FR2879676A1 - Four stroke direct injection diesel engine for motor vehicle industry, has injector delivering fuel spray along narrow slick with angle and along wide slick having angle so that fuel impact point at wide slick is placed on side wall of bowl - Google Patents

Abstract

The engine has a central fuel injector that delivers fuel spray along a narrow slick. An angle of the slick and an angle at top of a central tip (6) are determined, such that fuel spray is guided by a slope (62) of the tip. Fuel spray is delivered along wide slick having an angle, such that an impact point of the fuel spray at the wide slick is situated on a side wall (8) of a bowl.

Description

DIRECT INJECTION ENGINE

  The invention relates to a direct fuel injection engine, and in particular a four-stroke diesel direct injection engine, as used in the automotive industry.

  These engines conventionally comprise at least one cylinder with a cylinder head forming a lid above the cylinder, on which are mounted, substantially parallel to the axis of the cylinder, at least one fresh air intake valve, at least one exhaust, and a central fuel injector, and a piston slidably mounted in the cylinder between a top dead center and a bottom dead center and having on its upper surface a bowl provided with a central stud.

  Many bowl profile shapes have been proposed in order to improve engine performance and reduce emissions of pollutants, such as fumes, NOx, HC and CO.

  Conventionally, the bowl of the piston comprises a cone-shaped nipple or truncated cone, connecting to a side wall which can be vertical or have a concavity. The injector sprays the fuel under high pressure in several jets disposed on a cone, whose axis coincides with the vertical axis of the bowl. The web angle of the injector is such that the fuel jets intersect the side wall of the bowl when the piston is in the top dead center, and this results in a movement of the fuel / gas intake mixture downwardly and the center of the bowl. It has also been proposed, in particular in document EP 1 217 186, an injector with a low angle of coverage, so that the fuel jets coming from the injector are guided by the conical or frustoconical wall of the central nipple, the mixture then performing a reverse movement from that described above.

  To improve the mixing of fuel and intake gas, and therefore increase the efficiency of combustion in the chamber, it is known to generate a swirling flow of the intake gas, commonly called "swirl", about an axis substantially identical to that of the cylinder, adopting a geometry 10 and a particular arrangement of the air intake ducts.

  The invention aims to propose a new direct injection engine ensuring a good compromise between high specific performance and reduced emission of pollutants.

  For this purpose, the subject of the present invention is a direct fuel injection engine comprising at least one cylinder with a cylinder head forming a cover above the cylinder, on which are mounted, substantially parallel to the axis of the cylinder, at least one an intake valve, at least one exhaust valve, and a central fuel injector adapted to inject fuel jets into at least one sheet, and a piston slidably mounted in the cylinder and having on its upper surface a bowl provided with a central stud, characterized in that said central injector is adapted to simultaneously deliver fuel jets in a first narrow ply, the angle ((3 ') of said first ply and the angle (a) at the top of the stud being determined so that the jets of said first web are guided by the side of the nipple when the piston is in the vicinity of its top dead center, and fuel jets according to a second broad web ay an angle ((3 ") such that the point of impact of the jets of said second ply is at the side wall of the bowl, preferably in the lower half of the side wall of the bowl, when the plunger is near his top dead center.

  According to one feature, the side wall of the bowl has a concave recess, so that the fuel jets of the second web are guided by said concave reentrant when the piston is in the vicinity of its top dead center.

  According to one embodiment, the concave reentrant is formed of a curvilinear part and of an inclined rectilinear part, the angle of the second sheet and the angle of inclination of the rectilinear part being determined to allow the guidance towards the low jets from this wide tablecloth.

  Advantageously, the angle ((3 ') of the first ply is between 55 and 65, and / or the apex angle (a) of the bolt stud is greater than the angle ((3') of the first ply from 5 to 15, and / or the angle ((3 ") of the wide ply is between 120 and 160.

  According to another feature, the wide web and the narrow web each comprise at least three jets 25 distributed at regular angular intervals.

  Advantageously, the outlets of the two sheets are arranged in a same plane.

  According to another feature, the two plies are arranged in staggered rows, each ply comprises n jets, the outlet orifices of one ply being arranged at 360 / (2xn) degrees from those of the other ply.

  In another feature, the motor has a swirling movement or "swirl" whose intensity is less than lNd / N.

  According to one embodiment, the bowl comprises a side wall having a curvilinear portion of radius of curvature R2, a substantially rectilinear portion inclined with an inclination angle θ, and a retreating collar, said side wall being connected to the frustoconical wall or tapered cone of the nipple by a transition wall comprising a curvilinear portion of radius of curvature R1 and optionally a substantially flat wall, said bowl having an opening diameter of the bowl D1, a mean diameter of the bottom of the bowl D2, a neck diameter D3 , a bowl depth H1, a neck depth H2, a distance d between the top of the stud and the upper surface of the piston, an output section S and a total volume V, and fulfilling at least one of the following conditions.

  - D1 / H1 between 2 and 3.5; R2 / R1 between 0.6 and 0.85; - D2 / D1 less than 0.7; - D3 / D1 between 0.7 and 0.9; - H2 / H1 between 0.6 and 0.85.

  - 0 less than 35; and / or - S / V between 0.75 mm-1 and 1.5 mm-1.

  The Applicant has discovered that by using a two-angled web injector, with a particular bowl geometry, as defined above, and preferably with a low level of "swirl", it was possible to ensure optimal use of the oxidant present in the combustion chamber, usually oxygen from the air, and thus obtain good performance in terms of torque and specific power, a low level of pollution, including low combustion noise.

  The invention will be better understood, and other objects, details, features and advantages will become more clearly apparent from the following detailed explanatory description of a particular presently preferred embodiment of the invention, with reference to the schematic drawings. in which: - Figure 1 shows a schematic view from above of the cylinder head roof of the engine; - Figure 2 shows a partial sectional view along the plane II-II of Figure 1; FIG. 3 is an enlarged half-section of the bowl of the piston of FIG. 2; FIG. 4 represents a sectional view on an enlarged scale of the injection head of FIG. 2; and - Figure 5 shows a bottom view of the injector of Figure 4.

  Figures 1 and 2 illustrate a direct injection engine cylinder 1, in particular a diesel type engine. The cylinder is closed at its upper end by a cylinder head 2, and a piston 3 is slidably mounted, sealingly, in the bore of the cylinder. The combustion chamber 4 is delimited by the cylinder head and the upper face 31 of the piston which slides between its bottom dead center and its top dead center. The upper face 31 of the piston comprises a circular cavity or shaped bowl 5, substantially centered with respect to the axis A of the cylinder. The bottom of the bowl comprises a central elevation or cone-shaped taper 6 or angle cone frustum at the apex a, connected by a transition wall 7 and a side wall 8 to the upper face 31, the latter forming a zone annular frontal flush surrounding the bowl. The cylinder head 2 comprises the central fuel injector 9, a reheat plug 10, as well as intake and exhaust valves 11, for example two intake valves and two exhaust valves, arranged around the engine. Injector 9. The engine includes several cylinders with similar combustion chambers.

  Referring to Figures 4 and 5, the central injector 9 is disposed substantially along the axis A of the cylinder and comprises, in known manner, a head or injection nose 91 disposed projecting in the combustion chamber and provided with holes or passages for injecting fuel in jet form. An injection needle 92 is mounted in the injection head for adjusting the flow and pressure of the jets.

  According to the invention, the injector forms fuel jets disposed in two cones or sheets of different angles, whose axes coincide with the axis A of the cylinder. The fuel jets are arranged in a first so-called narrow ply, having a lap angle I ', and in a second so-called wide ply having a ply angle Pu. To do this, the injection nose comprises a first series of holes or passages 93a, 93b, 93c whose axes are arranged so as to form the narrow corner ply (3 'and a second series of passages or holes 94a, 94b, 94c for the formation of the wide angle ply (3 ") The passages of the two plies have identical cross-sectional, generally circular, and arranged in staggered rows at regular angular intervals.

  The passages of the two plies open into the combustion chamber at the same level, the outlet orifices of the passages being centered on the same plane P, perpendicular to the axis of the cylinder. In the present embodiment, each web comprises three passages 93a-b and 94a-b, the passages of one and the same web being spaced apart from one another, the adjacent passages of two different webs being arranged on one of the webs. other.

  With reference to FIG. 3, in which are shown diagrammatically the two plies of angles R 'and P', the stud 6 is arranged coaxially with the axes of the two fuel plies coming from the injector, the stud having a conical shape with a slightly rounded vertex continuing with a conical wall or flank 62 that is substantially rectilinear towards the bottom of the bowl The straight flank is continued by the transition wall 7 comprising a first curvilinear portion 71 of radius of curvature R1 and a substantially flat wall 72 forming the bottom of the bowl, and ends with the side wall 8 comprising a second curvilinear portion 81 of radius of curvature R2, a substantially straight inclined portion 82 forming an inclination angle A with the vertical, connected to the annular upper face 31 by a leave 83 forming a retreating collar.

  As a variant, the stud may have a generally frustoconical shape with a substantially horizontal vertex continuing along a substantially rectilinear flank, a transition portion formed of a single curvilinear portion, and a lateral wall formed of a curvilinear portion, possibly likewise radius of curvature than that of the transition portion, and a substantially vertical portion connected to the upper face of the piston.

  The angle at the apex of the stud is adapted to the angle R 'of the narrow ply of the injector, so that the jets of this narrow ply are injected substantially along the rectilinear flank of the stud when the piston is in the vicinity from the top dead center. The narrow ply angle R 'is between 55 and 65. The angle at the apex of the stud is greater than the ply angle of the narrow ply of 5 to 15, the fuel jets coming from the injector thus form an angle of intersection of at least 5 with the flank of the nipple. The height of the stud is less than the depth of the bowl, the distance d between the top 61 of the stud and the upper face of the piston is between 4 and 5 mm.

  The geometry of the bowl and the angle R "of the wide ply are such that, when the plunger is in the vicinity of the top dead center, the point of impact of the jets of this wide ply lies below the retreating collar 83, level of the rectilinear portion 82 of the side wall of the bowl, substantially at mid-depth (H1 / 2), so that the jets of this sheet are guided by this rectilinear part.

  The fuel flow from a jet of the narrow web and that from a jet of the wide web have been shown schematically in the same FIG. 3, by the arrows respectively referenced F1 and F2, these flows are, of course, angularly offset. , a fuel flow from a web being interposed between two fuel flows in the opposite direction of the other web. The jets of the broad ply wrap in the torus formed between the inclined wall 82 and the curvilinear portion 81, then back to the central nipple 6. Conversely, the jets of the narrow ply descend along the nipple and back up along the inclined wall. These fuel injections simultaneously in two staggered plies provide a good mixture of fuel and air in the room.

  Denote by D1 the opening diameter of the bowl, with a radius corresponding to the distance between the axis A and the furthest point of the second curvilinear portion 81, by D2 the mean diameter of the bottom of the bowl with a corresponding radius at the distance between the axis A and the middle of the horizontal plane wall 72 forming the bottom of the bowl, by D3 the neck diameter with a radius corresponding to the distance between the axis A and the end of the neck. H1 denotes the depth of the bowl, the distance between the upper face 31 and the horizontal wall 72, and H2 designates the neck depth considered at the neck diameter. Advantageously, the bowl fulfills the following conditions: the ratio D1 / H1 is between 2 and 3.5; the ratio R2 / R1 is between 0.6 and 0.85; the ratio D2 / D1 is less than 0.7; the angle of inclination θ is less than 35 - D3 / D1 is between 0.7 and 0.9; and, - H2 / H1 is between 0, 6 and 0.85.

  Furthermore, the ratio of the outlet section S of the bowl, considered at the neck diameter D3, to the total volume of the bowl V, ie S / V, is between 0.75 mm-1 and 1.5 mm. -1.

  The intensity of the "swirl" movement is relatively low, the ratio of the speed of the intake gases in the combustion chamber (Nd) in rev / min on the engine speed (N) in rev / min being less than 1 , the level of "swirl" in the engines of the prior art being conventionally between 2 and 3.5 Nd / N. This bowl geometry combined with an injector at two angles of the sheet, and with a low intensity "swirl" makes it possible to reconcile a high specific performance level, especially a specific power greater than 60 kW / l at 4000 rpm, and a low level of pollutants.

  Although the invention has been described in connection with a particular embodiment, it is obvious that it is not limited thereto and that it comprises all the technical equivalents of the means described and their combinations if they are within the scope of the invention.

Claims (10)

  1. Direct fuel injection engine comprising at least one cylinder with a cylinder head forming a cover above the cylinder, on which are mounted, substantially parallel to the axis of the cylinder, at least one intake valve, at least one valve exhaust, and a central fuel injector adapted to inject fuel jets in at least one sheet, and a piston slidably mounted in the cylinder between a top dead center and a bottom dead center and having on its upper surface a bowl provided with a central stud, characterized in that said central injector (9) is able to simultaneously deliver fuel jets in a first narrow web, the angle (0 ') of said first web and the angle (a) at top of the stud (6) being determined so that the jets of said first ply are guided by the flank (62) of the stud, and fuel jets according to a second wide ply having an angle (0 ") such that the point d impact of the jets from said second ply is at the side wall (8) of the bowl (5).   2. Engine according to claim 1, characterized in that the side wall (8) of the bowl (5) comprises a concave recess (81, 82), so that the fuel jets of the second sheet are guided by said concave reentrant when the piston is in the vicinity of its top dead center.   3. Motor according to claim 1 or 2, characterized in that the angle (0 ') of the first ply is between 55 and 65.   4. Motor according to any one of claims 1 to 3, characterized in that the apex angle (a) of the nipple (6) of the bowl is greater than the angle ((3 ') of the first ply of 5 at 15.   5. Motor according to any one of claims 1 to 4, characterized in that the angle ((3 ") of the wide web is between 120 and 160.   6. Motor according to any one of claims 1 to 5, characterized in that the wide web and the narrow web 10 each comprise at least three jets distributed at regular angular interval.   7. Motor according to any one of claims 1 to 6, characterized in that the outlets of the two sheets are arranged in a same plane (P).   8. Motor according to any one of claims 1 to 7, characterized in that each sheet comprises n jets, the outlet openings of a sheet being arranged at 360 / (2xn) degrees from those of the other sheet.   9. Motor according to any one of claims 1 to 8, characterized in that it has a swirling movement or "swirl" whose intensity is less than lNd / N.   10. Motor according to any one of claims 1 to 9, characterized in that - the bowl comprises a side wall (8) having a curvilinear portion (81) of radius of curvature R2, a substantially straight inclined portion (82) with an inclination angle θ, and a retreating collar (83), said lateral wall being connected to the frustoconical or conical wall (62) of the stud by a transition wall (7) comprising a curvilinear portion (71) of radius of curvature R1 and a substantially planar wall (72), - said bowl having an opening diameter of the bowl D1, a mean bowl bottom diameter D2, a neck diameter D3, a bowl depth H1, a neck depth H2, a distance d between the top (61) of the stud and the upper surface (31) of the piston, an output section S and a total volume V, and fulfilling at least one of the following conditions.   - D1 / H1 between 2 and 3, 5; R2 / R1 between 0.6 and 0.85; - D2 / D1 less than 0.7; - D3 / D1 between 0.7 and 0.9; - H2 / H1 between 0.6 and 0.85.   - 0 less than 35; and / or - S / V between 0.75 mm-1 and 1.5 mm-1.