FR2862343A1 - Combustion method for reciprocating engine, involves mixing comburant charge and fuel charge by diffusion near top dead center of piston for supporting diffusion flame with the mixed charges in contact - Google Patents

Abstract

The method involves introducing fuel in a zone (G1) of a cylinder for creating a homogenous recycled waste gas and fuel vapor mixture. A comburant charge in a zone (G2) and the fuel charge are separately heated to above the threshold of auto-ignition by compression. The charges are mixed by diffusion near the top dead center of the piston for supporting a diffusion flame with the mixed charges in contact.

Description

The present invention relates to a combustion method for an engine

alternative.

  The method provides for maintaining or introducing into the cylinder a load of recycled flue gases and introducing a charge of fresh air and keeping them separate during compression. Preferably the rate of recycled flue gas is sufficient to suppress the formation of NOX, for example greater than 30% of the total mass of gases in the cylinder.

  The fuel is distributed in the flue gas charge before or during the compression to obtain at the end of compression a fuel mixture where the vapor concentration is substantially homogeneous and where the concentration of flue gases is everywhere sufficient to limit the flame temperature below the NOX formation threshold, regardless of the oxygen supply.

  The combustion develops at the rate of mixing by diffusion of the carburized charge into the fresh air charge during transfers between the cylinder and the combustion chamber near the top dead center.

  The absence of local fuel accumulation in the reactive zone ensures particle-free combustion.

  Problem not solved by the prior art.

  In compression-ignition engines, efforts are made to homogenise the oxidizing charge composed of fresh air and recycled flue gases in order to limit the local flame temperature to the threshold of NOX formation.

  The fuel is usually introduced as a high-level fog when the gaseous charge has reached a temperature that allows rapid self-ignition.

  Despite improvements in common rail injection devices, this method creates local fuel accumulations that generate particles.

  In addition the small premixed areas come on with an unpleasant knock in urban traffic.

  In recent years, other methods of introducing fuel into the homogeneous gaseous feed have highlighted the possibility of eliminating NOX and particles at the source.

  They consist in creating during filling and / or during compression a more or less homogeneous premix of oxidizing gas and fuel vapor which ignites massively by self ignition at the end of compression. These processes are known under the acronym HCCI (Homogeanous) Charge Compression Ignition).

  Indeed, in a perfectly homogeneous mixture of air, more or less cooled flue gas and fuel vapor whose richness is lower than the stoichiometry, we can say in all respects: That every molecule of fuel is surrounded by enough oxygen for a total combustion without formation of soot.

  That the oxidizer and the fuel are heated simultaneously during the compression up to the threshold of auto-ignition without overheating of the oxidizing medium.

  That the presence at all points of gas not participating in the reaction makes it possible to maintain everywhere the temperature below the threshold of NOX formation.

  Alas, the implementation of these processes is limited by the explosive nature of auto-ignition when it occurs simultaneously in all points of a volume.

  The self-ignition is progressive only at low very dilute loads where it starts at certain discrete points distributed in the mass whose preoxidation was initiated early by active radicals present in the recirculated gases, by their order of arrival in the oxidizer or by small temperature gradients.

  After ignition, the kinetics of combustion due to compression heating can no longer be controlled for average effective pressures greater than 8 bar where the noise level becomes unacceptable.

  The other difficulty is to put the ignition at the TDC (top dead center). This imposes to act on the slow oxidation time, that is to say on the history of the carburized charge. Exercise is possible stabilized but perilous in the rapid transients of automotive engines.

  In addition, the development of cold flames promotes the formation of CO and HC which will be difficult to oxidize in the cylinder given the low temperatures at the end of the cycle, which are, moreover, insufficient for turbocharging.

  In conclusion it is very difficult to simultaneously control the initiation and development of the combustion of a perfectly homogeneous charge.

  Turbocharging makes it possible to recycle a large portion of the flue gases throughout the engine's operating range, as shown by the patent application filed in France on March 26, 2003 under the number 03 03728.

  The object of the present invention is to obtain at all the engine loads NOX-free combustion and NOX-free combustion of particles by a new spaciotemporal sequence of bringing into contact the species that will participate in the combustion.

Description of the invention

  The subject of the invention is a combustion method for an alternative engine intended to operate with a high rate of recycled flue gases, characterized in that during the compression phase the gaseous mass contained in the cylinder comprises an essentially occupied zone during any compression by recycled burned gases where the residual oxygen concentration is insufficient to allow early auto-ignition.

  An area that contains substantially all of the fresh air charge.

  The fuel is introduced into the first zone to create a mixture of burnt gases and fuel vapor as homogeneous as possible at the end of compression.

  The fresh air oxidizing charge and the fuel charge are heated separately by the compression above the self-ignition threshold.

  The two zones are diffusion mixed in the vicinity of the top dead center of the piston to maintain a diffusion flame with the contacted products.

  The invention also relates to engines adapted to this method.

  Unlike the prior art in which the mixture of fresh air and recycled flue gas present in the cylinder is homogeneous at the end of compression, the present invention provides for limiting the mixing zone as much as possible to conserve until the end of the compression a zone filled with burnt gas containing only the residual oxygen of the previous cycle and a zone filled with fresh air.

  In the mixed intermediate zone, the oxygen concentration therefore varies between the residual value of the preceding combustion and that of the fresh air.

  Unlike the prior art where the fuel is introduced into an oxidizing mixture where the oxygen concentration is sufficient to ensure oxidation by local diffusion, the present invention provides for introducing the fuel into the core of the gas-filled zone. burned slightly oxygenated.

  A more or less stratified mixture of burnt gas and fuel vapor is homogenized by heating up to the end of the compression in a zone of the cylinder while the fresh air and the mixing zone heat up in a other part of the cylinder.

  The fuel mixture must be organized so that, at the end of compression, the dilution of the fuel vapor by the flue gases is everywhere sufficient to prohibit the formation of NOX in a locally stoichiometric combustion.

  Schematically the prior art diluted by flue gases all the oxygen charge before introducing the liquid fuel. The local temperature is limited by the mass concentration of oxygen whatever the local fuel concentration created by the injector that accumulates fuel around the droplets by generating particles.

  In contrast, the present invention dilutes all fuel vapor with flue gas before introducing the fresh oxygen into the reaction zone.

  Local temperature is limited by the low local fuel concentration that simultaneously eliminates NOX formation and rich particle generating points.

  At the end of the compression, the temperatures of the carburized and oxidizing zones are sufficient for an autoignition to be triggered as soon as diffusion of the hydrocarbon molecules and the oxygen molecules is brought about without any major premix formation.

  Combustion can start by self-igniting the carbureted premix, which adds to the compression to activate the products to be burned.

  The residual oxygen concentration of the carburetted zone is sufficiently low that the possible auto ignition of the carburized premix develops on a silent HCCI mode.

  The possible ignition point of the premix can be controlled by the injection point, the richness, the compression ratio, the temperature of the recycled gas or any other known means to control the HCCI process.

  The main combustion develops in the vicinity of the top dead center at the rate of the turbulent diffusion of the carburized charge in the oxidizing charge following the flushing of the cylinder gases in the combustion chamber caused by the movement of the piston.

  This mixing process must be fast and complete to ensure complete oxidation of the fuel. It is advantageous to generate the mixing energy during the filling phase by communicating to the gaseous load a rotational kinetic energy which will degrade in turbulence during the centripetal transfer in a combustion chamber of a diameter much smaller than the bore.

  If the meeting between the oxidizing gas and the carburetted gas takes place at the periphery of the chamber in this rotational movement, the gases burned at high temperature evacuate towards the axis of the chamber to leave the periphery to fresh reaction products. The mixing phenomenon is thus accelerated by combustion.

  An additional advantage of this mechanism is to concentrate the hot gases at the heart of the load and to limit heat losses to the walls of the working chamber.

  The invention may also have the following characteristics. Preferably, the fuel is introduced in the form of a mist propelled by a high-pressure injector towards the zone of the flue gases when the latter has reached a temperature sufficient to vaporize the liquid droplets.

  Volatile fuel can be injected into the intake ports during and at the rate of introduction of recycled flue gases.

  For example, the recycled gases in the zone contain the majority of unburnt gases from the previous cycle.

  The gases recycled from the zone contain the gases having, for example, been cooled in contact with the walls of the working chamber during the preceding cycle.

  In an advantageous embodiment, the working chamber has a symmetry of revolution about the axis of the cylinder and the combustion chamber is a cavity coaxial with the cylinder located in the piston and / or the cylinder head, and whose diameter is less than that of the cylinder (50 to 60%). The recycled gas zone can be rapidly rotated around the cylinder axis and, at the end of compression, it is completely transferred to the combustion chamber while the fresh air charge is still in the combustion chamber. the annular space between the piston and the cylinder head.

  In one embodiment, the zone of the recycled gases can be located against the piston and the combustion bowl is a cavity arranged in the piston.

  In another embodiment, the cylinder head has a protrusion which enters the combustion chamber at the top dead center of the piston so as to leave a variable annular clearance depending on the position of the piston to maintain a transfer speed substantially independent of the position of the piston. piston.

  Alternatively, the charge of fresh air is concentrated against the cylinder, the burned gas charge occupies the central zone of the cylinder and the combustion bowl is located half in the piston and half in the cylinder head.

  Ignition may occur at the periphery of the combustion chamber when fresh air begins to oxygenate the carburetted charge.

  Ignition can also occur within the carburetted charge when it reaches the auto-ignition temperature and the fresh air charge begins to enter the combustion chamber.

  Preferably, the recycled gases are hot and the ignition occurs immediately after the injection of fuel therein a little before the top dead center.

  The stratification of the gaseous feedstock can be obtained by successively introducing the zones into the cylinder via the same orifices and preferably the zone of the recycled gases first. The separation of the zones can be prepared in an oblong stratification chamber external to the cylinder opening on one side in the air supply manifold and the other in the intake duct of the cylinder head.

  For example, in a motor adapted to the 4-stroke cycle, the lamination chamber is supplied with burnt gases through an exhaust pipe of the same cylinder, separate from the turbine supply duct, via a refrigerant and the intake duct. .

  For example, in a motor adapted to the two-stroke cycle, the gas cooler is located in the lamination chamber on the side of the cylinder head, an anti-return valve located between the lamination chamber and the air collector prohibits any flow from the chamber to the manifold, - the inlet ports are open before the exhaust ports to relax the gases in the lamination chamber via the refrigerant filled with air, and - the exhaust ports are then opened to allow the compressed stratified charge sweeps the cylinder through the intake ports and re-supplies fresh air through the check valve. Operation of the Invention The self-ignition of the very rich premix, when it exists, develops without knocking because of the lack of oxygen to accelerate the reaction in the ballast of burnt gas and excess fuel.

  It develops without NOX formation due to the very low oxygen concentration.

  It develops very below the soot formation temperature in a medium free of local fuel accumulation.

  The main combustion by diffusion does not form NOX because the dilution by flue gas of the fuel vapor limits the local temperature even in excess of oxygen.

  The main combustion by diffusion does not form particles because the fuel vapor has had time to disperse in the burnt gas mass by eliminating the accumulation points.

  The main combustion is not noisy because it develops at the rate of gaseous diffusion of the oxidizing charge in the carburetted charge.

  The autoignition of the carburetted charge must occur before its mixture with the oxidizing charge is sufficiently advanced to be the seat of a detonating combustion premix.

  The possible combustion in HCCI mode of premixed oxygen in the carburetted charge is associated with the movement of the piston to heat the oxidizing charge by compression above the autoignition threshold.

  The process implies that the gaseous charge remains stratified during compression to avoid the meeting of oxygen and fuel before the piston approaches top dead center.

  The gaseous charge trapped in the cylinder is constructed from the following components: The fresh air taken from the atmosphere for each cycle, for example, at about 350 K, The flue gases from previous cycles retained in the cylinder at about 900 K For example, if appropriate, the flue gases of the preceding cycles recirculated in the cylinder after external cooling to, for example, about 450 K.

  In a rotational movement about the axis of the cylinder, these three components are advantageously laminated radially with the fresh air against the cylinder, the burnt gases cooled inside the fresh air layer and the column of hot gases held in the center of the cylinder.

  At the end of compression, the mixtures between layers constitute a radial gradient of maximum oxygen concentration against the cylinder and low in the center, as well as a radial gradient of low temperature at the cylinder and maximum at the center.

  The combustion according to the invention is essentially organized during transfers between the cylinder and the combustion bowl created by the piston on, for example, 20 to 30 degrees of crankshaft on either side of the top dead center.

  The fuel introduction process depends on its volatility and flammability.

  The gas oil is advantageously atomized at high pressure early during the compression stroke in the center of the cylinder filled with burned gas too low in oxygen to trigger a top-dead high-explosive combustion.

  Under these conditions, the possible auto-ignition of the premix is regulated by the injection start angle which fixes the origin of the preoxidation phenomena.

  The mass of recycled flue gas must be sufficient to maintain the flame temperature everywhere below the thermal NOX formation threshold.

  It is advantageous to give the recycled gases a high degree of turbulence in order to homogenise the carburised charge after the injection of the fuel and to accelerate the subsequent diffusion of the oxygen during the transfers of gas between the cylinder and the combustion chamber in the vicinity of the neutral position. high.

  When the recycled gases are too hot to avoid early auto ignition the fuel must be injected later in the flue gas, for example at the beginning of the period of transfer of the oxidizing charge into the combustion chamber. At high temperature the vaporization is almost instantaneous and the mixing between the vapor and the residual gases can take place immediately before the diffusing penetration of the oxygen in the reaction zone. The organization of the mixture between the fuel and the flue gases is, in this case, essentially provided by the injector.

  The charge of fresh air admitted to oxidize the injected fuel is kept separate from the carburetted charge to the vicinity of the top dead center by a buffer zone containing fresh air outside and gases burned inside.

  During compression, the carburised filler, the oxygenated filler and the buffer zone heat up separately to the auto-ignition temperature.

  To limit the temperature of the nitrogen of the oxidizing charge, it is advantageous to bring the fuel mixture to a higher temperature to reach the threshold of autoignition associated with the presence of the preoxidized active radicals. This strategy takes into account the difficulty of cooling the flue gases to the same level as the fresh air.

  A little before the top dead center, the carburetted zone ignites possibly in the HCCI mode. Immediately afterwards, the two charges are mixed by the movement of the piston at the rate of the gas diffusion generated by the internal aerodynamics in the reaction zone. The main combustion develops at the rate of this diffusion.

  After the possible autoignition of the premix very poor in oxygen, the release of energy is punctuated by the development of the diffusion between the two reactive charges which must be organized near the top dead center.

  Turbulent diffusion requires a velocity gradient between the carburetted gases and the oxidizing gases. This speeding can be generated by the movement of the piston, the filling process, the injection of fuel and the local expansion of the gases due to combustion.

  The solutions are numerous and depend on the structure of the stratification generated by the transfers in open and closed phases.

  This process assumes that the combustion is close to the stoichiometry at least in the zone of the chamber which will be recycled and irrigated and that the carburized charge mixes little oxygenated zone until the end of the compression stroke. The possible unburnt present in this area can be recycled.

  On the contrary, the zone of the chamber that will be evacuated, for example, to a turbine may be more oxygenated to eliminate unburned in the exhaust gas.

  It is therefore preferable that the gases to be recycled are directed to a circuit independent of the turbine supply circuit.

  At the end of the relaxation stroke there are two zones in the cylinder A zone, low in unburned hydrocarbons which may contain residual oxygen for possible post-treatments. It will be relaxed in the turbine. Preferably, this zone does not comprise burnt gases that have been cooled on the walls of the working chamber.

  An area which optionally comprises unburnt hydrocarbons and which preferably comprises the burnt gases which have been cooled in contact with the walls. It will be retained in the cylinder or cooled externally for later recycling to oxidize the unburnt. This area will be irrigated by the new fuel load.

  It is advantageous to organize the combustion chamber to maintain the rich zone that will be recycled against the walls of the working chamber to include the heat losses of the closed cycle in the losses by cooling the recycled flue gases. warmer the gaseous charge is primarily discharged to the turbine.

  The delicate phases of the process are successively: The generation of the stratification and the maintenance during compression of the separation between the charge of burnt gas and the oxidizing charge.

  The creation of an almost homogeneous mixture between flue gas and fuel vapor.

  and total of the carburetted load at top dead center generating that some to implement in the 4-way and general cycles are as follows: at the homogeneous approach where the gases simultaneously for all the cylinders common with the fresh air, the The laminated approach requires cylinder-by-cylinder metering of the recycled gases.

  Unlike fresh air that is delivered by a compressor common to all cylinders, the gases are emitted by each cylinder individually during the precise and repetitive emptying process. The present invention provides for using this process to meter the amount of gas directed to the receiver cylinder.

  The geometry of the supply and discharge circuits of the rolls must be identical to ensure a balanced dosage of the recycled gases and the fresh air. 15

  Oxidative diffusion in combustion.

Generation of stratification.

  The methods are numerous for lamination and will not be described here after easy 2-step examples.

  The principles Unlike recycled are dosed in a fast mixer charge The parasitic mixing zone between the fresh air and the recycled gases develops substantially in proportion to the time of presence in the cylinder.

  The two-stroke cycle is more conducive to stratification than the four-stroke cycle because the coexistence time of the two charges in the cylinder is about three times shorter.

  The simplest solution for recycling hot gases is to hold them in the cylinder from one cycle to another.

  A precise dosage of the retained mass can be ensured by the setting of the valves which can be set in operation by a camshaft dephaser.

  In a four-stroke cycle the early closure of the exhaust is accompanied by a useless compression phase relaxation of the recycled gases generating friction losses.

  In a two-stroke cycle, it suffices to under-sweep the cylinder to retain burnt gases from the previous cycle.

  To stratify the load, the fresh air must be directed towards a part of the cylinder avoiding as much as possible mixing with the gases already present.

  The disadvantage of this method is the high temperature of the recycled gases which may be too high to eliminate NOx.

  This solution can be viable in a two-cycle very supercharged asymmetric high expansion rate to decrease the temperature at the end of relaxation and low compression rate to reduce heating during compression.

  The fuel is advantageously injected at the beginning of compression in order to cool the gases before compressing them.

  In general, the gases must be cooled outside the cylinder.

  In order to be able to recycle the polluted zone of the combustion chamber, only stratification processes will be described where the traceability of the recycled gases is saved between the emitting cylinders and the receiving cylinders.

  This implies that the emptying of the cylinder takes place in two distinct phases to the turbine and to the recycling circuit by preferably different orifices.

  It is very difficult to install stratification by simultaneously introducing fresh air and flue gases into the cylinder. The processes where the gases and the air are introduced successively and particularly where the gases are introduced first will therefore be preferred.

  The stratification could then be generated during filling by successively opening separate inlet ports for recirculated flue gases and for fresh air. The passage from one orifice to another, however, involves a mixing phase where one valve closes while the other opens.

  In order not to interrupt the filling and to take advantage of the entire intake section, it is more advantageous to prepare the stratified charge outside the cylinder and to introduce it without discontinuity through the same orifice which will successively pass gases. recycled then fresh air for example.

  To achieve this object, the invention advantageously provides an individual lamination chamber in the intake duct of each cylinder. Although a two-stroke engine of axisymmetric architecture would allow optimum application of the method, the invention will be described on a classic 4-stroke engine for ease of presentation.

  Reference is now made to the following description,

  by way of nonlimiting example and with reference to the appended drawing, in which: FIGS. 1 and 2 show a 4-stroke engine used in the invention; FIGS. 3 to 9 show schematically aerodynamics in meridian section; 1 during operation, FIGS. 10 and 11 show schematically the diffusions for two forms of combustion chambers, FIG. 12 represents a motor in a simplified embodiment.

  Referring now to Figure 1 which shows a 4-stroke engine, 4 cylinders and 4 valves per cylinder operated by two camshafts.

  The diametrically opposite intake valves A1, A2 are associated with a directional channel to create air jets tangent to the cylinder and very lying on the yoke plane to generate a helical flow of revolution that invades the cylinder from the breech, for example, in accordance with the French patent application No. 03 03728. A first camshaft AaCl actuates an exhaust valve And which

  feeds the turbine and an inlet valve Al.

  The other camshaft A to C2, preferably out of phase with the first, actuates an exhaust valve Er which feeds the recycling circuit and the other intake valve A2.

  The laminating chamber 1 with a volume close to the unit cubic capacity 2 preferably has an oblong shape to limit the contact surface 3 between the gases and the fresh air.

  The chamber 1 is placed between the intake ports 4 of the cylinder and the cooled air intake manifold 5 of the compressor 6.

  During each cycle, the chamber 1 undergoes a filling phase and a draining phase in the cylinder with which it is associated.

  It fills with fresh air through its junction 7 with the intake manifold 5 and cooled flue gases from the same cylinder through its junction 8 with the intake ports 4.

  Its flue gas supply must be repetitive from cycle to cycle and identical for all cylinders.

  We have seen previously the advantage of a cylinder emptying in two stages fixed by the offset opening of two exhaust ports respectively supplying the turbine and the recycling circuit. The phase shift between the valves can be adjusted in operation by a camshaft dephaser for dosing the mass of gas to be recycled.

  To maintain this dosage up to the receiver cylinder, it is advantageous to provide an individual recycling circuit comprising a refrigerant 9 per cylinder.

  An adjustment valve 10 located at the exit of the recycling orifice can replace or supplement the variable setting with the advantage of allowing to completely eliminate recycling during accelerations.

  An adjustable bypass 11 of the refrigerant 9 makes it possible to regulate the temperature of the recycled gases independently of their flow rate.

  A single organ can provide both functions. For example a cylindrical bush pierced with lights communicating with the inlet and the outlet of the refrigerant can be controlled in translation to adjust the flow rate and in rotation to adjust the temperature.

  The valves and bypass of all the cylinders are set simultaneously by a common control device.

  Referring now to Figure 2 which describes the movements of recycled gas in the ducts.

  The cylinder C1 is at the top dead center at the beginning of its filling stroke.

  The cooled gas charge is waiting in the lamination chamber 1.

  The hot gases to be cooled emitted during the preceding exhaust stroke occupy the entire volume between the valve Er and the intake valve A2.

  The cylinder C2 is at the bottom dead center where all the valves are closed.

  During the intake stroke the exhaust valves Et and Er being closed, the cylinder sucked through the intake valves the charge of cooled burnt gases waiting in the lamination chamber 1 followed by the charge of fresh air contiguous .

  The gases in the refrigerant are being cooled.

  The cylinder C3 is at the top dead center compression.

  The gases present in the refrigerant 9 continue their cooling by contracting. The boundary with the fresh air moves towards the refrigerant.

  The cylinder C4 is at the bottom dead center.

  The gases present in the refrigerant 9 complete their cooling by bringing the fresh air to the limit of the latter. The exhaust stroke that follows will push the boundary 3 to its position at the cylinder 1.

  Figures 3 to 9 schematically describe the aerodynamics internal to the cylinder during the combustion and expansion compression phases in a meridian section.

  If the intake ports are oriented tangentially to the cylinder with a small inclination on the yoke plane, the rotating gaseous charge approaches a stratification of revolution about the axis of the cylinder as shown in FIG. 3 The burnt gas charge G1 occupies the lower central part of the cylinder. The fresh air G2 occupies the upper peripheral part of the cylinder.

  Figure 4 shows the fuel irrigation of recycled gas during compression with its fuel rich zone Z1 and its poor zone Z2.

  FIG. 5 shows the situation at the beginning of combustion where the carburetted gases Z occupy the entire 22 'combustion bowl 12 located in the piston. It is at this point that the autoignition of the fuel mixture can possibly occur.

  FIG. 6 shows the diffusion combustion in the vicinity of the top dead center following the transfer of the fuel charge consisting essentially of fresh air G2, located in the annular space between the piston and the cylinder head in the combustion chamber full of burnt gases. Figure 7 shows the situation at the end of the expansion where the zone Z1 transformed after combustion and expansion can contain inbrûlés and the gases cooled by the walls while the transformed zone Z2 which contains an excess of oxygen is the hottest .

  The transformed zone Z2 will be evacuated first during the expansion of the gases towards the turbine via the valve Et.

  FIG. 8 shows the exhaust stroke where the transformed zone Z1 is discharged by the piston via the valve Er towards the recycling circuit by moving the cooled gases present in the refrigerant towards the lamination chamber 1 to take their place until next cycle.

  Figure 9 shows a section perpendicular to the cylinder axis of the reaction zone of Figure 6 where the combustion products are discharged to the center by centrifugation of the heavier carburetted gases.

  A simpler method is to supply gas to the lamination chamber through open intake ports during cylinder emptying. This involves placing the refrigerant in the lamination chamber.

  The gas charge goes back and forth in refrigerant during transfers.

  The disadvantage of the method is the short residence time of the gases in the refrigerant (during the closed phase of the cycle the refrigerant is full of air) as well as the heterogeneous cooling of the charge (the gases neighboring the arrival of air are much more cooled than the gases neighboring the valves.

  The advantage of the method is a precise dosage of the recycled mass.

  In a four-stroke cycle, the transfer sequence is as follows: During cylinder emptying, the flue gases are partially discharged to the turbine via the exhaust ports and partially to the refrigerant filled with fresh air through the ports. admission.

  After the evacuation of the gases, the cylinder successively re-sucks, via the intake ports, the burned gases from the previous cycle stored and cooled in the intake refrigerant and the fresh charge which replaces the gases supplied to the turbine.

  The intake and exhaust ports are open during the discharge stroke.

  During the suction stroke, the intake ports are open and the exhaust ports are closed.

  If the intake valves do not interfere with the piston, it is not necessary to close them at the top dead center.

  The percentage of recycled gas can be adjusted by the phase difference between the opening of the intake ports and that of the exhaust ports at the end of expansion by means of a camshaft angular phase shifter.

  In a two-cycle cycle, the transfer sequence is as follows: The recycled cooled flue gases must precede the fresh air to scan the flue gases intended for the turbine. The transfer sequence then comprises the following successive phases: fraction to recycle burnt gases to the gas refrigerant via the inlet ports.

  Return to the cylinder, through the intake ports, of the preceding gases cooled by the refrigerant to sweep a portion of the hot gases to the turbine via the exhaust ports.

  É Stratified introduction of the fresh charge via the refrigerant and the intake ports to complete the hot gas flow to the turbine via the exhaust ports.

  To accomplish this complex sequence in the short period allocated to scanning, (about 120 degrees crankshaft for a three-cylinder engine) the invention provides for utilizing the potential energy available in the end-of-expansion flue gases which is generally lost in the exhaust puff.

  To do this, the lamination chamber comprises the refrigerant and communicates with the air supply manifold via a non-return valve.

  To describe the transfer sequences we assume that: the purge air pressure delivered by the compressor is 3 bar the gas pressure at the turbine inlet is 2.5 bar the exhaust gas pressure at the end of expansion is 10 bar At the end of expansion, the inlet ports are open to communicate the cylinder filled with hot gases to 10 bar and the lamination chamber filled with fresh air at 3 bars isolated from the air intake duct by its anti-flap valve. return.

  The gases at 10 bars which relax and cool compress this air up to about 5 bars to occupy the closed cavity of volume equal to the sum of the cylinder and the lamination chamber.

  The volume of the refrigerant is set by these pressure conditions and the temperature of the gases cooled at the time of opening of the exhaust ports.

  The exhaust ports are then opened to communicate the overall volume at 5 bars with the turbine at 2.5 bars. The gases cooled to 5 bars sweep the hot gases present in the cylinder up to 3 bars where the anti-tamper valve The return opens to allow a new fresh charge to pass through, which propels the fresh charge stored in the cavity into the cylinder to complete the hot gas sweep up to 2.5 bars.

  If the refrigerant is of the tubular type it is possible to take advantage of the depression resulting from the setting of the speed of the gases to suck up the fresh charge via the nonreturn valve when the turbocompression is not primed.

  The flows are very fast considering the strong pressure drops between cavities.

  The refrigerant is alternately traversed by fresh air and recycled gases driven by the strong turbulence associated with fast flows that accelerate heat transfer.

  The tangential velocity induced in the cylinder during the sweep will be used in the closed phase to homogenize the carburized filler after the injection and accelerate the diffusion during combustion.

  During the closed phase of the cycle an acoustic back and forth can be maintained in the refrigerant to accelerate the cooling of the fresh charge pending.

  Generation of the mixture between the recycled gases and the steam of the fuel.

  To allow maximum time for the formation of the mixture, the fuel will be distributed in the burnt gas charge as soon as possible, preferably after the closing of the exhaust ports.

  For liquid fuels, the boiling temperature determines the optimum time and method for obtaining as homogeneous a mixture as possible at the end of compression.

  The sprayer will provide as homogeneous fog distribution as possible in the recycled feed.

  The turbulence of the recycled gases will complete the distribution of the fuel vapor during the compression stroke and especially during their centripetal transfer into the combustion bowl whose diameter is, for example, of the order of 50 to 60% of that of the cylinder and where the internal friction is very intense.

  The impacts of liquid fuel on the walls of the working chamber will be avoided.

  Gasoline, very volatile, or gaseous fuels can be injected into the intake ports simultaneously with the introduction of recycled gases whose temperature always exceeds 450 K.

  Gas oil, which is more difficult to spray, will be sprayed more or less later during the compression stroke depending on the temperature of the recycled gases.

  Beyond the temperature of the recycled gases generating an early autoignition of the fuel charge, the injection will take place immediately before the transfer of fresh air into the combustion bowl and the quality of the fuel mixture will rely largely on the injector.

  Diffusion of the oxidizing charge in the carburised charge near the top dead center.

  The rate of combustion is a function of the intensity of the diffusion between the products that enter the reaction zone, itself a function of the level of turbulence. The most efficient mechanism is to communicate to the recycled gases and to the fresh air a kinetic moment of rotation around the axis of the cylinder which generates a strong turbulence in their centripetal transfer towards the combustion bowl.

  It is also very important to quickly evacuate products during combustion outside the reaction zone. This occurs naturally when the latter is located at the periphery of the combustion bowl. Indeed the hot burnt gases are driven towards the axis of the bowl while the denser fresh products are centrifuged towards the periphery as shown in Figures 6 and 9.

  An optimal configuration is possible in radial stratification with half a combustion bowl in the piston and a half bowl of combustion in the cylinder head. The fresh air disk penetrating the equatorial plane of the reaction zone develops two zones of mixing with the carburized charge located in the upper and lower hemispheres of the combustion chamber.

  Figures 10 and 11 show two possible aerodynamic speeds according to the respective tangential velocities of fresh air and flue gases and the geometries of the chambers.

  The preferred geometry for maintaining the stratification in the cylinder and the kinetic energy of the load has a symmetry of revolution about the axis of the cylinder to receive rotational flows of revolution about this axis.

  In a four-stroke cycle, the classic architecture of a flat four-valve cylinder head associated with a combustion bowl located in the center of the piston makes it possible to approach an internal aerodynamics with symmetry of revolution between the end of the filling and the end of the evacuation of the cylinder.

  The intake ducts must generate jets tangential to the cylinder very lying on the cylinder head plane in order to form an axial stratification of the gaseous mass in rotation.

  At the end of the filling, the recycled gases are concentrated against the piston and the fresh air against the cylinder head.

  In a two-stroke cycle a coaxial valve architecture to the cylinder is best suited to the present process.

  It allows to locate the combustion chamber for half in the piston and half in the cylinder head.

  The working chamber is fed and emptied by an intake valve and an exhaust valve concentric to the cylinder and located in the cylinder head; The openings and closures may advantageously be out of phase with the motor shaft during operation in order to modulate the scanning angular duration as a function of the operating parameters. Once closed, the working chamber has a symmetry of revolution around the cylinder axis.

  The exhaust port is located in the center, the mass discharged to the turbine occupies the central and hot part of the cylinder, while the recycled mass occupies the cooled parietal area of the cylinder.

  In some cases, it may be advantageous to provide a circular prominence in the center of the cylinder head or the piston that enters the combustion chamber located in the opposite screw to increase and control the flushing speed generated by the movement of the piston during the transfer of the last charge.

  To limit the formation of the mixture, the fresh air is introduced into the cylinder after the burnt gases recycled in the form of a sheet tangential to the cylinder to form a torus oxygenated in rotation against the wall of the cylinder.

  The central portion of the cylinder closed by the piston, a central cavity of which constitutes a half-combustion chamber, is occupied by substantially oxygen-poor burnt gases.

  During compression the inert load occupies the central part of the cylinder while the fresh load is held against its wall.

  Once the compression has sufficiently heated the flue gases, the fuel is sprayed therein to form a mixture of fuel vapor and flue gas which is homogenized by penetrating into the half burning bowls.

  Towards the end of the compression, the carburized flue gases occupy the entire combustion bowl and the fresh air occupies the annular space limited by the cylinder, the piston face, the cylinder head sky and the outer surface of the cylinder. prominence of the breech.

  At the end of its compression stroke the piston transfers the oxygenated charge into the bowl full of carburetted gas to trigger the auto-ignition by total diffusion of the two charges.

  The combustion continues during the reverse transfer of the burnt gases from the bowl to the cylinder at the beginning of the expansion stroke by using the passage oxygen remaining in the game between the annular face of the piston and the head of the sky.

  For an implementation of the invention on a recirculating circuit motor common to all the cylinders, reference is made to FIG. 12, where the dosage of the recycled gases is ensured by identical nozzles 2 for all the cylinders.

  This method, however, does not allow total stratification because, at the end of filling, the fresh charge is introduced with the gas flow of the nozzle of the cylinder concerned. This corresponds to a loss of about 25% of the burned gas mass that will be carburized.

Claims (1)

32 Claims   1. A combustion method for an alternative engine designed to operate with a high rate of recycled flue gases, characterized in that during the compression phase: the gaseous mass contained in the cylinder comprises a substantially occupied zone G1 throughout the compression by recycled flue gases where the residual oxygen concentration is insufficient to allow early auto-ignition.   A G2 zone that contains substantially all of the fresh air charge.   The fuel is introduced into the zone G1 to create a mixture of burnt gases and fuel vapor Z that is as homogeneous as possible at the end of compression.   The oxidizing charge G2 and the fuel charge Z are heated separately by the compression above the threshold of auto ignition.   The Z zone and the G2 zone are diffusion mixed in the vicinity of the top dead center of the piston to maintain a diffusion flame with the products in contact.   2. Method according to claim 1 characterized in that the fuel is introduced in the form of a mist propelled by a high-pressure injector to the G1 area when it has reached a temperature sufficient to vaporize the liquid droplets.   3. Method according to claim 1 characterized in that a volatile fuel is injected into the intake ports during and at the rate of the introduction of recycled flue gases.   4. Method according to claim 1 characterized in that the recycled gases Zi of the G1 zone contain the majority of unburnt from the previous cycle.   5. Process according to claim 1, characterized in that the recycled gases Z1 of the zone G1 contain the gases which have been cooled in contact with the walls of the working chamber during the preceding cycle.   6. Method according to claim 1 characterized in that the working chamber has a symmetry of revolution about the axis of the cylinder and the combustion chamber is a coaxial cavity to the cylinder located in the piston and / or the cylinder head, whose diameter is less than that of the cylinder (50 to 60%).   7. A method according to claim 6 characterized in that the zone G1 is driven by a rapid rotational movement about the axis of the cylinder and that, at the end of compression, it is fully transferred into the combustion chamber while the charge of fresh air G2 is still in the annular space between the piston and the cylinder head.   8. The method of claim 7 characterized in that the G1 area is located against the piston and the combustion bowl is a cavity in the piston.   9. A method according to claim 8 characterized in that the cylinder head comprises a protrusion which enters the combustion chamber at the top dead center of the piston so as to leave a variable annular clearance depending on the position of the piston to maintain a speed of transfer substantially independent of the position of the piston.   10. The method of claim 7 characterized in that the charge of fresh air is concentrated against the cylinder, the burned gas load occupies the central zone of the cylinder and the combustion bowl is located half in the piston and for half in the breech.   11. The method of claim 1 characterized in that the ignition occurs at the periphery of the combustion chamber when the fresh air begins to oxygenate the carburetted charge.   12. The method of claim 1 characterized in that the ignition occurs within the carburetted charge when it reaches the auto-ignition temperature and that the charge of fresh air begins to enter the combustion chamber.   13. The method of claim 1 characterized in that the recycled gases are hot and the ignition occurs immediately after the injection of fuel therein a little before the top dead center.   14. The method of claim 1 characterized in that the stratification of the gaseous charge is obtained by successively introducing the G1 and G2 areas in the cylinder via the same orifices and preferably the G1 area first.   15. The method of claim 14 characterized in that the separation of the G1 and G2 areas is prepared in an oblong lamination chamber outside the cylinder opening on one side in the air supply manifold and the other in the intake duct of the cylinder head.   16.Procédé according to claim 15 adapted to the 4-cycle cycle, characterized in that the lamination chamber is supplied with burnt gas by an exhaust duct of the same cylinder, separate from the supply duct of the turbine, via a refrigerant and the intake duct.   17. The method of claim 15, adapted to the two-stroke cycle, characterized in that it comprises a gas cooler located in the lamination chamber on the side of the cylinder head, a check valve located between the laminating chamber and the air collector prevent any flow from the chamber to the manifold, - that the inlet ports are open before the exhaust ports to relax the gases in the lamination chamber via the refrigerant filled with air, and - the exhaust ports are then opened to allow the compressed stratified charge to sweep the cylinder through the inlet ports and to re-supply fresh air via the check valve.