Investigation of starting behaviour of a free-piston linear generator

A linear engine coupled to a permanent-magnet assembly becomes a linear generator engine (LG) which can produce electrical power. Its working principle is based on the free-piston two-stroke engine. The main difference between the LG and a conventional crank-slider engine is that the LG has only one moving part which is the piston-rod assembly (translator). The piston-rod assembly consists of two pistons and a rod, with one piston connected to each end of the rod and a magnet assembly at the center of the rod. Combustion energy will cause the piston-rod assembly to move freely back and forth between the two engine blocks. Magnetic field from the permanent magnet assembly will cut through conductor coils-which are externally located within the stationary part of the LG (stator iron)-to generate electricity. Thus, electrical power is generated directly from the moving piston. For starting of the generator, the LG is operated in a reverse process- as a motor, whereby current is injected into the coils to produce force to reciprocate the translator against the forces of compression of the engine blocks, in order to produce combustion. Experimental work described in this paper shows promising results on combustion pressure using an upgraded MOSFET inverter and gate driver. Previous work managed to produce only 9 bar of peak combustion pressure during starting, using 5 sets of standard automotive lead-acid batteries. With the upgraded system and further engine optimization, the LG managed to produce 12.7 bar of combustion pressure and a highest IMEP of 0.8 bar. This paper presents results of the newly installed drivers and optimization of the combustion process to achieve higher combustion pressure. © 2012 Asian Network for Scientific Information.