EP2356328A1

EP2356328A1 - Two-staged charging system for exhaust gas recirculation

Info

Publication number: EP2356328A1
Application number: EP09756725A
Authority: EP
Inventors: Alexander Mutter; Simone Bernasconi; Klaus Fussstetter; Ennio Codan
Original assignee: ABB Turbo Systems AG
Current assignee: Accelleron Industries AG
Priority date: 2008-11-18
Filing date: 2009-11-18
Publication date: 2011-08-17
Also published as: WO2010057910A1; KR20110086617A

Abstract

According to an exemplary embodiment of the invention, a charging system for an internal combustion engine is provided in which the charging is adapted to be in two stages, wherein the EGR turbocharger operates in parallel with the high pressure turbochargers. The two-stage charging brings about an improvement in the charging efficiency, whereby the EGR compressor has to overcome a higher pressure difference.

Description

Two-stage charging system for exhaust gas recirculation

T E C H N I S C H E S G E B I E T

The invention relates to the field of supercharged internal combustion engines. More particularly, the invention relates to a supercharging system for an internal combustion engine, an internal combustion engine having such a supercharging system, a vehicle having such an internal combustion engine, a method for supercharging an internal combustion engine with a supercharging system, a program element, and a computer readable medium.

Technological background

Exhaust gas recirculation (EGR) is a well-known method for reducing NOx emissions in internal combustion engines. For supercharged engines, the high pressure variant, i. the removal of exhaust gas in front of the turbine of the turbocharger and the admixture of the gas after the compressor, the most energetically favorable variant. It is very common in the field of small engines, especially for cars and trucks. The reason for this is that the exhaust pressure upstream of the turbine is higher in wide ranges of the engine map than the pressure of the charge air after the turbocharger compressor.

In large engines, this is not the case, since mostly by high efficiencies of charging a positive pressure difference between the conditions before and after the cylinder is generated. This is desirable for engine operation as it allows the purge of the combustion chamber and reduces the charge cycle work.

The positive pressure difference makes the EGR impossible without additional measures. The problem can be solved by using a blower for increasing the pressure of the gas (US5657630A1). This solution fulfills the task, but has the disadvantages that the blower with electric or mechanical drive is very large and consumes a considerable drive power, which has a negative effect on the energy balance of the entire system. From DE 44 36 732 A1 another solution is known, in which the blower is driven by a gas turbine. The engine for the EGR then looks like a turbocharger, although special components are used. This solution has been investigated in a research project and has proved to be the best thermodynamic variant (CIMAC Paper: H. Stebler et al., Reduction of NOx emissions of a medium-speed diesel engine using the milier system, exhaust gas recirculation, variable nozzle turbo charger and common rail fuel injection - Copenhagen 1998).

A big problem with this reconditioning turbocharger is that the compressor has to process a relatively large mass flow with a very low pressure ratio and the turbine has to process the smallest possible mass flow with a high expansion ratio.

This leads to a mismatching of the components. With a turbocharger normal diameter ratio DT / DV «0.9 (DT = turbine diameter, DV = compressor diameter), a running number of the turbine would be less than 0.2. The turbine speed is the ratio between the peripheral speed uT of the turbine and the isentropic speed cθ, which corresponds to the existing enthalpy gradient. This run number should be about 0.7 for optimum turbine efficiency. At the value below 0.2, the turbine efficiency becomes very low.

The situation can be improved by increasing the DT / DV ratio. However, there are also limits: The reduction of the compressor diameter leads to very large values of the specific absorption capacity of the compressor

V / Dv2, with V = volumetric flow. The increase of the turbine diameter leads to very low values of the specific absorption capacity of the turbine Seff / DT2, with Seff = effective area of the turbine equivalent nozzle.

In both cases, the achievable efficiency of the components (compressor or turbine) is reduced. Another improvement is known from DE 44 36 732 A1: When two EGR turbochargers are used and the turbines are arranged in series while If the compressors work in parallel, the problem of mismatching is partially alleviated (the number of turbine runs is doubled).

Brief description of the invention

It is an object of the invention to provide improved supercharging of internal combustion engines.

There is provided a supercharging system for an internal combustion engine, an internal combustion engine, a vehicle, a method, a program element and a computer-readable medium according to the features of the independent claims. Further developments of the invention will become apparent from the dependent claims. The described embodiments equally relate to the charging system, the internal combustion engine, the vehicle, the method, the program element and the computer-readable medium. In other words, the features described below for example with regard to the charging system, the internal combustion engine or the vehicle can also be implemented in the method, the program element and the computer-readable medium, and vice versa.

According to an exemplary embodiment of the invention, a supercharging system for an internal combustion engine is specified, which has a first turbocharger, a second turbocharger and a recirculation path. The first turbocharger has a first turbine and a first compressor and the second turbocharger has a second turbine and a second compressor. The two turbochargers are connected in series with each other. The recirculation path serves to recirculate exhaust gas of the internal combustion engine from the exhaust or exhaust receiver of the internal combustion engine to an inlet or intake receiver of the internal combustion engine. Furthermore, an exhaust gas compressor is arranged in the recirculation path, which serves to increase the pressure of the exhaust gas before it is fed back to the inlet of the internal combustion engine. To drive the exhaust gas compressor, the charging system has a third turbine, wherein the third turbine is connected in parallel with the second turbine of the second turbocharger and an exhaust gas flow emerging from the third turbine is supplied to the first turbine of the first turbocharger. - A -

In other words, the charge is made in two stages with the EGR turbocharger operating in parallel with the high pressure turbochargers. The 2-stage charging brings an improvement in the Aufladewirkungsgrades, which also has the side effect that the EGR compressor has to overcome a higher pressure difference. According to a further embodiment of the invention, the exhaust gas compressor is the second compressor of the second turbocharger.

According to this embodiment of the invention, the EGR flow is taken from the outlet receiver and, after conditioning (cooling, cleaning, filtration, ...) mixed before entering the high-pressure compressor of the main flow.

According to a further exemplary embodiment of the invention, the charging system has a third turbine for driving the exhaust gas compressor, wherein the third turbine is arranged in the recirculation path.

According to this embodiment of the invention, the EGR turbocharger is shorted. The EGR flow is expanded to the next in the turbine of the recirculation charger, then the conditioning (cooling, cleaning, filtration, ...) and then the compression in the compressor of the recirculation charger.

According to a further embodiment of the invention, the charging system further comprises a power turbine integrated in the recirculation path.

According to a further exemplary embodiment of the invention, at least one of the turbines has a variable, controllable flow area.

For example, the power turbine has a variable flow area. Furthermore, according to a further embodiment of the invention, a connection between the outlet of the EGR turbine and the outlet from the system for controlling the turbine power is provided. The regulation takes place via a corresponding regulator.

According to a further embodiment of the invention, at least two turbochargers operate as low-pressure stages parallel to one another. According to a further exemplary embodiment of the invention, at least one of the low-pressure turbochargers has a capacity which approximately corresponds to the EGR rate and can be switched off by valves.

According to a further embodiment of the invention, the valve timing of the internal combustion engine are variable. According to a further exemplary embodiment of the invention, the variable valve timing of the internal combustion engine when operating with EGR achieves a smaller miller effect than during operation without EGR.

According to a further embodiment of the invention, the system is designed such that the variable valve timing of the internal combustion engine when operating with EGR, a higher air flow, ie an increased purge is achieved as in operation without EGR.

According to a further exemplary embodiment of the invention, the charging system further has a first variable bypass line for connecting an outlet of the second compressor to an inlet of the second turbine.

According to a further exemplary embodiment of the invention, the charging system further has a second variable bypass line for connecting the outlet of the second compressor to an inlet of the first turbine.

According to a further exemplary embodiment of the invention, the charging system has a third variable bypass line for connecting an outlet of the first compressor to an inlet of the first turbine.

According to a further exemplary embodiment of the invention, the charging system has a fourth variable bypass line for connecting the inlet of the second turbine with an outlet of the second turbine. According to a further exemplary embodiment of the invention, the charging system has a fifth variable bypass line for connecting the inlet of the second turbine with an outlet of the charging system.

According to a further exemplary embodiment of the invention, the charging system has a sixth variable bypass line for connecting the inlet of the first turbine with an outlet of the charging system. It should be noted that the various variable bypass conduits may be provided individually or in various combinations with each other. To vary the bypass lines corresponding control valves or control valves are provided in, before or after the bypass lines. According to a further exemplary embodiment of the invention, the low-pressure compressor (first compressor) has a variable diffuser.

According to a further embodiment of the invention, the low-pressure compressor on a controllable means for generating Vordrall.

According to a further exemplary embodiment of the invention, the turbine of the recirculation charger (third turbine) has a controllable flow area.

According to a further embodiment of the invention, the high-pressure turbine has a controllable flow area and according to a further exemplary embodiment of the invention, the low-pressure turbine has a controllable flow area. According to a further embodiment of the invention, the gas flow in the fourth bypass line is expanded in a power turbine.

According to a further embodiment of the invention, this power turbine has a variable flow area.

According to a further embodiment of the invention, the gas flow in the fifth bypass line is expanded in a power turbine.

According to a further embodiment of the invention, the gas flow in the sixth bypass line is expanded in a power turbine. According to a further embodiment of the invention, this power turbine also has a variable flow area.

According to a further exemplary embodiment of the invention, the high-pressure turbocharger (second turbocharger) has a mechanical connection for power transmission (power take-in / power take-out). According to a further exemplary embodiment of the invention, the low-pressure turbocharger (first turbocharger) has a mechanical connection for power transmission (power take-in / power take-out).

According to a further embodiment of the invention, an internal combustion engine is specified with a charging system described above. In particular, this internal combustion engine is a large engine, which is used for example for driving a ship or a locomotive or even for stationary power generation in a power plant.

According to a further exemplary embodiment of the invention, a vehicle is specified with an internal combustion engine described above for driving the vehicle.

The vehicle is, for example, a ship, a locomotive or even a heavy road vehicle.

According to a further exemplary embodiment of the invention, a method is described for charging an internal combustion engine with a supercharging system (as described above), in which the internal combustion engine is charged in two stages by means of two serially arranged turbochargers. Furthermore, recirculation of exhaust gas of the internal combustion engine from an outlet of the internal combustion engine takes place through a recirculation path to an inlet of the internal combustion engine. In addition, a compressor is driven, which is arranged in the recirculation path. The compressor is driven by a turbine. By the compressor, the pressure of the exhaust gas is increased during recirculation.

According to a further exemplary embodiment of the invention, furthermore, the power of one or more of the turbines is regulated on the basis of a connection between an outlet of the turbine and an outlet of the charging system.

The target variables for the regulation of the charging system are: - The EGR quantity:

The amount of EGR can be practically in all cases through the control valve 23 or through the surface of the turbine 24 (the mass flow through the turbine determines the turbine power.) This results in the compressor power and then the recirculated exhaust gas amount. Exceptions: System of Fig. 2. The control is carried out here by the valve 26, possibly by the Nutzturbinenfläche 202. System of Fig. 3: Here, the valve 302 is needed, possibly only in the starting phase.

- Boost pressure (pressure in the exhaust gas receiver 1): The boost pressure can be influenced or regulated by the register charging, by the variable flow areas of the turbines (7 and 15) or by the different wastegate or turbine versions.

- Location in the compressor map:

The position of the operating point in the compressor map can be influenced or regulated by register charging, valve timing, variable compressor geometry, by-pass valves.

The two above sizes are not independent; The shift of the operating points gives a variation of boost pressure, the variation of the boost pressure, in particular by changing the pressure distribution between the stages, causes a shift in the maps.

- Cylinder filling (the air ratio and the compression pressure affect the maximum cylinder pressure at constant injection).

The cylinder fill can be varied primarily by the variable timing. For example, when controlling all four control variables mentioned the four control loops can be separated and it can be a pure on / off control for one or some of these sizes.

According to a further embodiment of the invention, a program element is specified which, when executed on a processor, instructs the processor to perform the method steps given above.

For example, the computer program element may be part of a software that is stored on a processor of the vehicle management. The processor can also be the subject of the invention. Furthermore, this embodiment of the invention comprises a computer program element which already uses the invention from the beginning, as well as a A computer program element which causes an existing program to use the invention by an update.

According to another embodiment of the invention, there is provided a computer readable medium having stored thereon a program element which, when executed on a processor, instructs the processor to perform the method steps given above.

In the following, embodiments of the invention will be described with reference to the figures.

Brief Description of the Drawings Fig. 1 shows a supercharging system with an EGR turbocharger in parallel with the high pressure supercharger according to an embodiment of the invention.

2 shows a supercharging system with EGR compression in the high-pressure compressor according to a further exemplary embodiment of the invention.

3 shows a supercharging system with a shorted EGR turbocharger in parallel with the high pressure supercharger according to another embodiment of the invention.

4 shows a supercharging system according to another embodiment of the invention with an EGR turbocharger in parallel with the high pressure supercharger with the ND charger in register. Fig. 5 shows a charging system according to another embodiment of the invention with an EGR turbocharger in parallel to the high-pressure charger with first control options.

6 shows a charging system according to a further exemplary embodiment of the invention with an EGR turbocharger in parallel to the high-pressure charger with second control options.

Fig. 7 shows two vehicles according to embodiments of the invention.

Fig. 8 shows a power plant with an internal combustion engine according to an embodiment of the invention.

9 shows a flow chart of a method according to an embodiment of the invention. DETAILED DESCRIPTION OF EMBODIMENTS The illustrations in the figures are diagrammatic and not to scale.

In the following description of the figures, the same reference numerals are used for the same or similar elements. FIG. 1 shows a turbocharger 100 having an EGR turbocharger 24, 34, 29 disposed in parallel with a high pressure loader 18, 33, 15.

An internal combustion engine 2 is provided, which has an air intake receiver 1 and an air outlet receiver or exhaust gas receiver 3. Via the line 5, a high-pressure gas turbine 15 of the high-pressure turbocharger is connected to the outlet receiver 3. In parallel, a control valve 23, via which the respective turbine can be switched off or regulated, and a gas turbine 24 for the EGR compressor 29 are connected via the lines 5, 22. In parallel, the EGR compressor 29 and an upstream module 27 for cleaning and cooling the EGR gas are also connected to the exhaust gas receiver 3, which in turn is preceded by a further control valve 26.

The exhaust stream is thus divided into three partial streams. The first partial flow drives the high-pressure turbine 15 and is then fed via the line 16 to a second exhaust gas receiver (medium pressure) 4. The second partial flow drives the recirculation turbine 24 and is also supplied via the line 25 to the second exhaust gas receiver. The third partial flow is fed to the compressor 29 of the EGR turbocharger 24, 34, 29. Reference numerals 33 and 34 designate corresponding drive shafts between the respective turbines and compressors.

The compressed exhaust stream is supplied via line 30 to an EGR cooler 31, which is optionally provided. Via the line 41, the resulting compressed exhaust gas stream is fed to the air receiver 1. For better reliability, a check valve 101 may be provided in the line 41.

From the second exhaust gas receiver 4, the exhaust gas stream via the line 6 of the low-pressure turbine 7 is supplied and then discharged via the line 8 to the outside or handed over to a downstream system, such as a system for heat recovery, exhaust aftertreatment or a chimney. Via the line 9, air is introduced into the system. The conduit 9 supplies the air to the low-pressure compressor 10, which is connected via the connecting shaft 32 to the low-pressure turbine 7. Via the line 11, the air expelled from the compressor 10 is transferred to an air cooler 12, which passes the cooled resulting air via the line 11 to the high pressure compressor 18. The discharged from the high-pressure compressor 18 air is passed via the line 19 to another air cooler 21 and then fed via the continuation of the line 19 to the air receiver 1.

An advantageous solution of the problem underlying the invention is to make the charging 2-stage and to let the EGR turbocharger operate in parallel to the high-pressure turbochargers. The 2-stage charging brings an improvement in the Aufladewirkungsgrades, which also has the side effect that the EGR compressor has to overcome a higher pressure difference.

On the other hand, the EGR turbine operates at a lower expansion ratio because it expands the gas only from the pressure in the exhaust gas receiver to the pressure at the entrance of the low pressure turbines.

Both effects mean that the mass flows on the compressor side and turbine side come to lie in a more favorable ratio and therefore the running speed of the turbine also increases against the optimum range. An additional advantage is that the remaining energy of the gas, which is used to drive the EGR turbine, remains usable in the low-pressure turbine (ND turbine).

The system allows the engine to operate at high EGR rates while still maintaining high efficiency of charge and engine. This is due to the good efficiencies of the 2-stage charging and the good efficiency of the recirculation charger. The costs for the recirculation loader can also be reduced, because by disarming the running number problem, components already known could be used, whereas in the case of the single-stage charging new developments with extreme target values would be necessary. The advantages of the 2-stage charging compared to the 1-stage need not be particularly explained here. The 2-stage charging with intermediate cooling allows significantly higher pressure conditions of the charge with significantly higher Achieve efficiencies. For the engine, this generally means higher efficiencies but also potential for power increase, emission reduction specifically due to the Miller process and higher flexibility for the control. All these advantages are accessible with the proposed system. FIG. 2 shows a supercharging system 100 with EGR compression in the high pressure compressor 18. A conduit 28 is provided which supplies a portion of the exhaust gas flow from the exhaust gas receiver 3 to a utility turbine 202 via a valve 26 for shutting off the EGR path. From the power turbine 202, the exhaust gas flow then passes to a cleaning module 27, which is also used for cooling the EGR gas. Thereupon, the cleaned and cooled exhaust gas passes via the line 201 and the line 11 to the high-pressure compressor 18.

In this embodiment of the invention, the compressor of the high-pressure supercharger is additionally used as a compressor for the recirculation flow. The EGR flow is taken from the outlet receiver and mixed with the main flow after conditioning (cooling, cleaning, filtration ...) before entering the high pressure compressor. The advantage of this design is that the EGR turbocharger is eliminated, thereby making the system easier. The power turbine is not essential for the function of this design. In a simplified embodiment, without a power turbine, the expansion energy of the EGR gas from the inlet pressure of the high-pressure turbine to the inlet pressure of the high-pressure compressor remains unused: the gas is throttled only in the valve 26. For very large engines, this expansion energy can not be negligible, therefore, the integration of a turbine in the EGR path is an interesting option. For better controllability of the system, it is also advantageous if the power turbine has a variable flow area.

3 shows a supercharging system 100 with a short-circuited EGR turbocharger in parallel to the high-pressure supercharger 18, 33, 15. The EGR supercharged by the module 27 (which is, for example, a so-called scrubber, cooler or heat exchanger) is cooled and cooled. Gas flow is supplied via the line 301 to the compressor 29. At the same time, a portion of the exhaust stream may be supplied to the outside via the valve 302 or to a connected, downstream system.

In this embodiment of the invention, the recirculation turbocharger is shorted. The EGR flow is next to the turbine of the Recirculation charger expands, then the conditioning (cooling, cleaning, filtration, ...) and then the compression in the compressor of the recirculation charger. This design requires a higher pressure ratio of the EGR compressor, but the gas flow to drive the EGR turbine can be spared. To start the engine and for power control it is opportune to provide the possibility to increase the mass flow of the turbine through a controllable blow-off valve 302.

There are applications, such as for marine engines, where it is advantageous to operate the engine without EGR. In that case, the high-pressure turbocharger can easily continue to drive. However, the low pressure loader would experience a large shift in the operating point in the compressor map. In order to keep the efficiency losses of the compressor within limits, a design at very moderate pressure conditions for the low-pressure supercharger is provided so that enough map width is still present. To allow engine operation with and without EGR, there is additional variability in the supercharger system.

A first option is to divide the entire capacity between several low-pressure turbochargers. One of the low pressure turbochargers has a capacity that approximates the EGR rate and is only active in register when the EGR is turned off. In this case, charging may provide comparable levels of boost pressure and efficiency in both modes of operation.

Another possibility is to make the valve timing of the engine variable. Many modern engines are operated with the so-called Miller process. For A-stroke engines, this can be achieved by closing the intake valve sooner or later than the optimum fill angle to give the cylinder significantly less charge than the mass corresponding to the density in the intake receiver and the displacement. In 2-stroke engines, this can be produced by a later closing of the exhaust valve. It is particularly advantageous if the Millereffekt in operation with EGR fails lower than in operation without EGR. As a result, the shift of the operating point in the compressor map can be reduced. The reduction of the charge in operation without EGR also allows the increase of air ratio and maximum cylinder pressure due to the higher boost pressure to reduce. In particular in the case of 4-stroke engines, the variation of the valve overlap can further influence the permeability of the engine, ie the relationship between charge pressure and throughput.

The turbomachine flow surfaces are designed to provide the drive power to the compressors to produce the required boost pressure when operating with EGR. In operation without EGR, the turbines get more mass and thus produce much more power. To reduce this performance, there are several possibilities:

- Provide the high-pressure turbine with variable flow area. - Provide the low-pressure turbine with variable flow area.

Providing a high pressure wastegate, i. a bypass line around the high-pressure turbine.

Providing a low pressure wastegate, i. a bypass line around the low-pressure turbine. Providing a system wastegate, i. a bypass line around both turbines.

The variable turbine area allows to reduce the turbine power with the lowest efficiency losses. These losses are higher with the high-pressure wastegate and even higher with the other wastegate variants.

The superfluous waste gas energy in operation without EGR can be converted into a utility turbine if this utility turbine is integrated into a turbine bypass line. For better controllability of the system, it is also advantageous if the

Nutzturbine has a variable flow area. Alternatively, the superfluous

Power can be withdrawn directly from the turbocharger shaft (power take-out). Is a

Connection to the turbocharger shaft, it can also be used as power take-in, i. external power can be fed in as needed.

The problem of shifting the operating points in the compressor map can be expressed as follows:

If the compressors are designed for optimal operation with EGR, they will operate with too high a flow rate and high pressure during operation without EGR; This leads to worse efficiencies and possibly to exceeding the intake limit or the speed limit of the compressor. If the compressors are designed for optimum operation without EGR, they will operate with too low a flow rate and too little pressure when operating with EGR; This can lead to exceeding the surge limit.

A bypass line around the engine can help prevent pumping. This bypass line can be represented as a connection:

- From the high pressure compressor to the high pressure turbine (HD bypass). - From the low pressure compressor to the low pressure turbine (LP bypass).

- From the high pressure compressor to the low pressure turbine (HD / ND bypass).

The variable compressor geometry is another way to move the optimal operating range of the compressor. The advantage is that less energy is needed for compaction compared to the bypass variants. The variability is preferably to be applied to the low-pressure compressor and can be realized as follows:

- Variable (rotatable) diffuser blades. - Adjustable device for generating swirl at the compressor inlet.

4 shows a supercharging system 100 with an EGR turbocharger connected in parallel with the high pressure supercharger, the low pressure supercharger 10, 32, 7 being in register. To the second exhaust gas receiver 4 via the line 13 and the valve 14 (to turn off the respective cabin), a turbine 36 is connected. The discharged gas stream is discharged via line 37 to the outside world or a downstream system. Via the shaft 35, the turbine 36 is connected to the compressor 38. The compressor 38 is supplied via the line 17 air that comes, for example, from the outside. The compressed air is supplied from the compressor 38 via the valve 20 to the air cooler 40 and then fed via the line 39 and the line 11 to the high-pressure compressor 18.

The cooled air of the low-pressure compressor 10 generated via the air cooler is likewise fed via the line 11 to the high-pressure compressor 18.

FIG. 5 shows a supercharging system 100 with an EGR turbocharger in parallel with the engine

High-pressure loader with first control options. A plurality of variable bypass lines 501 to 506 are provided. The bypass line 501 is between the

Outlet of the high pressure compressor and the inlet of the high pressure turbine 15th connected. The variable bypass line 502 is connected between the outlet of the high-pressure compressor 18 and the input of the low-pressure turbine 7. The variable bypass line 503 is connected between the outlet of the low-pressure compressor 10 and the inlet of the low-pressure turbine 7. The variable bypass line 504 is connected between the inlet of the high-pressure turbine 15 and its outlet. The variable bypass passage 505 is connected between the inlet of the high-pressure turbine 15 and the outlet of the low-pressure turbine 7. The variable bypass line 506 is connected between the inlet of the low-pressure turbine and its outlet. The variable bypass lines have corresponding control valves. Furthermore, a control valve 507 is connected between a power turbine 508 and the second exhaust gas receiver 4.

A second power turbine 509 is connected via the variable line 510 with a corresponding control valve to the line 5.

The variable bypass lines 504-506 are optional when the respective utility turbines are installed.

Fig. 6 shows a supercharging system 100 with an EGR turbocharger in parallel with the high pressure supercharger with second control possibilities. For example, the air is discharged from the utility turbine 509 to the outside (system exit) or to a downstream system and not supplied to the second exhaust gas receiver. Reference numerals 601, 602 designate the power take-in / power take-out (PTI / PTO) connections of the two turbochargers 18, 33, 15 and 10, 32, 7.

Reference numerals 203, 511, 512, 601 and 602 in Figs. 2, 5 and 6 respectively denote a generator and motor / generator. It is the consumer for the power turbine or PTI / PTO, i. a generator or electric motor / generator, a transmission for connection to the crankshaft of the engine, a pump or a hydraulic pump / turbine.

Reference numeral 303 in Figs. 3, 5 and 6 denotes an exit from the system which leads to the outside or is connected to a downstream system. The engine 2 has in the embodiments of Figures 5 and 6 variable timing. Fig. 7 shows two vehicles according to embodiments of the invention. The first vehicle 601 is a ship and the second vehicle 602 is a locomotive, each having a large engine with a charging system 100 according to the invention as a drive. Fig. 8 shows a power plant 700 with a charging system 100, which is intended for a power plant large engine.

9 shows a flow chart of a method according to an embodiment of the invention.

In step 901, a two-stage charging of the internal combustion engine takes place through two serially arranged turbochargers. By driving a compressor in the

Recirculation path is arranged by a turbine in step 902 is a

Recirculating exhaust gas of the internal combustion engine from an outlet of the engine

Internal combustion engine through a recirculation path to an inlet of the

Internal combustion engine and in step 903, an increase of a pressure of the exhaust gas when recirculating through the compressor.

Of the described embodiments, the register circuit of the low-pressure compressor is particularly advantageous. It should also be appreciated that features or steps described with reference to any of the above embodiments may also be used in combination with other features or steps of other embodiments described above. Prioritizing system efficiency or cost or complexity is critical to choosing the appropriate solution.

In addition, it should be noted that "comprising" and "having" does not exclude other elements or steps, and "a" or "an" does not exclude a plurality. Reference signs in the claims are not to be considered as limitations. List of Reference Numerals Air receiver Internal combustion engine Exhaust gas receiver 2. Exhaust gas receiver (medium pressure), 6, 13, 22 Connections from exhaust gas receiver to turbine inlet. 4, 23 valve for switching off the respective turbine, 15, 24, 36 gas turbine, 37, 303 connection to the downstream system

(Heat recovery, exhaust aftertreatment, chimney, ...) 6, 25 connection of turbine outlet to

Medium pressure exhaust gas receiver, 17 air inlets in system 0, 18, 29, 38 Compressor 9, connections from compressor outlet to air receiver 1, 39 Connections from compressor outlet to high pressure compressor 2, 21, 40 Air cooler 0 Valve for switching off the compressor 6 Valve for switching off the EGR path 7 Module for Cleaning and cooling of EGR gas (scrubber, radiator, heat exchanger, ...) 8, 201 Connection of exhaust gas receiver to EGR compressor 0, 41 Connection of EGR compressor to air receiver 1 EGR cooler (optional) 2, 33, 34, 35 turbocharger or connecting shaft between turbine and02 _, 508 _, 509 compressor 501 to 506 power turbines

507, 510 variable bypass lines with valves

203, 511, 512, variable pipes with valves

601 and 602 Generator resp _. Motor / generator

101 check valve

³⁰² control valve

Claims

PAT EN TA NSPR O CHE

A two-stage supercharging system for an internal combustion engine, the supercharging system (100) comprising: a low-pressure turbocharger (7, 10) having a first turbine (7) and a first compressor (10); a high pressure turbocharger (15, 18) having a second turbine (15) and a second compressor (18); wherein the low-pressure turbocharger (7, 10) is arranged serially to the high-pressure turbocharger (15, 18), so that an exhaust gas flow emerging from the second turbine (15) is fed to the first turbine (7) of the first turbocharger (7, 10), and a Recirculation path (28, 30, 41, 201) for recirculating exhaust gas of the internal combustion engine (2) from an outlet (3) of the internal combustion engine (2) to an inlet (1) of the internal combustion engine (2); an exhaust gas compressor (18, 29) disposed in the recirculation path (28, 30, 41, 201) and serving to increase the pressure of the exhaust gas; wherein the exhaust gas compressor (24) is driven by a third turbine (24), which is connected in parallel with the second turbine (15) of the high-pressure turbocharger (15, 18), so that an exhaust gas flow from the first turbine (24) emerging from the third turbine (24) 7) of the low-pressure turbocharger (7, 10) is supplied

A supercharging system according to claim 1, wherein the exhaust gas compressor (18) is the second compressor (18) of the second turbocharger (15, 18).

The charging system of claim 1, wherein the third turbine (24) is disposed in the recirculation path (28, 30, 41, 201).

The charging system of claim 1, further comprising: a utility turbine (202) integrated with the recirculation path (28, 30, 41, 201).

5. A charging system according to any one of the preceding claims, further comprising at least one element selected from the group consisting of: a first variable bypass line (501) for connecting an exit of the second compressor (18) to an inlet of the second turbine (15). a second variable bypass line (502) for connecting the exit of the second compressor (18) to an inlet of the first turbine (15). a third variable bypass line (503) for connecting an outlet of the first compressor (10) with an inlet of the first turbine (7); a fourth variable bypass line (504) for connecting the inlet of the second turbine (15) with an outlet of the second turbine (15). a fifth variable bypass line (505) for connecting the entrance of the second turbine (15) to an outlet (8) of the charging system; and a sixth variable bypass line (506) for connecting the entrance of the first turbine (7) to a discharge (507) of the charging system.

6. Charging system according to one of the preceding claims, wherein the valve timing of the internal combustion engine are variable.

7. Charging system according to one of the preceding claims, wherein at least one of the turbines or one of the compressor or a power turbine has at least one variable element.

8. Charging system according to one of the preceding claims, designed for register charging.

9. Internal combustion engine with a charging system according to one of claims 1 to 8.

10. Vehicle with an internal combustion engine according to claim 9 for driving the vehicle.

11. A method for charging an internal combustion engine with a supercharging system, the method comprising the steps of: two-stage supercharging of the internal combustion engine (2) by two serially arranged exhaust gas turbochargers in which a from a second turbine (15) of a high-pressure turbocharger (15, 18) exiting exhaust gas flow first turbine (7) of a low-pressure turbocharger (7, 10) is supplied; Recirculating exhaust gas of the internal combustion engine (2) from an outlet (3) of the internal combustion engine (2) through a recirculation path to an inlet (1) of the internal combustion engine (2);

Driving a compressor disposed in the recirculation path through a turbine (7, 15, 24) parallel to the second turbine (15) of the second

Exhaust gas turbocharger (15, 18) is arranged;

Increasing a pressure of the exhaust gas when recirculating through the compressor.

12. The method of claim 11, further comprising the step of:

Controlling an amount of exhaust gas through the recirculation path and / or a boost pressure in the exhaust gas receiver (1).

A program element which, when executed on a processor for controlling a charging system according to any one of claims 1 to 8, instructs the processor to perform the following steps:

A computer-readable medium having stored thereon a program element which, when executed on a processor for controlling a charging system according to any one of claims 1 to 8, instructs the processor to perform the following steps: controlling an amount of exhaust gas through the recirculation path and / or one

Boost pressure in the exhaust gas receiver (1).