Methane emissions from LNG-powered vessels

The use of liquefied natural gas (LNG) as shipping fuel has increased in recent years with the most popular way to use LNG in low-pressure dual-fuel (LPDF) engines together with diesel fuel for ignition. Lower sulphur and nitrogen oxides, together with lower particulate emissions are reported with LNG use compared to diesel use. Moreover, CO2 emissions are lower as well but there is an issue with the methane slip with the LNG used in low-pressure dual fuel engines. The methane being a strong greenhouse gas and regulations introduced to consider methane emissions from ships, have made the engine manufacturers to take further development steps in preventing the methane slip. By today, there are still only few studies presenting emissions of methane from LNG-powered vessels with engines built in 2020 or after. The present study provides the results of the emission studies conducted onboard two LNG-powered vessels built in 2021 and 2022. The first campaign took place on-board a Ro-Pax ferry (built in 2021) operating in the Baltic Sea and the second was conducted on-board a cruise ship (built in 2022) operating in the Mediterranean.

The results indicate that the current state-of-the-art LPDF engines show lower methane levels compared to previous studies, which is good news when thinking of the climate effects. Air pollution levels from LNG use are again proven to be lower than from diesel use, contributing to better air quality. Overall, LNG is considered to be a transition fuel and the technologies developed today should be capable of utilizing biobased gas or a renewable synthetic in origin. Methane slip minimization and avoiding other pollutants produced are not only important today but also for future fuels, even though such fuels could be produced sustainably.

Acknowledgements: This research was funded by European Union, grant number 101056642.