WO2018087418A1

WO2018087418A1 - Prechamber component and method of manufacturing same

Info

Publication number: WO2018087418A1
Application number: PCT/FI2016/050799
Authority: WO
Inventors: Mikko Turunen; Jyrki SUUTALA
Original assignee: Wärtsilä Finland Oy
Priority date: 2016-11-14
Filing date: 2016-11-14
Publication date: 2018-05-17

Abstract

The prechamber component (7) for a piston engine com- prises a body (7a) made of a first material and a thermal conduction portion (7b), which is an integral part of the prechamber component (7) and which is made of a second material having higher thermal conductivity than the first material.

Description

Prechamber component and method of manufacturing same

Technical field of the invention

The present invention relates to a prechamber component for a piston engine in accordance with the preamble of claim 1 . The invention also concerns a method of manufacturing a prechamber component for a piston engine as defined in the preamble of the other independent claim.

Background of the invention

Internal combustion engines can be provided with prechambers, also called as precombustion chambers. In prechamber engines, each cylinder is provided with a prechamber, and part or all of the fuel is introduced into the prechamber. Depending on the engine, the fuel can be self-ignited, or a spark plug or some other device can be used for igniting the fuel. The combustion thus starts in the prechamber, but main part of the combustion takes place in a main combustion chamber outside the prechamber. The prechamber construction is beneficial especially in lean burn engines, where part of the fuel is introduced into the prechamber and part of the fuel is mixed with the air before the intake valves. This kind of arrangement can be used, for instance, in spark ignited gas engines. The gas-air mixture in the prechamber is rich compared to the mixture in the cylinder. The rich mixture in the prechamber is ignited by a spark plug and the flames from the prechamber ignite the mixture in the cylinder.

A disadvantage of prechamber engines is the high temperature in the prechamber, which causes, for instance, high temperature corrosion (also called hot corrosion). Especially in gas engines, the prechamber is subject to extreme high-pressure gradients and maximum pressures. This sets very high standards for the materials and construction of the prechamber. The problems related to high thermal loads have been addressed for example by providing prechambers with different inserts or sleeves made of materials with good thermal conductivity. However, due to reduced strength and stiffness, such arrange- ments often lead to reduced reliability. Summary of the invention

An object of the present invention is to provide an improved prechamber component for a piston engine. The characterizing features of the prechamber component according to the invention are given in the characterizing part of claim 1 . Another object of the invention is to provide an improved method for manufacturing a prechamber component for a piston engine. The characterizing features of the method are given in the characterizing part of the other independent claim.

The prechamber component according to the invention comprises a body made of a first material and a thermal conduction portion, which is an integral part of the prechamber component and which is made of a second material having higher thermal conductivity than the first material.

The method of manufacturing a prechamber component for a piston engine comprises a step of forming a body of the component using a first material and a step of forming a thermal conduction portion that is an integral part of the prechamber component using a second material having higher thermal conductivity than the first material.

The prechamber component according to the invention effectively transfers heat away from the component and also distributes the heat more evenly in the component. Thermal stresses and corrosion of the component are thus decreased and the component lifetime is increased. Compared to a prechamber component that is provided with a separate thermally conductive sleeve or insert, greater strength and stiffness and therefore also longer lifetime can be achieved with a component having an integral thermal conduction portion. According to an embodiment of the invention, the thermal conduction portion forms a cylindrical portion encircling the body. A thermal conduction portion surrounding the body can effectively conduct heat to an adjacent component.

According to another embodiment of the invention, the thermal conduction portion forms a core encircled by the body. A core arranged inside the body re- duces effectively temperature differences in the component.

According to an embodiment of the invention, the prechamber component comprises a plurality of thermal conduction portions forming cores encircled by the body. By providing the component with several thermal conduction portions, the strength of the body can be increased while ensuring effective heat transfer within the component.

The thermal conduction portion can comprise, for instance, aluminum bronze, copper, brass or nickel.

According to an embodiment of the invention, the body is made of a nickel-, nickel-chromium- or cobalt-based alloy. Such alloys have good resistance to high-temperature corrosion.

According to an embodiment of the invention, the thermal conduction portion extends to an outer surface of the prechamber component. The thermal conduction portion can thus be brought into contact with an adjacent component for effectively conducting heat away from the prechamber component.

According to an embodiment of the invention, the component forms a nozzle part for a prechamber. The portion comprising the nozzles of a prechamber is directly exposed to the heat in a combustion chamber and cooling of the nozzle portion is difficult to arrange. Effective heat transfer is thus needed especially in the nozzle portion.

According to an embodiment of the invention, the body is formed in a first step, and the thermal conduction portion is formed in a second step following the first step. Alternatively, the body and the thermal conduction portion are formed in two steps that are at least partly overlapping.

According to an embodiment of the invention, the thermal conduction portion is formed using additive manufacturing. For example cold metal transfer or laser sintering can be used for forming the thermal conduction portion. With additive manufacturing, complex shapes can be manufactured. Also the body can be made using additive manufacturing.

Brief description of the drawings

Embodiments of the invention are described below in more detail with refer- ence to the accompanying drawings, in which Fig. 1 shows a cylinder head and a prechamber arrangement of a piston engine,

Fig. 2 shows a cross-sectional view of a nozzle part of a prechamber according to a first embodiment of the invention, Fig. 3 shows a cross-sectional view of a nozzle part of a prechamber according to a second embodiment of the invention,

Fig. 4 shows a cross-sectional view of a nozzle part of a prechamber according to a third embodiment of the invention,

Fig. 5 shows a cross-sectional view of a nozzle part of a prechamber according to a fourth embodiment of the invention, and

Fig. 6 shows a cross-sectional view of the nozzle part of figure 4 taken along line A-A.

Description of embodiments of the invention In figure 1 is shown a cylinder head 1 and a prechamber arrangement of a piston engine. The engine is a large internal combustion engine, such as a main or an auxiliary engine of a ship or an engine that is used at a power plant for producing electricity. The cylinder diameter of the engine is at least 150 mm. The engine is provided with a number of cylinders, and each cylinder of the engine is provided with a prechamber arrangement. Each cylinder of the engine is provided with a cylinder head 1 , which closes the upper end of the cylinder. The term "upper" refers here to that end of the cylinder, which is farther from the crankshaft. The cylinders do not need to be arranged vertically, but they can be in some other angle in relation to the base of the engine. A main combustion chamber 2 is formed inside the cylinder between the cylinder head 1 and the piston. In the example of figure 1 , the engine is a spark ignition gas engine, where part of the gaseous fuel is introduced into the intake duct to form a lean air/fuel mixture, and part of the fuel is introduced into a prechamber 3 to form a rich mixture, which is ignited by a spark plug. The leaner mix- ture in the main combustion chamber 2 is ignited by the combustion of the richer mixture formed in the prechamber 3. Each cylinder of the engine is provided with a prechamber 3 having a first end 3a, i.e. an upper end, and a second end 3b, i.e. a lower end. The first end 3a is thus located farther from the cylinder and the main combustion chamber 2 than the second end 3b. In the example of figure 1 , the prechamber 3 is almost spherical, but the prechamber 3 can alternatively have a different shape, such as an ellipsoidal shape. The cylinder head 1 is provided with a space 5 for accommodating the prechamber 3.

The prechamber arrangement comprises a body part 6 and a nozzle part 7. The body part 6 and the nozzle part 7 are separate parts. The body part 6 de- limits a major part of the prechamber 3, including the first end 3a of the prechamber 3. The upper part of the prechamber 3 is thus defined by the body part 6. The body part 6 defines at least the upper half of the prechamber 6. The nozzle part 7 delimits the second end 3b of the prechamber 3, and the lower part of the prechamber 3 is thus defined by the nozzle part 7. Together the body part 6 and the nozzle part 7 define the whole prechamber 3. The prechamber 3 could also be defined solely by the body part 6.

The nozzle part 7 protrudes into the body part 6 and extends from the body part 6 towards the combustion chamber 2. The portion of the nozzle part 7 inside the body part 6 is conical, tapering slightly towards the main combustion chamber 2. The cylinder head 1 is provided with an opening 8, through which the nozzle part 7 protrudes into the combustion chamber 2. The opening 8 of the cylinder head 1 is slightly conical, corresponding thus to the form of the nozzle part 7. The nozzle part 7 is introduced into the opening 8 from above. The diameter of the nozzle part 7 is slightly smaller than the diameter of the opening 8. The diameters are selected so that when the cylinder head 1 and the nozzle part 7 are at the ambient temperature, i.e. when the engine is not running, there is a clearance, i.e. a small gap, between the nozzle part 7 and the cylinder head 1 . When the engine is running, the temperature of the cylinder head 1 rises less than the temperature of the nozzle part 7 due to the more effective cooling of the cylinder head 1 . When the cylinder head 1 and the nozzle part 7 are at the operating temperature, the nozzle part 7 is in contact with the cylinder head 1 . There may be even a shrink fit between the nozzle part 7 and the cylinder head 1 at the operating temperature. The nozzle part 7 is attached to the body part 6 with a shrink fit. The nozzle part 7 is provided with a conduit 9, through which gases are discharged from the prechamber 3 into the combustion chamber 2. The conduit 9 is divided into several branches 9a, which end to nozzle holes 10 opening onto the outer surface of the nozzle part 7 in the combustion chamber 2. The nozzle part 7 is thus configured to establish fluid communication between the prechamber 3 and the main combustion chamber 2. Instead of a branching conduit 9, the nozzle part 7 could be pro- vided with several conduits, each of which is connected to a nozzle hole. Instead of several nozzle holes 10, the nozzle part 7 could be provided with a circular slot, to which one or more conduits are connected and through which the fluids are discharged into the combustion chamber 2.

The nozzle part 7 protrudes into the combustion chamber 2 and is exposed to high thermal loads. A cooling jacket is formed in a space 1 1 between the body part 6 and the cylinder head 1 . Cooling water can be introduced into the cooling jacket through an inlet conduit 12 and discharged from the cooling jacket through an outlet conduit 13. Because of the more effective cooling that has been arranged for the upper part of the prechamber 3, the body part 6 is not exposed to as high thermal loads as the nozzle part 7. Less strict requirements are thus set for the material of the body part 6 than for the material of the nozzle part 7. The body part 6 of the prechamber arrangement can thus be made of, for instance, steel.

Due to the location of the nozzle part 7, effective cooling of the nozzle part 7 is difficult to arrange. For keeping the temperature of the nozzle part 7 within an acceptable range, a nozzle part 7 according to the invention is provided. Different embodiments of the invention are shown in figures 2 to 6. The nozzle part 7 according to the invention comprises a body 7a made of a first material and a thermal conduction portion 7b made of a second material, which has higher thermal conductivity than the first material. The second material has thus a higher coefficient of thermal conductivity than the first material. The thermal conduction portion 7b is an integral part of the nozzle part 7. As the first material is preferably used a material with a good high-temperature corrosion resistance, such as a nickel-, nickel-chromium- or cobalt-based alloy. The second material can be, for instance, aluminum bronze, copper, brass or nickel. Because of the thermal conduction portion 7b, heat is effectively transferred from the nozzle part 7 to other parts of the engine, such as the body part 6 of the prechamber 3 and the cylinder head 1 . The thermal conduction portion 7b also distributes heat in the nozzle part 7 more evenly, which decreases thermal stresses and corrosion. The lifetime of the component is thus increased. The body part 7a and the thermal conduction portion 7b form an integrated struc- ture. The nozzle part 7 is thus formed as a one-piece part 7. Compared to pre- chamber components that are provided with separate thermally conductive sleeves or inserts, the nozzle part 7 according to the invention has greater strength and stiffness, which ensures reliable operation. The thermal conduc- tion portion 7b can be configured such that when the nozzle part 7 is assembled in a cylinder head 1 , the thermal conduction portion 7b is in contact with an adjacent component of the engine for effectively transferring heat away from the nozzle part 7. In the configuration of figure 1 , the thermal conduction portion 7b could thus be formed so that it is in contact with the cylinder head 1 and/or the body part 6 of the prechamber arrangement.

In the embodiments of figures 2 to 4, the thermal conduction portion 7b forms a core, which is arranged within the piece formed by the first material. The thermal conduction portion 7b is thus encircled by the body 7a. On one side of the nozzle part 7, the thermal conduction portion 7b extends to an outer surface of the nozzle part 7. In the embodiment of figure 2, the thermal conduction portion 7b forms a continuous core having a shape of a cylinder with a closed lower end. The thermal conduction portion 7b extends below the conduit 9. Heat is thus effectively conducted away from the area of the nozzle holes 10. At the upper end of the nozzle part 7, the thermal conduction portion 7b extends to the upper surface of the nozzle part 7, which forms the second end 3b of the prechamber 3. However, the thermal conduction portion 7b could also be completely encircled by the body 7a. In the embodiment of figure 2, the thermal conduction portion 7b has a large contact surface with the body 7a and heat is thus evenly distributed in the nozzle part 7. In the embodiment of figure 3, the shape of the thermal conduction portion 7b is similar to the shape in the embodiment of figure 2. However, the upper end of the thermal conduction portion 7b does not extend to the upper surface of the nozzle part 7. Instead, the thermal conduction portion 7b is shaped so that it extends to the outer surface of the nozzle part 7 in an area that is brought in- to contact with the body part 6 of the prechamber 3. The thermal conduction portion 7b of the nozzle part 7 thus contacts the body part 6 of the prechamber arrangement and heat is effectively conducted from the nozzle part 7 to the body part 6.

In the embodiment of figure 4, which is shown from a different direction in fig- ure 6, the nozzle part 7 is provided with several thermal conduction portions 7b. The thermal conduction portions 7b are cores, which are elongated in the direction that extends from the prechamber 3 towards the nozzle holes 10 of the nozzle part 7. In the embodiment of figures 4 and 6, the nozzle part 7 comprises four thermal conduction portions 7b, but the number of thermal conduc- tion portions 7b could also be different. Also in this embodiment, the thermal conduction portions 7b extend to the upper surface of the nozzle part 7. However, the thermal conduction portions 7b could also be completely encircled by the body 7a. By providing the nozzle part 7 with a plurality of thermal conduction portions 7b, uniform heat distribution and effective heat conduction can be achieved, while also the strength of the nozzle part 7 can be optimized. The thermal conduction portions 7b could also extend to the cylindrical outer surface of the nozzle part 7 in a similar way as in the embodiment of figure 3 for improving heat transfer to adjacent components.

In the embodiment of figure 5, the thermal conduction portion 7b is formed on an outer surface of the body 7a of the nozzle part 7. The thermal conduction portion 7b is a cylindrical portion encircling the body 7a. The thermal conduction portion 7b forms a sleeve-like portion, which is, however, an integral part of the nozzle part 7. Compared to a thermally conductive sleeve that is attached to a prechamber component with a shrink fit, with the integrated ther- mal conduction portion greater strength and stiffness can be achieved. In addition, heat transfer to the thermal conduction portion 7b is more effective due to the complete contact between the body 7a and the thermal conduction portion 7b. In the embodiment of figure 5, the thermal conduction portion 7b surrounds the conduit 9 of the nozzle part 7. The thickness of the thermal conduction por- tion 7b is 50-80 % of the wall thickness of the nozzle part 7. Also in the embodiment of figure 5, the thermal conduction portion 7b is located such that it is in contact with one or more adjacent components of the engine, such as the cylinder head 1 and/or the body part 6 of the prechamber. Heat is thus effectively conducted away from the nozzle part 7. The nozzle parts 7 of figures 2 to 4 can be manufactured by additive manufacturing, for instance by 3D laser sintering or cold metal transfer. Both the body 7a and the thermal conduction portion 7b are made by additive manufacturing with a process where steps of forming the body 7a and the thermal conduction portion 7b alternate or take place simultaneously. The material used for the thermal conduction portion 7b can be, for example, aluminum bronze, copper, brass or nickel. The material used for the body 7a has preferably good high- temperature corrosion resistance. The material can be, for instance, a nickel- or nickel-chromium-based alloy comprising at least 40 % nickel. In addition, the material can comprise 10-25 % chromium. Nickel-based alloys preferably contain up to 5 weight percent of gamma and gamma prime forming elements, such as aluminum, titanium and/or niobium. Examples of suitable materials for the body 7a are Nimonic 80A or Inconel 718. Also cobalt-based alloys could be used for manufacturing the body 7a. A cobalt-based alloy can contain, for instance, 12-30 weight percent of chromium, 10-22 weight percent of nickel and 1 -10 weight percent of tungsten, iron and/or molybdenum. Also the nozzle part 7 of the embodiment of figure 5 can be manufactured by additive manufacturing. Alternatively, additive manufacturing and other methods can be combined. The body 7a of the nozzle part 7 can be manufactured in a first step by a conventional manufacturing process. The thermal conduction portion 7b can be added to the nozzle part 7 in a second step following the manufacturing of the body 7a. In the second step, cold metal transfer process could be used. The whole nozzle part 7 could be manufactured using additive manufacturing, such as laser sintering in a similar way as in the embodiments of figures 2 to 4. The material used for the thermal conduction portion 7b can be, for instance, aluminum bronze or nickel. The material of the body 7a can be, for instance, a nickel- or nickel-chromium-based alloy. The body 7a could also be made of steel, if conventional manufacturing methods are used for making the body 7a.

Additive manufacturing allows making of complex shapes. Also many other shapes of the thermal conduction portions 7b than those shown in the figures are thus possible. In the design of the thermal conduction portions 7b, the cooling of the body part 6 of the prechamber can be taken into account for optimizing heat transfer from the nozzle part 7 to the cooling water or other cooling medium or thermally conductive part. Instead of a unitary thermal conduction portion 7b, the nozzle part 7 can comprise several separate thermal conduc- tion portions 7b (as in the embodiment of figures 4 and 6) for optimizing the mechanical strength of the nozzle part 7.

It will be appreciated by a person skilled in the art that the invention is not limited to the embodiments described above, but may vary within the scope of the appended claims. For instance, the construction comprising a body and a thermal conduction portion could also be used in the body of the prechamber. The prechamber could also be formed of more than two components, and the construction could be used in any of the prechamber components. With additive manufacturing, the whole prechamber could be formed as one piece. The prechamber component could thus comprise both a prechamber and a nozzle portion connecting the prechamber to a main combustion chamber.

Claims

1 . A prechamber component (7) for a piston engine, the component (7) comprising a body (7a) made of a first material, characterized in that the component (7) comprises a thermal conduction portion (7b), which is an inte- gral part of the prechamber component (7) and which is made of a second material having higher thermal conductivity than the first material.

2. A prechamber component (7) according to claim 1 , wherein the thermal conduction portion (7b) forms a cylindrical portion encircling the body (7a).

3. A prechamber component (7) according to claim 1 , wherein the thermal conduction portion (7b) forms a core encircled by the body (7a).

4. A prechamber component (7) according to claim 3, wherein the prechamber component (7) comprises a plurality of thermal conduction portions (7b) forming cores encircled by the body (7a).

5. A prechamber component (7) according to any of the preceding claims, wherein the thermal conduction portion (7b) comprises aluminum bronze, copper, brass or nickel.

6. A prechamber component (7) according to any of the preceding claims, wherein the body (7a) is made of a nickel-, nickel-chromium- or cobalt-based alloy.

7. A prechamber component (7) according to any of the preceding claims, wherein the thermal conduction portion (7b) extends to an outer surface of the prechamber component (7).

8. A prechamber component (7) according to any of the preceding claims, wherein the prechamber component (7) forms a nozzle part for a prechamber (3).

9. A prechamber component (7) according to any of the preceding claims, wherein the thermal conduction portion (7b) is made by additive manufacturing, such as laser sintering or cold metal transfer.

10. A method of manufacturing a prechamber component (7) for a piston en- gine, the method comprising a step of forming a body (7a) of the component (7) using a first material, characterized in that the method comprises a step of forming a thermal conduction portion (7b) that is an integral part of the pre- chamber component (7) using a second material having higher thermal conductivity than the first material.

1 1 . A method according to claim 10, wherein the body (7a) is formed in a first step, and the thermal conduction portion (7b) is formed in a second step following the first step.

12. A method according to claim 10, wherein the body (7a) and the thermal conduction portion (7b) are formed in two steps that are at least partly overlap- ping.

13. A method according to any of claims 10 to 12, wherein the thermal conduction portion (7b) is formed using additive manufacturing.

14. A method according to any of claims 10 to 13, wherein the thermal conduction portion (7b) is formed using cold metal transfer.

15. A method according to any of claims 10 to 13, wherein the thermal conduction portion (7b) is formed using laser sintering.

16. A method according to any of claims 10 to 15, wherein the body (7a) is formed using additive manufacturing.

17. A method according to any of claims 10 to 16, wherein the body (7a) is made of a nickel-, nickel-chromium- or cobalt-based alloy.

18. A method according to any of claims 10 to 17, wherein the prechamber component (7) forms a nozzle part for a prechamber (3).