A free piston linear power generator (FPEG), which uses combustion to generate electricity directly, using no drive shaft, could provide an EV range extender that’s far smaller and more efficient than a legacy ICE. Several research groups, including a Toyota R&D team, are investigating this intriguing technology.
UK startup Libertine LPE has developed an FPEG design that it says overcomes a number of challenges having to do with motion control, emissions and power conversion efficiency.
“A free piston engine eliminates the entire mechanical drivetrain of a conventional engine, allowing ultra-efficient combustion cycles to be developed, and reducing the parts count and cost,” said Libertine CEO Sam Cockerill. “It completely removes the crankshaft constraint placed on piston movement that actually hinders efficient combustion, and allows piston motion to be optimized to deliver a cleaner, more efficient combustion process.”
The FPEG has a combustion chamber at one or both ends of the free piston, and a linear electrical generator to capture power from the piston during its movement cycle. However, in the absence of a crankshaft, multiple pistons must somehow be accurately positioned and synchronized. If each piston’s motion is not controlled precisely, the compression rate and ratio will vary, harming efficiency.
Libertine’s technology addresses this issue with a combination of piston geometry, electrical machine design and cylinder construction. All three are relatively long and smaller in diameter than those used in other designs. This reduces the moving mass of the piston relative to the electrical machine’s force, allowing more accurate control of the piston motion.
Libertine says its design is 90% smaller, 80% lighter and up to 30% more efficient compared to currently available systems. Its modular design can be scaled for applications from 1 kWe to over 100 kWe.
An institution backed by Malaysian oil giant Petronas has partnered with Libertine to fund a feasibility study.