Elliptically-shaped combustion chamber

Abstract

The present invention relates to a combustion chamber of a combustion engine. The combustion chamber comprises a single intake valve (2), a single exhaust valve (3), a fuel injector (5) and two plugs (4). According to the invention, the combustion chamber is substantially elliptical (6) and the components of the combustion chamber are arranged as follows: valves (2, 3) are located at the ends of the major axis (8) of ellipse (6), plugs (4) are located close to the minor axis (9) of ellipse (6), fuel injector (5) is located on the periphery of ellipse (6) between intake valve (2) and a plug (4).

Claims

1. A combustion chamber of an internal-combustion engine comprising at least one cylinder in which a piston moves, the combustion chamber comprising a single intake valve, a single exhaust valve, a single fuel injector and two plugs, wherein the combustion chamber substantially has the shape of an ellipse having a major axis and a minor axis shorter than the major axis, the intake valve and the exhaust valve are arranged at ends of the major axis of the ellipse, the plugs are located close to the minor axis of the ellipse and the fuel injector is located inside the ellipse, closer to a periphery of ellipse than to a center of the ellipse and between the intake valve and one of the two plugs, and wherein the ellipse comprises a recess extending towards the intake valve and arranged substantially symmetrically to the fuel injector with respect to the major axis of the ellipse.

2. A combustion chamber as claimed in claim 1, wherein the recess is substantially rectilinear.

3. A combustion chamber as claimed in claim 1, wherein the intake valve is tangential to the ellipse.

4. A combustion chamber as claimed in claim 1, wherein the exhaust valve is tangential to the ellipse.

5. A combustion chamber as claimed in claim 1, wherein the ratio of the diameter of the intake valve to the diameter of the exhaust valve ranges between 1 and 3.

6. A combustion chamber as claimed in claim 1, wherein the length of the major axis of the ellipse is substantially equal to the radius of the cylinder of the combustion engine.

7. A combustion chamber as claimed in claim 1, wherein the length of the minor axis of the ellipse ranges between 70 and 90% of the radius of the cylinder of the combustion engine.

8. An internal-combustion engine comprising at least one cylinder in which a piston slides and a combustion chamber as claimed in claim 1.

9. A combustion engine as claimed in claim 8, wherein the combustion engine comprises a gas intake pipe configured to initiate a rotating motion of the air about the axis of cylinder and a rotating motion about an axis perpendicular to the axis of the cylinder.

10. Use of a combustion engine as claimed in claim 8 with a Miller cycle.

11. A method of using the combustion engine as claimed in claim 8, comprising operating the combustion engine in a Miller cycle in which the intake valve closes before bottom dead center of the piston.

12. A combustion chamber as claimed in claim 1, wherein the ratio of the diameter of the intake valve to the diameter of the exhaust valve ranges between 1.5 and 2.

13. A combustion chamber as claimed in claim 1, wherein the ratio of the diameter of the intake valve to the diameter of the exhaust valve ranges between 1.65 and 1.75.

14. A combustion chamber as claimed in claim 1, wherein the length of the minor axis of the ellipse ranges between 75 and 85% of the radius of the cylinder of the combustion engine.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Other features and advantages of the device according to the invention will be clear from reading the description hereafter, given by way of non limitative example, with reference to the accompanying figures wherein:

(2) FIG. 1 illustrates a combustion chamber according to an embodiment of the invention,

(3) FIG. 2 illustrates the evolution of the tumble ratio as a function of the intake valve lift for a combustion chamber according to the invention,

(4) FIG. 3 illustrates the evolution of the swirl ratio as a function of the intake valve lift for a combustion chamber according to the invention, and

(5) FIG. 4 illustrates the structure of the swumble formed in a cylinder by means of the combustion chamber according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(6) The present invention relates to a combustion chamber for an internal-combustion engine. The internal-combustion engine comprises at least one cylinder in which a piston moves.

(7) According to the invention, the combustion chamber comprises: a single intake valve, allowing delivery of the gas mixture to the combustion chamber before the combustion phase, a single exhaust valve, allowing discharge of the burnt gas after the combustion phase, a single fuel injector, allowing direct injection of the fuel into the combustion chamber, and two plugs, allowing ignition of the gas/fuel mixture in the combustion chamber.

(8) The gas mixture can comprise supercharged air or not, or a mixture of air, supercharged or not, with recirculated burnt gas.

(9) The fuel can notably be gasoline or diesel fuel.

(10) Using only two valves (one for the intake and the other for the exhaust) involves several design advantages. Indeed, such an engine is less expensive (with a limited number of parts), lighter and more compact. Furthermore, this design provides more space for the plugs and the injector.

(11) Using a single intake valve facilitates the creation of swumble. Indeed, it is more difficult to create swumble with two dispensing intake pipes.

(12) According to the invention, the combustion chamber substantially has the shape of an ellipse. This shape promotes considerable squish. Indeed, the ratio of the surface area of this ellipse to the surface area of a section of the cylinder is particularly small, which corresponds to a great squish.

(13) In order to promote swumble and squish, the components of the combustion chamber are arranged in a specific manner: the intake valve and the exhaust valve are arranged at the ends of the major axis of the ellipse, thus the valves are positioned opposite one another and spaced apart, the plugs are arranged close to the minor axis of the ellipse, thus the plugs are located between the intake valve and the exhaust valve, and the fuel injector is arranged on the periphery of the ellipse between the intake valve and a plug, this location promoting mixing of the gas and the fuel thanks to the swumble motion.

(14) This elliptical design of the combustion chamber associated with this arrangement of the components allows to generate an aerodynamic swumble structure and to promote homogenization of the fuel mixture. Furthermore, it enables a high combustion rate while preventing autoignition phenomena. Indeed, it is reminded that swumble allows to benefit from excellent homogenization and a better combustion rate thanks to a higher turbulence level during the intake phase than those observed with the best current spark-ignition engines.

(15) According to an embodiment of the invention, the ellipse can comprise a recess extending towards the intake valve. The recess is arranged substantially symmetrically to the fuel injector with respect to the major axis. In other words, the recess is on the side of the intake valve opposite the side on which the fuel injector is positioned. The recess thus is located between a plug and the intake valve. A recess is understood to be a modification in the outer shape of the ellipse, this modification being achieved towards the inside of the ellipse. The recess enables swirl type turbulences to be intensified. Indeed, the purpose of the recess is to promote the formation of the swirl part of the swumble motion. This recess creates an extension of the pipe in the chamber, which provides continuation of the aerodynamic structure formation.

(16) Advantageously, the recess can have a substantially rectilinear shape. For example, the rectilinear recess can be achieved with fillet radii ranging between 2 and 10 mm, preferably between 4 and 6 mm.

(17) According to an embodiment of the invention, the intake valve can be tangential to the ellipse. Thus, filling of the combustion chamber is optimized.

(18) According to a characteristic of the invention, the exhaust valve can be tangential to the ellipse. Thus, emptying of the combustion chamber is optimized.

(19) According to an embodiment of the invention, the ratio of the diameter of the intake valve to the exhaust valve can range between 1 and 3, preferably between 1.5 and 2, and more preferably between 1.65 and 1.75. Such a ratio provides the best compromise between engine performances (related to the amount of air admitted) and sufficient engine drain capacity.

(20) According to an embodiment of the invention, the length of the semi-major axis of the ellipse can be substantially equal to the radius of the cylinder of the combustion engine. Thus, the greater dimension of the ellipse substantially corresponds to the diameter of the cylinder, which allows the volume to be optimized for the combustion chamber.

(21) According to an implementation of the invention, the length of the semi-minor axis of the ellipse can range between 70 and 90%, preferably between 75 and 85%, of the radius of the cylinder of the combustion engine.

(22) According to a configuration of the invention, the plugs are not positioned on the periphery of the ellipse. This arrangement of the plugs provides optimal propagation of the flame front in order to prevent engine knock and unburnt gas.

(23) Furthermore, the combustion chamber can be designed to withstand compression ratios ranging between 6:1 and 22:1, preferably between 10:1 and 20:1, and more preferably between 14:1 and 18:1.

(24) FIG. 1 schematically illustrates, by way of non limitative example, a combustion chamber 1 according to an embodiment of the invention. Combustion chamber 1 substantially has the shape of an ellipse 6. Ellipse 6 is defined by the major axis 8 and the minor axis 9 thereof. Combustion chamber 1 comprises a single intake valve 2 located at one end of a semi-major axis 8. Intake valve 2 is tangential to ellipse 6. Combustion chamber 1 comprises a single exhaust valve 3 located at one end of a semi-major axis 8. This end lies opposite the end on which intake valve 2 is positioned. Exhaust valve 3 is tangential to ellipse 6. Combustion chamber 1 further comprises two plugs 4. Plugs 4 are substantially arranged on minor axis 9 (close to minor axis 9). Furthermore, combustion chamber 1 comprises a single fuel injector 5. Fuel injector 5 is positioned on the periphery of ellipse 6. Besides, fuel injector 5 is located between intake valve 2 and a plug 4. On the side opposite to injector 5, ellipse 6 comprises a rectilinear recess 7. Rectilinear recess 7 is positioned between a plug 4 and intake valve 2. Rectilinear recess 7 extends towards intake valve 2.

(25) In addition to promoting squish, elliptical shape 6 as presented also promotes the development of the swirl motion that starts in the intake pipe. This chamber is somehow the extension thereof.

(26) The present invention also relates to an internal-combustion engine comprising: at least one cylinder in which the piston moves, a combustion chamber associated with the cylinder, the combustion chamber being achieved according to any one of the variants or according to any one of the combinations of variants described above.

(27) According to an aspect of the invention, the internal-combustion engine comprises between one and eight cylinders. For example, the combustion engine can comprise two, three or four cylinders.

(28) According to a characteristic of the invention, the combustion engine can comprise a burnt gas recirculation circuit (EGR).

(29) According to an embodiment of the invention, the combustion engine can comprise an air intake pipe connected to the combustion chamber, in which the intake valve is positioned, configured to initiate a swumble motion, i.e. a rotating motion of the air about the cylinder axis (tumble) and a rotating motion about an axis perpendicular to the cylinder axis (swirl).

(30) The invention relates to a combustion chamber specifically designed to obtain a higher combustion rate than the current spark-ignition engines and thus to provide better combustion efficiency.

(31) In particular, said combustion chamber according to the invention is particularly suited for use with a so-called Miller cycle over a wide operating range. This cycle is characterized by an intake valve(s) closure before the bottom dead center of the piston. This allows to have increased work recovery, in addition to cooling of the charge admitted.

(32) Such a combustion engine can be used in the field of transport, road or air transport for example, or in the field of stationary installations such as a generator set.

APPLICATION EXAMPLE

(33) The features and advantages of the combustion chamber according to the invention will be clear from reading the application example below.

(34) The present invention was evaluated and compared with the current spark-ignition engines. FIGS. 2 and 3 respectively show the evolution of the tumble ratio and of the swirl coefficient for a combustion chamber according to the invention.

(35) FIG. 2 illustrates the evolution of tumble coefficient ct as a function of the lift l, in mm, of the intake valve. FIG. 2 also shows the flow rate d in kg/h of the gas through the intake valve. It can be seen that the tumble coefficient increases and remains high upon lift of the intake valve.

(36) FIG. 3 illustrates the evolution of swirl coefficient cs as a function of the lift l, in mm, of the intake valve. FIG. 3 also shows the flow rate d in kg/h of the gas through the intake valve. It can be seen that the swirl coefficient remains high (in absolute value) upon lift of the intake valve. The combustion chamber according to the invention therefore enables a swumble motion.

(37) FIG. 4 schematically shows, by way of non limitative example, a graphic representation of the aerodynamic swumble structure within intake pipe 10 and cylinder 11, for an engine provided with a combustion chamber according to the invention. FIG. 4 illustrates various gas streams 13 in these elements.

(38) It is also observed that the combustion duration is independent of the distribution law spread and calibration, which is not found in current spark-ignition engines. This enables the overall efficiency of the internal-combustion engine to be positively impacted.

(39) Thus, the combustion chamber according to the invention enables a high swumble in the cylinder, which optimizes the efficiency of the combustion and therefore of the combustion engine.