Recycled lubricants and pulp by-products could be solution to emission challenges in marine and off-road engines

In her doctoral dissertation at the University of Vaasa, Michaela Hissa demonstrates that fuels refined from waste and industrial by-products can help reduce emissions in existing engine applications.

Electric and hybrid propulsion systems are developing rapidly, but they do not yet offer a practical alternative for the high-power engines used in marine and off-road applications. Therefore, more climate-friendly solutions must be developed within the constraints of the current engine fleet. Michaela Hissa’s dissertation in energy technology investigates how renewable naphtha, derived from crude tall oil, and marine gas oil refined from recycled lubricants, can serve as alternative fuels.

“When blended with fossil diesel, renewable naphtha burns efficiently and reduces smoke emissions. Marine gas oil, on the other hand, decreases hydrocarbon and carbon monoxide emissions. Both fuels significantly reduced particulate emissions, which are hazardous to human health,” says Hissa.

The studied fuels are derived from industrial side streams: renewable naphtha is a processed product of crude tall oil from the pulp industry, while marine gas oil is produced from used lubricating oils classified as hazardous waste. Scaling up their use requires a functioning collection and refining infrastructure.

“Lubricating oils are needed in a wide range of rotating machinery, from power plant turbines and paper machines to engines in vehicles, off-road machines, and ships. As a result, large volumes of used oil are generated globally,” Hissa explains.

Strong foundation in Finland for wood-based fuels

The fuels examined in the study are classified as drop-in fuels, meaning they require no significant modifications to existing engine systems. This makes them attractive as transitional solutions.

“The number of existing marine and off-road engines is substantial and replacing them won’t happen overnight. To reduce emissions, it is essential to find solutions that support the transition without requiring the replacement of the entire infrastructure,” Hissa notes.

In the future, wood-based residues may play a significant role as raw material for renewable fuels. Finland’s forest industry provides a strong foundation for their development and use. However, availability, cost-effective production, and competitive pricing remain key issues for large-scale deployment.

“In the future, engines will need to adapt to an increasingly diverse range of fuels. Therefore, more research is needed to understand how different fuels behave in engines,” Hissa concludes.