Methane slip prevention in the combustion chamber - Finding the biggest methane slip problems for 4-stroke dual fuel marine engines

Abstract

LNG is an alternative to conventional marine engine fuels. It consists mainly of methane which has a significantly higher global warming potential (GWP) equivalent than carbon dioxide. GWP20 is 86 according to (IMO, 2020). Due to the lower carbon dioxide, NOx, sulphur, and particulate matter (PM) emissions, it is seen as a cleaner fuel. But if methane emissions occur the global warming impact will rise. Methane emissions do occur and are unregulated. But work is done to decrease it. This thesis is regarding what can be done regarding internal combustion engines releasing methane due to incomplete combustion, also known as methane slip. In the results it is shown what is causing the methane slip from the most common engine concept 4-stroke low pressure dual fuel engines. The major challenge in reducing methane slip is during low engine load and the major contributor during low load is by far quenching in the combustion. By reviewing literature, it has been shown that there are still possibilities for improvement in the combustion chamber, by reducing crevices, optimizing the piston geometry, timing the valve operation and by finding solutions to reduce the air fuel ratio during low load.