What is methane slip and ways to reduce

Answer

What is Methane Slip?

Methane slip occurs in LNG dual-fuel internal combustion engines when unburnt methane gas (CH₄) escapes past the combustion chamber into the exhaust duct without being oxidized. Since methane's Global Warming Potential (GWP) is ~28 times greater than CO₂, methane slip severely degrades the lifecycle environmental benefit of using LNG fuel.

Methods to Reduce Methane Slip:

• Engine Technology Selection: Utilize High-Pressure Gas Injection (HPDF) engines (such as 2-stroke Diesel-cycle engines like ME-GI), which keep methane slip below 0.2–0.5 g/kWh, compared to low-pressure Otto-cycle engines.
• Combustion Optimization: Adjust variable valve timing (VVT), optimize ignition spark timing, and improve pre-chamber fuel nozzle design to maximize combustion efficiency in lean-burn modes.
• Exhaust After-treatment Systems: Install Methane Oxidation Catalysts (MOC) in the exhaust line to oxidize unburnt methane into CO₂ and H₂O before emission.
• Direct Cylinder Injection Tuning: Optimize pilot fuel injection pressure and timing to eliminate combustion quench zones near the cylinder liner walls and top piston crevice volumes.