NOVELTY - Generating (P1) a main fuel composition comprising methanol and water and not greater than 20 wt.% of dimethyl ether, and a fumigant comprising dimethyl ether, comprises: (a) providing a pre-fuel composition comprising methanol and dimethyl ether; (b) adding water to pre-fuel composition to cause or aid evaporation of at least a portion of the dimethyl ether from pre-fuel composition; (c) collecting the portion of dimethyl ether evaporated from pre-fuel composition for use as a fumigant; and (d) using the remainder of pre-fuel composition comprising methanol and water as a main fuel composition.    USE - The process is useful for generating a main fuel composition which is used to operate a compression ignition engine, where the compression ignition engine is used to generate power (claimed).    ADVANTAGE - The process: provides fuel compositions which exhibit improved emissions profile with low impurities; is safe and cost effective; and treats the engine exhaust to capture and then re-use or re-direct heat and water from exhaust gases, thus increasing system efficiency.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for:    (1) operating (P2) a compression ignition engine using a main fuel comprising methanol and water and not greater than 20 wt.% dimethyl ether, including (a)-(d) as above per se, (e) fumigating an intake air stream of the compression ignition engine with the fumigant comprising dimethyl ether, introducing the fumigated intake air into a combustion chamber in the engine and compressing the intake air, introducing the main fuel into the combustion chamber, and igniting the main fuel/air mixture to drive the engine;    (2) generating (P3) power using a compression ignition engine fuelled by a main fuel composition comprising methanol and water and not greater than 20% dimethyl ether, comprising (a)-(d) as above per se, operating a compression ignition engine using the main fuel composition to generate power, (e) as above per se, treating engine exhaust to recover exhaust heat and/or water from the engine, and redirecting the heat and/or water for further use; and    (3) supplying fuel to a compression ignition engine, comprising supplying a pre-fuel composition comprising methanol and dimethyl ether, (b) as above per se, supplying the portion of dimethyl ether evaporated from the pre-fuel composition to an air intake of the compression ignition engine, or to a tank that is in fluid connection to the air intake of the compression ignition engine, for use as a fumigant, and supplying the remainder of the pre-fuel composition comprising methanol and water to a second tank that is in fluid connection to a combustion chamber of the compression ignition engine for use as a main fuel composition.