Internal combustion engine and method for operating an internal combustion engine

Abstract

An internal combustion engine (1), specifically a spark ignition engine, comprises a spark plug (23) projecting into a prechamber (24) of a combustion chamber (21), and a fuel injector (20) which can be switched over in such a way that a variable proportion of the injected fuel reaches the prechamber (24).

Description

[0001] Internal combustion engine and methods for operating an internal combustion engine

[0002] The invention relates to an internal combustion engine designed as a spark-ignition engine, in particular in the form of a reciprocating piston engine. The invention further relates to a method for operating an internal combustion engine.

[0003] EP 3 001 008 B1 discloses a combustion system with a turbulent jet ignition prechamber for spark-ignition engines, i.e., gasoline engines. In the cylinder head of an internal combustion engine incorporating this combustion system, a prechamber is formed within a housing. An ignition device, which is mounted in the housing, faces the prechamber, i.e., is located behind the prechamber when viewed from the combustion chamber of the internal combustion engine. Additionally, an injection valve is located behind the prechamber. A further fuel injector injects fuel into an intake manifold of the internal combustion engine.

[0004] Further designs of spark-ignition combustion engines featuring a pre-chamber are described, for example, in documents DE 10 2018 114 035 A1 and DE 10 2019 111 091 B3. In both cases, fuel is injected into the pre-chamber, which contains a spark plug.

[0005] An internal combustion engine with a prechamber, which provides for fuel injection exclusively outside the prechamber, is described, for example, in US 2022 / 0275748 A1. The injection of fuel is intended to create a rich fuel-air mixture centrally in the combustion chamber. During the compression stroke, this mixture partially enters the prechamber, where it is ignited.

[0006] From EP 3 453 856 B1, a gasoline internal combustion engine with a combustion pre-chamber and two spark plugs is known. One of the spark plugs is located inside the pre-chamber and the other outside. Furthermore, according to EP 3 453 856 B1, the internal combustion engine has two gasoline injection devices, one of which injects gasoline into an intake port and the other directly into the combustion chamber.

[0007] DE 10 2021 212 503 A1 discloses an injection device for gaseous fuel directly into the combustion chamber of an internal combustion engine. The injection device comprises an inlet valve, near the valve seat of which a fuel line section for the gaseous fuel opens. According to DE 10 2021 212 503 A1, the injection of the gas, which is supplied at a pressure of approximately 700 bar, is pressure-controlled.

[0008] The invention is based on the objective of further developing pre-chamber spark-ignition engines designed for liquid or gaseous fuels compared to the aforementioned prior art, whereby a favorable ratio between the possibility of varying injection and ignition processes on the one hand and the equipment effort on the other hand is sought.

[0009] This problem is solved according to the invention by an internal combustion engine with the features of claim 1. Likewise, the problem is solved by a method for operating an internal combustion engine, namely a gasoline engine, designed according to claim 5. The embodiments and advantages of the invention explained below in connection with the operating method also apply mutatis mutandis to the device, i.e., the internal combustion engine, and vice versa.

[0010] The invention is based on the premise that, in pre-chamber gasoline engines, a fundamental distinction must be made between active and passive pre-chamber combustion processes. A passive pre-chamber is a defined volume around the spark plug, which is connected to the rest of the combustion chamber, i.e., the main combustion chamber, via several openings. During compression, fuel-air mixture also enters the pre-chamber. When the fuel-air mixture is ignited, the pressure in the pre-chamber initially rises. This pressure increase causes gas to flow at high velocity into the main combustion chamber, thereby igniting the fuel-air mixture there as well. Compared to a gasoline engine without a pre-chamber, the gas flowing from the pre-chamber in the form of individual jets achieves a very high penetration depth very quickly.

[0011] An active pre-chamber provides an additional fuel supply to the pre-chamber, allowing for separate adjustment of the fuel-air ratio. This enables the fuel-air mixture in the main combustion chamber to be leaned out during partial load operation, while a rich, ignitable mixture is present in the pre-chamber. Overall, this allows for more efficient operation with less throttle valve use, although it results in a more complex design compared to an engine with a passive pre-chamber.

[0012] The solution as described in the application combines the advantages of an active prechamber with the simple design of a passive prechamber due to the switching capabilities of the fuel injector located outside the prechamber. A second fuel injector located inside the prechamber is not required.

[0013] The fuel injector, as well as the pre-chamber and the spark plug protruding into the pre-chamber, can be located in the area of ​​the combustion chamber roof of a single- or multi-cylinder internal combustion engine. Other methods of external ignition, such as laser ignition, are also conceivable.

[0014] The fuel injector can be adjusted primarily by means of an adjustable nozzle needle. Additionally or alternatively, the pressure on the inlet side of the fuel injector can be adjusted. In any case, these adjustments ensure that defined, clearly distinguishable flow conditions can be set. A continuum of transitioning flow states is therefore not possible. Adjusting the nozzle needle longitudinally is one of several ways to influence the flow of the injected fuel. Furthermore, the flow state of the hydrogen at the nozzle outlet depends on the fuel pressure at the nozzle inlet and the back pressure in the combustion chamber, assuming that the fuel is only supplied to the combustion chamber after the intake valve has closed.Within the short time available for supplying the gaseous fuel, the cross-sectional area of ​​the channel inlet can be altered by longitudinally shifting the nozzle needle, causing the flow to reverse direction within the nozzle after exiting the channel. A control cross-section is thus present at the channel inlet, i.e., at the narrowest gap of the nozzle. Overall, the nozzle is designed as a supersonic nozzle.

[0015] In general, the method for operating an internal combustion engine, namely a gasoline engine, is characterized by the fact that fuel is introduced in variable proportions into the pre-chamber and into combustion chamber areas outside the pre-chamber, i.e., into the main combustion chamber, with the help of an adjustable injector, which is located outside a pre-chamber equipped with an ignition device.

[0016] In this process, the injector can be set to a first configuration, meaning the fuel injector is configured to produce a richer mixture in the pre-chamber than in the main combustion chamber. In a second configuration, the fuel injector can produce a homogeneous mixture in both the pre-chamber and the main combustion chamber, or even a leaner mixture in the pre-chamber compared to the main combustion chamber. The fuel used can be gaseous or liquid gasoline. Methane, hydrogen, and ammonia are among the possible fuel types.

[0017] In a first operating mode, fuel is injected in such a way that, utilizing the Coanda effect, it flows close to the walls of the combustion chamber and thus reaches the pre-chamber. Regarding the Coanda effect, reference is made to US 4,574,754 A, which deals with flows within the combustion chamber of an internal combustion engine. In this case, fuel is directed along a combustion chamber wall to a spark plug or an arrangement of multiple spark plugs.

[0018] The patented method for operating an internal combustion engine can include a second operating mode in which fuel is injected in such a way that it is introduced, in the form of a flow detached from the combustion chamber wall, specifically into combustion chamber areas outside the pre-chamber, i.e., into the main combustion chamber. A switch between the first and second operating modes can occur in one and the same engine cycle. The changeover between the different flow states can take place while maintaining a constant nozzle geometry at the channel outlet, which, by definition, is located at the end of the nozzle needle.

[0019] An embodiment of the invention is explained in more detail below with reference to a drawing. The drawing shows:

[0020] Fig. 1 schematically shows a section of an internal combustion engine designed as a gasoline engine, including a fuel injector, a spark plug and a pre-chamber.

[0021] Fig. 2 shows a detail of the fuel injector of the internal combustion engine according to Fig. 1.

[0022] A fuel injector 20, in this case a hydrogen injector, is intended for use in an internal combustion engine designated by reference numeral 1, i.e., a hydrogen-powered spark-ignition engine. In this case, the internal combustion engine 1 is a reciprocating piston engine of a motor vehicle. Alternatively, the internal combustion engine 1 could, for example, be a stationary gas engine in a combined heat and power plant. The actuators of the fuel injector 20 are not shown. Figure 2 shows a partial view of a nozzle 2 of the fuel injector 20. Means upstream of the nozzle 2 for reducing the pressure of the hydrogen to be combusted in the spark-ignition engine 1 are also not shown. Alternatively, the spark-ignition engine 1 could be designed to combust another liquid or gaseous substance.

[0023] The fuel injector 20 has a housing 3, which is only partially visible in Fig. 2. A nozzle needle 5 is slidably guided in the housing 3, i.e., the injector housing. A stem of the nozzle needle 5 is designated 6, and a valve disc of the nozzle needle 5 is designated 7. Between the valve disc 7 and the inner wall of the housing 3, designated 10, an annular flow channel 4 is formed, widening in the direction of hydrogen flow – from right to left in the arrangement shown in Fig. 2. The narrowest point of the nozzle cross-section, at the transition between the stem 6 and the valve disc 7 of the nozzle needle 5, is defined as the channel inlet 8. The channel outlet, designated 9, is located, by definition, at the combustion chamber-side end of the valve disc 7, which is in the form of an end face 13 of the valve disc 7, also referred to as the end face.The end surface 13 has a planar shape in this case, with the central axis of the shaft 6 forming a surface normal to the end surface 13. The diameter of the shaft 6 is designated d6. The diameter of the housing 3, designated d3 in Fig. 2, does not necessarily represent a maximum dimension of the housing 3; rather, the diameter d3 refers exclusively to the depicted cylindrical section of the housing 3.

[0024] The valve plate 7 of the nozzle needle 5 has a curved surface section 11 and an adjoining cylindrical surface section 12, the latter extending, apart from any edge rounding, to the end surface 13. The diameter of the valve plate 7, designated d12, corresponds to the diameter of the cylindrical surface section 12 and, in this case, is more than 1.5 times, but not more than four times, the diameter d6 of the shaft 6. A plane formed at the end face of the housing 3 at the outlet side of the fuel injector 20 constitutes an end face 14. A distance a2_7 exists between this end face 14 and the parallel end face 13 of the valve plate 7. The end face 13 is located within the interior formed by the housing 3 in every setting of the hydrogen injector 1.

[0025] In its section extending beyond the end face 13 to the end plane 14, the housing 3 has a curved end section 15, which, as part of the inner wall 10, adjoins an outer cylindrical region 16 of the inner wall 10. At least one region of the cylindrical surface section 12 of the valve disc 7, bordering the end face 13, is arranged concentrically within the outer cylindrical region 16 of the inner wall 10 in every setting of the nozzle needle 5, so that the geometry of the channel outlet 9 located on the valve disc 7 of the nozzle needle 5 is unchanging.

[0026] Towards the shaft 6, the outer cylindrical section 16 of the inner wall 10 transitions into a concave wall section 18, to which a convex wall section 17 adjoins. An inner cylindrical section of the inner wall 10, designated 19, adjoins the convex wall section 17, which is located in the region of the channel inlet 8. In the exemplary embodiment, the diameter d19 of the inner cylindrical section 19 is at least one-third, but not more than 80%, of the diameter d16 of the outer cylindrical section 16 of the inner wall 10.

[0027] In the setting sketched in Fig. 2, the nozzle 2 is opened as wide as possible, meaning the channel inlet 8 is set to its maximum cross-sectional area. The distance a2_7 is minimal in this setting. Compared to all other possible settings of the nozzle 2, the hydrogen flows at the channel outlet 9 at the highest velocity, presenting as an underexpanded jet. Expansion of the hydrogen jet occurs in the direction of the central axis of the nozzle 2, i.e., inwards, which is accompanied by the jet detaching from the inner wall 10 at the transition between the outer cylindrical section 16 and the end section 15. Fuel, in this case hydrogen, is thus introduced into the combustion chamber 21 of the internal combustion engine 1 in the form of a narrow, only slightly expanding hollow jet HS, which is shown in Fig.1 is shown in simplified form and exits from the annular gap formed between the cylindrical surface section 12 of the valve plate 7 and the also cylindrical area 16 of the inner wall 10 of the housing 3.

[0028] If the flow cross-section at the channel inlet 8 is narrowed by retracting the nozzle needle 5, a more extreme expansion ratio exists within the flow channel 4 compared to the setting shown in Fig. 2. This results in a lower static outlet pressure of the hydrogen at the channel outlet 9, which in turn means that the flowing hydrogen has a reduced tendency to expand towards the central axis of the nozzle 2. Instead, the hydrogen flow remains in contact with the inner wall 10 of the housing 3 even in the end region 15. The hydrogen flow then spreads further as a Coanda flow CS, indicated by dashed arrows, initially along the combustion chamber roof, labeled 26.

[0029] The Coanda effect causes the hydrogen jet to form a hollow cone jet with a large opening angle even within the nozzle 2. The angle denoted by 'a', which is enclosed between a tangent applied to the curved end section 15 and the front plane 14, is 45° ± 15° in the exemplary embodiment. Even a slight, defined axial movement of the nozzle needle 5 is sufficient to switch the hydrogen flow from the detached flow shown in Fig. 2 (illustrated with solid arrows in Fig. 1), which is in the form of the hollow jet HS, to the Coanda flow CS (indicated by dashed lines in Fig. 1).

[0030] In Fig. 1, which illustrates various possible flow conditions, namely the hollow jet HS and the Coanda flow CS, the piston designated 22 is located between bottom dead center and top dead center. The internal combustion engine 1 is a multi-cylinder engine whose gas exchange valves are not shown in Fig. 1. In addition to the fuel injector 20, a spark plug 23 is located in the area of ​​the combustion chamber roof 26.

[0031] The spark plug 23, which is generally referred to as the ignition device, is arranged within a pre-chamber 24, which has several openings 25, which in at least some cases are open to the side - and thus, among other things, to the fuel injector 20 - as can be seen from Fig. 1.

[0032] If the fuel injector 20 is adjusted such that the Coanda flow CS is formed, ignitable mixture passes through at least one of the openings 25 into the pre-chamber 24. At this moment, the mixture in the pre-chamber 24 is richer than in the main combustion chamber designated 27, which constitutes by far the largest part of the combustion chamber 21.

[0033] When the mixture in the pre-chamber 24 is ignited by the spark plug 23, the resulting hot gases spread at high speed in a jet form into the main combustion chamber 27. Synchronized with this, the fuel injector 20 is switched so that, instead of the now unnecessary Coanda flow CS, the detached flow HS, which is directed directly into the main combustion chamber 27, is formed.The ability to switch between the Coanda flow CS and the comparatively narrow hollow jet HS, which is present as a separated flow, during one and the same cycle of the internal combustion engine 1, together with the targeted supply of fuel to the pre-chamber 24, creates the prerequisite for operating the internal combustion engine 1 in a wide range of different operating conditions with a mixture finely tuned to the respective condition, without requiring an additional fuel supply to the pre-chamber 24 by means of a separate injector. (See list of reference symbols.)

[0034] 1 Internal combustion engine

[0035] 2 nozzles

[0036] 3 cases

[0037] 4 Flow channel

[0038] 5 jet needle

[0039] 6 shaft

[0040] 7 valve plates

[0041] 8 Channel entry

[0042] 9 Channel outlet

[0043] 10 Inner wall of the housing

[0044] 11 Curved surface section of the valve disc

[0045] 12 cylindrical surface section of the valve disc

[0046] 13 End surface, face of the valve disc

[0047] 14 Front plane at the opening of the housing

[0048] 15 curved end section of the housing

[0049] 16 outer cylindrical area of ​​the inner wall

[0050] 17 convex wall section

[0051] 18 concave wall section

[0052] 19 Wall section, inner cylindrical area of ​​the inner wall

[0053] 20 fuel injectors

[0054] 21 Combustion chamber

[0055] 22 pistons

[0056] 23 Spark plug

[0057] 24 Antechamber

[0058] 25 Opening

[0059] 26 Combustion chamber roof

[0060] 27 Main combustion chamber

[0061] Angle a2 7 Distance between the end face of the valve disc and the housing end plane

[0062] CS Coanda flow d3 Casing diameter d6 Stem diameter d12 Valve disc diameter d16 Cylindrical section diameter 16 d19 Cylindrical section diameter 19 HS Detached flow, narrow jet

Claims

Patent claims 1. Internal combustion engine (1) , with a spark plug (23) projecting into a pre-chamber (24) of a combustion chamber (21) and a fuel injector (20) which is switchable such that a variable proportion of the injected fuel reaches the pre-chamber (24).

2. Internal combustion engine (1 ) according to claim 1 , characterized in that the fuel injector (20) is arranged outside the pre-chamber (24).

3. Internal combustion engine (1 ) according to claim 2, characterized in that the fuel injector (20) as well as the pre-chamber (24) is located in the area of ​​the combustion chamber roof (26).

4. Internal combustion engine (1 ) according to one of claims 1 to 3, characterized in that the fuel injector (20) comprises an adjustable nozzle needle (5).

5. Method for operating an internal combustion engine (1), namely a gasoline engine, wherein fuel is introduced in variable proportions into the pre-chamber (24) and into combustion chamber areas outside the pre-chamber (24) by means of an adjustable fuel injector (20) which is located outside a pre-chamber (24) equipped with an ignition device (23).

6. Method according to claim 5, characterized in that in a first operating mode fuel is injected in such a way that it flows close to the wall in the combustion chamber (21) using the Co-anda effect and thus reaches the pre-chamber (24).

7. Method according to claim 6, characterized in that in a second operating mode fuel is injected in such a way that it is introduced in the form of a flow detached from the combustion chamber wall into combustion chamber areas outside the pre-chamber (24).

8. Method according to claims 6 and 7, characterized in that a switch between the first and the second operating mode takes place in one and the same cycle of the internal combustion engine (1 ).

Images