KR101461869B1 - Method for preventing absorption of hydrocarbon in selective catalytic reduction catalyst and system thereof - Google Patents

Abstract

The present invention relates to a method and apparatus for preventing the occlusion of hydrocarbons in a selective reduction catalyst which causes a hydrocarbon to be desorbed by increasing the temperature of the selective reduction catalyst when the hydrocarbon is occluded in the selective reduction catalyst.

The method for preventing the occlusion of hydrocarbons in the selective reduction catalyst (SCR catalyst) for reducing the nitrogen oxide included in the exhaust gas according to the embodiment of the present invention includes: predicting the temperature of the downstream end of the selective reduction catalyst; Measuring the temperature of the downstream end of the selective reduction catalyst; Comparing a value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst with the set temperature; And entering the fast heat-up mode when the value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is equal to or higher than the set temperature.

SCR catalysts, soot filters, hydrocarbons, nitrogen oxides

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method for preventing the adsorption of hydrocarbons in a selective reduction catalyst,

The present invention relates to a method and apparatus for preventing the adsorption of hydrocarbons in a selective reduction catalyst, and more particularly, to a selective reduction catalyst for increasing the temperature of a selective reduction catalyst and desorbing hydrocarbons To a method and device for preventing the storage of hydrocarbons therein.

Generally, the exhaust gas discharged from the engine through the exhaust manifold is guided to a catalytic converter formed in the middle of the exhaust pipe to be purified, passes through the muffler and attenuates the noise, and then is discharged to the atmosphere through the tail pipe. The above-described catalytic converter is a type of diesel particulate filter (DPF), which treats contaminants contained in exhaust gas. A catalyst carrier for trapping particulate matter (PM) contained in the exhaust gas is formed in the catalytic converter, and various exhaust gases discharged from the engine are purified through a chemical conversion process.

A selective catalytic reduction (SCR) catalyst is one of the catalyst types applied to the above catalytic converter. Selective reduction (SCR) catalysts are named selective catalytic reduction in the sense that reducing agents such as Urea, Ammonia, carbon monoxide and hydrocarbons (HC) react better with nitrogen oxides in oxygen and nitrogen oxides have.

When the engine starts to operate, exhaust gas is generated. The generated exhaust gas is discharged to the outside of the vehicle through the exhaust pipe. In this process, the nitrogen oxide contained in the exhaust gas is removed from the SCR catalyst mounted on the exhaust pipe by the reducing agent injected from the injection module mounted on the exhaust pipe.

At the beginning of operation of the engine, since the temperature of the SCR catalyst is lower than the SCR catalyst activation temperature, the nitrogen oxide contained in the exhaust gas is not reduced. Therefore, the concentration of nitrogen oxides at the downstream of the SCR catalyst is high.

Thereafter, when the temperature of the SCR catalyst rises and reaches the SCR catalyst activation temperature, the nitrogen oxide contained in the exhaust gas starts to be reduced. Therefore, the concentration of nitrogen oxides at the end of the SCR catalyst is lowered. At this time, hydrocarbons contained in the exhaust gas start to be occluded in the SCR catalyst. When the amount of hydrocarbons occluded in the SCR catalyst is small, the purifying performance of the SCR catalyst hardly drops. However, as the amount of hydrocarbons occluded in the SCR catalyst increases, the purification performance of the SCR catalyst deteriorates, and the concentration of nitrogen oxides at the downstream end of the SCR catalyst increases.

According to the conventional exhaust device equipped with the SCR catalyst, the predetermined amount of the reducing agent is injected into the exhaust gas irrespective of whether or not the hydrocarbon is occluded in the SCR catalyst. Therefore, there is a problem that the purification performance of nitrogen oxides in the SCR catalyst deteriorates.

In addition, a method of predicting the amount of hydrocarbons occluded in the SCR catalyst and regulating the amount of the reducing agent according to the predicted hydrocarbon storage amount has been devised, but it has been difficult to accurately predict the amount of hydrocarbons occluded in the SCR catalyst.

Furthermore, the above-described methods prevent hydrocarbons from being stored in the SCR catalyst, and thus can not fundamentally prevent deterioration of the nitrogen oxide purification performance of the SCR catalyst.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method for preventing the storage of hydrocarbons in an SCR catalyst in which the efficiency of an SCR catalyst is increased by reducing the amount of hydrocarbons occluded in the SCR catalyst And a device therefor.

According to an aspect of the present invention, there is provided a method for preventing the storage of hydrocarbons in a selective reduction catalyst (SCR catalyst) for reducing nitrogen oxides contained in an exhaust gas, the method comprising: predicting a temperature at a downstream end of a selective reduction catalyst; Measuring the temperature of the downstream end of the selective reduction catalyst; Comparing a value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst with the set temperature; And entering the fast heat-up mode when the value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is equal to or higher than the set temperature.

If the value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is less than the set temperature, the normal mode can be entered.

If the measured temperature at the downstream end of the SCR catalyst is greater than the desorption temperature of the hydrocarbon, it can always enter the normal mode.

In the rapid heating-up mode, post-injection may proceed.

When the measured temperature at the rear end of the SCR catalyst is less than the minimum catalyst activation temperature, it can always enter the normal mode.

The above method can be repeatedly performed as long as the engine is driven.

An apparatus for preventing the storage of hydrocarbons in a selective reduction catalyst according to another embodiment of the present invention includes: an engine for generating a driving force of a vehicle by burning fuel; An exhaust pipe through which exhaust gas generated in the engine flows; A spray module mounted on the exhaust pipe and spraying a reducing agent to the exhaust gas; A selective reduction catalyst for reducing the nitrogen oxide contained in the exhaust gas mixed with the reducing agent; A temperature sensor for measuring a temperature of a downstream end of the selective reduction catalyst (SCR catalyst); And a control unit for calculating a predicted temperature at the rear end of the SCR catalyst and comparing the measured temperature at the rear end of the SCR catalyst with the predicted temperature at the rear end of the SCR catalyst to determine the normal mode or the rapid temperature rise mode.

The control unit may enter the rapid temperature increase mode when the value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is equal to or higher than the set temperature.

Wherein a value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from a measured temperature of the downstream end of the SCR catalyst is less than a set temperature or a measured temperature at the downstream end of the SCR catalyst is greater than a desorption temperature of the hydrocarbon, If the temperature is lower than the activation temperature, the controller can enter the normal mode.

In the rapid heating-up mode, the controller can advance the temperature of the exhaust gas including the post-injection.

As described above, according to the present invention, if hydrocarbons are stored in the SCR catalyst, the exhaust gas is rapidly heated to induce desorption of hydrocarbons in the SCR catalyst. Therefore, the purification performance of the SCR catalyst is improved.

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

1 is a schematic view of an exhaust apparatus to which an apparatus for preventing the storage of hydrocarbons in a selective reduction catalyst according to an embodiment of the present invention is applied.

1, the exhaust system includes an engine 10, an exhaust pipe 20, an exhaust gas recirculation (EGR) device 30, a particulate filter 40, an SCR catalyst (50), and a control unit (60).

The engine 10 converts chemical energy into mechanical energy by burning a mixture in which fuel and air are mixed. The engine 10 is connected to the intake manifold 18 to receive air into the combustion chamber 12 and connected to the exhaust manifold 16 so that the exhaust gas generated in the combustion process is collected in the exhaust manifold 16. [ And then discharged to the outside of the vehicle. An injector 14 is mounted in the combustion chamber 12 to inject fuel into the combustion chamber 12.

Although a diesel engine is exemplified here, a gasoline engine may be used. When a gasoline engine is used, the mixer is introduced into the combustion chamber 12 through the intake manifold 18, and an ignition plug (not shown) for ignition is mounted on the combustion chamber 12.

Further, an engine having various compression ratios, preferably compression ratios of 16.5 or less, can be used.

The exhaust pipe 20 is connected to the exhaust manifold 16 to exhaust the exhaust gas to the outside of the vehicle. A particulate filter 40 and an SCR catalyst 50 are mounted on the exhaust pipe 20 to remove particulate matters (PM), hydrocarbons, carbon monoxide, and nitrogen oxides contained in the exhaust gas. For this purpose, a diesel oxidation catalyst (DOC) (not shown) may be provided on the exhaust pipe 30 to remove hydrocarbons and carbon monoxide.

The exhaust gas recirculation device 30 is mounted on the exhaust pipe 20 so that the exhaust gas discharged from the engine 10 passes through the exhaust gas recirculation device 30. The exhaust gas recirculation device 30 is connected to the intake manifold 18 to control the combustion temperature by mixing a part of the exhaust gas with air. The combustion temperature is controlled by the control unit 60. That is, the controller 60 controls the amount of exhaust gas supplied to the intake manifold 18 by controlling ON / OFF of an EGR valve (not shown) provided in the exhaust gas recirculation device 30.

A soot filter (40) is mounted on an exhaust pipe (20) behind the exhaust gas recirculation device (30). The particulate filter 40 collects the particulate matter contained in the exhaust gas discharged through the exhaust pipe 20. In addition, the soot filter 40 may be coated with an oxidation catalyst. This oxidation catalyst oxidizes hydrocarbons and carbon monoxide contained in the exhaust gas to carbon dioxide and oxidizes nitrogen monoxide contained in the exhaust gas to nitrogen dioxide. The oxidation catalyst may be coated on a certain portion of the soot filter 40 or may be uniformly coated on the entire area of the soot filter 40.

A differential pressure sensor 45 is mounted on the exhaust pipe 20. The differential pressure sensor 45 measures a pressure difference between the front end and the rear end of the particulate filter 40 and transmits a signal to the controller 60. The control unit 60 may control the particulate filter 40 to be regenerated when the pressure difference measured by the differential pressure sensor 45 is equal to or greater than a set value. In this case, the soot trapped in the particulate filter 40 can be burned by injecting fuel in the injector 40.

An injection module (70) is mounted on an exhaust pipe (20) behind the smoke filter (40). The injection module (70) injects a reducing agent into the exhaust gas that has passed through the particulate filter (40). The reducing agent may be ammonia. Generally, in the injection module 70, the element Urea is injected and the injected element is decomposed into ammonia. That is, the element is decomposed into ammonia by the following formula.

_{(NH 2) 2 CO → NH} 3 + NHCO

HNCO + H ₂ O → NH ₃ + CO ₂

The exhaust gas mixed with the reducing agent is supplied to the SCR catalyst (50).

The SCR catalyst 50 is installed at the downstream end of the injection module 70 and includes a zeolite catalyst in which a transition metal is ion-exchanged. The SCR catalyst 50 reduces the nitrogen oxide contained in the exhaust gas to nitrogen gas by using the reducing agent injected from the injection module 70.

The chemical formula of the SCR catalyst 50 is as follows.

4NH ₃ + 4NO + O ₂ ? 4N ₂ + 6H ₂ O

_{2NH 3 + NO + NO 2 →} 2N 2 + 3H 2 O

8NH ₃ + 6NO ₂ ? 7N ₂ + 12H ₂ O

A temperature sensor 55 is mounted on the exhaust pipe 20 behind the SCR catalyst 50 to measure the temperature of the downstream end of the SCR catalyst 50. The temperature sensor 55 is connected to the controller 60 and transmits the measured temperature of the SCR catalyst downstream to the controller 60.

The control unit 60 controls the amount of fuel injected from the injector 14 based on the operating state of the engine 10 and controls the amount of fuel injected from the injector 14 based on the pressure difference measured by the differential pressure sensor 45 And controls post-injection. The control unit 60 calculates a predicted temperature at the downstream of the SCR catalyst and compares the predicted temperature at the downstream end of the SCR catalyst with the measured temperature at the downstream end of the SCR catalyst to determine the entry into the normal mode or the rapid temperature rise mode. The prediction of the downstream temperature of the SCR catalyst proceeds based on the engine operation time, the operation history of the engine, and the fuel injection amount. In Fig. 3, the dotted line indicates the predicted temperature of the SCR catalyst rear end.

If the control unit 60 determines that the hydrocarbon is not stored in the SCR catalyst 50, the control unit 60 controls the injector 14 to inject the fuel normally, (70).

If the control unit 60 determines that the rapid heating mode is entered, the control unit 60 controls the injector 14 to inject fuel. The post-injected fuel increases the temperature of the exhaust gas, so that the temperature in the SCR catalyst 50 rises above the desorption temperature of the hydrocarbon. Therefore, hydrocarbons occluded in the SCR catalyst 50 are desorbed.

Here, the hydrocarbon is referred to as both the exhaust gas and the compound composed of carbon and hydrogen contained in the fuel.

Hereinafter, a method for preventing the adsorption of hydrocarbons in the selective reduction catalyst according to an embodiment of the present invention will be described in detail.

2 is a flow chart of a method for preventing the occlusion of hydrocarbons in a selective reduction catalyst according to an embodiment of the present invention.

As shown in FIG. 2, when the engine 10 starts operating, the controller 60 predicts the temperature of the downstream end of the SCR catalyst (S100). As described above, the SCR catalyst rear end temperature is predicted based on the engine running time, the operation history of the engine, and the fuel injection amount and the like. In this case, the SCR catalyst rear end temperature is predicted on the assumption that the SCR catalyst 50 does not store hydrocarbons.

The temperature sensor 55 measures the temperature of the SCR catalyst rear end (S110), and transmits the measured value to the controller 60. [

Then, the control unit 60 compares the measured temperature at the rear end of the SCR catalyst with the predicted temperature at the rear end of the SCR catalyst.

When hydrocarbons are stored in the SCR catalyst 50, heat is generated. The heat thus generated makes the measured temperature at the downstream end of the SCR catalyst higher than the predicted temperature at the downstream end of the SCR catalyst calculated on the assumption that the hydrocarbon is not occluded in the SCR catalyst 50. That is, as shown in FIG. 3, the temperature measured at the downstream end of the SCR catalyst differs from the predicted temperature at the downstream end of the SCR catalyst, and this difference is related to the amount of hydrocarbon occluded in the SCR catalyst 50. Therefore, as the amount of the hydrocarbon occluded in the SCR catalyst 50 increases, the measured temperature at the downstream end of the SCR catalyst becomes higher than the predicted temperature at the downstream end of the SCR catalyst.

The control unit 60 determines whether a value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is less than a set temperature (S120). Here, the set temperature may be 5 ° C, but is not limited thereto. The set temperature can be arbitrarily set by the designer in consideration of the purification efficiency of the SCR catalyst (50).

If the value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is less than the predetermined temperature, the control unit 60 enters the normal mode at step S130. In this case, assuming that no hydrocarbon is stored in the SCR catalyst 50, the injection module 70 is controlled so as to control the injector 14 so as to inject the fuel normally and to inject an amount of the predetermined reducing agent.

If the value obtained by subtracting the predicted temperature at the rear end of the SCR catalyst from the measured temperature at the rear end of the SCR catalyst is greater than or equal to the set temperature at step S120, the control unit 60 determines whether the measured temperature at the rear end of the SCR catalyst is greater than the desorption temperature of the hydrocarbon ).

If the measured temperature at the downstream end of the SCR catalyst is greater than the desorption temperature of the hydrocarbon in step S140, the hydrocarbon occluded in the SCR catalyst 50 may be desorbed. Therefore, the control unit 60 enters the normal mode (S130).

If the measured temperature at the downstream end of the SCR catalyst is lower than the desorption temperature of the hydrocarbon in step S140, it is necessary to raise the temperature in the SCR catalyst 50 to the desorption temperature of the hydrocarbon. Therefore, the control unit 60 enters the rapid heating-up mode (S150). In this rapid heating-up mode, the controller 60 controls the injector 14 so that the fuel is injected backward. The post-injection of fuel raises the temperature of the exhaust gas, so that the temperature in the SCR catalyst 50 is raised to the desorption temperature of the hydrocarbon. Therefore, hydrocarbons occluded in the SCR catalyst 50 are desorbed. Further, in the rapid heating-up mode, fuel may be further injected from an additional injector (not shown) mounted on the exhaust pipe 20. [ That is, the additional injector is mounted on the exhaust pipe 20, and the control unit 60 can control the additional injector so that the fuel is further injected so that the temperature in the SCR catalyst 50 is raised to the desorption temperature of the hydrocarbon. Accordingly, in this specification and / or in the claims, post-injection should be interpreted to include additional injection.

On the other hand, when the measurement temperature at the downstream of the SCR catalyst is less than the initial catalyst activation temperature (for example, 200 ° C), nitrogen oxides may be occluded in the SCR catalyst 50 to generate heat. Therefore, when the measured temperature at the rear end of the SCR catalyst is less than the initial catalyst activation temperature, the control unit 60 enters the normal mode and does not induce desorption of hydrocarbon.

In addition, the steps from S100 to S150 are always repeatedly performed while the engine is running. Therefore, after performing step S130 or step S150, the method returns to step S100.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, Including all changes in scope that are deemed to be valid.

1 is a schematic view of an exhaust apparatus to which an apparatus for preventing the storage of hydrocarbons in a selective reduction catalyst according to an embodiment of the present invention is applied.

2 is a flow chart of a method for preventing the occlusion of hydrocarbons in a selective reduction catalyst according to an embodiment of the present invention.

FIG. 3 is a graph showing a predicted temperature and a measured temperature at the downstream of the selective reduction catalyst with respect to time. FIG.

Claims (10)

A method for preventing the occlusion of hydrocarbons in a selective reduction catalyst (SCR catalyst) for reducing nitrogen oxides contained in an exhaust gas, Predicting the temperature of the downstream end of the selective reduction catalyst; Measuring the temperature of the downstream end of the selective reduction catalyst; Comparing a value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst with the set temperature; And Entering a fast heat-up mode when a value obtained by subtracting a predicted temperature of the downstream end of the SCR catalyst from a measured temperature of the downstream end of the SCR catalyst is equal to or higher than a set temperature; ≪ / RTI > wherein the method comprises the steps of: The method according to claim 1, Wherein when the value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is less than a predetermined temperature, the normal mode is entered. 3. The method of claim 2, Wherein when the measured temperature at the downstream end of the SCR catalyst is greater than the desorption temperature of the hydrocarbon, the hydrocarbon enters the normal mode at all times. The method according to claim 1, Wherein the post-injection is advanced in the rapid heating mode. 5. The method according to any one of claims 1 to 4, Wherein when the measured temperature at the downstream end of the SCR catalyst is less than the minimum catalyst activation temperature, the system enters the normal mode at all times. 6. The method of claim 5, Wherein the method is repeatedly performed as long as the engine is driven. An engine for burning fuel to generate a driving force of the vehicle; An exhaust pipe through which exhaust gas generated in the engine flows; A spray module mounted on the exhaust pipe and spraying a reducing agent to the exhaust gas; A selective reduction catalyst for reducing the nitrogen oxide contained in the exhaust gas mixed with the reducing agent; A temperature sensor for measuring a temperature of a downstream end of the selective reduction catalyst (SCR catalyst); And A control unit for calculating a predicted temperature at the rear end of the SCR catalyst and comparing the measured temperature at the rear end of the SCR catalyst with the predicted temperature at the rear end of the SCR catalyst to determine entry into the normal mode or rapid heating mode; ≪ / RTI > wherein the selective reduction catalyst comprises a hydrocarbon. 8. The method of claim 7, Wherein the control unit enters the rapid temperature increase mode when the value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from the measured temperature of the downstream end of the SCR catalyst is equal to or higher than a set temperature. 9. The method of claim 8, Wherein a value obtained by subtracting the predicted temperature of the downstream end of the SCR catalyst from a measured temperature of the downstream end of the SCR catalyst is less than a set temperature or a measured temperature at the downstream end of the SCR catalyst is greater than a desorption temperature of the hydrocarbon, Wherein the control unit enters the normal mode when the temperature of the selective reduction catalyst is lower than the activation temperature. 8. The method of claim 7, Wherein the control unit advances the temperature of the exhaust gas including the post-injection in the rapid-temperature-increase mode.

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