Marine free-piston engine

The first generation free-piston engines, used commercially around 1930-1960, were large-scale diesel engines and much operational experience with free-piston systems was reported in this period. The absence of any load-carrying bearings allows a free-piston diesel engine to operate with very high in-cylinder gas pressures and compression ratios, benefiting thermodynamic efficiency and power to weight ratio.

A further advantage of the free-piston engine is its operational flexibility, allowing the engine operation to be optimised for any operating condition, such as varying load levels or changes in fuel type. This is of particular interest when using fuels of low or varying quality, such as marine heavy fuel oil or bio-oils, which can have poor ignition and combustion characteristics. The multi-fuel capability of the first-generation free-piston engines was widely reported, with one author stating "It seems that these engines do not care whether they get fuel with octane or cetane numbers." (Flynn, G. Observations on 25,000 hours of free-piston-engine operation. SAE Transactions 1957; 65:508–515.)

The marine free-piston engine concept under development at Newcastle University is based around a turbocharged single piston or a dual piston free-piston engine. Extensive investigations into this concept have been carried out and published. The research shows that brake fuel efficiency advantages in the order of 5 percentage points can be realised compared with conventional engines, with reductions in nitrogen oxides emissions of approximately 20 per cent. For more information please see the publications page.