WO2006048120A1

WO2006048120A1 - Method for operating an internal combustion engine with an scr catalyst

Info

Publication number: WO2006048120A1
Application number: PCT/EP2005/011243
Authority: WO
Inventors: Berthold Keppeler; Detlef Scharr
Original assignee: Daimlerchrysler Ag
Priority date: 2004-11-03
Filing date: 2005-10-19
Publication date: 2006-05-11
Also published as: DE102004053041A1

Abstract

The invention relates to a method for operating an internal combustion engine, especially a reciprocating piston engine of a motor vehicle. Said engine comprises a plurality of combustion chambers (3) in which a fuel/air mixture is combusted in a multiple stroke cycle, thereby releasing energy. Exhaust gas produced in the combustion chambers (3) is fed to an exhaust gas cleaning system, said exhaust gas cleaning system comprising a reducing catalyst, especially an SCR catalyst, in which especially nitrogen oxides are chemically reacted using a reducing agent. The inventive method is characterized in that during operation of the internal combustion engine fuel supply is suspended during a first combustion cycle of a combustion chamber. A reducing agent is fed to the combustion chamber (3) in said first combustion cycle and is then transported to the SCR catalyst. For this purpose, an injector (11) for the reducing agent is used to inject the reducing agent into the combustion chamber (3), the inlet channel (7) or the outlet channel (8). The inventive method can for example be used for diesel engines or lean mix spark-ignited engines.

Description

Method for operating an internal combustion engine with an SCR catalytic converter

The present invention relates to a method for operating an internal combustion engine, in particular a motor vehicle reciprocating engine, having a plurality of combustion chambers, in each of which a fuel / air mixture is burned with release of energy by a multi-stroke process, wherein generated in the combustion chambers exhaust gas is fed to an exhaust gas purification system, said the emission control system comprises a catalyst, in particular a reduction catalyst, further comprising in particular an SCR catalyst in which pollutants are reduced by physical and / or chemical reactions, in which in particular nitrogen oxides are chemically reacted by means of a reducing agent. The present invention further relates to an internal combustion engine for carrying out said method.

A method for operating a diesel engine is known from EP 0 708 809 B1, in which particles of a platinum group metal metal are added to the diesel fuel for exhaust gas purification and an aqueous reducing agent solution near the end of the working stroke (third cycle) of a working cycle is injected into the combustion gases. Subsequently, the thus treated combustion exhaust gases in a reduction catalyst for the decomposition of nitrogen oxides be reduced. NH 3 -containing compositions such as urea, cyanuric acid, ammonium carbonate, etc., which form or release ammonia in the reduction catalyst, are selected as the reducing agent.

From DE 41 26 705 C2 a method for reducing nitrogen oxide emissions of self-igniting internal combustion engines is known. In this case, during the operation of the engine, a reducing agent in the form of ammonia or urea in a solution is injected directly into the combustion chamber of the engine, independently of the fuel supply. This is preferably done after ignition at a crank angle of 35 ° after top dead center, wherein the amount of the injected reducing agent is adapted to the current engine power.

US Pat. Nos. 5,404,841 and 5,535,708 each discloses a method for reducing nitrogen oxide emissions of a diesel internal combustion engine, in which an emulsion is prepared from a urea solution and a diesel fuel. The emulsion is optionally further admixed with a number of catalytically active metal particles of a metal of the platinum group, copper, iron or manganese, etc. For this purpose, a mixer for mixing water and urea solution and an emulsifier are assigned to the fuel supply system of the internal combustion engine in addition to a fuel tank. The emulsion produced is added and co-incinerated during a normal engine operating process, with a reduced flame temperature and chemical reaction of urea, water, and nitrogen oxides to elemental nitrogen, water, and carbon dioxide being expected. In JP-A-03-213614, a device for exhaust aftertreatment is disclosed in which by means of an injector, a reducing agent in the form of urea is injected into the exhaust gas of the internal combustion engine. Coordinated with the injection of fuel for normal operation is brought at an exhaust gas temperature of about 850 ⁰ C urea in the combustion chamber or in the exhaust manifold.

Object of the invention is in contrast to provide a method of the type mentioned above and a suitable for carrying out the method of internal combustion engine, in which in a cost effective manner a particularly effective treatment of reducing agent for use of the processed reducing agent in the exhaust line of the internal combustion engine is made possible.

This object is achieved by a method having the features of claim 1 and an internal combustion engine having the features of claim 7. Advantageous embodiments and further developments of the invention are the subject of the respective dependent claims.

Characteristic of the method according to the invention is that a fuel supply is exposed during operation of the internal combustion engine in a first cycle of a combustion chamber and in this first cycle a reducing agent is supplied into the combustion chamber and subsequently transported into the catalyst. A working cycle includes in a known manner two or four strokes in which the working element (piston o. Ä.) Moves through the combustion chamber, sucks combustion air (intake stroke), compressed (compression stroke), expansion work on a (crankshaft) transmits wave (power stroke ) and if necessary, combustion exhaust gases ausschiebt (Ausschiebetakt). In normal Operation of the internal combustion engine is injected into at least one cycle fuel, which is burned in the power stroke. In special modes such as the shift operation is often a fuel supply for a long time, ie interrupted for several cycles in all combustion chambers of the internal combustion engine. According to the invention, in a working cycle in which the fuel supply to a combustion chamber is interrupted, a particular nitrogen-containing reducing agent is introduced into the respective combustion chamber. The introduced reducing agent should not be burned, but mainly physically and / or chemically treated, mixed with air and / or exhaust gas and homogenized. In particular, it is provided that the reducing agent is subjected to thermal decomposition to release ammonia compounds or pure ammonia. For this purpose, it is transported together with air or exhaust gas through one or more cycles of the working cycle and then into the exhaust system. In addition, a heat removal from the combustion chamber is realized by a suspension of combustion with simultaneous supply of non-burning reducing agent and air, which is thus cooled for a subsequent cycle.

In an embodiment of the invention, a reducing agent in the form of a urea-water solution is provided. In particular, such a solution requires the treatment strategy of the invention, since it is difficult to handle in the exhaust system of an internal combustion engine. With the aid of the method according to the invention, a urea / water solution is particularly well conditioned and mixed with a carrier gas. It is then ready in an advantageous state for storage in a close-coupled SCR catalyst. In a further embodiment of the invention, a reducing agent is injected directly into the combustion chamber, into an outlet channel or into an inlet channel of the combustion chamber. This can be accomplished by means of an injector arranged directly on the combustion chamber, on the inlet or outlet channel of the combustion chamber. In particular, a fuel injector of a direct-injection engine set to a "bivalent" operation for alternately injecting fuel and reducing agent may also be used.

In a further embodiment of the invention, the first cycle comprises four cycles, and a reducing agent is placed in a first and / or in a third cycle in the combustion chamber. In the first or third cycle of a cycle, there is generally an expansion movement of the working element, and gas may be selectively drawn into the combustion chamber from the inlet port or the exhaust port when an intake or exhaust valve is opened. At the same time, a reductant injected into the cycle at an early stage can be swirled during the entire cycle and brought into contact with the combustion chamber surface.

In a further embodiment of the invention, the first cycle after one or more preceding in the same combustion chamber working games with normal fuel injection is selected. In this case, a setting of the fuel injection at one or more combustion chambers of the internal combustion engine is selected, which can be used selectively during normal working operation, in particular also at medium or higher load of the internal combustion engine, in particular during a lean operation of the internal combustion engine. Positive effect is that the Combustion chamber temperature is effectively lowered. During cold start operation, such a procedure may also be expedient, since a metered addition of the reducing agent into the combustion chamber generally requires that a noble metal-containing oxidation catalyst close to the engine has not yet reached its light-off temperature for a conversion of the reducing agent. Consequently, in the cold start operation by means of the inventive method, a storage of reducing agent in an SCR catalyst can be realized, even if an oxidation catalyst is connected between the engine and SCR catalyst.

In a further embodiment of the invention, the first cycle after one or more preceding in the same combustion chamber working cycles without fuel injection is selected at operating-warming internal combustion engine. A particularly good conditioning is obtained, for example, during coasting of the internal combustion engine when both the combustion chamber and the exhaust line each have an average temperature which allows a homogenized sluice of urea / water solution and / or ammonia-containing decomposition products into an SCR catalyst.

The above and other advantages, features and advantageous developments of the subject invention will become apparent from the following description and the drawings. Therein, the single figure shows schematically a combustion chamber of a running as reciprocating engine internal combustion engine to which the inventive method is feasible.

The present invention relates to a multi-cylinder reciprocating internal combustion engine configured internal combustion engine (eg passenger car gasoline engine), the lean at least in some operating conditions with a total Air / fuel ratio is operated (air / fuel ratio λ> 1 based on a working cycle). The internal combustion engine comprises an engine block in which cylindrical bores 1 for guiding a respective movable piston 2 are provided, wherein the bores are closed to form combustion chambers 3 upwards with a known cylinder head 4 (see FIG.). The piston 2 transmitted via associated connecting rod 2a forces on a crankshaft mounted on the engine block, at which the engine output torque is to be removed.

The internal combustion engine further comprises a fuel injection system each having a fuel injector 5 per combustion chamber mounted in the cylinder head 4. Accordingly, the fuel can be injected directly into the combustion chamber 3 by means of the fuel injector 5. The embodiment selected by way of example relates to a spark-ignition internal combustion engine with direct injection (Otto-DE engine), with which all types of homogeneous and / or stratified charge operation can be carried out, and therefore has a spark plug 6. In a modified embodiment, a self-igniting internal combustion engine is provided which operates according to the diesel process. As a fuel injector both pump-nozzle systems and common rail systems come into question.

In the cylinder head 4, an inlet channel 7 and an outlet channel 8 are provided for the charge exchange of each combustion chamber 3, which can be closed against the combustion chamber 3 via an inlet valve 9 or an outlet valve 10.

The internal combustion engine further comprises a

In an exhaust gas purification system, in a manner not shown an optional oxidation catalyst known per se and a known SCR catalyst in succession in an exhaust pipe are arranged. Under an SCR catalyst (SCR = Selective Catalytic Reduction) is here as usual to understand a catalyst which is able to store NH ₃ (ammonia) and under oxidizing exhaust gas conditions supplied nitrogen oxides with stored or supplied with NH ₃ predominantly to reduce harmless N ₂ (nitrogen). Optionally, the SCR catalytic converter can be combined with an upstream nitrogen oxide storage catalytic converter. Nitrogen oxide storage catalytic converter and SCR catalyst thus serve mainly to remove nitrogen oxide during lean operation of the associated internal combustion engine. The catalysts are preferably designed as honeycomb body.

In the case of a predominantly lean-running internal combustion engine, it is not possible to generate sufficient NH ₃ as a reducing agent on-board, so that a metered addition of externally supplied reducing agent is required Above all with regard to the temperature and the mixing with a carrier gas (air, exhaust gas, etc.), certain boundary conditions must be observed in order to avoid deposits and poor reaction behavior.

According to the invention is therefore provided in the context of a method for operating an internal combustion engine, a reducing agent, in particular a conventional urea / water solution or the like to pass through a combustion chamber 3 of the internal combustion engine. In this case, this function can be extended to a single combustion chamber of the internal combustion engine or to several or all combustion chambers. This is associated with at least one combustion chamber, an injector 11 for supplying the reducing agent. After the reducing agent has left the combustion chamber 3, it is transported to the exhaust gas purification plant and in particular to an SCR catalyst with ammonia storage function contained therein.

A supply of reducing agent into a combustion chamber preferably takes place during a first work cycle, in which a fuel supply to the respective combustion chamber 3 is interrupted. This results in a good treatment of the reducing agent in the warm combustion chamber 3, which in turn briefly, namely during the first cycle (without combustion process with simultaneous supply of cool reducing agent) is cooled by heat to reducing agent and intake air. Due to the inventive heating of the reducing agent on the component heat of a (warm operating) combustion chamber, the reducing agent can also be metered at temperatures in the exhaust line of below 180 ⁰ C and stored in the SCR catalyst. Especially in this case, if necessary, a close-coupled oxidation catalyst (without a possible bypass) of reducing agent can be passed unchanged, because the oxidation catalyst should not have reached its light-off temperature for the oxidation of ammonia. Optionally, of course, bypass pipes can be provided for certain exhaust gas cleaning elements upstream of the SCR catalytic converter, which can be activated when reducing agent is added to a combustion chamber.

In a first working cycle (immediately) following a second working cycle, a combustion process in the combustion chamber 3 can again be carried out. Alternatively, the supply of fuel is again suppressed, with optionally a supply of reducing agent and / or fresh air and / or exhaust gas is performed. In a first work game (immediately) preceding third cycle, a combustion process is performed when a particularly good heating of the reducing agent is to be achieved. In a third working cycle preceding the first working cycle, a supply of fuel is interrupted, in particular when the internal combustion engine is at operating temperature, if cooling of the combustion chamber and / or an exhaust gas purification system is to be achieved before a reducing agent is added.

According to the invention, the reducing agent in the combustion chamber is particularly well swirled and mixed with air and / or exhaust gas when it is injected in a first power stroke (intake stroke) of the respective working cycle and discharged from the combustion chamber in a fourth power stroke (Ausschiebetakt). Further, intake valve 9 and exhaust valve 10 are operated in the usual manner (corresponding to a normal cycle with combustion process). Exhaust gas recirculation may be on or off during the first cycle. A supply of reducing agent is accomplished as shown in the figure by means of an additional injector 11, wherein the injector 11 injects directly into the combustion chamber. In a modified exemplary embodiment, the injector 11 is arranged close to the combustion chamber in the inlet channel 7. In a further modified embodiment, the fuel injector 5 is designed for a bivalent operation, so that it can take over an injection of reducing agent.

A supply of reducing agent into the combustion chamber 3 also preferably takes place in a third power stroke (working or expansion stroke) of the relevant first working cycle, wherein it is again discharged from the combustion chamber in a fourth power stroke (exhaust stroke). Again, intake valve 9 and exhaust valve 10 in the usual way (corresponding to a normal cycle with combustion process) actuated when a supply of reducing agent as shown in the figure can be accomplished by means of an injector which injects directly into the combustion chamber. In a modified embodiment, the injector is arranged in the inlet channel or in the outlet channel, with the inlet valve and / or outlet valve "out of the row" being opened in the third working cycle of the first working cycle An arrangement of the injector 11 in the inlet channel and a corresponding metering in the inlet channel have structural Advantages and results in a good homogenization and a significant reduction in the combustion chamber temperature, the latter aims at a better combustion chamber filling and lower overall combustion temperatures in a subsequent second cycle in the affected combustion chamber.

The inventive method allows a particularly effective homogenization and processing of reducing agents for SCR catalysts and the like, with a separate unit to provide a serving as a carrier gas purge air is unnecessary. Further, an advantageous cooling of a corresponding combustion chamber of the internal combustion engine is achieved, which allows a better filling of the combustion chamber and lower raw emissions subsequent to the implementation of the method according to the invention.

The features of the exemplary embodiments of the method according to the invention that are described by way of example can be combined with one another almost arbitrarily, so that further advantageous features and feature combinations can result.

Claims

claims

1. A method for operating an internal combustion engine, in particular a motor vehicle reciprocating engine, with a plurality of combustion chambers, in each of which a fuel / air mixture is burned with energy release after a multi-stroke process, wherein generated in the combustion chambers exhaust gas is fed to an emission control system, wherein the emission control system a Catalyst, in particular a reduction catalyst, further comprising in particular an SCR catalyst are reduced in the pollutants by physical and / or chemical reactions in which in particular nitrogen oxides are chemically reacted by means of a reducing agent, characterized in that during operation of the internal combustion engine in a first Working cycle of a combustion chamber (3) is exposed to a fuel supply, and in this first cycle, a reducing agent is fed into the combustion chamber and subsequently transported into the catalyst.

2. The method according to claim 1, characterized in that a reducing agent is provided in the form of a urea / water solution.

3. The method of claim 1 or 2, characterized in that a reducing agent is injected directly into the combustion chamber (3), in an outlet channel (8) or in an inlet channel (7) of the combustion chamber.

4. The method according to any one of claims 1 to 3, characterized in that the first cycle comprises four cycles and the reducing agent in a first and / or a third cycle in the combustion chamber (3) is brought.

5. The method according to any one of claims 1 to 4, characterized in that the first cycle after one or more in the same combustion chamber (3) previous working cycles with normal fuel injection is selected.

6. The method according to any one of claims 1 to 5, characterized in that the first cycle after one or more preceding in the same combustion chamber working cycles without fuel injection is selected at operating-warming internal combustion engine.

7. Internal combustion engine for carrying out the method according to one of claims 1 to 6, characterized in that in an inlet channel (7) of a combustion chamber (3) of the internal combustion engine, an injector for supplying reducing agent, in particular a urea / water solution is arranged.