FR2861425A1 - Heat engine e.g. diesel engine, has two connection zones formed between respective pipes and intake units to create pairs of adjacent air streams within combustion chamber, where air streams form concentric stratums along sliding axis - Google Patents

Abstract

The engine has intake (3, 4) and exhaust (5,6) units allowing gaseous combustive-fuel and burnt gas to enter and escape into and from a combustion chamber (1), respectively. Two connection zones (15, 16) are formed between pipes (7, 8) and the intake units respectively, for creating pairs of adjacent air streams (9,10,13,14) within the chamber. The streams form concentric stratums along a pistons sliding axis (2). An independent claim is also included for an injection method for a heat engine.

Description

PROCESS FOR ADMISSION OF RECOVERED BURN GASES INTO

  COMBUSTION CHAMBER AND ENGINE IMPLEMENTING THIS

PROCESS

  The present invention relates, in a general manner, to the field of the injection of oxidizer and of burnt gases recycled in a heat engine such as a diesel engine.

  More particularly, the invention relates to a cyclic operating heat engine such as a diesel engine with direct injection, comprising in particular a combustion chamber in which a piston slides, along a sliding axis of the piston, fuel injection means in the chamber, first and second intake means for selectively admitting into the chamber a gaseous oxidizer containing air, exhaust means for selectively allowing the escape of flue gas from the chamber and recycling means including a flow control means for recycling burnt gases, and a first flue gas line connected on the one hand by means of flow control and connected on the other hand by a first connection zone, to the first means of admission.

  The invention also relates to an injection method for a cyclic thermal engine such as a diesel engine with direct injection, comprising in particular a combustion chamber in which a piston slides, along a sliding axis of the piston, means of combustion. injecting fuel into the chamber, first and second intake means for selectively admitting into the chamber a gaseous oxidizer containing air, exhaust means for selectively allowing the escape of flue gas from the chamber and recycling means including a flow control means for recycling burnt gases.

  The use of so-called recirculating gas or EGR or recycled gas in the combustion chamber of an alternating engine and more particularly of a compression ignition engine is well known to those skilled in the art. The recycled gases are gases from the combustion of previous cycles and are therefore depleted of oxygen. They are used, mixed with air, to reduce polluting emissions or to control the course of combustion. More precisely, the ignition time of an air / fuel mixture containing recycled gases is greater than that of an equivalent mixture that does not contain them. It is therefore possible to delay the ignition of an air / fuel mixture by adding recycled gases to a maximum concentration limit beyond which fuel combustion will be difficult and incomplete at the risk of producing pollutant particles. .

  External EGR is referred to when the recycled gas supply is via a circuit located outside the combustion chamber and internal EGR when these residual combustion gases have remained trapped in the combustion chamber. The proposed invention relates primarily to the management of external EGR and the method of controlling the flow of recycled gas admitted into the chamber to achieve the desired effects.

  The combustion noise is related to the rate of combustion, that is to say the speed at which the energy resulting from the oxidation of the fuel by the oxidizer is released. The use of recycled gases makes it possible to spread the combustion time and, in a corresponding manner, to reduce the noise of the engine.

  However, the reduction of engine noise by the use of recycled gas can be detrimental to engine efficiency.

  This is the reason why many engine manufacturers have developed various solutions to control the addition of recycled gas and particularly the creation of gas strata in the combustion chamber or chambers.

  A previously defined type of engine, allowing the creation of a fluid stratum containing an oxidant and a fluid stratum containing recycled burnt gases, is for example described in patent document GB 2 328 716.

  This document describes a cyclic thermal engine, comprising a combustion chamber in which a peripheral layer containing an oxidant and a central stratum containing a mixture of recycled air and recycled gases is injected, these strata being substantially concentric with respect to a sliding axis of the piston in the combustion chamber and with respect to the fuel injection means in the chamber 1.

  This stratification is performed by means of a first gaseous oxidizer inlet means to which is connected a first flue gas supply line and a second pure gaseous oxidizer inlet means.

  The first pipe is oriented towards the center of the combustion chamber so as to create the central stratum composed of recycled oxidant and burnt gas.

  Thus, a layer rich in burnt gas is created near the fuel injection means which is in the center of the combustion chamber, in the axis of sliding of the piston. The volume of nitrogen oxide which is mainly generated in the ignition region of the combustion, ie near the injection means is thus reduced. The ignition of the combustion is also delayed on order by injection of burned gases in the central part of the chamber.

  Despite the advantages of this device of the prior art, it is necessary to improve the concentric and symmetrical distribution of the layers inside the combustion chamber relative to the axis of sliding of the piston. Such an improvement would make it possible to better control the relative positioning of the different layers with respect to the ignition point of combustion in the chamber and thus reduce the pollutant emissions of nitrogen oxide.

  In this context, the object of the present invention is to propose an engine and an engine injection method making it possible to improve the symmetrical distribution in the combustion chamber, around the axis of sliding of the piston, of the different gaseous strata having different levels of oxidizer and recycled flue gas.

  To this end, the engine of the invention, moreover in conformity with the generic definition given in the preamble above, is essentially characterized in that it comprises a second flue gas duct connected on the one hand by means of flow control device and connected on the other hand, by a second connection zone, to the second intake means, the first connection zone between the first pipe and the first intake means being adapted to create in the combustion chamber a first fluid stream containing an oxidant and a second fluid vein contiguous to the first and containing burnt gases, the second connection zone between the second pipe and the second intake means being adapted to create in the combustion chamber a third fluid vein containing the oxidant and a fourth fluid vein contiguous to the third and containing burnt gases, and these fluid veins forming fluid layers concentric with respect to the axis of sliding of the piston.

  For this purpose also, the method of the invention, moreover, in accordance with the generic definition given in the preamble above, is essentially characterized in that a first fluid vein containing an oxidant and a second fluid vein contiguous to the first and containing burnt gases are injected into the combustion chamber by the first intake means and in that a third fluid stream containing an oxidant and a fourth fluid vein contiguous to the third and containing burnt gases are injected into the combustion chamber by the second intake means, these fluid veins forming fluid layers concentric with respect to the axis of sliding of the piston.

  The fact of creating a gaseous layer in a chamber by means of two different admission means makes it possible to improve the distribution of the sources of intake of recycled burned gases or of oxidizer in the chamber and thus to reduce the asymmetries of admission. of these gaseous fluids relative to the main axis of the chamber.

  In addition, the fact that the same admission means is used to generate in the same chamber two fluid veins contiguous to one another makes it possible to reduce the risk of occurrence of turbulence between these fluid veins, which favors the generation of strata inside the chamber.

  The combination of these two advantages therefore makes it possible to create layers whose thicknesses can be easily adjusted by varying the flow rate of each fluid stream and also to improve the symmetrical distribution of these layers in the combustion chamber.

  Thus, thanks to the engine and the method according to the invention, the efficiency of the engine can be improved, and the noise and the volume of polluted gas generated can be reduced compared to the engines of the prior art.

  For example, it is possible for the first and third fluid veins to form a first stratum and for the second and fourth fluid veins to form a second stratum.

  Thus, the first and second strata are respectively composed of the gases of the first and third fluid veins for the first stratum and gases of the second and fourth fluid veins for the second stratum.

  In cases where the first and third fluid veins have the same composition, then the first layer will have a homogeneous composition. Similarly for the case where the compositions of the second and third fluid veins are of the same composition, then the second layer will have a homogeneous composition. 15 20

  Preferably, the layers have homogeneous compositions so as to carry out concentric lamination with respect to the axis of sliding of the piston.

  The device according to the invention may alternatively be used to create a first and / or a second layer of non-homogeneous nature (s).

  For this: the first and third fluid streams have gaseous compositions different from each other, which generates a first heterogeneous layer composed of at least two different gases; and / or the second and fourth fluid streams have gaseous compositions different from each other, which generates a second heterogeneous layer composed of at least two different gases.

  The heterogeneous stratum or layers may for example be used when the combustion chamber has a plurality of fuel injection points offset relative to the axis of sliding of the piston. In this case it may be useful to generate one or more portions of strata having high concentrations of flue gases around each fuel injection point at the time of ignition. In this way the volume of nitrogen oxide generated by a chamber with multiple fuel injection points can be reduced without having to inject a large amount of recycled flue gas.

  Preferably, the first and third fluid veins create a first layer containing an oxidizer and the second and fourth fluid veins create a second concentric layer of the first and containing recycled burnt gases.

  In the case of a chamber having a fuel injection point centered in the chamber and substantially aligned with the sliding axis of the piston, the first stratum containing an oxidant is preferably peripheral of the second stratum containing flue gas.

  In this way the recycled burned gas stratum is distributed symmetrically and facing the axis of sliding of the piston and therefore at the injection point.

  Alternatively the second stratum containing flue gas is peripheral to the first stratum containing an oxidant, this may for example be useful when the ignition point or points of combustion are offset with respect to the axis of sliding of the piston.

  Other features and advantages of the invention will emerge clearly from the description which is given below, by way of indication and in no way limiting, with reference to the accompanying drawings, in which: FIG. 1 shows a combustion chamber of a motor according to the invention; Figure 2 shows a sectional view of the combustion chamber of the engine according to the invention 5 containing two concentric gaseous layers.

  As previously announced, the invention relates to a heat engine comprising a combustion chamber 1 in which a piston slides, along a sliding axis 2 of the piston. Fuel injection means in the chamber 1, not shown, are generally placed in the sliding axis of the piston 2, on a wall of the chamber 1.

  The first and second intake means 3, 4, which are generally valves, make it possible to selectively admit into the chamber 1 a gaseous oxidizer containing air.

  Exhaust means 5, 6 selectively permit the escape of flue gases from chamber 1. Recycling means comprises a main line for collecting and transporting a portion of the flue gases to a flow control means 17. These recycling means allow the recycling of flue gases in the combustion chamber.

  A first flue gas pipe 7 is connected on the one hand to the flow control means 17 and connected on the other hand by a first connection zone 15 to the first intake means 3.

  A second flue gas duct 8 is connected on the one hand to the flow control means 17 and connected on the other hand by a second connection zone 16 to the second intake means 4.

  The first connecting zone 15 between the first pipe 7 and the first intake means 3 is adapted to create in the combustion chamber 1 a first fluid stream 9 containing an oxidant and a second fluid vein 10 contiguous to the first 9 and containing burnt gases.

  Similarly, the second connection zone 16 between the second pipe 8 and the second intake means 4 is adapted to create in the combustion chamber 1, a third fluid stream 13 containing the oxidant and a fourth fluid stream 14 contiguous to the third 13 and containing burnt gases.

  The first connection zone 15 is formed by a first tangential tapping 15 of the first pipe 7 on an oxidant feed pipe 18 of the first intake means 3.

  This first tapping is thus adapted to allow a tangential flow of the second fluid vein 10 with respect to the flow of the first fluid vein 9 in the first intake means 3.

  Likewise, the second connection zone 16 is formed by a second tangential tapping 16 of the second pipe 8 on an oxidizer feed pipe 19 of the second intake means 4.

  This second stitching 16 is adapted to allow a tangential flow of the fourth fluid stream 14 with respect to the flow of the third fluid stream 13 in the second admission means 4.

  These connections 15 and 16 are adapted so that the oxidant and the recycled flue gases flow to the combustion chamber 1 according to laminar flows, minimizing the mixture between the first and second fluid veins and between the third and fourth veins fluids.

  The first and third fluid veins 9, 13 form a first stratum 11 and the second and fourth fluid veins 12, 14 form a second stratum 12, these strata being arranged concentrically with respect to the sliding axis 2 of the piston.

  As shown in the example of FIG. 2, the first stratum containing an oxidant is peripheral to the second stratum 12 containing flue gas.

  According to a particular embodiment of the invention, at least one of the fluid veins can be admitted into the chamber through intake ports forcing the fluid vein to swirl on itself.

Claims (8)

  1. Cyclically operating thermal engine such as a diesel engine with direct injection, comprising in particular a combustion chamber (1) in which a piston slides, along a sliding axis (2) of the piston, fuel injection means in the chamber (1), first and second intake means (3, 4) for selectively admitting into the chamber (1) a gaseous oxidant containing air, exhaust means (5, 6) for allowing selectively exhausting gases burned out of the chamber (1) and recycling means including a flow control means (17) for recycling burnt gases, and a first conduit (7) of burnt gas connected on the one hand by means of flow control (17) and connected on the other hand, by a first connection zone (15), to the first intake means (3), the engine being characterized in that it comprises a second pipe ( 8) of flue gas connected on the one hand by means of flow control (17) and connected to on the other hand, by a second connection zone (16), to the second intake means (4), the first connection zone (15) between the first pipe (7) and the first intake means (3) being adapted to create in the combustion chamber (1) a first fluid vein (9) containing an oxidant and a second fluid vein (10) contiguous to the first (9) and containing flue gases, the second connection zone (16) between the second duct (8) and the second intake means (4) being adapted to create in the combustion chamber (1) a third fluid duct (13) containing the oxidant and a fourth fluid duct (14) contiguous to the third (13) and containing burnt gases, and these fluid veins (9, 10, 13, 14) forming fluid layers (11, 12) concentric with respect to the axis of sliding (2) of the piston.   2. Motor according to claim 1 characterized in that the first and third fluid veins (9, 13) form a first layer (11) and in that the second and fourth fluid veins (12, 14) form a second layer (12). ).   3. Motor according to one of claims 1 or 2   characterized in that the first connection zone (15) is formed by a first tangential tapping (15) adapted to allow a tangential flow of the second fluid vein (10) with respect to the flow of the first fluid vein (9) in the first intake means (3).   4. Motor according to one of claims 1 to 3 characterized in that the second connecting zone (16) is formed by a second tangential tapping (16) adapted to allow a tangential flow of the fourth fluid stream (14) relative to at the flow of the third fluid vein (13) in the second intake means (4).   5. Injection method for a cyclically operating thermal engine such as a direct injection diesel engine, comprising in particular a combustion chamber (1) in which a piston slides, along a sliding axis (2) of the piston, means for injecting fuel into the chamber (1), first and second intake means (3, 4) to selectively admit into the chamber (1) a gaseous oxidant containing air, exhaust means (5), , 6) for selectively allowing escape of flue gases from the chamber (1) and recycling means including flow control means (17) for recycling flue gases, the method being characterized in that a first fluid vein (9) containing an oxidant and a second fluid vein (10) contiguous to the first (9) and containing flue gases are injected into the combustion chamber (1) by the first intake means (3) and what a third fluid vein (13) containing a and a fourth fluid vein (14) contiguous to the third (13) and containing flue gases are injected into the combustion chamber (1) by the second intake means (4), these fluid veins (9, 10, 13, 14) forming fluid layers (11, 12) concentric with respect to the sliding axis (2) of the piston.   6. Method according to claim 5 characterized in that the first and third fluid veins (9, 13) create a first layer (11) containing an oxidant and in that the second and fourth fluid veins (10, 14) create a second stratum (12) concentric of the first (11) and containing recycled burnt gases.   7. The method of claim 6 characterized in that the second layer (12) containing flue gas is peripheral to the first layer (11) containing an oxidant.   8. The method of claim 6 characterized in that the first layer containing an oxidant is peripheral to the second layer (12) containing flue gas.