FR2879247A1 - Combustion chamber for direct injection internal combustion engine, has central injector delivering fuel jet along reduced cord angle, and peripheral part, of tulip, with bursting units to burst injected fuel jets against part along angle - Google Patents

Abstract

The chamber has a central injector (2) delivering a fuel jet along a determined reduced cord angle (b), when a piston (40) is between a top dead center and a determined intermediate distance with respect to the center, such that a concave tulip (14) surrounds a base of a cone formed by a jet surface. A peripheral part (44) of the tulip has fuel jet bursting units (142) for bursting injected fuel jets against the part along the angle.

Description

Engine combustion chamber and combustion engine piston

  TECHNICAL FIELD OF THE INVENTION The present invention relates to combustion chamber and piston configurations. The invention more particularly relates to an engine combustion chamber and an internal combustion engine piston for a large injection phase in the cycle.

  BACKGROUND OF THE INVENTION When injecting high pressure fuel into the combustion chamber, the risk of impact of the liquid jets on the cylinder oil film is important when the piston is relatively far from the neutral position. high (so far from the injection hole). However, this phenomenon greatly affects the durability of the oil, or even the reliability of the engine. Moreover, this type of injection can also cause a fouling of the oil in case of ignition of the jet in the vicinity of the cylinder in which the piston slides. Such fouling can occur during the relaxation phase.

  It is known in the prior art solutions to this problem, to reduce the cone angle or ply angle corresponding to the angle between the axes of the injector jets out through the injection holes vis-à-vis -vis the piston head. The ply angle is based on the axes of the jets projected by a hole injector, the jets being distributed around the axis of the piston. This type of configuration certainly allows to centralize the jet to avoid impacts on the cylinder oil but it becomes more difficult to properly exploit the entire mass of oxidizer. The wall of the piston on which the jets are directed defines a cavity forming a concave bowl having in its center a pin pointing towards the cylinder head. This wall of the piston effectively guides each jet but the fuel injected at high pressure with a reduced opening angle of the jet does not manage to mix optimally with the gases present in the center of the chamber.

  EP 1 340 891 or its equivalent US Pat. No. 6,691,670 proposes combustion chamber shapes that allow early injections with a reduced web angle. It is possible with this type of chamber to make injections when the piston is away from the top dead center. However, the quality of the mixture obtained is not optimal when the injection is close to top dead center.

  It is known from the applicant's patent application FR 2,849,900, a combustion chamber providing an intimate mixture of fuel and oxidant through two successive concave portions. However, the envisaged angle of coverage is in this case relatively large and promotes the risk of impact of liquid jets on the cylinder oil film. Patent application FR 2,839,114, which also uses a large angle of coverage of between 40 and 100, does not make it possible to remedy this type of disadvantage.

  There is therefore a need for solutions without risk of alteration of the cylinder oil to improve the mixture in the combustion chamber of a direct injection internal combustion engine, so as to reduce pollutant emissions and increase the specific power of the engine.

GENERAL DESCRIPTION OF THE INVENTION

  The present invention therefore aims to overcome one or more of the disadvantages of the prior art by providing a combustion chamber of suitable shape to optimize the oxidizer / fuel mixture while maintaining a reduced ribbon angle.

  This object is achieved by a combustion chamber of a direct-injection internal combustion engine, formed by a cylinder in which a piston is able to slide, said cylinder being closed off by a portion of a cylinder head arranged opposite a free wall of the piston. said free wall of the piston comprising a cavity forming a concave bowl having a central pin pointing towards the breech portion and a peripheral portion surrounded by an annular hunting area, said breech portion having a central injector projecting to inject fuel against said peripheral portion, characterized in that the central injector is arranged to deliver, when the piston is located between the top dead center and a predetermined intermediate distance away from the piston with respect to this top dead center, fuel jets according to a sufficiently determined lap angle so that said concave bowl surrounds the base of the cone formed by the a ply of jets when the piston is at said intermediate distance, said peripheral portion of the bowl comprising on an outer portion remote from the central stud means for allowing bursting of fuel jets injected against said peripheral portion at said determined lap angle.

  In another feature, said peripheral portion comprises: a main concave portion joining the central pin to guide centrifugally and / or centripetally at least one jet of fuel from the central injector; in an adjacent external position to the main concave portion, means for bursting the fuel jet guided by the main concave portion to detach the jet from the peripheral portion; and - an upper portion joining said annular flush to contain the fuel jets in a volume between the main concave portion and said yoke portion.

  Thus, the fuel / oxidant mixture is made homogeneous by bursting the jet guided in the bowl and the fuel is kept confined away from the oily walls of the cylinder.

  According to another feature, the web angle of the central injector is less than or equal to 100 and preferably less than 40, the lap angle and the diameter of the concave bowl being determined so that the fuel jets are injected against said peripheral portion in a piston position for which the C / D ratio is of the order of 0.5 where C is the distance between the free end of the piston and the central injector and D the internal diameter of the cylinder.

  The invention therefore makes it possible to ensure a good mixture between fuel and oxidant even for an early or late injection, the lap angle being sufficiently reduced so that there is no risk of impact of the liquid jets on the fuel. cylinder oil film.

  According to another feature, the burst means of the jet comprises at least one recess formed in said peripheral portion vis-à-vis the top of the central pin.

  According to another feature, the piston has a central axis of symmetry and the main concave portion comprises in association with the central pin a profile of revolution in W with respect to the central axis of the piston, the main concave portion having of share and other than the central axis XX 'a cross section U, a first end of the U forming relative to the central axis of the piston a first angle equal to half the angle at the top of the central nipple, the second end of the U forming relative to the central axis of the piston a second angle substantially equal to said first angle.

  According to another feature, the jet bursting means comprise at least one recess formed by an outgoing portion and a reentrant portion, said reentrant portion forming a generator cone frustum having with the central axis of the piston an angle substantially equal to said second angle, the outgoing portion and the reentrant portion forming between them an angle between 70 and 140.

  According to another feature, said recess forms on an outer edge of the main concave portionle an edge whose distance relative to said upper portion of the peripheral portion of the bowl is less than one third of the depth of the concave bowl.

  According to another feature, the central pin has a determined height at least equal to half the depth of the concave bowl.

  In another feature, the recess is substantially annular and continuous to form a perimeter around the main concave portion 5.

  According to another feature, the distance corresponding to the height of the recess in the concave bowl is between a tenth and a quarter of the depth of the bowl.

  Another object of the invention is to propose a piston of the type used in a combustion chamber which has a shape specifically adapted to allow the combustion / fuel mixture to be optimized by limiting the risk of impact of the liquid jets on the film. of cylinder oil.

  This object is achieved by a combustion chamber piston of the abovementioned type, having a central axis of symmetry and being arranged to move in translation along this central axis, comprising an upper wall and comprising a cavity forming a concave bowl having a central nipple. and a peripheral portion surrounded by an annular hunting area, characterized in that said peripheral portion comprises: a main concave portion joining the central nipple; in an adjacent external position to the main concave portion, means for bursting a jet of fuel guided by the main concave portion to detach said jet from the peripheral portion; and an upper portion joining said annular flush.

  The invention, with its features and advantages, will emerge more clearly on reading the description given with reference to the appended drawings in which: FIG. 1 is a diagrammatic view in longitudinal section of a combustion chamber according to the invention; FIG. 2 represents a view similar to that of FIG. 1 showing certain characteristics of the piston according to the invention; FIG. 3 represents a schematic view of a piston used in the prior art for reduced injection angles; FIG. 4 is a view similar to that of FIG. 1 showing an early or late injection, FIG. 5 is a partial schematic view in longitudinal section of an embodiment of the invention, and FIG. a view similar to that of FIG. 1 showing an injection close to top dead center.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION FIG. 1 illustrates a combustion chamber according to the invention intended for a direct-injection type internal combustion engine. This chamber is delimited by a cylinder (10) and a breech portion (12) of a flat-front cylinder head of an engine. The piston (40) is slidable in the cylinder (10) closed by the yoke portion (12), the latter being disposed opposite a free wall of the piston (40). The axis of translation of the piston in the cylinder (10) coincides with the central axis XX 'of symmetry of the piston (40). In the preferred embodiment of the invention, the upper wall or free wall of the piston (40) is machined around the central axis XX 'of the piston (40) and comprises a cavity forming a concave bowl (14). A projecting central stud (42) whose axis of symmetry coincides with the central axis XX 'of the piston (40) is provided in this bowl (14).

  As illustrated in FIG. 1, the central stud (42) points towards the breech portion (12), while a central injector (2) projecting from the breech portion (12) is located opposite said stud (42). ) along the axis XX '. In alternative embodiments, the injector (2) may also be slightly offset relative to the central axis XX 'of the piston (40). The injector (2) has at least one injection hole for injecting at least one ply of micronised fuel jets into the combustion chamber and is more specifically arranged to direct jets (20) of fuel against a peripheral portion (44). ) of the bowl (14) surrounding the central pin (42). This peripheral portion (44) is surrounded by s an annular hunting area (45) and mainly comprises a concave portion (141) joining the central pin (42) to guide at least one jet of fuel from the central injector (2). ). This guide (3) of the jet (20) can be made centrifugally as in the example of Figures 1, 5 and 6 for a position of the piston (40) relatively close to the top dead center or o centripetal as in l example of Figure 4 corresponding to a case of early or late injection. Said main concave portion (141) may comprise, in cross section, an axis of symmetry coaxial with a direction of injection of the central injector (2) at a point of the piston stroke (40) located between the top dead center and the bottom dead center. The guide (3) of the jet (20) can then be both centrifugal and centripetal for such an intermediate position of the piston (40) in the cylinder (10) for which the jets (20) of fuel are directed towards the bottom of the bowl (14).

  The central injector (2) is arranged to deliver, when the piston (40) is located between the top dead center and a determined intermediate distance away from the piston with respect to this top dead center, fuel jets at an angle of reduced web (b) determined, for example less than 40. This angle (b) is chosen low enough that said concave bowl (14) can completely surround the base of the cone formed by the jet ply when the plunger (40) is at said intermediate distance. In other words, the earliest and the latest injections occur at a distance away from the piston (40) less than or equal to this intermediate distance which is the maximum distance where the injection occurs. Said peripheral portion (44) of the bowl (14) comprises on an outer portion remote from the central pin (42) means (142) to allow the bursting of the injected fuel jets against said third said peripheral portion (44) according to said angle of web (b) determined.

  The peripheral portion (44) of the piston (40) according to the invention specifically comprises, in an adjacent position external to the concave portion (141), means (142) for bursting the fuel jet guided by the concave portion ( 141). As illustrated in FIGS. 1, 5 and 6, these fuel jet burst means (142) make it possible to detach the jet from the peripheral portion (44). The bursting (30) of the jet therefore occurs at the outer edge of the concave portion (141). With reference to FIG. 1, an upper annular portion (143) of said peripheral portion (44) is formed, for example, substantially perpendicular to the annular flush (45) for containing the fuel jets in a volume (V, FIG. 2) located between the concave portion (141) and said breech portion (12).

  The concave portion (141) surrounding the central stud (42) has a curvilinear concave shape in cross-section and forms a main concave portion of the peripheral portion (44) of the bowl (14), while the means (142) jet burst may consist of a secondary concavity adjacent to said main concave portion (141). In a preferred embodiment of the invention, the means (142) for bursting the jet comprise at least one outward radial recess (6) formed in said peripheral portion (44) facing the apex the central pin (42), as illustrated in Figures 1 and 2. Alternatively, asperities or projections of low vertical drop can be used to peel the jet and burst. The main concave portion (141) comprises two halves symmetrical with respect to the central axis XX 'of the piston (40) each having a U-shaped cross-section. A first end of the U forms with respect to the central axis XX' of the piston (40) a first angle equal to half the angle (a, Fig. 1) at the top of the central pin (42), while the second end of the U forms relative to the central axis XX 'of the piston (40). ) a second angle (e) substantially equal to said first angle. In other words, each of the symmetrical halves of the main concave portion (141) comprises, in cross section as shown in the figures, an axis of symmetry which may be parallel to the direction of injection of the fuel jets. The ply angle (b) may be less than or equal to the angle (f, FIG. 4) of the cone formed by the axes of symmetry of the main concave portion (141).

  With reference to FIG. 5, the jet burst means (142) may comprise at least one recess formed by a substantially straight outgoing portion (51) and a substantially reentrant substantially straight portion (52). These portions (51, 52) form between them an angle, for example between 70 and 140. In one embodiment of the invention with a recess formed by an outgoing portion (51) and a reentrant portion (52), said reentrant portion (52) is shaped for example lo a cone frustum whose generator forms with the central axis XX 'of the piston (40) an angle substantially equal to said second angle (e, Figure 1). The configuration of the jet burst means (142) is provided to prevent fuel jet deflections to the walls of the cylinder (10). The reentrant portion (52) is extended by the upper portion (143) which joins the annular hunting area (45). This upper portion of the peripheral portion (44) of the bowl (14) is substantially parallel to the central axis XX 'of the cylinder and sufficiently extended so that the burst means (142) are not too close to the hunting area annular (45).

  With reference to FIG. 2, the recess (6) forms on an outer edge of the main concave portion (141) an edge whose distance (50) with respect to said upper portion (143) is less than one-third of the depth ( 140) of the bowl (14). In other words, the recess (6) formed inside the bowl (14) is dimensioned in a reduced manner. This allows in particular to minimize the embrittlement of the piston (40) at this edge.

  By way of nonlimiting example the distance (50) corresponding to the height of the recess (6) is between one tenth and one quarter of the depth (140) of the bowl (14). The recess (6) is for example continuous to form a perimeter around the main concave portion (141). Alternatively, one or more recesses are arranged only in the path of each of the injection jets.

  FIG. 6 illustrates the case of injections close to top dead center. For this type of injection, the guidance of the jet is provided centrifugally through the presence of a central nipple (42) of relatively large dimensions. The angle (a, FIG. 1) at the top of the central pin (42) may be between 20 and 100, for example greater than the rib angle (b). As an illustration, the central pin (42) has a determined height (H, Figure 2) at least equal to half the depth (140) of the concave bowl (14). The oxidant / fuel mixture is thus also optimized for such injections close to top dead center. By way of comparison, the type of bowl used in the prior art for receiving injected fuel jets with reduced angles, as illustrated in FIG. 3, does not make it possible to obtain a mix quality as good as when a traditional combustion chamber is used, with a shallow piston and a large lap angle of at least 140. Indeed the jet guide (3 ') plates the jet against the concavity of the bowl, so that a significant amount of hydrocarbon can remain unburned.

  In the embodiment of FIG. 1, the ply angle (b) of the central injector (2) is less than or equal to 100, and may be preferentially less than 40. The web angle (b) and the diameter of the concave bowl (14) are determined so that the fuel jets are injected against said peripheral portion (44) of the bowl (14) in a position of the piston (40) for which the ratio C / D between the distance C between the free end of the piston (40) and the central injector (2) and the internal diameter D of the cylinder (10) is for example of the order of 0.5. This means that for positions relatively far from the top dead center, the fuel jets will not be directly projected onto the ring hunting area (45). Figure 4 illustrates a borderline case of early or late injection where the C / D ratio is 0.6. It is understood that a dimensioning adapted to the diameter of the bowl (14) avoids the risk of fuel projections on the walls of the cylinder (10).

  It is understood that a piston (40) designed according to the invention specifically comprises on the so-called peripheral portion (44) of the bowl (14) not only said means (142) of bursting jet fuel but also an upper portion (143) joining said annular flush (45) to contain fuel jets projected onto said peripheral portion (44). The jets can thus be contained in a defined volume (V) consisting of a first volume delimited by the main concave portion (141) and a second volume formed by the cylindrical extension of said first volume along an axis parallel to the axis translation XX 'of the piston (40).

  One of the advantages of the piston (40) according to the invention is to allow the use of reduced injection angles while avoiding to degrade the quality of the fuel / oxidant mixture. Unlike the combustion chambers of the prior art, the jet sent with a reduced angle (b) does not remain plated on the surface of the piston. It is thus obtained a strong mixture between air (or air + exhaust gas recirculation) and fuel despite the strong interaction between the jet and the piston that imposes the reduced injection angle.

  It should be obvious to those skilled in the art that the present invention allows embodiments in many other specific forms without departing from the scope defined by the scope of the appended claims, and the invention should not be limited. to the details given above.

Claims (12)

  1. Combustion chamber of direct injection internal combustion engine, formed by a cylinder (10) in which a piston (40) is slidable, said cylinder (10) being closed by a portion of yoke (12) disposed at view of a free wall of the piston (40), said free wall of the piston (40) comprising a cavity forming a concave bowl (14) having a central pin (42) pointing to the breech portion (12) and a peripheral portion (44) surrounded by an annular hunting zone (45), said yoke portion (12) having a central injector (2) projecting to inject fuel lo against said peripheral portion (44), characterized in that the injector central (2) is arranged to deliver, when the piston (40) is located between the top dead center and a predetermined intermediate distance away from the piston with respect to this top dead center, fuel jets at a lap angle ( (b) determined to be sufficiently low for said concave bowl (14) surrounds the base of the cone formed by the layer of jets when the piston (40) is at said intermediate distance, said peripheral portion (44) of the bowl (14) comprising on an outer portion remote from the central nipple (42) means (142) for allowing bursting of fuel jets injected against said peripheral portion (44) at said determined lap angle (b).   2. Combustion chamber according to claim 1, characterized in that said peripheral portion (44) comprises: a main concave portion (141) joining the central pin (42) to guide centrifugally and / or centripetally at least one jet of fuel from the central injector (2); in an adjacent external position to the main concave portion (141), means (142) for exploding the fuel jet guided by the main concave portion (141) to detach the jet from the peripheral portion (44); and an upper portion (143) joining said annular flush (45) to contain the fuel jets in a volume (V) located between the main concave portion (141) and said yoke portion (12).   Combustion chamber according to claim 1 or 2, wherein the ply angle (b) of the central injector (2) is less than or equal to 100 and preferably less than 40, the ply angle (b ) and the diameter of the concave bowl (14) being determined so that the fuel jets are injected against said peripheral portion (44) in a position of the piston (40) for which the C / D ratio is of the order of 0, Where C is the distance between the free end of the piston (40) and the central injector (2) and D the internal diameter of the cylinder (10).   4. Combustion chamber according to one of claims 1 to 3, wherein the means (142) for bursting the jet comprise at least one radial recess (6) outwardly formed in said peripheral portion (44) vis-à-vis -vis the top of the central nipple (42).   5. Combustion chamber according to one of claims 2 to 4, wherein the piston (40) has a central axis XX 'of symmetry and the main concave portion (141) comprises in association with the central pin (42) a profile of revolution in W relative to the central axis XX 'of the piston (40), the main concave portion (141) having on either side of the central axis XX' a U-shaped cross section, a first end of the U forming with respect to the central axis XX 'of the piston (40) a first angle equal to half the angle (a) at the apex of the central pin (42), the second end of the U forming with respect to the central axis XX 'of the piston (40) a second angle (e) substantially equal to said first angle.   6. Combustion chamber according to claim 5, wherein the means (142) for bursting the jet comprise at least one recess formed by an outgoing portion (51) and a reentrant portion (52), said reentrant portion (52) forming a generator cone frustum having with the central axis XX 'of the piston (40) an angle substantially equal to said second angle (e), the outgoing portion (51) and the reentrant portion (52) forming between them an angle between 70 and 140.   7. Combustion chamber according to one of claims 4 to 6, wherein said recess (6) forms on an outer edge of the main concave portion (141) an edge whose distance (50) relative to said upper portion (143). the peripheral portion of the bowl is less than one third of the depth (140) of the concave bowl (14).   8. Combustion chamber according to one of claims 1 to 7, wherein the central pin (42) has a determined height (H) at least equal to half the depth (140) of the concave bowl (14).   9. Combustion chamber according to one of claims 4 to 8, wherein the recess (6) is substantially annular and continuous to form a perimeter around the main concave portion.   10. Combustion chamber according to one of claims 4 to 9, wherein the distance (50) corresponding to the height of the recess (6) in the concave bowl (14) is between one tenth and one quarter of the depth (140) of the bowl (14).   11. Piston (40) specifically adapted for a combustion chamber of the type according to one of claims 1 to 10, having a central axis XX 'of symmetry and being arranged to move in translation along this central axis XX', comprising a top wall and comprising a concave bowl-shaped cavity (14) having a central stud (42) and a peripheral portion (44) surrounded by an annular hunting area (45), characterized in that said peripheral portion (44) comprises: a portion main concave (141) joining the central stud (42); in an adjacent external position to the main concave portion (141), means (142) for bursting a fuel jet guided by the main concave portion (141) to detach said jet from the peripheral portion (44); and an upper portion (143) joining said annular flush (45).   12. Piston according to claim 11, wherein the jet burst means (142) comprise at least one outward radial recess (6) formed in said peripheral portion (44) facing the apex of the central nipple (42).