EP0296899A1 - Arrangement of a fuel feed system in a combustion chamber of a two-stroke engine in relation to the exhaust port - Google Patents

Abstract

The invention relates to a two-stroke internal combustion engine having at least one combustion chamber fitted with a delayed fuel feed system (8) opening out into a cylinder head (1), the wall of the cylinder comprising at least one exhaust port (10) located next to a first reference point (10a) through which passes a first axial plane of the cylinder or exhaust plane and at least one admission port (11) located next to a second reference point (11a), or admission reference point. This engine is characterised in that the plane perpendicular to the exhaust plane and containing the axis (P) of the cylinder (2) defines two cylinder control zones in which the first (4a) complementary to the second (4b) contains the reference point (10a) for the exhaust port and in that the feed system is located in the second control zone (4b).

Description

The present invention relates to an arrangement of the various members inside a combustion chamber of a two-stroke internal combustion engine.

More particularly, the invention relates to the combustion chambers of a two-stroke engine comprising intake and exhaust lights and a deferred fuel supply system, placed at the level of the cylinder head.

The study of the combustion of the two-stroke engine has revealed the importance of the conditions for initiating combustion in order to obtain correct and complete combustion of the fuel introduced.

This initiation of combustion essentially depends on the internal aerodynamics and the conditions prevailing in the vicinity of the ignition point, in particular with regard to the richness of the mixture in the vicinity of this point.

The complete combustion of the fuel introduced depends in particular on the quantity of fuel introduced remaining in the chamber for combustion.

Indeed, in engines where the fuel is introduced before the exhaust port is closed, a certain part of the fuel can be found in the exhaust without having burned in the combustion chamber.

This results in significant consumption and pollution of the engine.

This annoyance is particularly increased in engines admitting carbureted air for sweeping the burnt gases.

Also, the use of a non-fueled fresh air intake ensuring the scavenging of the burnt gases, combined with a deferred fuel supply system triggered once the fresh air is introduced into the chamber, would be able to prevent the unburnt fuel exhaust, if it was not essential for combustion (especially with regard to the homogenization of the fuel mixture in fresh air) to introduce the fuel before the exhaust is closed , with the risk that part of the fuel will escape.

The deferred fuel supply system can comprise either an injector opening directly or indirectly into the combustion chamber and controlled for example electronically or by cam depending on the rotation of the crankshaft, or even a pneumatic injector, as described in the Patent FR-A-2,575,521.

In a two-stroke engine comprising a pneumatic injector placed in the cylinder head, the respective positions of the pneumatic injector and of the ignition point in the combustion chamber represent important parameters of the internal aerodynamics and therefore the conditions of initiation of combustion.

Mainly with the aim of reducing unburnt and improving the conditions for initiating combustion, and therefore combustion, the present invention provides different arrangements of the combustion chamber. combustion.

The arrangements developed according to the invention have been studied theoretically and experimentally, in particular by means of a numerical simulation and tests on engines.

For two-stroke engines equipped with a pneumatic fuel injector in the cylinder head, the arrangements imagined and selected for their interest are characterized in that the ignition point is placed on the side of the exhaust, or even that the injector pneumatic is placed on the side opposite the exhaust, or also that the pneumatic fuel injector is installed on the side of the rear intake lights, such as rear transfer lights.

Fortunately for engine manufacturing, these layout conditions are compatible with a simple engine architecture.

Thus, the present invention relates to a two-stroke internal combustion engine having at least one combustion chamber equipped with a delayed fuel supply system opening into a cylinder head which covers a cylinder cooperating with a piston, the cylinder head, the cylinder and the piston delimiting the combustion chamber, the cylinder wall comprising at least one exhaust port located in the vicinity of a first reference point through which passes a first axial plane of the cylinder or exhaust plane and at least one port located near a second reference point, or admission reference point.

It is characterized in particular in that the plane perpendicular to the exhaust plane and containing the axis of the cylinder delimits two zones for fitting out the cylinder, the first complementary to the second containing the reference point of the exhaust light and in what the power system is located in the second development area.

The cylinder head may include a spark plug which may be located in the first development zone.

The admission reference point may be located in the second zone.

The supply system may be adapted to produce a converging jet in the second development zone and substantially oriented towards the reference point of the intake.

The supply system may be adapted to produce a diverging jet which on the one hand crosses said second development zone and is oriented towards the reference point of the intake and which on the other hand is directed towards the first zone d in the vicinity of the cylinder head.

The supply system may be a pneumatic injection system and this may include a deflector adapted to modify the shape of the jet.

The pneumatic injection system which produces the jet of fuel gas may include a valve. This valve can be controlled by an electromagnetic system such as a solenoid, be controlled automatically by the upstream and downstream pressure of the gases and be optionally equipped with a return means, such as a spring, or be controlled mechanically from a kinematic chain. connected to the crankshaft, this chain can include return sprockets, a camshaft, etc. The injection system may include a rotating plug.

The supply system may be adapted to produce a diverging jet in said perpendicular plane.

The supply system may be adapted to produce a jet oriented substantially against the current of the gas scanning loop (s).

The intake lumen may be a transfer lumen and therefore be connected to the cylinder crankcase.

The intake light can be connected to a pipe inclined upwards. Thus, the fluid coming from this light will be directed towards the cylinder head.

In addition, the present invention relates to a method of designing a two-stroke internal combustion engine having at least one combustion chamber equipped with a deferred fuel supply system, the chamber being delimited by a cylinder head, a cylinder and a piston, the cylinder wall comprising at least one exhaust port located in the vicinity of a first reference point and at least one intake port located in the vicinity of a second reference point, or reference point admission.

This method is notably characterized in that the arrangement and the shapes of at least one intake lumen are adapted so as to produce a stream of fresh gas initially substantially directed towards the supply system, and in that the 'The supply system is placed as close as possible to the intake reference point, following the flow of fresh gas.

• - la figure 1 schématise en coupe l'agencement d'un moteur selon l'art antérieur,
• - la figure 2 illustre schématiquement en coupe un mode d'agencement d'un moteur selon l'invention,
• - les figures 3A à 3F montrent, au cours du déplacement du piston, les isoconcentrations de combustible obtenues par une simulation numérique pour l'agencement d'un moteur selon l'art antérieur illustré par la figure 1,
• - les figures 4A à 4F représentent, au cours du déplacement du piston, les isoconcentrations de combustible obtenues par une simulation numérique pour le mode d'agencement d'un moteur selon l'invention illustré par la figure 2,
• - la figure 5 schématise en coupe un deuxième mode d'agencement d'un moteur selon l'invention utilisant un déflecteur divergent,
• - la figure 6 schématise en coupe un troisième mode d'agencement d'un moteur selon l'invention utilisant un déflecteur convergent,
• - la figure 7 illustre schématiquement en coupe par un plan perpendiculaire au plan de coupe des figures 1, 2, 5 et 6, un mode d'agencement d'un moteur selon l'invention utilisant un déflecteur divergent dans ce plan perpendiculaire,
• - la figure 8 montre un système d'alimentation comportant une soupape commandée automatiquement par les différences de pression régnant de part et d'autre de sa partie évasée,
• - la figure 9 illustre un système d'alimentation comportant une soupape commandée électromagnétiquement par un solénoïde, et
• - la figure 10 représente un système d'alimentation comportant un boisseau tournant.

The invention will be able to be well understood and all of its advantages will appear very clearly on reading the description which follows, illustrated by the appended figures in which:

• FIG. 1 diagrammatically shows in section the arrangement of a motor according to the prior art,
• FIG. 2 schematically illustrates in section an arrangement mode of an engine according to the invention,
• FIGS. 3A to 3F show, during the displacement of the piston, the isoconcentrations of fuel obtained by a numerical simulation for the arrangement of an engine according to the prior art illustrated by FIG. 1,
• FIGS. 4A to 4F represent, during the displacement of the piston, the isoconcentrations of fuel obtained by a numerical simulation for the arrangement mode of an engine according to the invention illustrated by FIG. 2,
• FIG. 5 diagrammatically shows in section a second mode of arrangement of an engine according to the invention using a divergent deflector,
• FIG. 6 diagrammatically shows in section a third mode of arrangement of an engine according to the invention using a convergent deflector,
• FIG. 7 schematically illustrates in section through a plane perpendicular to the section plane of FIGS. 1, 2, 5 and 6, a mode of arrangement of an engine according to the invention using a divergent deflector in this perpendicular plane,
• FIG. 8 shows a supply system comprising a valve automatically controlled by the pressure differences prevailing on either side of its flared part,
• FIG. 9 illustrates a supply system comprising a valve electromagnetically controlled by a solenoid, and
• - Figure 10 shows a supply system comprising a rotating plug.

In FIG. 1 which schematically represents the arrangement of an engine according to the prior art, the reference 1 designates the cylinder head closing the upper part of the cylinder 2 inside which moves a piston 3 connected by a connecting rod 6 to a crankshaft 7.

The combustion chamber has the reference 4 and the lower casing the reference 5.

The cylinder head 1 comprises a spark plug 9 creating an ignition point by an electric arc and a system 8 for delayed fuel supply which may be a pneumatic injection system.

The exhaust manifold communicates with the cylinder 2 by a light 10.

The intake manifold communicates with the cylinder 2 by a rear light 11 and by one or more side lights 12. All these lights may have one or more orifices.

The cylinder 2 like the piston 3 sliding therein, are assumed to revolution around an axis P, as in practice. It will not depart from the scope of the invention to use substantially different shapes of cylinders and piston from those of revolution.

If we consider that the exhaust port 10 is located around a first reference point 10a, and that the exhaust plane contains this point and the axis of the cylinder, the plane perpendicular to the exhaust plane and passing through the axis of the cylinder delimits in the combustion chamber two separate development zones, the first 4a complementary to the second 4b contains the reference point 10a of the exhaust port.

According to the prior art (FIG. 1) the fuel supply system 8 is located in the first development zone 4a, that is to say say on the same side as the reference point 10a of the exhaust port 10 relative to the perpendicular plane.

Similarly, the second reference point 11a, or intake reference point, around which the rear 11 and side 12 intake lights are located, is located in the second arrangement zone 4b with the spark plug 9, so that the supply system 8 is located in the first development zone 4a.

According to the invention (Fig. 2), the reference point 11a of the intake such as the fuel supply system 8 is located in the second arrangement zone, that is to say on the side opposite the point 10a reference of the exhaust port, with respect to the perpendicular plane whose line P is the frontal trace on the plane of the figure. Finally, the candle 9 is located in the first development zone 4a.

The supply system 8 supplies the fuel only when the cylinder 3 is in the rising phase. Thus, the injection valve opens only after the cylinder has reached bottom dead center.

The positions of the intake and exhaust lights are given from a first and a second reference point respectively around which the lights are located.

The reference points correspond substantially to the points of application of the vectorial results of the gas velocities at the intake and exhaust ports.

However, since obtaining the results is difficult, it can often be considered that the reference point corresponds to the barycenter of the surfaces of the openings on the one hand, intake and exhaust.

Thus, when an exhaust system has two lights, the reference point of the exhaust is located between the two lights or the lights are located around said reference point of the exhaust.

According to the present invention, the intake lights can advantageously be transfer lights and therefore be connected to the engine crankcase.

In addition, according to the present invention, the transfer conduit 11 advantageously forms, at the level where it opens into the cylinder 4, an angle α less than 90 °, this angle being defined by the axis of the conduit 11 and the axis of the cylinder. . Thus the conduit 11 targets the cylinder towards the cylinder head.

Advantageously, this angle can be between 30 and 45 °, so that the fluid which leaves it targets the cylinder head.

FIGS. 3A to 3F and 4A to 4F illustrate the variations in fuel concentration appearing in a combustion chamber during the rotation of the crankshaft. These figures were obtained by a two-dimensional modeling of a combustion chamber taking into account the interaction of the scanning loop formed by the mass of fresh gas admitted by the intake light, with the jet of the pneumatic injector. .

The straight segment 14 above the figures illustrate the cylinder head, while the location 15 corresponds to the fuel supply zone. The vertical straight segments 16 represent the walls of the cylinder and the lower straight segment 17 represents the piston.

So that the modeling reproduces as correctly as possible the behavior of the gases inside the combustion chamber, in particular with regard to sweeping, it is considered that admission takes place through two lights symbolized by zones 19a and 19b and the exhaust takes place through a light symbolized by zone 18.

The intake lights open at 55 ° before bottom dead center and close 55 ° after bottom dead center (i.e. 125 ° and 235 ° crankshaft angle respectively).

The exhaust light opens at 71 ° before bottom dead center and closes at 71 ° after bottom dead center (i.e. 109 ° and 251 ° crank angle).

A first intake lumen 19a introducing air at an initial angle of zero degrees to the horizontal is placed opposite a second intake lumen 19b introducing air at an initial angle of 60 degrees with respect to the horizontal.

The exhaust port 18 is placed above the first intake port 19a.

Since the fuel concentration is the mass of fuel relative to the mass of the fresh air, burnt gas and fuel mixture, the isoconcentration lines delimit richness ranges comprising references corresponding to the following values of the fuel concentration:

FIGS. 3A to 3F illustrate the modeling of a combustion chamber substantially in accordance with that of FIG. 1.

The different figures have been produced for different angles of the crankshaft corresponding to the following indications:

For these figures (3A to 3F), the supply system includes a deflector making it possible to give an initial direction to the jet inclined by 20 ° relative to the axis of the cylinder towards the rear intake lumen.

The modeling of FIGS. 3A to 3F shows that the jet retains its initial direction for a very short time and that very quickly it is deflected towards the exhaust by the scanning loop which is driven in a substantially gyratory movement, clockwise , in the plane of the figures.

FIG. 3F which represents the isoconcentrations in the chamber when the crankshaft angle is 330 ° (that is to say at the time of ignition), shows that the interaction of the pneumatic jet with the scanning loop generated a richer fuel area on the exhaust side where the pneumatic injector is also located. However, the candle for architectural considerations difficult to respect, cannot be on the rich side and is placed on the opposite side.

This result fully illustrates the experimental observations made on an engine of similar configuration which becomes unstable, especially at high speed. This manifestation fully confirms the poor combustion conditions.

As FIG. 3C represents the chamber at the time of closing of the exhaust port, it can be understood, with the help also of FIG. 3B, that part of the fuel leaves directly at the exhaust. The modeling calculations make it possible to evaluate the losses by unburnt at 8% for the engine configuration studied.

FIGS. 4A to 4F illustrate the modeling of a combustion chamber according to the invention substantially in accordance with that of FIG. 2 and in which the supply system comprises a deflector making it possible to give the jet an initial direction inclined by 20 ° by relative to the axis of the cylinder towards the exhaust port.

Grâce à la modélisation montrée aux figures 4A à 4F, on observe, comme précédemment, que le jet de carburant conserve très peu de temps sa direction initiale et qu'il est dévié vers l'échappement par la boucle de balayage circulant comme dans les moteurs antérieurs.The different figures have been produced for different crankshaft angles corresponding to the following indications:

Thanks to the modeling shown in FIGS. 4A to 4F, it is observed, as before, that the jet of fuel retains its initial direction for a very short time and that it is deflected towards the exhaust by the scanning loop circulating as in the engines. earlier.

The various figures show that with the configuration according to the invention, the rich zones take longer to reach the exhaust due to the length of the path to be traveled between the supply system and the exhaust, that they spread better through the chamber and that finally the gas mixture is generally more uniform at the time of ignition (Fig. 4F).

The modeling calculations allow for this engine configuration to assess unburnt losses at 4%.

In addition, the spark plug placed on the exhaust side is located in a rather richer area where an excellent combustion initiation can take place. This result is confirmed experimentally on an engine where high operating speeds are reached without any particular manifestation of combustion instability.

FIGS. 5, 6 and 7 show the importance of the direction of the initial jets coming from the supply system 8.

In these embodiments, a pneumatic injector 8 such as that described in patent FR-A-2,575,522 is used.

A member 20 injects fuel inside the nozzle 23 placed in a stream of compressed air. An injection valve 22 resting on a seat 24 makes it possible to isolate the injection system 8 from the chamber 2 when the compression pressure has reached a certain threshold.

The system includes deflectors 25, 26, 27 integrated into the seat making it possible to modify the initial incidence of the jet.

The deflectors create very favorable conditions for the initiation of combustion and slow down the path of the pneumatic jet of fuel towards the exhaust port, in order to reduce the quantities of unburnt fuel.

Thus, in FIG. 5, a divergent deflector 26 is used, slowing down the penetration of the pneumatic jet. Part of this jet 26a is directed towards the face of the cylinder closest to the injector 8 in order to reduce, by opposing it, the drive of the scanning loop.

FIG. 6 illustrates an engine comprising a counter-current deflector making it possible, on the one hand, to increase the path followed by the scanning loop, in order to avoid losses of unburnt matter at the exhaust and, on the other hand, to keep part of the jet along the wall of the cylinder, closest to the injection system.

Figure 7 shows schematically a combustion chamber comprising a deflector 27 diverging in a plane parallel to said perpendicular plane. This arrangement makes it possible to slow down, in this plane parallel to said perpendicular plane, the penetration of the pneumatic fuel jets so as to reduce the losses by unburnt.

The valve 22 can be controlled in several ways. In the case of FIG. 2, the valve 22 is electrically controlled, for example by a cam 29 driven in rotation at the speed of the motor. This cam controls the movement of the valve 22 by means of a pusher 30. The valve is returned by a spring 31.

The references 35 and 36 respectively designate a fuel metering device and a venturi nozzle. Reference 37 designates a deflector.

In the particular case of FIG. 8 which illustrates another variant, the valve 22 does not include a control system in the literal sense. It can be simply fitted with a return spring 32. It is left free to move as a function of the pressure differences upstream 33 and downstream 34. It then acts in the manner of a flap or automatic valve, it will be said to be controlled automatically. The spring 32 is calibrated so as to obtain the openings valve.

In FIG. 9, the valve is controlled by a solenoid 38. This solenoid can be controlled electronically so as to open the valve 22 at the most suitable time.

FIG. 10 represents a supply system comprising a rotary plug 39 driven by the rotation of the motor and which thus controls the opening of the orifice 40 for penetration into the cylinder of the jet comprising the fuel.

Claims (17)

1. - Two-stroke internal combustion engine having at least one combustion chamber equipped with a deferred fuel supply system (8) opening into a cylinder head (1) which covers a cylinder (2) cooperating with a piston ( 3), the cylinder head, the cylinder and the piston delimiting said combustion chamber (4), the cylinder wall comprising at least one exhaust port (10) located in the vicinity of a first reference point (10a) through which passes a first axial plane of the cylinder or exhaust plane and at least one intake port (11) located in the vicinity of a second reference point (11a), or admission reference point, this engine being characterized in that the plane perpendicular to the exhaust plane and containing the axis (P) of the cylinder delimits two zones for fitting out the cylinder, the first (4a) complementary to the second (4b) containing the reference point (10a) of the exhaust light and that the fuel system is located in said second (4b) development zone. 2. - Engine according to claim 1, characterized in that said cylinder head comprises a spark plug (9) and in that said spark plug is located in said first development zone (4a). 3. - Engine according to one of claims 1 and 2, characterized in that the reference point of the intake (11a) is located in said second area (4b). 4. - Motor according to one of claims 1 to 3, characterized in that the supply system (8) is adapted to produce a jet (25a) converging (Fig. 6) in said second development area and substantially oriented towards said admission reference point (11a). 5. - Motor according to one of claims 1 to 3, characterized in that the supply system (8) is adapted to produce a diverging jet (26a) which passes through said second development zone (4b) and is oriented towards the reference point (11a) of the intake and which is directed towards said first development zone in the vicinity of the cylinder head (1). 6. - Engine according to one of claims 1 to 5, characterized in that said supply system (8) is a pneumatic injection system. 7. - Engine according to claim 6, characterized in that said pneumatic injection system (8) producing a jet of fuel gas comprises a valve (22) and a suitable deflector (25, 26, 27) for modifying the shape of said jet. 8. - Motor according to claim 7, characterized in that said valve is controlled by an electromagnetic system such as a solenoid. 9. - Engine according to claim 7, characterized in that said valve is controlled automatically by the upstream and downstream pressure of the gases and in that said valve is optionally equipped with a return means. 10. - Engine according to claim 7, characterized in that said valve is mechanically controlled from a kinematic chain connected to the crankshaft. 11. - Motor according to claim 7, characterized in that it is equipped with a deflector (25, 26, 27) adapted to modify the shape of said jet. 12. - Engine according to claim 6, characterized in that said injection system (8) comprises a rotating plug. 13. - Motor according to one of claims 1 to 12, characterized in that the supply system is adapted to produce a diverging jet in said perpendicular plane (Fig. 7). 14. - Motor according to one of claims 1 to 12, characterized in that the supply system is adapted to produce a jet oriented substantially against the current or the loop (s) of gas scanning. 15. - Engine according to one of the preceding claims, characterized in that said intake light is a transfer light connected to a pump housing. 16. - Engine according to one of the preceding claims, characterized in that said intake light is connected to a pipe inclined upwards. 17. - Method of designing a two-stroke internal combustion engine having at least one combustion chamber equipped with a deferred fuel supply system (8), said chamber being delimited by a cylinder head (1), a cylinder (2) and a piston (3), the wall of the cylinder comprising at least one exhaust port (10) located in the vicinity of a first reference point (10a) and at least one intake port (11) located in the vicinity of a second reference point (11a), or admission reference point, this method is characterized in that the arrangement and the shapes of at least one intake lumen are adapted so to produce a flow of fresh gas initially substantially directed towards the supply system, and in that the supply system is placed as close as possible to the reference point of the intake, following the flow of fresh gas .

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