCR catalyst device decreases.

  When this thermal deterioration progresses, the NOx emission amount on the downstream side of the SCR catalyst device exceeds the purification target level, and there is a possibility that NOx is discharged into the atmosphere. At the same time, the amount of ammonia that has not been used for NOx reduction in the SCR catalyst device increases, and the ammonia may not be oxidized in the downstream oxidation catalyst device, and ammonia may be released to the atmosphere. Arise.

  Even in cases other than forced regeneration of the upstream DPF device, when the intake air amount decreases at high altitudes, the intake air temperature increases, the cooling performance of the intercooler decreases, the injection timing delays, etc. When the fuel injection system operates abnormally, when the air amount decreases due to the abnormal operation of the actuator of the VGS (variable displacement type) turbocharger, the temperature of the selective catalytic reduction catalyst device increases due to the cooling capacity of the EGR cooler or the like. .

As a countermeasure against thermal degradation of this selective catalytic reduction catalyst (NOx catalyst), a DPF device is not provided on the upstream side, but from the viewpoint of protecting the NOx catalyst, the catalyst temperature of the NOx catalyst is monitored and based on the catalyst temperature. The amount of urea water added is set, and when the catalyst temperature is equal to or higher than the predetermined temperature (overheating temperature), the urea water to be injected is allowed to be restricted from the saturated vapor pressure in the exhaust based on the tube wall temperature. The amount of urea water added is corrected within the range below the amount of water added, and the exhaust temperature is lowered by the latent heat of vaporization of the water in the urea water. Techniques for suppressing the rise and preventing thermal deterioration of the catalyst have been proposed (see, for example, Patent Document 2 and Patent Document 3).
JP-A-2002-250220 Japanese Patent Laid-Open No. 2003-293736 JP 2003-293740 A

  An object of the present invention is to release ammonia into the atmosphere in an exhaust gas purification system in which a selective catalytic reduction catalyst device (SCR catalyst device) and an oxidation catalyst device are arranged in order from the upstream side in an exhaust passage of an internal combustion engine. Of exhaust gas purification system and exhaust gas purification system capable of preventing thermal degradation of selective catalytic reduction catalyst while minimizing NOx purification performance while minimizing NO There is to do.

  In order to achieve the above object, a control method for an exhaust gas purification system of the present invention includes a selective catalytic reduction catalyst device and an oxidation catalyst device for purifying NOx in order from the upstream side in an exhaust passage of an internal combustion engine. An aqueous solution supply device for supplying an ammonia-based aqueous solution to the selective catalytic reduction catalyst device is arranged upstream of the selective catalytic reduction-type catalyst device, and an aqueous solution supply for adjusting the supply amount of the ammonia-based aqueous solution An amount adjusting means for reducing NOx by the selective catalytic reduction catalyst device when a catalyst temperature index value indicating the catalyst temperature of the selective catalytic reduction catalyst device is higher than a predetermined determination temperature; In addition to the ammonia-based aqueous solution for NOx reduction, the exhaust gas flowing into the selective catalytic reduction catalytic device is cooled to lower the catalyst temperature of the selective catalytic reduction catalytic device. In the control method of the exhaust gas purification system for supplying the cooling ammonia-based aqueous solution, the supply amount of the cooling ammonia-based aqueous solution corresponds to a first amount corresponding to the amount of ammonia that can be consumed by the selective catalytic reduction catalyst device. Calculation based on the ammonia aqueous solution supply amount and a second ammonia aqueous solution supply amount corresponding to the ammonia amount that can be consumed by the oxidation catalyst device, and the first ammonia aqueous solution supply amount from the internal combustion engine The second ammonia-based aqueous solution supply amount is calculated from the NOx emission amount discharged and the NOx purification rate of the selective catalytic reduction type catalytic device, and the second ammonia-based aqueous solution supply amount is calculated from the exhaust gas amount discharged from the internal combustion engine and the oxidation catalyst device. It is calculated from the ammonia conversion efficiency.

The ammonia-based aqueous solution here refers to an aqueous solution that generates ammonia, such as urea water, ammonia, and ammonia water.
Further, the catalyst temperature index value indicating the catalyst temperature of the selective catalytic reduction catalyst device means a measured value of the catalyst temperature of the selective catalytic reduction catalyst device or a physical quantity capable of estimating the catalyst temperature. Use the catalyst bed temperature of the reduction catalytic device, the temperature of the exhaust gas flowing into the selective catalytic reduction catalytic device (inlet exhaust gas temperature), the average value of the exhaust gas temperature before and after the selective catalytic reduction catalytic device, etc. be able to. Further, when the catalyst temperature of the selective catalytic reduction catalyst device is estimated by referring to the map data from the engine load and the engine rotational speed, the estimated catalyst temperature can be used as the catalyst temperature index value.

  With this configuration, the amount of ammonia flowing out downstream of the oxidation catalyst device is taken into account based on the amount that can be consumed by the selective catalytic reduction catalyst device and the amount that can be consumed by the oxidation catalyst device. The amount of ammonia aqueous solution to be supplied can be determined. Therefore, in order to prevent the thermal degradation of the selective catalytic reduction type, when the selective catalytic reduction type catalytic device becomes high temperature, even when injecting the ammonia-based aqueous solution more than the supply amount for normal NOx purification, The supply amount of the ammonia-based aqueous solution is adjusted in consideration of the amount of ammonia that can be oxidized by the oxidation catalyst device, so that selective catalytic reduction thermal degradation is achieved while keeping the amount of ammonia released to the atmosphere below the specified level. Can be prevented.

  In addition, if the ammonia-based aqueous solution is supplied into the exhaust gas flowing into the selective catalytic reduction catalytic device, the latent heat (evaporation heat) is removed by evaporation, so the temperature of the exhaust gas can be lowered, and the supply amount of the ammonia-based aqueous solution can be reduced. When the temperature increases, the temperature lowering effect increases, and the selective catalytic reduction catalyst device can be cooled by the exhaust gas whose temperature has decreased.

  In the control method of the exhaust gas purification system, when a diesel particulate filter device (DPF device) for purifying particulate matter in the exhaust gas is disposed upstream of the selective catalytic reduction catalyst device In the regeneration control of the DPF device, the PM accumulated in the DPF device burns and the temperature of the exhaust gas flowing into the selective catalytic reduction catalyst device becomes high. Especially effective.

  In the control method of the exhaust gas purification system, the second ammonia-based aqueous solution supply amount is set within a range in which the ammonia outflow amount flowing out downstream of the oxidation catalyst device is equal to or less than a predetermined limit value. Further, the predetermined limit value is set to 10 ppm. With this configuration, the smell of ammonia in the exhaust gas released into the atmosphere can be eliminated.

  The exhaust gas purification system of the present invention for achieving the above object includes a selective catalytic reduction catalyst device and an oxidation catalyst device for purifying NOx in order from the upstream side in an exhaust passage of an internal combustion engine. An aqueous solution supply device for supplying an aqueous ammonia solution to the selective catalytic reduction catalyst device is disposed upstream of the selective catalytic reduction catalyst device, and an aqueous solution supply amount for adjusting the supply amount of the ammonia aqueous solution. Adjusting means for reducing NOx by the selective catalytic reduction catalyst device when the catalyst temperature index value indicating the catalyst temperature of the selective catalytic reduction catalyst device is higher than a predetermined determination temperature. In addition to the ammonia-based aqueous solution for NOx reduction, the exhaust gas flowing into the selective catalytic reduction catalytic device is cooled to lower the catalyst temperature of the selective catalytic reduction catalytic device. In the exhaust gas purification system for supplying the cooling ammonia-based aqueous solution, the aqueous solution supply amount adjusting means has a supply amount of the ammonia-based aqueous solution corresponding to an ammonia amount that can be consumed by the selective catalytic reduction catalyst device. 1 based on an ammonia aqueous solution supply amount and a second ammonia aqueous solution supply amount corresponding to the amount of ammonia that can be consumed by the oxidation catalyst device, and the first ammonia aqueous solution supply amount The second ammonia-based aqueous solution supply amount is calculated from the NOx emission amount discharged from the engine and the NOx purification rate of the selective catalytic reduction catalyst device, and the exhaust gas amount discharged from the internal combustion engine and the oxidation catalyst are calculated. It is configured to calculate from the ammonia conversion efficiency of the apparatus.

  In the exhaust gas purification system, a diesel particulate filter device (DPF device) for purifying particulate matter in the exhaust gas is disposed upstream of the selective catalytic reduction catalyst device. Further, the second ammonia-based aqueous solution supply amount is set within a range in which the ammonia outflow amount flowing out downstream of the oxidation catalyst device is equal to or less than a predetermined limit value. Further, the predetermined limit value is set to 10 ppm.

  With these configurations, it is possible to provide an exhaust gas purification system that can implement the control method of the exhaust gas purification system, and it is possible to achieve the same operational effects as the control method of the exhaust gas purification system.

  In addition, as the above DPF device, a filter-only DPF device, a continuous regeneration type DPF device in which an oxidation catalyst is supported on the filter, a continuous regeneration type DPF device in which an oxidation catalyst is provided on the upstream side of the filter, and a catalyst in the filter In addition, any one or a combination of continuous regeneration type DPF devices in which an oxidation catalyst is provided on the upstream side of the filter can be employed.

  According to the exhaust gas purification system control method and exhaust gas purification system of the present invention, an exhaust gas in which a selective catalytic reduction catalyst device (SCR catalyst device) and an oxidation catalyst device are arranged in order from the upstream side in the exhaust passage of the internal combustion engine. In the gas purification system, it is possible to prevent thermal degradation of the selective catalytic reduction catalyst while practically suppressing release of ammonia into the atmosphere. Therefore, it is possible to minimize the decrease in the NOx purification performance of the selective catalytic reduction catalyst device.

Hereinafter, an exhaust gas purification system control method and an exhaust gas purification system according to an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 shows a configuration of an exhaust gas purification system 1 according to this embodiment. The exhaust gas purification system 1 includes a diesel particulate filter device (hereinafter referred to as a DPF device) 13, a selective catalytic reduction catalyst device (hereinafter referred to as an SCR catalyst device) from an upstream side in an exhaust passage 12 of a diesel internal combustion engine (engine) 11. 14), and an oxidation catalyst device 15 is provided.

  In the exhaust gas purification system 1, PM (particulate matter) in the exhaust gas is collected (trapped) by the upstream DPF device 13. This DPF device 13 is a monolith honeycomb wall flow type filter in which the inlet and outlet of a porous ceramic honeycomb channel are alternately plugged, a felt-like filter in which inorganic fibers such as alumina are randomly laminated, and the like. It is formed. In order to promote the combustion of PM, a catalyst such as platinum or cerium oxide may be supported on the filter portion.

  When a monolith honeycomb wall flow type filter is adopted for the DPF device 13, PM in exhaust gas is collected by a porous ceramic wall, and when a fiber type filter type is adopted. , PM is collected by the inorganic fiber of the filter.

Then, in order to estimate the amount of PM accumulated in the DPF device 13, a differential pressure sensor 13 a is provided in the conduction pipe connected before and after the DPF device 13.
The SCR catalyst device 14 has a honeycomb structure carrier (catalyst structure) formed of cordierite, aluminum oxide, titanium oxide or the like, titania-vanadium, zeolite, chromium oxide, manganese oxide, molybdenum oxide, titanium oxide. Further, it is formed by supporting tungsten oxide or the like.

  In this SCR catalyst device 14, an ammonia-based aqueous solution (urea water in this embodiment) S such as urea water, ammonia, and ammonia water is injected into the exhaust passage 12 in an oxygen-excess atmosphere, and is generated from the ammonia-based aqueous solution. The ammonia to be supplied is supplied to the SCR catalyst device 14, and the NOx in the exhaust gas G is selectively brought into contact with and reacted with ammonia, whereby the NOx is reduced to nitrogen and purified.

  A urea water injection valve 21 as an aqueous solution supply device is provided upstream of the SCR catalyst device 14 in the exhaust passage 12 downstream of the DPF device 13, and an inlet exhaust gas temperature sensor 31 is provided on the inlet side of the SCR catalyst device 14. An outlet exhaust gas temperature sensor 32 is provided on the outlet side.

  In this embodiment, highly safe urea water is used as the NOx reducing agent, but this urea water S is supplied from the urea water injection valve 21 into the exhaust gas. Urea in the urea water S is decomposed into ammonia by hydrolysis. With this ammonia, NOx in the exhaust gas is reduced to nitrogen by the catalytic action of the SCR catalyst. The urea water S is adjusted in its supply amount and injected into the exhaust passage 12 from a urea water tank 22 by a urea water injection control device (control unit) 23 which is an aqueous solution supply amount adjusting means.

  The oxidation catalyst device 15 is formed by carrying an oxidation catalyst such as platinum (Pt) on a carrier such as a porous ceramic honeycomb structure. The oxidation catalyst device 15 oxidizes ammonia that is not consumed and flows out from the SCR catalyst device 14 when the supply amount of the urea water S is larger than the amount consumed by the SCR catalyst device 14, It serves to greatly reduce the ammonia released into it. As a result, release of ammonia into the atmosphere (ammonia slip) is suppressed. The exhaust gas purification system 1 purifies the exhaust gas G, and releases the purified exhaust gas Gc into the atmosphere.

  Next, control of the exhaust gas purification system 1 having the above configuration will be described. The exhaust gas purification system 1 includes a control device (engine control unit: ECU) 30 that performs operation control of the engine 11 and a urea water injection control device 23.

  The control device 30 is provided with DPF regeneration control means for controlling regeneration control of the DPF device 13. In normal operation control, PM is collected by the DPF device 14. During this normal operation control, DPF Whether or not the regeneration time is reached is monitored by the differential pressure before and after the DPF detected by the differential pressure sensor 13a as to whether the device 14 is clogged. If the regeneration time is determined, forced regeneration control is performed.

  In this forced regeneration control, the exhaust temperature is generally raised by in-cylinder injection control of the engine 11 such as post injection. After this forced regeneration control, the normal operation is resumed. Then, the vehicle is driven while repeating normal driving and forced regeneration control of the DPF device 14.

  On the other hand, the urea water injection control device 23 is provided with urea water injection control means, and a supply amount adjusting device (aqueous solution supply amount adjusting means: ECU) 23A for calculating and adjusting the supply amount Qt of the urea water S, urea It is comprised from the injection valve control apparatus (injection valve control means: DCU) 23B which controls the water injection valve 21 and performs urea water injection.

  The urea water injection control device 23 is detected by the engine operation status data from the control device 30 and the SCR catalyst inlet exhaust gas temperature T14a detected by the inlet exhaust gas temperature sensor 31 and the outlet exhaust gas temperature sensor 32. Data such as the SCR catalyst outlet exhaust gas temperature T14b is input, and based on these data, the urea water supply amount Qt is calculated and urea water injection is performed.

  This urea water injection control device 23 is used when the catalyst temperature index value (in this embodiment, the SCR catalyst inlet exhaust gas temperature) T14a that indicates the catalyst temperature Tc of the SCR catalyst device 14 becomes higher than a predetermined judgment temperature Th. In addition to the NOx reducing urea water (NOx reducing ammonia aqueous solution) for reducing NOx by the SCR catalyst device 14, the exhaust gas flowing into the SCR catalyst device 14 is cooled to reduce the catalyst temperature of the SCR catalyst device 14. A cooling urea solution (a cooling ammonia-based aqueous solution) for reducing Tc is supplied.

  Further, the supply amount adjusting device 23A uses the supply amount Qt of the urea water S as a first urea water supply amount (first ammonia aqueous solution supply amount) Q1 corresponding to the ammonia amount that can be consumed by the SCR catalyst device 14. The second urea water supply amount (second ammonia aqueous solution supply amount) Q2 corresponding to the ammonia amount that can be consumed by the oxidation catalyst device 15 is calculated. In this embodiment, the supply amount Qt of the urea water S is calculated as the sum of the first urea water supply amount Q1 and the second urea water supply amount Q2, but after correcting these supply amounts Q1 and Q2, The sum may be calculated or may be calculated by correcting the sum.

  The first urea water supply amount Q1 is calculated from the NOx emission weight Won discharged from the engine 11 and the NOx purification rate ηnox of the SCR catalyst device 14. Further, the second urea water supply amount Q2 is calculated from the exhaust gas amount Vg discharged from the engine 11 and the ammonia conversion efficiency ηnh3 of the oxidation catalyst device 15. Further, the second urea water supply amount Q2 is set within a range of an amount in which the concentration of ammonia flowing out downstream of the oxidation catalyst device 15 is equal to or less than a predetermined limit value C0.

  Next, a control method in the exhaust gas purification system 1 having the above configuration will be described. In this embodiment, the temperature of the exhaust gas flowing into the SCR catalyst device 14 (SCR catalyst inlet exhaust gas temperature) T14a is adopted as the catalyst temperature index value, but the exhaust gas before and after the SCR catalyst device 14 is used. An average value of the temperatures T14a and T14b can be adopted, and when the catalyst bed temperature of the SCR catalyst device 14 can be measured, the temperature Tc can be adopted. In short, any physical quantity may be used as long as the measured value of the catalyst temperature Tc of the SCR catalyst device 14 and the catalyst temperature Tc can be estimated.

  In this control, the control flow as shown in FIG. 2 is repeatedly called from the high-level control flow for controlling the main engine and the like. When this control starts, is executed, and returns, this high-level control flow is again. It is shown as returning to

  When the control flow of FIG. 2 starts, a first urea water supply amount Q1 is calculated in step S11. In the next step S12, it is determined whether or not the exhaust gas temperature (SCR catalyst inlet exhaust gas temperature) T14a at the inlet of the SCR catalyst device 14 is higher than a predetermined determination temperature Th at which thermal degradation of the SCR catalyst occurs.

  If it is determined in step S12 that the SCR catalyst inlet exhaust gas temperature T14a is equal to or lower than the predetermined determination temperature Th, the SCR catalyst device 14 does not reach a high temperature and the supply of cooling urea water is unnecessary. Go to step S15. In step S15, the supply of the cooling urea water is stopped, that is, the second urea water supply amount Q2 is set to 0 (zero), and NOx reduction is performed at the first urea water supply amount Q1 (= total supply amount Qt). Supply only urea water. This NOx reduction control is performed for a predetermined time (time related to the check interval of the SCR catalyst inlet exhaust gas temperature T14a, etc.) to purify NOx and return. The NOx reduction control in step S12 is the same control as the normal operation control for supplying the urea water S with the supply amount Q1 of the urea water for NOx purification.

  If the SCR catalyst inlet exhaust gas temperature T14a is higher than the predetermined determination temperature Th in the determination in step S12, the SCR catalyst device 14 may become hot and thermally deteriorate. As it is necessary to cool the SCR catalyst device 14, the process proceeds to step S13.

  In this step S13, the second urea water supply amount Q2 is calculated, and in the next SCR catalyst cooling control step S14, the supply of cooling urea water for cooling the exhaust gas G flowing into the SCR catalyst device 14 is performed. In addition to supplying urea water for NOx reduction. In this step S14, the urea water S is supplied at the total supply amount Qt that is the sum of the first urea water supply amount Q1 and the second urea water supply amount Q2, and the urea water increased while reducing NOx. The SCR catalyst device 14 is cooled by cooling the exhaust gas G by evaporating the gas.

  In the SCR catalyst cooling control in step S14, the second urea water supply amount Q2 is added in addition to the first urea water supply amount Q1 so that the catalyst temperature of the SCR catalyst device 14 does not rise excessively and causes thermal degradation. Supply. In addition to the evaporation of the urea water of the first urea water supply amount Q1, the exhaust gas G flowing into the SCR catalyst device 14 is cooled by the evaporation of the urea water of the second urea water supply amount Q2. The urea water of the second urea water supply amount Q2 does not contribute to the reduction of NOx, and the ammonia generated from the urea water flows out downstream of the SCR catalyst device 14, so that the oxidation catalyst device 15 The spilled ammonia is oxidized and rendered harmless. The second urea water supply amount Q2 is set in step S13 so that the ammonia concentration that can be oxidized by the oxidation catalyst device 15 is taken into account so that the concentration of the effluent ammonia is equal to or lower than the predetermined determination concentration C0.

  In step S14, the SCR catalyst cooling control is performed for a predetermined time (time related to the check interval of the SCR catalyst inlet exhaust gas temperature T14a, etc.), and then the process proceeds to step S16.

  In step S16, it is determined whether or not the SCR catalyst inlet exhaust gas temperature T14a at the inlet of the SCR catalyst device 14 is higher than a predetermined determination temperature Th at which thermal degradation of the SCR catalyst occurs. If it is determined in step S16 that the SCR catalyst inlet exhaust gas temperature T14a is equal to or lower than the predetermined determination temperature Th, it is determined that the exhaust gas G flowing into the SCR catalyst device 14 is cooled, and the process returns.

  If it is determined in step S16 that the SCR catalyst inlet exhaust gas temperature T14a is higher than a predetermined determination temperature Th, it is determined that the exhaust gas G flowing into the SCR catalyst device 14 is not cooled, and the process goes to step S17. The SCR catalyst inlet exhaust gas temperature T14a, the total time when the SCR catalyst cooling control is performed, and the like are stored as a history of cooling control.

  In step S18, the history of the cooling control is checked, and the total time of the SCR catalyst cooling control becomes longer than a predetermined time, or the SCR catalyst inlet exhaust gas temperature T14a is higher than a predetermined second determination temperature Th2. When the measured time exceeds the predetermined time, the process goes to step S19 because it is abnormal, and if the SCR catalyst cooling control is not successful, the SCR catalyst cooling error is stored and the process returns. On the other hand, if it is not determined in step S18 that there is an abnormality, the process returns.

  Next, calculation of the first urea water supply amount Q1 in step S11 and calculation of the second urea water supply amount Q2 in step S13 will be described. The sum of the first urea water supply amount Q1 and the second urea water supply amount Q2 is defined as the final urea water supply amount Qt. The actual value of this final urea water supply amount Qt depends on the engine used, It depends on the regulation level (NOx emission level).

First, calculation of the first urea water supply amount Q1 in step S11 will be described with reference to the control flow of FIG.
In step S11, as shown in FIG. 3, the NOx concentration Cnox in the exhaust gas discharged from the engine 11 is calculated in step S11a, and the exhaust gas amount Wg related to the weight is calculated in step S11b. In step S11c, the NOx discharge weight Won is calculated from the NOx concentration Cnox, the exhaust gas amount Wg, and the exhaust gas density ρg. In step S11d, the first urea water supply amount Q1 is calculated from the NOx discharge weight Won. .

  More specifically, in step S11a, the NOx concentration Cnox is determined based on the NOx concentration Cnox (ppm) based on the engine load Ac (vertical axis:%) and the engine rotational speed Ne (horizontal axis: rpm) as shown in FIG. ) Is mapped from the engine load Ac indicating the engine operating state and the engine rotation speed Ne. The accelerator opening degree Acc may be used instead of the engine load Ac.

  In step S11b, the exhaust gas amount Wg is calculated as the sum of the air flow rate (intake air amount) Wa and the fuel flow rate Wf. This air flow rate Wa is calculated as a boost pressure Pb (vertical axis: mbar) and the air flow rate map obtained by mapping the air flow rate Wa (kg / h) based on the engine rotational speed Ne (horizontal axis: rpm), and is calculated from the boost pressure Pb and the engine rotational speed Ne. Further, the fuel flow rate Wf is a fuel obtained by mapping the fuel flow rate Wf (kg / h) based on the engine load Ac (vertical axis:%) and the engine rotational speed Ne (horizontal axis: rpm) as shown in FIG. With reference to the flow rate map, calculation is made from the engine load Ac indicating the engine operating state and the engine rotational speed Ne. The accelerator opening degree Acc may be used instead of the engine load Ac.

In step S11c, this exhaust gas amount Wg is divided by the exhaust gas density ρg, and this is multiplied by the NOx concentration Cnox to calculate the NOx emission weight Won.
In step S11d, the first urea water supply amount Q1 is calculated as follows.

  The catalyst temperature Tc of the SCR catalyst device 14 is estimated from the SCR catalyst inlet exhaust gas temperature T14a and the SCR catalyst outlet exhaust gas temperature T14b, for example, the average temperature T14m of both (= (T14a + T14b) / 2), etc. To calculate. A NOx purification rate ηnox (%) is calculated from the catalyst temperature Tc and the amount of ammonia accumulated in the catalyst with reference to a NOx purification rate map as shown in FIG. This NOx purification rate map maps the NOx purification rate ηnox (%) based on the catalyst temperature Tc (vertical axis: ° C.) and the ammonia amount Wcnh3 (vertical axis: g) accumulated in the SCR catalyst device 14. Is.

  A NOx weight Wan that can be processed is calculated by multiplying the NOx purification rate ηnox by the NOx discharge weight Won. The amount of urea water containing urea corresponding to this processable NOx weight Wan becomes the first urea water supply amount Q1. The first urea water supply amount Q1 corresponds to the amount of urea that can be consumed by the SCR catalyst device 14.

More specifically, the first urea water supply amount Q1 is calculated as follows.
From 1 mol (60 g) of urea, 2 mol (34 g) of ammonia is generated, and 1 mol (17 g) of ammonia reacts with 1 mol (46 g) of NOx. Therefore, 0.5 mol (30 g) of urea is required for 1 mol (46 g) of NOx. Here, if the urea water S supplied to the SCR catalyst device 14 is a urea aqueous solution of P (%) (32.5% is often used), the number of moles of NOx generated from the engine 11 (= NOx emission weight (= Won) / 46), urea needs half the number of moles (= Q1 × (P / 100) / 30). That is, Q1 = (NOx emission weight (Won) / 46) × 30 × (100 / P). This first urea water supply amount Q1 is an amount necessary for purifying NOx in the exhaust gas.

Next, calculation of the second urea water supply amount Q2 in step S13 will be described with reference to the control flow of FIG.
The upper limit value Qu of the second urea water supply amount Q2 is calculated as follows.

In step S13a, the ammonia purification rate ηnh3 (%) is calculated from the relationship between the catalyst temperature (° C.) of the oxidation catalyst device 16 and the ammonia purification rate ηnh3 (%) shown in FIG.
In the next step S13b, the upper limit value Qu of the second urea water supply amount Q2 is calculated. This upper limit value Qu (kg / h) is calculated by Qu = K × (C0 × Vg / P) / (1−ηnh3 / 100). Here, C0 is a predetermined judgment concentration (ppm), Vg is an exhaust gas amount (m ³ / h) related to volume, P is urea water concentration (%), and K is (3 × 10 ⁻³ /22.4). is there. The exhaust gas amount Vg (m ³ / h) related to this volume is a value obtained by dividing the exhaust gas amount Wg (kg / h) related to the weight by the exhaust gas density ρ (kg / m ³ ). That is, Vg = Wg / ρg.

  In the next step S13c, the second urea water supply amount Q2 is set to a value not more than the upper limit value Qu. The second urea water supply amount Q2 may be equal to or less than the upper limit value Qu, but is determined in consideration of the balance between the cooling effect of the SCR catalyst device 14 and the consumption amount of the urea water S.

  The second urea water supply amount Q2 is determined according to the SCR catalyst inlet exhaust gas temperature T14a of the exhaust gas G flowing into the SCR catalyst device 14 or according to the change of the SCR catalyst inlet exhaust gas temperature T14a. Is preferred. For example, when the cooling effect needs to be strengthened, it is increased by a predetermined supply amount increment ΔQ2 from the previous second urea water supply amount Q2 (Q2 = Q2 + ΔQ2), and the cooling effect is maintained as it is. (Q2 = Q2) When the cooling effect needs to be weakened, the amount is decreased by a predetermined supply amount increment ΔQ2 from the previous second urea water supply amount Q2 (Q2 = Q2−ΔQ2). When the predetermined supply amount increment ΔQ2 is increased to exceed the upper limit value Qu, the second urea water supply amount Q2 is set to the upper limit value Qu (Q2 = Qu).

The calculation of the upper limit value Qu of the second urea water supply amount Q2 is derived from the following idea. The number of moles ΔM of ammonia generated from the urea water of the second urea water supply amount Q2c (kg / h) is ΔM = Q2c × (32.5 / 100) × (2/60) × 10 ³ . The amount of gas ΔVnh3 (m ³ / h) in the standard state of ammonia (0 ° C., 1 atm) is ΔM × 22.4.

This ammonia gas amount ΔVnh3 (m ³ / h) is multiplied by the non-ammonia purification rate (1-ηnh3 / 100), and the ammonia gas amount ΔVsnh3 (m ³ / h) flowing out downstream of the oxidation catalyst device 15 Is calculated. The non-ammonia purification rate is calculated by subtracting the ammonia purification rate ηnh3 (%) by the oxidation catalyst device 15 from 1.0. This ammonia purification rate ηnh3 (%) is calculated by the oxidation catalyst device 16 shown in FIG. Is calculated from the relationship between the catalyst temperature (° C.) and the ammonia purification rate ηnh3 (%).

Then, the ammonia outflow gas amount ΔVsnh3 (m ³ / h) is divided by the exhaust gas flow rate Vg (m ³ / h) calculated in step S11b to calculate the outflow ammonia concentration Csnh3 (ppm). Csnh3 = ΔVsnh3 × (1-ηnh3 / 100) / Vg × 10 ⁶ = (Q2c / Vg) × (1-ηnh3 / 100) × (P / 100) × (2/60) × 22.4 × 10 ⁶ Become.

  The second urea water supply amount (kg / h) Q2c at which the outflow ammonia concentration Csnh3 (ppm) becomes a predetermined determination concentration C0 (ppm) is set to the upper limit value Qu (kg / h) of the second urea water supply amount Q2. And The predetermined determination concentration C0 (ppm) is set to a level at which ammonia odor does not matter, for example, 10 ppm or less.

In reverse calculation, from (Qu / Vg) × (1-ηnh3 / 100) × (P / 100) × (2/60) × 22.4 × 10 ⁶ = C0, Qu = K × (C0 × Vg / P) / (1-ηnh3 / 100). Here, K = 3 × 10 ⁻³ /22.4.

  When the catalyst temperature index value T14a indicating the catalyst temperature Tc of the SCR (selective catalytic reduction type) catalyst device 14 becomes larger than the predetermined judgment temperature Th by the control according to the control flow of FIGS. In addition to the NOx reducing urea water Q1 for reducing NOx by the catalyst device 14, the cooling urea water for cooling the exhaust gas flowing into the SCR catalyst device 14 to lower the catalyst temperature Tc of the SCR catalyst device 14 Q2 can be supplied.

  Furthermore, the urea water supply amount Qt is divided into the first urea water supply amount Q1 corresponding to the urea amount that can be consumed by the SCR catalyst device 14 and the second urea amount corresponding to the urea amount that can be consumed by the oxidation catalyst device 15. It can be calculated based on the water supply amount Q2.

  Then, the first urea water supply amount Q1 is calculated from the NOx discharge amount (NOx discharge weight) Won discharged from the engine 11 and the NOx purification rate ηnox of the SCR catalyst device 14, and the second urea water supply amount Q2 is calculated. Can be calculated from the exhaust gas amount Vg discharged from the engine 11 and the ammonia conversion rate ηnh3 of the oxidation catalyst device 15.

  In the embodiment shown in the control flow of FIGS. 2 to 4 described above, the temperature of the exhaust gas G flowing into the SCR catalyst device 14, that is, the SCR catalyst inlet exhaust gas temperature T 14 a is set even when the DPF device 13 is not forcedly regenerated. The SCR catalyst cooling control is performed when the SCR catalyst inlet exhaust gas temperature T14a becomes higher than a predetermined judgment temperature Th for some reason.

  However, since the SCR catalyst inlet exhaust gas temperature T14a tends to increase during the forced regeneration of the DPF device 13, the SCR catalyst cooling control may be performed only during the forced regeneration of the DPF device 13. In this case, the control flow of FIGS. 2 to 4 is entered only when the DPF device 13 is forcedly regenerated, and when it is not during forced regeneration, the NOx reduction control in step S15 may be performed.

  In the exhaust gas temperature increase control during forced regeneration of the DPF device 13, post-injection (post-injection) or multi-injection (multistage delay injection) and post-injection are performed in the cylinder (in-cylinder) injection of the engine 11 and exhaust is performed. Perform throttle and intake throttle. In this exhaust gas temperature raising control, intake throttle control or EGR control that throttles an intake throttle valve (not shown) may be used in combination.

  In the above description, the DPF device 13 in the exhaust gas purification system 1 is described as an example of a DPF device having only a filter that does not carry a catalyst. However, the present invention is not limited to this, and the filter is oxidized. Others such as a continuous regeneration type DPF device carrying a catalyst, a continuous regeneration type DPF device provided with an oxidation catalyst on the upstream side of the filter, a DPF device comprising a catalyst supported on the filter and an oxidation catalyst provided on the upstream side of the filter, etc. This type of DPF can also be applied.

1 is a system configuration diagram of an exhaust gas purification system according to an embodiment of the present invention. It is a control flowchart which shows the control method of the exhaust gas purification system of embodiment which concerns on this invention. It is a figure which shows an example of the flow of calculation of the 1st urea water supply amount. It is a figure which shows an example of the flow of calculation of the 2nd urea water supply amount. It is a figure which shows an example of a NOx density | concentration map. It is a figure which shows an example of an air flow rate map. It is a figure which shows an example of a fuel flow map. It is a figure which shows an example of a NOx purification rate map. It is a figure which shows an example of the relationship between an ammonia purification rate and the inlet exhaust gas temperature of an oxidation catalyst apparatus.

Explanation of symbols

1 Exhaust gas purification system 11 Diesel internal combustion engine (engine)
12 Exhaust passage 13 DPF device 14 Selective catalytic reduction catalyst device (SCR catalyst device)
15 Oxidation catalyst device 21 Urea water injection valve 30 Control device (ECU)
31 Inlet exhaust gas temperature sensor 32 Outlet exhaust gas temperature sensor Ac Engine load Acc Accelerator opening C0 Predetermined concentration Cnox NOx concentration in exhaust gas discharged from engine Csnh3 Outflow ammonia concentration K constant (= 3 × 10 ⁻³ / 22.4)
Ne Engine rotational speed P Urea water concentration Pb Boost pressure Q1 First urea water supply amount Q2 Second urea water supply amount Qu Upper limit value of second urea water supply amount T14a SCR catalyst inlet exhaust gas temperature T14b SCR catalyst outlet exhaust Gas temperature Tc Catalyst temperature Vg Exhaust gas volume (volume / hour)
Wa Air flow rate (intake air amount)
Wan NOx weight that can be processed Wf Fuel flow rate Wg Exhaust gas volume related to weight (weight / hour)
Won NOx emission weight Wcnh3 Amount of ammonia accumulated in the SCR catalyst device ηnox NOx purification rate ηnh3 Ammonia purification rate ΔVsnh3 Ammonia outflow gas amount

Claims (8)

A selective catalytic reduction catalyst device and an oxidation catalyst device for purifying NOx in order from the upstream side in an exhaust passage of an internal combustion engine, and an aqueous solution supply device for supplying an ammonia-based aqueous solution to the selective catalytic reduction catalyst device And an aqueous solution supply amount adjusting means for adjusting the supply amount of the ammonia-based aqueous solution.
A NOx reducing ammonia system for reducing NOx by the selective catalytic reduction catalyst device when a catalyst temperature index value indicating the catalyst temperature of the selective catalytic reduction catalyst device becomes higher than a predetermined determination temperature. In addition to an aqueous solution, an exhaust gas purification system for supplying an ammonia-based aqueous solution for cooling to cool the exhaust gas flowing into the selective catalytic reduction catalyst device and lower the catalyst temperature of the selective catalytic reduction catalyst device In the control method of
The supply amount of the ammonia aqueous solution for cooling is equivalent to the first ammonia aqueous solution supply amount corresponding to the ammonia amount that can be consumed by the selective catalytic reduction catalyst device and the ammonia amount that can be consumed by the oxidation catalyst device. And calculating based on the second ammonia-based aqueous solution supply amount,
Calculating the first ammonia aqueous solution supply amount from the NOx emission amount discharged from the internal combustion engine and the NOx purification rate of the selective catalytic reduction catalyst device;
A control method for an exhaust gas purification system, wherein the second ammonia-based aqueous solution supply amount is calculated from an exhaust gas amount discharged from an internal combustion engine and an ammonia conversion efficiency of the oxidation catalyst device.   The exhaust gas purification system control according to claim 1, wherein a diesel particulate filter device for purifying particulate matter in the exhaust gas is disposed upstream of the selective catalytic reduction catalyst device. Method.   The second ammonia aqueous solution supply amount is set within a range of an ammonia outflow amount that flows out downstream of the oxidation catalyst device to be a predetermined limit value or less. The control method of the exhaust gas purification system as described.   The control method for an exhaust gas purification system according to claim 3, wherein the predetermined limit value is 10 ppm. A selective catalytic reduction catalyst device and an oxidation catalyst device for purifying NOx in order from the upstream side in an exhaust passage of an internal combustion engine, and an aqueous solution supply device for supplying an ammonia-based aqueous solution to the selective catalytic reduction catalyst device And an aqueous solution supply amount adjusting means for adjusting the supply amount of the ammonia-based aqueous solution.
A NOx reducing ammonia system for reducing NOx by the selective catalytic reduction catalyst device when a catalyst temperature index value indicating the catalyst temperature of the selective catalytic reduction catalyst device becomes higher than a predetermined determination temperature. In addition to an aqueous solution, an exhaust gas purification system for supplying an ammonia-based aqueous solution for cooling to cool the exhaust gas flowing into the selective catalytic reduction catalyst device and lower the catalyst temperature of the selective catalytic reduction catalyst device In
The aqueous solution supply amount adjusting means consumes the ammonia aqueous solution supply amount in the first ammonia aqueous solution supply amount corresponding to the ammonia amount that can be consumed in the selective catalytic reduction catalyst device, and in the oxidation catalyst device. While calculating based on the second ammonia aqueous solution supply amount corresponding to the possible ammonia amount,
Calculating the first ammonia aqueous solution supply amount from the NOx emission amount discharged from the internal combustion engine and the NOx purification rate of the selective catalytic reduction catalyst device;
The exhaust gas purification system characterized in that the second ammonia-based aqueous solution supply amount is calculated from the amount of exhaust gas discharged from an internal combustion engine and the ammonia conversion efficiency of the oxidation catalyst device.   The exhaust gas purification system according to claim 5, wherein a diesel particulate filter device for purifying particulate matter in the exhaust gas is disposed upstream of the selective catalytic reduction catalyst device.   The aqueous solution supply amount adjusting means sets the second ammonia-based aqueous solution supply amount within an amount range in which the ammonia outflow amount flowing out downstream of the oxidation catalyst device is equal to or less than a predetermined limit value. The exhaust gas purification system according to claim 5 or 6, characterized in that The exhaust gas purification system according to claim 7, wherein the aqueous solution supply amount adjusting means sets the predetermined limit value to 10 ppm.

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