EP3025038A1

EP3025038A1 - Method for controlling a two-stroke internal combustion engine

Info

Publication number: EP3025038A1
Application number: EP14755865.4A
Authority: EP
Inventors: Guillaume LABEDAN; Hugues Denis JOUBERT; Norbert Lartigue
Original assignee: Societe Motorisations Aeronautiques SA
Current assignee: Societe Motorisations Aeronautiques SA
Priority date: 2013-07-23
Filing date: 2014-07-21
Publication date: 2016-06-01
Also published as: FR3009025B1; US20160177812A1; CA2919141A1; FR3009025A1; WO2015011390A1

Abstract

The invention relates to a method for controlling (100) a two-stroke internal combustion engine (1), said control method (100) comprising the following steps: longitudinal movement of a piston (3) in the direction of the bottom dead centre of an engine (101), said movement (101) being triggered by the expansion of burned gases (8) in the master cylinder (2), during said longitudinal displacement (101) of said piston (3), there is a step of admission air pressurisation (102), adjustment of the pressure of said burned gases to a value lower than said admission air pressure (103), and introduction of pressurised admission air (105) into said cylinder, the air introduced forming a stratification layer (9) redirecting said burned gases (8) towards said exhaust port (4).

Description

METHOD FOR CONTROLLING A COMBUSTION TWO-STROKE ENGINE

INTERNAL

TECHNICAL AREA

The present invention relates to a control method of a two-stroke internal combustion engine and a two-stroke internal combustion engine to be controlled according to the control method according to the invention. Such a motor and such a control method can be advantageously implemented in the aeronautical field.

STATE OF THE PRIOR ART

Equivalent two-stroke internal combustion engines are known, such engines comprising:

• a motor cylinder having a longitudinal axis X,

A piston disposed in the engine cylinder, the piston being capable of moving along the longitudinal axis X,

An exhaust port located at one end of the engine cylinder for exhausting the flue gases, and

• an air intake port in the engine cylinder.

Such an internal combustion two-stroke engine is characterized by a driving time for each crankshaft revolution. The piston contained in the engine only contributes to the compression and expansion of the gases contained in the engine cylinder, the evacuation of the burnt gases and the filling of the engine cylinder in air being achieved by other mechanisms. More particularly, a source of compressed air at the bottom dead center of the engine ensures the air filling of the engine cylinder by simultaneously pushing the flue gases towards the exhaust port. The opening of the exhaust port allows the evacuation of burnt gases.

To promote the filling of the engine cylinder, it is necessary to achieve a vacuum in the engine cylinder. However, such a depression increases the rate of entry of compressed air into the cylinder and generates a phenomenon of mixing compressed air and flue gases. The mixing of the compressed air and the flue gas is all the higher as the turbulence is important in the cylinder. The mixture of the introduced air and the burnt gases causes, on the one hand, a loss of a part of the air introduced towards the exhaust without this one participating in the combustion, and on the other hand, a air pollution introduced by hot and flammable gases into the cylinder reducing the efficiency of combustion de facto.

Conventionally, the development of the engine is to ensure the escape of all the flue gas, which implies in return that a portion of air introduced, due to the phenomenon of mixing, is lost directly to the exhaust .

SUMMARY OF THE INVENTION

The invention therefore aims to overcome the disadvantages of the state of the art. In this context, the present invention aims to provide a method for controlling an internal combustion two-stroke engine having an optimized combustion efficiency.

To this end, the invention relates to a method for controlling an internal combustion two-stroke engine, said engine comprising:

• a motor cylinder having a longitudinal axis X,

A piston disposed in said engine cylinder, said piston being able to move along said longitudinal axis X,

An exhaust port having at least one exhaust valve,

An air intake port in said engine cylinder,

said driving method comprising the following steps:

• longitudinal displacement of said piston towards the bottom dead center of said engine, said displacement being generated by the expansion of burnt gases in said engine cylinder, during said longitudinal displacement of said piston the process comprises a step of pressurizing intake air,

Adjusting the pressure of said flue gases to a value lower than said intake air pressure,

Introduction into said pressurized admission air cylinder, the intake air forming a lamination layer pushing said flue gases towards said exhaust port. For the rest of the description, a stratification layer is understood to mean a layer of air admitted into the cylinder that is not mixed with the flue gases. This layer of air (also called layer of air stratification) comprises only introduced air unmixed with burnt gases contained in the engine cylinder.

Thanks to the invention, the intake air is introduced before the opening of the exhaust port, the pressure of the intake air being greater than the pressure of the flue gases, which allows to stratify the air admitted inside the cylinder. Once the exhaust port is open, the action of the intake air slightly overpressure compared to the flue gas combined with the rise of the piston after the bottom dead point, flushes the flue gases while avoiding a mixture of air admitted with the flue gases. In addition, since no mixing is performed, the intake air is not ejected outside the engine cylinder.

The control method of a two-stroke internal combustion engine according to the invention may also have one or more of the following characteristics, considered individually or in any technically feasible combination.

In a non-limiting embodiment, the adjustment of the flue gas pressure to a value lower than said intake air pressure is achieved via the opening of a restricted flow relief valve.

In a non-limiting embodiment, the method according to the invention comprises a step of closing the discharge valve as soon as the flue gases have a pressure lower than the intake air pressure.

In a non-limiting embodiment, since the pressure contained in the cylinder formed by the lamination layer and the flue gases is substantially equal to the value of the intake air pressure, the method comprises a step of opening the exhaust port, the introduction of pressurized intake air into the engine cylinder continuing.

In a non-limiting embodiment, the adjustment of the pressure of the flue gases to a value lower than the intake air pressure is achieved by opening the exhaust port and creating a back pressure at the beginning. said opening of the exhaust port to limit the exhaust flow of the burnt gases. This back pressure can be generated by reflection of acoustic waves in the exhaust pipes (not shown). In alternative engines, the exhaust sees flushes of gas that creates Acoustic waves of pressure and vacuum in the exhaust pipes. In this particular configuration of the solution, the lengths of the pipes and positions of the junctions between the exhausts of each cylinder are defined so as to reflect an overpressure at the exhaust port to limit the rate of gas discharge at the beginning of its opening.

In a non-limiting embodiment, the method according to the invention comprises a step of closing the exhaust port when all the burnt gases are evacuated.

In a non-limiting embodiment, the adjusted flue gas pressure is at least 150 mbar lower than the intake air pressure, or for example of the order of 150 mbar.

The invention also relates to an internal combustion two-stroke engine comprising:

• a motor cylinder having a longitudinal axis X,

An exhaust port having at least one exhaust valve,

• intake air pressurization means,

At least one intake port of pressurized air into said engine cylinder.

The engine further comprises a pressure regulator adapted to adjust the pressure of the burnt gases contained in said engine cylinder to a value lower than said intake air pressure.

In a non-limiting embodiment, the pressure regulator is formed by a restricted flow relief valve, the opening of which enables the pressure of the flue gases contained in said engine cylinder to be adjusted to a value lower than the air pressure. 'admission.

BRIEF DESCRIPTION OF THE FIGURES

Other features and advantages of the invention will clearly be described in the description given below, by way of indication and in no way limitative, with reference to the appended figures, among which: FIG. 1 illustrates a nonlimiting example embodiment of a two-stroke internal combustion engine according to the invention,

FIG. 2 illustrates a block diagram of the steps of a possible implementation of a control method of a two-stroke internal combustion engine according to the invention, and

FIGS. 3A, 3B, 3C and 3D schematically illustrate various steps of the method for controlling an internal combustion two-stroke engine according to the invention detailed in support of FIG. 2.

For the sake of clarity, only the elements useful for understanding the invention have been shown and this, without respect for the scale and schematically. In addition, the similar elements in different figures have identical references.

DETAILED DESCRIPTION OF AT LEAST ONE EMBODIMENT OF THE INVENTION

FIG. 1 illustrates a nonlimiting example embodiment of a two-stroke internal combustion engine 1 according to the invention. The two-stroke internal combustion engine 1 illustrated in FIG. 1 comprises:

a driving cylinder 2 having a longitudinal axis X,

a piston 3 disposed in the engine cylinder 2, the piston 3 being capable of reciprocating in the engine cylinder 2 along the longitudinal axis X,

an exhaust port 4 formed by an exhaust valve, the exhaust port 4 being located at the top dead center of the engine 1,

intake air pressurization means 5,

two pressurized air intake ports 6 in the engine cylinder 2, the two intake ports 6 being located at the bottom dead center of the engine 1, and

- A pressure regulator 7 (formed by a restricted flow relief valve) adapted to adjust the pressure of the burnt gases 8 contained in the engine cylinder 2 to a value less than the intake air pressure. This relief valve 7 is also located at the top dead center of the engine 1. Thus, the two-stroke internal combustion engine 1 according to the invention is provided with two types of valves whose opening is sequenced in order to optimize the discharge rate of the burnt gases contained in the engine cylinder 2.

In a particularly advantageous but non-limiting implementation, the restricted flow relief valve 7 is opened before the opening of the exhaust valve 4 in order to reduce the difference between the intake pressure and the pressure of the burnt gases of the engine cylinder 2. This decrease in pressure difference makes it possible to control the inlet air speed of the inlet air in the engine cylinder 2.

The two-stroke internal combustion engine 1 illustrated in FIG. 1 comprises a single exhaust valve 4 and a single discharge valve 7, but it is understood that the engine 1 according to the invention is not limited to such an embodiment. and it may comprise a plurality of discharge valves 7 and / or a plurality of exhaust valves 4.

In another non-illustrated embodiment of the two-stroke internal combustion engine according to the invention, the exhaust port is located near the bottom dead center of the engine and the intake port, for example controlled by a valve, is located near from the top dead center of the engine. This embodiment makes it possible to take advantage of the inertia of the gases burned during the relaxation for the exhaust of the latter.

FIG. 2 illustrates a block diagram of the steps of a possible implementation of a control method 100 of a two-stroke internal combustion engine 1 according to the invention, and FIGS. 3A, 3B, 3C and 3D illustrate schematically certain steps of the control method 100 according to the invention detailed in support of Figure 2.

In a nonlimiting implementation, the control method 100 of a two-stroke internal combustion engine 1 comprises the following steps.

The control method 100 comprises a longitudinal displacement step 101 of the piston 3 in a direction X-opposite to the exhaust port 4 (FIG. 3A), the displacement being generated by the expansion of burned gases in the engine cylinder 2 and continuing until the piston 3 unclogs the intake ports 6. Simultaneously with the longitudinal displacement in the direction X- of the piston 3, the control method 100 comprises a step of pressurizing the intake air 102.

The control method 100 comprises an additional step 103 of adjusting the pressure of the burnt gases contained in the engine cylinder 2 to a value lower than the pressurized intake air pressure during the previous step 102. For example, the adjusted flue gas pressure is 150 mbar lower than the intake air pressure. In a nonlimiting implementation, the adjustment of the flue gas pressure to a value lower than the intake air pressure is achieved via the opening of the restricted flow relief valve 7 (Figure 3B). The opening of the relief valve 7 precedes the unclogging of the intake ports 6 by the piston 3.

In a nonlimiting implementation, since the flue gases have a lower pressure than the intake air pressure, the closure 104 of the relief valve 7 is triggered.

As soon as the intake ports 6 are unobstructed (FIG. 3C) by the piston 3, the piloting method 100 comprises a step of introducing pressurized admission air 105 into the engine cylinder 2, the intake air forming a layer laminating layer 9 covering the top 10 of the piston 3. The lamination layer 9 formed of pressurized intake air forms a layer separating the top 10 of the piston 3 of the burnt gases 8. Thus, this layer 9 lamination repels the burnt gases 8 towards the exhaust port 4.

In other words, the piston 3 discovers the intake ports 6 allowing the arrival of the intake air to form the lamination layer 9. The burned gases 8 are then pushed up the engine cylinder 2. As the exhaust port 4 remains closed during this phase, the cylinder pressure is restored to the value of the intake air pressure.

As soon as the pressure contained in the engine cylinder 2 formed by the lamination layer 9 and the flue gases 8 is substantially equal to the value of the intake air pressure, the control method 100 comprises an opening step the exhaust port 106 (Figure 3D), the introduction of pressurized intake air continuing. In our example, to open the exhaust port 4, the exhaust valve is opened. The lifting of the valve exhaust 4 is adapted to allow to control the maximum exhaust flow by maintaining the cylinder pressure close to the intake pressure.

Then the control method 100 includes a step of moving the piston 107 in the X + direction of the exhaust port 4 causing the escape of the burnt gases 8 via the exhaust valve 4 while the engine cylinder 2 fills with air from the exhaust port 4. admission to the rear of the laminated layer 9, in other words between the top 10 of the piston 2 and the laminated layer 9. The mixture between the intake air and the flue gas is almost non-existent because of the low speed of movement of the these, the low pressure difference of the latter and the low speed of movement of the piston 3.

In a non-limiting embodiment, the intake ports are formed by intake ports. Thus, the intake flow during the exhaust phase of the burnt gases can be adapted by the shape of the intake ports to prevent the gas column, which moves upwards in the engine cylinder 2, from entering in oscillation. In another embodiment of the invention, the inlet ports are oriented to feed the cylinder tangentially, giving the flow a vortex movement (well known as English swirl). The expected advantages are a better stability of the stratified layer of fresh air during the movement of the piston and greater robustness to turbulence, which may appear in particular at the exhaust valve.

When all the burned gases 8 is evacuated, the control method 100 includes a closing step 108 of the exhaust valve 4. The displacement of the piston 3 in the X + direction of the exhaust port 4 is continued until the intake ports 6 are closed by the piston 3 (Figure 3D). In this embodiment, the skirt 11 of the piston obstructs the intake ports 6 when the piston 3 is at top dead center. This feature prevents the escape of fresh air to the crankcase. In this embodiment, the piston 3 may comprise a sealing segment at the bottom of the skirt 11 in order to limit the loss of air under pressure towards the housing. In another embodiment not illustrated, to limit the loss of air under pressure to the housing, the opening and closing of the intake port 6 can be controlled, for example, by a bushel or spinning liner.

Furthermore, it should be noted that the role of the exhaust valve 4 is to evacuate most of the flue gas 8, while controlling the exhaust rate of the flue gas 8 throughout the piston sweeping. This makes it possible to limit the amount of air introduced into the exhaust and to limit the turbulence and therefore the mixing between the intake air and the flue gases. This exhaust valve is defined to limit the distortion of the burnt gas velocity field in the exhaust zone, and thus avoid disturbing the stratified air layer created on the piston head.

The method and the motor according to the invention advantageously allow:

an improvement in engine efficiency, in fact:

o The almost non-existence of a mixture between the intake air and the flue gases makes it possible to limit the residual portion of flue gases during each engine cycle. Therefore, the proportion of available oxygen is greater to increase the pressure and the engine cycle temperature, and therefore its performance. The invention makes it possible to reduce the dilution of the exhaust gases by the air admitted during the engine cycle. The temperature of the exhaust gas is therefore higher than in a conventional engine, which makes it possible to increase the proportion of energy recoverable in the exhaust on a turbine for example.

- an increase in the specific power:

o A smaller part of the intake air (thus combustive) is lost directly to the exhaust, which reduces the need for engine air, and therefore the engine capacity.

o The solution requires the use of an air pressurization, typically performed by a compressor driven by the crankshaft or a turbocharger. The supercharging increases the air and fuel masses at each cycle, so the power / displacement ratio.

Claims

CLAIMS 1. A method of controlling (100) an internal combustion two-stroke engine (1), said engine (1) comprising:

a driving cylinder (2) having a longitudinal axis (X),

a piston (3) disposed in said driving cylinder (2), said piston (3) being able to move along said longitudinal axis (X),

an exhaust port (4) for burnt gases (8),

an air intake port (6) in said engine cylinder (2), said control method (100) comprising the following steps:

longitudinal displacement of said piston towards the bottom dead center of said engine (101), said displacement (101) being generated by the expansion of burnt gases (8) in said engine cylinder (2), during said longitudinal displacement (101) of said piston (3) the method (100) includes an intake air pressurization step (102),

adjusting the pressure of said flue gases to a value lower than said intake air pressure (103),

introduction into said pressurized admission air cylinder (105), the exhaust port (4) remaining closed during this intake air introduction phase (105), the intake air forming a lamination layer (9) ) pushing said burnt gases (8) towards said exhaust port (4).

2. Control method (100) according to claim 1, characterized in that the adjustment of the pressure of said flue gases to a value lower than said intake air pressure (103) is achieved via the opening of a restricted flow relief valve (7).

3. Control method (100) according to claim 2, characterized in that it comprises a step of closing the discharge valve (104) when the flue gases (8) have a pressure lower than the pressure of intake air.

4. Control method (100) according to any one of claims 1 to 3, characterized in that since the pressure contained in said engine cylinder (2) formed by the lamination layer (9) and the flue gases ( 8) is substantially equal to the value of the intake air pressure, the method comprises a step of opening the exhaust port (106), the introduction of pressurized intake air into the engine cylinder ( 2) continuing.

5. Control method (100) according to claim 1 characterized in that the adjustment of the pressure of the burned gases to a value lower than the intake air pressure (103) is achieved by opening the port of exhaust (4) and the creation of a back-pressure at the beginning of said opening of the exhaust port (4) in order to limit the exhaust flow rate of the burnt gases.

6. Control method (100) according to any one of claims 4 or 5 preceding characterized in that it comprises the additional step of closing the exhaust port (108) when all the burnt gases (8) is escaping from the driving cylinder (2).

7. A control method (100) according to any one of the preceding claims characterized in that the adjusted flue gas pressure is of the order of 150 mbar less than the intake air pressure.

8. Two-stroke internal combustion engine (1) comprising:

a driving cylinder (2) having a longitudinal axis X,

a piston (3) disposed in said driving cylinder (2), said piston (3) being able to move along said longitudinal axis X,

an exhaust port (4) for the flue gases,

- Intake air pressurizing means (5),

an intake port (6) of pressurized air in said engine cylinder (2), said engine (1) being characterized in that it further comprises a discharge valve (7) with a restricted flow rate, the opening of which allows adjusting the pressure of the burnt gases contained in said engine cylinder to a value lower than the intake air pressure.