JP2009540208A - Method of operating an exhaust gas purification system disposed in an exhaust gas region of an internal combustion engine - Google Patents

Abstract

A method of operating an exhaust gas purification system disposed in an exhaust gas region of an internal combustion engine that enables regeneration of a filter without increasing fuel consumption of the internal combustion engine.
A catalyst layer (130) arranged in an exhaust gas region of an internal combustion engine and causing an oxidation reaction and a particulate filter (140) are provided, and at least one exhaust gas component is adhered during operation of the internal combustion engine. In a method of operating an exhaust gas purification system, which is regenerated from their exhaust gas components during a pre-determined operating phase, a pre-determined operating phase of regeneration of the particulate filter (140) In between, the air flow rate through the at least one combustion chamber (100) of the internal combustion engine is reduced.
[Selection] Figure 1

Description

  The present invention relates to a method for operating an exhaust gas purification system arranged in an exhaust gas region of an internal combustion engine, which includes a catalyst layer for causing an oxidation reaction and a particulate filter, based on the superordinate concept of independent claim 1.

  From DE 199 06 287 A1, a method for the regeneration of a particulate filter arranged in the exhaust gas region of an internal combustion engine is known, depending on the last existing operating condition and Depending on the state of the particulate filter, alternating between different operating states is performed. At that time, the regeneration of the particulate filter from the adhered particulates is performed in one operating state. This regeneration is performed at a high temperature at which the fine particles, mainly soot fine particles and ash fine particles, are incinerated by an oxidation reaction.

  DE 103 23 561 A1 describes a component arranged in the exhaust gas region of an internal combustion engine, in particular a method for the operation of a particulate filter, and a device for the implementation of this method. In this case, the regeneration phase is started according to the operating state of the internal combustion engine and / or according to the operating state of the components, in particular the degree of adhesion of the particulate filter. In this case, the reproduction stage is arbitrarily started using an external start signal. By doing so, it becomes possible for the operator to create a regenerated state of the component parts. For example, when an automobile equipped with the internal combustion engine is brought into a service factory, the internal combustion engine and its components Can be diagnosed.

  The regeneration of the diesel particulate filter is then carried out intermittently, for example as a function of the exhaust gas back pressure. The exhaust gas temperature and the filter temperature required for the oxidation process for filter regeneration are generally about 600 ° C. or higher under the assumption of a sufficient oxidation rate. Such a temperature can only be expected in the 'average pressure / rotational speed characteristic map' above the internal combustion engine without additional measures, so the post-injection of diesel fuel into the combustion chamber or into the exhaust gas pipe The exhaust gas temperature required for regeneration of the filter is raised using the reaction heat generated at that time. This approach is associated with the drawback of increased fuel consumption.

  In addition to post-injection, the diesel particulate filter can be regenerated through additional electrical energy or fuel addition by means of additional burners in the main or side flow of exhaust gas, or intervention in the engine stroke that results in temperature rise. be able to. Regeneration by adding fuel is problematic from the viewpoint of durability of the diesel particulate filter. This is because, in this case, metal ash is taken in, which shortens the service life of the diesel particulate filter.

  The method according to the invention, on the other hand, provides a method for operating an exhaust gas purification system arranged in the exhaust gas region of an internal combustion engine, which enables regeneration of the filter without increasing the fuel consumption of the internal combustion engine. provide.

  According to the present invention, by reducing the air flow rate through at least one combustion chamber of an internal combustion engine, the heat generation amount of the air-fuel mixture is significantly increased while maintaining the fuel consumption almost the same, and the filter regeneration associated therewith is reduced. The required increase in exhaust gas temperature is achieved.

  The reduction of the air flow rate through at least one combustion chamber of the internal combustion engine is preferably carried out continuously during all predetermined operating phases. To some extent, continuous regeneration of the filter within the range defined by this continuous reduction in air flow is possible. In this case, even if the filter cannot be completely regenerated, it can be regenerated intermittently, for example by additional measures in the form of post-injection of diesel fuel into the combustion chamber or into the exhaust gas pipe, or by fuel addition, for example. The interval of is extended.

The predetermined operating stage in which the filter is regenerated is preferably a partial load region of the internal combustion engine.
The reduction of the air flow rate through the at least one combustion chamber of the internal combustion engine can be realized in various ways purely in principle. According to one advantageous embodiment, the reduction of the air flow rate through the at least one combustion chamber of the internal combustion engine is caused by the closing of the mirror moved by the early closing of the at least one intake valve of the at least one combustion chamber. It is considered to be realized in the same way as the method (Miller-Verfahren). In the present invention, the closing of at least one intake valve is understood to be the closing of the intake valve that is moved in the early direction in the case of an internal combustion engine having one intake valve per combustion chamber. The This is done in one or more combustion chambers of the internal combustion engine, depending on the number of cylinders and their operating strokes. In the case of an internal combustion engine with two intake valves per combustion chamber, for example, it is understood that the valve is moved in an early direction similar to the mirror method of both intake valves of one or more combustion chambers. The

  As an alternative or in addition, in addition to the early closing of one or more intake valves, one can also consider the early closing of one or more exhaust valves, which increases the residual gas volume. In addition, the air flow rate through the combustion chamber of the internal combustion engine is reduced. Also in this case, in the case of an internal combustion engine with one exhaust valve per combustion chamber, the exhaust valve of at least one combustion chamber is closed early. In the case of an internal combustion engine with two or more exhaust valves per combustion chamber, in particular two exhaust valves per combustion chamber, these two exhaust valves of at least one combustion chamber are closed early.

  These embodiments are based on variable valve drive. The basic idea of this design is the so-called Miller method, which has been used only in large diesel engines such as marine engines, and is used in direct injection diesel engines for automobiles. Accordingly, the heat generation amount of the air-fuel mixture and the accompanying increase in the exhaust gas temperature are brought about within the corresponding high air-excess partial load region. The advantages of this method are, in part, based on the early movement of the closing of one or more intake valves and / or the early movement of the closing of one or more exhaust valves. In addition to a significant increase in fuel consumption, this method does not cause deterioration of untreated exhaust gas.

According to another embodiment of the method, the reduction in air flow is provided by at least one throttle valve located in the intake manifold.
At that time, the exhaust gas purification system can be made by various methods. According to one design, a catalyst layer that brings about an oxidation reaction is made by an oxidation catalyst, behind which a diesel particulate filter is connected.

In another embodiment, a diesel particulate filter with an integrated catalyst coating, a so-called catalytic soot filter, is provided.
A combination of a catalyst layer and a particulate filter that provides an oxidation reaction is absolutely necessary for the method described herein. This is because the catalyst layer first oxidizes from nitric oxide to nitric oxide because this oxidation is necessary for the continuous regeneration of the particulate filter, in particular the diesel particulate filter. Such continuous regeneration occurs only when the ratio of nitric oxide NO ₂ to carbon C is greater than or equal to 8.

FIG. 1 schematically shows a combustion chamber 100 of an internal combustion engine as an example, in which a piston 105 moves up and down in a known manner. The combustion chamber 100 includes an inlet duct 110 and an outlet duct 120. The outlet duct 120 has an opening in the exhaust gas system 160, and an exhaust gas purification system including an oxidation catalyst 130 and a particulate filter 140 is disposed in the exhaust gas system. Instead of disposing the catalyst layer 130 and the particulate filter 140 that cause an oxidation reaction, a known CSF (Catalytic Soot Filter), that is, a coated particulate filter, in which the catalyst layer is subjected to an oxidation reaction, particularly nitric oxide. It may also include a filter that results in oxidation of the nitrogen dioxide NO ₂ from NO.

  The inlet duct 110 can be connected to the combustion chamber 100 by an intake valve 112. The outlet duct 120 can be connected to the combustion chamber by an exhaust valve 122. Both the intake valve 112 and the exhaust valve 122 are controlled by a variable valve drive so that the intake and exhaust times can be varied within defined limits. The intake valve 112 and the exhaust valve 122 can be controlled by, for example, an electrohydraulic valve driving device or the like. At this time, this control can be performed via the engine control device 150.

  Particulate adhesion on the particulate filter 140 is measured by a differential pressure sensor 145 that measures the pressure difference between the front and rear exhaust gas 140 as viewed in the direction of the exhaust gas flow. The output signal of the differential pressure sensor 145 is also sent to the control device 150. Various operating states of the internal combustion engine are measured by suitable sensors, for example, a sensor for measuring the rotational speed, a sensor for measuring the combustion temperature, and the like. As a representative of these many sensors, FIG. 1 shows a sensor 160, and an output signal of this sensor is sent to the control device 150.

A throttle valve 170 is further arranged in the inlet duct 110, and the position of this valve is determined by the control device 150 and can be electrically controlled.
A method for regeneration of the particulate filter 140 will now be described with reference to FIG.

The basic idea of the present invention is to reduce the air flow rate through the combustion chamber 100 of the internal combustion engine in a predetermined operating phase, i.e., particularly in the partial load region of the internal combustion engine. This idea is based on the idea that a reduction in the air flow rate through the combustion chamber 100 in a high excess air partial load region can result in a significant increase in the mixture heat generation and a concomitant increase in the exhaust gas temperature. Is based. In this case, the exhaust gas temperature can be increased to allow the particulate filter 140 to be passively and continuously regenerated. For this purpose, in a first step 210, it is checked whether or not it is in the operating stage necessary for regeneration, ie in the partial load region. If it is in the partial load region (affirmative: y), then in step 220 there is a desirable ratio of nitric oxide NO ₂ to the limiting conditions for regeneration, especially carbon C, which will be explained in more detail later. It is checked whether or not If the critical condition for regeneration exists (Yes: y), the air flow rate through the combustion chamber is reduced at step 230. This is because, for example, closing the intake valve 112 earlier, that is, 'moving toward the earlier crankshaft angle when the intake valve 112 is closed' (ie, closing the intake valve 112 earlier). By moving it toward the crankshaft angle.

  The movement at the valve closing time in the “earlier” direction is performed in the same manner as in the mirror method. However, unlike the Miller method, here the air flow reduced by the early closing of the intake valve is balanced by the higher pressure in the intake duct 110 generated using an exhaust gas turbocharger, compressor, etc. There is nothing. According to the present invention, due to the early closing of the intake valve 112, the combustion chamber 100 in the partial load region, which is the subject of the examination here, and in which a high excess air ratio already exists anyway. It is possible to reduce the amount of ballast air, which results in a significant increase in the heating value of the mixture and the exhaust gas temperature required for regeneration.

Purely in principle, a reduction in the air flow rate through the combustion chamber 100 can also be achieved by compression of the residual gas by the early closing of the exhaust valve 122 similar to the Miller method.
The reduction of the air flow rate through the combustion chamber 100 can also be performed as an alternative or additionally by corresponding control of the throttle valve 170.

  The advantages of the method described above are that, based on the thermodynamic limit conditions, only a slight increase in fuel consumption occurs when the new gas amount is narrowed down, and the particulate filter 140 is increased by raising the exhaust gas temperature. This will result in continuous and passive regeneration. Furthermore, the quality of the raw exhaust gas in the exhaust gas duct 120 is also improved. This creates the possibility of achieving complete regeneration of the particulate filter 140 even in a low temperature range.

This regeneration is then preferably carried out continuously during the entire operating phase, i.e. in the entire subregion. In this case, this continuous reproduction is performed by the method described below. Nitric oxide NO present in the exhaust gas in the oxidation catalyst 130 is oxidized to nitrogen dioxide NO ₂ . This is because the soot to carbon monoxide CO or carbon dioxide CO ₂ , ie the oxidation of carbon C, was much lower with nitrogen dioxide NO ₂ than with molecular oxygen O ₂ and was mentioned earlier. This is because it is performed at a temperature that can be realized by the method. Therefore, a large amount of nitrogen dioxide NO ₂ so that the oxidation catalyst 130 is always oxidised at the same time so that the soot is oxidized and undesirable soot deposition and the resulting pressure loss in the particulate filter 140 is avoided as much as possible. Must be generated. Soot oxidation is determined mainly by the ratio of carbon (soot) to nitrogen dioxide NO ₂ . Full regeneration is possible only when the ratio of nitrogen dioxide NO ₂ to carbon C is greater than 8.

  The method described above for the continuous regeneration of the particulate filter 140 located in the exhaust gas region requires only a slight increase in fuel consumption during the regeneration phase. This is because high pressure loss does not occur in the particulate filter 140, and the time interval until forced regeneration performed by, for example, post-injection is clearly extended, and thereby increase in fuel consumption is remarkably suppressed. It is. It is also very advantageous that the air-fuel mixture homogenization can be realized at the same time while suppressing the filling temperature before the start of combustion by closing the intake valve early. In this way, the soot discharge in the untreated exhaust gas can be significantly reduced.

  In addition, it is possible to improve cold start emissions, especially hydrocarbon and carbon monoxide emissions, and this emission is clearly suppressed by raising the heating value of the mixture and the associated average gas temperature. .

  The method described here can be adopted in parallel with the methods known from the prior art for the regeneration of particulate filters, in which a forced regeneration takes place in a defined operating phase. Should be pointed out. In that case, the additional interval between the two regeneration intervals in which forced regeneration is performed, for example by post injection, is clearly extended.

A schematic representation of the technical environment in which the invention is implemented; 2 is a flowchart of a method according to the present invention.

Claims (10)

A catalyst layer (130) that is disposed in the exhaust gas region of the internal combustion engine and brings about an oxidation reaction and a particulate filter (140). At least one exhaust gas component is deposited during the operation of the internal combustion engine, and is predetermined. In a method of operating an exhaust gas purification system, which is regenerated from their exhaust gas components during a possible operating phase,
The air flow rate through the at least one combustion chamber (100) of the internal combustion engine is reduced during a pre-determinable operating phase of the regeneration of the particulate filter (140);
A method for operating an exhaust gas purification system.   2. The operating method according to claim 1, wherein the reduction of the air flow is carried out continuously during a pre-determinable operating phase of the regeneration of the particulate filter (140).   The operating method according to claim 1, wherein the operation stage that can be determined in advance is a partial additional region of the internal combustion engine.   Similar to the Miller method, the reduction of the air flow rate through the at least one combustion chamber (100) of the internal combustion engine is similar to the Miller method due to the early closing of at least one intake valve (112) of the at least one combustion chamber (100). The operation method according to claim 1, wherein the operation method is performed as follows.   Using residual gas compression, as with the Miller method, the reduction in air flow through at least one combustion chamber (100) of the internal combustion engine is caused by a closed valve moved in the early direction of at least one exhaust valve (122). The operating method according to claim 1, wherein the operating method is performed.   4. Actuation according to claim 1, characterized in that the reduction of the air flow rate through the at least one combustion chamber (100) of the internal combustion engine is effected by a throttle valve (170) arranged in the intake manifold. Method.   The catalyst layer for causing an oxidation reaction is an oxidation catalyst (130), and the particulate filter is a diesel particulate filter (140) connected behind the catalyst. Actuation method.   7. The operating method according to claim 1, wherein the exhaust gas purification system is made by a coated particulate filter, in particular a catalytic soot filter.   A computer program for executing all the steps of the operating method according to any one of claims 1 to 8 when executed by a computing device.   A program code recorded on a machine-readable carrier for carrying out the operating method according to any of claims 1 to 8, when the program is executed on a computer or a control device (150). Computer program product.

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