CH₄ Methane Slip

Unburned methane passing through LNG-fuelled engines. Methane has ~28× the 100-year warming potential of CO₂, so slip can erode the climate advantage of LNG substantially.

PollutantsLNG

Engine cycleAverage engine powerkWAnnual operating hourshCH₄ slip overrideg/kWhDefaults from Fourth IMO GHG Study: 5.5 for Otto MS, 2.5 for Otto SS, 0.2 for Diesel cycle.

Annual CH₄

264.00t

CO₂-equivalent (GWP100=28)

7,392t CO₂e

CO₂-equivalent (GWP20=82.5)

21,780t CO₂e

20-yr horizon - IPCC AR6

Formula and context

CH₄ (t) = Power × Hours × Slip (g/kWh) / 1e6
CO₂e = CH₄ × GWP

LNG engines burn natural gas (~90 % CH₄). Any un-combusted methane that escapes through the exhaust (Otto cycle) or crankcase ventilation (all types) is "methane slip". Otto medium-speed four-strokes have the highest slip at ~5.5 g/kWh. Diesel-cycle high-pressure engines reach <0.5 g/kWh.