IT201800001661A1 - TWO-STROKE ENGINE WITH OPPOSING PISTONS - Google Patents

Description

DESCRIPTION

of the Italian Patent for Industrial Invention entitled:

"TWO-STROKE ENGINE WITH OPPOSING PISTONS"

Field of technique

The present invention relates to two-stroke engines with opposed pistons, in particular those operating in the Diesel cycle.

State of the art

As is known, two-stroke Diesel and opposed piston engines generally comprise a cylinder in which two mutually opposed pistons are slidingly received, which close the opposite ends of the cylinder and which define a combustion chamber inside it.

The pistons are connected to respective thrust cranks, so as to be individually able to slide back and forth within the single cylinder, cyclically making a forward stroke followed by a subsequent backward stroke.

During the advance stroke, the two pistons approach each other, progressively reducing the volume of the combustion chamber until a so-called top dead center position is reached.

Conversely, during the retraction stroke, the two pistons move apart, progressively increasing the volume of the combustion chamber until they reach a so-called lower dead center position.

When the pistons are in correspondence with the lower dead center position, the combustion chamber is in communication with at least one intake port (conventionally also called washing port) and with at least one exhaust port, which are formed on the lateral surface inside the cylinder and are positioned at the opposite axial ends of the combustion chamber.

The intake port is connected to a compressor designed to load the combustion chamber with a mass of fresh air which, at the same time, pushes the combustion gases generated during the previous engine cycle to exit through the exhaust port.

Subsequently, moving towards the top dead center position, the pistons, after closing the intake and exhaust ports, compress the mass of fresh air inside the combustion chamber.

During this compression phase, an injector, located substantially in the center of the cylinder, injects a certain amount of fuel into the combustion chamber which, upon reaching the top dead center position, ignites due to the pressure to which it is subjected, generating hot gases. rapidly expanding which push the pistons back to the bottom dead center position from where the cycle repeats.

This type of two-stroke diesel engines, whose general architecture has been known for decades, have the advantage of having a high thermodynamic efficiency, since the presence of two opposing pistons, and therefore the absence of a cylinder head, means that the heat generated by combustion can only be dispersed through the side surface of the cylinder, reducing losses and thus ensuring that most of the heat generated is effectively converted into mechanical work by the pistons.

On the other hand, in addition to some drawbacks related to the overall dimensions and the relative complication of the transmission components necessary to connect the two thrust crank mechanisms to a single crankshaft, these motors usually have the drawback that the position of the injector in the center and on the lateral surface of the cylinder does not allow fuel to be injected in order to obtain optimal combustion, which results in an increase in consumption and often also in harmful emissions.

Presentation of the invention

In light of the foregoing, an object of the present invention is to make available a two-stroke diesel engine with opposed cylinders which allows to obtain a better combustion efficiency with respect to the known art.

A further purpose is to achieve the aforementioned objective within the context of a simple, rational and relatively low cost solution.

These and other purposes are achieved by the characteristics of the invention reported in independent claim 1. The dependent claims outline preferred and / or particularly advantageous aspects of the invention.

In particular, an embodiment of the present invention makes available a two-stroke diesel engine with opposed pistons, comprising as usual:

- a cylinder having an internal lateral surface which extends around a predetermined central axis,

- two pistons, mutually opposed and both slidingly received inside said cylinder, to define a variable volume combustion chamber with the internal side surface,

- at least one intake duct extending along a predetermined longitudinal axis and afferent inside the cylinder through an intake port obtained on the internal side surface,

- at least one efferent exhaust duct from inside the cylinder through an exhaust port obtained on the internal side surface, and

- a fuel injector associated with the cylinder and able to inject a jet of fuel, typically a jet of atomized or sprayed fuel, inside the combustion chamber according to a predetermined injection axis.

Unlike the conventional known art, the present invention further provides that:

- the projection of the longitudinal axis of the intake duct, carried out on a reference plane orthogonal to the central axis of the cylinder and passing through a point of intersection between the longitudinal axis of the intake duct and the internal lateral surface of the cylinder, both inclined with respect to a diametrical plane containing the central axis of the cylinder and said point of intersection;

- the projection of the injection axis, carried out on a reference plane orthogonal to the central axis of the cylinder and passing through an intersection point between the injection axis and the internal lateral surface of the cylinder, is inclined with respect to a diametrical plane containing the central axis of the cylinder and said point of intersection; is that

- said projections of the longitudinal axis of the intake duct and of the injection axis are inclined, with respect to their respective diametrical planes, in a concordant manner.

Thanks to the inclination of the intake duct it is in fact possible to give the air entering the combustion chamber a swirl movement, i.e. a swirling movement with an axis substantially coinciding with the axis of the cylinder.

At the same time, thanks to the concordant inclination of the injection axis, the fuel is injected into the aforementioned air vortex substantially in co-current and is therefore dragged and spread rapidly throughout the combustion chamber.

The combination of these two effects causes a uniform and rapid mixing of the fuel in most of the air available inside the cylinder, allowing an effective and complete combustion of substantially all the fuel injected.

In this way, it is advantageously possible to make the engine work with relatively low air / fuel ratios, obtaining high specific powers with low consumption and without producing significant quantities of polluting substances, especially in terms of particulate matter.

According to one aspect of the invention, the angle formed by the aforementioned projection of the longitudinal axis of the suction duct and the corresponding diametrical plane can be between 10 ° and 20 °.

This angular value has proved particularly effective in generating the swirling motion of the air inside the cylinder.

According to another aspect of the invention, the longitudinal axis of the intake duct can lie in the corresponding reference plane or can be inclined with respect to the latter by an angle of less than 20 °.

Thanks to this solution, it is ensured that the swirling motion imparted to the incoming air does not have an excessive speed component in the direction of the cylinder axis, which has proved to be inessential in order to obtain optimal combustion in the cylinder.

A further aspect of the invention provides that the intake duct can be connected to a compressor, of the volumetric or rotary type, which is able to feed air into the cylinder at a pressure that can be such as to obtain a coefficient in the cylinder of swirl equal to or greater than 3.

The swirl coefficient, also known as swirl ratio, is defined by the ratio between the equivalent angular velocity of the generated air vortex (with respect to the central axis of the cylinder) and the angular velocity of the engine.

Thanks to the aforementioned value of the swirl coefficient it is advantageously possible to ensure that the air vortex inside the combustion chamber has a sufficiently high angular velocity to guarantee an excellent diffusion of the fuel, despite the short time available between the instant of injection. and the instant of combustion start.

According to a preferred embodiment of the invention, the engine can comprise a plurality of the aforementioned intake ducts, each of which reaches the inside of the cylinder through a respective intake port, extending along a respective longitudinal axis whose projection, carried out on a respective reference plane orthogonal to the central axis of the cylinder and passing through the point of intersection between the longitudinal axis of said intake duct and the internal lateral surface of the cylinder, is inclined with respect to a respective diametrical plane containing the axis center of the cylinder and said point of intersection.

For example, the engine can comprise at least four of said intake ducts, which can be connected to the same compressor, for example through a common intake manifold.

In this context, it is preferable that the projections of the longitudinal axes of all the aforementioned intake ducts are inclined, with respect to the respective diametrical planes and / or with respect to the respective reference planes, in a way that is concordant with each other and preferably at the same angle.

Furthermore, it is preferable that the points of intersection between the internal lateral surface of the cylinder and the longitudinal axes of all these intake ducts lie coplanar in a plane orthogonal to the central axis of the cylinder and, preferably, that all these intersection points are arranged in different positions around the central axis of the cylinder, for example angularly equidistant from each other.

In this way it is in fact advantageously possible to increase the swirling of the air flow entering the combustion chamber.

Turning to the injector, an aspect of the present invention provides that the angle formed by the projection of the injection axis and by the corresponding diametrical plane can be substantially equal to the angle formed by the projection of the longitudinal axis of the intake duct and by the corresponding plane diametrical.

In this way, the fuel injection takes place perfectly in equilibrium with the air vortex or almost, improving its entrainment and therefore its diffusion in the combustion chamber.

A further aspect of the invention therefore provides that the angle formed by the aforementioned projection of the injection axis and the corresponding diametrical plane can be between 10 ° and 20 °.

This angular value has proved particularly effective for uniformly mixing the fuel in the air that moves with a swirling motion in the cylinder.

Another aspect of the invention provides that the injection axis can lie in the corresponding reference plane or can be inclined with respect to the latter by an angle of less than 10 °.

In this way, the fuel injection develops substantially in a transverse plane with respect to the central axis of the cylinder, mixing optimally in the air vortex.

According to one aspect of the invention, the jet of fuel generated by the injector can be cone-shaped having an axis coinciding with the injection axis and widening towards the inside of the cylinder and away from the injector.

In this way it is possible to obtain a better diffusion of the fuel in the cylinder.

For example, said fuel jet can have a cone angle between 30 ° and 40 °.

Another aspect of the invention provides that the injector can be connected to a pumping device designed to feed fuel at a maximum pressure equal to or greater than 100 MPa.

In this way it is advantageously possible to obtain a high diffusion and penetration of the fuel jet inside the combustion chamber. According to a different aspect of the invention, each piston can comprise a top, that is a surface that delimits the combustion chamber, of a flat shape or at most with a cavity facing the other piston.

Thanks to this solution, the pistons are advantageously simpler and cheaper to manufacture. Furthermore, this solution advantageously allows to reduce the heat exchange surface between the pistons and the combustion chamber, reducing heat dissipation and therefore increasing the thermal efficiency of the engine.

Brief description of the drawings

Further features and advantages of the invention will become evident from reading the following description provided by way of non-limiting example, with the aid of the figures illustrated in the attached tables.

Figure 1 is a schematic longitudinal section of a two-stroke Diesel and opposed piston engine according to an embodiment of the present invention and shown with the pistons at bottom dead center.

Figure 2 is the section of Figure 1 shown with the pistons in an intermediate position between that of lower dead center and that of upper dead center.

Figure 3 is the section of Figure 1 shown with the pistons in the top dead center position.

Figure 4 is a simplified perspective view of the cylinder and the intake and exhaust system of the engine of Figure 1.

Figure 5 is the V-V section indicated in Figure 1 and shown on an enlarged scale. Figure 6 is the section VI-VI indicated in Figure 1 and shown on an enlarged scale.

Detailed description

A two-stroke Diesel engine according to the present invention, such as that indicated globally with 100 in the aforementioned figures, comprises a cylinder 105 which has an internal lateral surface 110 extending around a predetermined central axis X and which is open at both its sides. axial ends.

The engine 100 also comprises a pair of mutually opposed pistons, of which a first piston 115 and a second piston 120, both of which are slidably inserted inside the single cylinder 105, so as to be able to slide back and forth along the direction of the central axis X and so as to cooperate with each other and with the internal lateral surface 110 of the cylinder 105, to define a combustion chamber 125 with variable volume.

In particular, each piston 115 and 120 can comprise a crown 130 (see fig. 2), i.e. a surface facing the opposite piston, and a skirt 135 (see fig. 1), having a cross section complementary to the cross section of the cylinder 105, which faces the internal side surface 110.

The combustion chamber 125 is delimited between the crown 130 of the first piston 115, the crown 130 of the second piston 120 and the internal lateral surface 110 of the cylinder 105.

Preferably, the crown 130 of each piston 115 and 120 is a perfectly flat surface or with a cavity facing the other piston.

On the opposite side with respect to the combustion chamber 125, each piston 115 and 120 is associated with a respective thrust crank mechanism, illustrated only schematically and indicated respectively with 140 and 145, which is adapted to transform the linear movement of the respective piston 115 or 120 in a rotary movement of a shaft, 150 and 155 respectively.

The shafts 150 and 155 can be mechanically connected to drive a single drive shaft (not shown), for example by means of suitable transmission members which are per se unrelated to the present description.

The thrust cranks 140 and 145 are generally configured so that each piston 115 and 120 is cyclically able to make a forward stroke, during which it approaches the opposing piston, progressively reducing the volume of the combustion chamber 125, followed by a subsequent one. retraction stroke, during which the piston moves away from the opposite piston, progressively increasing the volume of the combustion chamber 125.

In particular, the retraction stroke of each piston 115 and 120 ends when the crown 130 of said piston reaches a corresponding lower dead center position, shown in figure 1 and indicated in figure 2 respectively with A1 for the first piston 115 and with B1 for the second piston 120, while the advance stroke ends when the crown 130 of said piston reaches a corresponding top dead center position, shown in figure 3 and indicated in figure 2 respectively with A2 for the first piston 115 and with B2 for the second piston 120.

Depending on the embodiments, the two pistons 115 and 120 can reach the respective top dead center positions A2 and B2 simultaneously or with a slight mutual angular offset with respect to the angular position of the crankshaft.

In any case, it is preferable that the top dead center positions A2 and B2 of the two pistons 115 and 120 are separated and spaced along the central axis X of the cylinder 105, so that at least a limited annular band of the internal lateral surface 110 , comprised between these two top dead center positions A2 and B2, and indicated as a whole with 160 in Figure 3, is never covered either by the skirt 135 of the first piston 115 or by the skirt 135 of the second piston 120.

A plurality of suction ports 165 (also known as washing).

The suction ports 165 can be four or more in number and can all have the same shape and size, in the example shown a rectangular shape.

Each intake port 165 leads to a respective intake duct 170, which is generally adapted to convey combustion air inside the cylinder 105 through the corresponding intake port 165.

As shown in Figure 5, each intake duct 170, at least in correspondence with its terminal portion, i.e. the one directly adjacent to the corresponding intake port 165 or, better said, the axial end of which coincides with said intake port 165, develops according to a respective longitudinal axis Y which intersects the internal lateral surface 110 of the cylinder 105 at a respective point of intersection K.

The intersection point K of the longitudinal axis Y of each intake duct 170 can for example coincide with the center of gravity of the corresponding intake port 165.

The intersection points K of the longitudinal axes Y of all the intake ducts 170 can be arranged in different positions around the central axis X of the cylinder 105, for example angularly equidistant from each other. Preferably, all these points of intersection K can also lie coplanar in a reference plane Q orthogonal to the central axis X of the cylinder 105 (see Figure 3)

The longitudinal axis Y of each intake duct 170 could also lie in said reference plane Q, in such a way that the speed of the combustion air entering the cylinder 105 substantially has no component parallel to the central axis X of the cylinder. 105 but only components orthogonal to it.

Nevertheless, in accordance with the embodiment illustrated in Figure 3, it is also possible that the longitudinal axis Y of each intake duct 170 is at least slightly inclined with respect to the aforementioned reference plane Q, preferably towards the second piston 120.

For example, the longitudinal axis Y of each suction duct 170 can form an inclination angle with the reference plane Q, which can be less than 20 ° sexagesimal, preferably between 10 ° and 20 ° sexagesimal, and can be equal to the angle of inclination of the longitudinal axes Y of all the other intake ducts 170.

Regardless of this, another aspect of the invention provides that the longitudinal axes Y of the intake ducts 170 do not intersect the central axis X of the cylinder 105 but are inclined so as to impart a whirling or swirl movement to the combustion air (see fig. 5).

In particular, it is envisaged that the projection of the longitudinal axis Y of each intake duct 170, carried out for example on the reference plane Q, is inclined with respect to a diametrical plane D containing both the central axis X of the cylinder 105 and the corresponding point of intersection K with the internal lateral surface of the cylinder 105.

For example, the minor angle formed by the aforementioned projection of the longitudinal axis Y of each intake duct 170 and the corresponding diametrical plane D can be between 10 ° and 20 ° sexagesimal, preferably equal to about 15 ° sexagesimal.

In particular, it is preferable that the projections of the longitudinal axes Y of all the intake ducts 170 are inclined, with respect to the respective diametrical planes D, in a way that is concordant with each other and preferably at the same angle, i.e. that they can be inclined so that all the corners are all right or left and preferably all have the same value.

The engine 100 can also comprise a single intake manifold 175, which is connected to all the intake ports 165 through the respective intake ducts 170.

For example, the intake manifold 175 can have an annular shape that coaxially surrounds the base of the cylinder 105, and the intake ducts 170 can individually comprise a respective initial section which, developing parallel to the central axis X of the cylinder 105, derives and protrudes from the intake manifold 175 to connect and join the terminal section described above.

The intake manifold 175 can receive the combustion air from a suction line (not shown) which can comprise a compressor, for example a volumetric or rotary compressor, which can be mechanically connected and driven directly by the crankshaft, and possibly a intercooler interposed between the compressor and the intake manifold 175 to lower the air temperature.

In any case, it is preferable that the compressor is suitable for supplying air at a pressure which, together with the geometry of the intake ducts 170, is able to guarantee a swirl coefficient equal to or greater than 3 inside the cylinder 105.

As illustrated in Figure 1, the cylinder 105 also comprises a plurality of exhaust ports 180, which are made on the internal lateral surface 110, for example in the section between the top dead center B2 and the bottom dead center B1 of the second piston 120 , preferably proximal to the bottom dead center B1.

The exhaust ports 180 can be four or more in number and can all have the same shape and size, in the example shown a rectangular shape.

The exhaust ports 180 are preferably arranged in the same axial position along the central axis X of the cylinder 105 but in different angular positions, for example angularly equidistant from each other.

Each exhaust port 180 leads to a respective exhaust duct 185, which is generally adapted to convey towards the outside the combustion gases generated inside the cylinder 105.

In particular, according to an embodiment of the invention, all the exhaust ducts 185 can connect the respective exhaust ports 180 to a single exhaust manifold 190.

For example, the exhaust manifold 190 can have an annular shape that coaxially surrounds the end of the cylinder 105 while the exhaust ducts 185 can develop radially to the central axis X of the cylinder 105.

The exhaust manifold 190 can convey the combustion gases to the outside through an exhaust line (not shown), which may include one or more devices capable of retaining particulate matter and / or other pollutants or transforming them into harmless substances.

The engine 100 also comprises a fuel injector 195, in this case diesel, which is associated with the cylinder 105 in such a way as to be able to inject a jet of fuel into the combustion chamber 125, typically a jet of atomized fuel. or spray.

The injector 195 can receive the fuel from a pumping device (not shown), which can be connected and operated directly by the crankshaft and can allow the injection pressure to be adjusted according to the operating conditions, preferably with maximum values of at least 100 MPa.

Preferably, the injector 195 is positioned at the annular band 160 of the cylinder 105 (see Fig. 3), so as to never be covered by the shell 135 of the first piston 115 or the second piston 120.

The injector 195 can be of the "pintle" type, or multi-hole with at least three holes, capable of generating a highly penetrating jet of fuel.

In particular, as illustrated in Figure 6, the injector 195 can be adapted to generate a jet of fuel which develops, inside the cylinder 105, according to a predetermined injection axis Z which intersects the internal lateral surface 110 of the cylinder 105. at a given point of intersection L.

For example, the injector 195 can be adapted to generate a cone-shaped fuel jet having an axis coinciding with the injection axis Z and extending towards the inside of the cylinder 105.

The angle at the vertex of this cone-shaped fuel jet can be between 30 ° and 40 ° sexagesimal.

According to one aspect of the invention (see Fig. 3), the injection axis Z of the injector 195 can lie in a reference plane P orthogonal to the central axis X of the cylinder 105 and passing through the point of intersection L with the internal side surface of the cylinder 105.

In this way, the fuel injection develops substantially in a transverse plane with respect to the central axis X of the cylinder 105.

In other embodiments, however, it is possible that the injection axis Z is at least slightly inclined with respect to the aforementioned reference plane P, preferably by an angle of less than 10 ° sexagesimal.

Regardless of this, as illustrated in Figure 6, an aspect of the invention provides that the projection of the injection axis Z, carried out on a reference plane P, is inclined with respect to a diametrical plane d containing the central axis X of the cylinder 105 and the intersection point L.

In particular, it is preferable that the aforementioned projection of the injection axis Z is inclined, with respect to the diametrical plane d, in a manner consistent with the projections of the longitudinal axes Y of the intake ducts 170.

In other words, it is preferable that the minor angle formed between the projection of the injection axis Z and the diametrical plane d has the same sign as the angle formed by the projection of the longitudinal axis Y of each intake duct 170 and the corresponding diametrical plane D, i.e. that they are all right-handed or all left-handed with respect to the central axis X of the cylinder 105.

In this way, the fuel is injected in equilibrium with respect to the vortex of air generated by the intake ducts 170, from which it is therefore rapidly dragged and diffused throughout the combustion chamber, obtaining a uniform and rapid mixing of the fuel in the greater part part of the air available inside the cylinder 105.

For example, the angle formed between the projection of the injection axis Z and the diametrical plane d can be equal to the angle formed by the projection of the longitudinal axis Y of each intake duct 170 and the corresponding diametrical plane D o, in any case , can be between 10 ° and 20 ° sexagesimal, for example equal to 15 ° sexagesimal.

During the operation of the engine 100, when the pistons 115 and 120 are in correspondence with the respective lower dead center positions A1 and B1, the combustion chamber 125 is in communication with both the intake ports 165 and the exhaust ports 180 .

In this way, the combustion air coming from the intake ports 165 fills the combustion chamber 125, simultaneously pushing the combustion gases generated during the previous engine cycle to exit through the exhaust ports 180.

Thanks to the geometry of the intake ducts 170, an intense swirling movement is imparted to the combustion air inside the cylinder 105 which develops around the central X axis.

Subsequently, moving towards the respective top dead center positions A2 and B2, the pistons 115 and 120, after having closed the intake ports 165 and exhaust 180, progressively compress the fresh air inside the combustion chamber 125.

During this phase, the injector 195 injects into the combustion chamber the jet of fuel which, thanks to the inclination of the injection axis Z, penetrates optimally into the air vortex and is dragged by the latter to spread evenly in the combustion chamber 125.

When the pistons 115 and 120 are in the vicinity of the respective top dead centers A2 and B2, the injected fuel begins to ignite due to the high pressure inside the combustion chamber 125, generating rapidly expanding hot gases which push the pistons 115 and 120 back to the respective lower dead center positions A1 and B1.

Combustion also continues during this retraction stroke, progressively affecting most of the volume of air available inside cylinder 105.

In this regard, thermo-fluid dynamics numerical simulations carried out with CFD-3D software, have shown how the volume of air affected by combustion progressively extends to the entire cylinder 105, and this even before the pistons 115 and 120 have reached the half of their back stroke.

All this unequivocally demonstrates that the air-fuel mixing process, which directly controls the combustion process, is extremely effective.

The definitive proof of the efficiency of the system, both from the point of view of performance and polluting emissions, was also identified in the fact that the simulations conducted showed the absence of unburned hydrocarbons at the end of the expansion.

This means that all the fuel has been burned, providing maximum energy to pistons 115 and 120 and throwing fumes into the atmosphere that contain negligible quantities of particulate matter.

Another advantage of the proposed system, which can also be deduced from the simulations, is the permanence, along the internal lateral surface 110 of the cylinder 105, of a thin layer or cushion of air that is never completely consumed by combustion.

This cushion makes it possible to reduce the dispersion of heat through the walls of the cylinder 105, already limited by the minimum surface of the crown of the pistons 115 and 120, thus helping to further increase the efficiency of the engine 100. Obviously, the engine 100 described above. a person skilled in the art will be able to make numerous modifications of a technical applicative nature, without thereby departing from the scope of the invention as claimed below.

Claims (12)

CLAIMS A two-stroke diesel and opposed piston engine (100), comprising: - a cylinder (105) having an internal lateral surface (110) which extends around a predetermined central axis (X), - two pistons (115, 120), mutually opposed and both slidingly received inside said cylinder (105), to define with the internal lateral surface (110) a combustion chamber (125) with variable volume, - at least one intake duct (170) extending along a predetermined longitudinal axis (Y) and afferent inside the cylinder (105) through an intake port (165) obtained on the internal side surface (110), - at least one exhaust duct (185) efferent from inside the cylinder (105) through an exhaust port (180) obtained on the internal side surface (110), and - a fuel injector (195) associated with the cylinder (105) and able to inject a jet of fuel into the combustion chamber (125) according to a predetermined injection axis (Z), characterized by the fact that the projection of the longitudinal axis (Y) of the intake duct (170), carried out on a reference plane (Q) orthogonal to the central axis (X) of the cylinder (105) and passing through an intersection point (K) between the longitudinal axis (Y) of the intake duct (170) and the internal lateral surface (110) of the cylinder (105), is inclined with respect to a diametrical plane (D) containing the central axis (X) of the cylinder (105) and said intersection point (K), that the projection of the injection axis (Z), carried out on a reference plane (P) orthogonal to the central axis (X) of the cylinder (105) and passing through an intersection point (L) between the injection axis (Z) and the internal lateral surface (110) of the cylinder (105), it is inclined with respect to a diametrical plane (d) containing the central axis (X) of the cylinder (105) and said intersection point (L), and that said projections of the longitudinal axis (Y) of the intake duct (170) and of the of injection (Z) are inclined, with respect to the respective diametrical planes (D, d), in a concordant way. 2. An engine (100) according to claim 1, characterized in that the angle () formed by said projection of the longitudinal axis (Y) of the intake duct (170) and by the corresponding diametrical plane (D) is comprised between 10 ° and 20 °. 3. An engine (100) according to any one of the preceding claims, characterized in that the longitudinal axis (Y) of the intake duct (170) lies in the corresponding reference plane (Q) or is inclined with respect to the latter by an angle of less than 20 °. 4. An engine (100) according to any one of the preceding claims, characterized in that the intake duct (170) is connected to a compressor adapted to feed air into the cylinder (105) at a pressure such as to obtain in the cylinder (105) a swirl coefficient equal to or greater than 3. 5. An engine (100) according to any one of the preceding claims, characterized in that it comprises a plurality of said intake ducts (170), each of which reaches the inside of the cylinder (105) through a respective intake port (165 ), extending along a respective longitudinal axis (Y) whose projection, carried out on a respective reference plane (Q) orthogonal to the central axis (X) of the cylinder (105) and passing through the point of intersection (K) between the longitudinal axis (Y) of said intake duct (170) and the internal lateral surface (110) of the cylinder (105), is inclined with respect to a respective diametrical plane (D) containing the central axis (X) of the cylinder (105) and said intersection point (K). 6. An engine (100) according to any one of the preceding claims, characterized in that the angle () formed by the projection of the injection axis (Z) and by the corresponding diametrical plane (d) is substantially equal to the angle () formed by the projection of the longitudinal axis (Y) of the intake duct (170) and the corresponding diametrical plane (D). 7. An engine (100) according to any one of the preceding claims, characterized in that the angle () formed by said projection of the injection axis (Z) and by the corresponding diametrical plane (d) is comprised between 10 ° and 20 °. An engine (100) according to any one of the preceding claims, characterized in that the injection axis (Z) lies in the corresponding reference plane (P) or is inclined with respect to the latter by an angle of less than 10 ° . An engine (100) according to any one of the preceding claims, characterized in that the jet of fuel generated by the injector (195) is cone-shaped having an axis coinciding with the injection axis (Z) and widening towards the inside the cylinder (105). An engine (100) according to claim 9, characterized in that said fuel jet has a cone angle comprised between 30 ° and 40 °. 11. An engine (100) according to any one of the preceding claims, characterized in that the injector (195) is connected to a pumping device capable of feeding fuel at a maximum pressure equal to or greater than 100 MPa. 12. An engine (100) according to any one of the preceding claims, characterized by the fact that each piston (115, 120) comprises a flat top (130) or with a concavity facing the other piston.