TECHNICAL FIELD

The present disclosure relates to a compression ignition engine as defined in the appended claims. The present disclosure also relates to a vehicle comprising such engine.

BACKGROUND ART

Internal combustion engines such as diesel engines, also known as compression ignition engines, and Otto engines, or spark- ignition engines, are commonly used in different types of motor vehicles, such as trucks and buses, cars, vessels, etc. Internal combustion engines are also used in many industrial applications. Internal combustion engines, hereinafter also referred to as engines, may be driven by a plurality of different types of fuel, such as diesel, petrol, ethanol, gaseous fuel, and biofuel. The engines have a number of cylinders in which a reciprocating piston is provided. In an upper end of the piston, a piston bowl is provided. Together with an upper part of the cylinder and a cylinder head, the piston bowl forms a combustion chamber in which fuel is injected and combusted. The piston bowl is designed to contribute to mixing of air and fuel and to create a flow pattern influencing combustion and emission formation within the combustion chamber.

In a diesel engine, the fuel is directly injected into the cylinder during a power stroke of the piston. The fuel is injected by means of an injection nozzle, which in turn is fluidly connected to a pressurized fuel accumulator. The internal combustion engine comprises at least one cylinder with a piston arranged in each cylinder. The piston is connected via a connecting rod to a crankshaft which at rotation moves the piston in a reciprocating manner in the cylinder, thereby providing the piston power stroke movement. At least one air inlet valve controlled by at least one camshaft is arranged in each cylinder, which inlet valve is connected with an air inlet system. Additionally, at least one exhaust valve is arranged in each cylinder, which exhaust valve is connected with an exhaust system.

The fuel is ignited by the compression heat and combusted almost immediately following the fuel injection. Air and fuel must therefore be mixed in a very short time, and it is desirable to ensure that the mixing is efficient and that the fuel becomes well-distributed within the combustion chamber so as to achieve a complete combustion. During the combustion, large amount of soot is created due to lack of oxygen in the non-pre-mixed diesel flame. To reduce the amount of soot created, there are known solutions, of which US2017051657 shows an example. According to this document, at least two fuel jet sheets having different sheet angles are injected to a rotationally symmetrical piston bowl. However, despite existing solutions, there is still a need to decrease particulate emissions from engines caused by incomplete combustion which forms soot. Additionally, there is a desire to further increase the combustion efficiency of fuel and lower the overall consumption of fuel. SUMMARY OF THE INVENTION

It is thus an objective of the present invention to decrease particulate emissions from engines.

Additionally, it is an objective to further increase the combustion efficiency of fuel.

Further, it is an objective to lower the overall consumption of fuel in internal combustion engines. The objectives above are attained by the present invention as defined in the appended claims. Especially, the objectives are attained by a compression ignition engine comprising at least one cylinder with a piston arranged movable in a reciprocating manner in the cylinder to provide a power stroke of the engine and a fuel injector having an injector nozzle comprising a plurality of apertures through which a fuel spray is provided to the cylinder. The piston has an upper end and a lower end in between which a central axis and a peripheral envelope surface extend. The piston comprises a piston bowl which is open towards the upper end. The upper end of the piston comprises an annular top surface defining an upper plane. The piston bowl further comprises an annular bottom portion and an axially elevated central bottom portion located radially inwards from the annular bottom portion. A side wall extends between the annular bottom portion and the annular top surface and the side wall comprises a radially extending annular ridge. According to the present invention, the annular top surface comprises at least one recess extending in the radial, circumferential and axial direction, the axial direction extending in the direction of the central axis. The injector nozzle comprises at least one first aperture arranged with a first spray angle directing a first fuel spray towards the recess or the area between the annular ridge and the recess. Additionally, the nozzle comprises at least one second aperture arranged with a second spray angle directing a second fuel spray towards the annular ridge, the area between the annular ridge and the annular bottom portion or the annular bottom portion. The recesses, also referred to as piston pockets, may contain air needed in the combustion of fuel. By the recesses are meant discrete recesses, i.e. recesses that are individually separate and distinct. Thereby, it is possible to increase the amount of air in a piston compared to a piston having no recesses. By directing part of the fuel towards the recesses, in addition to directing fuel towards the annular bottom portion which also comprises air, it is thus possible to improve the provision of fuel/air mixture in a synergistic manner. Thus, the combustion of the fuel may become more complete and the combustion efficiency may be improved. This in turn leads to less emissions of particulate matter and decreased fuel consumption. Therefore, the objectives mentioned above are attained by the present solution.

The amount of the first apertures or the groups of the first apertures may correspond to the amount of the recesses. In this way it may be possible to inject fuel such that each of the first apertures or the groups or apertures injects fuel to a respective recess. Thus, a more optimal of usage of air contained in the recesses may be obtained.

The first and second apertures may have substantially the same cross-sectional area. Thus, it can be easily ensured that the mass flow of fuel will be substantially equal from each aperture. However, in some situations, the first and second apertures may have different cross-sectional areas. Additionally or alternatively, the cross sectional shape of the apertures may be the same or different. Thus, it will be possible to adapt the apertures in the nozzle to the compression ignition engine in question in a suitable manner to optimize the combustion

The first spray angle may be adapted to the length of the radial, circumferential and axial extension of the recess such that a pre-determined optimal penetration of fuel in the recess is reached.

To ensure that correctly directed fuel sprays are provided in a continuous manner, the fuel injector and/or the nozzle may be rotationally fixed. The present solution is especially usable in connection with pistons in which a cross-section of the piston taken in the direction of the central axis is rotationally asymmetric. This means thus that cross sections taken at different circumferential positions differ from each other, since some of the positions contain a recess and some of the positions do not contain the recess. However, a cross section taken perpendicular to the central line of the piston may be symmetrical, i.e. when viewing the piston from above, the piston bowl with the recesses may be arranged in a symmetrical manner in respect of a diametrical line. Thus, the solution of the present invention is applicable also for pistons having piston bowls with complex shapes.

Each of the recesses may be placed such that at least a part of the projection of each respective air intake valve and/or exhaust valve crosses at least a part of a projection of the respective recess. In this way, the valves may be kept open also during the power stroke when the upper end of the piston contacts a cylinder head portion. This further improves the air supply to the combustion. The amount of the recesses may correspond to the amount of air intake and/or exhaust valves in the engine, whereby each of the valves may be arranged open during the power stroke of the engine.

The present invention further relates to a vehicle comprising a compression ignition engine as described above.

Further advantages as well as advantageous features of the present invention will appear from the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1a shows an upper end view of a piston of the present disclosure;

Fig. 1b shows a cross-section of the piston of Fig. 1 along the line A-A;

Fig. 2 shows schematically an axial section of a cylinder of an internal combustion engine of the present disclosure; Fig. 3 shows a section of the piston and fuel spray angles according to an embodiment of the present disclosure;

Fig. 4a-4f show example embodiments of multiple spray targeting according to the present disclosure. Fig. 5 shows a schematic side view of a vehicle comprising a compression ignition engine according to the present disclosure.

DETAILED DESCRIPTION

The present disclosure generally relates to a compression ignition engine, also commonly referred to as a diesel engine. In a conventional manner, the compression ignition engine comprises at least one cylinder with a piston arranged movable in a reciprocating manner in the cylinder to provide a power stroke of the engine. Further, an injector, which may be fluidly connected to a pressurized fuel accumulator, is comprised in the engine and has the aim to provide fuel to the cylinder, in which the fuel is combusted. The injector has an injector nozzle comprising a plurality of fuel apertures through which a spray plume is provided to supply the fuel to the cylinder.

Increasingly stringent emission regulations, relating primarily to soot and nitrogen oxide (NOx) emissions, make it necessary to aim at further improving the emission control of internal combustion engines. At the same time, it is desirable to decrease fuel consumption, which can be achieved by increasing the combustion efficiency. According to the present disclosure, it is possible to better utilize air contained in the piston bowl during the fuel combustion, whereby the combustion is improved. Thereby, it is possible to improve combustion efficiency, which makes it possible to decrease fuel combustion. Additionally, the amount of soot in the combustion exhaust gases can be reduced. Reference is made to the appended drawings, which illustrate the present solution more in detail. In Fig. 1a, an upper end view of a piston 2 of a diesel engine is shown. In Fig. 1b, a section taken along the line A-A is shown, and reference is made equally to both Fig. 1a and 1b in the description below.

The piston 2 may have an outer shape resembling an essentially right circular cylinder. The piston 2 has an upper end 11 and a lower end 12, in between which a central axis C and a peripheral envelope surface 13 extend. The piston 2 comprises a piston bowl 3, which is open towards the upper end 11. The upper end 11 of the piston 2 comprises an annular top surface 14, which defines an upper plane P1. The piston bowl comprises an annular bottom portion 15 and an elevated central bottom portion 16 located radially inwards from the annular bottom portion 15. The annular bottom portion 15 defines a lowest level of the piston bowl 3 in the direction of the central axis C. The central bottom portion 16 is cone shaped with a rounded or flattened top 17. Further, a side wall 18 extends between the annular bottom portion 15 and the annular top surface 14. The side wall 18 comprises an annular ridge 20, which projects towards the central axis C. Air will be gathered in the annular bottom portion, whereby combustion may occur.

The side wall 18 may have other cross-sectional shapes and may comprise an annular upper side wall portion, which extends downward and radially inward from the top surface, and an annular lower side wall portion, which extends upward from the annular bottom portion toward the upper side wall portion. Thus, an annular ridge may be formed between the upper side wall portion and the lower side wall portion. By providing the ridge 20, the annular bottom portion 15 and the side wall 18 may delimit an annular channel 26 surrounding the central bottom portion 16. Further shapes of the side wall portion may be possible to improve the combustion efficiency. According to the present disclosure, the annular top surface 14 comprises at least one recess 25 extending in the radial, circumferential and depth, i.e. axial, direction, which extends in the direction of the central axis C. By the recess is meant a discrete recess, i.e. a recess, which is individually separate and distinct from any other recess. By providing at least one such discrete recess, it is possible to keep an air inlet or outlet valve open also during the whole power stroke of the engine, whereby the combustion efficiency can be improved. The recess will contain air, which is mixed with fuel and thus utilized for combustion.

The cross-section of the piston may be rotationally asymmetric, meaning that an axial cross section of the piston can be different when the position of the section is taken at rotationally different positions. In this way, the piston may contact the piston head at certain points during the power stroke, while at the areas of the recesses, the piston is not in contact with the cylinder head. In this way, it is possible to keep a certain opening degree for the valves during the complete power stroke, which may thus further improve the combustion efficiency. Therefore, each of the recesses may be placed such that at least a part of the projection of each respective air intake valve and/or exhaust valve crosses at least a part of a projection of the respective recess. The amount of the recesses may correspond to the amount of air intake and/or exhaust valves in the engine, thereby improving the overall combustion efficiency of the engine and leading to less emissions and decreased fuel consumption.

Reference is now made to Fig. 2 which shows a section taken along a central axis C of a cylinder 1 of an internal combustion engine in the form of a diesel engine according to an example. In the cylinder 1, a piston 2, as shown in Fig. 1a and lb, is movably arranged in the cylinder, i.e. the piston is configured to reciprocate within the cylinder along the common central axis C. The piston bowl 3 of the piston 2 together with internal walls of the cylinder 1 and an internal surface of a cylinder head 4 creates a combustion chamber 5. A fuel injector 6 is positioned along the central axis C above the piston bowl 3, and two fuel sprays or beams 61' and 62' are illustrated in the drawing. The fuel spray may be in the form of a spray beam or a spray plume. In case the fuel spray is in the form of a spray plume, a principal longitudinal center axis of the plume is presented by the lines 61' and 62', thereby presenting the principal direction of the spray plume. An angle of the beam or the principal direction of the spray plume is calculated as an angle of the beam or principal direction of the beam in respect of the central axis C. In this context, when referring to the spray angle, the angle of the beam or principal direction of the plume in respect of the central axis C is meant. An intake port 7 is provided in the cylinder head 4 for supply of air into the combustion chamber 5 via an intake valve 8. Furthermore, an exhaust port 9 is provided in the cylinder head 4 for evacuation of exhaust gases via an exhaust valve 10.

The fuel injector 6 is configured for injecting fuel into the cylinder 1 as a pressurized fuel spray so that the fuel is mixed with air contained in the cylinder 1 to form a fuel/air mixture. The fuel injector may be fluidly connected to a pressurized fuel accumulator (not shown). The fuel/air mixture is after an ignition delay ignited by compression heat generated in the cylinder 1. The ignited part of the fuel spray forms a flame. The fuel can be injected with different injection pressures, from low to very high pressures. The fuel injector 6 comprises a nozzle 60 with a tip facing the piston 2 comprising a plurality of small injection first and second apertures 61, 62, providing the respective first and second fuel sprays 61', 62' as described above. The apertures are thus located in the lower end of the injector nozzle 60 of the fuel injector 6 for permitting the high pressure fuel to flow from the apertures 61, 62 of the fuel injector 6 into the combustion chamber 5 with high pressure to induce thorough mixing of the fuel with the hot compressed air within the combustion chamber 5. It should be understood that the fuel injector 6 may be any type of fuel injector capable of injecting high pressure fuel through the plurality of injector apertures into the combustion chamber 5. Also, the fuel injector need not necessarily be positioned on the central axis C.

In other embodiments, in which the internal combustion engine is e.g. an Otto engine, the fuel injector may be configured to inject a mixture of fuel and air into the combustion chamber. The injector may also be configured to inject other fluids such as gases or liquids, e.g. water, which are not combusted but are primarily used to induce a swirl motion.

Reference is now made to both Fig. 2 and 3. Figure 3 illustrates in more detail how the first and second fuel sprays 61'; 62' can be directed to different areas of the piston, i.e. in areas where the piston comprises a recess 25, also referred to as a pocket, and in the areas not comprising the recess. According to the present disclosure, the nozzle 60 comprises a first aperture 61 or a group of first apertures 61 arranged to provide a first fuel spray angle al directing a first fuel spray 61' towards the recess 25 or the area between the annular ridge and the recess. The nozzle additionally comprises a second aperture 62 or a group of second apertures 62 arranged with a second spray angle a2 directing a second fuel spray 62' towards the annular ridge 20 or the area between the annular ridge 20 and the annular bottom portion 15. Thus, the first angle al is different from the second angle a2, whereby air contained in the piston and/or combustion chamber can be maximally utilized for the fuel combustion. The first angle al may be larger than the second angle a2 in respect of the central axis C, when the direction of the spray is from the fuel injector 6 located in the cylinder head 4 towards the piston bowl 3. By providing the first fuel spray beam 61' towards the recess 25, the air contained in the recess can be utilized for the combustion, while the air in the bottom portion 15 can be utilized for the combustion of fuel injected by the second apertures 62. In this way, air in the piston can be maximally utilized, whereby the particulate emissions can be reduced and the combustion efficiency can be improved. The different angles may be provided by for example drilling the apertures 61, 62 in the nozzle with different angles, which is a simple and robust method of providing different angles. Also, the mass flow of the spray plumes exiting from the first and second apertures may be substantially the same, whereby the injector construction and the control of the injection can be further simplified. For example, the first and second apertures may have substantially the same cross-sectional area, whereby substantially the same mass flow can be provided in a simple manner. However, the spray angle of the first and second apertures may be directed differently to provide the desired spray angles. Alternatively, the first and second apertures may have different cross-sectional areas and/or shapes to provide different spray angles. The first spray angle may be adapted to the length of the radial, circumferential and axial extension of the recess 25 such that a pre-determined optimal penetration of fuel in the recess is reached. In this way it can be assured that the fuel mixes with the air in an optimal way to assure as complete combustion as possible.

To utilize the air in the recesses 25 in an optimal manner and/or to provide an optimal air/fuel mixture, the amount of the first apertures 61 or the groups of the first apertures may correspond to the amount of the recesses 25. Each of the first apertures 61 or the groups or apertures may be arranged to inject fuel to a respective recess 25. The amount of the recesses in the piston may usually vary from 1 to 5. To ensure that spray is directed into the recesses in a correct manner, the injector nozzle may be rotationally fixed.

In Fig. 4a -4f examples of multiple spray targeting are shown in an upper end view of a piston 2 of a diesel engine. For the sake of clarity, only one recess 25, first fuel spray 61' and second fuel spray 62' are depicted with reference signs in each drawing, but the same reference signs apply equally in each drawing to the same symbols. The first fuel spray 61' with an angle directing the fuel spray towards the recess 25 or the area between the annular ridge 20 and the recess 25 is shown with a dotted line and the second fuel spray 62' with an angle directing the fuel spray towards the annular ridge 20 or the area between the annular ridge 20 and the annular bottom portion 15. In the embodiment of Fig. 4a, the piston is provided with four recesses 25, and four first fuel sprays 61' are directed towards the recesses 25. There are two second fuel sprays 62' directed towards the annular ridge 20.

In the embodiment of Fig. 4b, two recesses 25 are provided and two first fuel sprays 61' are directed towards the recesses. Four second fuel sprays 62' are directed towards the annular ridge 20 and/or towards the area between the annular ridge 20 and the annular bottom portion

15.

In the embodiment of Fig. 4c, one recess 25 is provided and one first fuel spray 61' is directed towards the recess. Five second fuel sprays 62' are directed towards the annular ridge 20 and/or towards the area between the annular ridge 20 and the annular bottom portion 15. In the embodiment of Fig. 4d, four recesses 25 are provided and four first fuel sprays 61' are directed towards the respective recesses. Eight second fuel sprays 62' are directed towards the annular bottom portion 15 and/or towards the area between the annular ridge 20 and the annular bottom portion 15. In the embodiment of Fig. 4e, four recesses 25 are provided and three first fuel sprays 61' are directed towards the respective recesses. One of the first fuel sprays is directed slightly outwards of the recess 25 in the circumferential direction. Two second fuel sprays 62' are directed towards the annular bottom portion 15. One other second fuel spray 62' is directed towards the recess 25 and one towards the edge of the recess 25. Finally, in the embodiment of Fig. 4f, four recesses 25 are provided and four first fuel sprays 61' are directed towards the respective recesses. Eight second fuel sprays 62' are provided, whereby each of them is directed towards the annular bottom portion 15. One of the second fuel sprays 62' is directed towards an edge of the recess 25.

Thus, it is possible to vary the fuel spray direction in the radial, circumferential and depth (axial) direction. In this way, the provision of an air/fuel mixture can be optimized so that the combustion will be as complete as possible. The nozzle with the apertures providing the desired spray directions may be rotationally fixed to maintain the apertures in the desired position.

The compression ignition engine of the present disclosure is usable in different types of motor vehicles, such as trucks and buses, cars, vessels, etc. The compression ignition engine of the present disclosure may also be used as an independent unit in many industrial applications. The present disclosure also relates to a vehicle comprising a compression ignition engine as described above. Fig. 5 schematically shows a side view of a vehicle 100 comprising an internal combustion engine 50, which is a compression ignition engine, connected to a gearbox 55. The gearbox 55 is also connected to the driving wheels 80 of the vehicle 100 through an output shaft of the gearbox (not shown). The vehicle also comprises a chassis 70. The vehicle 100 may be a heavy vehicle, e.g. a truck or a bus. The vehicle 100 may alternatively be a passenger car. The foregoing description of the embodiments has been provided for illustration of the present invention. The embodiments are not intended to limit the scope of the invention defined in the appended claims and features from the embodiments may be combined with one another.