KR20010101549A - Method and arrangement for purifying an exhaust gas stream of a spark ignition engine flowing in an exhaust gas line - Google Patents

Abstract

The present invention relates to a method and an apparatus for purifying an exhaust gas stream of a spark ignition engine (1) that flows through an exhaust gas line (2). Preferably, the air / fuel mixer is supplied to the spark ignition engine by direct injection. In order to improve the purification of exhaust gas, the exhaust gas is introduced into the exhaust gas line 2 by at least one honeycomb body 3 having a catalytically activated coating part, preferably a three-way coating part, and at least one contaminating component, HC), carbon monoxide (CO), and / or nitrogen oxides (NO _x ) at least temporarily. The present invention is particularly suitable for the exhaust gas system of the spark ignition engine (1). The particle filter 4 not only functions to collect the soot particles but also advantageously performs the function of additionally oxidizing residual hydrocarbon (HC) and carbon monoxide (CO) during the cold start phase, (NO _x ), especially when it is operated in the state of the exhaust gas.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for purifying an exhaust gas stream of a spark ignition engine that flows through an exhaust gas line,

In the spark ignition engine, for example, during the combustion of hydrocarbons in gasoline using air, it contains substantially the hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO _x ) as well as the main combustion products carbon dioxide and steam May be formed as a by-product, and soot particles may also be formed. The amount of contaminants and soot particles in the exhaust gas is mainly dependent on the air-fuel ratio given. When the air-fuel ratio is low, the composition of the mixture is referred to as " rich " (lack of air) and when the air-fuel ratio is high, the composition of the mixture is expressed as " lean "

Soot is mainly formed when air shortage is burned in an excessive state. In a spark ignition engine this state is typically not reached, but such a condition may occur locally, especially due to non-uniformities during the cold start phase. The formation of soot is generally initiated by pyrolysis of the fuel molecules in the case of oxygen deficiency, the hydrogen is separated and the polymerization of the carbon-rich polymer takes place, after which these polymers aggregate and finally form soot particles. The reason that the soot is remarkably increased when the stoichiometric air-fuel ratio is reached is because the injection amount is increased and the rich mixture region is expanded more and more. Soot formed in the richer mixer region is generally not combusted without additional measures.

In order to ensure that these unburned soot particles do not contaminate the environment, for example, DE 41 17 676 A1 discloses the installation of one or more filters, in particular of a structure which improves the adhesion of soot particles in the exhaust system of a diesel engine . This kind of particle filter is regenerated, in other words, the soot particles attached by, for example, fuel and air are occasionally supplied in order to heat the particle filter, and soot particles formed in the state of lack of air are again burned. DE 40 12 719 A1 also discloses providing a filter with a catalytic converter for converting one or more pollutants, in particular hydrocarbons (HC), carbon monoxide (CO), and / or nitrogen oxides (NO _x ) have.

Further, when the air shortage is burned in an excessive state, the exhaust gas contains a relatively large amount of CO and HC, but in the air excess state, CO and HC can be almost completely oxidized to a certain level. The NO _X content reaches a maximum value in the mixer composition range, which is somewhat lean. However, the specific fuel consumption in a spark ignition engine is optimized just above this. Thus, if the spark ignition engine is set to have an optimum low consumption, there will be a high NO _x concentration as well as adequate CO and HC concentrations in the exhaust gas. However, so far, little has been taken of the fact that spark ignition engines are generally smaller in size than diesel engines and produce smaller overall volume particles. Nonetheless, these types of particles may contaminate the environment.

The present invention relates to a method and apparatus for purifying the exhaust gas flow through an exhaust system, preferably from a spark ignition engine, through which an air / fuel mixture is fed via direct injection.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 schematically shows an apparatus for purifying exhaust gas flow.

It is an object of the present invention to provide an improved method and apparatus for purifying the exhaust gas flow through the exhaust system from a spark ignition engine.

This object is achieved by the method according to claim 1 and the device according to claim 12. Advantageous configurations and fine features are described in the respective dependent claims.

A new method for purifying the exhaust stream from the spark ignition engine, which is preferably fed by direct injection, by means of an air / fuel mixer, in the exhaust system is characterized in that the exhaust gas of the exhaust system is supplied to the catalytically- One or more honeycomb bodies having a three-way coating and at least one or more contaminants, particularly hydrocarbon (HC), carbon monoxide (CO), and / or nitrogen oxides (NO _x ) Characterized in that the particle filter having the coated portion is continuously perfused, whereby the purification of the exhaust gas can be improved.

This may be achieved by placing a particle filter having a coating on the downstream side of at least one honeycomb body having a catalytically active coating thereon and at least one coating for storing at least one contaminating component so that the exhaust gas flowing through the exhaust system Because it has been found that it can be surprisingly purified for any soot particulate.

Thus, if, for example, a rich air / fuel mixer is supplied to the spark ignition engine during the cold start phase, the coating portion of the particle filter, in order to improve the purification of the exhaust gas, stores the unconverted residual HC and / or CO in the honeycomb body .

If a lean air / fuel mixer is supplied to the spark ignition engine, the coating portion of the particle filter will store the untransformed residual NO _x in the honeycomb body to improve the purification of the exhaust gas.

As a result, advantageously, in each case a high concentration of contaminants present in the exhaust gas can be removed in a controlled and most complete manner.

In order to further minimize the amount of nitrogen oxides (NO _x ), it is preferred that the reducing agent supplied via the at least one reducing agent line from the reducing agent reservoir, as a function of the residual NO _x concentration of the exhaust gas downstream of the honeycomb body, Are continuously supplied to the particle filter.

Alternatively, the reducing agent is supplied to the particle filter at intervals, in particular as a function of the amount of residual NO _x stored in the particle filter.

If a reducing agent, such as ammonia, is supplied as a function of the residual NO _x concentration of the exhaust gas downstream of the honeycomb body, it is almost completely prevented that the reducing agent is metered in excess and, thereby, the approximate chemistry between the residual NO _x and the reducing agent A stoichiometric ratio is achieved and the purification of the exhaust gas containing NO _x coming out of the spark ignition engine is advantageously improved. An additional advantage is that the amount of reducing agent required is much less than when the reducing agent is supplied to the exhaust gas prior to perfusion of the honeycomb body with the catalyst activation coating, for example.

According to the invention, it is preferred that the reducing agent line is terminated in a particle filter, which preferably has an integrated dispensing means connected to the reducing agent line.

To further minimize the amount of hydrocarbons (HC) and carbon monoxide (CO), an oxidant, preferably oxygen (O ₂ ), is supplied to the particle filter as a function of the residual HC-CO concentration of the exhaust gas downstream of the honeycomb body do.

Alternatively and / or additionally, it is preferred that the coating of the particle filter store oxygen (O ₂ ) at least occasionally.

Since the oxidant is supplied as a function of the residual hydrocarbon (HC) and the residual carbon monoxide (CO), the over-metering is almost completely prevented, which leads to a reduction in the amount of residual HC and / or CO and, on the other hand, Stoichiometric ratio is achieved and the purification of the exhaust gas containing HC and / or CO from the spark ignition engine is advantageously improved.

Modern spark ignition engines typically have electronic engine control units or similar control means. For example, in order to improve the exhaust gas purification control using the engine control unit, at least one measuring probe for measuring at least one contamination component not converted in the honeycomb body is disposed between the honeycomb body and the particle filter, according to, respectively, a probe for measuring at least one is preferably provided to measure hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NO _X) residual contaminants. In this way, advantageously, in the downstream particle filter, which can detect the residual contaminants which have not been converted in the honeycomb body and which also have a coating part with a corresponding storage capacity, for example by means of an electronic engine control unit, Can be controlled to convert the pollutant with the aid of a reducing agent or an oxidant supplied to the particle filter.

Preferably, according to the present invention, the particulate filter is regenerated by burning the particulate, this process occurring, in particular, by the heat of the engine and / or by the exothermic reaction in the honeycomb body, Lt; RTI ID = 0.0 > and / or < / RTI >

Unlike the individual arrangements described so far, at least some of the honeycomb bodies may also form a particle filter at the same time, which advantageously saves space.

Additional features, advantages, and configurations of the present invention will be described with reference to the accompanying drawings on the basis of illustrative embodiments.

1 schematically shows an apparatus for purifying the exhaust gas flow through the exhaust system 2 from a spark ignition engine 1, which is preferably supplied with an air / fuel mixture via direct injection. (HC), carbon monoxide (CO), and / or nitrogen oxides (NO _x ), at least one or more of the at least one contaminant component, A particle filter 4 provided with a coating part for storing the particles is arranged in a row along the flow direction S of the exhaust system.

The coated portion of the particle filter 4 is at least in part adapted to store the unconverted residual HC and CO in the honeycomb body 3 when a rich air / fuel mixer is fed into the spark ignition engine 1, / Fuel mixer is supplied to the spark ignition engine 1, it is preferable that the residual NO _x not converted in the honeycomb body 3 is stored.

In each case, to measure the residual contaminants in the hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NO _X) is provided for at least one measurement probe (5, 6, 7), these probes Honey For example, an electronic engine control unit (not shown) disposed between the comb body 3 and the particle filter 4, and this electronic engine control unit advantageously also incorporates a program for controlling exhaust gas purification have. In particular, the electronic engine control unit can be used to meter the reducing agent and / or the oxidant that need to be added.

Therefore, the reducing agent supplied from the reducing agent reservoir 8 via the reducing agent line 9 by the pump 11 is oxidized by the oxidizing agent or the reducing agent stored in the measured residual HC- CO < / RTI > concentration or the measured residual NO _x concentration. The particle filter (4) preferably comprises an integrated distribution means (10) connected to a reducing agent line (9), in particular for supplying a reducing agent.

The reducing agent to be used is preferably an ammonia fluid which is stored in the reducing agent reservoir 8 and can be supplied when necessary. Alternatively, the reducing agent may be stored in a reducing agent reservoir 8 as a stored precursor, e.g., urea, and may be stored, if necessary, as a fluid, especially after being generated by pyrolysis, Can be supplied to the particle filter (4).

The structure of the particle filter 4 improving the adhesion of the soot particles is preferably a porous structure or a channel structure, and in the case of a channel structure, these channels are preferably arranged at least partially offset and / or crossed. In order to regenerate the particle filter 4, i. E. To burn the soot particles attached in the particle filter, the particle filter 4 is arranged at least close enough to the back of the honeycomb body 3, Is burned at a time interval which can be preferably determined in advance due to the exothermic reaction in the step (3).

Preferably, according to the present invention, at least a part of the honeycomb body 3 may simultaneously form the particle filter 4.

It should be noted that the honeycomb body 3 and the particle filter 4 of the configuration according to the present invention as well as additional components may be provided in the exhaust system 2 of the spark ignition engine 1. [ Particularly, at least one water trap may be disposed upstream of the honeycomb body 3, and even if the exhaust gas has a temperature of several hundreds of degrees Celsius, the desired oxidation or reduction reaction may occur The honeycomb body 3 and the catalytic coating portion of the honeycomb body are kept as dry as possible so that they can occur in the comb body 3.

In addition, in order to at least occasionally raise the temperature of the exhaust gas, an electrically heatable catalytic converter can be arranged in the upstream exhaust system 2 of the honeycomb body 3, The material is converted by the catalyst. Finally, the honeycomb body 3 itself may be electrically heated.

The present invention is particularly suitable for emissions of a spark ignition engine. In this case, the particle filter 4 not only serves to collect any soot particles but also additionally oxidizes residual hydrocarbons (HC) and carbon monoxide (CO) during the cold start phase, (NO _x ), especially when the catalyst is running under the load condition.

Description of the Related Art [0002]

1: spark ignition engine 2: exhaust system

3: Honeycomb body 4: Particle filter

5: Measuring probe 6: Measuring probe

7: Measuring probe 8: Reducing agent reservoir

9: Reducing agent line 10: Dispensing means

11: pump S: flow direction

Claims (23)

A method for purifying an exhaust gas flow through an exhaust system (2) from a spark ignition engine (1), which is preferably fed via an air / fuel mixture via direct injection, comprising the steps of: (HC), carbon monoxide (CO), and / or nitrogen oxides (NO) and / or nitrogen oxides (NO) Characterized in that the particle filter (4) having a coating part for storing the particles ( _X ) is successively perfused. 3. The method according to claim 1, wherein when the spark ignition engine (1) is supplied with a rich air / fuel mixture, the coating of the particle filter (4) stores the unconverted HC and CO in the honeycomb body (3) . ≪ / RTI > 2. A method according to claim 1, characterized in that when the spark ignition engine (1) is supplied with a lean air / fuel mixture, the coating of the particle filter (4) stores the untransformed residual NO _x in the honeycomb body Lt; / RTI > 4. A particle filter according to any one of claims 1 to 3, characterized in that a reducing agent such as ammonia is supplied to the particle filter (4) as a function of the residual NO _x concentration of the exhaust gas downstream of the honeycomb body (3) How to. The method of claim 4, wherein the reducing agent is continuously supplied. 5. A process according to claim 4, characterized in that the reducing agent is supplied at a time interval, in particular as a function of the residual NO _x amount stored in the particle filter (4). 4. The exhaust gas purification device according to any one of claims 1 to 3, wherein an oxidizing agent, preferably oxygen (O ₂ ), is added to the particle filter (4) to reduce the residual HC-CO concentration of the exhaust gas on the downstream side of the honeycomb body ≪ / RTI > To claim 1, wherein according to any one of claim 7, characterized in that the additional coating of the particle filter (4) stores at least at times the oxygen (O _2). 9. The honeycomb body (3) according to any one of claims 1 to 8, wherein at least one measuring probe for measuring at least one residual contaminant component not converted in the honeycomb body (3) ≪ / RTI > Each of claim 9, wherein the at least one probe (5, 6, 7) for measurement is being provided to measure the residual contaminants hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NO _X) Way. 11. A process according to any one of the preceding claims, characterized in that the particle filter (4) is regenerated by burning the particles and this process is carried out in particular by the heat of the engine and / or by the exothermic reaction in the honeycomb body (3) , Preferably at a time interval that can be predetermined. An apparatus for purifying an exhaust gas flow through an exhaust system (2) from a spark ignition engine, which is preferably supplied with an air / fuel mixture via direct injection, characterized in that the catalyst (HC), carbon monoxide (CO), and / or nitrogen oxides (NO _x ), at least one or more components of the honeycomb body (3) Characterized in that a particle filter (4) having a coating for storing is installed in succession in the exhaust system (2). 13. The honeycomb structure according to claim 12, wherein, when a rich air / fuel mixture is supplied to the spark ignition engine, unconverted hydrocarbons (HC) and carbon monoxide (CO) ). ≪ / RTI > The method of claim 12, wherein the spark-ignition when a lean air / fuel mixture supplied to the engine 1, the honeycomb body 3 unconverted NOx in (NO _X), coating of the particle filter (4) RTI ID = 0.0 > 1, < / RTI > 15. A method according to any one of claims 12 to 14, wherein the reducing agent, such as ammonia, is supplied from the reducing agent reservoir (8) as a function of the residual NO _x concentration of the exhaust gas downstream of the honeycomb body (3) Can be fed to the particle filter (4) via line (9). 16. Apparatus according to claim 15, characterized in that the reductant line (9) is terminated in a particle filter (4). 17. An apparatus according to claim 16, characterized in that the particle filter (4) comprises an integrated distribution means (10) connected to the reductant line (9). 13. The method of claim 12 to claim 17 any one of items, as a function of the residual HC-CO concentration in the downstream exhaust gas of an oxidizing agent such as oxygen (O ₂₎ the honeycomb body (3) in the particle filter (4) Lt; RTI ID = 0.0 > 1, < / RTI > To claim 12 according to any one of claim 18, wherein the coating portion that is adapted to store at least at times the oxygen (O ₂₎ of the particle filter (4). The honeycomb structure (3) according to any one of claims 12 to 19, characterized in that, in order to measure at least one residual contaminant component not converted in the honeycomb body (3) Wherein a plurality of probes for measurement are arranged. The method of claim 20, wherein each at least one probe (5, 6, 7) for measurement is being provided to measure the residual contaminants hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxides (NO _X) Device. 22. A method according to any one of claims 12 to 21, wherein the particle filter (4) is preferably regenerated at a predetermined time interval, the process being performed by heat of the engine and / 3). ≪ / RTI > 23. Apparatus according to any one of claims 12 to 22, characterized in that at least part of the honeycomb body (3) simultaneously forms a particle filter (4).