EP2941558B1

EP2941558B1 - Arrangement for recirculation of exhaust gases at an internal combustion engine

Info

Publication number: EP2941558B1
Application number: EP13870300.4A
Authority: EP
Inventors: Fredrik Modahl; Henrik HÅKANSSON HOLST
Original assignee: Scania CV AB
Current assignee: Scania CV AB
Priority date: 2013-01-04
Filing date: 2013-12-16
Publication date: 2018-02-28
Anticipated expiration: 2033-12-16
Also published as: WO2014107126A1; EP2941558A4; SE536919C2; BR112015015193B1; KR101795699B1; KR20150097800A; BR112015015193B8; EP2941558A1; SE1350004A1; BR112015015193A2

Description

Technical area

The present invention relates to an arrangement and a method according to the preambles to the independent claims. To be more specific, the invention relates to an arrangement and a method for the supply of exhaust gases to the inlet air in a combustion engine.

Background to the invention

The recirculation of exhaust gases, known as "EGR" or "exhaust gas recirculation", is a generally known method for combustion engines used to influence the combustion, and it involves the recirculation of a part of the total exhaust gas flow from the engine to the inlet side of the engine, where it is mixed with inlet air to be introduced into the cylinders of the engine. It becomes in this way possible to reduce the amount of nitrogen oxides (NO_X) in the exhaust gases that are emitted to the surroundings. This technology has been used for a relatively long time in Otto engines, and as time has passed has become evermore interesting also for diesel engines. The technology has been used, in particular, in vehicular applications, where environmental requirements are relatively strict. However, as environmental requirements in general increase, so also does interest in EGR technology for use also in engines that are used in, for example, maritime transport and industrial applications.
The fraction of exhaust gases in the air/exhaust gas mixture that is supplied to the cylinders of the engine (the combustion chambers) must be accurately controlled since too small a fraction of exhaust gases normally gives an increased production of NO_X, and too large a fraction of exhaust gases may give a severely increased formation of soot. In order to achieve low emissions of NO_X and soot, it is important not only that the total fraction of exhaust gases is optimised but also that the fraction of exhaust gases is equal in all cylinders. Also from the point of view of wear with respect to, for example, pistons, piston rings, linings and bearings, it is important that the fraction of exhaust gases is equal in all cylinders. In order to obtain this even distribution of the fraction of exhaust gases to the different cylinders, it is important that the recirculated flow of exhaust gases is mixed into the incoming air in a suitable manner.
Through the remainder of this description, the term "EGR flow" will be used to denote the recirculated partial flow of the total exhaust gas flow of the engine.
The EGR flow is normally recirculated to the inlet air through an EGR line, normally designed as a small EGR pipe, which is connected to the exhaust gas side of the engine being connected to a part of a line that leads inlet air to the cylinders. Such a line for the inlet air is terminated with an inlet pipe (an inlet branch pipe) attached at the engine and that comprises connection ducts to the various cylinders of the combustion engine, which connection channels are arranged along one side of the inlet pipe. Inlet valves are arranged at the cylinders, and are opened in order to supply the relevant cylinder with inlet air. One practical problem that arises when the EGR pipe is connected to such an inlet pipe is that a limited path length is available for the mixing, and that this is normally not sufficient for the exhaust gases to have sufficient time to be thoroughly mixed before the mixture reaches the cylinders of the engine. Prior art embodiments result in different cylinders being supplied with different fractions of exhaust gases in the inlet air, depending on their different distances between the point at which the exhaust gases are added and the different cylinders.
Examples of prior art technology that show various types of EGR system will now be described.
EP-2133548 concerns a gas mixing system in association with an EGR system. The purpose is to improve the mixing of the recirculated exhaust gases in the air flow. This is achieved by, among other measures, providing the mixing pipe with a number of openings through which the exhaust gases can pass.
US-5957116 concerns an EGR pipe adapted to be arranged in the air intake and to comprise a number of holes through which the recirculated exhaust gases are passed to the flow of air.
DE-10303569 describes an EGR system in which the exhaust gases are recirculated into the inlet pipe via a mixing pipe that takes the flow of exhaust gases in a direction opposite to the flow in the inlet pipe before the exhaust gases are introduced into the inlet pipe via openings not only in the longitudinal wall of the mixing pipe but also in its end.
FR-2908471 concerns an EGR system in which the exhaust gases are recirculated in the inlet pipe via a pipe with a cross-section that increases in the direction of flow. The pipe is turned in one variant such that the exhaust gases are supplied to the inlet pipe in a direction that is opposite to the flow there.
US-7389770 concerns an arrangement and a method for the supply of recirculated exhaust gases. The arrangement includes an outlet section with a number of outlets for the supply of exhaust gases and where the outlet section demonstrates an outlet path in the duct for incoming air. One purpose with this prior art arrangement is to improve the distribution of the recirculating exhaust gases which is achieved through, among other properties, the outlets being spread along the longitudinal direction of the duct and distributed around a circumference of the outlet section. It is mentioned also that the outlet section may be located externally to the duct for incoming air. JP-200054915 concerns an EGR system in which the exhaust gases are passed to the flow of air through a number of outlets distributed around a circumference of an EGR outlet section arranged outside of an inlet pipe in a direction opposite to the direction of incoming air.
In order to achieve optimal function of the EGR system, it is important that the EGR gases have sufficient time to reach an even distribution in the flow of air before they reach the inlet valves of the various cylinders.
A further desire for an EGR system is that it should be possible to connect the inlet pipe in a simple manner to different types of connection line for the supply of air to the inlet pipe, which influences the design of the EGR injector. The connection lines often have different orientations in different applications and there is, therefore, a desire that the EGR injector be arranged at the inlet line in order to avoid the necessity to adapt the connection lines such that the EGR injector can be arranged there.
In consideration of the above discussion, the purpose of the present invention is to achieve an EGR system that contributes to a more even distribution of the EGR gases in the flow of air in the inlet line. A further purpose is to design the EGR system such that different types of connection line can be connected to the inlet pipe in a simple manner.

Summary of the invention

The purposes stated above are achieved with the invention defined by the independent patent claims. Preferred embodiments are defined by the dependent claims.
The recirculating exhaust gases (the EGR gases) are introduced according to the invention into the flow of inlet air through an EGR injector. The outlet part of the EGR injector is arranged upstream in the flow of inlet air relative to the connection point at the inlet pipe, and is located outside of the inlet pipe. In this way, a mixing path of a length that is as large as possible is achieved without requiring any specific changes of the connection lines depending on different applications.
The outlets for the emission of EGR gases in the inlet line are located asymmetrically, in order to obtain a more even EGR distribution between the different cylinders.
The outlet part extends a predetermined distance outside of the opening of the inlet pipe, which distance is of the order of magnitude of 50 mm, this distance being determined essentially by the design of the parts that are to be connected to the opening of the inlet line. The length of the protruding part of the EGR injector must, therefore, not be too long for it to be possible to connect different types of connecting part. This is, consequently, a desire that conflicts with that of achieving as thorough a mixing of the exhaust air as possible, since this is achieved by allowing the EGR injector to emit the exhaust gases distant from the first inlet suction valve.

Brief description of drawings

Figure 1 shows a schematic cross-section along the longitudinal axis of the inlet pipe according to two embodiments of connections lines for the inlet air.
Figure 2 is a flow diagram that illustrates the method according to the present invention.
Figure 3 is a perspective view that illustrates an inlet pipe with an EGR system according to the present invention.
Figure 4 is a perspective view that illustrates an inlet pipe with an EGR system according to the present invention where the connection line has been removed.
Figure 5 is a perspective view seen from the inlet end of an inlet pipe with an EGR system according to the present invention where the connection line has been removed.
Figure 6 is a view from the side of a part of the inlet duct with an EGR system according to the present invention where the connection line has been removed.
Figure 7 is a perspective view seen obliquely from above of a part of the inlet duct that shows the EGR system according to one embodiment of the present invention.
Figures 8 and 9 are schematic views from above that show two embodiments of the EGR system according to the present invention.

Detailed description of preferred embodiments of the invention

The same features, or features with similar functions, have systematically been given the same reference numbers in the drawings.
Embodiments given as examples of the invention will now be described in detail. Figure 1 shows schematically an arrangement for the recirculation of exhaust gases in a multicylinder combustion engine, otherwise known as an "exhaust gas recirculation" system, or "EGR system" 2. The combustion engine may be a multicylinder Otto engine or a diesel engine. The arrangement comprises an inlet pipe (an inlet branch line) 4 for inlet air 6 intended to be supplied to the cylinders of the combustion engine. The inlet line has an essentially rectangular cross-section such that plane surfaces are available at its external surfaces, but it may have another cross-sectional form in alternative embodiments, such as a circular or square form. The inlet pipe 4 demonstrates an inlet end 8. The inlet end is adapted to be connected to a connection line 9
through which air is supplied to the inlet pipe 4. The connection line may have many different designs, depending on the type of engine. In a first alternative embodiment the connection line 9 extends downwards, while in a second alternative embodiment the connection line 9 extends upwards. The two embodiments are otherwise the same.
Both of these embodiments are shown in Figures 1 and 3 in the same drawing, but the intention is that only one of the alternative embodiments is to be present in one and the same embodiment. The connection line 9 may in other applications have other directions and it may be, for example, arranged to be parallel to and concentric with the inlet line 4, or to be placed at a greater or lesser angle.
The EGR system 2 comprises further an EGR injector 10 for the supply of recirculating exhaust gases 12 to the inlet air 6, and adapted to be arranged in the inlet line 4 in association with the inlet end 8. The EGR injector 10 comprises an outlet part 14 comprising at least one outlet 16 for the distributed supply of exhaust gases 12, and an end part 18. An EGR line 22, also sometimes known as an "EGR pipe" is adapted to introduce the recirculating exhaust gases 12 to the EGR injector. The EGR line 22 has an inlet connected to the exhaust gas side of the engine, through which a partial flow of exhaust gases is diverted from its principal flow. The term "outlet" 16 is here used to denote holes through a wall of the outlet part 14 through which outlets, or outlet holes, exhaust gases can pass and be mixed with the inlet air 6.
The outlet part 14 is adapted to take recirculating exhaust gases 12 in a direction essentially opposite to the direction of the inlet air 6 in the inlet pipe 4 before the recirculating exhaust gases leave the outlet part through the outlets 16 and are mixed with the inlet air 6. The outlet part 14 is located essentially outside of the inlet pipe 4. The outlet part 14 comprises several outlets 16 distributed along the longitudinal direction of the inlet pipe. The term "outside of" is here used to denote that it extends essentially outside of the inlet line 4 while remaining inside of the connection line 9. This does not exclude that a small part of the same or its outlets may be located inside of the inlet pipe. When viewed along the direction of flow of the inlet air, the outlet part 14 is located essentially upstream of the inlet pipe 4.
The connection line 9 comprises upstream of what is shown in the drawings air intakes, air filters, etc., that are, in themselves, known and not shown in the drawings, according to what is normally present in combustion engines. These comprise in certain engines turbocharging units and intercoolers. In such cases, that part of the connection line 9 that connects to the inlet pipe 4 is often known as the "charge air pipe" since the air inside it has passed both a turbocharger unit and an intercooler.
The outlets 16 are asymmetrically distributed around a circumference that is transverse to the direction of motion of the incoming air. The purpose of distributing the outlets in the longitudinal direction and distributing them asymmetrically along the surface of the outlet part is to improve the mixing of the recirculated exhaust gases with the incoming air.
According to one embodiment, the outlets 16 are asymmetrically distributed around the circumference through most of the outlets being located around half of the circumference. The asymmetrical distribution can be seen clearly in Figure 7 where the outlets can be seen arranged on the right side of the outlet part 14.
The fact that most of the outlets are arranged around half of the circumference means preferably that more than 75% of the outlets are arranged there. The outlets are designed as round holes of the same size, and this in a corresponding manner results in also the total area of the outlets being greater on one side of the outlet part. The outlets 16 are asymmetrically distributed in such a manner that most of the outlets (the greatest total area of the outlets) are facing away from that side of the inlet pipe 4 at which the connection ducts to the cylinders of the combustion engine are located. The cylinders of the engine are located at the left or most distant side of the inlet pipe 4 in Figures 3-7.
According to one embodiment, the end part 18 is located at the outlet part 14, i.e. the outermost end of the outlet part, a predetermined distance L outside of the inlet end 8 of the inlet pipe 4. The end part should not protrude too far outside of the inlet end since it then may influence the possibility of mounting the connection line 9. The predetermined distance preferably lies in the interval 40-60 mm, for example approximately 50 mm.
For all embodiments it is the case that the said outlet part 14 may be an essentially circularly symmetrical pipe, and that the outlets 16 are arranged in the wall of the pipe. Other cross-sectional forms are, of course, possible within the scope of the innovative concept of the invention, such as, for example, an elliptical cross-section, a square or a rectangular cross-section. The end part 18 of the outlet part 14 is preferably closed, i.e. there are no outlets there. The number of outlets is a maximum of approximately 50 and the total area of the outlets 16 essentially agrees with the cross-sectional area of the injector inlet end 20 of the EGR injector 10 (see Figure 1).
According to one embodiment, the outlets 16 are essentially circular, but other forms, such as extended outlets, are also possible. In the case of circular outlets, they have a diameter of the order of magnitude of 5-6 mm.
According to one embodiment, the EGR injector 10 is a separate unit provided with an attachment collar 21, see, for example, Figures 6 and 7, at the injector inlet end 20. The attachment collar 21 is preferably attached at the outer surface of the inlet pipe 4 and is further connected to the EGR line 22 that takes the recirculating exhaust gases 12 to the inlet pipe 4.
Alternatively, the EGR injector constitutes an integral part of the said EGR line 22.
It is preferable that the EGR injector be manufactured from stainless steel.
Further, the inlet pipe 4 must be provided with an opening 23 (see, for example, Figures 1, 8 and 9) in one wall where the EGR injector is mounted, through which opening the EGR injector introduces the recirculating exhaust gases 12 into the inlet pipe 4.
The opening 23 may be located along a longitudinal central axis A1 (see Figures 8 and 9) of the inlet pipe 4. It may, on the other hand, sometimes be a design advantage to allow the opening 23 to lie displaced from the central axis A1. In order to distribute the recirculated exhaust gases as effectively as possible in the incoming air, it is desirable that the outlet part 14 be located as close to the centre of the inlet pipe 4 as possible. Two examples of how this can be achieved are given in the embodiments that are shown schematically in Figures 8 and 9, where the opening 23 is displaced relative to A1.
An embodiment is shown in Figure 8 in which the longitudinal central axis A2 of the outlet part 14 demonstrates an angle relative to the axis A1. The angle between A1 and A2 is preferably less than 20°. The outlets will in this way be optimally located to achieve an effective distribution of the recirculated exhaust gases. It is seen clearly also in Figure 7 that the outlet part 14 is set at an angle relative to the longitudinal axis A1 of the inlet pipe 4.
An embodiment is shown in Figure 9 in which the EGR injector has, instead, been set at an angle, such that the longitudinal axis of the outlet part 14 essentially coincides with A1.
Figure 3 is a perspective view that illustrates an inlet pipe 4 in an EGR system 2 according to the present invention. The drawing shows two alternative connection lines 9 connected to the inlet pipe 4, corresponding to what is shown in Figure 1. Figure 4 is a perspective view that illustrates an inlet pipe 4 in an EGR system 2 according to the present invention. The connection piece has here been removed in order to illustrate how the EGR injector and its outlet part 14 are arranged and oriented relative to the inlet pipe 4.
Also Figure 5 is a perspective view seen from the inlet end of an inlet pipe 4 with an EGR system according to the present invention where the connection line has been removed. A variant of the outlet part, among other things, is here shown in which the outlet end 18 is closed.
Figure 6 is a view from the side of a part of the inlet pipe with an EGR system according to the present invention where the connection line has been removed.
The attachment collar 21, among other things, is shown in this drawing, which attachment collar is used to attach the EGR injector 21 at the inlet pipe 4 according to one embodiment.
Figure 7 is a perspective view seen obliquely from above of a part of the inlet pipe that shows the EGR system according to one embodiment of the present invention, which embodiment has been discussed also in association with Figure 8.
A method for the recirculation of exhaust gases in an exhaust gas recirculation system (EGR system) will now be described with reference to the flow diagram shown in Figure 2. The EGR system 2 is the same as the system described above and thus comprises an inlet pipe 4 for incoming air 6 intended to be supplied to the cylinders of a combustion engine, where the inlet pipe 4 demonstrates an inlet end 8. The EGR system 2 comprises further an EGR injector 10 for the supply of recirculating exhaust gases 12 to the incoming air 6 and adapted to be arranged in the said inlet pipe 4 in association with the said inlet end 8, and the EGR injector comprises an outlet part 14 comprising at least one outlet 16 for the distributed supply of exhaust gases 12 and an end part 18, and tthe outlet part 14 is adapted to take the recirculating exhaust gases 12 in a direction essentially opposite to the direction of incoming air 6 in the inlet pipe 4.
The method according to the invention comprises:

supplying the exhaust gases 12 to the inlet air 6 outside of the inlet pipe 4 through the outlet part 14 extending outside of the inlet pipe 4,
supplying the exhaust gases 12 to the inlet air 6 through a number of outlets 16 distributed in the longitudinal direction of the outlet part 14, and supplying the exhaust gases 12 to the inlet air 6 through a number of asymmetrically distributed outlets 16 distributed around the circumference of the outlet part 14.

The said several outlets are asymmetrically distributed around the circumference through most of the outlets being located around one half of the circumference. It is preferable that most of the outlets means that more than 75% of the outlets are located around one half of the circumference.
The present invention is not limited to the preferred embodiments described above. Various alternatives, modifications and equivalents can be used. The embodiments above are, therefore, not to be considered as limiting the protective scope of the invention, which is defined by the attached patent claims.

Claims

An arrangement for the recirculation of exhaust gases in a combustion engine comprising an inlet pipe (4), intended to supply incoming air (6) to the cylinders of the combustion engine, which inlet pipe (4) demonstrates an inlet end (8), and an EGR injector (10) for the recirculation of exhaust gases (12) from the combustion engine to the incoming air (6) and arranged in the inlet pipe (4) in association with the inlet end (8) of the inlet pipe (4), whereby the EGR injector (10) comprises an outlet part (14) comprising a number of outlets (16) for the distributed supply of exhaust gases (12) to the incoming air (6), whereby the outlet part (14) is arranged in a direction that is essentially opposite to the direction of incoming air (6) in the inlet pipe (4), whereby the inlet pipe (4) is designed along one side with connections to the relevant cylinders of the combustion engine, whereby the outlet part (14) is arranged outside of the inlet pipe (4), whereby the outlets (16) are distributed along the longitudinal direction of the outlet part (14), characterized in that the outlets (16) are asymmetrically distributed around the circumference of the outlet part (14) in such a manner that most of the outlets (16) are facing away from the side of the inlet pipe (4) at which the connections to the cylinders of the combustion engine are located.
The arrangement according to claim 1, whereby the said several outlets (16) are asymmetrically distributed around the circumference of the outlet part (14) though most of the outlets (16) being located within an area that is limited by one half of its circumference.
The arrangement according to claim 1 or 2, whereby the said most of the outlets means more than 75%.
The arrangement according to any one of claims 1-3, whereby an end part (18) at the outlet part (14) is located at a predetermined distance L outside of the inlet end (8) of the inlet pipe.
The arrangement according to claim 4, whereby the said predetermined distance is in the interval 40-60 mm.
The arrangement according to any one of claims 1-5, whereby the EGR injector (10) comprises an injector inlet end (20), and whereby the EGR injector (10) is a separate unit provided with an attachment collar at the injector inlet end (20), which separate unit is attached at the outer surface of the inlet pipe (4).
The arrangement according to any one of claims 1-5, whereby the EGR injector (10) comprises an injector inlet end (20), and whereby the EGR injector (10) at the injector inlet end (20) is connected to an EGR line (22) that takes the recirculating exhaust gases (12) to the inlet pipe (4) and constitutes an integral part of the EGR line (22).
The arrangement according to any one of claims 1-7, whereby the total area of the outlets (16) essentially agrees with the cross-sectional area of the injector inlet end (20) of the EGR injector (10).
The arrangement according to any one of claims 1-8, whereby the said outlet part (14) is an essentially circularly symmetrical pipe and the outlets are arranged in the wall of the pipe.
The arrangement according to any one of claims 1-9. whereby the outlets (16) are essentially circular.
The arrangement according to any one of claims 1-10, whereby the inlet pipe (4) is provided with an opening in a wall, through which opening the EGR injector introduces recirculating exhaust gases (12) into the inlet pipe (4).