WO2014107130A1

WO2014107130A1 - System for recirculation of exhaust from a combustion engine and filter device for such a system

Info

Publication number: WO2014107130A1
Application number: PCT/SE2013/051530
Authority: WO
Inventors: Astrid Simovits
Original assignee: Scania Cv Ab
Priority date: 2013-01-04
Filing date: 2013-12-17
Publication date: 2014-07-10
Also published as: SE538192C2; SE1350005A1

Abstract

The invention relates to a system (100; 200; 300) for recirculation of exhaust gases of a combustion engine (2) and to a filter device (219; 319; 419; 519) for the system. The system (100; 200; 300) comprises an exhaust line (201; 301 ) adapted to leading exhaust gases out from the engine (2), a return line (211; 311 ) through which exhaust gases are recirculated from the exhaust line (201; 301 ) to the engine (2) and at least one EGR cooler (215; 315) which is situated in the return line (211; 311) and in which the recirculating exhaust gases are cooled before they are led to the engine (2). According to the invention at least one filter device (219; 319; 419; 519) is provided upstream of the EGR cooler (215; 315) with respect to the direction of flow of the exhaust gases. The filter device (219; 319; 419; 519) comprises a fibre filter (421; 521 ) formed of silicon dioxide fibres. The filter is adapted to filtering particles from the exhaust flow. The fibre filter (421; 521) is substantially baglike with an open first end (423; 523) and a closed second end (425; 525). The invention relates also to a combustion engine provided with the system and/or with the filter device, and to a vehicle provided with the combustion engine. The invention makes it possible to reduce fouling of the EGR cooler.

Description

System for recirculation of exhaust from a combustion engine and filter device for such a system

TECHNICAL FIELD

The present invention relates to a system for recirculation of exhaust gases of a combustion engine, to a filter device for the system, to a combustion engine provided with the system and/or the filter device and to a vehicle provided with the combustion engine.

BACKGROUND TO THE INVENTION AND PRIOR ART

Many modern combustion engines have a system for recirculation of exhaust gases, a so-called EGR (exhaust gas recirculation) system. In an EGR system, part of the exhaust gases is led back to the engine in order to reduce discharges of nitrogen oxides. The recirculating exhaust gases are mixed with inlet air for the combustion engine before the mixture is led to the engine's cylinders. Adding exhaust gases to the inlet air results in a lower oxygen content of the inlet air and a lower combustion temperature, thereby inter alia reducing the content of nitrogen dioxides in the exhaust gases.

Combustion engines may be employed in various different applications, e.g. in heavy vehicles such as trucks or buses. The vehicle may alternatively be a passenger car. Motorboats, steamers, ferries or ships, industrial engines and/or engine-powered industrial robots, power plants, e.g. an electric power plant provided with a diesel generator, locomotives and other applications may also have combustion engines.

An EGR system comprises at least one EGR cooler intended to cool the exhaust gases. The recirculating exhaust gases may for example be cooled in a coolant-cooled EGR cooler and/or an air-cooled EGR cooler. In an air- cooled EGR cooler the recirculating exhaust gases may be cooled to a temperature close to that of the surrounding air. An EGR cooler comes into contact with raw exhaust gases directly from the combustion engine, so fouling of EGR coolers is a major problem. The exhaust gases led through a return line back to the engine contain soot particles which may well, when passing through the EGR cooler, be deposited on the cooler's heat transfer surfaces, resulting in the formation of soot coatings. Soot particles contain carbon and hydrocarbons and may have a sticky surface. Soot coatings on the EGR cooler's heat transfer surfaces impair its ability to cool the exhaust gases. Insufficient cooling leads to uneven engine performance. Soot coatings may also obstruct the exhaust flow passages through the EGR cooler and thereby reduce the exhaust flow through the return line. This may lead to increased discharges of emissions from the combustion engine and to increased backpressure and consequently impaired engine performance.

The published Swedish patent application SE 0950427 A1 refers to an arrangement for recirculation of exhaust gases of a combustion engine. It refers to an arrangement intended to reduce corrosion problems in EGR coolers. The corrosion is caused by sulphuric acid in the exhaust gases. The sulphuric acid is neutralised downstream of the EGR cooler by means of a filter which contains basic material. This arrangement does however not prevent soot particles from passing through the EGR cooler.

SE 528878 C2 refers to another arrangement in which the return line is provided with a controlled valve device which makes it possible for a relatively large air flow to be caused to pass through the return line and the EGR cooler at high velocity so that the inside surfaces of the cooler are cleaned from soot coatings. This arrangement likewise does not prevent the soot particles from passing through the EGR cooler.

There is still need for a simple solution to prevent fouling of EGR coolers. There is in particular a great need to reduce the amount of soot particles which come into contact with the EGR cooler, so that impaired cooling performance can be forestalled and minimised. SUMMARY OF THE INVENTION

The object of the present invention is to reduce fouling of an EGR cooler in a system for recirculation of exhaust gases of a combustion engine. A particular object of the invention is to reduce the number of soot particles in the exhaust flow led into the EGR cooler.

Another object of the invention is to clean the exhaust flow without engine performance being substantially affected.

A further object of the invention is to propose a filter device which is adaptable to cramped spaces. These objects are achieved with a system which is defined in claim 1 and a filter device which is defined in claim 10.

A first aspect of the invention relates to a system for recirculation of exhaust gases of a combustion engine. The system comprises an exhaust line arranged to lead exhaust gases out from the combustion engine, a return line through which exhaust gases are recirculated from the exhaust line to the engine and at least one EGR cooler which is situated in the return line. The recirculating exhaust gases are cooled in the EGR cooler before being led to the engine. To prevent soot particles from passing through the EGR cooler, at least one filter device is provided upstream of the EGR cooler with respect to the direction of flow of the exhaust gases. The filter device comprises a silicon dioxide fibre filter adapted to filtering particles from the exhaust flow. The fibre filter is preferably substantially baglike with an open first end and a closed second end.

The filter device being situated upstream of the EGR cooler in the system results in the soot particles being filtered away at least partly before the exhaust flow passes through the EGR cooler. The fouling of the EGR cooler may thus be reduced. Another aspect of the invention relates to a filter device for the system. As described above in relation to the system, the filter device comprises a silicon dioxide fibre filter adapted to filtering particles from the exhaust flow. The fibre filter is substantially baglike with an open first end and a closed second end. Configuring the filter in the form of a bag makes it easy to increase its surface area. The larger the surface area of the filter, the better the degree of filtration which can be achieved.

Fibre filters have many advantages. They are flexible and easily adaptable to cramped spaces. They are easy to manufacture and may for example be formed by compression moulding to a desired shape which further improves their adaptation to cramped spaces. They comprise a large number of fibres resulting in a large effective surface area for receiving and capturing soot particles, which may be captured in tangled fibres and/or adhere firmly to the surface of the fibres. A high degree of cleaning may thus be achieved. The invention relates also to a combustion engine provided with a system and/or a filter device as above and to a vehicle provided with the combustion engine.

Further features, objects and advantages are indicated by the detailed description set out below. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic sideview of a truck provided with a recirculation system for exhaust gases.

Figure 2 depicts schematically a recirculation system for exhaust gases according to an embodiment of the invention. Figure 3 depicts schematically a recirculation system for exhaust gases according to an alternative embodiment of the invention.

Figure 4 is a schematic sideview of a filter device according to an embodiment of the invention. Figure 5 is a schematic cross-section of a filter device according to an alternative embodiment of the invention.

DETAILED DESCRIPTION

A system for recirculation of exhaust gases of a combustion engine comprises at least one EGR cooler. An EGR cooler is a device intended to cool the exhaust gases, e.g. by means of coolant or air.

There is no requirement for particle filtration in an EGR system, since the exhaust gases which pass through the EGR system and the engine go on to further cleaning. The exhaust cleaning may for example take place in a silencer provided with devices for exhaust cleaning. In a recirculation system a degree of particle filtration of about 60-80% is acceptable and makes it possible for the EGR cooler to be at least partly protected from fouling. The degree of filtration may of course be even greater.

The filter device according to the invention comprises a fibre filter made substantially from silicon dioxide fibres which are heat-tolerant and also tolerant of various chemicals. They are therefore extremely suitable for use in the context of combustion engines. As the silicon dioxide fibres tolerate high temperatures it is possible for the soot particles captured and/or adhering in the particle filter to burn spontaneously or in a controlled way and for the filter to be thereby regenerated.

The silicon dioxide fibres are preferably made of pure silicon dioxide. An example of fibre material of this kind is supplied by the company Saint Gobain Quartz, e.g. under a trademark Quartzel® Wool.

The fibres in the filter may also be coated with catalytic material in order to be able to burn particles away continuously at relatively low temperatures from 200 to 250°C. The catalytic material may for example be a noble metal, e.g. vanadium, rhodium and/or palladium, or some other catalytic material. The silicon dioxide fibres are packed to form a fibre filter. Packing means that the fibres, which are often supplied in the form of a fibre mat in which they are randomly arranged, are compressed, e.g. by mechanical means, to a desired volume and/or shape. The filter may also be formed by compression moulding. The fibres in the filter are tangled randomly and form a network, which means that soot particles, which may have a sticky surface, may both become attached to the surface of the fibres and be captured in the fibre network formed. The fibres are also formable and may assume almost any desired shape and thereby be adapted to different applications. The fibre filter may also follow pipe bends and thus also be usable in such systems in which there are pipe bends.

To achieve as high a degree of filtration as possible in a fibre filter, its surface area needs to be maximised, which according to the invention is done by forming the filter like a bag, resulting in a relatively large filtration surface. In one type of EGR system, for example, the filter may be substantially circular cylindrical with an outside diameter of 100 mm and a length of about 500 mm. This would result in an outside surface area of about 0.15 m². The surface area of the filter may for example range between 0.1 and 0.3 m², depending on the space in the exhaust system. To further maximise the effective surface area, the fibres have preferably a diameter of about 7-10 μιτι.

The thickness of the filter also affects its degree of filtration. The wall thickness of the filter depends on the space available for the filter, the air flow in the respective system and the desired degree of cleaning, but may vary between 10 and 30 mm and is preferably between 15 and 20 mm.

A further parameter which affects the degree of filtration is the porosity of the fibre filter, which defines the amount of air which the filter contains and is affected by how the fibres are packed in it. The tighter they are packed, the lower the porosity, i.e. the less air the filter will contain. The porosity is preferably as high as possible, e.g. between 92 and 96%, so that the backpressure in the system does not become too great. Porosity over 96% would increase the risk of the filter being compressed by the exhaust flow. The filter may have a porosity of between 92 and 96% so that the backpressure in the system can be kept at an acceptable level. The exhaust flow in the EGR system, i.e. the EGR flow, may vary between about 100 and 500 m³/h. Larger flows might compress the filter during operation.

The open first end of the baglike fibre filter has preferably a cross-section which corresponds to that of the exhaust line and/or that of the return line and may for example be circular. This makes it easier to fit the filter at a desired location in standard lines. The open end may also be provided with a flange or equivalent. The flange may be provided with fitting elements to further facilitate the fitting/removal of the filter device in/from a line. The size and shape of the flange will correspond to those of the line, e.g. the exhaust line and/or the return line.

The fibre filter may be surrounded by a metal mesh for the sake of firmness and stability.

The filter device may be situated in the return line of the recirculation system. This embodiment may for example be employed in a so-called short EGR system in which the exhaust gas is led out before a turbine and led back in after a compressor.

The filter device may also be situated in the exhaust line. This embodiment may for example be employed in a so-called long EGR system in which the exhaust gas is led out after the turbine and led in before the compressor. The principles of the respective systems are depicted in Figure 2 and Figure 3.

The invention relates also to a combustion engine provided with a recirculation system and/or a filter device according to any of the embodiments described above, and a vehicle provided with the combustion engine.

The invention is described below with further reference to Figures 1 -5.

Figure 1 depicts a vehicle 1 in a schematic sideview. The vehicle is provided with a combustion engine 2 which powers the vehicle's tractive wheels 4 via a gearbox 6 and a propeller shaft 8. The engine 2 is provided with an exhaust system 10 in which a silencer 12 is situated. The engine is powered by fuel 14 fed to it by a fuel system 16 which comprises a fuel tank 18. A recirculation system (EGR system) 100 for exhaust gases is provided adjacent to the engine 2.

Figure 2 is a simplified depiction of a recirculation system (EGR system) 200 for exhaust gases. It is a so-called short EGR system. Exhaust gases are led in it from the engine's cylinders 2a, 2b, 2c, 2d, 2e, 2f (2a-2f) to an exhaust line 201 via an exhaust manifold (not depicted). The exhaust gases are then led through a turbine 203 which is thus provided with driving force which is transferred via a connection to a compressor 205 which is thus enabled to compress air led to the engine 2 via an inlet line 207. The inlet line comprises a charge air cooler 209 for cooling the compressed air before it is led to the engine's respective cylinders 2a-2f via a manifold (not depicted). The system further comprises a return line 21 1 which has the function of recirculating part of the exhaust gases from the exhaust line 201 . The return line comprises a valve device 213 connected to an electrical control unit (not depicted) which controls the valve device in a desired way during the engine's operation. The return line comprises an EGR cooler 215 and an EGR mixer 217 by which the recirculating exhaust gases can be mixed with the compressed air in the inlet line 207. In the embodiment depicted in Figure 2 the return line 21 1 has a filter device 219 upstream of, i.e. before, the EGR cooler 215. Figure 3 depicts another embodiment of the system according to the invention, a so-called long EGR system 300. Exhaust gases are led in it from the engine's cylinders 2a, 2b, 2c, 2d, 2e, 2f (2a-2f) to an exhaust line 301 via an exhaust manifold (not depicted). The exhaust gases are then led through a turbine 303 which is thus provided with driving force which is transferred via a connection 304 to a compressor 305 which is thus enabled to compress the air flow from the inlet 306 which is led in via an inlet line 307. The air flow which passes through the inlet 306 is controlled by means of an inlet valve 308 which regulates the intake of air via an inlet 306 to the engine 2. The inlet line 307 comprises a charge air cooler 309 for cooling the compressed air before it is led to the engine's respective cylinders 2a-2f via a manifold (not depicted).

The system further comprises a return line 31 1 which has the function of recirculating part of the exhaust gases from the exhaust line 301 . A valve device 317 is provided between the exhaust line 301 and the return line 31 1 to control which part of the exhaust gases is recirculated and which part is led out from the system. The part of the exhaust gases which is not circulated is led out from the recirculation system via the valve device 317. This is represented in Figure 3 by an arrow to the right of the valve device 317. The embodiment depicted in Figure 3 further comprises the filter device 319 in the exhaust line 301 upstream of the EGR cooler 315.

Figure 4 depicts the filter device according to an embodiment of the invention. The filter device 419 comprises a fibre filter 421 . The fibre filter is adapted to filtering particles from the exhaust flow by their becoming attached to the filter's fibres. The filter 421 in the filter device 419 is substantially baglike and has an open first end 423 and a closed second end 425. The filter is surrounded by a metal mesh 427. The exhaust gases flow in through the filter device's open end 423 and out through the closed second end 425.

The filter device 419 may further comprise a flange 431 round the filter's open end 423 to make the filter device easier to fit at a desired location in a line in the recirculation system according to the invention. The size and shape of the flange will correspond to those of the line.

Figure 5 depicts in cross-section another embodiment of a filter device 519. The filter device comprises a fibre filter 521 . The fibre filter is baglike and has an open first end 523 and a closed second end 525. The soot particles may become attached to the whole filter's relatively large surface which includes its inside surface 526 and also partly the inside volume. The filter has also an outside surface 528. Where it is desired to achieve a high degree of filtration, the particles should not migrate through the whole filter even to the outside surface 528 but become attached to the filter's inside surface and in the internal volume. Where a lower degree of filtration of about 60-80% is acceptable, a proportion of the particles may migrate through the filter.

The exhaust gases flow in through the open end 523 of the filter device 519 and out through the closed second end 525. The filter device has also a tubular wall element 533 provided with flanges 531 , 531 ' or the like at its ends. The flange 531 surrounds the filter's open end 523 and the flange 531 ' is placed at the filter's closed end 525. The flanges 531 and 531 ' may have fitting elements such as screws or equivalents. The flanges make the filter device 519 easier to fit at a desired location in a line in the recirculation system according to the invention, and their size and shape will correspond to the cross-section of the line.

The filter device with a fibre filter described above is suitable for use in various different EGR systems. One example is a system with an EGR flow of 100 - 300 m³/h. These EGR flows occur mainly on small engines, i.e. engines with a cylinder volume of less than 10 dm³, particularly in so-called bus operation.

In a system which has an EGR flow of 100 - 300 m³/h the surface area of the fibre filter may be about 0.15 m², which means that the filter has an outside diameter of about 100 mm and a length of about 500 mm. The thickness may be about 15 mm to achieve a degree of filtration of soot particles of about 60-80%. The porosity of the filter may be about 92-96%. With these dimensions a degree of filtration of about 60-80% is achieved, the backpressure in the system will be acceptable and the engine's performance will not be disturbed.

The examples and embodiments indicated above are not restrictive of the invention, which may be varied freely within the scopes of the claims.

Claims

A system (100; 200; 300) for recirculation of exhaust gases of a combustion engine (2), which system (100; 200; 300) comprises an exhaust line (201 ; 301 ) adapted to leading exhaust gases out from the engine (2), a return line (21 1 ; 31 1 ) through which exhaust gases are recirculated from the exhaust line (201 ; 301 ) to the engine (2) and at least one EGR cooler (215; 315) which is situated in the return line (21 1 ; 31 1 ) and in which the recirculating exhaust gases are cooled before they are led to the engine (2), at least one filter device (219; 319; 419; 519) being provided upstream of the EGR cooler (215; 315) with respect to the direction of flow of the exhaust gases, characterised in that the filter device (219; 319; 419; 519) comprises a fibre filter (421 ; 521 ) formed of silicon dioxide fibres which are randomly tangled and constitute a network, which filter is adapted to filtering particles from the exhaust flow by the particles both becoming attached to the surface of the fibres and being captured in the fibre network formed.

A system according to claim 1 , characterised in that the fibre filter (421 ; 521 ) in the filter device (219; 319; 419; 519) is substantially baglike and has an open first end (423; 523) and a second closed end (425; 525).

A system according to claim 1 or 2, characterised in that the silicon dioxide fibres are coated with catalytic material, e.g. noble metal.

A system according to claim 1 , 2 or 3, characterised in that the fibres have a diameter of about 7-10 μιτι.

A system according to claims 1 -4, characterised in that the open first end (423; 523) of the fibre filter (421 ; 521 ) has a cross-section corresponding to that of the exhaust line and/or the return line.

A system according to any one of the foregoing claims, characterised in that the fibre filter (421 ; 521 ) is surrounded by a metal mesh (427).

7. A system according to any one of the foregoing claims, characterised in that the filter device (219; 319; 419; 519) has at least one flange (431 ; 531 ; 531 ') with fitting elements, which flange (431 ; 531 ; 531 ') surrounds the open first end (423; 523) of the fibre filter (421 ; 521 ) and has a shape and size corresponding to those of the exhaust line and/or the return line.

8. A system according to any one of the foregoing claims, characterised in that the filter device (219; 319; 419; 519) is situated in the return line (21 1 ; 31 1 ).

9. A system according to any one of claims 1 -7, characterised in that the filter device is situated in the exhaust line (201 ; 301 ).

10. A filter device (219; 319; 419; 519) for a system (100; 200; 300) according to any one of claims 1 -9, characterised in that the filter device (219; 319; 419; 519) comprises a fibre filter (421 ; 521 ) formed of silicon dioxide fibres which are randomly tangled and constitute a network, which filter is adapted to filtering particles from the exhaust flow by the particles both becoming attached to the surface of the fibres and being captured in the fibre network formed, which fibre filter (421 ; 521 ) is substantially baglike with an open first end (423; 523) and a closed second end (425; 525).

1 1 . A filter device according to claim 10, characterised in that the silicon dioxide fibres are coated with catalytic material, e.g. noble metal.

12. A filter device according to either of claims 10 and 1 1 , characterised in that the fibres have a diameter of about 7-10 μιτι.

13. A filter device according to any one of claims 10-12, characterised in that the open first end (423; 523) of the fibre filter (421 ; 521 ) has a cross-section corresponding to that of the exhaust line and/or the return line.

14. A filter device according to any one of claims 10-13, characterised in that the filter device is provided with at least one flange (431 ; 531 ; 531 ') to make the filter device (219; 319; 419; 519) easier to fit in a line and have a shape and size corresponding to those of the exhaust line and/or the return line.

15. A filter device according to any one of claims 10-14, characterised in that the fibre filter (421 ; 521 ) is surrounded by a metal mesh (427).

16. A combustion engine (2) characterised in that it is provided with a recirculation system (100; 200; 300) according to any one of claims 1 - 9.

17. A combustion engine (2) characterised in that it is provided with a filter device (219; 319; 419; 519) according to any one of claims 10-15.

18. A vehicle (1 ) characterised in that it is provided with a combustion engine (2) according to either of claims 16 and 17.