Discuss the issues that should be taken into consideration for changing over from high sulfur $(<3\mathrm{.}5\%)$ to low sulfur $(<0\mathrm{.}5\%)$ fuels in marine diesel engines after the IMO regulation for global maritime areas, which entered into forces in January, $1,2020.$ Discuss the terms of cat fine production, fuel compatibility for mixing different fuels, and mixing condition for settling or storage tank$$s filling.