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The German Aerospace Center (DLR) is developing a free-piston engine as an innovative internal combustion engine for the generation of electrical power. The arrangement of the Free Piston Linear Generator (FPLG) in opposed-piston design consists of two piston units oscillating freely, thereby alternately compressing the common combustion chamber in the center of the unit and gas springs on either side. Linear alternators convert the kinetic energy of the moving pistons into electric energy. Since the pistons are not mechanically coupled to a crank train, the bottom and top dead centers of the piston movement can be varied during operation e.g. to adjust the compression ratio. Utilizing these degrees of freedom, the present paper deals with the analysis of different combustion processes in a port scavenged opposed-piston combustion chamber prototype.

The proposed paper deals with the development process and initial measurement results of an opposed-piston combustion engine for application in a Free-Piston Linear Generator (FPLG). The FPLG, which is being developed at the German Aerospace Center (DLR), is an innovative internal combustion engine for a fuel based electrical power supply. With its arrangement, the pistons freely oscillate between the compression chamber of the combustion unit and a gas spring with no mechanical coupling like a crank shaft. Linear alternators convert the kinetic energy of the moving pistons into electric energy. The virtual development of the novel combustion system is divided into two stages: On the one hand, the combustion system including e.g. a cylinder liner, pistons, cooling and lubrication concepts has to be developed.

The present paper deals with the experimental investigation of homogeneous charge compression ignition in a free-oscillating two-stroke free-piston engine. The Free Piston Linear Generator (FPLG), which is being developed at the German Aerospace Center (DLR), is an innovative internal combustion engine for the generation of electrical power. This concept can for example be used in hybrid electric vehicles, as an auxiliary power unit or in combined heat and power units. The FPLG consists of three main components. In the two-stroke combustion unit, heat is released by burning a fuel-air mixture and a piston is accelerated. This energy is then converted into electric energy in the second component, the linear generator. This subsystem consists of electromagnetic coils as a stator and permanent magnets as a mover. The mover is rigidly coupled to the combustion piston.