Utförande parter: IVL,SSPA, Daphne Technology

Kontaktperson: Hulda Winnes, IVL Svenska miljöinstitutet Den här e-postadressen skyddas mot spambots. Du måste tillåta JavaScript för att se den.

The emissions from marine gas engines are determined partly by the fuel and partly by the combustion technology used. Natural gas, bunkered on ships in liquefied form as Liquefied Natural Gas (LNG), is a clean fuel compared to fuel oils, causing low levels of emissions of sulphur dioxide, particles and soot. Also, CO2 emissions per energy unit is relatively low from LNG combustion due to more chemically bound energy per carbon content in natural gas than in fuel oil. Further, the engines operating on natural gas are often of a “low-pressure” type. These engines have low NOX emissions compared to “high-pressure” diesel engines. The LNG engines are either spark ignited using the gas as the only fuel, or they use a dual fuel technology where a pilot fuel injection is used for ignition. The pilot fuel is responsible for a large part of emissions of SO2 and particles, although it only contributes 5% or less of the energy. Another type of dual fuel engine is the high-pressure engine using LNG as fuel in a diesel combustion cycle. Like in other diesel cycle engines, the NOX emissions from those engines are high, comparable to emissions from fuel oil combustion. The low-pressure dual fuel engines are by far the most used engine type on ships that are not LNG carriers. A side effect from the combustion in the low-pressure engines is a slip of unburnt methane through the combustion process. For some engines using LNG as main fuel, the methane slip causes total emissions of CO2-equivalents to be higher than from comparable engines using only marine gasoil. The issue of methane slip is addressed by engine manufacturers aiming for improved designs and combustion technology.