Libertine’s technology improves Free Piston cold-start performance with bioethanol


Libertine FPE, the creator of Smart Engine technology for hybrid electric vehicles and distributed power generation, has demonstrated developments that could help leading truck manufacturers to fulfil pledges to make all heavy-duty vehicles fossil free by 2040. Tests conducted late last year established Libertine’s innovative control platform could successfully vary a free piston engine’s compression ratio, leading to improved performance on cold start-up.

“This is an important result for Libertine that demonstrates the potential of variable compression ratio combustion control strategies made possible by Libertine’s intelliGEN Free Piston platform,” explained Libertine’s CEO Sam Cockerill. “Hybridisation with renewable fuels such as bioethanol could play an essential role in the rapid decarbonisation and electrification of transport, especially in heavy duty vehicle and off highway applications where battery technology and charging infrastructure could limit the pace of the transition to net zero.”

Libertine’s innovation is a linear electrical machine and control technology platform which addresses the challenge of free piston motion control, a challenge which has so far prevented the widespread adoption of Free Piston engine technology that could enable a revolution in sustainable fuel use in ‘hard to electrify’ heavy duty powertrain applications. With Libertine’s technology, hybrid heavy-duty powertrains using a combination of renewable grid power and renewable bioethanol fuel could offer OEMs a practical, cost effective solution to help achieve a vital transition to sustainable fuels and ‘net-zero’ (carbon neutrality).

The project has shown how a Free Piston engine can achieve an improvement in cold start performance using bioethanol, by briefly increasing the compression ratio at start-up, compensating for chamber wall cooling effects that contribute to misfiring under cold start conditions. The tests were conducted by MAHLE Powertrain at its Northampton test facilities using wet or ‘hydrous’ bioethanol fuel, a blend of 90% bioethanol and 10% water (E90W10).

For the tests, Libertine’s intelliGEN opposed free piston platform was modified for use with wet bioethanol, using a direct injection uniflow scavenged two stroke architecture. Over 100 tests were performed by MAHLE Powertrain in order to prove key performance metrics of the control platform, establish baseline combustion performance at a constant compression ratio and with a pre-heated combustion chamber, replicate cold start misfiring encountered in other studies, and finally to demonstrate improved cold start performance by using a variable compression ratio.

“Libertine’s work with MAHLE Powertrain and Ensus supports our view that there is a path to a fossil free future using renewable transport fuels such as bioethanol,” said Grant Pearson, Ensus Commercial Director. “We are pleased to have been involved in this work and look forward to further developments in 2021.”

Adrian Cooper, MAHLE Powertrain’s Head of New Technology, added “MAHLE Powertrain is excited to be able to utilise our experience in developing, testing and controlling novel concepts to support this successful demonstration of Libertine’s technology.”