JP2011094572A - Nox cleaning device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a device highly accurately calculating an SCR catalyst temperature and appropriately controlling input and input timing of a reducing agent, to secure denitrification rate efficiency, reduce slip of NH3, and reduce an operation cost of a diesel engine along with saving of urea aqueous solution. <P>SOLUTION: The NOx cleaning device for an internal combustion engine is disposed to an exhaust pipe 2 of the engine 1, calculates an internal temperature of the SCR catalyst 11 from exhaust gas temperatures of an inlet and an outlet of the SCR catalyst 11, and estimates an amount of adsorption of the reducing agent to the SCR catalyst based on the internal temperature of the SCR catalyst 11. Therefore, a reducing agent amount to be sprayed in exhaust gas is highly accurately calculated to spray the reducing agent into the exhaust gas by a urea aqueous solution spray device 6 and thereby to reduce slip quantities of the NH3 and NOx. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device and an exhaust gas purification method for an internal combustion engine, particularly a diesel engine, and a selective reduction type SCR in which urea water or ammonia (NH3) is added as a reducing agent to reduce and remove nitrogen oxides (NOx). The present invention relates to NOx purification technology for catalysts.

  Engine exhaust as an exhaust gas purification device for purifying nitrogen oxides (hereinafter referred to as NOx), which is one of air pollutants contained in exhaust gas of internal combustion engines, particularly diesel engines (hereinafter referred to as engines). A selective reduction SCR catalyst (hereinafter referred to as SCR catalyst) is disposed in the passage, and ammonia as a reducing agent (hereinafter referred to as NH3) is added to the SCR catalyst, thereby selectively reducing NOx in the exhaust gas. An exhaust gas purification device that purifies the gas has been developed.

  In such an exhaust gas purification device, urea water is sprayed into the exhaust gas by the spray nozzle upstream of the SCR catalyst, and NH3 generated by hydrolysis of the urea water by the heat of the exhaust gas is supplied to the SCR catalyst. The NH3 supplied to the SCR catalyst is once adsorbed by the SCR catalyst, and NOx purification (denitration) is performed by promoting the denitration reaction between the NH3 and NOx in the exhaust gas by the SCR catalyst.

By the way, in general, the NOx purification rate in the NOx purification device largely depends on the performance of the SCR catalyst, and a certain high temperature is required to purify NOx with NH3 as a reducing agent with high efficiency.
Since the SCR catalyst using NH3 as the reducing agent has a higher NOx purification rate as the amount of NH3 adsorbed on the SCR catalyst increases, it is necessary to control the amount of NH3 adsorbed higher in order to obtain a higher purification rate of the SCR catalyst in a low temperature range. is there.
On the other hand, there is a limit to the amount of NH3 adsorbed on the SCR catalyst. As the adsorption limit value, the NH3 adsorption amount is large when the SCR catalyst temperature is low, and the NH3 adsorption amount is small when the SCR catalyst temperature is high.
As the prior art document, Japanese Patent No. 3951774 (Patent Document 1) has been proposed.

Japanese Patent No. 3951774

According to Patent Document 1, the consumption amount of NH3 adsorbed on the SCR catalyst is derived based on the NOx emission amount detected or estimated by the NOx emission amount deriving means and the actual NOx purification rate by the SCR catalyst. Deriving the actual adsorption amount of NH3 adsorbed on the SCR catalyst according to the added amount of NH3 and the consumption amount of NH3 obtained by the adsorption amount deriving means, and controlling the reducing agent supply means according to the actual adsorption amount It is.
When these controls are performed, the catalyst temperature is detected more accurately, the denitration rate is improved, and NH3 slip (when the supply amount of NH3 is large and exceeds the adsorption limit on the catalyst, it is not adsorbed on the SCR catalyst. , A phenomenon in which NH3 is released into the atmosphere) needs to be prevented.
However, since only a part of the temperature of the SCR catalyst is measured by the temperature sensor, the temperature of the entire SCR catalyst may not be obtained.
Moreover, although exhaust gas temperature may be used, in general-purpose engines, etc., there are more transient operating situations than automobiles and plants as operating characteristics used. That is, since the load fluctuation is large and intermittent operation is performed, the representative value of the SCR catalyst temperature is often not always obtained depending on the length of the engine stop time.
Furthermore, due to the heat capacity of the SCR catalyst, that is, when the time from the previous stop to the current restart is relatively short, the SCR catalyst temperature may be higher than the exhaust gas temperature. In some cases, it is difficult to estimate an accurate adsorption amount.

  The present invention has been made to solve such problems. The SCR catalyst temperature is accurately calculated, and the amount and timing of reducing agent input are appropriately controlled to ensure the denitration rate and NH3 slip. It is an object of the present invention to provide an apparatus for reducing the operating cost of a diesel engine accompanying reduction and saving of a reducing agent.

  The present invention achieves such an object, and is provided in an engine exhaust system to adsorb NH3 as a reducing agent to selectively reduce NOx in exhaust gas, and to supply the reducing agent to the SCR catalyst. Reducing agent supply means, temperature measuring means for measuring the temperature of the exhaust gas at the inlet and outlet of the SCR catalyst, and the inside of the SCR catalyst based on the exhaust gas temperature difference between the inlet and outlet detected by the temperature measuring means A reducing agent that calculates the amount of NH3 adsorbed to the SCR catalyst based on the internal temperature of the SCR catalyst and an SCR catalyst temperature estimating unit that estimates temperature, and calculates the supply amount of the reducing agent based on the amount of adsorption In a NOx purification device for an engine having a control means having a supply amount control unit, the reducing agent supply amount control unit calculates the reducing agent supply amount when the engine is started or cold. As the SCR catalyst temperature (initial value), the exhaust gas temperature average value at the inlet and the outlet of the SCR catalyst based on the measurement result of the temperature measuring means, and the SCR catalyst estimated by the SCR catalyst temperature estimation unit When the exhaust gas temperature average value is higher than or equivalent to the internal temperature of the SCR catalyst, the exhaust gas temperature average value is compared with the internal temperature, and when the internal temperature of the SCR catalyst is higher, the SCR catalyst The reducing agent supply amount is calculated with the initial temperature as the initial value, and the reducing agent is controlled to be supplied from the reducing agent supply means to the SCR catalyst.

  With such a configuration, the SCR catalyst has a property that the NOx purification rate is higher as the amount of ammonia (reducing agent) adsorbed on the catalyst is larger. On the other hand, the NH3 adsorption amount changes depending on the temperature of the SCR catalyst. By measuring the internal temperature of the NOx catalyst accurately and controlling the amount of reducing agent supplied into the exhaust gas, the amount of reducing agent slip (the reducing agent does not react and is released into the atmosphere as ammonia) As a result, it is possible to improve the purification of exhaust gas.

  Preferably, in the present invention, the SCR catalyst temperature estimation unit continues to estimate the SCR catalyst temperature even after the engine is stopped, and the SCR catalyst temperature estimation unit by the SCR catalyst temperature estimation unit and the temperature measurement unit When the detected SCR catalyst inlet becomes lower than the exhaust gas temperature, the estimation of the SCR catalyst temperature is finished, and the engine is restarted in a state where the estimated SCR catalyst temperature is higher than the SCR catalyst inlet exhaust gas temperature. If the catalyst temperature is estimated, the reducing agent supply amount is calculated using the estimated catalyst temperature value at the time of restarting as the initial value, and the reducing agent is supplied from the reducing agent supply means to the SCR catalyst. It is good to control.

  In general-purpose engines, etc., the engine main body has a wide variety of operating conditions. For example, when the engine is restarted before the temperature drops, or when the engine is stopped for a long time and the engine is cold (when cold), etc. There are many usage examples, and it is possible to improve the exhaust gas purification efficiency at the time of restarting by estimating the NH3 adsorption amount to the SCR catalyst more accurately when restarting.

  Preferably, in the present invention, the SCR catalyst temperature estimation unit measures exhaust gas temperatures at the SCR catalyst inlet and the SCR catalyst outlet, and determines the exhaust gas temperature based on the exhaust gas temperature, the heat capacity and heat transfer characteristics of the catalyst. The SCR catalyst internal temperature may be estimated.

  With such a configuration, the exhaust gas temperature at the inlet and outlet of the SCR catalyst is measured and the estimated internal temperature of the SCR catalyst is estimated. Therefore, the average temperature of the entire SCR catalyst can be obtained. Therefore, it is possible to estimate the NH3 adsorption amount with higher accuracy on the SCR catalyst and to improve the purification of exhaust gas.

  In the present invention, preferably, the temperature of the SCR catalyst when the engine is in a cold state start is directly measured by a temperature sensor, and the measured value is set as the initial value.

Since the initial value of the catalyst temperature at the time of engine start is directly measured by the temperature sensor, the catalyst temperature is accurately measured from when the engine is started until the catalyst temperature reaches a state where the catalyst temperature can be efficiently reduced. it can. For this reason, it becomes possible to more appropriately execute the reducing agent adsorption amount of the SCR catalyst and its reduction and purification process.
Therefore, by setting the spray amount of the appropriate NOx reducing agent, NH3 slip can be prevented, the reducing agent can be eliminated, and the operating cost of the engine can be reduced.

  Preferably, in the present invention, a cylindrical SCR catalyst that is provided in an exhaust system of the engine, adsorbs NH3, selectively reduces NOx in the exhaust gas, and has a region divided into a plurality in the circumferential direction, and the SCR Reducing agent supply for supplying the reducing agent to the SCR catalyst by arranging a plurality of spray nozzles for ejecting the NH3 or urea water as the reducing agent at equal intervals in the circumferential direction of the SCR catalyst on the upstream side of the catalyst. And temperature sensors disposed at the exhaust gas inlet and outlet of the SCR catalyst, with the SCR catalyst sandwiched therebetween and in a state of being opposed to each other, and the temperature measuring means A catalyst temperature estimator for estimating a temperature distribution for each of the temperature sensors facing the internal temperature of the SCR catalyst based on the temperature; and an absorption of the NH3 to the SCR catalyst based on the internal temperature of the SCR catalyst. In the engine NOx purification device comprising: a control means having a reducing agent supply amount control unit that calculates an amount and calculates a reducing agent supply amount for each of the plurality of spray nozzles based on the adsorption amount; The reducing agent supply amount control unit controls the amount of the reducing agent ejected from each spray nozzle according to the temperature of the temperature distribution detected by the catalyst temperature estimation unit.

With such a configuration, the spray amount of the reducing agent can be adjusted for each catalyst temperature distribution in each circumferential direction of the catalyst divided into a plurality of parts, so that efficient denitration is possible and the amount of urea water used is reduced. And the slip amount of NH3 can be reduced.
In addition, the amount of exhaust gas flowing through the SCR catalyst is partially biased due to the drift of exhaust gas due to bending of the piping and the like, and the reduction rate of NOx varies depending on the distribution, but such a case can be effectively dealt with.
Furthermore, since a plurality of nozzles are used, even if a nozzle failure occurs, it is possible to prevent an extreme decrease in the denitration performance.

  In the present invention, each of the plurality of spray nozzles is disposed to face each of the SCR catalysts in the plurality of divided regions, and the reducing agent sprayed from the spray nozzles is sprayed onto the SCR catalyst. The area is sprayed over the entire area of the SCR catalyst on the exhaust gas inlet side by the spray nozzles, and the spray nozzles are sprayed with the reducing agent by overlapping the spray nozzles at least in the center of the SCR catalyst. It is good to be formed.

With such a configuration, the NOx catalyst center is generally the hottest, so that the reducing agent is sprayed from any nozzle to the center so that a large amount of reducing agent is present at the center of the upstream side of the exhaust system of the catalyst. NOx reduction and purification can be efficiently promoted by spraying NO.
Furthermore, since a plurality of nozzles are used, a plurality of small engine nozzles are used for a large engine, so that a large-diameter nozzle is not required, so that parts can be shared and a cost reduction effect can be obtained.

  In the present invention, each of the plurality of spray nozzles may include a plurality of the spray nozzles with respect to a distribution region of the temperature distribution distributed for each of the temperature sensors of the SCR catalyst in the plurality of divided regions. It is good to arrange.

  With such a configuration, it is not necessary to provide as many reducing agent spray nozzles as the number corresponding to each of the divided SCR catalysts, and the NOx reduction purification can be performed efficiently by providing an injection region that covers the front side of the exhaust system upstream of the catalyst. And the cost can be reduced by reducing the number of spray nozzles.

  In the present invention, an SCR catalyst that is provided in the exhaust system of the engine, adsorbs NH3 as a reducing agent, and selectively reduces NOx in the exhaust gas, and the SCR catalyst is spaced from the SCR catalyst downstream of the SCR catalyst. And an NH3 slip catalyst for purifying NOx and NH3 in the exhaust gas, a reducing agent supply means for supplying the reducing agent to the SCR catalyst, and the temperature of the exhaust gas at the inlet and outlet of the SCR catalyst An SCR catalyst temperature estimating unit for estimating an internal temperature of the SCR catalyst based on an exhaust gas temperature difference between the inlet and the outlet detected by the temperature measuring unit, and the SCR for the urea water spray amount An NH3 slip amount calculation unit for calculating the NH3 slip amount from the SCR catalyst based on the catalyst internal temperature and the NOx purification rate by the engine load, A NOx slip amount calculating unit that calculates a NOx slip amount in the SCR catalyst based on an Ox purification rate, a reducing agent amount calculating unit that calculates a reducing agent amount necessary for reducing the NOx slip amount, and the temperature measuring unit In a NOx purifying apparatus for an engine having a control means having an NH3 slip catalyst activity judgment unit for judging whether the NH3 slip catalyst is in an activated state based on a detection temperature of an exhaust gas temperature at an outlet, the NH3 slip catalyst activity When the determination unit determines that the NH3 slip catalyst is in an active state, the NH3 slip amount and the NOx slip amount from the SCR catalyst are calculated based on the internal temperature of the SCR catalyst, and the NOx slip amount is calculated as the NH3 slip amount. The internal temperature value of the SCR catalyst for determining the amount of the reducing agent necessary for purification with a slip catalyst; Comparing the exhaust gas temperature average value of the inlet and outlet of the SCR catalyst based on the measurement result of the temperature measuring means with the internal temperature of the SCR catalyst estimated by the SCR catalyst temperature estimating unit, The higher temperature is calculated as the internal temperature of the SCR catalyst by the reducing agent amount calculation unit and output to the reducing agent supply means.

With such a configuration, when it is necessary to attach an oxidation catalyst (hereinafter referred to as NH3 slip catalyst) to clear exhaust gas regulations, NH3 slip is intentionally slipped by the SCR catalyst. By supplying the amount of NH3 required for NOx purification by the catalyst, it is possible to maximize the NOx purification by the NH3 slip catalyst and improve the purification rate.
Further, by utilizing the NOx purification function of the NH3 slip catalyst, the size of the SCR catalyst can be reduced, leading to cost reduction.

According to the present invention, with such a configuration, the SCR catalyst has a higher NOx purification rate as the amount of adsorption of NH3 (reducing agent) on the catalyst increases, but the amount of adsorption of NH3 varies depending on the temperature. Therefore, by accurately measuring the internal temperature of the SCR catalyst and controlling the amount of reducing agent injected into the exhaust gas, it is possible to reduce the reducing agent slip amount as much as possible to improve the denitration effect in the exhaust gas. It becomes.
Furthermore, when it is necessary to install an NH3 slip catalyst to satisfy the exhaust gas regulations, the NH3 amount necessary for NOx purification with the NH3 slip catalyst is appropriately adjusted by intentionally slipping NH3 with the SCR catalyst. By supplying the maximum amount of NOx purification using the NH3 slip catalyst, the purification rate can be improved.
In addition, by utilizing the NOx purification function (denitration) of the NH3 slip catalyst, the size of the SCR catalyst can be reduced, the parts can be shared, the specification can be easily changed, and the actual cost can be reduced.

1 shows a schematic structural diagram of an engine NOx purification device according to a first embodiment of the present invention. FIG. The control flow figure concerning exhaust gas purification of a 1st embodiment of the present invention is shown. The relationship diagram of the temperature rise by the passage of time of exhaust gas temperature concerning the 1st embodiment of the present invention and SCR catalyst temperature is shown. The relationship figure of the SCR catalyst internal temperature which concerns on 1st Embodiment of this invention, and the allowable amount of ammonia adsorption | suction is shown. (A) which concerns on 3rd Embodiment of this invention is a schematic structure figure of a SCR catalyst purification apparatus, (B) is a spray pattern figure of the reducing agent sprayed on a SCR catalyst, (C) is a division area shape figure of a SCR catalyst Indicates. The schematic structure figure of the SCR catalyst purification device concerning a 4th embodiment of the present invention is shown. The control flow figure concerning exhaust gas purification of a 4th embodiment of the present invention is shown. An example of the map which estimates the purification | cleaning rate of an SCR catalyst from the SCR catalyst internal temperature and engine operating state of this invention is shown. An example of the map which estimates NH3 request | requirement amount from the NOx inflow amount to the NH3 slip catalyst which concerns on 4th Embodiment of this invention, and the temperature of NH3 slip catalyst is shown.

Hereinafter, the present invention will be described in detail with reference to the embodiments shown in the drawings.
However, the dimensions, materials, shapes, relative arrangements, and the like of the component parts described in this example are not intended to limit the scope of the present invention only to specific examples unless otherwise specified. Only.

(First embodiment)
The engine NOx purification device according to the first embodiment of the present invention will be described with reference to FIGS. 1 to 4.
In FIG. 1, a NOx purification device 10 includes a controller 5 that is a control means having a reducing agent supply amount control unit for NOx purification of exhaust gas discharged from the engine 1, and a reducing agent that sprays the reducing agent under the control of the controller 5. The apparatus comprises a urea water spray device 6 as supply means, an inlet side temperature sensor 12 and outlet side temperature sensor 13 as temperature measurement means for detecting the temperature of the SCR catalyst 11 and exhaust gas, and the like.

An intake flow rate sensor 31 for measuring an intake air amount and an intake air temperature (calculating intake air density) is attached to an inlet manifold 3 that guides intake air from an air cleaner (not shown) to a combustion chamber of the engine 1.
The exhaust gas combusted in the combustion chamber is led to the exhaust pipe 2 through the exhaust manifold 4 and released to the atmosphere.
In the exhaust pipe 2, a NOx sensor for detecting NOx concentration in the exhaust gas from the upstream side of the exhaust passage 24, a DOC catalyst 7 (oxidation catalyst) for oxidizing HC, CO, NO, etc. The honeycomb-shaped SCR catalyst 11 to which the spray nozzle 62 for spraying the reducing agent, the inlet side temperature sensor 12 as temperature measuring means for detecting the temperature of the exhaust gas entering the SCR catalyst 11, and the catalyst for purifying NOx in the exhaust gas are attached. An outlet side temperature sensor 13 that detects the temperature of exhaust gas that has passed through the SCR catalyst 11 and an NH3 slip catalyst 8 that processes NOx and NH3 that could not be processed by the SCR catalyst 11 are disposed.
A temperature sensor 22 that directly measures the temperature of the SCR catalyst 11 is attached to the SCR catalyst 11.

The SCR catalyst 11 is a honeycomb-structured catalyst carrier with a catalyst component attached, and is housed in the exhaust pipe 2. Vanadium-based and zeolite-based catalysts are known as selective reduction catalysts for NOx. The SCR catalyst 11 selectively reduces NOx in the exhaust gas. When the NH3 is adsorbed on the SCR catalyst 11, the NOx is reduced with high efficiency in the region where the temperature of the SCR catalyst 11 exceeds about 200 ° C. have.
Therefore, by detecting the temperature of the SCR catalyst 11 with high accuracy, it is possible to obtain a good effect for preventing the reducing agent (NH3) from slipping and improving the NOx purification process.

となる。ガス熱量の単位体積あたりの変化に対し、ＳＣＲ触媒から流出した排ガスに残った温度（熱）と、排ガスからＳＣＲ触媒に移動した熱として表される。
一方、排ガス側から移動した伝熱によるＳＣＲ触媒の温度変化
即ち、［ＳＣＲ触媒側の温度変化］＝［ＳＣＲ触媒と排ガス間の熱移動］
となり計算式では

となり、ＳＣＲ触媒の温度上昇分が算出される。
但し、（１）及び（２）の記号は

である。 The controller 5 will be described.
As shown in FIG. 3, the relationship between the internal temperature of the SCR catalyst and the exhaust gas temperature is such that the SCR catalyst temperature is lower than the exhaust gas temperature when the engine 1 is started. The exhaust gas temperature rises simultaneously with the operation of the engine 1, but the internal temperature of the SCR catalyst has a delay in heat transfer, so the rate of temperature rise is low (slow temperature rise) and about 800 seconds have not passed since the start of operation. It is not the same temperature.
Therefore, the SCR catalyst temperature estimation unit 55 for obtaining a highly accurate internal temperature of the SCR catalyst includes an inlet side temperature sensor 12 that detects the exhaust gas temperature at the inlet of the SCR catalyst 11 and an outlet side that detects the exhaust gas temperature at the outlet side of the SCR catalyst 11. Based on the difference in temperature detected by the temperature sensor 13, the following heat transfer equation is used.
<Heat transfer type>
The heat transfer relationship between the honeycomb structure solid and the exhaust gas is as follows.
That is, [temperature change on exhaust gas side] =-[convection term] + [heat transfer between SCR catalyst and exhaust gas]

It becomes. It is expressed as the temperature (heat) remaining in the exhaust gas flowing out of the SCR catalyst and the heat transferred from the exhaust gas to the SCR catalyst with respect to the change per unit volume of the gas calorific value.
On the other hand, the temperature change of the SCR catalyst due to heat transfer from the exhaust gas side, that is, [temperature change on the SCR catalyst side] = [heat transfer between the SCR catalyst and exhaust gas]
In the calculation formula

Thus, the temperature increase of the SCR catalyst is calculated.
However, the symbols (1) and (2)

It is.

The exhaust gas average temperature calculation unit 54 calculates based on the inlet side temperature sensor 12 which is a temperature measuring means for detecting the exhaust gas temperature at the inlet of the SCR catalyst 11 and the outlet side temperature sensor 13 which detects the exhaust gas temperature on the outlet side of the SCR catalyst 11. Is done.
Exhaust gas average temperature = (exhaust exhaust gas temperature + outlet exhaust gas temperature) / 2 (3)
Compared with the temperature estimated by the catalyst temperature estimation unit 55 when the engine 1 is just started and the SCR catalyst 11 is not sufficiently warmed, the higher temperature value is used as an initial value for estimating the catalyst adsorption amount. Use as a value.

  The target adsorption amount calculation unit 56 is determined on the basis of the characteristics of the engine 1, and in order to clear the exhaust gas regulation value, a necessary amount of reducing agent is created as an experimental value according to the engine load status (operation status). Read from the map.

The actual adsorption amount calculation unit 57 calculates the amount of reducing agent (NH 3) actually adsorbed on the SCR catalyst 11 based on the temperature estimated by the SCR catalyst temperature estimation unit 55.
This is due to the characteristics of the SCR catalyst 11 and is calculated from a map obtained by measuring the adsorption amount of the reducing agent (NH 3) based on the temperature of the SCR catalyst 11.
As shown in FIG. 4, the temperature of the SCR catalyst 11 and the NH 3 adsorption allowable amount of the SCR catalyst 11 are inversely proportional to the temperature of the SCR catalyst 11.

  The conversion coefficient 58 compares the required reducing agent amount obtained by the target adsorption amount calculation unit 56 with the reducing agent (NH 3) amount actually adsorbed on the SCR catalyst 11, finds the difference therebetween, and sets the exhaust gas regulation value. A correction value for correcting to be cleared is calculated and output.

The exhaust gas calculation unit 51 takes in the intake air flow rate flowing through the inlet manifold 3 and the intake air temperature (calculates the air density) from the sensor 31, and fuel pumped from the fuel flow meter (not shown) to the combustion chamber of the engine 1. Based on the flow rate of NOx, the NOx emission amount is calculated.
The NOx emission amount calculation unit 52 calculates the NOx emission amount from the exhaust gas amount calculated by the exhaust gas calculation means 51 and the NOx concentration (%) from the NOx sensor 19.
The urea water spray amount target calculation unit 53 calculates the amount of urea water that is a necessary reducing agent based on the NOx discharge amount calculated by the NOx discharge amount calculation unit 52.

In the conversion coefficient 58, the difference between the target adsorption amount calculated by the target adsorption amount calculation unit 56 and the actual adsorption amount calculated by the actual adsorption amount calculation unit 57 is obtained, and the actual adsorption amount is larger than the target adsorption amount. Is corrected to a value that decreases the spray amount of urea water based on the above-described difference.
Further, when the actual adsorption amount is smaller than the target adsorption amount, the urea water spray amount is corrected to a value that increases based on the above-described difference.
When the output unit 59 obtains a difference between the corrected correction value of the adsorption amount and the target value calculated by the urea water spray amount target calculation unit 53, and the urea water spray amount target value is larger than the adsorption amount correction value. Outputs a control signal to the urea water spraying device 6 which is a reducing agent supply means for reducing the difference urea water spray amount.
When the urea water spray amount target value is smaller than the adsorption amount correction value, a control signal is output to the urea water spray device 6 with the correction value corrected by the conversion coefficient 58. (Reducing agent supply control unit)
This prevents NH3 from slipping from the SCR catalyst 11, reduces the amount of urea water used, and reduces the operating cost of the engine 1.

  The urea water spray device 6 is disposed on the upstream side of the SCR catalyst 11 in the exhaust pipe 2 and a urea water spray control device 61 that controls the spray amount and timing of urea water based on the output signal from the controller 5. Based on the output signal from the urea water spray control device 61, the opening and closing of the opening / closing valve is controlled for the spray nozzle 62, the urea water from the urea water tank 63, and the air from the air tank 64 for atomizing the urea water. The dosing module 65 is configured to feed the spray nozzle 62 in a mixed state of air and urea water and adjust the amount of urea water ejected.

Hereinafter, the control content of 1st embodiment regarding the NOx purification apparatus of the engine which concerns on this invention comprised in this way is demonstrated.
Control executed by the controller 5 will be described with reference to FIG.

  When the engine 1 is equal to the atmospheric temperature (when cold), the engine 1 is started. In step S <b> 1, the temperature of the SCR catalyst 11 is directly measured and used as the initial value of the SCR catalyst 11. This is because the engine 1 has just started, and the temperature of the SCR catalyst 11 does not rise immediately as shown in FIG.

In step S2, the internal temperature of the SCR catalyst 11 is estimated and calculated. The calculation method is performed based on the above-described calculation formulas (1) and (2).
In step S3, average values of the inlet side temperature sensor 12 on the inlet side and the outlet side temperature sensor 13 on the outlet side of the SCR catalyst 11 are calculated. According to the calculation formula (3). This average value is used to estimate the temperature of the SCR catalyst 11 depending on how much heat of the exhaust gas is transferred to the SCR catalyst 11.
In step S4, the estimated catalyst internal temperature in step S2 is compared with the average value in step S3.

If the average value is higher or the same, the process proceeds to step S5 as Yes. If the estimated catalyst internal temperature is higher (No), the process proceeds to step S6.
That is, the higher the internal temperature of the SCR catalyst 11, the higher the efficiency of NOx reduction and purification. Therefore, the amount of urea water is determined based on the estimated value or the higher average value.

In step S7, when the engine 1 is in operation (No), the process returns to step S2, and the estimation calculation of the internal temperature of the SCR catalyst 11 is repeated. Based on the internal temperature of the SCR catalyst 11, an appropriate amount of urea water and its efficiency Control for obtaining a clean NOx purification action.
When the engine 1 is stopped (Yes), the process proceeds to step S8. In step S8, the estimation calculation of the internal temperature of the SCR catalyst 11 is continued.
In particular, in the case of the engine 1 to which a generator or an industrial machine is attached, the operation state on the work machine side is various, the operation interval of the engine 1 is long or short, and the load fluctuation is often large. It depends on the circumstances.
In any case, the internal temperature of the SCR catalyst 11 is always detected (when the engine is warm) so that proper NOx purification and NH3 slip reduction can be performed.

In step S9, when the estimated catalyst temperature becomes equal to or lower than the catalyst inlet exhaust gas temperature, the estimated calculation of the catalyst temperature is terminated as Yes.
This indicates that the engine 1 is in a cold state, and the exhaust gas temperature is used as an initial value when restarting, so that the estimation calculation of the catalyst temperature ends.
On the other hand, if the estimated catalyst temperature is higher than the catalyst inlet exhaust gas temperature, the process proceeds to step S11 as No. This state indicates a state where the catalyst temperature is not yet cooled and is warm. In step S11, it is determined whether the engine 1 is to be started. If the engine does not start, No is returned, and the process returns to step S8 and is repeated until the estimated catalyst temperature becomes equal to or lower than the catalyst inlet exhaust gas temperature.
When the engine 1 is to be started, the process proceeds to step S12 as Yes, returns to step S2 with the estimated internal temperature of the catalyst as an initial value, and repeats the control.

In the first embodiment, the temperature of the entire catalyst is estimated, the amount of reducing agent adsorbed on the catalyst is accurately estimated, and the NOx reducing agent spray amount and NH3 slip amount can be reduced at the initial start of the engine 1. It is said.
In addition, in the operating conditions peculiar to general-purpose engines, especially when the operation is repeatedly turned on and off, by setting an appropriate spray amount of the NOx reducing agent, reducing agent (urea water) is not wasted, and the operating cost of the engine 1 is reduced. Can be reduced.

The control contents of the second embodiment will be described.
In the control flow diagram (FIG. 2) of the first embodiment, “measurement of exhaust gas temperature is performed and the value is set as the initial value of the catalyst temperature estimation logic” in step S1, but in the second embodiment, the above step is performed. In S1, “the catalyst temperature is directly measured and the value is set as the initial value of the catalyst temperature estimation logic”. Since all the steps except step S1 are the same, the control flow and description thereof are omitted.

In the second embodiment, as described in the first embodiment, the exhaust gas temperature rises simultaneously with the operation of the engine 1, but the internal temperature of the catalyst has a delay in heat transfer, so the rate of temperature rise is low. (Temperature rise is slow) If about 800 seconds have not passed since the start of operation, the temperature will not reach substantially the same.
Therefore, since the initial value of the catalyst temperature at the time of starting the engine 1 is directly measured by the temperature sensor 22, the catalyst is accurately obtained until the engine 1 is started and the catalyst temperature reaches a temperature at which the catalyst can be efficiently reduced. Since the temperature can be measured, the reducing agent adsorption amount of the SCR catalyst and its reduction and purification process can be further appropriately executed.
By doing in this way, by making the spray amount of NOx reducing agent into an appropriate amount, waste of the reducing agent (urea water) can be omitted, and the slip amount of NH 3 can be suppressed, and the operating cost of the engine 1 can be reduced.

A third embodiment will be described based on FIGS. 5A, 5B, and 5C.
FIG. (A) shows a schematic structural diagram of the SCR catalyst portion of the SCR catalyst purification device. As shown in FIG. (C), the SCR catalyst 70 divided into four substantially equally in the circumferential direction in the exhaust passage of the exhaust pipe 2. (70a, 70b, 70c and 70d) are arranged. Four inlet side temperature sensors 71 (71a, 71b, 71c and 71d) are arranged along the four divided portions on the inlet side of the SCR catalyst 70 in the exhaust passage. Further, four outlet side temperature sensors 71 (71e, 71f, 71g and 71h) are disposed on the outlet side of the SCR catalyst 70 in the exhaust passage at positions facing the inlet side temperature sensor 71 and the SCR catalyst 70. ing.

Further, on the upstream side of the inlet side temperature sensor 71 of the exhaust passage, four mixture agents of air and urea water that are pumped from the dosing module 73 that adjusts the amount of urea water jetted are sprayed into the exhaust gas of the exhaust passage. Spray nozzles 72 (72a, 72b, 72c and 72d) are disposed.
The four spray nozzles 72 are arranged substantially equally in the circumferential direction in the vicinity of the center position of the exhaust gas inlet side of each of the SCR catalysts 70 (70a, 70b, 70c and 70d) divided into four substantially equally in the circumferential direction. ing.
Further, the arrangement and spray pattern of each of the spray nozzles 72 (72a, 72b, 72c and 72d) are as shown in FIG. It is arrange | positioned so that spraying is possible.

As described above, the SCR catalyst 70 is divided into four parts in the circumferential direction. As a result, the exhaust gas drifts due to the bending of the exhaust pipe 2 and the exhaust gas does not pass through the entire SCR catalyst 70 evenly.
Therefore, the internal temperature is measured by the temperature sensor 71 71a, 71b, 71c and 71d for each of the SCR catalyst 70a, 70b, 70c and 70d divided into four in the circumferential direction, and based on the measured temperatures. The spray amount of the reducing agent (NH 3) is individually determined for each catalyst by the controller 80 (see FIG. 1). The determined spray amounts are sprayed individually from the spray nozzles 72a, 72b, 72c and 72d to the catalysts 70a, 70b, 70c and 70d.
The control method is, for example,
・ Denitration rate: Low & NH3 slip rate: Low ⇒ Increase in spray amount of applicable spray nozzle ・ Denitration rate: Low & NH3 slip rate: High ⇒ Decrease in spray amount of applicable spray nozzle ・ Denitration rate: High & NH3 slip Rate: Low ⇒ Maintain or increase the spray amount of the spray nozzle
(Increase amount until denitration rate reaches theoretical increase amount)
・ Denitration rate: High & NH3 slip rate: High ⇒ Reduce the spray amount of the spray nozzle.

となる。ガス熱量各夫々の単位体積あたりの変化に対し、ＳＣＲ触媒から流出した排ガスに残った温度（熱）と、排ガスからＳＣＲ触媒に移動した熱として表される。
一方、排ガス側から移動した伝熱によるＳＣＲ触媒の温度変化
即ち、［ＳＣＲ触媒側の温度変化］＝［ＳＣＲ触媒と排ガス間の熱移動］
＋［隣り合う触媒からの熱移動］
となり、計算式では

となり、ＳＣＲ触媒の温度上昇分が算出される。
尚、上述の但し以外の記号は第一実施形態の伝熱式（段落〔００２５〕）で使用した記号と同じなので、本欄では省略する。
また、制御方法についても、夫々分割された触媒毎に、第一実施形態で説明した内容と同じなので、説明を省略する。 Further, the internal temperature estimating means 81 of each of the divided catalysts 70a, 70b, 70c and 70d of the SCR catalyst 70 is calculated by the following equation.
The catalyst temperature estimation unit 81 (see FIG. 1) includes temperature sensors 71a, 71b, 71c and 71d that detect the exhaust gas temperature at the inlet of the SCR catalyst 70, and temperature sensors 71e, 71f that detect the exhaust gas temperature at the outlet side of the SCR catalyst 70, It calculates | requires with the following heat-transfer types based on 71g and 71h.
<Heat transfer type>
For each of the catalysts 70a, 70b, 70c and 70d, the heat transfer relationship between the honeycomb structured solid and the exhaust gas is as follows.
That is, [temperature change on exhaust gas side] =-[convection term] + [heat transfer between SCR catalyst and exhaust gas]

It becomes. It is expressed as the temperature (heat) remaining in the exhaust gas flowing out from the SCR catalyst and the heat transferred from the exhaust gas to the SCR catalyst with respect to the change per unit volume of each gas calorific value.
On the other hand, the temperature change of the SCR catalyst due to heat transfer from the exhaust gas side, that is, [temperature change on the SCR catalyst side] = [heat transfer between the SCR catalyst and exhaust gas]
+ [Heat transfer from adjacent catalyst]
And in the calculation formula

Thus, the temperature increase of the SCR catalyst is calculated.
Since symbols other than those described above are the same as those used in the heat transfer type of the first embodiment (paragraph [0025]), they are omitted in this section.
Also, the control method is the same as that described in the first embodiment for each divided catalyst, and thus the description thereof is omitted.

In the third embodiment, the catalyst is divided into four parts (70a, 70b, 70c and 70d) in the circumferential direction of the SCR catalyst 70, and the spray amount can be adjusted for each of the divided catalysts. In particular, since it is possible to cope with the drift of exhaust gas due to bending of the exhaust pipe 2, etc., it is possible to efficiently denitrate, to reduce the amount of urea water used, and to reduce the slip amount of NH3.
Furthermore, generally, the catalyst has a large amount of exhaust gas passing through the center, and thus the temperature of the catalyst also increases, so that the reducing agent from each spray nozzle overlaps and adsorbs to the center to increase the amount of reducing agent in the center. By doing so, the efficiency of the denitration action is improved.
In addition, since spray is performed by a plurality of spray nozzles 72a, 72b, 72c and 72d, the nozzle diameter can be reduced, and it can be used in common for large engines (increase the number of spray nozzles), thereby reducing costs. It becomes possible.
In addition, since a plurality of spray nozzles are provided corresponding to the divided catalysts, even if any of the spray nozzles fails, it is possible to prevent an extreme decrease in the denitration performance.

In the third embodiment, an example in which the SCR catalyst is equally divided into four in the circumferential direction is shown. However, it is not necessary to divide the SCR catalyst equally in the circumferential direction due to the drift of the exhaust gas, If many reducing agents adhere, the same effect as this embodiment can be obtained easily.
Furthermore, in the third embodiment, the spray nozzle 72 corresponding to each divided catalyst is arranged.
Based on the measured temperature of the catalyst 70 by the temperature sensor 71, a temperature distribution divided in the circumferential direction of the catalyst 70 is calculated. The number of spray nozzles 72 corresponding to the calculated temperature distribution is arranged, the reducing agent spray amount to the catalyst is calculated by the controller 80 according to the temperature for each temperature distribution, and the spray nozzle 72 reduces the temperature distribution for each temperature distribution. Even if the agent is sprayed individually, the same effect as in the third embodiment can be obtained.

A fourth embodiment will be described with reference to FIGS. FIG. 6 illustrates a case where an NH3 slip catalyst 83 (hereinafter referred to as NH3 slip catalyst) is disposed on the downstream side of the SCR catalyst 82 mounted on the exhaust pipe 81.
In addition, the same code | symbol is used for the same components as 1st Embodiment.
Depending on the contents of exhaust gas regulations, particularly in trucks and buses equipped with diesel engines, an NH3 slip catalyst 83 is disposed downstream of the SCR catalyst 82 to efficiently purify NOx and NH3 in the exhaust gas.
In FIG. 6, reference numeral 80 denotes a NOx purification device, and the exhaust gas discharged from the engine 1 is guided to the exhaust pipe 81. An NH3 slip catalyst 83 is disposed in the exhaust pipe 81 at intervals from the DOC catalyst 7 (oxidation catalyst) that oxidizes HC, CO, NO, etc., the spray nozzle 84, the SCR catalyst 82, and the SCR catalyst 82 from the upstream side of the exhaust system. ing. On the upstream side of the exhaust system of the SCR catalyst 82, an inlet side temperature sensor 84 is disposed on the exhaust gas inlet of the SCR catalyst 82 downstream of the spray nozzle 84, and an outlet side temperature sensor 86 is disposed on the exhaust gas outlet side of the SCR catalyst 82. Yes.
The SCR catalyst 82 is obtained by adhering a catalyst component to a divided catalyst carrier having a honeycomb structure, and is accommodated in the exhaust pipe 2. Vanadium-based and zeolite-based catalysts are known as selective reduction catalysts for NOx. The SCR catalyst 11 selectively reduces NOx in the exhaust gas. When the NH3 is adsorbed on the SCR catalyst 11, the NOx is reduced with high efficiency in the region where the temperature of the SCR catalyst 11 exceeds about 200 ° C. have.
Moreover, Pt (platinum) type | system | group and Pt-Pd (platinum * palladium) type | system | group are used as an oxidation catalyst (DOC).

Since the estimated internal temperature of the SCR catalyst 82 is performed in the same manner as in the first embodiment described above, description thereof is omitted.
The NH3 slip catalyst 83 can oxidize NH3 that has not been used for NOx purification by the SCR, and can purify (denitrate) NOx by the reducing action of NH3.
Furthermore, trapping of suspended particulate matter (PM) in unburned exhaust gas is also performed.

The control flow will be described based on FIG.
In step S30, the engine output (load) state is calculated from the engine speed Ne and torque Tq. In step S31, the NOx emission amount is calculated from the output state of step S30.
In step S32, the spray amount of urea water is calculated based on the NOx amount calculated in step S31. The urea water spray amount calculated in step S33 is sprayed into the exhaust gas from the spray nozzle 84 which is a reducing agent supply means. In step S34, the temperature of the exhaust gas is measured by the inlet side temperature sensor 85 and the outlet side temperature sensor 86 which are temperature measuring means. In step S35, the internal temperature of the SCR catalyst 82 is calculated (SCR catalyst temperature estimation unit). Since the formula for the catalyst internal temperature is the same as the <heat transfer type> in the first embodiment, the description thereof is omitted in this embodiment.

In step S36, based on the internal temperature of the SCR catalyst 82 calculated in step S35, the internal temperature of the SCR catalyst 82 and the NOx purification rate% according to the engine load (engine speed Ne and torque Tq) state are mapped (see FIG. 8). ). The NOx purification rate% differs depending on the engine load, and is created from experimental value data.
In step S37, the NH3 slip amount from the SCR catalyst 82 is calculated by the NH3 slip amount calculator.
That is, NH3 slip amount = urea water ejection amount−purified NOx amount.
However, purification NOx amount = NOx emission amount from engine × NOx purification rate.

In step S38, the NH3 slip catalyst activity determination unit measures the exhaust gas that has passed through the SCR catalyst 82 by the outlet side temperature sensor 86, and estimates the temperature of the NH3 slip catalyst 83 from the measured value.
In step S39, it is determined whether the temperature of the NH3 slip catalyst 83 estimated in step S38 is in an active state. If it is not in the active state (No), the process returns to step S30 and is repeated until the NH3 slip catalyst 83 is in the active state.
When the temperature of the NH3 slip catalyst 83 reaches the temperature at which it is activated, it is determined that the NH3 slip catalyst 83 is in the active state.
In this case, spraying of urea water is stopped. The reason is that the portion of the sprayed urea water that is not used for NOx purification is adsorbed by the NH3 slip catalyst as NH3. The NH3 adsorbed on the NH3 slip catalyst may be detached due to a rise in the temperature of the NH3 slip catalyst or a change in the flow rate of the exhaust gas.
On the other hand, if it is in the active state (Yes), the process proceeds to step S40. In step S <b> 40, (inlet side temperature sensor 85 detected value + outlet side temperature sensor 86 detected value) / 2 is compared with the internal temperature of the SCR catalyst 82. This is because, in the operating state of the engine 1, the exhaust gas is higher and the internal temperature of the SCR catalyst 82 may be higher. The higher the temperature, the higher the temperature of the denitration rate. select. There are a wide variety of operating conditions of general-purpose engines, such as load fluctuations, repeated operation of the engine, and pauses. This is because even in such a case, a more efficient denitration action and a reduction in the slip amount of NH 3 can be achieved.

If it is determined in step S40 that the internal temperature of the SCR catalyst 82 is higher (No), the process proceeds to step S41. In step S41, the NH 3 slip amount of the SCR catalyst 82 is obtained based on the internal temperature of the SCR catalyst 82. In step S42, the NOx slip amount calculation unit obtains the NOx slip amount from the SCR catalyst 82. As a calculation method, the NOx emission rate from the engine 1 is obtained from the NOx purification rate based on the SCR catalyst temperature and engine load (Ne · tq) in FIG. In step S43, the amount of NH3 required to denitrate the NOx slip amount obtained in step S42 with the NH3 slip catalyst is calculated. FIG. 9 is a map of the amount of NH3 required for denitration with an NH3 slip catalyst.
That is, the amount necessary for NOx purification of NH3 depending on the temperature of the NH3 slip catalyst with respect to the amount of NOx slipped by the SCR catalyst 82 is created from experimental values.
Accordingly, assuming that the temperature of the exhaust gas that has passed through the SCR catalyst 82 is detected by the outlet side temperature sensor 86 as the temperature of the NH3 slip catalyst, the amount of NOx that slips the SCR catalyst 82 from FIG. Then, NH3 required for reducing and purifying NOx with the NH3 slip catalyst is calculated.
In step S44, the NH3 slip amount obtained in step S41 is compared with the required NH3 in the NH3 slip catalyst obtained in step S43. If urea water is insufficient, the urea water spray amount is increased. Correction is made so that the amount of NH3 slip required to purify the slipped NOx is obtained. The corrected value is output to step S33, and urea water is sprayed into the exhaust gas by the urea water spray device 87.

If the temperature of (inlet side temperature sensor 85 detected value Tg_i + outlet side temperature sensor 86 detected value Tg_o) / 2 is higher than the internal temperature of the SCR catalyst 82 in step S40, the process proceeds to step S45 as Yes. In step S45, based on the temperature of (detection value Tg_i and detection value Tg_o) / 2,
The NH3 slip amount of the SCR catalyst 82 is obtained. In step S46, the NOx slip amount of the SCR catalyst 82 is obtained. In step S47, the amount of NH3 required for denitration is calculated. In step S48, the urea water spray amount is corrected. The corrected value is output to step S33, and urea water is sprayed into the exhaust gas by the urea water spray device 87.
Since steps S46 to S48 have the same control content as steps S42 to S44, the description is simplified.

  According to the fourth embodiment that requires the NH3 slip catalyst 83 on the downstream side of the exhaust system of the SCR catalyst 82, the SCR catalyst is intentionally reduced and the slip amount of NH3 and NOx at the SCR catalyst is increased. , Make the most of NOx denitration with NH3 slip catalyst, reduce the cost by reducing the SCR catalyst, and reduce the overall shape of the general-purpose engine, increasing the flexibility in combination with work machines, Simplification is possible.

  For exhaust gas purification of diesel engines, urea water is adsorbed on the SCR catalyst to efficiently purify NOx in the exhaust gas, and slip of NH3 hydrolyzed from urea water is reduced, so that denitration with higher accuracy is achieved. Diesel engine exhaust gas purification system that reduces diesel engine operating costs due to a decrease in the amount of urea water used.

DESCRIPTION OF SYMBOLS 1 Engine 5, 80 Controller 6 Urea water spray apparatus 11, 70, 82 SCR catalyst 12 Inlet side temperature sensor 13 Outlet side temperature sensor 51 Exhaust gas calculation means 52 NOx discharge | emission amount calculation means 53 Urea water spray amount target calculation means 54 Exhaust gas average temperature Calculation means 55, 81 Catalyst temperature estimation unit 56 Target adsorption amount calculation means 57 Actual adsorption amount calculation means 61 Urea water spray control device 62 Spray nozzle 83 NH3 slip catalyst

Claims (8)

  An SCR catalyst that is provided in the exhaust system of the engine and that selectively reduces NOx in the exhaust gas by adsorbing NH3 as a reducing agent, a reducing agent supply means that supplies the reducing agent to the SCR catalyst, and an inlet of the SCR catalyst A temperature measuring means for measuring the temperature of the exhaust gas at the outlet, an SCR catalyst temperature estimating section for estimating the internal temperature of the SCR catalyst based on the exhaust gas temperature difference between the inlet and the outlet detected by the temperature measuring means, and A control unit having a reducing agent supply amount control unit that calculates an adsorption amount of the NH3 to the SCR catalyst based on an internal temperature of the SCR catalyst, and calculates a supply amount of the reducing agent based on the adsorption amount; In the engine NOx purification device provided, as the SCR catalyst temperature (initial value) for calculating the reducing agent supply amount by the reducing agent supply amount control unit at the time of starting or cooling the engine, The exhaust gas temperature average value of the inlet and the outlet of the SCR catalyst based on the measurement result of the temperature measuring means is compared with the internal temperature of the SCR catalyst estimated by the SCR catalyst temperature estimation unit, and the exhaust gas temperature When the average value is higher than or equivalent to the internal temperature of the SCR catalyst, the exhaust gas temperature average value is used. When the internal temperature of the SCR catalyst is higher, the temperature of the SCR catalyst is used as the initial value to supply the reducing agent. An NOx purification device for an engine characterized by calculating an amount and controlling the reducing agent to be supplied from the reducing agent supply means to the SCR catalyst.   The SCR catalyst temperature estimation unit continues to estimate the SCR catalyst temperature even after the engine is stopped, and the SCR catalyst estimated temperature by the SCR catalyst temperature estimation unit and the SCR catalyst inlet detected by the temperature measuring means are When the exhaust gas temperature becomes lower than the exhaust gas temperature, the estimation of the SCR catalyst temperature is finished. When the estimated SCR catalyst temperature is higher than the exhaust gas temperature at the SCR catalyst inlet and the engine is restarted, the estimation of the catalyst temperature is performed. The reductant supply amount is calculated using the estimated catalyst temperature value at the restart as the initial value, and the reductant is controlled to be supplied from the reductant supply means to the SCR catalyst. The engine NOx purification device according to claim 1.   The SCR catalyst temperature estimation unit measures exhaust gas temperatures at the SCR catalyst inlet and the SCR catalyst outlet, and estimates the internal temperature of the SCR catalyst based on the exhaust gas temperature, the heat capacity and heat transfer characteristics of the catalyst. The NOx purification device for an engine according to claim 1 or 2.   2. The engine NOx purification device according to claim 1, wherein the temperature of the SCR catalyst when the engine is in a cold state is directly measured by a temperature sensor, and the measured value is used as the initial value. A cylindrical SCR catalyst that is provided in an exhaust system of an engine and selectively reduces NOx in exhaust gas by adsorbing NH3 and having a plurality of regions divided in the circumferential direction, and a reducing agent upstream of the SCR catalyst A reducing agent supply means for supplying the reducing agent to the SCR catalyst by arranging a plurality of spray nozzles for ejecting NH3 or urea water at equal intervals in the circumferential direction of the SCR catalyst, and exhaust gas of the SCR catalyst Temperature sensors arranged at the inlet and outlet of the SCR catalyst with the SCR catalyst sandwiched therebetween, respectively, and the inside of the SCR catalyst based on the temperature measured by the temperature measuring means A catalyst temperature estimation unit that estimates a temperature distribution for each temperature sensor facing the temperature, and calculates the adsorption amount of the NH3 to the SCR catalyst based on the internal temperature of the SCR catalyst, and based on the adsorption amount In the NOx purification apparatus for an engine and a control unit having a reducing agent supply amount control section for calculating a supply amount of the reducing agent for each of the plurality of spray nozzles,
The reducing agent supply amount control unit controls the reducing agent ejection amount from each spray nozzle based on the temperature of the temperature distribution detected by the catalyst temperature estimation unit. .   Each of the plurality of spray nozzles is disposed to face each of the SCR catalysts in the plurality of divided regions, and the spray region of the reducing agent sprayed from each of the spray nozzles to the SCR catalyst is the all spray nozzles. The spray nozzle is sprayed over the entire area of the exhaust gas inlet side of the SCR catalyst, and the spray nozzles are formed so that the spray agent is sprayed at least in the center of the SCR catalyst. The engine NOx purification device according to claim 5, wherein   Each of the plurality of spray nozzles is provided with a plurality of spray nozzles arranged in the distribution region of the temperature distribution distributed for each of the temperature sensors of the SCR catalyst in the plurality of divided regions. An engine NOx purification device as defined in claim 5.   An SCR catalyst that is provided in an engine exhaust system, selectively adsorbs NH3 as a reducing agent and selectively reduces NOx in exhaust gas, and is arranged at a distance from the SCR catalyst downstream of the SCR catalyst in the exhaust system; NH3 slip catalyst for purifying NOx and NH3 in exhaust gas, reducing agent supply means for supplying the reducing agent to the SCR catalyst, temperature measuring means for measuring the temperature of the exhaust gas at the inlet and outlet of the SCR catalyst, An SCR catalyst temperature estimating unit for estimating the internal temperature of the SCR catalyst based on a difference in exhaust gas temperature between the inlet and the outlet detected by the temperature measuring means, and the internal temperature of the SCR catalyst and the engine with respect to the urea water spray amount An NH3 slip amount calculation unit for calculating the NH3 slip amount from the SCR catalyst based on a NOx purification rate by a load, based on the NOx purification rate The NOx slip amount calculating unit for calculating the NOx slip amount in the SCR catalyst, the reducing agent amount calculating unit for calculating the reducing agent amount necessary for the reduction of the NOx slip amount, and detection of the exhaust gas temperature at the outlet by the temperature measuring means And a control means having an NH3 slip catalyst activity determining unit for determining whether the NH3 slip catalyst is in an activated state based on a temperature, wherein the NH3 slip catalyst is determined by the NH3 slip catalyst activity determining unit. Is determined to be active, the NH3 slip amount and NOx slip amount from the SCR catalyst are calculated based on the internal temperature of the SCR catalyst, and the NOx slip amount is purified by the NH3 slip catalyst. As the internal temperature value of the SCR catalyst for obtaining the amount of the reducing agent necessary for the measurement, the temperature measuring means The average value of the exhaust gas temperature at the inlet and the outlet of the SCR catalyst based on the measurement result is compared with the internal temperature of the SCR catalyst estimated by the SCR catalyst temperature estimation unit. A NOx purification device for an engine, characterized in that the internal temperature of the catalyst is calculated by the reducing agent amount calculation unit and output to the reducing agent supply means.

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