WO2020154748A1

WO2020154748A1 - Pre-chamber assembly for an internal combustion engine

Info

Publication number: WO2020154748A1
Application number: PCT/AT2019/060039
Authority: WO
Inventors: Piotr OBARSKI; Mariusz Karpinski; Amy Lindblad; Andreas Koch; Alexander Sakotnig
Original assignee: Innio Jenbacher Gmbh & Co Og
Priority date: 2019-01-30
Filing date: 2019-01-30
Publication date: 2020-08-06

Abstract

Pre-chamber assembly for an internal combustion engine comprising - a boundary wall (2) of a pre-combustion chamber (3), - a riser passage (4), and - spray passages (5), wherein the riser passage (4) realises fluid communication between the pre-combustion chamber (3) and the spray passages (5), wherein the pre-chamber assembly (1) comprises at least one first component part (6) and at least one second component part (7) joined to the at least one first component part (6),wherein the at least one first component part (6) is manufactured with the use of at least one of the group consisting of primary shaping, forming and cutting, and wherein the at least one second component part (7) is manufactured with the use of an additive manufacturing method.

Description

Pre-chamber assembly for an internal combustion engine

The present invention concerns a pre-chamber assembly for an internal combustion engine according to the classifying portion of claim 1 and a method for manufacturing a pre-chamber assembly for an internal combustion engine.

Certain internal combustion engines of the prior art include pre-combustion chambers. For example gas engines for driving generators are favourably operated under lean burn conditions. The pre-combustion chamber allows for the ignition of a smaller volume of gas-air-mixture under less lean conditions. Through a riser passage and spray passages the ignited gas-air-mixture from the pre-combustion chamber is expelled as flame jets into a main combustion chamber of a cylinder effectively igniting the lean gas- air-mixture therein in order to ensure a stable ignition and burn inside the main combustion chamber.

The pre-chamber assembly experiences some of the highest thermal and mechanical loads of all components of an internal combustion engine. Even in current gas engines the lifetime of conventionally manufactured (i.e. not using additive manufacturing) pre chamber assemblies is negatively affected by said influences, leading to limited operating hours.

US 2016/0230646 A1 discloses a pre-chamber assembly with specially formed riser passage and spray passages in order to improve combustion efficiency. The possibility of manufacturing the pre-chamber assembly using an additive manufacturing method is also mentioned in this disclosure.

However, the relatively small amounts of gain in ignition and burn efficiency do in practice not warrant the large amounts of effort and expenditure of additively manufacturing a wear part like the pre-chamber assembly. In particular the relatively low expected lifetime of pre-chamber assemblies according to the prior art discourage a more involved manufacturing method for pre-chamber assemblies. The object of the invention is therefore to provide a pre-chamber assembly and a method for manufacturing a pre-chamber assembly, where the expected life time is increased.

Regarding the pre-chamber assembly this object is achieved with the characteristics of claim 1. Regarding the method for manufacturing a pre-chamber assembly this object is achieved with the characteristics of claim 14.

A central aspect of the invention is that that the pre-chamber assembly comprises at least one first component part and at least one second component part joined to the at least one first component part, wherein the at least one first component part is manufactured with the use of at least one of the group consisting of primary shaping, forming, and cutting, and wherein the at least one second component part is manufactured with the use of an additive manufacturing method.

While highly customized shaping and material choice (i.e. using materials with higher resistance to mechanical and thermal loading) is beneficial for some parts of the pre chamber assembly, the manufacturing of the whole pre-chamber assembly using an additive manufacturing method, as suggested by the prior art, would drive the effort and cost for the manufacturing very high to the point of impracticality. The invention allows for a balance between the manufacturing cost and finely tuned geometry, which is counter intuitive as usually the advantages of using a single manufacturing method easily outweigh the disadvantage of increasing the number of component parts. Initial testing of the applicant shows however, that pre-chamber assemblies according to the invention can reach life times of at least twice as long as in the prior state of the art with viable production cost and effort. The invention is expected to deliver life time increases of a factor of 3 or even 4.

Regarding the riser passage it is noted that the term“riser passage” does not imply a technical limitation on the orientation of the riser passage. While in many examples in reality the riser passage is aligned vertically within the internal combustion engine, it would in principle be no problem to have the riser passage aligned at an angle or even upside-down. The pre-chamber assembly includes a boundary wall of the pre-combustion chamber. This boundary wall can have a cylindrical base shape with a transition into the riser passage. There may be an additional part capping the pre-combustion chamber on the side facing away from the riser passage. What has been mentioned regarding the vertical (or non-vertical) alignment of the riser passage is analogously valid for the boundary wall, the pre-combustion chamber, and possibly the further part capping the pre-combustion chamber.

The spray passages preferably facing different directions, most preferably guide the flame jets from the pre-combustion in the pre-combustion chamber into a main combustion chamber of the internal combustion engine and therefore face different directions in order to distribute the flame jets inside the main combustion chambers to a certain extent.

According to the invention the first component part is manufactured using a manufacturing method including primary shaping, forming and/or cutting. Primary shaping, forming and cutting are to be understood to specify the manufacturing processes defined in DIN 8580, i.e. forming (German: Umformen) includes rolling, free forming, die forming, indentation forming, blasting techniques, deep drawing, hydroforming and the like. Cutting (German: Trennen) includes turning, drilling, milling, generally machining, grinding, honing and the like. Primary shaping (German: Urformen) includes different forms of casting, in particular (pressure) die casting, and certain pressing methods. However, primary shaping does not include additive manufacturing methods.

Additive manufacturing methods involve “directly” building up a work piece from a multitude of small - small in comparison with the final work piece - amounts of the material from which the work piece is produced. Additive manufacturing methods generally are“generative” in the sense that the work piece grows, e.g. in layers or other volume elements, into the finished work piece. A shaping tool, which is generally used in primary manufacturing methods, is not necessary.

The invention does not exclude the use of other than additive manufacturing techniques for the at least one second component part for additional working steps after additively manufacturing a work piece (e.g. coating or additional machining). Additionally, before (e.g. on the materials or base) or during the additive manufacturing process other than additive manufacturing methods can be used.

Protection is also sought for an internal combustion engine comprising a pre-chamber assembly according to the invention. The internal combustion engine can be a gas engine for driving a generator (genset) and also mechanical components (pumps or compressors). The combustion engine can also be used as a combined heat and power plant. In particular it can be a stationary piston-cylinder engine with any number of cylinders.

The riser passage as well as the spray passages can have (circular) cylindrical base shapes. In particular the spray passages, but also the riser passage, can have non circular, in particular elliptic, bases. Also cylindrical base shapes with polygonal bases for the cylinder are in principle possible.

Further preferable embodiments of the invention are defined in the dependent claims.

It can be provided that the at least one second component part forms at least one of - preferably all of - the spray passages and at least part of the riser passage, and wherein the at least one first component part forms at least another part of the riser passage and at least a part of the boundary wall of the pre-combustion chamber. Put differently, the at least one second component part can form the “tip” of the pre chamber assembly which is subject to the highest thermal and mechanical loads.

The at least one first component part and the at least one second component part can be joined together by at least one of the group consisting of an interference fit, a welded connection, a brazed connection, a positive lock, a threaded connection, and an axial mechanical load. In many cases an interference fit (may also be called press fit) can achieve the best balance between production effort, security against disjoining and longevity. Security against disjoining of the at least one first part and the at least one second part can be a very important factor, as a disjoining during operation most probably leads to catastrophic engine failure.

Other considerations in connection with the joint between the at least one first component part and the at least one second component part concern the matching of the materials for the at least one first component part and the at least one second component part and the location of the joint. Generally, the peak temperature gradient during operation at the location of the joint drives thermally induced stress which should not exceed a certain value which is dependent on the materials. Therefore, the choice of material and the choice of the type of joint used is interdependent. Similar considerations apply for mechanical stresses during operation.

An easy way to realize the interference fit can be provided in that the at least one first component part comprises a cylindrical recess and the at least one second component part comprises a cylindrical portion, wherein the interference fit is created by inserting the cylindrical portion into the cylindrical recess. Of course, it would also be possible to have the cylindrical portion on the at least one first component part. However, having the cylindrical portion on the at least one second component part can help to keep the amount of material manufactured additively as low as possible.

The term“cylindrical” does not necessarily refer to a right circular cylinder, although this is the primary embodiment. The base of the cylinder can also have other shapes than circular, i.e. elliptic or polygonal.

The insertion of the cylindrical portion into the cylindrical recess can be performed in different ways and the sizing of the cylindrical portion and the cylindrical recess can determine the firmness of the joint. E.g. a press can be used to introduce the cylindrical portion into the cylindrical recess and/or the cylindrical portion could be cooled to a low temperature prior to insertion.

A central axis of the cylindrical portion and/or the cylindrical recess can be parallel - and preferably can coincide with - a central axis of the riser passage. A positive substance joint between the at least one first part and the at least one second part can be formed by additively manufacturing the at least one second component part directly onto the at least one first component part.

The at least one first component part and the at least one second component part can be releasably joined together. Since the at least one second part will usually be the one under higher thermal and mechanical loading, it may be favourable to make an exchange of the at least one second part possible while keeping the same at least one first part.

In a preferred embodiment the additive manufacturing method can comprise a repetition of the steps of applying a powder - preferably a metal powder - and heating - preferably melting - at least part of the applied powder. A laser can be used in order to heat and/or melt the powder.

According to a preferred embodiment transitions between the riser passage and the spray passages can be rounded. This can be achieved using an additive manufacturing method. Because of the geometry of the pre-chamber assembly rounded transitions between the spray passages and the riser passage are in practice not possible when using only conventional manufacturing techniques. In pre-chamber assemblies in use up until now there were therefore ridges present which resulted in cracks in the areas of these transitions due to concentration of mechanical and thermal stresses over a long time (thermal and mechanical fatigue cracking). Avoiding these cracks through smooth geometry while keeping the cost and effort for production down can be one of the main advantages of the invention.

The riser passage can comprise a - preferably rotationally symmetric - circumferential indentation, which can preferably be located adjacent to transitions between the spray passages and the riser passage and/or adjacent to a terminus of the riser passage facing away from the pre-combustion chamber. Thermal and mechanical stress peaks near the transitions between the riser passage and the spray passages or near the terminus of the riser passage can be effectively mitigated which can be used to reach even longer life times. According to an embodiment of the invention there can be at least two second component parts manufactured with the use of the additive manufacturing method. Additional geometric details on the pre-chamber assembly can in this way be realised at viable cost and effort for manufacturing the same.

An example would be a coolant cavity or several coolant cavities for cooling the at least one second component part, preferably manufactured with the use of additive manufacturing. As is obvious, a cooling of the pre-chamber assembly could further reduce the thermal load on the pre-chamber assembly promoting a longer life time.

A further advantage of the cavities is, that the material is thinned out at certain areas. This leads to even better removal of heat and saves material and therefore costs.

For a pre-chamber assembly according to the invention it can be provided, that between the at least one first component part and the at least one second component part manufactured with the use of the additive manufacturing method at least one sealing is mounted.

The pre-chamber assembly can comprise a spark-plug liner, which is preferably separate from the at least one first component part and/or the at least one second component part. The spark plug liner can be the separate additional component to cap the pre-combustion chamber. The spark plug liner - or generally speaking - the separate additional component can have orifices to allow access to the pre-combustion chamber for the spark plug or other devices for promoting ignition of the fuel or for supplying fuel or (compressed) air.

Nickel based alloys can be used both for the first component part and the second component part.

The method for manufacturing a pre-chamber assembly for an internal combustion engine according to the invention comprises the following steps:

- at least one first component part is manufactured using at least one of the group consisting of primary shaping, forming, and cutting; - at least one second component part is manufactured using an additive manufacturing method; and

- the at least one first component part and the at least one second component part are joined together.

It can be provided, that the additive manufacturing method comprises a repetition of the steps of applying a powder - preferably a metal powder - and heating - preferably melting - at least part of the applied powder.

Preferably, the additive manufacturing method comprises heating and/or melting of the powder using a laser.

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 a to 1 c show a cross-section view, a bottom view and side view of a pre chamber assembly according to the invention,

Fig. 2 shows a cross section through the second component part,

Fig. 3a to 3c shows further embodiments of pre-chamber assemblies according to the invention, and

Fig. 4 an internal combustion engine according to the invention.

Figs. 1 a to 1 c show a pre-chamber assembly 1 according to the invention comprising a pre-combustion chamber 3 limited by a boundary wall 2, a riser passage 4 and spray passages 5. Not all spray passages 5 are visible easily as some face directly into or out of the plane of drawing. For this reason not all spray passages 5 are furnished with a reference numeral.

Fig. 1 a is the cross section through the A-A plane in Fig. 1 b (bottom view). Fig. 1 c is the side view.

The transition between the pre-combustion chamber 3 and the riser passage 4 is smooth. The pre-chamber assembly of Fig. 1 comprises furthermore a first component part 6 and a second component part 7. The first component part 6 incorporates the pre combustion chamber 3 and part of the riser passage 4. The second component part 7 incorporates the rest of the riser passage 4 and the spray passages 5.

The second component part 7 is manufactured from a material with a higher resistance to thermal and/or mechanical loading as the first component part 6.

The first component part 6 and the second component part 7 are joined via a interference fit 8 between surfaces of a (circular) cylindrical portion of the second component part 7 and a cylindrical recess of the first component part 6. The interference fit 8 is symbolized with two dashed lines. Both the cylindrical portion and the cylindrical recess share a coinciding central axis X with the riser passage 4 - and in this embodiment also the pre-combustion chamber 3.

Unlike the conventionally/traditionally manufactured first component part 6 the second component part 7 is manufactured using an additive manufacturing method, namely Direct Metal Laser Melting (DMLM).

Using an additive manufacturing method allows for sophisticated geometry for which also Fig. 2 is referenced, where the second component part 7 is shown in more detail.

The spray passages 5 have round transitions into the riser passage 4. Additionally, the spray passages 5 are themselves preferably not circular cylindrical, but have an elliptic cross section.

Furthermore, a circumferential indentation 9, which could also be called an undercut, is present in the riser passage 4 adjacent to the transitions to the spray passages 5 and the terminus 11 of the riser passage 4. The circumferential indentation 9 helps to compensate peaks in mechanical stress in the area shown in Fig. 2 which result from the impact of ignited fuel-air-mixture on the terminus 11 and on the transitions to the spray passages 5. Figures 3a to 3c show further embodiments of the invention. Both Fig. 3a and 3b show embodiments where the second component part is additively manufactured directly onto the first component part, which was manufactured using conventional manufacturing methods. An internal surface for an interference fit is therefore not necessary in these embodiments. Flowever, the remaining internal structure is similar to the one shown in Figures 1 and 2.

The difference between the embodiments of Fig. 3a and 3b is the position of the joint between the first component part 6 and the second component part 7. That is, in Fig. 3a the second component part 7 is smaller and consequently the transition sits lower. The advantage of this is the reduced effort and cost required to manufacture the second component part 7. Flowever, if the temperature during operation of the internal combustion engine and consequently the temperature gradient at the location of the joint of the first component part 6 and the second component part 7 is too high, there might be a risk of failure of the joint. In other words, the temperature gradient across the joint might be too high for reliable operation. Then an embodiment according to Fig. 3b or similar can be chosen or a cooling of the pre-chamber assembly 1 can be taken into consideration.

The embodiment of Fig. 3c comprises a gasket 18 in between the traditionally manufactured first component part 6 and the second component part 7, which provides at least one sealing between coolant and internal volume of the pre-chamber. For this design an additional axial mechanical load is needed to supply the required pressure onto the sealing. Said axial mechanical load is typically being realized through spark plug sleeve bolts, resulting from the required clamp load.

In this embodiment it can be provided, that the first component part 6 and the second component part 7 are not joined in an aforementioned way (interference fit, etc.), but rather only via the additional axial mechanical load.

Fig. 4 shows an abstracted schematic drawing of an internal combustion engine with a pre-chamber assembly 1 according to the invention in the vicinity of one cylinder. Fig. 4 includes a cylinder head 12, a piston 13, a cylinder liner 14, a spark plug 15, a spark plug sleeve 16, and valves 17. List of reference numbers: 1 pre-chamber assembly

2 boundary wall

3 pre-combustion chamber

4 riser passage

5 spray passage

6 first component part

7 second component part

8 interference fit

9 circumferential indentation

11 terminus

12 cylinder head

13 piston

14 cylinder liner

15 spark plug

16 spark plug sleeve

17 valves

18 gasket

X central axis

Claims

1. Pre-chamber assembly for an internal combustion engine comprising

- a boundary wall (2) of a pre-combustion chamber (3),

- a riser passage (4), and

- spray passages (5),

wherein the riser passage (4) realises fluid communication between the pre combustion chamber (3) and the spray passages (5), characterized in that the pre-chamber assembly (1 ) comprises at least one first component part (6) and at least one second component part (7) joined to the at least one first component part (6), wherein the at least one first component part (6) is manufactured with the use of at least one of the group consisting of primary shaping, forming and cutting, and wherein the at least one second component part (7) is manufactured with the use of an additive manufacturing method.

2. Pre-chamber assembly according to claim 1 , wherein the at least one second component part forms (7) at least one of - preferably all of - the spray passages (5) and at least part of the riser passage (4), and wherein the at least one first component part (6) forms at least another part of the riser passage (4) and at least a part of the boundary wall (2) of the pre-combustion chamber (3).

3. Pre-chamber assembly according to one of the preceding claims, wherein the at least one first component part (6) and the at least one second component part (7) are joined together by at least one of the group consisting of an interference fit (8), a welded connection, a brazed connection, a positive lock, a threaded connection, and an axial mechanical load.

4. Pre-chamber assembly according to claim 3, wherein the at least one first component part (6) comprises a cylindrical recess and the at least one second component part (7) comprises a cylindrical portion, wherein the interference fit (8) is created by inserting the cylindrical portion into the cylindrical recess.

5. Pre-chamber assembly according to claim 4, wherein a central axis (X) of the cylindrical portion and/or the cylindrical recess is parallel - and preferably coincides with - a central axis (X) of the riser passage (4).

6. Pre-chamber assembly according to one of the preceding claims, wherein the at least one second component part (7) is additively manufactured directly onto the at least one first component part (6).

7. Pre-chamber assembly according to one of the preceding claims, wherein the at least one first component part (6) and the at least one second component part (7) are releasably joined together.

8. Pre-chamber assembly according to one of the preceding claims, wherein transitions between the riser passage (4) and the spray passages (5) are rounded.

9. Pre-chamber assembly according to one of the preceding claims, wherein the riser passage (4) comprises a - preferably rotationally symmetric - circumferential indentation (9).

10. Pre-chamber assembly according to claim 9, wherein the circumferential indentation is located adjacent to transitions between the spray passages (5) and the riser passage (4) and/or adjacent to a terminus (11 ) of the riser passage (4) facing away from the pre-combustion chamber (3).

11. Pre-chamber assembly according to one of the preceding claims, wherein at least one sealing is mounted between the at least one first component part (6) and the at least one second component part (7) .

12. Pre-chamber assembly according to one of the preceding claims, wherein the at least one second component part (7) comprises a coolant cavity or several coolant cavities, preferably manufactured with the use of additive manufacturing.

13. Internal combustion engine comprising a pre-chamber assembly according to one of the preceding claims.

14. Method for manufacturing a pre-chamber assembly (1 ) for an internal combustion engine, in particular according to one of the claims 1 to 13, wherein

- at least one first component part (6) is manufactured using at least one of the group consisting of primary shaping, forming, and cutting;

- at least one second component part (7) is manufactured using an additive manufacturing method; and

the at least one first component part (6) and the at least one second component part (7) are joined together.

15. Method according to claim 14, wherein the additive manufacturing method comprises a repetition of the steps of applying a powder - preferably a metal powder - and heating - preferably melting - at least part of the applied powder.

16. Method according to claim 14 or 15, wherein the additive manufacturing method comprises heating and/or melting of the powder using a laser.