Technical field of the invention

The present invention relates to a Fe-based composition for use in a precham- ber component of a piston engine in accordance with the preamble of claim 1 . The invention also concerns a prechamber component and a method for manufacturing such a component, as defined in the preambles of the other independent claims.

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 the cylinder 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.

Good hot corrosion (high-temperature corrosion) resistance is needed from the materials of the prechamber. Similar properties are needed also in other engine components, such as exhaust valves and the turbine blades of turbo- chargers, and in many other applications, especially in machinery, where components are in contact with hot gases containing certain contaminants. In engines, the sodium content of the fuel together with the sulfur and vanadium contents are major factors contributing to hot corrosion.

Typically, the prechambers are made of a heat resistant steel or a superalloy. Examples of typical superalloys used for manufacturing prechamber components are FeCr- or Ni/Co-based superalloys. Despite of the use of the superalloys, hot corrosion is the limiting factor for the lifetime of the prechamber. Also, the materials conventionally used in the prechambers are relatively expensive. The lifetime of the prechamber is typically limited to 16 000 running hours, and in some cases the lifetime is much shorter. In addition, during the lifetime of the prechamber, the efficiency of the engine may be reduced, since the optimal geometry of the prechamber is not maintained due to wear.

One typical superalloy used for diesel engine pre-chamber is known from GB2275689, which discloses a diesel engine prechamber sleeve made of made of a heat-resistant iron-base alloy having a chemical composition comprising on the weight basis: Cr; 28 33 %; Ni: 26 32 %, Co: 2 10 %; Nb: 0.1 1 %, Mn: 0.1 1 .5%, Si: 0.1 1 .5 %,C: 0.02 0.5%, and N: 0.05 0.5%, and balance of iron.

Another Fe-based compound alloy is known from US6489043, which discloses iron-aluminide fuel injector component, that is manufactured from the material or is coated with the material. The iron-aluminide alloy can include 8 to 32 wt. % Al, up to 5 wt. % refractory metal, B and/or C in amounts sufficient to form borides and/or carbides.

Publication WO201 1 101541 discloses one known pre-chamber arrangement for a combustion engine, which comprises a separate body portion and nozzle portion, which are supported by one another and which together substantially define the pre-chamber, which is connected to a main combustion area of the cylinder through nozzle openings of the nozzle portion.

Summary of the invention

An object of the present invention is to provide an Fe-based composition for use in a prechamber component of a piston engine, the composition having a good resistance to hot corrosion and being relatively inexpensive to produce.

The characterizing features of the composition according to the invention are given in the characterizing part of claim 1 . Another object of the invention is to provide a prechamber component having a good hot corrosion resistance and a method for manufacturing such a component. The characterizing features of the prechamber component and the manufacturing method are given in the characterizing parts of the other independent claims. According to the invention, a Fe-based ferro-aluminide intermetallic alloy compound or composition for use in a prechamber component of a piston engine, comprises at least 55 percent by weight of iron, 10 to 40 percent by weight of aluminum, and at least one of the substances selected from the group of B, C, Cr, Zr, Nb, Ti; the total amount of each of the selected substances not more than 5 percent by weight (wt%).

The said Fe-based composition naturally comprises trace amounts of impurities.

According to the invention the prechamber component for a piston engine comprises the said Fe-based composition.

According to an embodiment of the invention the prechamber component is made of the said Fe-based composition.

According to an embodiment of the invention a prechamber component is coated with the said Fe-based composition. The coating is applied at least to the surfaces of chamber of the prechamber component. The coating can also be applied to the surfaces of the component that are subjected to hot corrosion or that are in in contact with fuel, air or combustion. In such case that the component is coated with Fe-based composition, the component itself can be made of some other material. The coating method utilized can be any method known by person skilled in the art. One further embodiment of this is to apply the coating by thermal spraying.

According to an embodiment of the invention, the prechamber component is a prechamber lower piece.

According to the invention, a method for manufacturing a prechamber compo- nent comprises a step of manufacturing a prechamber component or a component preform by a powder metallurgical process from the said Fe-based composition. The component preform relates to the characteristics of different powder metallurgical processes, where sintered components may require further working or finishing. According to an embodiment of the invention, a method for manufacturing a prechamber component or a component preform from the said Fe-based composition by a powder metallurgical process comprises a step of sintering. The sintering step can include any sintering methods known by a person skilled in the art.

According to further embodiment of the invention, the sintering step is performed by hot-isostatic-pressing (HIP) technique. Another embodiment of the invention for sintering is Spark Plasma sintering (= known as "Field Assisted Sintering Technique" FAST). Other sintering methods can also be utilized for sintering and/or for compacting the metal powder.

It is also possible that method for manufacturing comprises a step of thermal spraying. Thermal spraying can be used for coating the prechamber component or prechamber component preform.

When the prechamber component is prepared by powder metallurgical pro- cess, the metal powder of Fe-based composition can be prepared by atomizing technique (gas, liquid or other known techniques) or other powder producing technique known by a person skilled in the art.

After the providing the Fe-based composition powder, the powder is compacted and sintered with selected powder metallurgical process. The sintering yields a prechamber component, or a prechamber component preform that is machined/and or finished into the prechamber component.

The invention also includes a piston engine comprising a prechamber component for a piston engine, in which prechamber component comprises the said Fe-based composition. Furthermore, the invention also includes a marine vessel that comprises a prechamber component for a piston engine, where prechamber component comprises the said Fe-based composition.

The prechamber component comprised in a piston engine or in a marine vessel can further be made of or coated with the said Fe-based composition. One of the advantages of the Fe-based composition is that it provides a hot- corrosion resistant material for a prechamber component of a piston engine. The Fe-based composition is also more economic material for use in prechamber component. The prechamber component comprising the said Fe- based is more resistant to hot-corrosion than conventional materials and it provides longer service life. Furthermore, manufacturing the prechamber component through a powder metallurgical process provides the possibility to manufacture a near net shape preform, minimizing material-loss in machining stage.

The exemplary embodiments of the invention presented in this patent applica- tion are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in depending claims are mutually freely combinable unless otherwise explicitly stated. The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompa- nying drawings.

Brief description of the drawings

In the following, the invention and embodiments of the invention are described below by way of example with reference to the accompanying schematic drawings, in which:

Fig. 1 shows as a principle cross-section, an upper portion of a cylinder of the engine and a cylinder head and a prechamber component.

Fig. 2 shows a one example of prechamber component schematically. Description of embodiments of the invention

The illustration of Fig. 1 is only schematic; Fig. 1 shows a combustion engine 1 , which has a cylinder head 2 and at least one cylinder including a cylinder sleeve 6 and a main combustion area 7. The gas exchange of the cylinder is arranged, in a manner known per se, through the channels of the cylinder head 2 and the valves in connection with them.

As can be seen from Fig. 1 , in connection with the cylinder head 2, there is a separate pre-chamber arrangement, a prechamber component 4, connected to the cylinder. The pre-chamber 3 is connected through opening or openings 8 with the main combustion area 7 of the cylinder. The pre-chamber arrangement is arranged on the cylinder head so as to enable the operation of the prechamber and the cylinder.

The pre-chamber arrangement also comprises a pre-chamber top component 9 above the pre-chamber component 4. The pre-chamber top component 9 is secured tightly against pre-chamber component 4.

However, the shape and structure of the prechamber arrangement and prechamber component can vary from example presented in Fig. 1 and Fig. 2. The example of the prechamber component 4 is shown in Fig. 2.

The prechamber component comprises a Fe-based composition, ferro- aluminide intermetallic composition or compound for use in a prechamber component of a piston engine. The Fe-based composition comprises at least 55 percent by weight of iron, 10 to 40 percent by weight of aluminum, and at least one of the substances selected from the group of C, Cr, Zr, Nb, Ti; and the total amount of the substances selected from the group do not exceed 5 percent by weight. The said Fe-based composition naturally comprises trace amounts of impurities.

The prechamber component comprising the said Fe-based composition, can be made of the said Fe-based composition. Also, it is possible that the prechamber component is coated completely or partially with the said Fe-based composition. If the a prechamber component is coated with the said Fe-based composition, the coating is applied at least to the surfaces of chamber of the prechamber component. It is also possible that the coating can also be applied to the surfaces of the component that are subjected to hot corrosion or that are in in con- tact with fuel, air or combustion.

The prechamber component can be manufactured by a method that comprises a step of manufacturing a prechamber component or a component preform by a powder metallurgical process from the said Fe-based composition. In this relation, the component preform relates to the semifinished product because of characteristics of different powder metallurgical processes, where sintered components may require further working or finishing.

The prechamber component manufacturing method comprising a powder metallurgical process step can further comprise a step of sintering. The sintering step can be performed by methods known by a person skilled in the art. The sintering step can performed by hot-isostatic-pressing (HIP) technique. Another example for performing the sintering is Spark Plasma Sintering (= known as "Field Assisted Sintering Technique" FAST).

It is also possible that method for manufacturing comprises a step of thermal spraying. Thermal spraying can be used for coating the prechamber compo- nent or prechamber component preform.

Also, one example of the invention is that the prechamber component which comprises the said Fe-based composition is used in a piston engine.

Further example of the invention is that prechamber component of the present invention is used in a marine vessel. 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.

Reference numbers:

1 Combustion engine 2 Cylinder head

3 Prechamber

4 Prechamber component 6 Cylinder sleeve

7 Main combustion are

8 Prechamber opening

9 Prechamber top component