The invention relates to a method of manufacturing a cylinder head of reciprocating engine. The invention also relates to a cylinder head of a reciprocating engine.

The trends to reduce fuel consumption and emissions in reciprocating engines have placed increased demands on the performance of many components. One way to reduce fuel consumption and emissions is to increase the engine com- pression ratio. However, this increase in cylinder pressure typically results in increased bending of the cylinder head and the motion between the mating surfaces of the cylinder head and cylinder block. Consequently, the cylinder pressure may escape from the cylinder combustion space to the engine cooling system where the pressure pulses can cause damage to the coolant pump and other components of the cooling system.

The object of the present invention is to improve the stiffness of the cylinder head. The object is achieved as is disclosed in the independent claims. In the method according to the invention, a member made of ceramic foam is inserted into a cylinder head mould, molten cylinder head base material is poured into the mould, the mould and pores of the member are filled with the molten cylinder head base material, and the molten cylinder head base material is solidified in the mould and in the pores of the member.

According to the invention, a member made of ceramic foam is arranged in the cylinder head. Pores of the member are filled with cylinder head base material. Significant benefits can be achieved by means of the invention. When the cylinder head base material solidifies in the pores of the member, an iron-ceramic composite structure is formed in the member, which increases the stiffness of the cylinder head. This, in turn, reduces the bending of the cylinder head and problems resulting from it. Further, the cylinder head according to the invention can be manufactured easily and cost-effectively.

In the following the invention is described in more detail, by way of an example, with reference to the accompanying drawings, in which

Fig. 1 shows an embodiment of the cylinder head according to the invention, viewed from the side of a fire plate. Fig. 2 shows the cylinder head of fig. 1 as a side view.

The drawings show a cylinder head 1 of a large reciprocating engine, which can be used as a main or auxiliary engine of a ship or in power plant for the production of heat and/or electricity. The engine is a medium speed, four-stroke en- gine. The rotational speed of the engine is 300-1200 rpm. The cylinder bore of the engine is typically 20-80 cm.

Each cylinder is provided with a separate cylinder head 1 . The cylinder head 1 comprises bores 2 for fastening screws, by means of which the cylinder head 1 can be fastened to the cylinder block of the engine. Additionally, the cylinder head 1 comprises at least one inlet port 3 for combustion air and at least one outlet port 4 for exhaust gas. In the embodiment shown in the drawings the cylinder head 1 is provided with two inlet ports 3 and two outlet ports 4. Each port has a valve seat 5 surrounding the port opening. The cylinder head 1 comprises a fire plate 6. The fire plate 6 is a region on the cylinder head, which delimits the combustion space of the cylinder. Base material of the cylinder head 1 is cast iron, typically ductile cast iron.

To improve the stiffness, a member 7 made of ceramic foam is arranged in the cylinder head 1 . The member 7 is made of open cell ceramic foam. The foam material can be any suitable ceramic carbide or oxide compound such as silicon carbide (SiC), alumina, zirconium oxide (ZrO), zirconium carbide (ZrC) or com- binations thereof. The member 7 comprises pores, which are filled with the cylinder head base material.

The member 7 is arranged at a fire plate region 6 of the cylinder head. A layer 8 of cylinder head base material is provided between the fire plate 6 surface and the member 7. The thickness of the layer 8 depends on the dimensions, especially the thickness, of the cylinder head. Typically the thickness of the layer 8 is at least 1 cm. The member 7 extends over the entire fire plate region 6 or only part of the fire plate region 6.

Open porosity of the member 7 is 0.3 - 0.7. Open porosity refers to the ratio of volume in which fluid flow is effectively taking place (this excludes dead-end pores or non-connected cavities) to the total volume of porous material. The size of the open pores is 1 mm to 10 mm.

The cylinder head 1 can be manufactured as follows. The member 7 made of ceramic foam is inserted into the cylinder head mould at a desired location. The member 7 can be supported to the walls of the mould. Mould cores are also inserted into the mould at desired locations. Prefabricated valve seat rings can be placed in the mould. When necessary, the mould can be preheated before casting. Thereafter, molten cylinder head base material is poured into the cylinder head mould. The mould and open pores of the member 7 are filled with the molten cylinder head material. The cylinder head base material solidifies in the mould and in the pores of the member 7. As a result, an iron-ceramic composite structure is formed in the member 7. The mould is removed from around the solidified cylinder head. Thereafter, mould cores are removed from the cylinder head in a conventional manner. Finally, the cylinder head is finished by machining.