DE10357887A1 - Internal combustion engine for motor vehicle, is connected to exhaust gas purification device comprising precatalyst that is not made up of precious metal and disposed directly in downstream of exhaust gas collector - Google Patents

Abstract

The engine (10) is connected to an exhaust gas purification device having a precatalyst (14) and a main catalyst (18) disposed in the downstream of the precatalyst. The precatalyst is not made up of precious metal and has a support covered with a washcoat. The principal catalyst is connected to the precatalyst by an exhaust gas tube (16). The precatalyst is disposed directly in the downstream of an exhaust gas collector (12). An independent claim is also included for a method for operating an internal combustion engine.

Description

The The invention relates to an internal combustion engine and a method for operation an internal combustion engine respectively according to the preambles of the independent claims.

The for the Exhaust gas aftertreatment in combustion engines commonly used catalysts have a carrier on top of that with a surface enlarging Washcoat is coated. To increase the conversion performance and to reduce the temperature at which the catalyst starts, will be added used in the catalyst noble metal, such as platinum, palladium or rhodium. The washcoat is used in addition to the surface enlargement as a primer for the precious metal loading of the catalyst.

ever according to the engine concept and the emission standard to be respected, one or more Catalysts used. Multiple catalyst systems predominantly at least two carriers on. Common is a shoring of a system with two beams in the underbody area. Furthermore, it is often done a close to the engine attachment of a precatalyst in one in the underbody area arranged main catalyst.

The close to the engine arrangement of the precatalyst, for example, directly behind an exhaust manifold, is used when a particularly rapid heating or warming the entire catalyst system is to be achieved. The precatalyst improves the light-off of the overall system by On the one hand, he emit those from the combustion chamber of the internal combustion engine Partly converted exhaust gases or pollutants, on the other hand in this exothermic reaction additionally generates heat. Such a function of the precatalyst is especially at greater yardage the exhaust gas in the exhaust pipe between the engine and underfloor catalyst required because the heat losses on the pipes of the exhaust pipe are too large to a sufficient rapid heating of the underfloor catalyst to its working temperature guarantee.

One Disadvantage of a close-coupled arrangement of the precatalyst is a strong thermal load of the precatalyst at operating points of the combustion engine with full load or upper part load. thermal Loads can to an agglomeration of the precious metals and thus to a lower active Surface, and this in turn to a lower conversion performance as well to an increased Light-off temperature of the precatalyst lead.

To the Protection of the precatalyst against excessive thermal load In the prior art, operation of the engine with a greased one Engine lambda value used. This is an air / fuel mixture used that a higher proportion having fuel than to realize the required performance needed becomes. The excess fuel is transported unburned through the combustion chamber of the engine and cools as unburned portion of the exhaust gas the precatalyst. This method for temperature protection of the precatalyst is also called component protection (BTS). The enrichment of the air / fuel mixture for the BTS leads to a significantly higher fuel consumption than it for operating at the requested power would be necessary. Further can that be for the catalytic exhaust purification optimum air / fuel ratio lambda = 1.0 more frequently are not met, so that the conversion performance of the Emission control system drops.

To improve the temperature resistance of catalytic converters is already from the DE 44 31 134 A1 known to divide a catalyst in the flow direction into reactive and inert sections. As a result, the exhaust gas heated in the preceding reactive region is cooled in the reaction-inert regions, so that local overheating of the catalyst is avoided by the exhaust gas temperature of the boundary layer increasing in the flow direction in the region of the catalyst inlet. From DE OS 36 43 785 a method for detoxifying engine exhaust gases is known, in which the exhaust gases are passed through an exhaust gas catalyst containing uniformly coated with certain precious metals pellets or monoliths. Prior to coming into contact with the precious metals, the exhaust gases are first passed through a catalyst poison / precipitation zone that is free of noble metals.

From the DE 101 04 751 A1 is a device for cleaning exhaust gases of an internal combustion engine, consisting of a warm body with a near-motor and a motor remote end and an applied to this warm body active coating known.

in the The area of the proximal end of the warm body is at least a coating-free zone. The known device is intended to be a catalyst in such a way that even if in one Form exhaust shot channels reliably prevent local failure of the catalyst.

For further reduction of hydrocarbon (HC) emissions during cold start, the use of HC adsorbers is already known from the prior art. This is preferably to Zeolites added to the coating. Such zeolites can store hydrocarbons adsorptively at low temperatures and high concentrations. When cold starting an internal combustion engine, this situation is given because then the catalyst is cold and high concentrations in the Kaltstartanfettung on hydrocarbons are present. The start-up greasing is then taken back in the after-start and warm-up of the engine, while the catalyst heats up at the same time. This leads to a desorption of HC. Various coating techniques are known. Thus, in a first step washcoat is applied together with precious metal on a support. In a second step, a zeolite is applied. This ensures that the adsorption behavior is still very good even after aging, since the zeolite remains stable even up to higher temperatures than the precious metal contained in the washcoat. However, pollutant components from the exhaust gas must first penetrate the zeolite layer in order to be converted. As the temperature increases, the noble metal in the washcoat layer below the zeolite heats up more slowly, so that the desorption on the outer zeolite layer starts earlier and relatively many hydrocarbons are ejected without being converted. The coating process in the reverse order, this has the disadvantage that the noble metal-containing layer more thermally aging and thus has a higher light-off temperature and lower conversion rates. Furthermore, the adsorption behavior of the zeolite is impaired since the pollutant components must first diffuse through the overlying noble metal-containing washcoat. It is also known to mix noble metal, washcoat and zeolite before the actual coating process and apply together to the carrier. This results in a mixed behavior with regard to aging and adsorption.

From the EP 0 697 505 A1 For example, a system is known in which an apertured adsorber is placed in front of a three-way catalyst. At low penetration of exhaust gas, the flow should continue to rest outside. The guided through the hole partial flow of the exhaust gas heats up the downstream three-way catalyst. From the DE 39 287 60 C2 For example, an exhaust gas purification device is known in which an adsorption trap for the adsorption of a pollutant component from the exhaust gas contains a zeolite. A disadvantage of the mentioned systems is that the desorption temperature of the zeolites is below the light-off temperature of the downstream catalyst, so that hydrocarbons are desorbed that can not fully convert the downstream catalyst. The further hydrocarbon adsorbent and catalyst are separated, the more hydrocarbons pass through the catalyst and are released into the environment. From the DE 42 40 012 A1 For the purpose of solving this problem, an exhaust gas purification device comprising a catalytic converter and an adsorber contained downstream of the same arranged zeolite is known. Applies sufficiently far from the adsorber, a heater for the catalytic converter is provided so that it is already effective when the adsorber releases hydrocarbons.

task The present invention is the provision of an internal combustion engine with an emission control device that is cost effective and constructive easy, a 1 reduction of cold start emissions possible and an increased thermal resistance having.

Further The task includes the creation of a method for operating a Internal combustion engine with an exhaust gas purification device, which a low-consumption and structurally simple temperature protection of the precatalyst allows.

According to the invention Problem solved by the features of the respective independent claims.

According to the invention is provided in an internal combustion engine with an exhaust gas purification device with a precatalyst, and downstream of the precatalyst arranged, connected by an exhaust pipe to the primary catalyst main catalyst, wherein the precatalyst is formed free of noble metal.

The noble metal-free formation of the precatalyst leads to a significant increase in temperature stability in comparison to a precious metal having precatalyst. The noble metal-free design of the precatalyst also allows a faster light-off of the main catalyst. It will be the internal one temperature increase targeted by a certain amount, preferably 50 ° C K, compared to a correspondingly provided with noble metal precatalyst reduced. This thermal protection of the component is achieved. The inventive training the precatalyst allows a Cost reduction compared a noble metal loading of the precatalyst.

The exhaust pipe for connecting the pre-catalyst and the main catalyst has a length of at least 100 cm, a heat loss of at most 1 K / cm length of the exhaust pipe and / or is formed as an air gap-insulated pipe (LSI pipe). The invention therefore also aims at widely separated catalysts. The noble ones Although non-noble precatalyst does not reach the conversion rates of a noble metal-loaded catalyst, it acts as a light-off accelerator due to exothermic reactions. In particular, the main catalyst is brought to its operating temperature faster if only a small heat loss occurs in the exhaust pipe, especially if it is designed as an LSI pipe.

If the precatalyst with a support structure with Having zeolite coating, additional time can be gained, to bring the main catalyst to operating temperature. A increased Conversion performance of the precatalyst is achieved, if this a carrier structure having washcoat coating. The precatalyst can also be a metallic carrier structure, in particular of corrugated and / or wound metal foils, optionally equipped with a zeolite and / or washcoat coating is, bringing another increase thermal and mechanical stability is achieved.

According to the invention, an adaptation of the precatalyst and the main catalytic converter is provided in order to ensure a predetermined overall conversion, preferably of at least 98%, of at least one of the exhaust gas components hydrocarbon, carbon monoxide and nitrogen oxide. The adaptation preferably takes place in such a way that at least one of the following conditions is fulfilled for the conversion of the exhaust gas components hydrocarbon, carbon monoxide or nitrogen oxide:
More than 50%, preferably more than 60%, more preferably more than 70% of the hydrocarbon
More than 60%, preferably more than 70%, more preferably more than 80% of the carbon monoxide
More than 20%, preferably more than 30%, more preferably more than 40% of the nitrogen oxides
the total conversion of the respective exhaust gas component, based on the raw emission is taken over by the precatalyst. Such adaptation reduces the overall cost of the pre-catalyst and main catalyst exhaust system.

Particularly preferred is an adaptation comprising a relative increase in volume of the main catalyst. The inventive method for operating an internal combustion engine provides a noble metal-free precatalyst, wherein an enrichment of an engine lambda value for component protection takes place only at a higher temperature of the precatalyst T _VK , as in a non-precious metal-free precatalyst. Such operation of the internal combustion engine enables fuel economy and lower exhaust emissions due to lower component protection enrichment.

Further Embodiments, aspects and advantages of the invention are also independent of its summary in the claims, the following description and the associated To take drawing. The schematic drawing shows in

1 an internal combustion engine with an associated emission control device.

In 1 is a preferably used in a motor vehicle internal combustion engine 10 shown with several cylinders. To the internal combustion engine 10 is a known exhaust gas purification device with a connecting line 12 (Exhaust manifold), a precatalyst 14 , an exhaust pipe 16 and a main catalyst 18 and another exhaust pipe 20 arranged. Other embodiments of the invention may include more than one main catalyst. Preferably, the precatalyst is 14 close to the engine and the main catalyst 18 arranged in Unterbodenlage.

In addition, however, the invention also includes embodiments in which the precatalyst 14 also arranged in Unterbodenlage. The connection line 12 preferably has a heat loss> 1 K / cm length.

The precatalyst 14 comprises a carrier preferably coated with washcoat and according to the invention is formed free of noble metals. The washcoat is a porous metal oxide layer deposited on the support (substrate). The most common washcoat material is alumina, but other materials such as silica, cerium dioxide, titania, zirconia can also be used.

When carrier are extruded ceramic Honeycombmonolithe with honeycomb cells uses. Preferred is cordierite, a synthetic ceramic Material with a low thermal expansion coefficient.

Further are metallic carriers made of wound and / or corrugated metal foils, for example iron-chromium-aluminum alloys and a thickness of 60-25μm intended.

As in 1 is indicated, is the catalyst 14 housed in a housing with an inlet and an outlet for the exhaust gas.

The main catalyst 18 is downstream of the precatalyst 14 arranged and with the precatalyst 14 through an exhaust pipe 16 connected. The exhaust pipe 16 is preferably longer than 100 cm. To improve the heat coupling between precatalyzer 14 and main catalyst 18 indicates the exhaust pipe 16 a heat loss of at most 1 K / cm in length. Particularly preferred is an air gap-insulated tube (LSI tube). The LSI tube consists of a gas guide channel and an outer shell. Through the outer shell, the heat and noise insulation is improved. Depending on the engine concept used for the internal combustion engine 10 is the main catalyst 18 a three-way catalyst or a nitrogen oxide (NOx) storage catalyst.

According to the invention, the noble metal-free precatalyst is used 14 for heating and heating up to the light-off of the main catalytic converter 18 , In particular, the coating of the carrier of the precatalyst is 14 free of noble metals.

The light-off of the pre-catalyst 14 is based largely on the reaction of the exhaust gas components hydrocarbon (HC) and carbon monoxide (CO) with embedded oxygen (O ₂ ).

After a cold start of the engine 10 becomes the precatalyst 14 reach a light-off temperature within a short period of less than, say, 30s. Here, the light-off temperature is the temperature at which the conversion power has reached a predetermined value of, for example, 50% or 60%. Optionally, the light-off temperature may be different for different exhaust gas components such as HC or CO. In the conversion of HC and CO, there is a reaction of O ₂ incorporated in particular in the washcoat. Since this reaction is exothermic, there is a heating or soaking of the downstream of the precatalyst 14 arranged main catalyst 18 instead of. At a later time after the cold start also has the main catalyst 18 reached its light-off temperature.

In a further embodiment of the invention, the precatalyst 14 a zeolite for storing HC. Due to the improved temporary adsorptive storage of HC, a time is gained in which the downstream of the precatalyst 14 arranged main catalyst 18 can heat up. Since zeolite remains stable even at higher temperatures, the adsorption behavior is good even after thermal aging. Under cold start conditions, typical adsorption times of up to 15 s can be achieved before a noticeable HC desorption occurs. An additional heating of the main catalyst is thus not effected. However, the adsorptive storage of HC achieves a higher conversion rate of the main catalytic converter, for example by about 20%.

According to the invention, the zeolite is applied to a carrier structure of the precatalyst and / or mixed into a washcout coating. precatalyzer 14 and main catalyst 18 are preferably designed such that, depending on the raw emissions of the internal combustion engine 10 and the respectively to be observed exhaust gas limits an average conversion rate of 95 to 99%, preferably 98%, is achieved.

In comparison with the pre-catalysts loaded with noble metal known from the prior art, the precatalyst according to the invention has 14 a lower conversion performance and a lower exotherm.

However, to achieve a given high overall conversion performance, there is an adaptation of the precatalyst 14 and main catalyst 18 intended. The adaptation preferably takes place in such a way that a certain proportion of the total conversion of the respective exhaust gas component is taken over by the precatalyst for the conversion of the exhaust gas components HC, CO or NOx. The precatalyst preferably takes over 14 a proportion of more than 50%, more preferably more than 60% or 70% of the total conversion. For CO, a proportion of 60%, preferably more than 70%, more preferably more than 80% of the total conversion is provided. For NOx, a proportion of more than 20%, preferably more than 30%, more preferably more than 40% is provided. The adaptation can in particular by a relative increase in volume of the main catalyst 18 be achieved. Preferably, the volume increase of the main catalyst takes place 18 at a constant loading density with precious metals, so that the total load of the main catalyst 18 is increased with precious metal. At the same time, however, there is a saving due to the elimination of the noble metal loading of the precatalyst 14 takes place, a reduction of the precious metal loading of the entire system is possible.

In an alternative embodiment of the invention, it is provided that the precatalyst 14 and main catalyst 18 are adapted such that for the conversion of the exhaust gas components hydrocarbon, carbon monoxide and nitrogen at least one of the following conditions is met:
More than 50%, preferably more than 60%, more preferably more than 70% of the hydrocarbon
More than 60%, preferably more than 70%, more preferably more than 80% of the carbon monoxide
More than 20%, preferably more than 30%, more preferably more than 40% of the nitrogen oxides
the conversion performance for the respective exhaust gas component of a conventional noble metal having precatalyst is from the noble metal-free precatalyst 14 accepted.

For controlling the internal combustion engine 10 is like in 1 schematically illustrated, an engine control system MC is provided which determines the oxygen content of the air / fuel mixture or the exhaust gas in dependence on the signal or the signals of one or more lambda probes, not shown. As is known from the prior art, receives the control system MC during operation further engine-related values, such as the speed of the engine, the load value and preferably the signals from temperature sensors, by the temperature of the exhaust gas or of components such as precatalyzer 14 or the main catalyst 18 can be determined or determined.

In particular, a temperature monitoring of the catalyst system is carried out by the control system MC. To prevent too high a thermal load of the precatalyst 14 becomes the internal combustion engine 10 operated with a boosted engine lambda value when the precatalyst takes a critical temperature T _VK at least longer than a critical time interval. As the precatalyst according to the invention 14 has a higher temperature stability than a conventional pre-catalyst provided with noble metal, the temperature T _{VK can be set} higher. Preferably, a value of T _VK ≥ 900 ° C; preferably 1000 ° C, more preferably 1100 ° C optimally 1200 ° C. A corresponding design of the precatalyst 14 takes place by an appropriate choice of the parameters characterizing the carrier and / or the coating, such as thickness of the cell walls of the honeycomb cells, the metal foils or the thickness of the carrier coating. Furthermore, an adaptation of the exhaust pipe 16 provided at least in terms of their length, construction or thermal properties.

The internal combustion engine 10 must be operated in such a way that permanently ensures a maximum total emission of pollutants, in particular of HC, CO and NOx, which corresponds to the legally prescribed exhaust gas limit values. The level of the limits is usually prescribed during so-called driving cycles. In the EU countries, for example, according to EU Directive 91/441 / EEC, the new European NEDC driving cycle sets a speed profile that is to correspond to typical urban and interurban traffic. A test according to the NEDC has a total duration of 1180s, with the distance covered being 11.007 km. The measured cumulative emissions during the driving cycle are related to the route.

to Securing the component protection is a certain amount of time the operation of the internal combustion engine only with enrichment of the engine lambda value while NEDC or any other driving profile, in particular one Operation with full load or an upper part load possible. According to the invention temporal part of an operation without enrichment, especially at Full load or an upper part load for a given driving profile compared to the an internal combustion engine with an exhaust gas purification device with increased a non-noble metal catalyst. Preferably, an increase in the percentage without enrichment by at least 10%. Optionally, the exhaust gas purification device is designed such that no enrichment in the NEDC takes place.

Due to the lower conversion performance of the precious metal-free precatalyst 14 the temperature increase due to the exothermic reactions in the precatalyst is relatively low. The enrichment of the engine lambda value can therefore be reduced accordingly. It is preferably provided to reduce the enrichment by a 50K lower temperature increase due to the exothermic reaction. Since a noble metal-free precatalyst is already temperature-resistant in itself, and thus can be exposed to higher temperatures, a further withdrawal of the enrichment is also provided, which preferably corresponds to an exposure of the precatalyst with a higher temperature by 50K.

There for emission control systems in most countries An on-board diagnostic (OBD) is required by law is under circumstances an adaptation of such an application to that by a precious metal-free Pre-catalyst conditional change the emission control system required. As far as such OBD system on the surveillance the oxygen storage capacity based on the pre-catalyst, and as far as the oxygen storage capacity of the carrier and / or the washcoat and only to a limited extent from the noble metal loading dependent is, however, only a small adjustment requirement for the OBD system expected.

Claims (18)

Internal combustion engine having an exhaust gas purification device with a suitable as a starting catalyst precatalyst and at least one arranged downstream of the precatalyst main catalyst and an arranged between the primary catalyst and catalyst exhaust pipe, characterized in that the precatalyst is formed free of noble metal. Internal combustion engine according to claim 1, characterized that the precatalyst is formed as a hydrocarbon adsorber is. Internal combustion engine according to claim 1 or 2, characterized characterized in that the exhaust pipe is at least one of the following Features identifies: - one length of at least 100 cm - one heat loss from at most 1 K / cm length of exhaust pipe - when Air gap-insulated tube is formed. Internal combustion engine according to at least one of the preceding Claims, characterized in that the precatalyst having a support structure having a zeolite coating. Internal combustion engine according to at least one of the preceding Claims, characterized in that the precatalyst having a support structure having a washcoat. Internal combustion engine according to at least one of the preceding Claims, characterized in that the precatalyst as an all-metal catalyst preferably has corrugated and / or wound metal foils. Internal combustion engine according to at least one of the preceding Claims, characterized in that the internal combustion engine with the pre-catalyst via a Connecting line is connected, which has a heat loss of at least 1 K / cm length having the connecting line. Internal combustion engine according to at least one of the preceding Claims, characterized in that the pre-catalyst near the engine and / or the Main catalyst is arranged in subsoil position. Internal combustion engine according to at least one of the preceding Claims, characterized in that an adaptation of pre-catalyst and Main catalytic converter is provided, wherein for the conversion of the exhaust gas components Hydrocarbon, carbon monoxide and nitric oxide at least one of meets the following conditions is: more than 50%, preferably more than 60%, preferably more as 70% of the hydrocarbon more than 60%, preferably more than 70%, more preferably more than 80% of the carbon monoxide more than 20%, preferably more than 30%, more preferably more than 40% of the nitrogen oxides the total conversion of the respective exhaust gas component is taken over by the precatalyst. Internal combustion engine according to claim 9, characterized the adaptation comprises a relative increase in the volume of the main catalyst. Internal combustion engine according to at least one of the preceding claims, characterized in that the precatalyst is designed such that a enrichment of an engine lambda value for a component protection is required only at a higher temperature T _{VK of} the precatalyst than in a non-precious metal-free precatalyst. Internal combustion engine according to at least one of the preceding Claims, characterized in that additionally for adaptation and / or for the design of the precatalyst, an adaptation of Exhaust pipe at least in terms of their length, construction or thermal Properties is provided. Internal combustion engine according to at least one of the preceding claims, characterized in that an enrichment for component protection is provided only at a temperature T _VK ≥ 900 ° C, preferably ≥ 1000 ° C, more preferably 1100 ° C optimally 1200 ° C. Internal combustion engine according to at least one of the preceding Claims, characterized in that the main catalyst is a three-way catalyst is. Internal combustion engine according to at least one of the preceding Claims, characterized in that the main catalyst is a NOx storage catalyst is. Internal combustion engine according to at least one of the preceding Claims, characterized in that a temporal portion of an operation without Enrichment for a component protection, especially at full load or an upper Part load for a predetermined driving profile relative to an internal combustion engine with an exhaust gas purification device with a non-precious metal-free Catalyst increased can be, preferably by at least 10%. A method for operating an internal combustion engine having an exhaust gas purification device with a pre-catalyst, which comprises a preferably coated with washcoat carrier and arranged downstream of the pre-catalyst main catalyst and an arranged between the primary catalyst and catalyst exhaust pipe, characterized in that the pre-catalyst is formed noble metal and an enrichment of a Engine lambda value for a component protection takes place only at a higher temperature of the pre-catalyst T _VK than is usual or necessary for a non-precious metal-free pre-catalyst. Method for operating an internal combustion engine having an exhaust gas purification device with a pre-catalyst, which comprises a preferably coated with washcoat carrier and arranged with a downstream of the pre-catalyst Main catalyst and an arranged between the primary catalyst and catalyst exhaust pipe, in particular claim 17, characterized in that a temporal portion of an operation without enrichment for a component protection, especially at full load or an upper part load for a given driving profile compared to an internal combustion engine with an exhaust gas purification device with a not noble metal-free catalyst is increased, preferably by at least 10%.