Answer
With the advancement of technology and reducing carbon emission from ships. IMO has set an ambition of net-zero by 2050. Which involves zero carbon fuels usage onboard ships. Various less carbon and no carbon fuels are:
1.LNG(mainly methane)
2.LPG(butane & propane)
3.BIOFUEL(Gen 1:FAME, Gen 2:, Gen 3)
4.METHANOL(Highly reactive , toxic)
5.AMMONIA(corrosive to certain metals, require pilot fuel, NOx emission increase,Difficult to detect in high concentration, Ammonia slip)
6.HYDROGEN(tech in early stage, Highly flammable, Storage in cryogenic cylinders, Used in fuel cells)
7.Fuel cells (Tech in early stage, Costly, Uses Hydrogen as fuel)