The search for a cleaner choice of fuel for maritime transportation continues and is constantly becoming more complex. Currently, the hottest topic in this regard is decarbonization and meeting related goals. Despite being the most discussed topic, the decarbonization goals of the maritime industry are still off by quite a margin. For instance, with the current momentum, it is still 5% off the 2030 goals. But this is not the topic we should be arguing today; instead, we should be discussing whether decarbonization should be the main goal for the maritime industry.
According to the International Council on Clean Transportation (ICCT), LNG-fueled vessels emit 25% less carbon dioxide than conventional marine fuels in producing the same amount of propulsion power. Sounds good at first, but here is the catch: LNG is mostly made of methane, which is a far more potent greenhouse gas (GHG) than CO2. In fact, it traps 86 times more heat in the atmosphere over a 20-year cycle.
Methane slip is an event where methane, in gas form, leaks and escapes into the atmosphere. There are various ways this leakage can occur, including upstream emissions from leakage during the extraction phase and transportation, as well as downstream emissions from combustion and unburned methane.
Methane slip, as a measurement, is the proportion of LNG fuel that escapes unburned from the engine. In real-world measurements, methane slip averages 6.4%, based on data from 18 vessels using the most common type of LNG-fueled marine engine (LPDF 4-stroke). This is around double the size of what EU regulations assume (3.1%) and the International Maritime Organization's estimation (3.5%).
Some arguments suggest that the most modern LNG-fueled engines emit even less than the estimations of IMO and EU regulations, but this is not the case for low engine loads (25% or less); in that case, 4 to 7% methane slip is to be expected.
In conclusion, while LNG offers some reduction in carbon dioxide emissions, the overall impact on greenhouse gas emissions is more complex due to methane slip. This complexity highlights the need for a balanced and comprehensive approach to fuel choices and decarbonization strategies in the maritime industry.