FR2878906A1 - Direct injection internal combustion engine e.g. diesel engine, has fuel injector, and tulip with side wall forming negative inclination angle whose absolute value is equal to half crown angle of fuel jets and at least equal to zero degrees - Google Patents

Abstract

The engine has gas inlet and exhaust units, an injector for injecting fuel, and a piston sliding in each of cylinders. A combustion chamber delimited by the piston has a pilot (34) disposed at the center of a concave tulip (32). The tulip has a side wall (42) forming a negative inclination angle (a2) whose absolute value is almost equal to half of a crown angle (a1) of fuel jets and at least equal to 0 degrees. The injector injects the fuel with the crown angle (a1) less than or equal to 2*Arctg(CD/2F), where CD is the diameter of the cylinder and F is the distance between the origin point of fuel jets from the injector and the piston position corresponding to a crankshaft angle of 50 degrees with respect to top dead center.

Description

CD 2F

  The present invention relates to an internal combustion engine with direct fuel injection, in particular diesel type engine, and to a method for controlling the fuel injection of such an engine.

  It relates more particularly to diesel engines that can operate in two modes of combustion. A homogeneous mode, for low and medium engine loads, with a fuel injection to obtain a homogeneous mixture of fuel with air or with a mixture of air and recirculated exhaust gas before the start of operation. combustion. This homogeneous combustion mode is better known as Homogeneous Charge Compression Ignition (abbreviated to H.C.C.I). The other combustion mode, called traditional combustion, consists of an injection of the fuel around the top dead center of the piston and diffusion combustion, this mode being preferably used at high loads.

  Such engines make it possible to meet the demands of reducing pollutant emissions, fuel consumption, increasing torque and specific power and reducing combustion noise, while remaining compatible with the criteria of the invention. endurance wear.

  Thus, as better described in the patent applications EP 0 849 448 or EP 0 589 178, the fuel can be introduced into the combustion chamber by an injector placed in the axis of each cylinder so that the fuel jets are emitted by vaporizing without ever touching the wall of the cylinder and therefore without affecting its lubrication while improving the fuel mixture with the air or the mixture of air and flue gas before the start of combustion. To do this, it is necessary that the piston is close enough to its top dead center (TDC) and therefore only has a small latitude in the choice of fuel injection times.

  This is a significant disadvantage, since early or late fuel injections offer many advantages, especially in order to obtain a homogeneity of the fuel mixture.

  The applicant has solved these problems by means of an engine, as better described in his French patents Nos. 2,818,324 and 2,818,325 for a homogeneous combustion mode used under the name NADITM. This engine comprises at least one cylinder, a piston sliding in this cylinder, gas intake and exhaust means, a combustion chamber delimited on one side by the upper face of the piston comprising a pin disposed in the center of a cylinder. concave bowl having an inclined side wall and at least one injector for injecting fuel with a sheet angle of less than or equal to 2Arctg 2D where CD is the diameter of the cylinder and F is the distance between the point of origin of the fuel jets from the injector and the position of the piston corresponding to a crankshaft angle of 50 relative to the high point.

  Thus, in the case of early injections, that is to say when the position of the piston is in the vicinity of 50 angular of the crankshaft for the chosen injection phase relative to the top dead center of the piston, the fuel does not impact the wall of the cylinder and remains close to the wall while mixing with the air or mixture of air and recirculated flue gas present in the combustion chamber.

  Applicant has improved this type of engine with homogeneous combustion through a provision that allows early injections with an effective mixture of air or mixture of air and recirculated flue gas admitted and that in the bowl.

  For this purpose, the direct injection internal combustion engine comprising at least one cylinder, a piston sliding in this cylinder, gas intake and exhaust means, a combustion chamber delimited on one side by the upper face of said piston comprising a stud disposed in the center of a concave bowl comprising an inclined side wall, an injector for injecting fuel with a sheet angle of less than or equal to 2Arctg 2D where CD is the diameter of the cylinder and F the distance between the d-point origin of the fuel jet from the injector and the position of the piston corresponding to a crankshaft angle of 50 relative to the top dead center, characterized in that the bowl has a side wall forming a negative angle whose absolute value is at most equal to half of the lap angle and at least equal to 0.

  Preferably, the absolute value of the angle formed by the side wall may be at most equal to half the angle of the ply at which an angle of 15 is subtracted.

  Advantageously, the rib angle of the injector can be at most equal to 120.

  Even more advantageously, the ply angle of the injector 25 can be chosen between 40 and 100.

  The invention also relates to a method for controlling the fuel injection of a direct injection internal combustion engine comprising at least one cylinder, a piston sliding in this cylinder and comprising a concave bowl of diameter GD and an inclined side wall. a nipple disposed in the center of the bowl, an injector for injecting fuel with a sheet angle of less than or equal to 2Arctg - where CD is the diameter of the cylinder and F the distance between the point of origin of the fuel jets issued from the injector and the position of the piston corresponding to a crankshaft angle of 50 relative to the top dead center, characterized in that the fuel is injected at a position of the piston in such a way that the base of the jet cone of fuel is confused with the bowl opening section considered to diameter GD.

  The other features and advantages of the invention will appear on reading the description given below from non-limiting examples of embodiment, with reference to the appended drawings in which: FIG. 1 schematically shows an internal combustion engine according to the invention and - Figure 2 is a partial large-scale local view of the bowl profile of the piston of Figure 1.

  Referring to FIGS. 1 and 2, a direct injection internal combustion engine of the Diesel type comprises at least one cylinder 10 of axis XX 'and of diameter CD, a cylinder head 12, air intake means and means for exhausting the flue gases, in this case at least one intake manifold 14 of at least one gaseous fluid, such as air or a mixture of air and recirculated flue gas (EGR), respectively. minus an exhaust pipe 16 of burnt gases, the pipes being controlled in opening, or closing, by a closure means, such as respectively an intake valve 18 and an exhaust valve 20. This engine also comprises a piston 22 sliding in the cylinder 10 and a fuel injector 24 which is preferably disposed in the axis XX 'of the cylinder. This injector comprises in the vicinity of its nose 26 a multiplicity of orifices through which is sprayed the fuel in the combustion chamber 28, in jets 30.

  As better described in the French patents No. 2,818,324 and 2,818,325 of the applicant, the fuel injector is of the low-angle type of sheet a ,. This angle α1 is chosen so that the wall of the cylinder 10 is never wetted by the fuel for any position of the piston 22 between + 50 and + α or between -50 and α, where a represents the angle of the crankshaft for the phase selected injection relative to the top dead center of the piston, this angle being greater than 50 and less than or equal to 180 to obtain a homogeneous type combustion.

  If CD denotes the diameter (in mm) of the cylinder 10 and F the distance (in mm) between the point of origin of the fuel jets 30 and the position of the piston corresponding to a crankshaft angle of 50, then the angle of layer ai (in degree) will be less than or equal to 2Arctg CD 2F By sheet angle, it is understood the angle at the top that forms the cone coming from the injector and whose fictional peripheral wall passes through all the axes of the jets of fuel 30.

  A typical angular range for the lap angle a is at most 120 and preferably between 40 and 100.

  The combustion chamber 28 is delimited by the internal face of the cylinder head 12 opposite the piston, the circular wall of the cylinder 10 and the upper face of the piston 22.

  This upper face of the piston comprises a concave bowl 32 inside which is disposed a pin 34, located substantially in the center of this bowl, which rises towards the cylinder head 12.

  Referring additionally to Figure 2, the stud 34, of generally frustoconical shape, has an apex 36 preferably rounded, continuing, departing symmetrically outwardly of the piston 22, a sloping flank 38 substantially rectilinear towards the bottom 40 of the bowl, then, from this bottom, by a substantially rectilinear inclined lateral wall 42 pursued by a substantially vertical surface 44 joining the substantially horizontal surface 46 of the upper face of the piston 22 by a fillet 48.

  Advantageously, the sloping flank 38 is connected to the bottom 40 of the bowl by a curvilinear portion 50 of radius R1 and this bottom is connected to the inclined side wall 42 by another curvilinear portion 52 of radius R2.

  The intersection between the inclined side wall 42 and the substantially vertical surface 44 creates a circumferential edge whose diameter corresponds to a bowl opening diameter GD being located at a height L2 with respect to the bottom 40 of the bowl. Of course this edge, for technical reasons, is rounded in its protruding part and the diameter GD is to be considered between the points of these roundings closest to the axis XX '.

  The angle of inclination a2 that forms the side wall 42 of the bowl from this edge with a vertical V, passing through a point A of this inclined wall, is negative, that is to say considered in the opposite direction clockwise, making this wall is directed towards the axis XX ', as defined above.

  Preferably, the absolute value of this angle is at most equal to the half-ply angle of the jets a1 and at least equal to 0.

  Advantageously, the absolute value of the angle a2 is at most equal to this half-angle of the sheet from which an angle of 15 is subtracted.

  This angle of 15 a2 is justified by calculations and test results which have made it possible to update its maximum value so that the fuel jets do not come to strike this wall but rather slide along it. this.

  During early or late injections as defined above, a fuel injection phasing will be chosen in such a manner that, schematically, the base section of the fuel jet cone is merged with the fuel injection section. bowl opening considered at bowl opening diameter GD.

  This configuration, as shown in FIG. 1, causes a position P (function of the crankshaft angle) of the piston which is located beyond the piston position (at a crankshaft angle of 50) having served the determining the jet ply angle a1.

  The position P of the piston 22, and consequently the crankshaft angle, can be easily determined because the angle a1 is known and is calculated as defined above from a piston position at a crankshaft angle of 50.

  Therefore, the distance D (in mm), considered distance between the point of origin of the jets of the injector and the position P of the piston, can be determined from the formula a1 = 2A.rctg 2D where a1 is known as well as the bowl opening diameter GD.

  Thus, during the early or late fuel injection, the jets of this fuel will mix along the wall 42 with air (or a mixture of air and recirculated exhaust gas) previously admitted to the chamber 28 and then will be guided by the bottom 40 and go up along the side 38 of the pin 34 so that they are close to the axis XX 'of the cylinder and therefore can not come into contact with the walls of the cylinder 10. Thus, all the fuel introduced into the chamber will be distributed inside the bowl so as to optimize its mixing with the intake air, avoiding any containment of fuel in an area of the bowl.

  Thanks to the invention, it is possible to obtain a great latitude in the choice of injection times because the injector with a jet ply angle and an angle of inclination of the side wall of the bowl as defined above. above will prevent wetting the walls of the cylinder.

Claims (1)

9 CLAIMS   1) Internal combustion engine with direct injection comprising at least one cylinder (10), a piston (22) sliding in this cylinder, means (14, 18; 16, 20) for admission and exhaust gas, a combustion chamber (28) bounded on one side by the upper face of said piston comprising a stud (34) disposed in the center of a concave bowl (32) comprising an inclined side wall (42), an injector (24) for injecting fuel with a lap angle (a,) less than or equal to 2Arctg 2D where CD is the diameter of the cylinder (10) and F the distance between the point of origin of the fuel jets from the injector (24) and the position of the piston (22) corresponding to a crankshaft angle of 50 relative to the top dead center (TDC), characterized in that the bowl (32) has a side wall (42) forming a negative angle (a2) whose value absolute is at most equal to half of the lap angle (a1) and at least equal to 0.   2) Motor according to claim 1, characterized in that the absolute value of the angle (a2) formed by the side wall (42) is at most equal to half of the lap angle (a1) to which is subtracted a angle of 15.   3) Motor according to claim 1 or 2, characterized in that the ply angle (a1) of the injector (24) is at most equal to 120.   4) Motor according to claim 3, characterized in that the web angle (a1) of the injector (24) is selected between 40 and 100.