METHOD FOR OPERATING A SPARK-IGNITION INTERNAL COMBUSTION ENGINE

Abstract

Various embodiments of the present disclosure are directed to methods of operating a spark-ignition internal combustion engine. In one embodiment, a method is disclosed including fuel is injected centrally into a combustion chamber via at least one fuel injection device per cylinder in at least one operating range of the internal combustion engine and is ignited centrally in the combustion chamber via at least one ignition device. The fuel is injected into the combustion chamber at an injection pressure of over 500 bar in the second half of the compression stroke before the top dead center of combustion and the internal combustion engine is operated at an air-fuel ratio 1.

In at least one operating range of the internal combustion engine, the fuel is injected into the combustion chamber between 180 and 0 before the top dead center.

Claims

1. Method for operating a spark-ignition internal combustion engine which has at least one piston which reciprocates in a cylinder and adjoins a combustion chamber, the method including the following steps: injecting fuel centrally into the combustion chamber via at least one fuel injection device per cylinder in at least one operating range of the internal combustion engine; centrally igniting the combustion chamber via at least one ignition device; wherein the fuel is injected into the combustion chamber at an injection pressure of more than 500 bar in a second half of a compression stroke before top dead center of combustion, and the internal combustion engine is operated at an air-fuel ratio 1, characterized in that; wherein in at least one operating range of the internal combustion engine, the fuel is injected between 180, and 0 crank angle before the top dead center of the combustion into the combustion chamber in such a way that at least two injection jets of the fuel are directed at bowl walls of a piston bowl of the piston, which bowl walls are disposed substantially parallel to the cylinder axis and lie approximately diametrically opposite one another with respect to the cylinder axis; and wherein a jet axes of the at least two injection jetswhen viewed in a sectional view containing the cylinder axisenclose an angle of more than 30; and retaining combustion heat in the combustion chamber by at least one thermal insulation and/or coating.

2. The method according to claim 1, wherein the fuel is injected at an injection pressure above 900 bar, in such a way that a homogeneous mixture is formed in a region above the piston bowl.

3. The method according to claim 1, wherein the fuel is injected simultaneously into the combustion chamber via at least five injection jets.

4. The method according to claim 1, wherein fuel is injected on both sides of the ignition point of the ignition device via one injection jet each.

5. The method according to claim 4, wherein the at least two injection jetswhen viewed in plan viewenclose an angle of approximately between 50 and 80.

6. The method according to of claim 1, wherein at least one injection jet has a defined distance from the ignition point which is between 0.5 and 2.5 mm.

7. The method according to of claim 1, wherein the fuel is injected at at least two points in time, wherein at least one last injection takes place immediately before the top dead center of combustion.

8. The method according to claim 1, wherein at least two injections are carried out in the compression stroke.

9. The method according to claim 1, wherein at least two injections are carried out in the intake stroke and at least one injection in the compression stroke.

10. The method according to claim 1, wherein during each injection the fuel is injected over a maximum of 50 KW.

11. The method according to claim 1, wherein the entire injection of the fuel is terminated at or before the time of ignition.

12. The method according to claim 1, wherein until the time of ignition a homogeneous mixture is formed in a central region above the piston bowl and radially outside the central region a peripheral zone is formed with air or lean base mixture, so that after the time of ignition a premixed combustion is carried out.

13. The method according to claim 1, wherein the internal combustion engine is operated with a compression ratio between 12 and 18.

14. The method according to claim 1, wherein the internal combustion engine is operated with an air-fuel ratio =1.

15-28. (canceled)

29. The method according to claim 1, wherein the jet axes of the at least two injection jetswhen viewed in a sectional view containing the cylinder axisenclose an angle of more than 60.

30. The method according to claim 1, wherein the jet axes of the at least two injection jetswhen viewed in a sectional view containing the cylinder axisenclose an angle of more than 100.

31. The method according to claim 2, wherein the fuel is injected supercritically.

32. The method according to claim 1, wherein during each injection the fuel is injected over a maximum of 20 crank angle.

Description

[0033] The invention is explained in more detail below on the basis of the embodiment example shown in the non-limiting figures. The drawings show schematically:

[0034] FIG. 1 shows a cylinder of an internal combustion engine for carrying out the method according to the invention in a first embodiment variant in a longitudinal section;

[0035] FIG. 2 shows a cylinder of an internal combustion engine for carrying out the method according to the invention in a second embodiment variant in a longitudinal section;

[0036] FIG. 3 shows a cylinder of an internal combustion engine for carrying out the method according to the invention in a third embodiment variant in a longitudinal section;

[0037] FIG. 4 shows a cylinder of an internal combustion engine for carrying out the method according to the invention in a fourth embodiment variant in a longitudinal section;

[0038] FIG. 5 shows the cylinder in a section according to line IV-IV in FIG. 1, 2, 3 or 4,

[0039] FIG. 6 shows injection events when carrying out the method according to the invention in different variants of the invention;

[0040] FIG. 7 shows the cylinder from FIG. 4 in a longitudinal section with indicated core zone; and

[0041] FIG. 8 shows this cylinder in a section according to line VIII-VIII in FIG. 7.

[0042] FIG. 1 to FIG. 4 schematically show in each case a cylinder 1 of a spark-ignition internal combustion engine, in which a reciprocating piston 2 is displaceably arranged. Piston 2, which has a piston bowl 3, acts on a crankshaft via a connecting rod not shown further. A combustion chamber 6 is formed between piston 2 and the roof-shaped combustion chamber ceiling 5 formed by a cylinder head 4. A fuel injection device 7 and an ignition device 8for example a conventional spark plug with electrodes which open directly into the combustion chamber 6open centrally into the combustion chamber 6. The ignition device 8 can also be designed as a prechamber spark plugshown in the illustrationwith an integrated prechamber in which the electrodes are arranged, wherein the prechamber is connected to the combustion chamber 6 via several openings. It is also possible to provide more than one fuel injection device 7 and/or more than one ignition device 8 per cylinder 1.

[0043] The axis 7a of the fuel injection device 7 may be inclined to the cylinder axis 1a. Similarly, axis 8a of the ignition device 8 may be inclined to cylinder axis 1a. In the example shown, the angle of inclination between axis 7a and cylinder axis 1a, for example, is approximately 15, and the angle of inclination between axis 8a and cylinder axis 1a, for example, is approximately 10. The inclination angles , can preferably be between 0 and 30, and particularly preferably between 0 and 15.

[0044] The injection location 7b of the fuel injection device 7 and the ignition location 8b of the ignition device 8 are located near the cylinder axis 1a. The distance 7c between the injection location 7b and cylinder axis 1a is less than a quarter of the radius R of cylinder 1. The same applies to the distance 8c between the ignition location 8b and cylinder axis 1a.

[0045] The fuel injection device 7 is designed as a multi-hole injection device to inject the fuel into the combustion chamber 6 in several injection jets 9 via several (not shown) injection ports. The central axes 10 of two injection ports of the fuel injection device 7 for approximately diametrically opposed injection jets 9when viewed in a side view of the fuel injection device as shown in FIG. 1 and FIG. 2form an angle of over 30, preferably over 60, in particular over 80, particularly preferably over 100. This angle corresponds to the jet angle formed by the jet axes of the two approximately diametrically opposed injection jets 9. In the embodiment example shown, the angle is about 110.

[0046] The radius r of the substantially circular piston bowl is between 0.7 and 0.9 times the piston radius R. In the region furthest from the cylinder axis 1a, the piston bowl has 3 bowl walls 31 facing away from the piston edge 21, which are formed substantially parallel to the cylinder axis 1a.

[0047] The fuel injection (for single injection) or the last fuel injection (for multiple injection) takes place very late in the compression stroke near the top dead center TDC of the combustion, wherein the central axes 10 of the injection ports or the jet axes of the injection jets 9 are directed towards the bowl walls 31. The injection jets 10 thus travel the longest possible distance within combustion chamber 6 before they hit piston 2. The fuel can thus vaporize in the best possible way.

[0048] As can be seen from FIG. 5, the fuel injection device 7 has a star-shaped jet pattern of the injection jets 9, wherein six injection ports are provided in the embodiment example shown. Reference numeral 11 designates gas exchange valves arranged in the combustion chamber ceiling 5. At least two injection ports of the fuel injection device 7 are arranged so that fuel is injected via one injection jet 9 on each side of the ignition point 8b of the ignition device 8. The central axes 10 of these injection ports enclose an angle which is approximately between 50 and 80.

[0049] The injection jets 9 have a distance a from the ignition point 8b, which is between 0 mm and 2.5 mm. This ensures reliable ignition of the fuel-air mixture.

[0050] As can be seen from FIG. 1, walls or wall areas adjacent to the combustion chamber 6 have thermal insulations 12. In particular, thermal insulations 12 are provided in the area of the piston surface 22i.e. in the area of the piston bowl 3 and in the area between piston bowl 3 and piston rim 21, in the area of the combustion chamber ceiling 5, and in the area of cylinder 1 bordering on combustion chamber 6, but also in the area of the top land 23 of piston 2 and in an area of cylinder 1 opposite the top land 23. In FIG. 2 the insulations 12 are not shown.

[0051] The embodiment variant shown in FIG. 2 differs from FIG. 1 in that the piston bowl 3 has a central elevation 32. Furthermore, the areas of the piston surface 22 between the piston bowl 3 and the piston rim 21 facing the combustion chamber 6 are designed as squeezing surfaces 24, whose inclination and shape essentially corresponds to the roof inclination of the roof-shaped combustion chamber ceiling 5. The corresponding squeezing surfaces on the cylinder head side of the combustion chamber ceiling 5 are designated by reference numeral 25.

[0052] Squeezing surfaces 24 on the piston side between the piston bowl 3 and the piston rim 21 on the one hand and squeezing surfaces 25 on the cylinder head side of the combustion chamber ceiling 5 on the other hand are also provided in the third embodiment variant of the invention shown in FIG. 3. The squeezing surfaces 24, 25 are designed to be flat and parallel to the cylinder head sealing plane E. Within the cylinder-head-side squeezing surfaces 25, the combustion chamber ceiling 5 is roof-shaped.

[0053] FIG. 4 shows a further embodiment variant of the invention with areas of the piston surface 22 formed between the piston bowl 3 and the piston rim 21 as squeezing surfaces 24, wherein the squeezing surfaces 24 at least partially follow the shape of the roof-shaped combustion chamber ceiling 5. The squeezing surfaces 24 and the corresponding cylinder-head-side squeezing surfaces 25 of the combustion chamber ceiling 5 are slightly curved in FIG. 4, wherein the gradient of the piston surface 22 or the combustion chamber ceiling 5 are smaller in the region of the piston edge 21 or cylinder edge than in a region closer to the cylinder axis 1a. It is understood that thermal insulation can also be provided for the embodiments shown in FIG. 2 to FIG. 4.

[0054] According to the method according to the invention, the internal combustion engine is operated at least approximately adiabatically and with a stoichiometric air-fuel ratio =1 and the fuel is injected very late in the compression stroke near the top dead center TDC of the combustion with very high injection pressure of more than 500 bar, in particular more than 900 bar, for example 1000 bar.

[0055] Alternatively, the internal combustion engine can be operated at least approximately adiabatically and with a lean air-fuel ratio >1 and the fuel in the compression stroke can be injected very late near the top dead center TDC of the combustion with very high injection pressure of over 500 bar, especially over 900 bar, for example 1000 bar.

[0056] In any case, the fuel is injected very late and immediately before the mixture is ignited. In this case, the entire injection takes place before the ignition point. At the time of ignition, the mixture formation is predominantly complete, with more than 90%, preferably at least 95% of the fuel being mixed with air. At the time of ignition there is an approximately homogeneous mixture, in particular a quasi-homogeneous mixture in the cylinder. A zone with a homogeneous mixture is formed in a central region 40 of the combustion chamber 6 substantially above the piston bowl 3, and radially outside this central region 40 a substantially annular region 41 with a zone with air or a lean base mixture is formed, as shown in FIG. 7 and FIG. 8. This has the advantage that due to the after-reaction between oxygenO.sub.2 and carbon blackC to CO.sub.2, the premixed combustion takes place with very little carbon black. The exhaust gas also has a quasi-homogeneous composition with a content of CO<1%, especially between 0.6-0.8%, and a content of O.sub.2<1%.

[0057] The internal combustion engine can be operated according to the Miller or Atkinson cycle with an early or late intake closure. The intake ducts of the internal combustion engine and combustion chamber 6 are designed to achieve a low tumble number, in particular a tumble number 1.

[0058] The internal combustion engine may be of the two-stroke or four-stroke type.

[0059] The fuel injection E can be carried out once or several times as shown schematically in FIG. 6a to FIG. 6c. In FIG. 6a to FIG. 6c the injection events E are plotted over the crank angle for one work cycle at a time, wherein the top dead centers are marked TDC and the bottom dead centers BDC.

[0060] FIG. 6a shows a variant of the method according to the invention with a single fuel injection E during the compression stroke.

[0061] FIG. 6b shows a variant of the method according to the invention with two fuel injections E during the compression stroke.

[0062] FIG. 6c shows a variant of the method according to the invention with three fuel injections E, wherein the first two fuel injections E take place during the intake stroke and one fuel injection E during the compression stroke.

[0063] In addition, one or more injections can be provided in the intake stroke. The individual injections in the compression stroke and in the intake stroke can have different quantity distributions in a ratio between 10/90 and 90/10. Even with more than two injection events, the fuel quantities can be divided up differently. For example, the quantity distribution for three injection events can be 10/25/65 or 60/30/10.