KR101305187B1 - System for purifying exhaust gas and method for controlling the same - Google Patents

Abstract

The present invention relates to an exhaust gas purifying apparatus and a method of controlling the exhaust gas purifying apparatus to smoothly regenerate the soot filter by adjusting the amount of NOx discharged from the engine to make the amount of NOx slipped in the LNT catalyst constant.
Exhaust gas purifying apparatus according to an embodiment of the present invention occludes the nitrogen oxide contained in the exhaust gas in a lean atmosphere, desorbs the nitrogen oxide stored in a rich atmosphere, the nitrogen oxide desorbed according to the concentration of the nitrogen oxide Slipping LNT catalyst; A soot filter which collects particulate matter contained in the exhaust gas and regenerates the collected particulate matter using nitrogen oxide slipped from an LNT catalyst; And a controller for controlling the amount of NOx slipped by adjusting the amount of NOx discharged from the engine supplied according to the degree of deterioration of the LNT catalyst; . ≪ / RTI >

Description

Exhaust gas purification device and method for controlling the same {SYSTEM FOR PURIFYING EXHAUST GAS AND METHOD FOR CONTROLLING THE SAME}

The present invention relates to an exhaust gas purifying apparatus and a method for controlling the same. More particularly, the nitrogen oxide is desorbed from the LNT catalyst by maintaining a constant amount of NOx slipped regardless of the degree of deterioration of the LNT catalyst, and the desorbed nitrogen. An exhaust gas purifying apparatus for reducing or slipping an oxide to be used for regeneration of a soot filter and a method of controlling the same.

In general, 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 and purified, and the noise is attenuated while passing through the muffler and then released into the atmosphere through the tail pipe.

Denitrification Catalyst (DeNOx Catalyst) is a type of catalytic converter that purifies NOx contained in exhaust gas. When a reducing agent such as urea, ammonia, carbon monoxide and hydrocarbon (HC) is provided to the exhaust gas, in the nitrogen oxide reduction catalyst, the nitrogen oxide contained in the exhaust gas is subjected to redox reaction with the reducing agent. Will be reduced.

Recently, an LNT catalyst (Lean NOx Trap Catalyst) is used as the nitrogen oxide reduction catalyst. The LNT catalyst adsorbs nitrogen oxides contained in the exhaust gas when the engine is operated in a lean atmosphere, and desorbs the adsorbed nitrogen oxides to nitrogen gas when the engine is operated in a rich atmosphere.

Meanwhile, a soot filter for collecting particulate matter (PM) contained in the exhaust gas is mounted on the exhaust pipe. If excessive soot is collected in the soot filter, it becomes difficult for the exhaust gas to pass through the soot filter and the pressure of the exhaust gas becomes high. The high pressure of the exhaust gases can degrade the engine's performance and damage the soot filter. Therefore, when the amount of soot collected in the soot filter is equal to or more than the set amount, the exhaust gas is heated to burn the soot collected in the soot filter. This process is called regeneration of the soot filter.

Regeneration of such a soot filter includes natural regeneration and forced regeneration. Natural regeneration means that the nitrogen oxide contained in the exhaust gas supplies nitrogen dioxide necessary for the regeneration of soot. Forced regeneration means that after injection of fuel into the combustion chamber of the engine, the post-injected fuel is oxidized and heat of oxidation is released. It generates and burns the soot collected in the soot filter by this heat of oxidation. In the case of forced regeneration, a high regeneration temperature consumes a lot of energy to enter regeneration. Therefore, the reproduction period is long. Natural regeneration has a lower regeneration temperature compared to forced regeneration, which consumes less energy to enter regeneration. Therefore, the reproduction period can be shortened.

By the way, when the LNT catalyst is disposed upstream of the soot filter, nitrogen dioxide contained in the exhaust gas is occluded in the LNT catalyst to interfere with the natural regeneration of the soot filter.

In addition, if the LNT catalyst is new, it is difficult to supply nitrogen dioxide necessary for the natural regeneration of the soot filter because the amount of NOx slipped due to excellent purification efficiency is small.

The present invention has been made to solve the above problems, and an object of the present invention is to purify exhaust gas by changing the amount of NOx slipped by changing the amount of NOx discharged from the engine according to the degree of deterioration of the LNT catalyst. An exhaust gas purifying apparatus for naturally regenerating a soot of a soot filter of a device, regardless of the degree of degradation of an LNT catalyst, and a method of controlling the same.

In order to solve the above problems, the exhaust gas purifying apparatus according to the embodiment of the present invention occludes the nitrogen oxide contained in the exhaust gas in a lean atmosphere, desorbs the nitrogen oxide stored in a rich atmosphere, the nitrogen oxide LNT catalyst for slipping the desorbed nitrogen oxides according to the concentration of; A soot filter which collects particulate matter contained in the exhaust gas and regenerates the collected particulate matter using nitrogen oxide slipped from an LNT catalyst; And a controller for controlling the amount of NOx slipped by adjusting the amount of NOx discharged from the engine supplied according to the degree of deterioration of the LNT catalyst; . ≪ / RTI >

The controller may maintain the amount of NOx discharged from the supplied engine when the integration distance is smaller than the first set value or larger than the second set value.

The amount of NOx discharged from the engine decreases in proportion to the difference between the NOx discharged from the engine required at the first setpoint and the second setpoint when the integration distance is increased between the first setpoint and the second setpoint. It is done.

In addition, the amount of NOx discharged from the engine is characterized in that it is controlled by the EGR rate, the boost pressure, the main injection time, the pilot (pilot) injection time.

In addition, the exhaust gas purifying apparatus according to the embodiment of the present invention is characterized in that the amount of emission in the exhaust pipe is constant.

Further, in one or more embodiments of the present invention, an LNT catalyst for occluding or desorbing nitrogen oxides contained in exhaust gas, and a soot filter disposed downstream of the LNT catalyst and collecting particulate matter contained in exhaust gas, is provided. A control method of an exhaust gas purifying apparatus, comprising: determining whether an integration distance is equal to or greater than a first predetermined value during engine operation; Determining whether the integration distance is greater than or equal to the second preset value when the integration distance is greater than or equal to the first preset value; When the integration distance is between the first setpoint and the second setpoint, the NOx discharged from the engine is proportional to the difference between the amount of NOx exhausted from the engine at the first setpoint and the amount of NOx exhausted from the engine at the second setpoint. Adjusting the amount; Creating a rich atmosphere to desorb NOx from the LNT catalyst; And slipping the desorbed NOx to regenerate the soot filter. A control method of an exhaust gas purification apparatus may be provided.

In one or more embodiments of the present invention, when the integration distance is smaller than the first set value or larger than the second set value, the amount of NOx discharged from the engine to be supplied is kept constant.

In addition, the amount of NOx discharged from the engine is characterized in that it is controlled by the EGR rate, the boost pressure, the main injection time, the pilot (pilot) injection time.

As described above, according to the embodiment of the present invention, the soot of the soot filter may be naturally regenerated to a certain level at all times regardless of the degree of deterioration of the LNT catalyst by changing the amount of NOx discharged from the engine.

1 is a block diagram of an exhaust gas purification apparatus according to an embodiment of the present invention.
2 is a flowchart of a control method of an exhaust gas purifying apparatus according to an embodiment of the present invention.
3 is a control flowchart of an exhaust gas purifying apparatus according to an embodiment of the present invention.
4 is a graph showing a change in the supply amount of NOx discharged from the engine, the amount of NOx in the exhaust pipe, the amount of carbon dioxide discharged according to the integration distance according to an embodiment of the present invention.

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

1 is a block diagram of an exhaust gas purification apparatus according to an embodiment of the present invention.

As shown in FIG. 1, an exhaust gas purifying apparatus according to an exemplary embodiment of the present invention includes an engine 10, an exhaust pipe 20, a Lean NOx Trap (LNT) catalyst 30, a soot filter 40, and a controller. And 50.

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 to allow air to flow into the combustion chamber, and the exhaust gas generated in the combustion process by being connected to the exhaust manifold is collected in the exhaust manifold to be discharged to the outside of the vehicle. An injector is mounted in the combustion chamber to inject fuel into the combustion chamber.

An exhaust pipe 20 is connected to the exhaust manifold to exhaust the exhaust gas to the outside of the vehicle. The LNT catalyst 30 and the soot filter 40 are mounted on the exhaust pipe 20 to remove particulate matter (PM), nitrogen oxide, and the like contained in the exhaust gas.

In some embodiments, the exhaust pipe 20 includes an EGR line for increasing intake using energy of exhaust gas, an oxidation catalyst (DOC) for oxidizing hydrocarbons and carbon monoxide contained in the exhaust gas, and an exhaust gas. It may be equipped with a selective reduction catalyst (SCR) to remove nitrogen oxides, hydrocarbons and carbon monoxide. It may also be equipped with a pilot injection device for pre-injecting some fuel before main injection.

The LNT catalyst 30 is mounted on the exhaust pipe 20 so that the exhaust gas discharged from the engine 10 passes through the LNT catalyst 30. The LNT catalyst 30 is configured to occlude nitrogen oxide contained in exhaust gas in a lean atmosphere and to desorb the occluded nitrogen oxide in a rich atmosphere. At this time, the LNT catalyst 30 occludes the nitrogen oxide in the form of nitrate and desorbs it in the form of nitrogen dioxide.

In general, as the deterioration progresses, the LNT catalyst 30 deteriorates the purification performance of NOx. The LNT catalyst 30 is not used for the reduction (regeneration) of NOx among the reducing agents introduced into the LNT catalyst 30, but slips to the rear end of the LNT catalyst 30 ( The amount of slip) increases. When the soot filter 40 is disposed at the rear end of the LNT catalyst 30, the soot filter 40 is regenerated only by a certain amount of NOx slip. However, in the case of the new LNT catalyst 30, since the amount of NOx slip is small, a method of inducing NOx slip is required for the natural regeneration of the DPF.

To this end, in an embodiment of the present invention, when the vehicle's mileage is less than the first set value or exceeds the second set value, the supply amount of NOx discharged from the engine is kept constant so that the amount of NOx slipped is constant. Let's do it. In other words, when the integration distance is low, the LNT catalyst 30 may have excellent purification performance, and thus the amount of NOx slipped may not be large, so that the smoke filter 40 installed at the rear of the LNT catalyst 30 may not be properly regenerated. Therefore, to prevent this, the NOx emitted from the engine is increased.

In the embodiment of the present invention NOx (Raw NOx) discharged from the engine means NOx generated by the combustion of the engine.

The amount of NOx emitted from the engine required decreases as the LNT catalyst 30 deteriorates. When the integration distance exceeds the second set value, the supply amount of NOx emitted from the engine is kept constant.

The LNT catalyst 30 includes a noble metal and an occlusion material. The noble metal may include platinum, palladium, and rhodium, and the occlusion material may include a weakly basic material such as barium carbonate. However, the scope of the present invention is not limited to the noble metals or occluding materials exemplified herein.

The exhaust pipe 20 behind the LNT catalyst 30 is equipped with a soot filter 40, as shown in FIG. 1. The soot filter 40 collects particulate matter (or soot) contained in the exhaust gas discharged through the exhaust pipe 20. In addition, the soot filter 40 allows for natural regeneration of the soot trapped using NOx (eg, nitrogen dioxide) slipped from the LNT catalyst 30. As such, the natural regeneration is performed in the soot filter 40 whenever the NOx slips in the LNT catalyst 30, and thus the forced regeneration procedure of the soot filter 40 may be omitted. As a result, fuel efficiency is improved.

The controller 50 according to the embodiment of the present invention controls the exhaust gas purification apparatus according to the embodiment of the present invention. To this end, the controller 50 receives the integration distance of the vehicle and compares it with the first setpoint and the second setpoint, when the received integration distance is between the first setpoint and the second setpoint. Differently supply NOx discharged from the engine in proportion to the difference between the amount of NOx emitted from the engine and the amount of NOx required in the second set point. As a result, the amount of NOx slipped becomes constant.

In addition, after determining the amount of NOx exhausted from the required engine, the combustion atmosphere of the engine is controlled. Control of the combustion atmosphere of the engine is performed by controlling the amount of fuel injected. In other words, if the amount of fuel injected into the engine 10 is increased, the combustion atmosphere becomes rich, and if the amount of fuel injected into the engine 10 is reduced, the combustion atmosphere becomes thin.

According to an embodiment of the present invention, the amount of NOx emitted from the engine is controlled by variables including the EGR rate, the boost pressure, the main injection time and the pilot injection time.

If the EGR rate is increased, the combustion temperature is lowered by decreasing the oxygen concentration, so that the amount of NOx is decreased, while if the EGR rate is decreased, the combustion temperature is increased with the increase of the oxygen concentration, and the amount of NOx is increased.

Boost pressure means the pressure of the amount of intake air supplied to the engine, and increasing the boost pressure has the same effect as increasing the EGR rate, and decreasing the boost pressure has the same effect as reducing the EGR rate.

In addition, when the main injection timing is advanced, the combustion start point is delayed to increase the amount of NOx, whereas when the main injection timing is delayed, the combustion start point is advanced, and the amount of NOx is decreased. There is the same effect as the time of perception of time, and when the pilot injection time is perceived, the same effect as the time of advance of the main injection time.

Therefore, in order to increase the amount of NOx, the EGR rate and boost pressure may be decreased, or the main injection timing may be advanced and the pilot injection timing may be delayed.

At this time, the pilot injection (Pilot injection) is to reduce the noise by reducing the combustion explosion caused by the strong combustion through the main injection by pre-burning a small amount of fuel before the main injection of fuel in the diesel engine occurs. In other words, it means a combustion progression method that prevents a sudden rise in temperature in the combustion chamber and slows down the increase of NOx emissions in the exhaust gas.

3 is a schematic control flowchart of an exhaust gas purification apparatus according to an embodiment of the present invention.

Hereinafter, a control flow of the exhaust gas purifying apparatus according to the embodiment of the present invention will be described with reference to FIG. 3. First, the engine operating state (for example, fuel injection amount, fuel injection timing, integration distance of the vehicle, etc.) is detected (S210), and accordingly, the degree of deterioration of the LNT catalyst 30 is determined (S220). Degradation degree of the LNT catalyst 30 according to the embodiment is determined according to the integration distance. However, since there are various methods for determining the deterioration of the LNT catalyst 30, it should not be interpreted to be limited thereto. Since the LNT catalyst 30 deteriorates according to the integration distance, the amount of NOx slipped from the LNT catalyst 30 is constant by changing the supply amount of NOx discharged from the engine according to the integration distance.

2 is a detailed flowchart of a control method of an exhaust gas purifying apparatus according to an embodiment of the present invention.

As shown in Figure 2, the control of the exhaust gas purification apparatus according to an embodiment of the present invention is performed when the engine is in operation (S100). When the engine 10 is in operation, the integration distance and the first set value of the vehicle are transmitted to the controller 50 to compare them (S110).

The first set value means the integration distance from the fresh LNT catalyst 30 to supply NOx discharged from a large amount of engine due to high slip ratio of NOx. Up to this point, NOx is emitted from a certain amount of engine. The first set value may be, for example, 10,000 Km, but is not limited thereto.

When the integration distance is greater than the first set value in step S110, it is determined whether the integration distance is greater than the second set value (S160). When the integration distance is larger than the second set value, a certain amount of supply of NOx discharged from the engine is supplied (S180). If necessary, the supply can be discontinued. The second set value means the integration distance at the point where the supply of NOx discharged from the engine in the aged LNT catalyst (Aged LNT) 30 is not necessary or only a small amount is required. The second set value may be, for example, 160,000 km, but is not limited thereto.

After the step S180 to create a rich atmosphere in the LNT catalyst 30 to desorb NOx (S130), the desorbed NOx is reduced to nitrogen gas in the part of the LNT catalyst 30, the rest is slipped, the engine The slip amount of the desorbed NOx is constant by the supply of NOx discharged from (S140), and the regeneration is normally performed in the soot filter 40 using the slipped NOx.

In the step S110, if the integration distance is smaller than the first set value, since the LNT catalyst 30 is determined to be fresh and the NOx slip amount will be less, the NOx discharged from the engine of a predetermined amount is supplied (S120) to desorb the NOx ( S130) After a certain amount of slip (S140) to regenerate the soot filter 40 installed in the rear (S150).

In addition, when the integration distance is between the first set value and the second set value, the NOx discharged from the engine is differentially supplied according to the integration distance (S170). The amount of NOx discharged from the engine decreases as the integration distance increases in proportion to the difference between the amount of NOx discharged from the engine required at the first setpoint and the amount of NOx discharged from the engine required at the second setpoint. As described above, after differentially supplying NOx discharged from the engine, NOx is desorbed and slipped from the LNT catalyst 30 to smoothly regenerate the soot filter 40. (S130 to S150)

At this time, the slip NOx is supplied to the soot filter 40 is reduced in the soot filter 40 and supplies oxygen for regeneration of the soot (soot). Accordingly, the soot filter 40 is naturally regenerated (S150), and the control method of the exhaust gas purifying apparatus according to the embodiment of the present invention is terminated.

On the other hand, the method for controlling the exhaust gas purifying apparatus according to the embodiment of the present invention is continuously performed while the engine 10 is in operation.

4 is a graph illustrating a change in the supply amount of NOx discharged from the engine, the NOx amount in the exhaust pipe 20, and the amount of carbon dioxide discharged according to the integration distance according to the embodiment of the present invention.

In FIG. 4, when the integration distance is less than 10,000 km, 0.18 g / km is supplied to the NOx discharged from the engine, and when the integration distance is 160,000 km or more, 0.11 g / km is illustrated.

Below 10,000 km, it can be seen as a fresh (fresh) LNT catalyst (30), up to this time by providing more than 64% NOx to increase the slip rate.

At this time, the amount of NOx in the exhaust pipe 20 is almost constant, it can be seen that the carbon dioxide emitted is reduced from 196g / km to 192g / km 2% is reduced.

That is, the new LNT catalyst 30 supplies a large amount of NOx so that the slip ratio of the NOx is always the same level, thereby allowing the soot filter 40 to normally regenerate soot regardless of the degree of catalyst degradation. have.

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, And all changes to the scope that are deemed to be valid.

Claims (8)

An LNT catalyst which occludes nitrogen oxide contained in exhaust gas in a lean atmosphere, desorbs nitrogen oxide stored in a rich atmosphere, and slips desorbed nitrogen oxide according to the concentration of the nitrogen oxide;
A soot filter which collects particulate matter contained in the exhaust gas and regenerates the collected particulate matter using nitrogen oxide slipped from an LNT catalyst; And
It includes a control unit for controlling the amount of NOx slipped by adjusting the amount of NOx discharged from the engine supplied according to the degree of degradation of the LNT catalyst according to the integration distance of the vehicle,
And the control unit maintains a constant amount of NOx discharged from the supplied engine when the integration distance is smaller than the first set value or larger than the second set value. delete The method of claim 1,
The amount of NOx discharged from the engine decreases in proportion to the difference between the NOx discharged from the engine required by the first setpoint and the second setpoint when the integration distance is increased between the first setpoint and the second setpoint. An exhaust gas purification device characterized by the above-mentioned. The method of claim 3,
The amount of NOx discharged from the engine is controlled by the EGR rate, boost pressure, main injection timing, pilot injection timing. The method according to any one of claims 1, 3, and 4,
An exhaust gas purification device according to claim 1, wherein the amount of emission in the exhaust pipe is constant. A control method of an exhaust gas purifying apparatus comprising an LNT catalyst for occluding or desorbing nitrogen oxide contained in exhaust gas, and a soot filter disposed downstream of the LNT catalyst and collecting particulate matter contained in exhaust gas.
Determining whether the integration distance is equal to or greater than the first predetermined value during engine operation;
Determining whether the integration distance is greater than or equal to the second preset value when the integration distance is greater than or equal to the first preset value;
When the integration distance is between the first setpoint and the second setpoint, the NOx discharged from the engine is proportional to the difference between the amount of NOx exhausted from the engine at the first setpoint and the amount of NOx exhausted from the engine at the second setpoint. Adjusting the amount by at least one of EGR rate, boost pressure, main injection timing and pilot injection timing;
Creating a rich atmosphere to desorb NOx from the LNT catalyst; And
Slipping the desorbed NOx to regenerate the soot filter;
Control method of the exhaust gas purification apparatus comprising a. The method according to claim 6,
And when the integration distance is smaller than the first set value or larger than the second set value, the amount of NOx discharged from the engine to be supplied is kept constant. delete

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