WO2021174266A1

WO2021174266A1 - Cylinder head having a pre-chamber and internal combustion engine

Info

Publication number: WO2021174266A1
Application number: PCT/AT2020/060058
Authority: WO
Inventors: Tobias TRIENDL; Wolfgang Fimml
Original assignee: Innio Jenbacher Gmbh & Co Og
Priority date: 2020-03-03
Filing date: 2020-03-03
Publication date: 2021-09-10

Abstract

Cylinder head for an internal combustion engine (1) having a prechamber (4), wherein the pre-chamber (4) is arranged eccentrically relative to a main combustion chamber (12) and comprises at least two transfer passages (17,18), wherein the pre-chamber (4) and the main combustion chamber (12) are fluidically connected by the at least two transfer passages (17,18), wherein one of the at least two transfer passages (17), which has a largest distance (SLarge) from an opposing wall (19) of the main combustion chamber (12), has a larger cross-sectional area than each of the at least two transfer passages (18), which has or have a smaller distance (SSmall) from an opposing wall (19) of the main combustion chamber (12).

Description

Cylinder head having a pre-chamber and internal combustion engine

The present invention relates to a cylinder head for an internal combustion engine having a pre-chamber and an internal combustion engine having such a cylinder head.

In Otto-cycle operated internal combustion engines, in particular in gas engines, in which a fuel-air mixture is ignited, for larger combustion chamber volumes often a lean burn concept is applied. This means that a relatively large air excess is present, so that at maximum power and simultaneously high efficiency of the engine, the harmful emissions and the thermal loading of the components are minimized. The ignition and combustion of very lean fuel-air mixtures represent a considerable challenge for the development and/or operation of modern high-performance gas engines.

Starting from a certain size of gas engines (generally with cylinder capacity above about six liters) it is necessary to use ignition amplifiers, in order to properly ignite the lean air- fuel-mixture in the large volume of the cylinders.

Pre-chambers usually serve as these ignition intensifiers, wherein the fuel-air mixture that is highly compressed at the end of the compression stroke is ignited in a relatively small secondary space separate from the main combustion chamber of the cylinders. In this case a main combustion chamber may be delimited by the working piston, the cylinder liner forming a cylinder wall and (a flame plate of) the cylinder head, wherein the secondary space (the pre-chamber) is connected via one or a plurality of transfer passages with the main combustion chamber.

Often these pre-chambers are flushed or filled with fuel gas during the gas exchange phase, in order to enrich the fuel-air mixture in the pre-chamber and thus improve the ignition and combustion properties. For this, a small amount of fuel gas may be diverted from the fuel supply line to the main combustion chamber and fed into the pre-chamber via a suitable feed device provided with a non-return valve. This amount of fuel gas flushes the pre-chamber during gas exchange and so is known as flushing gas.

During the compression phase, the very lean fuel-air mixture of the main combustion chamber flows through the transfer passages into the pre-chamber, where it mixes with the flushing gas. The ratio of fuel to air in the mixture is stated as the excess-air coefficient l. An excess-air coefficient of l = 1 means that the amount of air present in the mixture corresponds exactly to the amount that is required to allow complete combustion of that amount of fuel. In such a case combustion takes place stoichiometrically.

At full load, large gas engines are usually run lean, at l of approx. 1.7 to2.1, i.e. the amount of air in the mixture corresponds to about twice the stoichiometric amount of air. Owing to the flushing of the pre-chamber with fuel gas, after mixing with the fuel gas-air mixture of the main combustion chamber an average l in the pre-chamber is approx. 0.8 to1,4. Therefore the ignition conditions are close to optimal and flame jets extend through the transfer passages into the main combustion chamber, which lead to a rapid, thorough combustion of the fuel-air mixture in the main combustion chamber. To get an optimal ignition result and subsequently an optimal combustion process pre chambers are preferably provided centrically in the main combustion chamber at the cylinder head, wherein the flame jets can extend symmetrically into the main combustion chamber. But such a central arrangement of the pre-chamber in the main combustion chamber is in some cases not possible, because of structural conditions (e.g. if the preferred space is needed for other components of the internal combustion engine, if the space in the center above the main combustion engine is too small to arrange a pre-chamber gas valve or a spark plug or if different inlet- and outlet valve diameters shift the position of the pre-chamber outside the center line of the main combustion chamber). In these cases the pre-chamber has to be arranged eccentrically at the main combustion chamber.

The EP 3095981 A1 describes described to configure the transfer passages in size and/or position in such a way that fuel and ignition is concentrated to one side of the combustion chamber, wherein a flow dynamic in the main combustion chamber can be controlled. The actual disadvantage of such configurations is that the ignition of the combustion is not homogenously in the main combustion chamber, wherein increased loads appear to components of the internal combustion engine. For example, an eccentrical thermal and mechanical load appears on the piston because of the inhomogeneous combustion, which leads to an increased wear, higher necessary maintenance effort and therefore increased costs.

The object of the invention is to provide a cylinder head for an internal combustion engine having a pre-chamber and an internal combustion engine having such a cylinder head, wherein more homogeneously distributed combustions are achieved compared to the prior art despite an eccentric arrangement of the pre-chamber.

This object is achieved by a cylinder head for an internal combustion engine with the features of claim 1 and an internal combustion engine having such a cylinder head.

According to the invention, it is provided that a pre-chamber arranged eccentrically relative to the main combustion chamber at the cylinder head comprises at least two transfer passages, wherein that one of the at least two transfer passages, which has a largest distance from an opposing wall of the main combustion chamber, has a larger cross-sectional area than each of the at least two transfer passages, which has or have a smaller distance from an opposing wall of the main combustion chamber (than the one which has a largest distance from an opposing wall).

By the variation of the size of the cross-sectional area of a transfer passage the speed of the flame jets can be controlled.

The speed of the flame jets can be controlled in that an increase of the cross-sectional area of the transfer passage increases the speed of expansion of the flame jets. This results from the fact that the speed of the flame jets almost reaches the speed of sound. In other words, if the speed of the flame jets would be faster than the speed of sound, this correlation between the cross-sectional area and the expansion speed would not be present. As mentioned, the advantage of the present invention is that despite the eccentrically arranged pre-combustion chamber the flame jets can be spread homogeneously in the main combustion chamber, which results to a much more homogeneous and efficient combustion.

The invention can be used for the already in the introduction of the description described embodiments of the prior art. Already present internal combustion engines can be upgraded with a new pre-chamber or by a rework of the transfer passages according to the invention.

The distance of the transfer passage from an opposing wall of the main combustion chamber can be understood as distance from an opening of the according transfer passage into the main combustion chamber up to an opposing wall (or a point near the opposing wall) of the main combustion chamber in a fluid-technical flow direction given by the orientation of the transfer passages (e.g. along a bore axis of the transfer passage).

The fluidic connection, which is provided by the transfer passages, between the main combustion chamber and the pre-chamber can be understood as fluid communication between the main combustion chamber and the pre-chamber, wherein a fluid can circulate.

The eccentric arrangement of the pre-chamber in the main combustion chamber means that a center line of the pre-chamber has a distance to a center line of the main combustion chamber (greater than zero).

Advantageous embodiments are defined in the dependent claims.

Preferably at least three - particularly preferred six or more than six - transfer passages are provided, wherein that one of the transfer passages, which has the largest distance from an opposing wall of the main combustion chamber, has a larger cross-sectional area than each of the remaining transfer passages, which has or have a smaller distance from an opposing wall of the main combustion chamber. It can be provided that the sizes of the cross-section areas of the at least two transfer passages are selected in such a way that flame jets extending from the pre-chamber into the main combustion chamber from the at least two transfer passages reach a defined distance from the wall (e.g. in the form of an imaginary circle, see below) of the main combustion chamber essentially at the same time.

It can be provided that the pre-chamber projects into the main combustion chamber.

It can be provided that the an arbitrary one of the at least two transfer passages, which has a certain distance from an opposing wall of the main combustion chamber, has a larger cross-sectional area than each of the at least two transfer passages, which has or have a smaller distance from an opposing wall of the main combustion chamber (than the arbitrary one of the at least two transfer passages).

In this way, it can be provided that a distance to the wall or the defined, imaginary circle (see below) is proportional to the cross-sectional areas of the transfer passages (and therefore the speed of expansion of the ignition).

It can be provided that the at least two transfer passages are bores. This bores can for example be manufactured by a drilling process. But it could also be provided that the pre-chamber is produced by using an additive manufacturing process.

It can be provided that the at least two transfer passages have a - preferably different - angular position relative to a centerline of the main combustion chamber. Using different angles for the at least two transfer passages generates a further degree of freedom to control or direct the flame jets to a desired position in the main combustion chamber.

It can be provided that the angular positions of the at least two transfer passages are selected in such a way that flame jets extending from the pre-chamber into the main combustion chamber reach a defined height in the main combustion chamber essentially at the same time. Igniting the main combustion chamber by the flame jets at the same height above the piston an especially preferred combustion condition is generated, wherein the main combustion chamber combusts very homogenously. Further, it can be prevented that the flame jets do not directly impact the surface of the piston facing the main combustion chamber. The “height” can be understood as length along the center line of the main combustion chamber or along the center line of the pre-combustion chamber. It can be provided that the sizes of the cross-section areas and the angular positions of the at least two transfer passages are selected in such a way that flame jets extending into the main combustion chamber from the at least two transfer passages each reach a point of a defined, imaginary circle concentric to the center line of the main combustion chamber essentially at the same time. The defined, imaginary circle is arranged within the main combustion chamber.

The imaginary circle can preferably have a diameter in the range of 50 % to 99 % of the bore diameter of a cylinder defining the main combustion chamber. The orientation of the at least two transfer passages can be chosen such that the distance of the imaginary circle from the cylinder head is in the range of 14 % to 50 % of the bore diameter of a cylinder defining the main combustion chamber.

The “defined distance from the wall” can be constant around the whole main combustion chamber, wherein the sum of these points can for example form the defined, imaginary circle within the main combustion chamber. The distance to the opposing wall according to the invention can be viewed as the distance from the opening of the according transfer passage to these points. It can be provided that at least one ignition source is arranged in the pre-chamber or extends into the pre-chamber. Such an ignition source can for example be a spark plug.

It can be provided that the at least one of the at least two transfer passages has a tapering cross-section area that slopes toward the main combustion chamber. Further details and advantages of the invention are apparent from the accompanying figures and the following description of the drawings. The figures show:

Fig. 1 schematically a cylinder-piston-unit of an internal combustion engine,

Fig. 2a, 2b an embodiment according to the invention, Fig. 3a, 3b diagrams regarding the coefficient of velocity and Fig. 4 a further embodiment of the invention. Fig. 1 schematically shows a cylinder-piston-unit of an internal combustion engine 1. The cylinder 2 in which a piston 3 is arranged so as to be movable up and down, whereby a main combustion chamber 12 is formed between the piston 3 and the cylinder 2, more specifically the wall 19 of the main combustion chamber 12. An intake duct 10 can be closed by an intake valve 6 and an outlet duct 11 can be closed by an outlet valve 7 opposite the main combustion chamber 12. The intake valve 6 and the outlet valve 7 are actuated by the actuators 8.

A pre-chamber 4 communicates with the main combustion chamber 12 via transfer passages 17, 18 and has an ignition source 13 and a pre-chamber gas valve 5 in the form of a non-return valve, which is connected to a source for a gas-air mixture.

In this exemplary embodiment, the intake duct 10 itself serves as this source for the pre chamber 4, and a connecting line 9, which is formed as a cavity in the cylinder head, is provided for the pre-chamber gas valve 5. To regulate the quantity of gas-air mixture that can be fed into the pre-chamber 4, an adjustable throttle 14 is arranged in the connecting line 9 in this exemplary embodiment.

But it is also imaginable to provide the pre-chamber 4 with a separate fuel source, wherein the fuel-air mixture provided for the pre-chamber 4 differs from the fuel-air mixture provided for the main combustion chamber 12.

The pre-chamber 4 is arranged eccentrically at the main combustion chamber in relation to the centerline 21 of the main combustion chamber 12 and the centerline 20 of the pre-chamber 4. This eccentricity e can for example result by different valve seat diameters of the intake valves 6 and the outlet valves 7.

Fig. 2a and Fig. 2b show an embodiment of the present invention, wherein schematically a cylinder head 16 is shown in top view and in a cross-sectional side view, respectively. In the following it is explained in more detail how the transfer passages 17, 18 could be designed by making reference to Fig. 2a and Fig. 2b.

It can be seen in Fig. 2a and Fig. 2b that the pre-chamber 4 is arranged eccentrically in the main combustion chamber 12 by the eccentricity e. The main combustion chamber 12 is limited by the wall 19 of the main combustion chamber 12 and the top end surface of the piston 3.

The pre-chamber 4 (which projects into the main combustion chamber 12) and the main combustion chamber 12 are fluidically connected by the transfer passages 17, 18. The transfer passages 17, 18 are different in the size of their cross-sectional areas, wherein in this embodiment the transfer passages 17, 18 are designed as bores with constant diameter.

That one of the transfer passages 17, which has a largest distance Si__arge from an opposing wall 19 of the main combustion chamber 12, has a larger cross-sectional area than that one of the at least two transfer passages 18, which has a smaller distance Ssmaii from an opposing wall 19 of the main combustion chamber 12. In this embodiment the cross-sectional areas of the transfer passages 17, 18 are defined by the diameter, wherein the smaller transfer passage 18 has a smaller diameter d_Smaii and the larger transfer passage 14 has a larger diameter d_Large·

Furthermore, the transfer passages 17, 18 have different angular positions a, b relative to a centerline 20 of the pre chamber 4.

Flow the size of the diameters dsmaii, d_Large and the angles a, b of the transfer passages 17, 18 can for example be calculated is described in the following. First of all, positions in the main combustion chamber 12 have to be defined where the flame jets during the ignition event have to be essentially in the same time. This is defined in the shown embodiment by the imaginary circle 22, which is arranged centrically and horizontally (in the view of Fig. 2b) in the main combustion chamber 12 in a defined height h_(ti). The defined height h_(ti) is indicated in this embodiment by the distance between the transfer passages 17, 18 and the imaginary circle 22, wherein the center of the openings of the transfer passages 17, 18 to the main combustion chamber are selected as reference point. The difference in the heights between the transfer passage 17 and the transfer passage 18 resulting out of the different angles a, b can be neglected.

On the basis of this chosen imaginary circle 22, the known outer diameter d_Spc of the pre-chamber 4 and the eccentricity e the horizontal distances Ssmaii-x, SLarge-x between the transfer passages 17, 18 and the imaginary circle 22 can be calculated by the following equations:

Using this horizontal distances Ssmaii-x, SLarge-x the distances Ssmaii, SLarge from the transfer passages 17, 18 to the opposing wall 19 of the main combustion chamber 12 and the angles a, b can be calculated, wherein the distances Ssmaii, SLarge are the geometric distances of the openings of the transfer passages 17, 18 (having an angle a, b) to the main combustion chamber 12 to the imaginary circle 22. This can be calculated as follows: cos(a) = (analogous for b and "Large")

For calculating the diameters dsmaii, d_Large of the transfer passages 17, 18 it has to be known that the speed of expansion of the ignition (or the flame jets) extending through the transfer passages 17, 18 reaches almost speed of sound, wherein the coefficient c_V(d) of velocity behaves according to - Fig. 3a regarding a diameter change of the transfer passages and

Fig. 3b regarding change of pressure difference between the pre chamber 4 and the main combustion chamber 12.

The coefficient c_V(d) of velocity is defined (using this knowledge) by:

On this basis the diameters dsmaii, d_Large of the transfer passages 17, 18 can be calculated on the basis of the theoretical velocity of the flame jet under critical conditions v_theor(t) = _L /K * R * T as follows. The distance S(t1 ) which the flame jet covers during a time t1 is given by:

The velocity v(t) of a flame jet can be expressed as

where Dr(ί) and p(t) are the pressure drop and the density, respectively. The pressure drop is an empirically known quantity. Using these relations s_Smau and s_Larqe(tl ) can expressed in the following way:

The density is furthermore generally related to the mass flow by rh = p * v * A, where v is the velocity and A is the cross-sectional area or the mass flow. Applied to the present case this results in the following relation This total mass flow can be calculated or measured given the design of the pre chamber and the amount and composition of the mixture ignited in the pre-chamber.

For transfer passages with circular cross-section the area is given by A = — — in terms of the diameter of the transfer passages. Therefore there is a direct relationship between the distance of the transfer passages to the respective opposing wall which can be solved for the diameters of the transfer passages. Fig. 4 shows a schematic depiction of an embodiment of the invention with four transfer passages, namely a largest transfer passage 17, a smallest transfer passage 18 and two further transfer passages 23.

The transfer passages 17 and 18 are of substantially the same configuration as in the embodiment of Fig. 2a and 2b.

The further transfer passages 23 have a distance from the opposing wall which is between the distances of the respective opposing walls of the transfer passages 17 and 18. In this preferred embodiment they therefore also have cross-sectional areas which are between the cross-sectional areas of the transfer passages 17 and 18.

With an embodiment according to Fig. 4, where there is a monotonic correspondence between the distance from the opposing wall of the transfer passages 17, 18 and 23 and their cross-sectional areas, a particularly homogeneous ignition in the main combustion chamber 12 can be achieved. List of reference signs:

1. internal combustion engine

2. cylinder

3. piston

4. pre-chamber

5. pre-chamber gas valve

6. intake valve

7. outlet valve

8. actuator

9. connecting line

10. intake duct 11. outlet duct 12. main combustion chamber

13. ignition source

14. throttle valve

15. temperature control device

16. cylinder head

17. (larger) transfer passage

18. (smaller) transfer passage

19. wall of the main combustion chamber

20. centerline of the pre-chamber 21. centerline of the main combustion chamber

22. imaginary circle

23. further transfer passages e eccentricity dsmaii smaller diameter di_arg_e larger diameter h₍n₎ defined height a angle b angle d_Spc diameter of the pre-chamber

Ssmaii-x horizontal distance

Si_arge-x horizontal distance

Ssmaii distances

Si_arge distances c_V(d) coefficient of velocity v_tat actual velocity v_theor theoretical velocity

Ap pressure difference k isentropic exponent

R gas constant

T temperature

P density

D imaginary circle bore diameter

Claims

Claims:

1. Cylinder head for an internal combustion engine (1) having a prechamber (4), wherein the pre-chamber (4) is arranged eccentrically relative to a main combustion chamber (12) and comprises at least two transfer passages (17,18), wherein the pre-chamber (4) and the main combustion chamber (12) are fluidically connected by the at least two transfer passages (17,18), characterized in that one of the at least two transfer passages (17), which has a largest distance (Si_arge) from an opposing wall (19) of the main combustion chamber (12), has a larger cross-sectional area than each of the at least two transfer passages (18), which has or have a smaller distance (Ssmaii) from an opposing wall (19) of the main combustion chamber (12).

2. Cylinder head as set forth in claim 1 , characterized in that the sizes of the cross- sectional areas of the at least two transfer passages (17,18) are selected in such a way that flame jets extending from the pre-chamber (4) into the main combustion chamber (12) from the at least two transfer passages (17,18) reach a defined distance from the wall (19) of the main combustion chamber (12) essentially at the same time.

3. Cylinder head as set forth in one of the preceding claims, characterized in that the pre-chamber (4) projects into the main combustion chamber (12).

4. Cylinder head as set forth in one of the preceding claims, characterized in that an arbitrary one of the at least two transfer passages (17), which has a certain distance (Si_arge) from an opposing wall (19) of the main combustion chamber (12), has a larger cross-sectional area than each of the at least two transfer passages (18), which has or have a smaller distance (Ssmaii) from an opposing wall (19) of the main combustion chamber (12).

5. Cylinder head as set forth in one of the preceding claims, characterized in that the at least two transfer passages (17,18) are bores.

6. Cylinder head as set forth in at least one of the preceding claims, characterized in that angular positions (a, b) of the at least two transfer passages (17,18) are selected in such a way that flame jets extending from the at least two transfer passages (17,18) into the main combustion chamber (12) reach a defined height (h) in the main combustion chamber (12) essentially at the same time.

7. Cylinder head as set forth in at least one of the preceding claims, characterized in that the at least two transfer passages (17,18) have a different angular position (a, b) relative to a centerline (20) of the pre chamber (4).

8. Cylinder head as set forth in claim 6 or 7, characterized in that the sizes of the cross-sectional areas and the angular positions (a, b) of the at least two transfer passages (17,18) are selected in such a way that flame jets extending from the pre chamber (4) into the main combustion chamber (12) from the at least two transfer passages (17,18) each reach a point of a defined, imaginary circle (22) - preferably concentric to the center line (20) of the main combustion chamber (12) - essentially at the same time.

9. Cylinder head as set forth in at least one of the preceding claims, characterized in that at least one ignition source (13) is arranged in the pre-chamber (4) or extends into the pre-chamber (4).

10. Cylinder head as set forth in at least one of the preceding claims, characterized in that at least one of the at least two transfer passages (17,18) has a tapering cross- sectional area that tightens towards the main combustion chamber (12).

11. Internal combustion engine having at least one cylinder head (2) as set forth in at least one of the preceding claims.