The present invention relates to an internal-combustion engine, notably of direct injection type, with a piston provided with a bowl comprising a teat.
It more particularly relates to a diesel type direct-injection engine that can run according to two combustion modes. A homogeneous mode, for low and medium engine loads, with a fuel injection allowing to obtain homogeneous mixing of the fuel with air or with a mixture of air and of recirculated exhaust gas, before combustion starts. The other combustion mode, referred to as conventional combustion, consists of a fuel injection in the vicinity of the piston top dead centre and of a diffusion combustion, this mode being preferably used at high loads.
Such an engine type, as better described in French patent applications No. 2,818,324 and 2,818,325 filed by the applicant, comprises at least a cylinder, a piston sliding in this cylinder, a combustion chamber delimited on one side by the upper face of the piston comprising a teat arranged in the centre of a concave bowl and at least one injection nozzle for injecting fuel with a nappe angle less than or equal to
where CD is the diameter of the cylinder and F the distance between the point of origin of the fuel jets from the injection nozzle and the position of the piston corresponding to a crank angle of 50° to the top dead centre.
Thus, in case of early injection, i.e. when the position of the piston is in the vicinity of 50° crank angle for the injection phase selected in relation to the piston top dead centre, the fuel does not come into contact with the cylinder wall and it mixes with the air or the mixture of air and of recirculated exhaust gas present in the combustion chamber.
In this type of engine, the applicant has used a bowl with particular values for the vertex angle of the teat (0° to 30° greater than those of the nappe angle) that allow to obtain homogeneous mixing of the fuel mixture upon injection.
The applicant has continued its research on this vertex angle and has obtained results according to which this vertex angle can be increased even further while improving the engine performances, as regards power as well as emissions such as soot emissions.
The present invention therefore relates to an internal-combustion engine, notably of direct injection type, comprising at least a cylinder, a piston sliding in this cylinder, a combustion chamber delimited on one side by the upper face of said piston comprising a concave bowl within which a teat of vertex angle a2 is arranged and a fuel injection nozzle for injecting fuel with a jet nappe angle a1 less than or equal to
where CD is the diameter of the cylinder and F the distance between the point of origin of the fuel jets from the injection nozzle and the position of the piston corresponding to a crank angle of 50° to the top dead centre (TDC), characterized in that vertex angle a2 of the teat is greater than jet nappe angle a1 by an angle greater than 30° and less than 60°.
Other features and advantages of the invention will be clear from reading the description hereafter, given by way of non limitative example, with reference to the accompanying figures wherein:
In connection with
As better described in French patents No. 2,818,324 and 2,818,325 filed by the applicant, fuel injection nozzle 22 is of small jet nappe angle a1 type. This angle a1 is so selected that the wall of cylinder 10 is never wetted by the fuel for any position of piston 30 between +50° and +α or between −50° and −α, where α represents the crank angle for the injection phase selected in relation to the piston top dead centre, this angle a being greater than 50° and less than or equal to 180° so as to obtain a homogeneous type combustion.
If CD represents the diameter (in mm) of cylinder 10 and F the distance (in mm) between the point of origin of fuel jets 28 and the position of the piston corresponding to a crank angle of 50°, then nappe angle a1 (in degrees) is less than or equal to
What is referred to as nappe angle is the vertex angle formed by the cone from the nozzle and whose fictitious peripheral wall passes through all the axes of fuel jets 28.
Advantageously, the angular range for nappe angle a1 is at most 120° and preferably between 40° and 100°.
As mentioned above, piston 30 comprises a bowl 32 whose concavity is turned towards the cylinder head and that is provided with teat 34.
The teat, which is located in the centre of bowl 32 and can be coaxial to the axis of fuel jet nappe a1, has a conical shape with a slightly rounded vertex 36. This vertex is continued by an inclined flank 38 substantially rectilinear in the direction of bottom 40 of the bowl. Vertex angle a2 of the teat is suited to nappe angle a1 in such a way that the fuel is injected substantially along flank 38 of this teat. Preferably, this vertex angle a2 of the teat is greater by an angle of 30° than nappe angle a1 and smaller by an angle of 60° than this nappe angle.
It can be noted that, in
This can also be seen in
The present invention is not limited to the embodiments described above by way of examples and it encompasses any variant and equivalent.
Number | Date | Country | Kind |
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05 02648 | Mar 2005 | FR | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/FR2006/000593 | 3/15/2006 | WO | 00 | 4/25/2008 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO2006/097639 | 9/21/2006 | WO | A |
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