FR2818324A1 - Direct injection i.c. engine has injector spray angle of predetermined dimensions relative to cylinder diameter and piston position - Google Patents

Abstract

The engine, comprising at least one cylinder with a head (1), a piston (5), inlet and exhaust valves (3, 4) and a combustion chamber between the cylinder head and recessed piston face, has an injector (6) which delivers fuel with a spray angle (a1) that is under or equal to 2Arctg CD/2F, where CD is the diameter of the cylinder and F is the distance between the point of origin of the fuel jets issuing from the injector and the position of the piston corresponding to a crankshaft angle of 50 deg from TDC. The angle (a2) of the central tip (7) of the piston face is selected according to the angle of the fuel spray and is designed so that the fuel is deflected outwards and vaporises before coming into contact with the cylinder wall.

Description

The present invention relates to a combustion system for a combustion engine

  internal combustion with direct injection.

  STATE OF THE ART The state of the art in the field can be illustrated by the following patents:

  EP 849,448, EP 589,178 (US 5,363,820), JP10184362, JP10184363, US3,945,351,

GB 214 134 181, DD-147386.

  The developments of combustion systems must meet the demands of reduction of pollutant emissions, increase of torque and specific power and reduction of combustion noise, while remaining

  compatible with endurance resistance criteria.

  The engineer currently has a wide range of possible modifications to achieve these objectives. It can change for example design or adjustment parameters, such as the shape of the combustion chamber, called bowl, arranged in the upper part of the piston, in order to facilitate the air / fuel mixture. It can also change the compression ratio, some parameters of the injection system: pressure, control law, etc., and fuel jets: number of holes, diameter, etc., the adjustment of the boost, the rate of EGR or the intake temperature. Unfortunately, it is increasingly difficult to improve one point, without damaging another. The best-known example is the compromise improvement: NOx emissions / particulate emissions. The problem becomes even more difficult to solve when the stamina criteria have to be taken into account. This is the case, for example, with regard to the liquid fuel or soot in the vicinity of the jacket, the presence of which, detrimental to the resistance of the lubricant, depends on the lap angle of the injector retained, the shape of the bowl or phasing and injection pressure. An adjustment of these parameters unfortunately has a detrimental effect on combustion leading to an increase in pollutant emissions and / or a reduction in full load performance and / or an increase in noise. The patents EP-A 849 448 or EP-A 589 178 in particular relate to combustion chambers for an internal combustion engine. These combustion chambers are delimited on one side by the piston wall which comprises a conical portion pointing towards the cylinder head and of the same axis as it, in the center of a circular bowl or bowl. The fuel is injected by a multi-jet injector placed in the axis of each cylinder with a very wide lap angle of the order of 160. The angle at the apex of the conical portion is adapted to the ply angle of the injector, so that the fuel jets are emitted substantially along the slopes of the cone and deflected by them and the rounding of the bowl, to the top of the cylinder and vaporize without ever touching the walls of the cylinder and thus without affecting their lubrication. For this effect to occur, it must of course that the pistons are close enough to their top dead center (TDC). We only have this fact

  a low latitude in the choice of fuel injection times.

  This is a disadvantage as it is also known that early and late fuel injections offer many advantages. Thus, a pilot injection before the top dead center and the main injection, reduces the combustion noise. The regeneration of particulate filters triggered, according to the known technique, by increasing the temperature at the exhaust, requires a fuel injection shortly before the opening of the exhaust valves. A fuel injection during the expansion or during the exhaust phase can also be useful to obtain the conditions favorable to the exhaust to regenerate the NOx traps. Since the combustion systems generally use ribbon injectors between 140 and 165, the adjustment range of these injections is reduced to limit the problems of dilution of the

  lubricant by fuel or soot.

  To overcome this limitation, it is useful to develop a system of

  combustion with a variety of injection conditions.

  The combustion system according to the invention The direct injection internal combustion engine according to the invention comprises at least one cylinder, a piston sliding in this cylinder, of diameter CD, means of admission and exhaust gas, a combustion chamber bounded on one side by a wall of the piston comprising a pin pointing towards the head of the

  cylinder, in the center of a bowl or concave bowl of depth L and diameter BD.

  It is characterized in that it comprises at least one injector for injecting fuel with a relatively low angle of coverage (A) chosen so that the fuel jets do not touch the walls of the cylinder, for any position of the piston (5). ) between + 50 and +180 or between -50 and -180 relative to top dead center

(TDC).

  The use of a relatively narrow angle of coverage injector, allows a wide latitude in the choice of fuel injection times while avoiding the disadvantages associated with the wide dispersion of the fuel injected. This type of injector

  lends itself well to the so-called homogeneous combustion mode.

  According to one embodiment, an angle at the apex of the stud is preferably chosen which is substantially in agreement with the ply angle of the injector and the bowl is shaped so that the injected fuel is deflected towards the cylinder head according to its concavity. out of the bowl for any position of the piston up to + 30 by

report at the top dead center (TDC).

  The combined use of the relatively narrow web angle injector and a specially shaped bowl allows a traditional mode of operation for fuel injection near top dead center but within an angular range.

  larger than is usually allowed.

  According to one embodiment, an injector with an angle of web included for example in the angular range 0 to 120 is chosen, for example, which can advantageously be restricted to the angular range 50 to 100. The angle at the top of the nipple is chosen to be greater than the lap angle (A1) of

  preferably in an angular range of between 0 and 30.

  According to one embodiment, for example, a piston with a bowl is chosen.

  whose cross-section along a diameter of the piston, is curvilinear from half

  i length b and obtained by connecting, from the center to the periphery of the piston, at least two parts, the first portion having a radius of curvature R1, the second portion having a radius of curvature R2, the dimensions of the bowl satisfactory at least one of the following conditions: the ratio BD / L is less than 6 and preferably less than 4; the ratio BD / R1 is greater than 4; the ratio R2 / R1 is between 0.4 and 1; the ratio FD / BD is less than 0.8; and the ratio Cb / BD is less than 2,

  FD designating the diameter of the bowl at the bottom of it.

  The method according to the invention makes it possible to improve the operating latitude of a direct injection internal combustion engine comprising at least one cylinder, a piston sliding in this cylinder, gas intake and exhaust means, a combustion chamber bounded on one side by a wall of the piston comprising a pin pointing towards the cylinder head, in the center of a

bowl or bowl.

  It comprises injecting fuel into each cylinder by a relatively small angle-of-web injector chosen so that the fuel jets do not touch the walls of the cylinder, for any position of the piston (5) between + 50 and +180 or between -50 and -180 relative to the top dead center (TDC) According to one embodiment, a piston is used such that the angle at the apex of the stud is substantially in agreement with the angle of the ply of the injector , and the bowl wall is shaped so that the injected fuel is deflected towards the cylinder head by following its concavity towards the outside of the bowl and vaporized without wetting the walls of the cylinder, for any position of the piston to + 30 per

  I0 ratio to top dead center (TDC).

  The combustion system according to the invention with its low angle injector and its adapted combustion chamber, avoids the presence of liquid fuel on the walls of the cylinder while offering wide possibilities of

  pollution control and engine performance.

  At full load and at high loads, the shape of the bowl allows a good entrainment of steam fuel thus promoting its mixing with the air to obtain a good burn rate and high operating wealth, reflecting a good use of the air admitted. At partial loads, a reduced web angle allows a great deal of latitude in the system settings

  injection without the wetting of the walls.

  DESCRIPTION OF THE FIGURES Other features and advantages of the system according to the invention,

  will appear on reading the following description of a non-limiting example of

  embodiment, with reference to the accompanying drawings, where: FIG. 1 schematically shows a combustion system with narrow-web fuel injector and profiled piston surface to provide greater latitude in the choice of possible injection times; and FIGS. 2a to 2e model different stages of fuel combustion (between -15 V and +40 V) performed using the system according to the invention and for full load operation. In these figures, what is black represents the fuel injected, what is shaded lighter represents air, and what is dark gray represents a mixture of air and vaporized fuel.

detailed description

  The combustion system according to the invention is suitable for an internal combustion engine with a fuel injector, of diesel type, comprising at least one cylinder 1 with a head 2, comprising one or more intake valves 3, one or more valves 4, a piston 5 sliding in the cylinder 1 and

  a fuel injector 6 disposed in the axis of the cylinder.

  The fuel injector is of the low-angle type A1. One chooses an angle of ply AI at most of 120. The lap angle is chosen so that the cylinder walls are never wetted by the fuel for any position of the piston between + 50 and + a or between -50 and -a, where a represents the maximum angle of the crankshaft for the chosen injection phase with respect to the top dead center (TDC) (a <180) to obtain a homogeneous combustion type. If F denotes the maximum distance between the point of origin of the jets of the injector 6 and the lowest position of the piston during the injection, this means that the angle of the ply AI is such that

AI CD

  that Arctg - C-. The distance F is therefore at most that between the point

2 2.F

  original jets of the injector 6 and the bottom dead center PMB.

  A typical angular range for the lap angle AI is, for example

between 50 and 100.

  The combustion chamber is delimited on one side by the cylinder head 2 and on the opposite side, by the upper face of the piston 5. This face is shaped in the following manner. It comprises a pin 7 rising in the center of a bowl or bowl 8 whose concavity is turned towards the cylinder head 2. The angle at the apex A2 of the pin 7 is adapted substantially to the angle of the lap AI of the injector 6, so that the piston is in the vicinity of the top dead center (TDC), the fuel is injected substantially along the sides of the stud. The diametral section of the bowl 8 is curvilinear and comprises, from the top of the stud 7, deviating symmetrically towards the outside of the piston 5, on either side of its axis, a first part of radius of curvature R1, a second part of radius of curvature R2. The depth of the bowl 8 is preferably greater than the height of the stud. The top of the pin 7 may be conical or be flattened or rounded. We denote by L the depth of the bowl 8, by BD,

  the diameter of the bowl, by CD, the diameter of the cylinder, by -, the length of the half

  diametral section of the bowl 8 from the top of the pin 7 to its connection with the upper face of the piston 5 (the developed length of the diametral cup of the bowl is therefore Cb) and A3, the angle with respect to the face top of the piston, what does the outer wall of the bowl. FD denotes the diameter of the bowl 8 at the bottom thereof.

  The shape of the bowl 8 is compatible with the angle of the sheet A1 that is chosen.

  It is adapted so that, in the operating mode of traditional type (for any position of the piston 5 up to + 30 relative to the top dead center (TDC) for example), one obtains the desired effect of deflection of the injected fuel. towards the head of the cylinder (following its concavity towards the outside of the bowl) and its vaporization without it being able to go to wet the walls of the cylinder. This form is preferably obtained while complying with the following conditions: the ratio BD / L is less than 6 and preferably less than 4; the ratio BD / R1 is greater than 4; the ratio R2 / R1 is between 0.4 and 1; the ratio FD / BD is less than 0.8; and

  the ratio Cb / BD is less than 2.

  For A3, an angle of less than 45 is preferably chosen.

  It is verified in Fig.2a to 2e which model different stages of the combustion at full load, that the fuel injected is well guided along the

concavities of the bowl.

Claims (7)

  1) Direct injection internal combustion engine comprising at least one cylinder (1), a piston (5) sliding in this cylinder of diameter CD, means (3, 4) for admission and exhaust gas, a chamber combustion device defined on one side by a wall of the piston (5) comprising a pin (7) pointing towards the head (2) of the cylinder, in the center of a bowl or concave bowl (8) of depth L and of diameter BD, characterized in that it comprises at least one injector (6) for injecting fuel with a relatively low angle of coverage (A1) chosen so that the fuel jets do not touch the walls of the cylinder (1), for any position of the piston (5) between + 50 and +180 or between -50 and -180 relative to the point dead high (PMH).   2) Engine according to claim 1, characterized in that the apex angle (A2) of the stud (7) is chosen substantially in accordance with the ply angle (AI) of the injector (6) and the bowl ( 8) is shaped so that the fuel injected is deflected towards the cylinder head by following its concavity towards the outside of the bowl and vaporized without reaching the walls of the cylinder, for any position of the piston (5) up to + 30 by report at the top dead center (TDC).   3) Motor according to claim 1 or 2, characterized in that the angle of   web (AI) of the injector (6) is selected between 0 and 120.   4) Motor according to claim 1 or 2, characterized in that the angle of   web (A1) of the injector (6) is selected between 50 and 100.   Motor according to claim 3 or 4, characterized in that the angle at the apex (A2) of the stud (7) is chosen to be greater than the lap angle (A1) in a   range between 0 and 30.   6) Motor according to one of claims 1 to 5, characterized in that each   piston (5) comprises a bowl (8) whose cross section along a diameter of the piston, is curvilinear half-length b and obtained symmetrically with respect to the axis of the piston, by the connection, from the center to the periphery of the piston, of at least two parts, the first part having a radius of curvature R1, the second part having a radius of curvature R2, characterized in that the dimensions of the bowl satisfy at least one of the following conditions: - the BD / L ratio is less than 6 and preferably less than 4; the ratio BD / R1 is greater than 4; the ratio R2 / R1 is between 0.4 and 1; the ratio FD / BD is less than 0.8; the ratio Cb / BD is less than 2; and the angle A3, with respect to the upper face of the piston, that the outer wall of the bowl, is less than 45,   FD designating the diameter of the bowl at the bottom of it.   7) A method for improving the operating latitude of a direct injection internal combustion engine comprising at least one cylinder (1), a piston (5) sliding in this cylinder, means (3, 4) for admission and exhaust gas, a combustion chamber delimited on one side by a wall of the piston (5) comprising a pin (7) pointing towards the head (2) of the cylinder, in the center of a bowl or bowl (8), characterized in that it comprises injecting fuel into each cylinder by a relatively low angle-of-coverage injector (Ai) chosen so that the fuel jets do not touch the walls of the cylinder (1), for any position of the piston (5) between + 50 and + 180 or between -50 and   -180 compared to the top dead center (TDC).   8) Method according to claim 8, characterized in that a piston (5) is used such that the apex angle (A2) of the stud (7) is substantially in agreement with the lap angle (AI) of the injector (6), and a bowl (8) whose wall is shaped so that the injected fuel is guided towards the outside thereof and vaporized without reaching the walls of the cylinder (1), for any position of the piston (5) up to + 30   compared to the top dead center (TDC).