DE10304205A1 - Exhaust system of an internal combustion engine without a pre-catalyst and method for treating an exhaust gas of the internal combustion engine - Google Patents

Abstract

The invention relates to an exhaust system (10) of a spark-ignited and at least temporarily lean-burn internal combustion engine (12) with at least one NO¶x¶ storage catalytic converter (24) arranged close to the engine in an exhaust line (22) of the internal combustion engine (12) and with at least one exhaust-gas-driven charge air compressor ( 32), which, by lowering an energy of the exhaust gas flowing into the NO¶x¶ storage catalytic converter (24), causes compression of an air to be supplied to the internal combustion engine (12), an exhaust gas run length (L) between the internal combustion engine (12) and the engine closest to the NO¶ x¶ storage catalytic converter (24) is selected as a function of the amount of energy extracted from the exhaust gas by the charge air compressor (32). The invention further relates to a method for treating an exhaust gas of a spark-ignited and at least temporarily lean-burn internal combustion engine (12).

Description

The invention relates to an exhaust system a spark-ignited and at least lean-burn internal combustion engine as well a method for treating an exhaust gas of such an internal combustion engine.

For the treatment of exhaust gases from spark-ignition internal combustion engines (Otto engines), which are operated at least occasionally in a lean operating mode, i.e. with excess air (lambda> 1), for consumption reasons, it is known to pass the exhaust gas through downstream NO _x storage catalytic converters. NO _x storage catalysts store nitrogen oxides (NO _x ) in the form of nitrate in lean operating phases and are regenerated in intermediate regeneration phases with lambda ≤ 1. In addition to the storage component (usually a barium salt), NO _x storage catalysts also have a catalytic noble metal component which converts pollutants in the exhaust gas into more environmentally compatible components.

NO _x storage catalytic converters are usually arranged in a position remote from the engine, exhaust gas run lengths of at least 500 mm being required between a cylinder head of the internal combustion engine and the NO _x storage catalytic converter in order to achieve sufficient cooling of the exhaust gas. On the one hand, this is necessary because the storage capacity of the storage catalytic converters is limited compared to 3-way catalytic converters. In addition, frequent exposure of the catalytic converter to exhaust gas temperatures above 450 ° C., in particular above 500 ° C., should be avoided, since the catalytic converter only has a limited working temperature window in which NO _x storage occurs during lean operation. This is because, especially in mixed traffic with alternating low-load lean operating phases and high-load homogeneous phases (with Lambda - 1), there are high storage catalyst temperatures which do not allow efficient NO _x storage in lean operation. A disadvantage of this arrangement of the NO _x storage catalytic converter remote from the engine, however, is that the lightoff temperature of the catalytic converter, from which conversion and storage of pollutants takes place, is delayed.

As a result, the resulting pollutant slip becomes more difficult the fulfillment strict emission limits. It is therefore common connect a small-volume 3-way catalytic converter upstream of the storage catalytic converter, which takes over the conversion up to the lightoff of the storage catalytic converter. This measure is however with an increased Associated costs.

On the other hand, it has long been known in stoichiometrically operated internal combustion engines (lambda = 1 engines) that the 3-way catalytic converters used here in the form of a single main catalytic converter arranged close to the engine, in particular with an exhaust gas run length behind the cylinder head of less than 400 mm, use. NO _x storage is not required for these engines, since the stoichiometric exhaust gas converts nitrogen oxides practically completely. As a result of the arrangement of the 3-way main catalytic converter close to the engine, a pre-catalytic converter can be dispensed with, since the light-off temperature of the main catalytic converter takes place quickly enough in this position even for strict exhaust gas limit values.

The object of the present invention is to provide an exhaust system for lean-burn, spark-ignition internal combustion engines, which is structurally simplified and less expensive than known NO _x storage catalytic converter arrangements, but without accepting emissions disadvantages. A method for exhaust gas aftertreatment of such an internal combustion engine is also proposed.

This task is accomplished with an exhaust system the features of claim 1 and by a method according to claim 15 solved.

The exhaust system according to the invention comprises a NO _x storage catalytic converter arranged close to the engine in an exhaust line of the internal combustion engine and at least one charge air compressor which, while lowering an energy of the exhaust gas flowing into the storage catalytic converter, compresses an air to be supplied to the internal combustion engine. According to the invention, an exhaust gas run length between the internal combustion engine and the NO _x storage catalytic converter is selected as a function of the amount of energy extracted from the exhaust gas by the charge air compressor. The ending thus makes use of charge air compressors known per se, which charge the engine by utilizing the exhaust gas energy, with a decrease in the exhaust gas temperature. This lowering of temperature allows the NO _x storage catalytic converter to be arranged close to the engine without putting excessive thermal stress on it. In this way it is advantageously possible to dispense with a precatalyst upstream of the NO _x storage catalytic converter. It is therefore preferably provided that no further catalytic converter, in particular no 3-way catalytic converter, is arranged between an exhaust gas outlet of the internal combustion engine and the NO _x storage catalytic converter closest to the engine. An exception to this may be a catalyst arranged in an exhaust gas recirculation line. The specific arrangement of the storage catalytic converter is realized in accordance with the temperature drop caused by the charge air compressor.

Despite the non-existing pre-catalytic converter, compliance with strict exhaust gas standards is possible through the exhaust system according to the invention. It is preferably provided that the exhaust system is designed such that the exiting exhaust gas is new European NEDC driving cycle with an undamaged NO _x storage catalytic converter and a fired lean operating time with lambda ≥ 1.15 within a period of at least 250 s, in particular at least 350 s, an HC emission of less than 0.07 g / km and a NO _x -Emission less than 0.05 g / km. An undamaged catalyst is understood to mean a fresh catalyst that is not thermally damaged and has a stored sulfur mass of at most 0.02 g / l catalyst volume.

In any case, such charge air compressors come in accordance with the invention used to compress the charge air by using Cause exhaust gas energy. Exhaust gas turbochargers are particularly suitable which cause fresh air compression via a compressor wheel, by a turbine wheel driven by the exhaust gas is driven. This is where the pressure drops here of the exhaust gas at the turbine to the desired temperature reduction. Also for the Exhaust system according to the invention So-called Comprex loaders are suitable, in which pressure and suction waves of the pulsating exhaust gases compress fresh air in direct contact. However, the additional use of others is also conceivable Charge air compressors, where the compression is essentially mechanical or electrical energy.

NO _x storage catalytic converters are usually arranged at least 500 mm behind the cylinder head. In contrast, the storage catalytic converter of the exhaust system according to the invention is closer to the exhaust point. In particular, provision is made to arrange the NO _x storage catalytic converter at most 400 mm, preferably at most 350 mm, downstream of the cylinder head. In a particularly advantageous embodiment, the catalytic converter is located at most 300 mm behind the cylinder head. In the case of air compression via an exhaust gas turbocharger, the exhaust gas run length between an axis of rotation of the exhaust gas turbocharger acting on it and an end face of the NO _x storage catalytic converter is at most 300 mm, in particular at most 250 mm, preferably at most 200 mm. Exhaust gas run lengths of at most 150 mm are particularly preferably provided here.

The exhaust gas run length can be reduced the more the exhaust gas temperature is lowered as a result of the function of the charge air compressor. Therefore, the concept according to the invention comes into play particularly favorably with increasing supercharging, that is to say increasing compression and output of the internal combustion engine as a result of the increasing relaxation work of the exhaust gas. Internal combustion engines with a specific output of at least 70, in particular at least 80, preferably at least 90, particularly preferably at least 100 kW / l engine stroke volume are therefore particularly advantageous. This is especially advantageous at low engine units for so-called downsizing concepts in which a specific vehicle weight capacity of the supercharged engine at most 1.2, especially at most 1.1, preferably at most 1.0, particularly preferably at most 0.9 dm ^3/1000 kg of empty vehicle weight.

The consumption advantage of lean operation, in particular stratified charge operation, is limited to the lowest partial load range, in particular in the case of engine units according to the above specification. At speeds n above 0.3 · n _nominal and / or at loads p _me above 0.25 · p _{me, max} , at most small consumption advantages over lambda = 1 operation can be achieved. As a result of the reduced lean operating times, the requirements for the NO _x storage capacity of the storage catalytic converter decrease. A further cost advantage can thus be achieved by reducing the mass of storage material per storage catalytic converter compared to conventional catalysts. It is therefore particularly preferred to use NO _x storage catalysts which, after embedding a NO ₂ mass of 200 mg per liter of catalyst volume, have an NO _x storage efficiency of at most 95%, in particular at most 90%, preferably at most 80%. These relatively low efficiencies are only achieved by today's NO _x storage catalytic converters after an embedded NO ₂ mass of 500 mg / l catalyst volume. In contrast, the storage catalytic converter designed according to the invention has an NO _x storage efficiency of at least 80%, in particular of at least 70%, but at least 60%, with an embedded NO ₂ mass of 500 mg / l catalyst volume. As a result, this means that the storage material mass of the catalyst according to the invention can be reduced by at least 30%, in particular by at least 50%, preferably even by at least 70, compared to conventional concepts. This results in further cost and weight advantages. (All of the above efficiencies relate to a storage capacity that occurs immediately after a regeneration phase on a NO _x storage catalytic converter in the fresh state (unused but conditioned) when it is exposed to an exhaust gas with an HC input concentration of maximum 100 ppm HC ₃ and a NO _x -Inlet concentration of 250-500 ppm at an average catalyst temperature of 350 ± 20 ° C, lambda = 2.2 ± 0.2 and a space velocity of 40,000 ± 20,000 h ^{-1 were} measured. See an exemplary embodiment below.)

A further reduction of the exhaust run length, that is, a still further arrangement of the motor NO _x storage catalytic converter can be achieved by using high temperature-capable main storage components of the NO _x storage catalytic converter. Alkali and alkaline earth components, for example barium, potassium, Caes, are generally suitable for this ium, sodium and / or magnesium, in particular compounds and / or salts, preferably carbonates and / or oxides thereof. Compounds of potassium, cesium, sodium and / or magnesium, but preferably compounds of potassium, can be used particularly advantageously because of their heat resistance. Compared to today's storage catalytic converters, which mainly work on a barium basis and have a working temperature window for NO _x storage in lean operation from 250 ° C. to a maximum of 500 ° C., a catalyst is used according to the invention whose NO _x storage temperature window is widened towards the top. It has an upper limit of the temperature window of at least 550 ° C, in particular at least 580 ° C, preferably at least 610 ° C, particularly preferably at least 640 ° C. Such a formulation is particularly advantageous in the case of engine units with the specific outputs and cubic capacities described above, the emission limits specified above being complied with in the new European driving cycle. The high-temperature formulation can also be used particularly advantageously in connection with the reduced storage material mass.

It is also advantageously possible to lower a noble metal content of the NO _x storage catalytic converter compared to the catalysts customary today. In particular, catalysts with a noble metal content of at most 3.59 g / dm ³ (100 g / ft ³ ), preferably of at most 2.87 g / dm ³ (80 g / ft ³ ), are used according to the present invention. In contrast, there are currently common storage catalysts with precious metal contents of at least 3.95 g / dm ³ (110 g / ft ³ ), more often even with at least 4.67 g / dm ³ (130 g / ft ³ ). Such a reduction in precious metals leads to a further cost advantage without significant losses in the conversion of pollutants being observed.

According to the method according to the invention, the exhaust gas is passed through at least one NO _x storage catalytic converter arranged in the exhaust gas duct of the internal combustion engine, with at least one charge air compressor compressing an air to be supplied to the internal combustion engine and an energy required for this by lowering an energy of the NOx storage catalytic converter inflowing exhaust gas applied. An exhaust gas run length between the internal combustion engine and the NO _x storage catalytic converter is selected as a function of the amount of energy extracted from the exhaust gas by the charge air compressor.

Further advantageous configurations the invention are the subject of the remaining subclaims.

The invention is hereinafter in embodiments based on the associated Drawings closer explained. Show it:

1 an exhaust system according to the prior art and

2 an exhaust system according to the invention.

1 shows schematically a total with 10 Designated exhaust system, as it is according to the prior art for spark-ignited, lean-burn internal combustion engines 12 is common. The internal combustion engine 12 has four cylinders according to the example shown 14 on, each through a common air intake pipe 16 be supplied with fresh air and thus with oxygen. The amount of fresh air is regulated via a in the air intake pipe 16 arranged, adjustable throttle valve 18 ,

Modern, lean-burn gasoline engines 12 are often still equipped with direct fuel injection, not shown here. This as well as a specially designed combustion chamber geometry of the cylinders 14 enables the internal combustion engine 12 to operate in the lower and middle load range in a so-called stratified charge mode, in which only in the area of a spark plug of a cylinder 14 an ignitable mixture cloud is shown. Stratified charge mode enables the internal combustion engine to operate particularly lean and thus fuel-saving 12 ,

Exhaust gases, the cylinders 14 the internal combustion engine 12 leave via a cylinder head, not shown, are via manifold pipes 20 into a common exhaust line 22 directed.

An exhaust gas aftertreatment takes place with the help of in the exhaust line 22 arranged catalyst system 24 and 26 , The main catalytic converter comprises a large-volume NOx storage catalytic converter 24 , The NO _x storage catalytic converter 24 has a catalytic function due to its precious metal components to convert pollutants contained in the exhaust gas such as carbon monoxide, unburned hydrocarbons and nitrogen oxides. It also has a NO _x storage function in lean operation of the internal combustion engine 12 on. As a result, nitrogen oxides that are not fully convertible in lean operation are usually stored on a barium storage component in the form of nitrate and are desorbed and converted in short intervening regeneration phases (at lambda <1).

Because of its increased temperature sensitivity compared to 3-way catalysts and because of a limited temperature window in which the lean NO _x storage can take place, the NO _x storage catalyst is located 24 according to the prior art at a position remote from the engine in the exhaust system 22 , so that sufficient cooling of the exhaust gas takes place over the exhaust gas run length L. The remote arrangement of the NO _x storage catalytic converter 24 has the disadvantage, however, that it only reaches its minimum operating temperature, the so-called lightoff, after a cold engine start. A pollutant generated in this way Minimizing slip is customary in the prior art, a small-volume pre-catalyst 26 , which is usually designed as a 3-way catalytic converter, at a position close to the engine, the NO _x storage catalytic converter 24 upstream. The arrangement of such pre-catalysts 26 is associated with an additional cost.

The exhaust system 10 further includes an exhaust gas recirculation line 28 , with the exhaust gases in the air intake pipe 16 returned and the internal combustion engine 12 be fed again. An exhaust gas recirculation rate is via an exhaust gas recirculation valve 30 adjustable.

2 also provides a simplified exhaust system 10 according to a preferred embodiment of the present invention 2 same elements with the same reference numerals as in 1 designated.

The exhaust system according to the invention 10 is characterized by the absence of a pre-catalytic converter and by an arrangement of the NO _x storage catalytic converter close to the engine 24 out. This configuration, which is inexpensive compared to the prior art, is made possible by making use of the mode of operation of conventional air charging compressors in the manner according to the invention. Although the additional installation of other compressors is not ruled out, according to the invention at least those air charging compressors are used which extract an energy required for the air compression from the exhaust gas, an exhaust gas energy being reduced and the exhaust gas temperature being reduced. In 2 is an example of an exhaust gas turbocharger 32 indicated. Exhaust gas turbochargers essentially consist of a turbine wheel in contact with the exhaust gas, which is coupled to a compressor wheel via a shaft. The air is thus compressed using the energy of the exhaust gas that drives the turbine wheel. A relaxation work of the exhaust gas taking place on the turbine wheel ensures its cooling and allows the NO _x storage catalytic converter to be arranged close to the engine. According to the in 2 In the example shown, the charge air is compressed only indirectly by compressing it through the EGR line 28 recirculated exhaust gas. Of course, the compression of the entire internal combustion engine is also a matter of course 12 supplied air mass possible in a conventional manner.

The specific position of the NO _x storage catalytic converter in the exhaust system 22 is dependent on the exhaust gas from the exhaust gas turbocharger 32 withdrawn amount of energy, that is, the degree of exhaust gas cooling. The exhaust gas run length L is between the axis of rotation of the exhaust gas turbocharger, not shown here 32 and an inflow surface (end face) of the NO _x storage catalytic converter 24 preferably at most 200 mm, in a particularly advantageous embodiment even at most 150 mm.

As already explained above, the invention is particularly advantageous in the case of highly supercharged internal combustion engines based on the downsizing concept. In the 2 illustrated internal combustion engine 12 therefore assigns in addition to 1 explained features a specific power of at least 90, particularly preferably of at least 100 kW / I engine stroke volume. Further, it is specific vehicle weight capacity most 1.0, particularly preferably at most 0.9 dm ^3/1000 kg vehicle curb weight.

The arrangement of the NO _x storage catalytic converter close to the engine 24 is also made possible by a modified catalyst design and formulation of the basic chemistry compared to the prior art. In particular, the fact is used of the above-mentioned special specifications of the motor unit, according to which the lean operation, and very particularly the stratified charge operation, on the lowest partial load range, in particular on a speed n = 0.3 · n _nominal and on a more effective power p _me = 0.25 · p _{me, max is} limited. Due to the limited lean operation, the NO _x raw emissions of the internal combustion engine 12 less than in conventional concepts, so that the requirement for the NO _x storage capacity of the NO _x storage catalytic converter 24 are lowered. For this reason, a storage material mass of the storage catalytic converter 24 can be reduced by more than 50% compared to conventional formulations. In the preferred example, it is even reduced by more than 70%. The preferred NO _x storage catalyst used 24 After storing a NO ₂ mass of 200 mg / l catalyst volume, the NO _x storage efficiency is only at most 80% and after storing 500 mg / l catalyst volume only at most 70%, but at least 60%, without being unacceptable high NO _x emissions (see below).

The storage catalytic converter used here 24 also has a reduced precious metal content of 2.87 g / dm ³ (80 g / ft ³ ) compared to the prior art.

Furthermore, the storage catalytic converter 24 equipped with a high-temperature base chemical. For this purpose, compounds of potassium as the base component are used as the main storage component instead of barium.

HC and NO _x emissions

The final emissions of the NO _x storage catalyst according to the invention 24 were in the New European Driving Cycle NEDC in the thermally undamaged state and with a stored sulfur mass below 0.2 g / l catalyst volume with a fired lean operating period (without overrun phases) with lambda> 1.15 of at least 250 s, in particular even at least 350 s, below of 0.07 g / km for unburned hydrocarbons (HC) and below 0.05 g / km for nitrogen oxides (NO _x ).

After furnace aging of the NO _x storage catalytic converter according to the invention 24 for four hours at 1,100 ° C in an atmosphere with 2% O ₂ and 10% H ₂ O in the same vehicle in the NEDC, this had an HC emission below 0.1 g / km and a NO _x emission below 0, 08 g / km on.

Determination of the NO _x storage temperature window

The special design of the storage catalytic converter 24 According to the present invention, an expansion of the NO _x storage temperature window in lean operation compared to today's concepts. It is therefore provided that the lean operation, in particular the stratified charge operation of the internal combustion engine 12 expand up to catalyst temperatures above 600 ° C, especially above 610 ° C or even 640 ° C. The lower temperature limit is optimally at the previous level of about 250 ° C, but can be increased by 20 K, possibly even by 50 K or even 70 K due to the other prevailing temperature conditions.

The exact NO _x storage temperature window of a specific NO _x storage catalytic converter 24 in lean operation, each catalyst formulation has to be determined in detail. The determination is carried out in an alternating lean-rich operation, the catalyst according to the invention and any catalyst of the prior art also being operated on any stratified, direct-injection gasoline engine according to the prior art.

Both unused catalysts are first conditioned by applying gas at lambda = 1 ± 0.03 for four hours at an average catalyst temperature of 650 ± 30 ° C, with an oxygen content below 1.5% and at a space velocity of 20,000 ± 5,000 h ^-1 occurred. In this state (= fresh state), both catalysts are immediately after a regeneration phase of at least 60 s with lambda> 0.9 at a space velocity of 40,000 ± 20,000 h ⁻¹ with lambda = 2.2 ± 0.2 with an HC input concentration < 100 ppm HC ₃ and an NO _x input concentration of 250 to 500 ppm.

The determination of the deviation of the temperature window of the catalyst according to the invention from the catalyst according to the prior art takes place in such a way that first the minimum and maximum temperatures are determined at which the catalyst according to the prior art after storage of a predetermined NO ₂ mass of 500, for example mg / l catalyst volume has a predetermined NO _x storage efficiency of, for example, 75%. Subsequently, those temperatures are determined for the storage catalytic converter according to the invention at which the same storage efficiency is present after the same NO ₂ mass has been stored. These temperatures are then used as minimum and maximum temperatures of the NO _x -Speichertemperaturfensters for operation of the invention NO _x storage.

Measurement of NO _x storage efficiency

The NO _x storage efficiency in the lean exhaust gas according to the invention reduced NO _x storage catalysts and a conventional NO _x storage catalyst were determined as follows. The storage material masses of the tested catalysts were reduced by approximately 30%, 50% and 70% compared to the storage material mass of the conventional NO _x storage catalytic converter.

First, all unused catalysts were conditioned by applying an exhaust gas at lambda = 1 ± 0.03 for four hours at an average catalyst temperature of 650 ± 30 ° C, with an oxygen content below 1.5% O ₂ in the incoming exhaust gas and at a space velocity of 20,000 ± 5,000 h ^-1 . A regeneration phase of at least 60 s was then carried out at lambda <0.9.

Immediately after this regeneration phase, the NO _x storage catalytic converters were exposed to an exhaust gas with an HC input concentration of maximum 100 ppm HC ₃ and an NO _x input concentration of 250-500 ppm at an average catalyst temperature of 350 ± 20 ° C, lambda = 2.2 ± 0.2 and a space velocity of 40,000 ± 20,000 h ^-1 .

After storage of a NO ₂ mass of 200 mg per liter of catalyst volume, the reduced-storage catalysts still had an NO _x storage efficiency of at least 95% (catalyst with 30% reduced storage material mass), at least 90% (50% storage material mass) or at least 80% ( storage material mass reduced by 70%). After storage of a NO ₂ mass of 500 mg / l catalyst volume, the reduced-storage catalysts had a NO _x storage efficiency below 80% (catalyst with a storage material mass reduced by 30%) or below 70% (50% storage material mass). With this storage filling, all storage-reduced catalysts still had an efficiency of at least 60%. In comparison, the NO _x storage catalyst according to the prior art had a storage efficiency above 95% with an embedded NO _x mass of 500 mg / l catalyst volume.

10

exhaust system

12

Internal combustion engine

14

cylinder

16

air intake pipe

18

throttle

20

manifold pipes

22

exhaust gas line

24

NO _x storage catalytic converter

26

precatalyzer

28

Exhaust gas recirculation line

30

Exhaust gas recirculation valve

32

Air charging compressor

L

Exhaust Yardage

Claims (15)

Exhaust system ( 10 ) a spark-ignited and at least temporarily lean-burn internal combustion engine ( 12 ) with at least one in an exhaust line ( 22 ) of the internal combustion engine ( 12 ) NO _x storage catalytic converter arranged close to the engine ( 24 ) and with at least one exhaust gas-driven charge air compressor ( 32 ), which reduces the energy of the NO _x storage catalytic converter ( 24 ) incoming exhaust gas compression of an internal combustion engine ( 12 ) air to be supplied, with an exhaust gas run length (L) between the internal combustion engine ( 12 ) and the nearest NO _x storage catalytic converter ( 24 ) depending on the exhaust gas from the charge air compressor ( 32 ) withdrawn amount of energy is selected. Exhaust system according to claim 1, characterized in that between an exhaust gas outlet of the internal combustion engine ( 12 ) and the nearest NO _x storage catalytic converter ( 24 ) no further catalyst, in particular no 3-way pre-catalyst, is arranged. Exhaust system according to one of claims 1 or 2, characterized in that the at least one exhaust gas-driven charge air compressor ( 32 ) is an exhaust gas turbocharger. Exhaust system according to one of claims 1 or 2, characterized in that the at least one exhaust gas-driven charge air compressor ( 32 ) is a Comprex loader. Exhaust system according to one of the preceding claims, characterized in that the exhaust gas run length (L) between a cylinder head of the internal combustion engine ( 12 ) and an inflow surface of the closest NO _x storage catalytic converter ( 24 ) is at most 500 mm, in particular at most 400 mm, preferably at most 350 mm, particularly preferably at most 300 mm. Exhaust system according to one of the preceding claims, characterized in that the exhaust gas run length (L) between an axis of rotation of the exhaust gas turbocharger and an inflow surface of the NO _x storage catalytic converter closest to the engine ( 24 ) is at most 300 mm, in particular at most 250 mm, preferably at most 200 mm, particularly preferably at most 150 mm. Exhaust system according to one of the preceding claims, characterized in that a specific power of the internal combustion engine ( 12 ) is at least 70, in particular at least 80, preferably at least 90, particularly preferably at least 100 kW / l engine stroke volume. Exhaust system according to one of the preceding claims, characterized in that a vehicle weight-specific displacement of the internal combustion engine ( 12 ) At most 1.2, especially at most 1.1, preferably at most 1.0, particularly preferably at most 0.9 dm ³ / is 1000 kg Vehicle curb weight. Exhaust system according to one of the preceding claims, characterized in that the NO _x storage catalytic converter ( 24 ) has a storage material mass per catalytic converter which is designed such that with an embedded NO ₂ mass of 200 mg / l catalytic converter volume it has a NO _x storage efficiency of at most 95%, in particular at most 90%, preferably at most 80%. Exhaust system according to one of the preceding claims, characterized in that the NO _x storage catalytic converter ( 24 ) has a storage material mass per catalyst, which is designed such that it has an embedded NO ₂ mass of 500 mg / l catalyst volume, a NO _x storage efficiency of at most 80%, in particular at most 70%, and at least 60%. Exhaust system according to one of the preceding claims, characterized in that the NO _x storage catalytic converter ( 24 ) has as the main storage component barium, potassium, cesium, sodium and / or magnesium and / or compounds and / or salts thereof, in particular compounds and / or salts of potassium. Exhaust system according to claim 11, characterized in that the NO _x storage catalytic converter ( 24 ) has a NO _x storage temperature window with an upper limit of at least 550 ° C, in particular at least 580 ° C, preferably at least 610 ° C, particularly preferably at least 640 ° C. Exhaust system according to one of the preceding claims, characterized in that the NO _x storage catalytic converter ( 24 ) has a precious metal content of at most 3.59 g / dm ³ (100 g / ft ³ ), in particular at most 2.87 g / dm ³ (80 g / ft ³ ). Exhaust system according to one of the preceding claims, characterized in that the exhaust system ( 10 ) leaving exhaust gas in the New European Driving Cycle (NEDC) with an undamaged NO _x storage catalytic converter ( 24 ) and a time-fired lean operating component without overrun phases with lambda ≥ 1.15 within a period of at least 250 s, in particular at least 350 s, an HC emission of less than 0.07 g / km and an NO _x emission of less than 0 .05 g / km. Method for treating an exhaust gas from a spark-ignited and at least temporarily lean-burn internal combustion engine ( 12 ), the exhaust gas being passed through at least one in an exhaust line ( 22 ) of the internal combustion engine ( 12 ) NO _x storage catalytic converter arranged close to the engine ( 24 ) is carried out with at least one exhaust gas-driven charge air compressor ( 32 ) compression of an internal combustion engine ( 12 ) air to be supplied and an energy required for this by lowering an energy of the NO _x storage catalyst ( 24 ) flowing exhaust gas is applied, and wherein an exhaust gas run length (L) between the internal combustion engine ( 12 ) and the NO _x storage catalytic converter ( 24 ) depending on the exhaust gas from the charge air compressor ( 32 ) withdrawn amount of energy is selected.