The design of combustion chambers and pistons for combustion engines has in one respect focused primarily on reducing the load on the actual cylinder and the piston with associated piston rings, oil rings and piston pins moving therein. This has often been done by using different cooling arrangements for effectively leading off heat from said parts and thereby lowering the working temperature in them. The purpose thereof is to reduce the actual temperature load on the parts and also to reduce problems arising due to the different degree of heat expansion of the different relatively moving, cooperating parts, i.e. primarily between piston/piston rings and cylinder bore.
In a partly different respect efforts have been made to configure combustion engine combustion chambers and pistons so that combustion work may without negative consequences be performed at very high temperatures. The purpose thereof has been to increase engine efficiency by reducing heat losses and to improve combustion and thereby lower the fuel consumption and to a certain degree obtain a reduction of pollutions. Such elevated temperatures could as a consequence of heat expansion phenomena cause damage to the actual pistons and to their piston rings, usually in the form of gas sealing rings and oil scraper rings. In efforts to avoid these problems it has e.g. been suggested, in such connections, to provide a divided piston configuration, with a heat insulation gap between a piston crown portion being exposed to the highest temperatures and a piston skirt supporting the piston rings. By means of the gap between the piston parts and special seals provided therein it is possible to eliminate or at least subdue the effect of different heat expansion between the piston crown portion and its skirt portion. Often, different materials are also used for these parts, so that e.g. the piston crown portion is made of steel and the piston skirt of an aluminum alloy.