DE102007028493A1 - Internal combustion engine with two-stage turbocharging and oxidation catalyst - Google Patents

Abstract

The invention relates to an internal combustion engine (2) with an exhaust gas tract (8) and with two-stage turbocharging, wherein the exhaust gas tract (8) has two turbines (22, 24) of a first and a second exhaust gas turbocharger (18, 20) and at least one oxidation catalytic converter (34, 36) in series and a bypass line (46) in parallel with the turbine (22) of the first exhaust gas turbocharger (18, 20). It is envisaged that the oxidation catalyst (34) is arranged in front of the turbine (22) of the first turbocharger (18) and behind the branch of the bypass line (46).

Description

The The invention relates to an internal combustion engine, in particular a diesel engine, with two-stage turbocharger according to the preamble of claim 1, and a method for operating such Internal combustion engine according to claim 11.

State of the art

Internal combustion engines with two-stage turbocharging are equipped with two exhaust gas turbochargers whose turbines are arranged in series in the exhaust tract of the internal combustion engine. Such internal combustion engines are among others in the DE 102 22 919 A1 , of the DE 10 2004 009 794 A1 and in the DE 10 2005 025 885 A1 disclosed.

According to http://media.gm.com/be/opel/de/news/pr_old/pressrelease_3149.htm was further presented by the company OPEL at the Essen Motor Show in November 2003, a diesel engine of the type mentioned with two-stage turbocharging for a car in the two-stage turbocharging a high specific performance without the other disadvantages in fuel consumption and emissions behavior was achieved. In this diesel engine, a smaller fast-response high-pressure turbocharger even at low speeds of up to 1800 min ^-1 for a spontaneous response of the internal combustion engine without starting weakness and without so-called turbo lag, while above 1800 min ^-1 a large, is laid out on a high throughput low pressure turbocharger connecting them. At speeds between 1800 min ^-1 and 3000 min ^-1 , the turbines of both turbochargers run simultaneously, while at speeds above 3000 min ^-1 only the low-pressure turbocharger compresses compressed air into the cylinders of the internal combustion engine. The two turbochargers are controlled by means of load- and speed-controlled exhaust or bypass valves in the exhaust gas tract.

The Use of oxidation catalysts in the exhaust tract of diesel engines for reducing the proportion of unburned hydrocarbons (HC) and carbon monoxide (CO) in the combustion exhaust gases is well known. Here are the oxidation catalysts of conventional diesel engines designed for the conversion of very low HC / CO emissions and are in diesel engines with an exhaust gas turbocharger usually behind the Output of the turbine arranged. However, the turbine acts due to their mass as a heat sink, so in particular after a Cold start and in transient operation the temperature of the Exhaust gases behind the turbine significantly lower levels than before Turbine can own. However, since oxidation catalysts only at Reaching the so-called light-off temperature of about 200 ° C. work satisfactorily, lower exhaust gas temperatures lead to that the light-off temperature is reached later. The time delay gets even bigger if the exhaust gases in internal combustion engines of the type mentioned must flow through two turbines connected in series, both act as a heat sink. Furthermore this problem is likely to be exacerbated in the future, since concepts for reducing the internal engine emissions of nitrogen oxides, z. B. the so-called HCCI (Homogeneous Charge Compression Ignition) method, greater homogenization and dilution of the Provide cylinder charge by recirculated exhaust gas, which in the combustion chamber of the cylinders lower process temperatures Episode has. This in turn leads to a higher one Proportion of unburned hydrocarbons and carbon monoxide in the exhaust gases and thus to larger requirements to the oxidation catalyst, while on the other hand less favorable due to the lower process temperatures Conditions for post-oxidation of these exhaust constituents in the exhaust tract or the downstream oxidation catalyst, its heating to the light-off temperature also by the lower Exhaust gas temperature is further delayed.

If the oxidation catalyst closer to the internal combustion engine In the exhaust tract is arranged, but this also leads to disadvantages. First, the catalyst causes at high speeds and high engine load a pressure drop in the exhaust tract, the one corresponding loss of power of the internal combustion engine result Has. On the other hand lead the higher exhaust gas temperatures in the catalyst to a faster aging.

outgoing This is the object of the invention, an internal combustion engine of the aforementioned type and a method for operating the internal combustion engine to improve that despite an arrangement of the catalyst in closer proximity to the internal combustion engine At high speeds and high engine load pressure losses in the exhaust system be avoided and the aging of the catalyst is slowed down.

Disclosure of the invention

These Task is in terms of the internal combustion engine according to the invention thereby solved that the oxidation catalyst behind the branch the bypass line and in front of the turbine of the first turbocharger and is arranged.

The feature combination according to the invention makes it possible, the exhaust gases at high speeds and / or high engine load not only on the turbine of the first exhaust gas turbocharger but also on the passing upstream of this turbine arranged oxidation catalyst. As a result, pressure losses in the exhaust gas tract can be avoided and the aging of the oxidation catalytic converter arranged in front of the turbine caused by high exhaust gas temperatures as a result of a high engine load can be delayed. On the other hand, the oxidation catalyst is heated quickly before the turbine of the first exhaust gas turbocharger after the start of the internal combustion engine, so that it reaches its light-off temperature early and ensures exhaust gas aftertreatment. Another advantage of the arranged upstream of the turbine oxidation catalyst is that the exhaust gas temperature is increased at the entrance of the turbine by the exothermic oxidation reaction, which leads to an increase in the performance of the first exhaust gas turbocharger and thus to build a higher boost pressure.

at Internal combustion engines that operate according to the HCCI process can with the feature combination according to the invention on the one hand, even at very low speeds and very low Engine load unburned hydrocarbons and carbon monoxide in the Exhaust gases despite the relatively low Exhaust gas temperature oxidized with good efficiency and thereby the HCCI operation are extended to lower speeds. On the other hand allows it is the heating of the exhaust gases due to the exothermic reaction in the Oxidation catalyst also, the HCCI operation towards higher Expand loads. This mutual expansion of the HCCI map area in turn leads to a further reduction of nitrogen oxide and soot emissions, which in series internal combustion engines Use of the HCCI process can accelerate. About that In addition, it allows the reduction of soot emissions, the Regeneration interval of a downstream diesel particulate filter to enlarge, which is not only a consumption advantage offers, but also to a lower thermal load of Oxidation catalyst and thus to an extension its life leads.

A preferred embodiment of the invention provides that the bypass line contains a load- and / or speed-controlled exhaust or bypass flap, so that the exhaust gases are dependent on the speed and / or Engine load either through the catalyst and the turbine or through the bypass line can be routed. In order to avoid, that passed through the bypass line past the catalyst Exhaust gases pass through the exhaust untreated, is behind the junction the bypass line in the exhaust tract another oxidation catalyst arranged, which preferably behind the turbine of the second exhaust gas turbocharger is installed, but can also be installed in front of this.

Around unburned hydrocarbons and carbon monoxide in the by the Exhaust tract flowing exhaust gases as soon as possible after a cold start of the internal combustion engine to oxidize, sees one Another preferred embodiment of the invention, in an exhaust manifold to arrange the internal combustion engine at least one further oxidation catalyst, preferably one behind each cylinder.

The Internal combustion engine is also useful with a branching off from the exhaust tract upstream of the oxidation catalyst an intake tract of the internal combustion engine leading exhaust gas recirculation line provided with advantage both before and behind the exhaust manifold arranged branch off oxidation catalysts.

The inventive method provides that the Bypass line at low speeds and / or low engine load is closed and at high speeds and / or high engine load is opened to the exhaust gases on the turbine of the first exhaust gas turbocharger and past the oxidation catalyst located in front of the turbine to lead.

To open and closing the bypass line serves a bypass flap, their position for boost pressure control also continuously between "closed" and "open" can be varied, for example at medium speeds or medium load. The oxidation of unburned hydrocarbons and carbon monoxide then occurs in both oxidation catalysts, one part in the oxidation catalyst and another part in the further, arranged behind the junction of the bypass line Oxidation catalyst is oxidized.

Of the Use of an internal combustion engine according to the invention and a method of the invention is particular advantageous in internal combustion engines using an HCCI process operate. However, an insert is also conventional Internal combustion engines with two-stage turbocharging advantage, especially if a significant proportion of the exhaust gases in the Intake tract is recycled, resulting in a high Proportion of unburned hydrocarbons and carbon monoxide in the Exhaust and to relatively low Exhaust gas temperatures leads.

Brief description of the drawings

in the Following is the invention with reference to some shown in the drawing Embodiments explained in more detail. Show it:

1 a schematic view of an internal combustion engine with two-stage turbocharging and two oxidation catalysts in the exhaust system;

2 a view accordingly 1 , each but with four additional oxidation catalysts in an exhaust manifold of the exhaust tract;

3 a view accordingly 2 , but with a modified exhaust gas recirculation.

embodiments the invention

The four-cylinder internal combustion engine shown in the drawing 2 with two-stage turbocharging have an intake tract 4 for the intake of fresh air into the cylinders 6 the internal combustion engine 2 and an exhaust tract 8th to remove the combustion gases from the cylinders 6 on. The intake tract 4 includes an air filter 10 while the exhaust tract 8th an exhaust manifold 12 and one from the exhaust manifold 12 to an exhaust 14 leading exhaust or exhaust pipe 16 includes.

For charging the internal combustion engine 2 this has a first high-pressure exhaust gas turbocharger 18 and a second low pressure exhaust gas turbocharger 20 on. The two turbochargers 18 and 20 each have one along the exhaust pipe or exhaust pipe 16 arranged, with the combustion exhaust gases from the cylinders 6 actable turbine 22 respectively. 24 , as well as one from the turbine 22 respectively. 24 over a wave 26 respectively. 28 driven compressor 30 respectively. 32 , The turbine 22 the high-pressure exhaust gas turbocharger 18 is in the flow direction of the exhaust gases in front of the turbine 24 the low-pressure exhaust gas turbocharger 20 in the exhaust or exhaust pipe 16 arranged. The two compressors 32 and 30 are also in series in the intake system 4 arranged and compact through the air filter 10 Fresh air sucked in from the environment before being fed into the cylinders 6 ,

For the treatment of the exhaust gases of the internal combustion engine 2 is between the exhaust manifold 12 and the turbine 22 the high-pressure exhaust gas turbocharger 18 a first oxidation catalyst 34 into the exhaust pipe or exhaust pipe 16 installed while behind the turbine 24 the low-pressure exhaust gas turbocharger 20 and in front of the exhaust 14 a second oxidation catalyst 36 and an oxidation catalyst 36 downstream diesel particulate filter 38 in the exhaust or exhaust pipe 16 are arranged.

To reduce the nitrogen oxide emissions of the internal combustion engine 2 and for faster heating of the internal combustion engine 2 after a cold start are the exhaust tract 8th and the intake tract 4 through an exhaust gas recirculation line 40 connected by the part of the exhaust gases from the exhaust tract 8th in the intake tract 4 can be returned. The exhaust gas recirculation line 40 contains an exhaust gas recirculation valve 42 for controlling the amount of recirculated exhaust gases and an exhaust gas recirculation cooler 44 for cooling the recirculated exhaust gases.

The exhaust tract 8th further includes a bypass line 46 that are parallel to a portion of the exhaust or exhaust pipe 16 extends into which the oxidation catalyst 34 and the turbine 22 of the high pressure turbocharger 18 are installed. The bypass line 46 branches in front of the oxidation catalyst 34 and flows between the turbines 22 and 24 back into the exhaust or exhaust pipe 16 , The bypass line 46 contains a continuously adjustable bypass flap 48 , which is speed and / or load-dependent adjustable to the exhaust gases from the cylinders 6 either with the flap closed 48 through the oxidation catalyst 34 and the turbine 22 , with the flap open 48 through the bypass line 46 on the catalyst 46 and at the turbine 22 to pass by or with partially open flap 48 each part of the exhaust gases through the catalyst 34 and the turbine 22 or to pass them by. In the latter case, both turbines are located 22 and 24 in operation, but with the turbine 22 only proportionate flows through the exhaust gases. The turbine 24 may comprise an integrated bypass (not shown), which is also provided with a speed-dependent and / or load-controllable bypass flap in the form of a so-called wastegate (not shown) through which at least a portion of the exhaust gases to the turbine 24 can be bypassed.

The first oxidation catalyst 34 is closer to the cylinders 6 and before the turbines acting as heat sinks 22 and 24 the exhaust gas turbocharger 18 and 20 arranged so that he after a cold start of the internal combustion engine 2 achieves its light-off temperature more quickly and provides early oxidation of unburned hydrocarbons and carbon monoxide. As the oxidation in the oxidation catalyst 34 In addition, the temperature of the turbine is exothermic 22 entering exhaust gases increased. As a result, at low speeds and low load, the compression ratio of the fresh air through the turbocharger 18 increased and so the response of the internal combustion engine 2 improved in this speed range or the so-called "turbo lag" can be avoided. The first turbocharger 18 preferably operates alone in this speed range to the temperature of the exhaust gases at the inlet of the second oxidation catalyst 36 keep as high as possible. This catalyst 36 becomes like the catalyst 34 flows through the exhaust gases and ensures complete conversion of unburned hydrocarbons and carbon monoxide before exiting the exhaust 14 ,

In a medium speed and load range, the second exhaust gas turbocharger 20 by closing the exhaust flap of the turbine 24 to the first exhaust gas turbocharger 18 switched on, so that in this speed range both turbines 22 and 24 run simultaneously and also both oxidation catalysts 34 and 36 be traversed by the exhaust gases.

At high speeds and high load becomes the exhaust flap 48 in the bypass line 46 open so that the exhaust gases on the oxidation catalyst 34 and at the turbine 22 passed by. In this way, in this operating condition, the pressure losses in the exhaust system 8th and thus the power losses of the internal combustion engine 2 kept low and the aging of the oxidation catalyst 34 slowed due to high exhaust gas temperatures at high engine load. The exhaust gases flow in this operating state through the bypass line 46 , the turbine 24 and the oxidation catalyst 36 which then alone takes over the conversion of unburned hydrocarbons and carbon monoxide.

In the 2 illustrated internal combustion engine 2 has four additional oxidation catalysts 50 . 52 . 54 . 56 on, each behind one of the four cylinders 6 in the exhaust manifold 12 are installed. Because of their close proximity to the cylinders 6 become the oxidation catalysts 50 . 52 . 54 . 56 heated very rapidly to the light-off temperature, whereby the oxidation of unburned hydrocarbons and carbon monoxide in the exhaust gases used early and thus the emission of pollutants is reduced after a cold start. In addition, by the oxidation catalysts 50 . 52 . 54 . 56 At low speeds and at low engine load, the overall oxidation efficiency can be improved because at the entrance of the catalysts 50 . 52 . 54 . 56 significantly higher temperatures than at the entrance of the two catalysts 34 respectively. 36 to rule. In addition, the additional oxidation of unburned hydrocarbons and carbon monoxide in the four oxidation catalysts 50 . 52 . 54 . 56 to further increase the temperature of the exhaust gases before they enter the turbine 22 and thus to an increase in the efficiency of the high-pressure exhaust gas turbocharger 18 in comparison to the internal combustion engine 2 out 1 where in front of the turbine 22 only in the oxidation catalyst 34 an oxidation of unburned hydrocarbons and carbon monoxide takes place.

To the cooling capacity of the exhaust gas recirculation cooler 44 can reduce the intake into the intake 4 recycled exhaust even before passing through one of the catalysts 50 . 52 . 54 . 56 from the exhaust manifold 12 be dissipated, as in 3 shown. However, the exhaust gas volume flow then drops through the catalysts 50 . 52 . 54 . 56 , so that they are heated a little slower and the achievement of the light-off temperature after a cold start of the engine is delayed somewhat.

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - DE 10222919 A1 [0002]
• - DE 102004009794 A1 [0002]
• - DE 102005025885 A1 [0002]

Cited non-patent literature

• - http://media.gm.com/be/opel/en/news/pr_old/pressrelease_3149.htm [0003]

Claims (11)

Internal combustion engine with an exhaust tract and with two-stage turbocharging, wherein the exhaust tract comprises two turbines of a first and a second exhaust gas turbocharger and at least one oxidation catalyst in series and a bypass line in parallel to the turbine of the first exhaust gas turbocharger, characterized in that the oxidation catalyst ( 34 ) in front of the turbine ( 22 ) of the first turbocharger ( 18 ) and behind the branch of the bypass line ( 46 ) is arranged. Internal combustion engine according to claim 1, characterized in that the bypass line ( 46 ) a load- and / or speed-controlled exhaust flap ( 48 ) contains. Internal combustion engine according to claim 1 or 2, characterized in that the bypass line ( 46 ) between the turbines ( 22 . 24 ) of the first and the second exhaust gas turbocharger ( 18 . 20 ) opens. Internal combustion engine according to one of the preceding claims, characterized by a further, behind an opening of the bypass line ( 46 ) arranged oxidation catalyst ( 36 ). Internal combustion engine according to claim 4, characterized in that the further oxidation catalyst ( 36 ) behind the turbine ( 24 ) of the second exhaust gas turbocharger ( 20 ) is arranged. Internal combustion engine according to one of the preceding claims, characterized by at least one more still, in an exhaust manifold ( 12 ) arranged oxidation catalyst ( 50 . 52 . 54 . 56 ). Internal combustion engine according to claim 6, characterized in that behind each cylinder ( 6 ) another oxidation catalyst ( 50 . 52 . 54 . 56 ) in the exhaust manifold ( 12 ) is arranged. Internal combustion engine according to one of the preceding claims, characterized by a front of the oxidation catalyst ( 34 ) from the exhaust tract ( 8th ) branching off to an intake tract ( 4 ) leading exhaust gas recirculation line ( 40 ). Internal combustion engine according to one of the preceding claims, characterized in that the internal combustion engine ( 2 ) is a diesel engine operated by a HCCI process or with a significant amount of recirculated exhaust gas. Method for operating an internal combustion engine according to one of the preceding claims, characterized in that the bypass line ( 46 Closed at low speeds and / or low engine load and opened at high speeds and / or high engine load to the exhaust gases on the turbine ( 22 ) of the first exhaust gas turbocharger ( 18 ) and in front of the turbine ( 22 ) arranged oxidation catalyst ( 34 ) to pass by. A method according to claim 10, characterized in that the bypass line ( 46 ) is partially closed at medium speeds and / or average engine load, a portion of the exhaust gases at the turbine ( 22 ) of the first exhaust gas turbocharger ( 18 ) and in front of the turbine ( 22 ) arranged oxidation catalyst ( 34 ) to pass by.