Without countermeasures, there are several routes by which unburnt methane can escape from both two- and four-stroke gasburning engines via the engine exhaust as well as the crankcase ventilation, a phenomenon called »meth-ane slip«. LNG is typically 85 % to 95 % CH_4, a greenhouse gas considerably more potent than CO_2. As MAN lays out in a recent Whitepaper entitled »Managing methane slip«, the phenomenon is most prevalent on gas-burning engines operating according to the Otto combustion process, where gas fuel and air are mixed homogenously prior to ignition and combustion. It affects engines in which the premixed fuel and air are ignited by a spark-plug (spark-ignited (SI) gas engines) as well as dual-fuel (DF) engines where a liquid fuel »pilot« initiates ignition of the air-gas mixture.
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