A process for generating a main fuel composition comprising methanol and water and not more than 20% by weight dimethyl ether, and a fumigant comprising dimethyl ether, the process comprising: providing a pre-fuel composition comprising methanol and dimethyl ether, adding water to the pre-fuel composition to cause or aid evaporation of at least a portion of the dimethyl ether from the pre-fuel composition, collecting the portion of dimethyl ether evaporated from the pre-fuel composition for use as a fumigant, and using the remainder of the pre-fuel composition comprising methanol and water as a main fuel composition. The water may be at a temperature above ambient.