FR3034467A1 - METHOD FOR COMBUSTING A CARBIDE MIXTURE OF AN INTERNAL COMBUSTION ENGINE - Google Patents

Abstract

The present invention relates to a method of combustion of a fuel mixture contained in the combustion chamber (18) of an internal combustion engine, said chamber being connected to at least one intake means (24) with a nozzle of intake (26) controlled by an intake valve (28) and with at least one exhaust means (30) with an exhaust manifold (32) controlled by an exhaust valve (34), and means for injecting (40, 44) at least one fuel. According to the invention, the motor operates in a cycle with an admission phase (A), with at least "n" periods of successive compression / expansion phases (C / D), where "n" is greater than or equal to two, and an escape phase (E).

Description

The present invention relates to a method of combustion of a fuel mixture of an internal combustion engine. It relates more particularly but not exclusively engines with direct fuel injection in the combustion chamber of these engines. This invention can also relate to internal combustion engines operating with two distinct fuels, said engines with concomitant fuel injection ("Dual fuel"), which combine a direct injection of fuel into the combustion chamber with an indirect injection of another. fuel in the intake manifold of the engine to achieve a fuel mixture to be introduced into the combustion chamber. Ignition of this fuel mixture is then carried out in a preferred manner at the time of the direct injection of fuel, through or not a system that controls the ignition.

This invention can also relate to engines equipped with a direct injection system that injects two separate fuels directly into the combustion chamber. Generally, these types of engines operate according to a "4T" cycle (four times) which is divided into four phases, an intake phase (A) during which an oxidizer, such as air, is admitted into the combustion chamber. , or an "air + fuel" mixture in the case where the engine is equipped with an indirect injection system, a compression phase (C) with the compression of air or fuel mixture, a relaxation phase (D) which results from the combustion of the fuel mixture and an exhaust phase (E) where the burnt gases are removed from the combustion chamber. These engines have the disadvantage of requiring a transfer of fluid (intake air or fuel mixture and burnt gases) which is penalizing given the work to be provided by the engine to move these fluids and allow them to enter the chamber. combustion via the intake valve or valves (for air or fuel mixture) or to be discharged from the combustion chamber via the exhaust valve or valves.

3034467 2 Valve actuation and fluid transfer (intake and exhaust) work costs energy and, for the vast majority of engine operating areas, reduces the work done by hot gases from combustion . It then follows a loss of overall performance of the engine. Another major disadvantage of these transfers is the case of engines for which the recourse to the external recirculation of burnt gases (EGR system: Exhaust Gas Recirculation) is necessary. In this case, the management of the amount of flue gas and its introduction into the intake circuit is complex and impacts the quantities of fluid admitted into the combustion chamber, thereby increasing the work to be performed. In addition, in the case of four-stroke engines, for a work phase useful for the production of the power delivered by the engine, three other phases are necessary.

15 This results in a certain irregularity of the engine torque, which the engine manufacturers try to limit: - By increasing the number of engine cylinders and cleverly shifting the "ignition of each cylinder" - By using the cycle "2T" (two stages): in this case, the four previously described phases take place on a single motor revolution, while for the "4T" motor, two motor revolutions are required. In addition, under certain operating conditions of these engines (very low load, idle, operation after a cold start, ...), the exhaust gas treatment system lacks efficiency essentially during temperature conditions. very cold outside. In this case, it is necessary to resort to devices that are equally complex and have an impact on the overall efficiency of the powertrain.

The present invention proposes to overcome the aforementioned drawbacks by means of a simple and economical combustion process.

For this purpose, the present invention relates to a method of combustion of a fuel mixture contained in the combustion chamber of an internal combustion engine, said chamber being connected to at least one intake means with a nozzle of intake controlled by an intake valve and with at least one exhaust means with an exhaust manifold controlled by an exhaust valve, and means for injecting at least one fuel, characterized in that the motor operates according to a cycle with an admission phase, with at least "n" periods of successive compression / expansion phases, "n" being greater than or equal to two, and an exhaust phase. After formation of a fuel mixture in the combustion chamber during the intake phase, the intake and exhaust valves can be held in the closed position and fuel can be injected into the combustion chamber, while the "n" periods of successive phases of compression / relaxation. The fuel mixture formed in the combustion chamber, during the compression / expansion phases, may comprise a minimum richness for the combustion of this mixture. The compression / expansion phase may be followed by an exhaust phase, when the fuel mixture contained in the combustion chamber may comprise a richness close to the stoichiometric.

During the intake phase, an oxidant may be introduced into the combustion chamber to produce a fuel mixture. During the intake phase, a fuel mixture can be introduced into the combustion chamber during the intake phase. During the intake phase, a mixture of a fluid and a fuel can be introduced into the combustion chamber, and another fuel can be injected into the combustion chamber at the end of each compression phase. /relaxation. The fuel can be a fuel injected into the combustion chamber.

The fuel may be a fuel injected into the combustion chamber admission means. The fuel may be a fuel injected into the combustion chamber intake means and the other fuel may be a fuel injected into the combustion chamber. The invention also relates to a system for controlling the combustion of a fuel mixture contained in the combustion chamber of an internal combustion engine, said chamber being connected to at least one intake means with an intake manifold. controlled by an intake valve and with at least one exhaust means with an exhaust manifold controlled by an exhaust valve, characterized in that the control system comprises intake valve control means and exhaust and the injection of a fuel into the combustion chamber, said control means being adapted to implement the combustion process of the invention. The other features and advantages of the invention will now appear on reading the following description, given solely by way of illustration and without limitation, and to which are appended: FIG. 1 is a diagram showing a combustion engine internal use of the method according to the invention, and - Figure 2 which illustrates another combustion engine using the method 30 according to the invention. In FIG. 1, the engine illustrated by way of example is a direct injection internal combustion engine with compression ignition or autoignition, preferably a diesel engine.

This example is not limiting and the invention described below can also be applied to a direct injection internal combustion engine with spark ignition, in particular of the gasoline type.

This engine comprises at least one cylinder 10 with a cylinder body 12 closed by a cylinder head 14. Inside the cylinder body 12 slides a piston 16 in a rectilinear reciprocating movement under the effect of a connecting rod connected to a cylinder. crankshaft (not shown) forming a combustion chamber 18. This chamber is thus delimited by the cylinder head, the side wall 20 of the cylinder body and the upper part 22 of the piston. The cylinder head carries at least one intake means 24 with an intake manifold 26 whose access to the combustion chamber 18 is controlled by an intake valve 28. The cylinder head also carries at least one exhaust means 30 with an exhaust pipe 32 associated with an exhaust valve 34 for communication with this chamber. The intake and exhaust valves are controlled in opening / closing by specific means. In the context of the invention, these must make it possible to disconnect the valves at all times, synchronously, the intake and exhaust valves then being kept in the closed position, ie no fluid can pass admission pipes to the combustion chamber, or the combustion chamber to the exhaust pipes. At the gas leakage rates of the combustion chamber via the segmentation, the mass enclosed in the combustion chamber can only increase according to the amount of fuel injected (direct injection mode). Systems commonly known as Variable Valve Actuation (VVA) or any other system that allows simultaneous disconnection of intake and exhaust valves are particularly suitable. In the example described with reference to FIG. 1, the intake valve (s) 28 and the exhaust valve (s) 34 are provided with means 36 and 38, respectively, which make it possible to control their opening moments. closing. The cylinder head also carries direct fuel injection means 40, such as a direct multi-hole injector, which project pressurized fuel into the combustion chamber 18 to produce a fuel mixture with the intake fluid (oxidant) which is admitted through admission means. This fluid is advantageously air which can be supercharged or not, a mixture of air (supercharged or not) and recirculated flue gas, or a fuel mixture and / or recirculated flue gas. The fuel injection means and the ignition systems (in the case of gasoline-ignition engines of the gasoline type) are controlled by an electronic control unit (not shown), more commonly called a motor-calculator, which is usually provided with an engine. . This calculator serves in particular to control the fuel injection parameters, such as the fuel injection time in the engine cycle and / or the fuel injection time.

For many engines, the valves 28, 34 are controlled by autonomous mechanical systems (camshafts), the simplest of which are not designed to vary the moments of lifting and closing of the valves nor the duration and opening height. For other engines, additional mechanisms make it possible to vary the moments of lifting and closing of the valves, or even for the most complex systems also the duration and the opening height of the valves: in these cases, the means of control 36, 38 of the valves 28, 34 are also controlled by said computer. In the case of a diesel engine with direct fuel injection, the carbureted mixture formed as a result of the fuel injection phase in the combustion chamber is thus brought to thermodynamic conditions, called autoignition conditions. allowing it to burn at the end of a short time spontaneously (and therefore without additional energy supply) whereas in the case of a direct injection engine of a fuel adapted to the engines "spark ignition", 3034467 7 as of gasoline, the fuel mixture is ignited under the effect of a spark plug 42 (represented by a dashed line in the figure). The following description of the process will be made in connection with a Diesel direct injection engine. Generally, this type of engine operates in a four-stroke cycle, consisting of four phases. This cycle begins with a phase 1 where the piston 16 moves from its top dead center (TDC) to its bottom dead center (TDC), this phase 1 is followed by a phase 2 during which the piston 16 moves from its PMB towards its PMH, then by a phase 3 with a displacement of the piston of its PMH towards its PMB and ends with a phase 4 with the displacement of the piston of its PMB towards its PMH. For the conventional operation of an engine, phase 1 corresponds to the intake phase (A), phase 2 to the compression phase (C) followed by combustion of the fuel mixture, phase 3 to the phase of combustion. expansion (D) and phase 4 to that of the exhaust (E). These piston displacements will be used appropriately to carry out the method according to the invention as described below.

To use this method, the motor operates in a cycle with an admission phase (A), followed by at least "n" periods of compression / expansion phases (C / D), where "n" is greater than or equal to two, then an escape phase (E).

The number n depends, inter alia: on the richness of the mixture enclosed in the combustion chamber at the moment when the intake and exhaust valves are closed simultaneously. In the context of the invention, this wealth should theoretically be less than 1 30 - the amount of fuel injected at each compression / expansion phase In general, the wealth enclosed in the simultaneous closure of the valves must be sufficiently high to allow a combustion (value 3034467 8 which depends in particular on the operating point of the engine, the atmospheric conditions and the basic geometrical adjustments of the engine such as the geometric compression ratio): in the case of a diesel engine with low load, and for example, this wealth can be close to 0.2. If at each new fuel injection, the wealth increases for example by 0.2, the overall wealth will then be 0.4, then 0.6, 0.8 and finally R = 1: in this case n = 4. By way of example and with reference to FIG. 1, the operation applies to a diesel engine and "n" is equal to 3.

The engine has the following operation: - During the first cycle and at the beginning of phase 1 (conventional A intake phase), the intake valve 28 is open and the exhaust valve 34 is closed and the intake fluid is admitted into the combustion chamber 18 as the PMH piston moves to its PMB; - After the closing of the intake valve, the phase 2 (compression phase C of the fluid) is performed and the compression is made by the piston which moves from its PMB to its TDC; Around the end of the compression phase, the injector 40 introduces diesel-type fuel into the compressed fluid with a very small amount to reach the minimum total level of richness, for example of the order of 0.15. 0.20 which allows the initiation of a combustion; - The fuel mixture thus formed is burned during phase 3 (expansion phase D) always with the intake and exhaust valves 25 closed when moving the piston from its PMH to its PMB; This makes it possible to carry out a first period of a compression phase followed by an expansion phase (compression / expansion phase). - In the next phase 4 with the displacement of the PMB piston to its PMH, which usually corresponds to the exhaust phase, the 30 intake and exhaust valves remain closed so as to achieve a recompression phase. The mixture contained in the combustion chamber, which consists solely of flue gases and oxygen, is then recompressed by the piston (compression phase C); 3034467 9 - In the vicinity of the end of this recompression phase, the injector introduces a second quantity of fuel (very low) to reach a new level of overall wealth greater than the initial richness (because oxygen has been consumed at during the first combustion) but as low as possible, which allows the triggering of a second combustion in a medium charged with recirculated flue gas; - The fuel mixture created in burnt gases present in the combustion chamber and resulting from the first combustion is burned again during the second phase 1 which is here a reducting phase (expansion phase D) 10 instead of a phase intake, always with the intake and exhaust valves closed when moving the piston from its PMH to its PMB; A second period of a compression phase followed by a relaxation phase is thus performed. 15 - Following this period of compression / expansion, a recompression phase of the mixture contained in the combustion chamber is carried out during the second phase 2, with the intake and exhaust valves always closed, this recompressed mixture consisting of a larger amount of flue gases and a smaller amount of oxygen than the previous recompression phase (compression phase C); a third quantity of fuel is introduced by the injector 40 to reach a new level of overall wealth greater than the previous richness of recirculated flue gases; - The fuel mixture created in burnt gases present in the combustion chamber which is stoichiometric or very close burned again during the third phase 1 which is here a redetente phase (expansion phase D). This third period of compression / expansion phases is followed by an exhaust phase since at the end of "n" periods the mixture is stoichiometric.

From here, two cases arise: - after the exhaust phase (exhaust valve open), one resumes a mode of operation with the resumption of a mode with "n" periods of combustion / expansion phases preceded by a phase 1 5 (admission phase) conventional. - We resume a normal operating cycle said to "4 Times". Note that for a motor with multiple cylinders, it is possible to activate this mode of combustion on all or part of the cylinders, and phaser these modes all in different ways.

In the case of an internal combustion engine with direct injection and spark ignition, the process is substantially the same, with the difference that ignition of the fuel mixture which takes place as a result of the compression of the mixture is caused by the spark plug 42.

The advantage of successive injections in a medium containing more and more flue gas without having to maintain a transfer of intake fluid, makes it possible to obtain a very good compromise nitrogen oxides / fumes / fuel consumption.

This process can thus be applied in the case where the drastic reduction of the nitrogen oxides is necessary because of the lack of efficiency of the post-treatment system (very low load, slowed down, etc.) or even under conditions very cold outdoor temperature that is not conducive to controlled combustion and rapid engine temperature rise.

FIG. 2 illustrates another example of an internal combustion engine that can use the method according to the invention. This engine differs from that of FIG. 1 in that it comprises other fuel injection means 44, here in the form of an indirect injector, which makes it possible to operate this engine in an injection mode. Concomitant fuel (Dual Fuel) that allows: - to associate the indirect injection of a fuel, NGV, or gasoline, or Ethanol, or LPG for example, to a direct injection 3034467 11 another fuel of the Diesel type: the combustion of the mixture will then be controlled by the auto-ignition of the injected diesel fuel: the case of Dual-Fuel; associating the indirect injection of a fuel, for example CNG, with a direct injection of another fuel, petrol, or ethanol, or with LPG the use of a candle ignition will be required to ignite the mixture. This indirect injector 44 is placed on the inlet pipe 26 upstream of the inlet valve 28 and makes it possible to introduce the other fuel into the pipework so that it mixes with the fluid circulating therein. to form a fuel mixture. In the case of the Dual-Fuel, for the fuel used in indirect injection, the latter is predominantly a fuel in the gaseous state, such as NGV (Natural Gas for Vehicles), LPG (Liquefied Petroleum Gas), an biogas or any other liquid fuel having volatile properties sufficient to be vaporized completely before the initiation of combustion by the diesel fuel.

The dual-fuel mode of operation of this type of engine is similar to that previously described. Thus, this engine operates according to a cycle with an admission phase (A), with at least "n" periods of compression / expansion phases (C / D), where "n" is greater than or equal to two, and one exhaust phase (E), with the steps below. - At the beginning of the engine intake phase (Phase A), the intake valve 28 is open and the exhaust valve 34 is closed. The indirect injector 44 is operated to introduce gaseous fuel (or any other suitable fuel) into the intake manifold 26 to mix with the fluid flowing therethrough. The fuel mixture thus constituted is introduced into the combustion chamber 18 during the movement of the piston from its PMH to its PMB, this mixture being at a minimum overall strength, order of 0.15-0.2 which allows the initiation of the ignition of this mixture by the auto-ignition of diesel fuel as described below; After closing the intake valve, the compression phase of the fuel mixture is performed by the piston which moves from its PMB to its TDC during phase 2; At the end of this compression phase, the direct injector 40 is controlled to inject diesel type fuel into the fuel mixture present in the combustion chamber. The fuel mixture is thus ignited under the combined effect of the heat released by the compressed carburetted mixture and the radicals emitted by the combustion of diesel and is burned during the expansion phase D still with the intake and exhaust valves closed. when moving the piston from its PMH to its PMB; During the next phase of movement of the piston with the displacement of the PMB piston towards its TDC, the intake and exhaust valves remain closed and the mixture, consisting essentially of flue gases and oxygen, contained in the chamber of combustion is then recompressed by the piston; In the vicinity of the end of this recompression phase, the direct injector 40 introduces another small quantity of diesel type fuel to reach a new level of overall wealth greater than the initial richness (because oxygen has been consumed during the first combustion) but as low as possible, which allows the triggering of a new combustion in a medium containing flue gas from the previous combustion; The fuel mixture created in burnt gases present in the combustion chamber and resulting from the previous combustion is burned again during the redetext phase always with the intake and exhaust valves closed during the movement of the piston from its PMH to his PMB; Following this redetext phase, a recompression phase of the mixture contained in the combustion chamber, with the intake and exhaust valves closed, this recompressed mixture being constituted by a larger amount of flue gas and exhaust gas. a lower amount of oxygen than the previous recompression phase. - The different phases are renewed during the "n" periods until a final combustion is obtained at stoichiometry 5 - As a result of this last combustion, the conventional cycle is resumed with the opening of the exhaust valve for the phase exhaust. Note that the number "n" can be chosen without having reached the last combustion with richness 1: the process can be stopped at any moment.

The advantage of successive injections of fuel in a medium containing more and more flue gas without having to maintain a transfer of intake fluid, makes it possible to obtain a good compromise nitrogen oxides / fumes / fuel consumption .

This method can thus be applied in the case where the drastic reduction of the nitrogen oxides is necessary because of the lack of efficiency of the post-treatment system or even under very cold external temperature conditions which are not conducive to controlled combustion. and a temperature rise of the fast motor. The mode of operation in concomitant injection (Dual Fuel) by spark ignition of this type of engine is similar to those described above.

Thus, this engine also operates in a cycle with an admission phase (A), with at least "n" periods of compression / expansion phases (C / D), where "n" is greater than or equal to two, and an escape phase (E), with the steps below. At the beginning of the engine intake phase (Phase A), the intake valve 28 is opened and the exhaust valve 34 is closed. The indirect injector 44 is operated to introduce gaseous fuel (or any other suitable fuel) into the intake manifold 26 to mix with the fluid flowing therethrough. The fuel mixture thus formed is introduced into the combustion chamber 18 during the displacement of the piston from its PMH to its PMB, this mixture being at a minimum overall richness, from order of 0.55-0.6 which allows the initiation of the ignition of this mixture by a spark plug; After the closing of the intake valve, the compression phase C of the fuel mixture is carried out by the piston which moves from its PMB to its PMH .; At the end of this phase 2, the direct injector 40 is still not controlled. The fuel mixture injected during the preliminary intake phase is ignited by the spark plug and burns during the expansion phase D always with the intake and exhaust valves closed when the piston moves from its PMH to its PMB; In the next phase, with the displacement of the PMB piston towards its TDC, the intake and exhaust valves remain closed and the mixture, consisting essentially of flue gases and oxygen, contained in the combustion chamber is then recompressed by the piston; In the vicinity of the end of this recompression phase, the direct injector 40 introduces a small amount of gasoline type fuel to reach a new level of overall wealth greater than the initial richness (because oxygen has been consumed during the first combustion) but as low as possible, which allows the triggering of a new combustion type ignition controlled in a medium charged with flue gas from the previous combustion; The fuel mixture created in burnt gases present in the combustion chamber and resulting from the preceding combustion is burned again during the redetention phase D always with the intake and exhaust valves closed during the displacement of the piston of its TDC. towards his PMB; Following this redetext phase, a recompression phase C of the mixture contained in the combustion chamber, with the intake and exhaust valves closed, this recompressed mixture consisting of a larger amount of flue gases and a smaller amount of oxygen than the previous recompression phase. 3034467 15 - The different phases are renewed during the "n" periods until a final stoichiometric combustion is obtained. - Following this last combustion, the conventional cycle is resumed with the opening of the exhaust valve for the exhaust phase.

5 Note that the number of periods "n" can be chosen without having reached the last combustion with richness 1: the process can be stopped at any moment. The advantage of successive injections of fuel in a medium containing more and more flue gas without having to maintain a transfer of intake fluid, makes it possible to obtain a good compromise nitrogen oxides / fuel consumption. This method can thus be applied in the case where the drastic reduction of the nitrogen oxides is necessary because of the lack of efficiency of the post-treatment system or even under very cold external temperature conditions that are not conducive to controlled combustion. and a rapid engine temperature rise.

Claims (11)

REVENDICATIONS1. A method of combustion of a fuel mixture contained in the combustion chamber (18) of an internal combustion engine, said chamber 5 being connected to at least one intake means (24) with an intake manifold ( 26) controlled by an intake valve (28) and with at least one exhaust means (30) with an exhaust manifold (32) controlled by an exhaust valve (34), and injection means (40, 44) of at least one fuel, characterized in that the engine operates on a cycle 10 with an intake phase (A), with at least "n" periods of successive phases of compression / expansion (C / D), "n" being greater than or equal to two, and an escape phase (E). 2) Process according to claim 1, characterized in that, after the formation of a fuel mixture in the combustion chamber (18) during the intake phase (A), the intake valves (28) and exhaust (34) are held in the closed position and the fuel is injected into the combustion chamber during the "n" periods of successive phases of compression / expansion (C / D). 20 3) A combustion method according to one of the preceding claims characterized in that the fuel mixture formed in the combustion chamber (18) during the compression / expansion phases (C / D) comprises a minimum richness for the combustion of this mixture. 4) Combustion method according to one of the preceding claims, characterized in that the compression / expansion phase (C / D) is followed by an exhaust phase, when the fuel mixture contained in the combustion chamber comprises a wealth close to the stoichiometric 5) A combustion process according to one of claims 1 to 4, characterized in that, during the intake phase, an oxidant is introduced into the combustion chamber to make a fuel mixture. 3034467 17 6) A combustion process according to one of claims 1 to 4, characterized in that, during the intake phase, a fuel mixture is introduced into the combustion chamber during the cradmission phase. 7) Combustion method according to one of claims 1 to 4, characterized in that, during the intake phase, a mixture of a fluid and fuel is introduced into the combustion chamber, and in that another fuel is injected into the combustion chamber at the end of each compression / expansion phase (C / D). 8) A combustion method according to one of claims 1 to 4, characterized in that the fuel is a fuel injected into the combustion chamber. 9) A combustion method according to one of claims 1 to 4, characterized in that the fuel is a fuel injected into the combustion chamber admission means. 10) Combustion method according to claim 7, characterized in that the fuel is a fuel injected into the combustion chamber intake means and the other fuel is a fuel injected into the combustion chamber. 11) Control system for the combustion of a fuel mixture 25 contained in the combustion chamber (18) of an internal combustion engine, said chamber being connected to at least one intake means (24) with a tubing d intake (26) controlled by an intake valve (28) and with at least one exhaust means (30) with an exhaust manifold (32) controlled by an exhaust valve (34), characterized in that the control system comprises means for controlling the intake (26) and exhaust (34) valves and for injecting a fuel into the combustion chamber (18), said control means being suitable to implement the combustion method according to one of the preceding claims.