Device for mixing exhaust gases to be recirculated to an engine with the intake air and a method for recirculating exhaust gases

Abstract

 Device for introducing exhaust gases recirculated from an internal combustion engine into the intake air supplied to such engine, in which the exhaust gas is divided into several flows that are introduced perpendicularly, through specific channels (3, 3'), into the intake air flow, preferably downstream of an elbow (8) on a duct (1) for such air.
Method for recirculating exhaust gases in an internal combustion engine, in which such gases are introduced into the intake air by means of a device as described above, upstream of the intake manifold of the engine.

Description

SCOPE OF THE INVENTION

[0001] This invention relates to a device for mixing exhaust gases that are to be recirculated in an internal combustion engine, more specifically in a compression ignition engine, for example a diesel engine of an industrial vehicle.

PRIOR ART

[0002] Exhaust gas recirculation, or EGR, is common practice in the field of internal combustion engines. In this system a portion of the exhaust gases from the engine are recirculated upstream of such engine into the air intake system and reintroduced into the combustion chambers with the intake air. This results in a lower combustion temperature, which leads to a reduced formation of nitrogen oxides, one of the main pollutants in internal combustion engine emissions.

[0003] The exhaust gases are usually recirculated by means of a specific line that picks up the exhaust gases downstream of the engine, for example from the exhaust gas manifold, and then reintroduces the gases into the intake manifold; the line may incorporate a number of devices, such as a recirculation compressor, to overcome any differences between the intake and exhaust pressures, a control valve, a cooling system, to reduce the temperature of the recirculating gases.

[0004] Direct introduction into the intake manifold is not a satisfactory solution, as it does not guarantee good mixing of the exhaust gases with the intake air. As a result, the gaseous mixture entering the various cylinders does not always contain the same percentage of recirculated gases. This reduces the efficiency of the recirculation system as far as its ability to limit the formation of harmful pollutants is concerned, leads to a deterioration of combustion performance and, since the intake air-recirculating gas ratio is not the same in all the cylinders, the cylinders present different levels of wear and corrosion due to the different concentrations of the corrosive elements, which are always present in exhaust gas fumes, being supplied to the cylinders.

[0005] These phenomena, that may be hardly noticeable when small amounts of gas are recirculated, become more important when, also in view of the need to comply with stricter emissions standards, higher exhaust gas recirculation rates are required (for example, in diesel engines for industrial vehicles, where the exhaust gas recirculation rate may be as high as 50%). In that case, it is clear that supplying mixtures with different levels of intake air and recirculating gases to the various cylinders can constitute a serious problem.

[0006] There is thus a need for a system that can enhance the mixing of the recirculated gases and air fed to the motor, while avoiding the use of complex space-consuming and expensive equipment, and ensuring ease of maintenance and constant efficiency during operation.

SUMMARY OF THE INVENTION

[0007] The problems described above have now been solved with a mixing device comprising:

• a duct through which a current of gas can flow;
• at least two lateral channels that open out into a wall of such duct through the respective openings in the wall.

[0008] The purpose of such channels is to introduce a gas, preferably a gas other than that which constitutes such current of gas, transversely, preferably perpendicularly, in relation to such duct in the section of introduction. The gas is preferably introduced in a direction that is perpendicular to the wall of the duct at the point of introduction.

[0009] According to one aspect of the invention, the openings of the channels in the wall of the duct are arranged on a plane that is perpendicular to a longitudinal axis of the duct. Such openings are preferably arranged uniformly along the perimeter of the section on such plane; if there are two channels, they may be arranged with the relative openings the maximum distance apart along such perimeter. In that case the gases are preferably introduced in the opposite directions.

[0010] Such duct preferably incorporates an elbow upstream of the openings of the channels. The device may also incorporate an appropriate seat to house a control valve, for example a butterfly valve, upstream of such openings and, if present, of such elbow.

[0011] This invention also relates to a method for recirculating exhaust gases in an engine, wherein a portion of the exhaust gases coming from the engine are picked up and divided into at least two flows, and such flows are then fed into a current of air that is supplied to such engine. Such flows are introduced transversely, preferably perpendicularly, in relation to the direction of such current of air. Such flows are preferably introduced into such air current upstream of the intake manifold of such engine.

[0012] This invention refers in particular to that set forth in the claims, which are attached hereto.

LIST OF DRAWINGS

[0013] This invention will now be illustrated through a detailed description of the preferred but not exclusive embodiments, furnished merely by way of example, with the aid of the drawings attached, of which:

figure 1 is a schematic perspective view of a device according to this invention;

figure 2 schematically shows another perspective view of the device in figure 1;

figure 3 schematically shows a further perspective view of the device in figure 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0014] The device according to the present invention is now described with reference to the drawings attached hereto. There is a duct 1 through which the intake air can flow to an internal combustion engine in the direction indicated by the arrow A. In correspondence with a cross-section 2 of the duct, preferably at one end, there are a plurality of channels 3 and 3', for example two, that terminate in the duct 1 through the openings 4 and 4' in the wall of the duct. According to a preferred embodiment of the invention, the ducts are suitable for introducing a gaseous flow transversely, preferably perpendicularly, in relation to the current of gas flowing through the duct. The respective openings are preferably arranged uniformly along the perimeter of a cross-section of the duct; in the case shown in the drawing, in which there are two openings, these may be arranged opposite one another in relation to the cross-section of the duct.

[0015] Preferably the direction of introduction is substantially perpendicular to the wall of the duct, and may be incident with a longitudinal axis of symmetry of the duct, if the latter has one.

[0016] There may be a common inlet 5 through which the recirculated gas is introduced. Such inlet communicates with the various channels 3, 3'. The channels may be of any appropriate shape and connect an exhaust gas recirculation line, preferably through the inlet 5. According to a specific aspect of the invention, the channels and the inlet may be made integral with the device; they may be delimited by walls that are integral with the device, or be partly delimited by other structures, to which the device must be secured. The device illustrated in the drawings, for example, is to be attached directly to the intake manifold of an engine, in correspondence with a suitable opening on the manifold, and have a shape corresponding to the section of the duct 1 at the end 2, for example by means of suitable fastening devices, for example, screws placed through the holes 6. The structure 7 acts as a flange for securing the device to the manifold and also houses the channels 3, 3' and the inlet 5. This and other construction solutions may be carried out according to specific requirements. In the embodiment illustrated in the drawing, the device is secured by means of a gasket that is placed between the structure 7 and the intake manifold, in order to ensure tightness while at the same time closing the side of the channels 3 and 3' facing towards the end 2, and thus towards the intake manifold once the device and manifold have been assembled. Other suitable means may be used instead of a gasket, for example, adhesive paste.

[0017] According to a preferred embodiment of the invention, the openings 4, 4' number between two and six, two being a particularly preferred number.

[0018] The inlet 5 must be appropriately connected to a gas recirculation line, that picks up the exhaust gases, for example from the engine exhaust manifold.

[0019] The openings may be of any suitable shape, for example they may be round, rectangular, rectangular with all or some corners rounded ...

[0020] In vehicle engines, it is often necessary, due to lack of space or in view of other construction requirements, to install an elbow in the air supply line immediately upstream of the intake manifold (for example between the outlet from an intake air cooling unit, located after an intake air compression stage, and the intake manifold). Such elbow may be an integral part of the device according to this invention, upstream of the section containing the openings of the channels. Considering (figure 3) a longitudinal axis 9 of the duct 1 immediately downstream of such elbow in the duct 1 (that may be in the area that includes the openings 4, 4') and a longitudinal axis 10 of the duct 1 immediately upstream of such elbow 8, the angle α between such axes preferably ranges from between 0 and 90° (where 0 is the condition in which the two axes are aligned and the pipe is straight).

[0021] The area of the perpendicular cross-section of the duct may be variable or constant and is preferably substantially constant for the entire length of the device. The shape, which may advantageously be round or almost round, may also be of another appropriate type.

[0022] Should it be necessary to include the elbow as described above, whether such elbow is an integral part of the device or located immediately upstream of such device, the inside of the elbow must preferably have a certain radius of curvature and must not form a sharp corner; this has been found to ensure good mixing even in the presence of such elbow. If D is the average equivalent inside diameter of the duct, and R is the minimum inside radius of curvature of the duct, that in figure 3 is the minimum radius of curvature of the dotted line 11, (which represents the longitudinal section of the inside wall of the duct in the inside part of the elbow), according to a preferred aspect of the invention the following is true: DR/α > 15 mm²/°. Furthermore, if a is the total area of the exhaust gas inlets, obtained from the sum of all the areas of the various openings 4, 4' of the channels 3, 3', and n is the number of such openings, preferably 1 mm < a/nD < 10 mm, and more preferably 3 mm < a/nD < 6 mm.

[0023] The higher the rate of exhaust gas recirculation, in order to reduce polluting emissions, the more important it is to control the amount of air being supplied to the engine. If deemed necessary, the device may incorporate a seat for a control valve, preferably a butterfly valve. Such seat is preferably located upstream of the openings through which the recirculated exhaust gases are introduced, more preferably upstream of the elbow if present. The integration of the valve seat in the device according to this invention may be advantageous, both in order to reduce the size and complexity of the system, thus facilitating assembly, and also to ensure the correct location of the control valve in relation to the other parts that make up the device and compliance with project specifications, in order to enhance mixing. The drawings illustrate a device with such seat 12 made integral with the device; they also illustrate an opening 13 for a valve of an appropriate shape and type, and the means for securing such valve. Such seat is preferably located on a straight section of the duct, upstream of the elbow 8. It is, of course, possible to provide a device that does not incorporate such seat, if the valve is already incorporated in the air supply line upstream of the actual device. As an alternative, a valve body, preferably of the butterfly type, may be connected to the device, for example by means of an appropriate flange at the end at which the inlet of the duct 1 is located, or in any other way that is known.

[0024] The centers of gravity of the areas of the openings of the ducts are preferably on the same plane perpendicular to the axis of the duct 1, and arranged uniformly along the perimeter of the duct.

[0025] If the elbow is present, there is also preferably a straight duct portion between the end of such elbow and the openings of the ducts. In that case, if L is the length of a straight duct portion extending from the end section of such elbow to a transverse plane on which the centers of gravity of the areas of such openings lie (which defines a perpendicular section of the duct that is also called the mixing section), according to a preferred embodiment of the invention, the following is true: LD/α > 5 mm²/°, more preferably >10 mm²/°. Irrespectively or, preferably, in addition to that established by the ratios set forth above, according to a preferred embodiment of the invention: nLDR/α > 500 mm⁴/°.

[0026] If the elbow is not present, there is preferably a straight duct portion between the valve seat, if present, and the mixing section. The straight duct portion may, of cause, be omitted if the device, with no elbow or valve seat, is to be connected to conduits, upstream of the duct 1, with a straight duct portion whereby the same results can be achieved.

[0027] If the centers of gravity, as specified above, do not lie on the same perpendicular plane, the length L is calculated from the perpendicular plane containing the center of gravity furthest upstream.

[0028] The device according to this invention can be installed in all internal combustion engines with compression ignition or controlled ignition, for example, diesel engines, but is also suitable for use in petrol engines or other types of engines, in which a portion of the exhaust gases are recirculated. The device may advantageously be installed on the intake line of the engine. In case of a supercharged engine, it may be installed between the compressor and the intake manifold, preferably downstream of the intake air cooling system, if present. The recirculation system connected via the exhaust gas inlet to the device may be fitted with valves to regulate the flow of the recirculating gases, flow compressors and/or cooling systems, according to the specific requirements.

Claims

1. Mixing device comprising:

a duct through which a current of gas can flow;

characterized by comprising
at least two lateral channels (3, 3') that open out into a wall of such duct through the respective openings (4, 4');
in which such channels are suitable for introducing a flow of gas transversely, in relation to such duct, into the introduction section.

2. Device according to claim 1 characterized in that the channels are suitable for introducing a flow of gas perpendicularly, in relation to such duct, into the introduction section.

3. Device according to claim 1 or 2 characterized in that such channels are suitable for introducing a flow of gas perpendicularly to the wall of the duct at the point of introduction.

4. Device according to any of the previous claims characterized in that the openings of the channels in the wall of the duct are arranged on a plane that is perpendicular to a longitudinal axis of the duct.

5. Device according to claim 4 characterized in that such openings are arranged uniformly along the perimeter of the section on such plane.

6. Device according to any of the previous claims characterized in that such channels number between two and six.

7. Device according to claims 5 and 6 characterized in that there are two channels, placed so that their respective openings are the maximum distance apart from each other on such perimeter.

8. Device according to any of the previous claims characterized in that such duct has an elbow (8) upstream of the openings of the channels.

9. Device according to claim 8 characterized in that the angle (α) between a longitudinal axis (9) of the duct (1) immediately downstream of such elbow in such duct and a longitudinal axis (10) of the duct (1) immediately upstream of such elbow, is between 0 and 90°.

10. Device according to any of the previous claims characterized by comprising a seat (12) suitable for housing a control valve upstream of such openings.

11. Device according to claim 8 or 9 characterized in that DR/α > 15 mm²/° where D is the average equivalent inside diameter of the duct, and R is the minimum inside radius of curvature of the duct in correspondence with such elbow.

12. Device according to claim 9 characterized by comprising a straight portion of such duct immediately upstream of a plane that is perpendicular to the axis of the duct on which the centers of gravity of the openings lie and that LD/α > 5 mm²/° where L is the length of such straight portion.

13. Device according to any of the previous claims characterized in that 1 < a/nD < 10, where a is the area of each opening (4, 4') of the channels (3, 3'), and n is the number of such openings.

14. Device according to claim 9 characterized by comprising a straight portion of such duct immediately upstream of a plane that is perpendicular to the axis of the duct on which the centers of gravity of the openings lie and that nLDR/α > 500 mm⁴/° where L is the length of such straight section.

15. Device according to any of the previous claims characterized in that it can be installed on the intake line of an internal combustion engine.

16. Device according to claim 15 characterized in that it can be fitted to the intake manifold of an internal combustion engine.

17. Method for recirculating exhaust gases in an engine, wherein a portion of the exhaust gases coming from such engine are picked up, characterized by comprising the division of such portion into at least two flows, and the introduction of such flows into a current of air that is supplied to such engine, transversely in relation to the direction of such current of air, upstream of the intake manifold of such engine.

18. Method according to claim 17 characterized in that the exhaust gases are introduced perpendicularly to such current of air.

19. Method according to claim 17 or 18 characterized by being carried out by means of a device according to any of the claims from 1 to 15 and that such flows are introduced through such channels (3, 3') into such current of air that flows through such duct (1).

Drawing