WO2015071093A1 - Method for mixing at lest one oxidant and at least one fuel in the combustion chamber of a compression-ignition direct-injection internal combustion engine, and engine using such a method - Google Patents

Abstract

The present invention relates to a method for mixing at least one oxidant and at least one fuel for a compression-ignition direct-injection internal combustion engine comprising a cylinder (10), a cylinder head (12) bearing fuel-injection means (14), a piston (16) sliding in this cylinder, a combustion chamber (34) delimited on one side by the upper face (44) of the Mexican-hat piston comprising a cone (48) rising up toward the cylinder head and positioned at the centre of a concave bowl (46), said method consisting in injecting the fuel in at least two sheets of fuel jets (36, 38) with different sheet angles (A1, A2), and in admitting the oxidant into the combustion chamber with a swirling movement with a degree of swirl (Ts). According to the invention, the method consists, for a position D of the piston (16), in injecting the fuel of the lower sheet (36) into a zone (Z1) which comprises a toric volume (64) of centre B in such a way that the axis C1 of the fuel jets of the sheet lies between the centre B and the cone (48) and in introducing the oxidant with a level of swirl less than or equal to 1.4.

Description

 Process for mixing at least one oxidant and at least one fuel in the combustion chamber of a direct injection direct injection internal combustion engine

 compression and motor using such a method.

The present invention relates to a method for mixing at least one oxidant and at least one fuel in the combustion chamber of a compression-ignition direct injection internal combustion engine.

The invention also relates to an internal combustion engine using such a method. It relates more particularly to such an engine used in the aeronautical or automotive field or in the field of stationary installations, such as a generator.

It is already known in conventional combustion engines to use a particular inlet of the oxidant, such as air (at ambient pressure or supercharged) or a mixture of supercharged air or not and recirculated exhaust gas, for promote mixing between this oxidizer and the fuel injected.

By fuel is meant a liquid fuel, such as diesel, kerosene or any other fuel having the physico-chemical characteristics for the operation of a compression ignition type engine including a direct injection system of the fuel.

Some of the known embodiments to promote this mixture consist in giving a swirling movement, that is to say a rotational movement of the oxidizer around an axis substantially parallel or coincident with that of the combustion chamber, either after admission to the room combustion, either from its entry into this chamber so that the oxidant mixes "by mixing" with the fuel injected.

 This swirling movement of the oxidizer is better known as "swirl".

 This swirl can be generated either by an intake manifold arranged tangentially and radially to the combustion chamber, said tangential tubular, or by a spiral-shaped tubing, called helicoidal tubing, shaped to create a swirling movement of the oxidant as soon as its introduction into the combustion chamber.

This swirl has the advantage of improving the mixing of the fuel with the fuel while decreasing the emissions of pollutants, such as fumes particularly low load and low engine speed when the internal aerodynamics of the combustion chamber is insufficient to mix the oxidant with the fuel.

Generally, the swirl is characterized by a rate which is equal to N _D / N where N _D is evaluated by integration on the piston path, during the intake stroke, of the rotation of the elementary charge (fuel) introduced by holding the valve lift and the piston speed, followed by a division by the total amount of oxidant introduced while N is the rotational speed of the engine.

However, the use of a high swirl rate, of the order of 3, has the significant disadvantage of circumferentially deflecting the fuel jets which superimpose on each other. This results in a significant increase in pollutant emissions, such as soot or hydrocarbons.

In the case of engines operating at low speed and in homogeneous combustion, the ignition is done by auto ignition of the fuel mixture and this implies in particular to promote the mixture of the oxidant with the fuel.

One of these types of motor, which is more precisely described by the document JP 5-71347, comprises at least one cylinder, a piston sliding in this cylinder in a reciprocating rectilinear motion, means for admitting an oxidizer, exhaust gas exhaust means, a combustion chamber, and injection means for injecting a fuel into the combustion chamber.

In this type of engine, the combustion chamber is delimited by the circular wall of the cylinder, the inner face of the cylinder head and the upper face of the piston which comprises a bowl, inside which is arranged a nipple whose top is erects towards the breech, and includes two volumes of combustion.

 The combustion chamber is supplied with oxidant by at least one tangential or helical inlet manifold, and with fuel by injection means for injecting the fuel jets in at least two corners of the ply.

 In view of the increase in the number of fuel jets, the swirl circumferentially and axially deflects the fuel jets of the two plies which overlap one another and mix with each other. This results in even greater increases in pollutant emissions, such as soot or hydrocarbons, with a noticeable reduction in engine performance.

The present invention proposes to overcome the drawbacks mentioned above by means of a method and a motor which make it possible to obtain a better mixture of the oxidant with the fuel injected into the combustion chamber while allowing the use of a system injection at at least two web angles. For this purpose, the present invention relates to a method for mixing at least one oxidant and at least one fuel for a direct injection internal combustion engine with compression ignition comprising at least one cylinder, a bearing cylinder head fuel injection means, a piston sliding in this cylinder, a combustion chamber defined on one side by the upper face of the piston having a pin extending in the direction of the cylinder head and disposed in the center of a concave bowl, said method of injecting the fuel into at least two different ply angle fuel jet plies, a lower jet axis ply C1 and an upper jet axis ply C2, and admitting the oxidant into the combustion chamber according to a swirling movement with a swirl ratio, characterized in that it consists, for a position of the piston considered between the bottom of the bowl and the origin of the fuel jets of the upper layer, to inject the fuel from the lower layer into an area which has a central B-ring volume in such a way that the axis C1 of the fuel jets of the sheet is located between the center B and the pin and introducing the oxidant with a swirl rate of less than or equal to 1 .4, the position D of the piston corresponding to L4 + ID1 / tangent a2 where L4 is the height between the bottom of the bowl and the point of impact of the fuel jets of the upper layer, ID1 is the injection diameter high considered between the points of impact and a2 is the half-angle at the top of the upper layer.

The method may include introducing the oxidant into the combustion chamber in a swirling motion coaxial with that of the bowl. The method may include injecting the fuel in at least two fuel jet plies axially located one above the other.

The method may consist in injecting the fuel according to a fuel jet layer with a lap angle at most equal to 130 ° and in another fuel jet layer with a lap angle of at least 130 °.

The invention also relates to a direct injection internal combustion engine with compression ignition comprising at least one cylinder, a cylinder head carrying fuel injection means, a piston sliding in this cylinder, a combustion chamber delimited on one side by the upper face of the piston having a stud running in the direction of the cylinder head and disposed in the center of a concave bowl, said injection means projecting fuel according to at least two layers of different angle fuel felts, a lower plane of jet axis C1 and an upper layer of jet axis C2, at least two mixing zones of the combustion chamber, characterized in that one of the zones comprises a toric volume of center B in which the fuel streams of the lower layer are injected in such a way that the axis C1 of the jets of the lower layer is situated between the center B and the pin and in that the engine comprises means for admitting the oxidizer with a swirl rate of less than or equal to 1 .4.

The other features and advantages of the invention will appear on reading the description which follows, given by way of illustration and not limitation, and to which are appended:

 - Figure 1 which shows an internal combustion engine according to the invention;

- Figure 2 which is a partial view on a large scale of a half-section of the profile of the piston bowl of the engine of Figure 1;

 - Figure 3 which is a graph illustrating the evolution of the engine power (P) in base 100 according to the swirl rate (Ts);

 FIG. 4 which illustrates the evolution of the mass mass (mS) in base 100 as a function of the swirl rate (Ts) and

 - Figure 5 shows the evolution of the mass of unburned hydrocarbons (mHC) in base 100 according to the swirl rate (TS).

In FIGS. 1 and 2, the engine illustrated is a compression-ignition direct injection internal combustion engine comprising at least one cylinder 10, a cylinder head 12 closing the cylinder at the top, fuel injection means 14 carried by the cylinder head and a piston 16 of axis XX 'sliding in the cylinder in a reciprocating rectilinear motion.

By fuel is meant a liquid fuel, such as diesel, kerosene or any other fuel having the physico-chemical characteristics for the operation of a compression ignition type engine including a direct injection system of the fuel.

This engine also comprises a flue exhaust means 18 with at least one exhaust pipe 20 whose opening can be controlled by any means, such as for example an exhaust valve 22 and an intake means 24. an oxidizer with at least one intake manifold 26 whose opening can be controlled by any means, such as an intake valve 28. This inlet means is shaped so as to admit the oxidizer into the combustion chamber in a swirling motion (MT deflection), that is to say a rotational movement of the oxidant stream around a substantially parallel axis or confused with the axis XX ', either after admission to the combustion chamber, or as soon as it enters the chamber so that the oxidant mixes with the fuel injected.

 This swirling movement of the oxidizer or swirl can be generated either by the inlet pipe 26 arranged tangentially and radially to the combustion chamber, said tangential pipe, or by the inlet pipe 26 with a helical shape, called helical pipe. , shaped to create a swirling movement of the oxidant as soon as it is introduced into the combustion chamber.

By the term oxidizer, it includes air at ambient pressure or supercharged air or a mixture of air (supercharged or not) with flue gas.

The injection means comprise at least one fuel injector 30, preferably disposed in the axis XX 'of the piston whose nose 32 comprises a plurality of orifices through which the fuel is sprayed and projected towards the chamber of combustion 34 of the engine.

It is from these injection means that the projected fuel forms at least two plies of fuel jets, here two plies 36 and 38 of fuel jets 40 and 42, which, in the example shown, have an axis general confused with that of the piston 16 while being located axially one above the other.

 More specifically, the ply 36 which is located closest to the piston 16 is referred to below in the description of the lower ply while the ply 38 placed furthest from this plunger is called the upper ply.

As can be seen in FIG. 1, these two plies form plane angles A1 and A2 that are different from one another. By nappe angle, it is understood the angle at the summit that forms the cone coming from the injector and whose imaginary peripheral wall passes through all the axes C1 and C2 of the fuel jets 40 and 42. Advantageously, the ply angle A1 of the low ply is at most 130 °, preferably between 40 ° and 130 °, so that the ply angle A2 of the high ply is at most 180 °, preferably between 130 ° and 180 °. For reasons of simplification in the rest of the description, the angle a1 corresponds to the half-angle A1 while the angle a2 corresponds to the half-angle of A2.

The gap between the two ply angles thus makes it possible to limit overlaps of fuel jets between the two plies and therefore the formation of pollutants, such as soot.

Of course, it can be expected that the injection means are not arranged in the axis XX ', but in this case, the general axis of the fuel jet layers from the fuel injector is at least substantially parallel to this axis XX '.

 Similarly, it may be provided that each web is carried by a separate injector (single-web injector) with dedicated targeting in separate areas of the combustion chamber.

The combustion chamber 34 is delimited by the internal face of the cylinder head 12 opposite the piston, the circular inner wall of the cylinder 10 and the upper face 44 of the piston 16.

This upper face of the piston comprises a concave bowl 46, here of axis coincident with that of the cylinder, whose concavity is turned towards the cylinder head and which houses a pin 48 located substantially in the center of the bowl, which rises towards the cylinder head 12 , being preferably coaxial with the axis of the fuel plies from the injector 30. Of course, it can be expected that the axis of the bowl is not coaxial with that of the cylinder but the essential lies in the provision wherein the axis of the fuel jet web, the axis of the pin and the axis of the bowl are preferably coaxial. Referring more particularly to Figure 2, the stud 48, of generally frustoconical shape, has an apex 50 preferably rounded, continuing, deviating symmetrically from the axis XX 'towards the outside of the piston 16, by a substantially rectilinear inclined surface 52 continuing with an inclined flank 54 to reach a bottom 56 of the bowl.

Of course and without departing from the scope of the invention, the inclined surface 52 may be non-existent (zero length) and the inclined side 54 then connects the top of the stud to the bottom of the bowl.

In the example of FIG. 2, the bottom of this bowl is rounded with a concave curved surface 58 in the form of an arc of radius R1, referred to as the inner rounded surface, connected to the bottom of the inclined sidewall 54 and another concave rounded surface 60 in an arc of radius R2, said outer rounded surface, connected by one of its ends to the lower end of the inner rounded surface at a point M and the other of its ends to a side wall 62, here substantially vertical, at a point N.

 The two rounded surfaces 58 and 60 thus delimit the lower part of a toric volume, here a torus of substantially cylindrical section 64 and center B whose role will be explained in the following description.

 The lateral wall 62 continues, always deviating from the axis XX ', by a rounded convex surface 66 in a circular arc of radius R3, called a reentrant, ending in an inclined plane 68 connected to a concave inflexion surface. 69 This flat surface is continued by an outer convex surface 72 in an arc of radius R5 which arrives at a flat surface 74 extending to the vicinity of the wall of the cylinder.

The combustion chamber thus comprises two distinct zones Z1 and Z2 which ensure the mixing between the oxidant they contain (air-supercharged or non-mixed air or recirculated flue gas and the fuel coming from the injector as well as the combustion of the fuel mixture thus formed.

The zone Z1 delimited by the stud 48, the torus 64 of the bottom of the bowl, the wall 62 and the rounded convex surface 66 form the lower zone of the chamber of combustion which is associated with the lower ply 36 of C1 axis fuel jets, and zone Z2 demarcated by the inclined plane 68, the concave surface 69, the substantially planar surface 70, the convex surface 72, the plane surface 74, the peripheral inner wall of the cylinder and the cylinder head 12 constitutes the upper zone of this chamber which is associated with the upper layer 38 of C2 axis fuel jets.

In this configuration, the bowl comprises, for a piston position close to the top dead center:

 a bottom diameter of the bowl FD with a radius considered between the axis XX 'and the lowest point M of the bowl, that is to say at the intersection between the radiating surfaces R1 and R2,

 a diameter of the bowl opening BD with a radius considered near the bottom of the bowl and corresponding to a distance taken between the axis XX 'and the point furthest from the external concave surface 60,

 a neck diameter GD with a radius which corresponds to the distance between the axis XX 'and the vertical wall 62 which delimits the outlet section of this bowl,

 a high injection diameter ID1 with a radius corresponding to the distance between the axis XX 'and the beginning of the inflection surface 69 at the point P between the inclined plane 68 and the concave surface 70 delimiting a length L6 jets 38 between the origin T2 of the axis C2 of the jets on the axis of the nose of the injector and the point P and which corresponds to the formula ID1 / sinus a2,

 a developed length of the diametrical half-cut Cb of the bowl constituted by the length from the intersection of the top of the stud with the axis XX 'to the wall of the cylinder,

 a height H of nipple between the bottom of the bowl at point M to the top of the nipple,

 a height L of the bowl between the bottom of the bowl at the point M to the flat surface 74,

 a junction height L3, which corresponds to the extent of the lateral wall

62, considered between the end of the outer rounded surface 60 at the point N and the beginning of the outer rounded surface 66,

 a height L4 considered between the point P and the point M,

an angle of inclination a3 with respect to a vertical for the inclined sidewall 54, an angle of inclination a4 formed by the main axis C1 of the fuel jets of the lower ply 36 impacting the torus with the tangent at the point of impact F by delimiting a length L5 of the jets 40 between the origin T1 of the C1 axis of the jets on the axis of the nose of the injector and the point F. This length L5 corresponds to the formula ID2 / sine A1 with ID2 which corresponds to a low injection diameter with a radius which corresponds to the distance between axis XX 'and point F,

 an angle of inclination a5 considered at the tangency of the outer rounded surface 60 with the side wall 62 at the point N,

 an angle of inclination a6 with respect to the horizontal and the tangent to the substantially plane wall 70,

 an angle of inclination a7 with respect to the horizontal and the inclined plane 68 at the point of intersection P.

All these parameters are appreciated for a position of the piston 16 in the vicinity of the top dead center which corresponds to a distance D considered between the point M and the origin T2 of the axis C2 of the jets 42.

 More precisely, this distance D is equal to the sum of the height L4 and the height C, height C which corresponds to the axial height between the origin T2 and the point P. This height corresponds to the formula I D1 / tangent a2 .

Thus, the dimensional and angular parameters of this bowl satisfy at least one of the following conditions:

 the angle a4 is greater than 80 °. This amounts to passing more than half of the fuel jet between the center B of the torus 64 and the pin and more precisely the lower part at the point M and thus to ensure an aerodynamic movement in the torus going back up the cylinder,

 the angle a5 must be positive and less than 90 °. Preferably, it must be of the order of 30 ° to 40 ° in order to direct the fuel jets 40 of the lower ply 36 to the volume of oxidant S1 to use the oxidant of this zone while limiting the rise of this fuel towards the upper sheet 38,

the volume S1 of oxidant located between the jets 40 of fuel of the lower layer is minimized, again with a view to optimizing the use of the oxidant in the chamber; the position of the top of the stud 48 is as close as possible to the nose 32 of the injector 30 in order to limit the volume of oxidizer under the injector which will not be impacted by the fuel jets, which again amounts to minimize the volume S1. Thus the H / L ratio is greater than 40% and preferably greater than 60%,

 - The angle a3 is substantially equal to or greater than the angle a1 of the lower layer (-10 ° <a3-a1 <10 °). This is to use the side 54 of the stud to guide the fuel jets 40 in the torus 64 while allowing these jets to vaporize completely before impacting the piston,

the volume of oxidant S2 between the two layers is not zero since the interaction between the layers is harmful to the pollutants. The volume S2 must nevertheless be minimized. To do this, the junction length L3 between the torus and the reentrant 66 (convex rounded surface of center R3) must be such that L3 / (2 ^* length of R2) <1 or (L3 / length of R2 <2) so to ensure that the volume of oxidizer S2 available between the upper 38 and lower 36 layers is small compared to the volume of fuel generated by the jets of the lower layer,

 the second combustion zone Z2 located in the upper part of the piston which starts from the reentrant 66 is intended for the fuel jets 42 of the upper sheet 38,

 the combustion volume of zone Z2 is at least equal to one tenth of the total volume of the bowl,

the so-called hunting zone is formed by the inclined plane 68, the concave surface 69, the flat surface 70, the convex surface 72 and the flat surface 74. The angle a6 is between 10 ° and 75 °, which allows the fuel jets 42 to burst to create an aerodynamic movement above the piston and additionally to use the oxidizer in the hunting zone. This aerodynamics allows a better fuel / oxidant mixture above the piston, especially during the relaxation and thus promote the oxidation of burnt gases, - to promote the impact of the jets 42 on the flush, a guide surface 68 is provided between the reentrant 66 and the surface 70. This guide surface may be rounded in extension of the reentrant or substantially flat. This guide surface serves to concentrate the fuel jets 42 and to guide them towards the convex surface 72. Thus this guide surface has an angle a7 at the point of intersection P whose distance from the ply angle α2 is less than 45 °,

 the location of the inflection surface 69 is such that the distances L5 and L6 are approximately of the same order (0.5 <L5 / L6 <2). Thus, advantageously the fuel jets will substantially impact at the same time the piston in the torus and the inflection zone respectively. More generally, the diameter I D1 must be such that I D1 / GD> 1 and I D1 <(GD + (Cb-GD) * 2/3). This allows the fuel jets 42 to optimize the aerodynamics above the piston.

Moreover,

 The ratio BD / L is less than 6, preferentially less than 4,

The ratio R2 / R1 is less than 1, preferably less than 0.6,

The ratio FD / BD is less than 1,

 The ratio Cb / BD is less than 2 to maintain complete vaporization of the fuel and to prevent wetting of the wall of the cylinder,

• the ratio GD / BD is between 0.7 and 1 for the torus aerodynamics and the recovery of the fuel jets,

 The ratio H / L is greater than 40%, preferably greater than 60% to minimize the volume of oxidant between the nose of the injector and the nipple,

 The ratio L5 / L6 is between 0.5 and 2 for the impact of the two layers at the same time,

 A1 is between 40 ° and 130 ° with a1 = A112,

 • A2 is between 130 ° and 1 80 ° with a2 = A2 / 2,

 A3 is substantially equal to a1,

 • a4 is greater than 80 °,

 A5 is between 0 ° and 90 °, preferably between 30 ° and 40 °,

 The angle a6 is between 15 ° and 75 °,

 • a7-a2 is less than 45 °,

 The ratio I D1 / GD is greater than 1,

• I D1 is less than (GD + (Cb-GD) * 2/3). Thus, thanks to this setting of the bowl, the fuel jets of the lower sheet 36 directly target the torus 64 and do not directly impact the reentrant 66.

 As a result, the combustion of the fuel / lower oxidant mixture takes place essentially in the volume of the torus while the combustion of the fuel / higher oxidant mixture takes place essentially in the flush and above the piston.

 In addition, the interaction of the jets of the upper layer with the jets of the lower layer is limited, which makes it possible to homogenize the oxidant / fuel mixture while complying with high-load mechanical strength constraints.

In the case where a high rate of swirl is used, the tangential velocities of the oxidizer become predominant in front of the substantially axial speeds of the vaporized fuel jets which impact the bowl.

 As a result, the fuel jets of the lower sheet can not get out of the bowl since they are redirected by the oxidizer. This is especially true that the speed of the fuel jets is low and therefore the injection pressure is low.

 It is important that the fuel does not remain confined in the bowl but can stand out to use a maximum of oxidizer during combustion, including that available in the volume S2 and thus reduce the emissions of pollutants such as soot and unburned hydrocarbons. This increases the wealth in the combustion chamber and therefore increase the performance of the engine.

In the case of an injection system with at least two ply angles and two combustion zones, as described above, the high swirl rates are all the more problematic since the fuel plies are not subject to the same conditions. intensity of swirl.

Indeed, the intensity of swirl in the bowl is stronger than in the rest of the room. Thus the fuel jets of the lower water table will be even more deviated by the swirl than those of the upper water table, which increases the superposition of the lower and upper fuel jets.

 This superposition degrades the combustion and increases the emission of pollutants such as fumes and unburnt.

By using a low swirl rate of the order of 1 .4, the vaporized fuel can get out of the bowl since the tangential velocities of the oxidizer are lower and no longer deviate the substantially axial speed of the jets, which thus have enough energy to get out of the bowl.

In addition, the use of a low swirl rate, coupled with the use of a double-ply injection system and a combustion chamber with two combustion zones makes it possible to avoid the superposition of the jets, which does not can only lower emissions of pollutants such as soot and unburned hydrocarbons by improving the mixing and quality of combustion.

For example, the applicant has performed numerical simulations of fluid mechanics in reactive flows whose results are shown in Figures 3 to 5.

 For these simulations, the applicant to use an internal combustion engine with a diesel type fuel and comprising a combustion chamber having two combustion zones and an injection system with two ribs angles. According to the results of Figure 3, which shows a graph showing the power of the engine (P base 100) and the abscissa rates swirl (Ts), the engine power drops by nearly 5% for a rate of 2. For a swirl rate of up to 1 .4, the decrease in power is less important since it is only 1 .5%.

According to the results of FIG. 4, which shows a graph showing the mass of soot particles (mS in base 100) and the abscissa of swirl (Ts), the soot mass decreases significantly by lowering the of swirl. For a swirl rate falling from 2 to 1 .4, the decrease in soot mass is about 40%.

According to the results of FIG. 5, which shows a graph plotting the mass of unburnt hydrocarbons (mHC in base 100) and the swirl rates (Ts) in the abscissa, the mass of unburnt decreases significantly by lowering the rate of swirl. For a swirl rate falling from 2 to 1 .4, the decrease in the mass of unburnt is about 50%. Thus, it can be seen that a swirl rate of less than or equal to 1 .4 makes it possible to obtain a combustion that gives maximum power to the engine while improving the quality of combustion, thereby reducing unburned hydrocarbon emissions. and soot particles. In addition, it can be noticed that the use of a low swirl rate allows the use of a cylinder head with high permeability and is therefore advantageous for a high performance engine.

Claims

A method for mixing at least one oxidant and at least one fuel for a compression-ignition direct injection internal combustion engine comprising at least one cylinder (10), a cylinder head (12) carrying fuel injection means (14), a piston (16) sliding in said cylinder, a combustion chamber (34) delimited on one side by the upper face (44) of the piston comprising a stud (48) the direction of the cylinder head and disposed in the center of a concave bowl (46), said method of injecting the fuel into at least two different ply angle fuel jet plies (A1, A2), a lower ply (36); ) of jet axis C1 and an upper layer (38) of jet axis C2, and to admit the oxidant in the combustion chamber in a swirling motion with a swirl ratio (Ts), characterized in that consists, for a position D of the piston (16) considered between the bottom of the bo 1 (M) and the origin (T2) of the fuel jets of the upper layer, injecting the fuel from the lower layer (36) into an area (Z1) which has a center volume B (64) of in such a way that the axis C1 of the fuel jets of the ply is situated between the center B and the stud (48) and introducing the oxidant with a swirl ratio of less than or equal to 1 .4, the piston position D corresponding to L4 + ID1 / tangent a2 where L4 is the height between the bottom of the bowl and the point of impact (P) of the fuel jets of the upper layer, ID1 is the high injection diameter considered between the point of impact (P) and a2 is the half-angle at the top of the upper layer. 2) Process according to claim 1, characterized in that it consists in introducing the oxidizer into the combustion chamber in a swirling motion coaxial with that of the bowl (46). 3) Process according to claim 1 or 2, characterized in that it consists in injecting the fuel in at least two layers of fuel jets (36, 38) located axially one above the other. 4) Process according to claim 3, characterized in that it consists in injecting the fuel in a layer of fuel jets (36) with a lap angle (A1) at most equal to 130 ° and according to another this sheet of fuel jets with a lap angle (A2) of at least 130 °. 5) Direct injection internal combustion engine with compression ignition comprising at least one cylinder (10), a cylinder head (12) carrying fuel injection means (14), a piston (16) sliding in this cylinder, a combustion chamber (34) delimited on one side by the upper face (44) of the piston having a pin (48) extending towards the cylinder head and disposed in the center of a concave bowl (46), said means for injection projecting fuel according to at least two different ply angle fuel jet plies (A1, A2), a lower jet plane ply (36) C1 and an upper C2 thrust plane ply (38) at least two mixing zones (Z1, Z2) of the combustion chamber, characterized in that one of the zones comprises a toric volume (64) of center B into which the fuel jets (40) of the lower ply in such a way that the axis C1 of the jets of the lower ply is situated between the center B and the stud (48) and in that the engine comprises means for admitting the oxidizer with a swirl rate of less than or equal to 1 .4.