Environmental groups are advocating for stricter regulations on LNG-powered ships, while some experts believe that the complex nature of the issue requires a more nuanced approach, according to Seatrade Maritime.
Methane Emissions
Currently, the EU and IMO use methane slip emission factors that are provided by a few studies that used a mix of lab tests, engine manufacturers data, and a limited amount of onboard testing, according to the International Council on Clean Transportation (ICCT).
LNG-powered vessels suffer from unburnt methane emissions from the exhausts of both main and auxiliary engines. Actual operational emissions for some low-pressure four-stroke LNG engines have been found to be around double the figures published by engine manufacturers.
Korean NGO Solutions For Our Climate (SFOC) lead on the energy supply chain Rachel Eunbi Shin, said: “Engine manufacturers and classification societies claimed in 2014 that methane slip was ‘practically eliminated’ in modern engines”, yet slip rates continue to rise, “raising serious credibility concerns”.
According to Shin it is crucial to monitor individual ships to get a clearer picture of their operational emissions.
“We’ve discovered significant discrepancies between manufacturer-claimed emissions and real-world performance – much like the automotive sector’s emissions scandal. Operational profiles vary dramatically between vessels, particularly with slow steaming becoming more common to meet CII regulations,” she explained.
Findings And Solutions
ICCT has approached both the EU and IMO with its findings and its solutions: “There are no guidelines for FuelEU as yet, but we are hopeful that we can get guidelines for 2026, when FuelEU payments for LNG are introduced,” said Comer.
The same methodology is being discussed at IMO. In its report on the study, based on 22 measurements from 18 vessels, the group’s findings showed that low-pressure, dual-fuel, four-stroke (LPDF 4-stroke) engines, had methane slip at an average 6.42% and a median of 6.05%, “more than twice as much methane slip than assumed by the EU and over 80% more than assumed by the IMO.”
Six measurements at or above a combined engine load of 50%, registered 6.07% average and 6.59% median emissions.
“Methane slip was greater than the EU assumption of 3.1% in 77% of the measurements. These same 77% of measurements were also greater than the IMO assumption of 3.5% methane slip,” said the joint report.
However, vessels with LPDF 2-stroke main engines and LPDF 4-stroke auxiliary engines (L2L4) emitted the least methane slip, averaging of 2.50% methane slip across all engine loads and 1.58% at more than 10% engine load; Median values were 1.47% and 1.35%, respectively.
Measurements on 2-stroke high pressure dual fuel engines (HPDF) main engines combined with LPDF 4-stroke auxiliaries were limited to two readings with a ship operating at below 10% load, “when we assume that only the LPDF 4-stroke auxiliary engines were operating on LNG,” which recorded 3.47% and 6.12% methane slip.
Other measurements were performed at 36% main engine load, when both the HPDF main engine and LPDF 4-stroke auxiliary engines were expected to be operating on LNG, resulting in 2.69% methane slip.
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Source: Seatrade Maritime
