EP1096118A1 - Controlled self-ignition combustion process and four cycle engine with transfer conduits between exhaust and intake conduit - Google Patents

Abstract

The control procedure, for use on a multi-cylinder 4-stroke engine with each cylinder (1) having at least one inlet (2) and exhaust (3) duct, consists of taking a quantity of the exhaust gas from one cylinder when the engine is under partial load and transferring it to the inlet duct of another via valves (4, 7). During the transfer the gas can be thermally insulated and/or reheated by catalysis in a common transfer duct (5). At the same time as the gas is heated, the catalyst (10) can be used to reduce the pollutants in it.

Description

The present invention relates to internal combustion engines 4 controlled self-ignition time.

Controlled self-ignition is a known phenomenon in 2-stroke engines. This type of combustion has advantages level of pollutant emissions: in particular, low levels are obtained emissions of hydrocarbons and nitrogen oxides. In addition, a remarkable cyclical regularity is achieved during self-ignition combustion.

Self-ignition is a phenomenon that initiates the combustion thanks to residual burnt gases which remain in the chamber after combustion.

Self-ignition is achieved by controlling the amount of gas residuals and its mixture with fresh gases (not yet burnt). Gas residuals (hot burnt gases) initiate the combustion of fresh gases thanks to a combination of temperature and presence of active species.

In 2-stroke engines, the presence of residual gases is "inherent" to combustion. Indeed, when the engine load decreases, the quantity of fresh gas decreases which results in a increase in the quantity of residual gases (burnt gases from the cycle (s) which have not left the cylinder). 2-stroke engine therefore works with an internal circulation (or internal EGR) of gases burned at partial load. However, the presence of this internal EGR is not not sufficient to obtain the desired function in self-ignition.

Researchers' work also shows that it is necessary to control and limit the mixture between this internal EGR and the fresh gases.

Controlled self-ignition technology applied to the engine four stroke is particularly interesting because it allows you to do operate this type of engine with an extremely diluted mixture, with very low wealth and therefore oxide emissions ultra low nitrogen.

However, this technology faces a difficulty important technological which is the fact that to get it without benefit of the internal EGR effect of the 2-stroke engine, it is necessary either greatly increase the compression ratio of the engine (with knocking problems at high load), or to heat very strongly (several hundred degrees Celsius) fresh gas admitted, or combine the two phenomena.

Solutions exist to reduce the level requirements pressure and temperature for 4-stroke engines, in particular by the use of appropriate additives added to the fuel. The request of French patent FR 2 738 594 illustrates a solution of this type.

For 4-stroke engines, it is known, in particular by the demand WO-93/16276, to combine a variable calibration of the distribution with a non-return system on admission with the aim of reduce pumping losses at partial load. This solution allows then operate with the intake valve as open as possible.

Patent application FR-97 / 02.822 filed in the name of the Applicant describes a control of self-ignition in an engine four stroke. More specifically, this document recommends, dependent partial, to minimize the mixing of fresh gases with burnt gases enclosed in the combustion chamber, acting on the closing of the exhaust. It is therefore a solution close to the technique of "internal" recycling which allows stratification of the gases in the combustion.

Patent application FR-97 / 11.279 filed in the name of the plaintiff also aims to minimize, at partial charge, the mixing of fresh gases with the burnt gases contained in the combustion chamber, in order to control and promote self-ignition combustion. However, this teaching proposes to transfer the burnt gases from the exhaust of a cylinder into the intake of the same cylinder. This solution creates a very significant dilution of the recycled burnt gases, by air, before entering the combustion chamber, which can pose problem.

The present invention aims to achieve controlled self-ignition in very simple multi-cylinder 4-stroke engines, so reliable, easy to use and which promotes maximum stratification of the burnt gases in the combustion chamber. Moreover, the burnt gases retain or even increase, according to the invention, their temperature which is favorable for self-combustion.

Thus the subject of the present invention is a combustion process by controlled self-ignition of a 4-stroke engine comprising several cylinders each having at least one inlet and at least one exhaust port, the ports and the means of controlling the closure being conventional, i.e. according to the knowledge of the skilled person. The invention can be applied to injection engines direct (FDI) or indirect.

According to the invention, the method consists during operation at partial load, to be transferred via an appropriate gas transfer means exhaust from a cylinder, usually in phase exhaust, to another cylinder, generally in phase of admission. The exhaust gases are routed through a valve specific placed after the exhaust means, towards the means of transfer. Thanks to a second valve, the exhaust gases transferred arrive in the intake duct, upstream of the intake means. For more efficiency, it is desirable that a means of admission be dedicated to the entry of exhaust gases into the cylinder (it is necessary in this case at least two means of admission) to reduce the mixing between fresh and burnt gases.

Exhaust gases can also be recovered from a cylinder at the end of the relaxation phase. They can also be introduced into a another cylinder at the start of the compression phase.

The method according to the invention also consists in controlling the distribution of exhaust gas flow between the system exhaust and transfer means. In addition, the method can consist of thermally insulating and / or heating gases exhaust transferred into said appropriate transfer means, so further improve self-ignition.

In order to heat the burnt gases passing through the means of transfer, catalysis means can be placed in the means of transfer. The positioning of the catalyst is a compromise between a positioning close to the cylinder intake valve, in order to have a higher temperature of the burnt gases when they enter the cylinder, or close to the exhaust valve, to facilitate priming of this catalyst during cold starts. Besides the fact that the primary function of this catalyst is to heat the burnt gases to facilitate controlled self-ignition, in the case of a cold start, it will participate, from its inception, in the reduction of polluting emissions during a phase where the main catalyst of the pot is generally not not fully primed. The means of catalysis may include a mass of catalyst or catalyst-coated walls. In this place, at full load, the catalyst does not receive the burnt gases, therefore does not risk no early deterioration and does not create pressure loss additional.

Indeed, at full load, the transfer means do not communicate plus with conduits associated with exhaust and intake ports cylinders. At full load, the engine configuration becomes conventional.

In order to increase the temperature of the exhaust gases under load partial, we can increase the richness of the exhaust gases, especially in the case of a direct injection engine. In this case, a fuel injection at the end of the exhaust phase allows gases exhaust to increase in temperature thanks to the reaction in the catalyst. It is possible to place a fuel injector specific upstream of the catalysis means.

According to one embodiment of the invention, a conduit is used common for the transfer of exhaust gases.

According to another embodiment of the invention, one uses for the exhaust gas transfer, a set of conduits connecting the specific exhaust ducts to specific intake ducts two by two.

The present invention further relates to a combustion engine internal 4-stroke operating in controlled self-ignition and comprising several cylinders each having at least one inlet orifice and at minus an exhaust port.

According to the invention, each cylinder further comprises a specific means for the passage of exhaust gases from the exhaust of a cylinder, generally in the exhaust phase, towards at least one other cylinder, generally in the intake phase, as well an associated means of transfer, the transfer taking place during the partial load operation.

A means of thermal insulation and / or heating of the means of transfer can also be provided without departing from the scope of the invention. Advantageously, the engine further comprises a means of distribution of exhaust gases between the exhaust system and the means of transfer, partial load.

In addition to the specific valve to divert (totally or partially) the exhaust gases to the transfer means, the exhaust gas distribution means may include means valve placed near the exhaust means.

According to one embodiment, said transfer means comprises a common conduit.

In accordance with another embodiment of the invention, the transfer means comprises a set of conduits connecting the specific exhaust ducts and valves to ducts and valves specific admission two by two.

• La figure 1 est une coupe schématique d'un mode de réalisation de l'invention;
• La figure 2 est une coupe schématique d'un autre mode de réalisation de l'invention.
• La figure 3 représente une variante pour les deux modes précédents.

Other characteristics, details and advantages of the present invention will appear more clearly on reading the description which follows, given by way of illustration and in no way limiting, with reference to the appended drawings in which:

• Figure 1 is a schematic section of an embodiment of the invention;
• Figure 2 is a schematic section of another embodiment of the invention.
• FIG. 3 represents a variant for the two previous modes.

FIG. 1 illustrates the case of an engine having four cylinders 1. The invention in fact applies to all engines comprising at least two cylinders. The letter A represents the admission in a cylinder, the letter E the exhaust in the same cylinder.

Each cylinder 1 comprises at least one inlet port 2 of a charge. The present invention preferably comprises two orifices intake (as shown in the figures). By means of admission of a load, it is necessary here to understand: an admission orifice to which is associated a valve and the conduit associated with this orifice. So equivalent, the same is true for the name exhaust means.

Each cylinder further includes an exhaust port 3 conventionally equipped with an associated conduit and valve.

Furthermore, each cylinder 1 comprises means for valve type 4 distribution placed in the exhaust duct, well obviously downstream of the exhaust port. This valve, or device equivalent, allows burnt gases leaving the exhaust port to go to a transfer means 5. In this variant, the means of transfer 5 is a conduit which communicates with all the conduits cylinder exhaust, as well as with all intake ducts. These distribution means are used to control the flow of transfer of gases between exhausts and inlets. In full load, these valves 4 close the communication to the conduit 5.

Each cylinder 1 also includes a valve 7 placed in the intake, close to the intake port 2. It allows burnt gas to go from the transfer means 5 to the cylinder 1, via the distribution valve 7 and the inlet port 2. When fully loaded, these valves 7 are preferably closed.

In each cylinder, a valve means 6 is arranged at proximity to exhaust 3. Appropriate control and coordinated controls the opening of each valve means 4, 6, 7, and regulates and distributes the gas flow between the exhaust and the transfer medium 5.

It is possible, without departing from the scope of the invention, not to consider winnowing 6.

At partial load, exhaust gases are transferred from a cylinder generally in the exhaust phase to another cylinder generally in the admission phase.

The table below illustrates the transfers thus carried out over a cycle, for a 4-cylinder engine.

The present invention can use a standard distribution for the opening of all exhaust and intake valves. In this case, at partial loads, the burnt gases and the fresh gases will come together in the cylinder in the intake phase.

• Pour l'échappement, dans le cas d'au moins 2 moyens d'échappement (3 et 3'), l'orifice 3 pour les gaz frais peut être faiblement ouvert en début d'échappement et l'orifice 3' associé à la vanne 4, ouvert normalement oblige alors les gaz brûlés à se diriger vers le moyen de transfert 5. Cette stratégie permet d'envoyer une plus grande quantité de gaz brûlés dans le moyen de transfert 5 et donc dans l'autre cylindre en phase d'admission. Par faiblement ouvert, on doit comprendre que l'on agit sur la hauteur de la levée de soupape, ou sur la durée de la levée, ou sur les deux. Dans ce cas, le vannage 6 n'est pas nécessaire. L'ouverture de l'orifice 3' peut aussi commencer et/ou se faire pendant la fin du temps de détente afin de récupérer des gaz brûlés très chauds et sous pression. Cela peut servir aussi à chauffer rapidement le catalyseur 10 lors du démarrage à froid.
• Pour l'admission, dans le cas d'au moins 2 moyens d'admission , l'orifice 2 peut être ouvert en début de phase d'admission et rapidement refermé. L'orifice 2' est alors ouvert en fin de phase d'admission, en limitant le croisement entre les soupapes 2 et 2' afin de limiter le mélange des gaz brûlés avec les gaz frais. Cette configuration permet, avec une stratégie adéquate de gestion des soupapes d'échappement, d'augmenter la pression dans le cylindre en forçant l'entrée de gaz brûlés après l'entrée de la charge de gaz frais. L'entrée des gaz brûlés peut aussi se terminer pendant le début du temps de compression pour augmenter la quantité de gaz brûlés (si la pression disponible dans le moyen de transfert le permet).
• Une autre possibilité est de faire d'abord entrer dans le cylindre les gaz brûlés par l'orifice 2', et ensuite de faire entrer la charge par l'orifice 2, avec un croisement de soupape limité afin de limiter le mélange des gaz brûlés et des gaz frais. On ne sortira pas du cadre de la présente invention si les gaz frais sont comprimés, par exemple par un compresseur.

In the case where a known variable valve opening system is available, a few strategies can be effectively used with the present invention:

• For the exhaust, in the case of at least 2 exhaust means (3 and 3 '), the orifice 3 for the fresh gases may be slightly open at the start of the exhaust and the orifice 3' associated with the valve 4, normally open, then forces the burnt gases to go towards the transfer means 5. This strategy makes it possible to send a larger quantity of burnt gases to the transfer means 5 and therefore to the other cylinder in the phase of admission. By slightly open, it should be understood that one acts on the height of the valve lift, or on the duration of the lift, or on both. In this case, winnowing 6 is not necessary. The opening of the orifice 3 ′ can also begin and / or take place during the end of the expansion time in order to recover very hot and pressurized burnt gases. This can also be used to quickly heat the catalyst 10 during cold start.
• For admission, in the case of at least 2 admission means, the orifice 2 can be opened at the start of the admission phase and quickly closed. The orifice 2 ′ is then opened at the end of the intake phase, by limiting the crossing between the valves 2 and 2 ′ in order to limit the mixing of the burnt gases with the fresh gases. This configuration allows, with an adequate strategy for managing the exhaust valves, to increase the pressure in the cylinder by forcing the entry of burnt gases after the entry of the charge of fresh gas. The entry of the burnt gases can also be terminated during the start of the compression time to increase the quantity of burnt gases (if the pressure available in the transfer means allows it).
• Another possibility is to first bring the burnt gases into the cylinder through the orifice 2 ', and then bring the charge through the orifice 2, with a limited valve crossing in order to limit the mixing of the burnt gases. and fresh gas. It will not depart from the scope of the present invention if the fresh gases are compressed, for example by a compressor.

According to one embodiment of the invention, illustrated by FIG. 1, the transfer means comprises a common conduit with accesses to all specific valves 4 and 7.

It is still possible, without departing from the scope of the invention, to provide as a means of transfer a set of conduits connecting the conduits and specific exhaust valves to conduits and valves specific admission two by two, and which allow for example a four cylinder engine, to have the transfers according to the table above as illustrated in figure 2.

Advantageously, the transfer tube (s) 5 can be thermally insulated, using a ceramic 8 for example. She can also be heated by specific means 8 '. So the gases that pass through transfer tubing 5 do not lose or even gain calories when they arrive in the cylinder. Self-ignition is thus improved since it is known that the temperature of the recycled gases is an important parameter, which promotes self-ignition. A catalyst 10 can also be used to heat the burnt gases and advantageously, at the same time, reduce the level of pollutants present in the burnt gases passing through the transfer means 5.

Figure 3 shows a variant where the exhaust does not include than an orifice. It is clear that the means of admission, such as are not limited to a double exhaust and a double admission.

The present invention has the definite advantage of not having need specific transfer ports, since it uses conduits conventional four-stroke engine intake and exhaust considered.

Claims (15)

Method of controlling combustion by self-ignition of a 4-stroke engine comprising several cylinders (1) each having at at least one intake means (2) comprising an intake duct and at at least one exhaust means (3) comprising a duct exhaust, characterized in that during load operation partial of said engine, a quantity of exhaust gas is taken from the exhaust pipe of a cylinder, and we transfer a amount of gas burned to the intake duct of at least one other cylinder. Process according to claim 1, in which one isolates thermally and / or the transferred exhaust gases are reheated. Process according to claim 2, in which the gases are reheated by catalysis in the transfer conduits. Method according to any one of the preceding claims, in which the flow rate of the transferred gas is regulated. Method according to any one of the preceding claims, in which a common conduit (5) is used for the transfer of gases exhaust. Method according to one of the preceding claims, in which, at full and heavy loads, no gas is taken or transferred exhaust. Process according to any one of Claims 1 to 4, in which is used for the transfer of exhaust gases, a set of ducts connecting the specific exhaust ducts to the ducts specific admission two by two. 4-stroke internal combustion engine operating in self-ignition controlled and comprising several cylinders (1) each having at at least one intake means (2) comprising an intake duct and at at least one exhaust means (3) comprising a duct exhaust, characterized in that each cylinder (1) comprises means for transferring (5) the exhaust gases from said duct exhaust from a cylinder to an intake duct of at least one other cylinder. Internal combustion engine according to claim 8, in which the transfer means further comprises an isolation means thermal (8) and / or heating (8 ') of said transferred gases. Internal combustion engine according to any one of claims 8 or 9, wherein said exhaust means (3) includes means for controlling (4) the communication between the conduit exhaust and the conduit (5) of the transfer means. Internal combustion engine according to claim 10, in which said intake means (2) comprises means (7) for controlling communication between the intake duct and the means duct transfer (5). Internal combustion engine according to any one of claims 8 to 11, wherein said transfer means comprises a common duct (5) which communicates with the intake ducts and exhaust of each of the cylinders. Internal combustion engine according to any one of claims 8 to 12, wherein said transfer means include catalysis means (10). Internal combustion engine according to any one of claims 8 to 11, wherein said transfer means include a set of conduits connecting specific valves exhaust to specific two by two intake valves. Internal combustion engine according to one of claims 8 to 14, in which it has only one exhaust orifice.

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