Classifications

• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B27/00—Use of kinetic or wave energy of charge in induction systems, or of combustion residues in exhaust systems, for improving quantity of charge or for increasing removal of combustion residues
  • F02B27/04—Use of kinetic or wave energy of charge in induction systems, or of combustion residues in exhaust systems, for improving quantity of charge or for increasing removal of combustion residues in exhaust systems only, e.g. for sucking-off combustion gases
  • F02B27/06—Use of kinetic or wave energy of charge in induction systems, or of combustion residues in exhaust systems, for improving quantity of charge or for increasing removal of combustion residues in exhaust systems only, e.g. for sucking-off combustion gases the systems having variable, i.e. adjustable, cross-sectional areas, chambers of variable volume, or like variable means
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
  • F02B23/08—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition
  • F02B23/10—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder
  • F02B23/104—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder the injector being placed on a side position of the cylinder
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
  • F02B25/14—Engines characterised by using fresh charge for scavenging cylinders using reverse-flow scavenging, e.g. with both outlet and inlet ports arranged near bottom of piston stroke
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B25/00—Engines characterised by using fresh charge for scavenging cylinders
  • F02B25/20—Means for reducing the mixing of charge and combustion residues or for preventing escape of fresh charge through outlet ports not provided for in, or of interest apart from, subgroups F02B25/02 - F02B25/18
• • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
  • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
  • F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
  • F02B23/00—Other engines characterised by special shape or construction of combustion chambers to improve operation
  • F02B23/08—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition
  • F02B23/10—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder
  • F02B23/101—Other engines characterised by special shape or construction of combustion chambers to improve operation with positive ignition with separate admission of air and fuel into cylinder the injector being placed on or close to the cylinder centre axis, e.g. with mixture formation using spray guided concepts
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
  • Y02T10/00—Road transport of goods or passengers
  • Y02T10/10—Internal combustion engine [ICE] based vehicles
  • Y02T10/12—Improving ICE efficiencies

Definitions

• the present invention relates to a two-stroke engine with direct injection of liquid fuel. More particularly, the invention relates to a two-stroke engine with direct injection comprising a combustion chamber delimited by: a cylinder having a longitudinal axis, which is provided with at least one intake lumen and at least one lumen exhaust; a piston having a substantially flat bottom and displaced along the longitudinal axis by a connecting rod connected to a crankshaft; a cylinder head fitted with a spark plug and an injector adapted to spray a jet of pressurized fuel into the combustion chamber along a spraying axis, the combustion chamber having a first diametrical plane comprising the longitudinal axis of the cylinder and centered on the exhaust port and a second diametral plane perpendicular to said first diametrical plane, the spark plug being arranged in a first portion of the cylinder head extending from the second diametrical plane towards the intake port, the injector being arranged on a second portion of the cylinder head complementary to the first portion, and the
• the operating cycle of two-stroke engines includes, for each crankshaft revolution, a first intake / compression time and a second combustion / exhaust time.
• the piston performs a translational movement from a low neutral position to a high neutral position by successively closing the intake and exhaust ports of the cylinder.
• Fresh gases compressed in the crankcase are then admitted, via a transfer channel, into the combustion chamber through the intake ports until they are closed by the piston.
• the fresh gases admitted into the combustion chamber are then compressed until the piston reaches top dead center, while fresh gases are drawn into the crankcase.
• the piston translates from top dead center to bottom dead center by successively unmasking the exhaust and intake ports.
• the ignition is caused by the spark plug when the piston is approximately in its top dead center position.
• This type of engine has the advantage of offering a relatively high power compared to a four-stroke engine of similar weight, due to the existence of an engine time for each revolution of the crankshaft. In addition, its manufacturing cost is particularly low, because the number of parts is less than that of a four-stroke engine.
• this type of engine generally has the disadvantage of a high fuel consumption and a significant emission of pollutants compared to a four-stroke engine.
• the object of the present invention is to improve two-stroke direct injection engines, in particular in order to satisfy the anti-pollution standards in force and to come, and this, by minimally modifying the geometry of the combustion chamber so that the present invention can be applicable to existing engines.
• the subject of the present invention is a engine of the aforementioned type, characterized in that the opening angle ⁇ of the fuel jet is between 15 ° and 75 °, in that the injection of fuel begins when the crankshaft is located in an angular position between 45 ° and 20 ° before the angular closing position of the exhaust port, and in that the fuel injection pressure and the orientation of the spray axis are determined as a function of the gas circulation in the chamber combustion to obtain a substantially stoichiometric air / fuel mixture in the region of the spark plug at the time of ignition.
• the opening angle ⁇ of the jet limited to 75 ° makes it possible to form the fuel droplets in a limited area of the combustion chamber where the gases have a particular speed profile, and above all avoids the spraying of droplets against the walls of the combustion chamber, which would increase pollutant emissions.
• the fact of starting the injection of the fuel at least 20 ° before the closing of the exhaust lights, that is to say in advance compared to the prior direct injection devices in which the injection generally begins when the exhaust light is closed to prevent the passage of fuel droplets towards the exhaust, increases the time the fuel droplets mix with the fresh gases and the vaporization of the fuel, so as to obtain a more homogeneous air / fuel mixture time of ignition.
• the orientation of the spray axis included in the values of the first angle ⁇ and the second angle ⁇ mentioned reduces the passage of fuel through the exhaust port during the compression phase, despite the early injection of the fuel.
• This adaptation must be made as a function of the gas circulation in the combustion chamber which can be determined by numerical simulation. From the profile of the gas stream lines in the combustion chamber, which is substantially constant during the intake / compression phase, it is possible to adapt the orientation of the spray axis so that that the fuel droplets sprayed by the injector meet gases flowing against them.
• the fuel injection pressure is variable depending on the engine speed and / or engine load, in order to obtain an optimal reduction in pollutant emissions over the entire engine operating range;
• the fuel injection pressure is between 50 and 150 bars;
• the fuel injection pressure is adjusted to different values according to an engine speed / load map;
• the fuel injection pressure is constant over the entire operating range of the engine, the engine preferably having a displacement of at most equal to 125 cm 3 , to reduce pollutant emissions with a relatively simple injection system;
• the injector is disposed in a bore of the cylinder head oriented along a given axis and in which the spray axis forms a non-zero angle ⁇ with said axis of the bore;
• the injector is arranged through the cylinder head at the level of the first diametrical plane, which allows it to be mounted in a small displacement engine; fuel injection begins when the crankshaft is located in an angular position included between 40 ° and 30 ° before the ang
• FIG. 1 is a simplified view in section on a diametrical plane the cylinder, a two-stroke direct injection engine produced according to the invention
• - Figure 2 is a simpli sectional view along the line II-II of Figure 1
• FIG. 3 is a view obtained by numerical simulation representing the gas flow lines in a two-stroke engine
• - Figures 4 to 6 show the propagation of the fuel jet and the evolution of the region where a substantially stoichiometric mixture is obtained in an engine produced according to the invention between the start of injection and the time of ignition.
• identical references have been kept to designate identical or similar elements.
• FIG. 1 a section of a single-cylinder two-stroke engine provided with a direct injection system.
• the structure of this engine, excluding the injection device, is known and in all respects similar to the structure of a two-stroke carburetor engine produced in large series today.
• This structure includes a pump casing 2, inside which a crankshaft 3 is rotatably mounted.
• the crankshaft 3 is connected to a piston 4 by means of a connecting rod 5.
• the piston 4 has a bottom 4a, a head 4b provided with sealing segments and a skirt 4c.
• the bottom 4a of the piston may be flat as in the mode of shown or slightly curved realization.
• the piston 4 is movable in a cylinder 6 along the longitudinal axis X of the cylinder.
• the wall 6a of the cylinder is provided with intake lights (7, 8) and an exhaust light 9. More particularly, the intake lights comprise a main light 7 disposed opposite the exhaust light 9 and four additional intake lights 8, called scanning lights, which are arranged on either side of the main intake light.
• the intake and exhaust lights could have other known configurations, such as for example a single intake light, scanning lights 8 arranged in a non-symmetrical manner with respect to the main light 7 or even multiple exhaust lights 9.
• the end of the cylinder 6 opposite the piston 4 is closed by a cylinder head 10, substantially hemispherical in the embodiment shown, and provided in known manner with a spark plug 11.
• the bottom 4a of the piston, the internal wall 6a of the cylinder and the internal face of the cylinder head 10 delimit the combustion chamber 12 of the engine.
• Fresh gases are admitted into the pump casing 2 through an intake duct 15, in particular under the effect of the vacuum created therein when the piston 4 rises towards the cylinder head 10, that is to say during the admission / compression time.
• the fresh gases contained in the pump casing 2 are transferred by a transfer channel 16 to the intake ports (7, 8).
• the intake duct 15 can, in known manner, be fitted with non-return valves and / or be masked by the flanges of the crankshaft to prevent a backflow of fresh gases through the intake duct during the combustion time / exhaust.
• the intake lights (7, 8) are located at. a longitudinal distance from the cylinder head 10 greater than the exhaust port 9, so that they are closed by the piston 4 before the exhaust port 9 during the intake / compression phase.
• the exhaust port 9 is closed by the piston 4 from a certain angular position of the crankshaft, which is called the angular position of closing the exhaust port or even angle closing the exhaust. This angular position is precisely defined by the structure of the motor.
• Two-stroke engines with such a structure are well known and can be produced in very large series at a particularly competitive price. Their displacement varies quite significantly depending on their use. For example, to motorize portable tools such as a chainsaw or a hand-held brushcutter, the displacement is generally between fifteen and forty cubic centimeters while to motorize a two-wheeled vehicle of the moped, motorcycle or recreational vehicle type, the displacement generally varies between 50 cm 3 and 400 cm 3 . However, the total displacement of the engine can be even greater in the case of a multi-cylinder engine.
• a first diametrical plane of the combustion chamber is defined, which comprises the longitudinal axis X of the cylinder and which is centered on the exhaust port 9.
• the first diametrical plane must be centered on a fictitious light having a geometric surface equivalent to all of the surfaces of the exhaust lights.
• This first diametral plane corresponds to the section plane of the embodiment shown in FIG. 1 and its trace (Pl-Pl) is visible in FIG. 2.
• a second diametral plane is also defined which is perpendicular to the first diametral plane (Pl- Pl) and the trace of which (P2-P2) is visible in FIGS. 1 and 2.
• the second diametral plane (P2-P2) delimits a first portion of the internal face of the cylinder head 10, including the second diametral plane, which s extends towards the main intake lumen 7.
• the spark plug 11 is arranged in this first portion of the cylinder head, that is to say that the spark plug well must open into this region, either at an angle with the longitudinal axis X as in the embodiment shown, either by being collinear or coincident with the longitudinal axis X.
• the engine 1 is equipped with an injection device comprising an injector 20 adapted to spray liquid and pressurized fuel in the room re combustion 12 along a spray axis P.
• the injector 20 is arranged in a second portion of the cylinder head complementary to the first portion of the cylinder head, that is to say that the spray end of one injector 20 opens into the second portion of the internal face of the cylinder head. More particularly, as is apparent from FIGS.
• the injector 20 is arranged in the cylinder head at the level of the first diametrical plane (Pl-Pl) centered on the exhaust, to allow its mounting in a small displacement engine.
• the spray axis P defined by the axis of symmetry of the fuel jet created by the injector, forms a first angle ⁇ which is measured from a transverse plane (TT) of the cylinder, that is to say perpendicular to the longitudinal axis X.
• TT transverse plane
• the spray axis P also forms a second angle ⁇ , visible in FIG.
• the spray axis P having the first and second angles ⁇ , ⁇ , included in these values is generally directed towards the half-portion of the cylinder opposite the exhaust port.
• the fuel jet has in the embodiment shown a conical shape with a symmetry of revolution about the axis P, but it is possible to use a fuel jet of more complex shape, such as for example a jet having a cross section transverse oval.
• the opening angle ⁇ of the fuel jet which is defined by two opposite edges of the droplet jet, must be between 15 and 75 ° in order to be able to be directed towards a relatively localized area of the combustion chamber, and above all, so that the droplets do not directly reach the walls of the combustion chamber, which would have a very unfavorable effect on pollutant emissions.
• the injection device of course comprises a control device, not shown, which makes it possible to control the time when the injection must start as well as the duration of the latter.
• the control device is connected to means for determining the angular position of the crankshaft to send a signal to open the injector 20 at an appropriate time, and to means for determining the operating parameters of the engine, such as for example an engine speed sensor and / or a load sensor to determine the duration of the injection and, consequently, the quantity of fuel injected.
• the control device acts on the injector 20 so that, at least for certain operating ranges, the injection of fuel begins when the crankshaft is in an angular position between 45 and 20 ° before the closed position of the exhaust port, and preferably in an angular position between 40 and 30 ° before the closing angle of the exhaust. This injection is relatively early, since it begins when the exhaust gases are still discharged to the exhaust port.
• the injection pressure and the orientation of the spray axis P are preferably determined using a digital simulation of the circulation of gases in the combustion chamber during the intake / compression phase.
• the opening angle ⁇ due to the compromise between the opening angle ⁇ and the injection pressure (momentum of the jet), the fuel particles near the cylinder head are not yet finely atomized and their kinetic energy is high, so that the gas flows flowing near the injector 20 have little effect on the propagation of the jet in the combustion chamber 12.
• the second angle ⁇ of the spray axis P must be substantially zero.
• the angle ⁇ should be more or less pronounced depending on the importance of this vortex movement, so that the propagation of the jet is as much as possible against the flow fresh gas.
• the positive or negative value of the second angle ⁇ is of course determined as a function of the direction of rotation of the vortex movement of the gases.
• the injection pressure must also be adapted as a function of the circulation of gases in the combustion chamber. This injection pressure must not be too high because it must be avoided the projection of fuel droplets directly on the wall 6a of the cylinder or on the bottom 4a of the piston. However, this pressure must be high enough for the fuel droplets to reach a region where they will meet flows of gas circulating against the current and not to be entrained towards the exhaust port 9 by flows of gas circulating along of the cylinder head wall 10.
• the suitable injection pressure can be determined using a gas velocity diagram, which is also obtained by numerical simulation.
• This velocity diagram consists of vectors oriented along the current lines and of more or less important length as a function of the speed of the gases at the point considered.
• the jet has a frustoconical shape which has a symmetry of revolution around the axis P.
• the opening angle ⁇ of the jet is approximately 50 °.
• the curves 23 indicate the outline of the zones of the combustion chamber where there are different values of ⁇ (Lambda), ⁇ being defined by the ratio between the proportion of air and fuel actually present, and the proportion of air and theoretical fuel which is necessary to have a stoichiometric mixture.
• ⁇ Limbda
• a mixture of air and fuel is said to be stoichiometric when the oxidation of the C-H chains is ideally consumed at one hundred percent.
• a region of the combustion chamber where there is a value ⁇ equal to 1 therefore means that the air / fuel mixture is stoichiometric therein.
• the region defined by the contours 23 is slightly offset towards the exhaust port relative to the spray axis P, but however, this portion of mixture is not entrained up to the exhaust port 9
• the large amount of movement of the injected fuel drives it towards the half-portion of the cylinder located on the side of the intake ports (7,8).
• the situation shown in Figure 5 corresponds to around the time when the exhaust light is closed, about forty degrees after Figure 4. In this situation, the amount of movement of the fuel is canceled out by the amount of movement of the fresh gases, the movement continues although the intake lights are closed. Note that the fuel injection can be extended after closing the exhaust port 9.
• the injection pressure varies as a function of the speed or of the engine load, or as a function of these two parameters. This variation of the injection pressure can be controlled in a known manner by the injection device.
• the injection device can be connected to an engine speed sensor and an intake gas throttle opening sensor, and include pressure regulation means prevailing in a pressurized fuel accumulator.
• pressure regulation means prevailing in a pressurized fuel accumulator.
• the injection control device is also suitable for controlling the injection duration so as to inject only the quantity of fuel required.
• the injection pressure can vary continuously over the entire operating range of the engine, or according to different discrete values according to a speed / load map of the engine.
• small-displacement engines that is to say with a displacement of approximately 125 cm 3 or less, it is possible to adopt a constant injection pressure over the entire operating range. engine while having a significant reduction in pollutant emissions and consumption.
• the embodiment shown in the different figures corresponds to a two-stroke engine comprising a main intake light, four scanning lights and an exhaust light arranged symmetrically with respect to the first diametrical plane (Pl-Pl), but it will be clear to those skilled in the art that the injection device according to the invention can be adapted to a two-stroke engine comprising a different number of lights, or arranged in a non-symmetrical manner, as well as to a multi-cylinder two-stroke engine.

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• Engineering & Computer Science (AREA)
• Chemical & Material Sciences (AREA)
• Combustion & Propulsion (AREA)
• Mechanical Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Combustion Methods Of Internal-Combustion Engines (AREA)
• Fuel-Injection Apparatus (AREA)

Applications Claiming Priority (2)

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• 2003
  • 2003-12-31 FR FR0315612A patent/FR2864578B1/fr not_active Expired - Fee Related
• 2004
  • 2004-12-28 CN CNB2004800394050A patent/CN100489282C/zh not_active Expired - Fee Related
  • 2004-12-28 EP EP04817611A patent/EP1706612A1/de not_active Withdrawn
  • 2004-12-28 WO PCT/FR2004/003400 patent/WO2005073533A1/fr not_active Application Discontinuation
  • 2004-12-28 BR BRPI0417886-6A patent/BRPI0417886A/pt not_active IP Right Cessation
  • 2004-12-28 US US10/584,987 patent/US20090139485A1/en not_active Abandoned

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