Natural Gas Slip

Natural gas slip, almost always called methane slip, is the unburned methane that passes through a gas-fueled marine engine and leaves in the exhaust. It comes from the lean premixed Otto-cycle charge filling piston-ring crevices that quench combustion, so the methane escapes oxidation. Four-stroke low-pressure dual-fuel engines slip the most, with measured fleet averages near 6 percent against IMO’s older 3.5 percent default. The climate cost is large: methane has a GWP100 of 28, so FuelEU Maritime and the IMO count slip well-to-wake. IMO default slip factors now sit in MEPC.391(81), with onboard measurement guidelines in MEPC.402(83).