Container ships and car carriers have been major beneficiaries of the a dual-fuel engine that can run on liquefied natural gas or heavy fuel oil, according to an interpretation of data from German engine maker MAN.
MAN’s B&W dual-fuel ME-GI engine is expected to shortly reach 1,000 orders since its the group began accepting orders in 2012 and following its market debut in 2014*. There have been more than 400 orders for container ships, over 225 for various kinds of tankers, and more than 175 for car and carriers.
Ocean shipping carrier, Mediterranean Shipping Company, has more than 125 of the engines in its fleet, which means it is currently the largest owner of MAN ME-GI engines. Giuseppe Gargiulo, head of newbuildings at MSC, said in an official statement that “the two-stroke ME-GI provides us with the lowest methane slip, best gas consumption, and an attractive pilot-oil consumption as we navigate towards net zero. We have around 150 dual-fuel vessels on our order book…”.
How it works
The two-stroke engine has anywhere between 5 to 12 cylinders depending upon bore size and it runs on liquefied natural gas. It has a guaranteed 0.2g/kWh methane slip with a tolerance of +/- 0.2g/ kWh and has so far racked up more than four million running hours, according to the manufacturer. The engine uses a pilot fuel (1) – which can be heavy fuel oil (the residual material after all the distillates have been produced), marine gas oil (fuel comprised exclusively of distillates of crude), or marine diesel oil (an blend of distillates (i.e. marine gas-oil) and heavy fuel oil) (2). Dual fuel operation sees the injection of both the pilot fuel and natural gas into the combustion chamber (3). In general terms, pilot fuel is injected into the combustion chamber and then ignites, which, in turn, causes the natural gas to burn.
LNG as a cleaner(ish) fuel
Liquefied natural gas (LNG) is basically methane with a range of other gases contained within it such as ethane, propane and the like. During production, the trace gases are removed and the remaining methane is cooled to minus 160 degrees Celsius at near-atmospheric pressure, which liquefies it. Combustion of LNG is considerably less polluting that burning heavy fuel oil with 20% to 30% less carbon dioxide emissions, 90% less nitrous oxides, 99% less sulphur oxides, and almost no particulate matter, according to engine manufacturer Wartsila.
Unfortunately, as methane is a hydrocarbon with one carbon atom to four hydrogen atoms (hence “CH4”), combustion produces carbon dioxide emissions.
Typically, natural gas is a fossil fuel that has formed when natural organic matter from eons ago was compressed under the earth at high temperatures and pressures for millions of years. Processing and then combustion of such natural gas returns carbon dioxide from millions of years ago to the modern atmosphere. This process adds to the carbon dioxide burden.
But LNG does have the potential to be a green fuel because it doesn’t have to originate from fossil sources.
Green and sustainable methane
Bi0-methane can be made from the decomposition of organic material – such as agricultural or livestock wasted – through the activity of bacteria in a non-oxygen environment. Bio-methane could reduce emissions by up to 80% when compared to heavy fuel oil, reckons engine manufacturer Wartsila.
Alternatively, methane can be made from its raw ingredients – carbon and hydrogen – in an industrial process known as Sabatier method. Provided the hydrogen is obtained through green processes (such as such as the splitting of water using electricity generated by solar power) and the carbon is obtained from non-fossil fuel sources then the resultant “synthetic methane” could be a source of green fuel. Well, in theory, anyway. A 2023 techno-economic assessment synthetic methane production by adding hydrogen to carbon dioxide (where that carbon is sourced from direct air capture) produced methane at a cost greater than the current cost of market-methane, suggesting that further improvements are necessary.
A 2022 position paper from the International Energy Agency (an independent inter-governmental organization) noted that, at the time, “biomethane is cheaper than green hydrogen and is expected to remain so for some time in the future”. Another techno-economic assessment in 2022 (Janke et al), this time focused on synthetic methane for use in public transport (buses, specifically) found that the use of synthetic methane increased the total cost of ownership in all cases when compared to diesel-powered buses.
It’s clear that synthetic methane as a fuel still has some way to go before it hits commercial viability.
Still, the shipping industry is far distant focused as its main assets (i.e. ships) are long-lived assets of usually at lest 20 years (barring accidents) with some vessels still in service after 30 years.
Shipping’s uptake of LNG as a marine fuel
It is clear that the shipping industry is adopting LNG as a marine fuel in large numbers. Class society DNV reports that, in 2025, 871 ships were on order that will be fuelled by LNG, which accounts for just under 70% of ship on order that will be powered by alternative fuels (the other alternative fuels being ammonia, hydrogen, methanol and Liquefied Petroleum Gases). DNV is forecasting that, by 2033, the number of LNG ships on order will be at least 1,334 vessels, accounting for about 64% of the forecast total (DNV forecasts that methanol will gain market share rising from about 10% of today’s orderbook to just under 20% by 2033).
From the perspective of the ship’s engine, and, indeed, from global LNG pipework, storage tanks and other infrastructure, there’s no real difference between the different forms of LNG whether that’s bio-methane, fossil fuel methane, or synthetic methane. From the viewpoint of the infrastructure, it’s all methane and it’s handled the same way. Ships with LNG-capable engines can handle the different forms of LNG as fuel without retrofit.
Meanwhile, if the shipping industry opts for – or is required by the IMO to adopt – ammonia or methanol, then according to Wartsila, dual fuel engines can be converted to new fuels (although proper planning will be need to take into account the greater space requirements that methanol or ammonia will require).
A markedly-different perspective
However, applying looking at those figures while taking into account the conventionally powered fleet puts a markedly different spin on the situation. Today, about 99.08% of the existing world shipping fleet is powered by conventional power sources. Meanwhile, conventionally powered ships make up 82.77% of the orderbook, with the other 17.23% being alternatively-fuelled, with LNG-powered ships accounting for 9.41% of the orderbook, followed by methanol-powered ships which account for just over 5% of the orderbook.
Looks like there’s still some way to go to get to de-carbonisation.
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- Sources vary, but the manufacturer itself states the year of the market debut was 2014
- “ME-GI Dual Fuel MAN B&W Engines A Technical, Operational and Cost-effective Solution for Ships Fuelled by Gas,” p13
- Ibid, p.11
