A diesel engine fuel composition comprising methanol at a level of at least 20% by weight of the fuel; water at a level at least 20% by weight of the fuel; a ratio of water to methanol of between 20:80 to 80:20; a total amount of water and methanol of at least 60% by weight of the fuel composition, and one or more additives, in a total amount of at least 0.1% by weight of the fuel, wherein the level of sodium chloride, if present as an additive, is between 0 to 0.5% by weight of the fuel, and the level of flavourant, if present as an additive, is between 0 to 1.5% of the composition is provided. Also provided is a process for powering a compression ignition engine using a fuel comprising methanol and water, including inlet air pre-heating, and associated systems and uses of the fuel composition.