Liquified Natural Gas (LNG)

There are two types of dual fuel engines. Low pressure engines provides high energy efficiency at high load and low emissions but results in a challenge to control the methane slip, in particular at low load of the engine. A high pressure engine gives less issues with methane slip. However the NOx reduction is limited due to higher combustion temperatures. It would therefore require for example SCR technologies to bring down the NOx levels to the required emission standards (e.g. Stage 4B or Stage 5).

It is possible to convert existing diesel engines into dual fuel engines. Room is required to retrofit onboard LNG tanks resulting in a loss of cargo capacity.

Gas to Liquids (GTL)

On the downside, GTL fuel lifecycle greenhouse gas emissions are approximately 25 percent higher than conventional oil.