Novel technology aims to enable free piston engine development

Libertine says its technology has the potential to transform the automotive range extender market, power generation, heating, cooling and transport sectors, and conducted its own research into its efficiency. According to Libertine's research, a 10kWe portable generator based on Libertine’s technology architecture, compared against the most efficient currently available systems for static power generation, shows a saving of 90% in package size, 80% in weight, significantly reduced cost and up to 30% higher efficiency.

In a free piston combustion engine, Libertine’s linear gas expander extracts power from the expansion stroke directly in the form of electrical energy. This technology architecture can be applied to many different combustion cycles, and its modular design can be readily scaled for applications from 1kWe to over 100kWe.

The key to Libertine’s success is a combination of piston geometry, electrical machine design and cylinder construction. All three are relatively long and smaller in diameter than those currently used by free piston developers. This architecture reduces the moving mass of the piston relative to the electrical machine’s force, giving more effective and accurate control of the piston motion. This geometry also reduces heat losses from the combustion chamber which, at top-dead-centre, has an improved surface-to-volume ratio. By integrating the electrical machine into the cylinder wall, rather than attempting to isolate it with seals, the high friction losses often encountered by free piston engine developers are dramatically reduced.

One of the first institutions to invest in the technology is the Universiti Teknologi Petronas (UTP) in Malaysia, which is supported by the PETRONAS oil and gas company. The university has entered a partnership with Libertine, funding a feasibility study that is expected to lead to the supply of free piston research engine hardware upon successful completion. A leading centre for free piston combustion research, UTP is primarily interested in the combustion process and requires a reliable, efficient linear power system as a platform for its work.

“The technology will help our partners create better, smaller generators that produce more power and waste less heat,” explained Libertine’s CEO, Sam Cockerill. “A free piston power module based on our technology could also produce electrical power for range extended electric vehicles and low cost hybrids. 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. It completely removes the crankshaft constraint placed on piston movement that actually hinders efficient combustion, and allows piston motion to be optimised to deliver a cleaner, more efficient combustion process.”

“UTP has an established programme of free piston engine research and development. Building Libertine’s linear power systems technology into our research engine is expected to improve piston motion control and allow us to accelerate our research into high efficiency combustion systems,” said Professor Abdul Rashid Abd Aziz, Deputy Vice Chancellor, Research and Innovation, Universiti Teknologi Petronas.