Real-world methane emissions from LNG-fueled ships are higher than current regulations assume, new study finds
Policymakers urged to consider increasing the default methane slip value to at least 6% for the most common LNG engine
The International Council on Clean Transportation (ICCT) released a new report characterizing methane emissions from ships fueled by liquefied natural gas (LNG) operating in Europe and Australia. It is based on data collected by drones, helicopters, and onboard sensors during the two-year Fugitive and Unburned Methane Emissions from the Ships (FUMES) project.
FUMES is a collaboration between the ICCT, Explicit ApS, and the Netherlands Organization for Applied Scientific Research (TNO). The FUMES report contains the most comprehensive dataset of real-world methane emissions from LNG-fueled ships to date, including “methane slip” from engines and fugitive methane emissions from LNG cargo unloading operations. Methane slip is the proportion of LNG fuel, which consists mainly of methane, that escapes unburned from the engine. Real-world methane slip measured in the plumes of 18 ships using the most common type of LNG marine engine (LPDF 4-stroke) averaged 6.4%, whereas EU regulations currently assume 3.1% methane slip and the United Nations International Maritime Organization (IMO) assumes 3.5%.
The report therefore recommends that EU and IMO policymakers consider increasing the default methane slip value for LPDF 4-stroke engines to at least 6%.
Other results:
- A modern LPDF 4-stroke engine can emit lower methane slip than assumed by the EU (3.1%) and the IMO (3.5%), but methane slip can still be substantial, especially at low engine loads, ranging from approximately 4% to 7% when engine loads are 25% or lower.
- Unloading large LNG tankers can result in 24–40 kg/h of fugitive methane emissions, including approximately 8 kg/h of methane slip from the ships’ LPDF 4-stroke engines.
- Onboard measurements found that methane slip and work-specific NOx emissions were highest at the lowest engine loads.
Other recommendations for policymakers include:
- EU policymakers should consider requiring LNG-fueled ships to plug into shore power or otherwise eliminate their at-berth emissions.
- EU policymakers should consider requiring monitoring, reporting, and verification of methane emissions at LNG storage and refueling points.
- IMO policymakers should consider adding a 10% engine load test point and adjusting how emissions at each point are weighted in engine certification procedures to more accurately reflect real-world operations.
