KR101836271B1 - ASSUMING METHOD OF DESULFURIZATION AMOUNT OF LEAN NOx TRAP AND APPARATUS OF PURIFYING EXHAUST GAS - Google Patents

Abstract

The method for estimating the amount of sulfur oxides trapped immediately before desulfurization in a nitrogen oxide storage catalyst apparatus (Lean NOx Trap: LNT) comprises the steps of: extracting the amount of sulfur oxides immediately before desulfurization; A step of detecting an air-fuel ratio of an exhaust gas flowing into the storage catalyst device, a step of detecting an average temperature of the nitrogen oxide storage apparatus, a step of detecting a rich condition operation holding time after the start of the desulfurization operation, Information on the amount of sulfur oxide poisoned immediately before desulfurization, the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage apparatus, the average temperature of the nitrogen oxide storage apparatus, the operation time of the rich condition, and the minimum holding time of the rich condition To calculate a current desulfurization rate.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for calculating the amount of desulfurization of a nitrogen oxide storing < RTI ID = 0.0 > storage catalyst < / RTI &

More particularly, the present invention relates to a method for more easily and accurately calculating the amount of desulfurization discharged during a desulfurization process of a nitrogen oxide storage apparatus, and a method for purifying exhaust gas ≪ / RTI >

Today, with the implementation of the EU6 emission gas regulations, which have greatly enhanced the emission standards for nitrogen oxides, the company is producing nitrogen dioxide purification equipment in passenger diesel vehicles in order to comply with regulations. Accordingly, in order to enhance cost competitiveness and convenience for users in terms of producers and sellers, nitrogen oxides are stored and stored under lean operating conditions, and nitrogen oxide storage catalysts for desorbing and purifying nitrogen oxides under rich operating conditions (Lean NOx Trap: LNT) devices for small and medium-sized automobiles.

However, due to the sulfur component contained in the fuel, the nitrogen oxide storage catalyst device is poisoned over time to deteriorate the nitrogen oxide purification performance. As a result, in order to maintain the nitrogen oxide purification performance of the nitrogen oxide storage catalyst, My poisoned sulfur must be removed periodically. The removal of poisoned sulfur compounds in a nitrogen oxide storage catalyst called 'desulfurization' requires a high temperature and rich atmosphere above about 500 ° C.

The desulfurization operation generally starts when the sulfur content of the nitrogen oxide storage catalyst calculated by the electronic control unit (ECU) during the operation of the internal combustion engine exceeds a certain level based on the sulfur content of the nitrogen oxide storage catalyst. In the desulfurization operation, When the poisoning amount falls below a certain level or when the operation can no longer be performed, the desulfurization operation is terminated. At this time, the sulfur content in the nitrogen oxide storage catalyst fixed in the desulfurization process is calculated through time integration with respect to the desulfurization rate obtained from various engine operating conditions. However, the desulfurization rate obtained from various engine operating conditions used in this calculation process is not only difficult to accurately model but also imposes a burden on the electronic control unit because it requires real-time integral calculation.

In order to solve the above problems, the present invention provides an internal combustion engine operating under lean burn conditions, in which a normal distribution formula based on the nitrogen oxide storage catalyst desulfurization characteristic for the calculation of the desulfurization amount discharged during the desulfurization process of the nitrogen oxide storage apparatus, Based desulfurization rate modeling, it is possible to improve the prediction accuracy of the sulfur content in the nitrogen oxide storage catalyst.

The method for estimating the amount of sulfur oxides trapped immediately before desulfurization in a nitrogen oxide storage catalyst apparatus (Lean NOx Trap: LNT) comprises the steps of: extracting the amount of sulfur oxides immediately before desulfurization; A step of detecting an air-fuel ratio of the exhaust gas flowing into the storage catalyst device, a step of detecting an average temperature of the nitrogen oxide storage apparatus, a step of detecting a rich condition operation holding time after the start of the desulfurization operation, The amount of sulfuric acid poisoned immediately before desulfurization in the catalyst device, the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage catalyst device, the average temperature of the nitrogen oxide storage catalyst device, the rich condition operation time, Calculating a desulfurization rate of the present point through the information, and calculating a desulfurization amount therefrom.

The desulfurization rate can be estimated by applying the normal distribution probability density function expressed by Equation (1) below.

[Equation 1]

(Where m is the mean value, σ ² is the variance, and exp is the natural constant (e).)

The integrated value of the normal distribution probability density function may be one.

The integration value of the normal distribution probability density function is always 1, and the desulfurization rate of the nitrogen oxide storage apparatus can be calculated by the following equation (2).

&Quot; (2) "

(Where V is a desulfurization rate, t is the start rich operation of the desulfurization operation time from the time, _{t-rich conditions the operating time} is maintained rich conditions driving into the desulfurizer operating time, σ ² is a variance, exp is the natural constant, (e) , A and σ may vary depending on the exhaust gas air-fuel ratio (λ), the amount of sulfur oxide poisoned immediately before desulfurization in the nitrogen oxide storage device, the average temperature of nitrogen oxide storage catalyst device (T) It is a constant.)

The amount of sulfur oxides to be desulfurized from the nitrogen oxide storage apparatus can be calculated as a time integral with respect to the desulfurization rate, and the integrated value is A since the desulfurization rate takes a normal distribution x A form.

The nitrogen oxide storing < Desc / Clms Page number 7 > storage catalytic device may start desulfurization from the point of time when the rich condition operation is maintained for a certain period of time after the start of the desulfurization operation, which is characteristic of the nitrogen oxide storage apparatus.

According to another aspect of the present invention, there is provided an exhaust gas purifying apparatus comprising: an internal combustion engine that is operated under lean-burn conditions; and an internal combustion engine that absorbs nitrogen oxides (NOx) contained in exhaust gas discharged from the internal combustion engine under lean- A nitrogen oxide storing catalyst for purifying the exhaust gas through a reducing action under the operating condition and causing toxic toxicity of the exhaust gas; a soot particulate filter for trapping particulate matter contained in the exhaust gas discharged from the internal combustion engine; Wherein the control unit controls the amount of sulfur oxide poisoned immediately before desulfurization in the nitrogen oxide storage apparatus, the amount of the nitrogen oxides stored in the nitrogen oxide storage catalyst apparatus, The air-fuel ratio of the exhaust gas flowing into the storage catalyst, the average temperature of the nitrogen oxide storage apparatus, And the rate of desulfurization at the present time is calculated based on the information on the minimum retention time.

The control unit may control the desulfurization of the nitrogen oxide storing < RTI ID = 0.0 >

According to the present invention, the pre-desulfurization amount discharged during the desulfurization process of the nitrogen oxide storage apparatus can be more easily and accurately predicted by the pre-modeled mapping data, Deterioration of the nitrogen oxide storage catalyst apparatus can be minimized.

In addition, the amount of mapping work for predicting the desulfurization performance of the nitrogen oxide storage apparatus can be reduced.

In addition, since the integrator in the electronic control unit (ECU) for calculating the amount of debris is not used, the electronic control unit load can be minimized.

1 is a flowchart showing a method for calculating the amount of dehydrogenation of a nitrogen oxide storage apparatus according to an embodiment of the present invention.
FIG. 2 is a graph illustrating an example of a desulfurization rate distribution according to a rich operation time according to an embodiment of the present invention. Referring to FIG.
3 is a graph showing the maximum desulfurization rate according to the amount of sulfuric acid poisoned immediately before desulfurization in the nitrogen oxide storage apparatus according to an embodiment of the present invention.
4 is a graph showing a desulfurization rate according to an air-fuel ratio, a temperature, and a rich operating time of an exhaust gas according to an embodiment of the present invention.
5 is a schematic view of an exhaust gas purifying apparatus according to an embodiment of the present invention.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, which will be readily apparent to those skilled in the art to which the present invention pertains. The present invention may be embodied in many different forms and is not limited to the embodiments described herein.

In addition, in the various embodiments, elements having the same configuration are denoted by the same reference numerals, and only other configurations will be described in the other embodiments.

The drawings are schematic and illustrate that they are not drawn to scale. The relative dimensions and ratios of the parts in the figures are shown exaggerated or reduced in size for clarity and convenience in the figures, and any dimensions are merely illustrative and not restrictive. Also, to the same structure, element, or component appearing in more than one of the figures, the same reference numerals are used to denote similar features. When referring to a portion as being "on" or "on" another portion, it may be directly on the other portion or may be accompanied by another portion therebetween.

The embodiments of the present invention specifically illustrate one embodiment of the present invention. As a result, various variations of the illustration are expected. Thus, the embodiment is not limited to any particular form of the depicted area, but includes modifications of the form, for example, by manufacture.

Hereinafter, with reference to FIG. 1 to FIG. 4, a description will be given of a method for estimating the amount of dehalization of a nitrogen oxide storage apparatus according to an embodiment of the present invention.

FIG. 1 is a flow chart illustrating a method for calculating the amount of desulfurization of a nitrogen oxide storage apparatus according to an embodiment of the present invention. FIG. 2 is a graph illustrating an example of a desulfurization rate distribution according to a rich operation time according to an embodiment of the present invention. Graph.

Referring to FIGS. 1 and 2, in the method of estimating the amount of desulfurization of a nitrogen oxide storage catalyst apparatus (Lean NOx Trap: LNT), the amount of sulfur oxide poisoned immediately before desulfurization is extracted in the nitrogen oxide storage apparatus (S101).

The amount of sulfuric acid poisoned immediately before desulfurization in the nitrogen oxide storage catalyst apparatus can be calculated in consideration of the sulfur content discharged from the internal combustion engine and the sulfur slip rate of the nitrogen oxide storage catalyst apparatus and information about the sulfur poisoning Is reflected.

The sulfur content emitted from the internal combustion engine can be calculated based on the time the internal combustion engine maintains the normal operating state, the fuel consumption, and the oil consumption of the engine.

The sulfur content emitted from the internal combustion engine can be calculated based on the time the internal combustion engine maintains the normal operating state, the fuel consumption, and the oil consumption of the engine.

After that, the exhaust gas air-fuel ratio flowing into the nitrogen oxide storage catalyst device is detected (S102). Fuel ratio measuring means may be provided between the downstream end of the exhaust manifold of the internal combustion engine and the nitrogen oxide storing catalyst so that the air-fuel ratio at which the nitrogen oxide storing catalyst is exposed during the desulfurization process can be detected.

Thereafter, the average temperature of the nitrogen oxide storage apparatus is detected (S103). The nitrogen oxide storage catalyst temperature sensor may be provided at a front end of the nitrogen oxide storage apparatus, and the time average of the temperature detected by the nitrogen oxide storage catalyst temperature sensor may be estimated as an average temperature of the nitrogen oxide storage apparatus, The time average of the temperature obtained through the temperature modeling of the storage catalyst device may be estimated as the average temperature of the nitrogen oxide storage apparatus.

Thereafter, the rich-condition operation holding time is detected after the start of the desulfurization operation (S104). The dense operation requires a high temperature and rich atmosphere of more than about 500 ° C., and the desulfurization operation starts when the nitrogen oxide storage catalyst device exceeds a certain level based on the sulfur content. The nitrogen oxide storage catalyst apparatus can start desulfurization from the point of time when the rich condition operation is maintained for a certain period of time after the desulfurization operation starts, which is characteristic of the nitrogen oxide storage apparatus. When the amount of sulfur poisoning in the nitrogen oxide storage catalyst device drops below a certain level during the desulfurization operation or when the operation can no longer be performed, the desulfurization operation is terminated.

Thereafter, the desulfurization rate of the nitrogen oxide storage apparatus is calculated (S105). The desulfurization rate is determined by the amount of sulfur oxide poisoned immediately before desulfurization in the nitrogen oxide storage apparatus, the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage catalyst apparatus, the average temperature of the nitrogen oxide storage apparatus, the operation time of the rich condition, Can be calculated from the information on < RTI ID = 0.0 >

The desulfurization rate (V) can be estimated by applying the normal distribution probability density function expressed by the following equation (1).

[Equation 1]

In this case, m is the average value, σ ² is the variance, exp is the natural constant (e), and the integral value of the normal distribution probability density function (f (x)

As shown in FIG. 2, a curve indicated by a dotted line takes a form of a normal distribution curve according to Equation (1), and a solid line is a curve showing a desulfurization rate distribution according to an actual rich operation time. 2, when the air-fuel ratio (?) Of the exhaust gas is 0.922, the average temperature (T) of the nitrogen oxide storage apparatus is detected at 660 degrees, and the rich operating time exceeds 13 seconds, Draws the rising and falling curves similarly to the normal distribution curve indicated by the dotted line.

The desulfurization rate (V) of the actual nitrogen oxide storage apparatus can be calculated by the following equation (2).

&Quot; (2) "

Where V is the time, _{t-rich conditions the operating time} is kept driving rich conditions after the desulfurization operation time, σ ² is a variance, exp is the natural constant, (e) from the desulfurization rate, t is the start rich operation of the desulfurization operation time, A and? Can be varied depending on the exhaust gas air-fuel ratio (?), The amount of sulfur oxide poisoned immediately before desulfurization (S) in the nitrogen oxide storage apparatus, the average temperature of nitrogen oxide storage catalyst apparatus (T) It is a constant.

The nitrogen oxide storage apparatus can start desulfurization from the point of time when the rich condition operation is maintained for a certain period of time after the desulfurization operation is started, which is characteristic of the nitrogen oxide storage apparatus.

When the desulfurization rate (V) is calculated, the amount of sulfur oxides to be desulfurized from the nitrogen oxide storage apparatus can be calculated as a time integral with respect to the desulfurization rate (V), and the desulfurization rate takes the form of the normal distribution x A , And the integral value thereof is A.

3 is a graph showing the maximum desulfurization rate according to the amount of sulfuric acid poisoned immediately before desulfurization in the nitrogen oxide storage apparatus according to an embodiment of the present invention.

Referring to FIG. 3, the air-fuel ratio of the exhaust gas is 0.92, and the maximum desulfurization rate (V) according to the sulfur content (S _Loading ) of the nitrogen oxide storage apparatus can be known. As shown in FIG. 3, the higher the average temperature (T) of the nitrogen oxide storage apparatus, the greater the maximum desulfurization rate (V).

4 is a graph showing a desulfurization rate according to an air-fuel ratio, a temperature, and a rich operating time of an exhaust gas according to an embodiment of the present invention.

Referring to FIG. 4, the lower the air-fuel ratio of the exhaust gas, the larger the maximum desulfurization rate V is. The bottom area of the curve shown in FIG. 4 is the desulfurization amount of the nitrogen oxide storage apparatus, and as a result, the lower the air-fuel ratio of the exhaust gas and the higher the average temperature T of the nitrogen oxide storage apparatus, have.

5 is a schematic view of an exhaust gas purifying apparatus according to an embodiment of the present invention.

5, the exhaust gas purifying apparatus includes an internal combustion engine 10 that provides lean burn, a nitrogen oxide storage catalyst apparatus 20, a soot particle filtering filter 30, and a control unit 40.

The internal combustion engine 10 is operated under lean burn conditions and under the control of the control unit 40, the mixture ratio of air and fuel is lean burned to generate power, and the high temperature exhaust gas generated in the combustion process is supplied to the exhaust manifold 15 ), The nitrogen oxide storage device 20 and the soot particle filter 30 to be discharged into the atmosphere.

The nitrogen oxide storage apparatus 20 is mounted at the downstream end of the exhaust manifold 15 of the internal combustion engine 10 to store nitrogen oxides (NOx) contained in the exhaust gas under lean operation conditions and store the nitrogen oxides (NOx) (N2) which is harmless to the human body through its action.

The nitrogen oxide storing < Desc / Clms Page number 10 > storage catalytic device 20 is poisoned by sulfur components contained in the fuel and the engine oil and is deteriorated in the function of storing nitrogen oxides (NOx), and thus is periodically exposed to a high- Is reproduced.

The soot particle filter 30 physically collects particulate matter (PM) such as soot contained in the exhaust gas and prevents it from being discharged to the atmosphere.

The soot particle filter 30 filters the particulate matter PM collected according to the mileage calculated by the collection amount of the particulate matter PM determined as the differential pressure between the upstream and downstream stages or the travel distance and time of the vehicle by periodic regeneration Empty.

The regeneration of the soot particle filter 30 is carried out by raising the temperature of the exhaust gas to a high temperature of about 600 ° C or more.

A pressure sensor 31 and a soot particle filtering filter temperature sensor 35 are mounted on the front and rear ends of the soot particle filtering filter 30.

The pressure sensor 31 detects the differential pressure of the exhaust gas that is input to the soot particle filter 30 and provides information on the differential pressure to the control unit 40 as an electrical signal.

The soot particle filtering filter temperature sensor 35 detects the temperature of the soot particle filtering filter 30 and provides information about the soot particle filtering filter 30 to the control unit 40 as an electrical signal.

The control unit 40 controls the amount of particulate matter PM filtered according to mileage calculated from the amount of captured particulate matter PM and the distance and time from the differential pressure information detected by the pressure sensor 31 provided at the front and rear ends of the particulate matter particulate filter 30 It can be determined whether or not the filter 30 needs to be regenerated.

When the regeneration condition of the soot particle filtering filter 30 is satisfied, the control unit 40 raises the temperature of the exhaust gas to a predetermined temperature of about 600 ° C. to 700 ° C. or higher to remove the particulate matter trapped in the soot particle filtering filter 30 (PM) is burned.

The control unit 40 repeats the lean burn operation and the rich combustion operation of the internal combustion engine 10 so that the desulfurization of the nitrogen oxide storage apparatus 20 is performed under the rich combustion operation condition, So that regeneration of particulate matter PM such as soot not removed by the filter 30 is performed.

When the desulfurization and regeneration completion are judged in the process of controlling the desulfurization of the nitrogen oxide storage apparatus 20 and the regeneration of the particulate filter 30 by repeating the lean burn operation and the rich combustion operation The normal control is executed without repeating the operation of lean burn and the operation of rich combustion.

The control unit 40 can determine that desulfurization has been completed when the sulfur content poisoned in the nitrogen oxide storage apparatus 20 has been removed to a predetermined amount or less or when the predetermined period of time has elapsed after the desulfurization time of the nitrogen oxide storage apparatus 20 .

The control unit 40 controls the amount of sulfur oxides poisoned immediately before desulfurization in the nitrogen oxide storing and storing catalyst device 20, the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storing catalyst device, the nitrogen oxide storing device catalyst temperature T, The desulfurization rate (V) of the present time can be calculated from the information on the rich condition operation time and the rich condition minimum maintenance time.

When the desulfurization rate (V) is calculated, the amount of sulfur oxides desulfurized from the nitrogen oxide storage apparatus (20) can be calculated through time integration with respect to the desulfurization rate (V).

Thus, the pre-desulfurization amount discharged during the desulfurization process of the nitrogen oxide storage apparatus can be more easily and accurately predicted by the pre-modeled mapping data, and it is possible to accurately determine whether the desulfurization operation of the nitrogen oxide storage apparatus is necessary, Deterioration of the oxide storage catalyst device can be minimized.

In addition, the amount of mapping work for predicting the desulfurization performance of the nitrogen oxide storage apparatus can be reduced.

In addition, since the integrator in the electronic control unit (ECU) for calculating the amount of debris is not used, the electronic control unit load can be minimized.

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.

10: Internal combustion engine 15: Exhaust manifold
20: nitrogen oxide storage catalyst device 22: nitrogen oxide storage catalyst temperature sensor
30: Soot particle filter 31: Pressure sensor
35: Soot particle filter temperature sensor 40:

Claims (7)

Extracting an amount of sulfuric acid poisoned immediately before desulfurization in a nitrogen oxide storage catalyst apparatus (Lean NOx Trap: LNT);
Detecting an air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage apparatus;
Detecting an average temperature of the nitrogen oxide storage apparatus;
Detecting a rich operation condition holding time after the desulfurization operation starts; And
Wherein the amount of sulfur oxide poisoned immediately before desulfurization, the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage catalyst device, the average temperature of the nitrogen oxide storage catalyst device, the rich condition operation time, Calculating a desulfurization rate at a current point through information on time and calculating a desulfurization amount therefrom,
Wherein the desulfurization rate is predicted by applying a normal distribution probability density function expressed by Equation (1) below.
[Equation 1]

(Where m is the mean value, σ ² is the variance, and exp is the natural constant (e).) delete The method of claim 1,
Wherein the desulfurization rate of the nitrogen oxide storage apparatus is calculated by the following equation (2).
&Quot; (2) "

(Where, V is a desulfurization rate, t is the start rich operation of the desulfurization operation time from the time, _{t-rich conditions the operating time} is maintained rich conditions driving into the desulfurizer operating time, σ ² is a variance, exp is the natural constant, (e) , A and σ may vary depending on the exhaust gas air-fuel ratio (λ), the amount of sulfur oxide poisoned immediately before desulfurization in the nitrogen oxide storage device, the average temperature of nitrogen oxide storage catalyst device (T) It is a constant.) The method of claim 1,
Wherein the amount of desulfurized sulfur oxides in the nitrogen oxide storage apparatus is calculated as a time integral with respect to the desulfurization rate, and the integrated value is A. The method of claim 1,
Wherein the nitrogen oxide storing < Desc / Clms Page number 19 > storage catalytic device can start desulfurization from the point of time when the rich condition operation is maintained for a certain period of time after the start of the desulfurization operation, and the richest condition minimum holding time is characteristic of the nitrogen oxide storage apparatus Method for estimating dehalogenation of a catalytic device. An internal combustion engine operating under lean burn conditions;
A nitrogen oxide storage catalyst for storing nitrogen oxides (NOx) contained in exhaust gas discharged from the internal combustion engine under lean operating conditions, purifying through reduction action under rich operating conditions, and causing toxic toxicity;
A soot particle filter for collecting particulate matter contained in the exhaust gas discharged from the internal combustion engine; And
And a control unit for controlling the combustion of the internal combustion engine and for controlling the purification of nitrogen oxides of the nitrogen oxide storing catalyst, the desulfurization, and the regeneration of the soot particle filtering filter,
Wherein,
The amount of sulfur oxides poisoned immediately before desulfurization, the air-fuel ratio of the exhaust gas flowing into the nitrogen oxide storage catalyst, the average temperature of the nitrogen oxide storage apparatus, and the minimum maintenance time of the rich condition are stored in the nitrogen oxide storage apparatus, The desulfurization rate is calculated,
Wherein the desulfurization rate is predicted by applying a normal distribution probability density function expressed by Equation (1) below.
[Equation 1]

(Where m is the mean value, σ ² is the variance, and exp is the natural constant (e).) The method of claim 6,
Wherein,
Wherein the nitrogen oxide storage catalyst apparatus controls the desulfurization to be performed from the point of time when the rich condition operation is maintained for a certain period of time after the desulfurization operation starts.

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