Queseanians,
Will methane slip in LNG-fuelled Main Engines be regulated?
And how it can be reduced?
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Hi @George,
There are various proposals for the development of measures to reduce methane slip since methane is a more potent GHG than CO2.
Discussions on the proposed regulations to control methane slip consider that these regulations should be goal based and non-proscriptive, similar to those which govern emissions of NOX.
The draft lifecycle assessment (LCA) GHG/Carbon Intensity Guidelines refers to the assessment of greenhouse gas emissions from the fuel production to the end-user by a ship (Well-to-Wake), and methane slip is to be addressed by the LCA guidelines.
Thus, in the future we shall await such requirements, at least until we reach 2050 and the zero emissions ships 
Methane emissions from LNG-fueled engines are commonly referred to as methane slip. Methane slip is unburned fuel passing through the combustion without oxidizing.
The methane slip can occur as direct slip or as combustion slip.
Direct slip is when unburned methane escapes form the cylinder unit because the gas is admitted a point lower from the top dead center. The exhaust valve timing plays a role as well.
Combustion slip is when the gas in the combustion mixture is not fully burned due to low combustion temperatures.
High pressure LNG-fueled engines (Diesel Cycle) have lower methane slip compared to Low pressure LNG-fueled engines (Otto cycle)
Some of the reasons are: High combustion temperatures, high compression ratio, rich combustion mixture, design of combustion chamber.
Although, for the time being there is no official regime to regulate the methane slip emissions, at some point we expect that it will be taken into account by IMO delegations and local authorities.
Undoubtedly it is a factor that can influence the EEDI/EEXI of vessels.
A reduction method for methane slip proposed by various is EGR (exhaust gas recirculation).
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