
If your vessel uses LNG, there’s always a small amount of the fuel that doesn’t burn in the engine and escapes with the exhaust gases instead. This is known as methane slip – a challenge that engine manufacturers like Wärtsilä have been working on reducing for years. What is methane slip, why is reducing it essential and what smart solutions are on offer for methane slip reduction?
LNG is predominantly methane. If your vessel’s engines burn LNG as a fuel, most of the methane will be used up in the energy conversion process. However, some of it remains unburned and escapes into the atmosphere. This is known as methane slip. If not addressed, it reduces the climate-related advantages of LNG.
When it comes to cutting the shipping industry’s emissions, liquefied natural gas (LNG) is never far from the conversation. LNG emits 25% less CO2 (carbon dioxide) than other common marine fuels for the same propulsion power, as well as lower NOx (nitrous oxide), SOx (sulphur oxide) and particulate emissions. It’s no surprise, then, that it’s often touted as shipping’s clean fuel of the future.
If you’re thinking about switching to LNG-capable engines, methane slip is probably a term you’ve already come across.
Hand-picked content: Time to take another look at LNG conversion?
If your vessel’s engines burn LNG as a fuel, most of the methane will be used up in the energy conversion process. However, some of it remains unburned and escapes into the atmosphere.
As it stands there are no international regulations on methane emissions from maritime vessels. But, according to the Maersk Mc-Kinney Møller Center for Zero Carbon Shipping report, Reducing methane emissions onboard vessels, regulations are likely to appear soon. The report mentions the FuelEU for Maritime regulation as an example, which will include methane slip in its CO2-eq methodology.
Although a lean-burn LNG engine uses up most of the methane contained in the fuel in the energy conversion process, some of it remains unburned. There are three main sources of unburned hydrocarbon emissions in these types of engines:
Manufacturers have been working hard to reduce methane slip since the 1990s. For example, since 1993 Wärtsilä has cut methane slip from its dual-fuel engines by 85%.
There are various ways to tackle these different sources of methane slip in LNG-fuelled ships, including:
Manufacturers have been working hard to reduce methane slip since the 1990s. For example, since 1993 Wärtsilä has cut methane slip from its dual-fuel engines by 85%.
“In 1993, the methane slip was 16 grams per kilowatt hour (kWh),” says Kaj Portin, General Manager, Sustainable Fuels & Decarbonisation at Wärtsilä, “By optimising engines and leakages, slip has been reduced to just two to three grams today. To put this into perspective, this represents a 4% improvement in efficiency and means that a vessel will sail almost 10% farther on the same amount of fuel,” Portin explains.
“We’ve also been developing a new combustion concept that will reduce methane slip by a further 50%, to around 1 gram per kWh. This concept will come with the added bonus of even further reductions in NOx, SOx and particulate emissions.”
It might surprise you to learn that that addressing methane slip does not need to involve lots of time-consuming and costly engineering work. If your vessel is already powered by a Wärtsilä dual-fuel engine, a single field service technician and their laptop could be all that’s needed for a cleaner, greener machine.
Hand-picked content: A cleaner, greener machine – Wärtsilä 34DF control software upgrade cuts greenhouse gas emissions
The software upgrade – which is available for Wärtsilä 20, 34 and 50 dual-fuel engines – works by marginally reducing the engine’s charge air pressure and lambda – the air-fuel ratio in the combustion chamber. It is quick and easy to install and can cut methane slip by up to 60% when your engines are operating in gas mode below 85% load.
Find out how you can optimise engine behaviour to reduce emissions including methane slip.
Editor’s note: This article was first published in October 2020. It has since been reviewed and rewritten, in February 2023.