The on-board catalytic conversion of a portion of the ethanol fuel into diethyl ether and water is a possible solution to cold-start problems of an ethanol-fueled vehicle. Before an appropriate catalyst can be selected, it is necessary to obtain information about the thermodynamic properties and flammability limits of an ethanol, diethyl ether, and water fuel mixture system. According to the computational results, the on-board catalyst requires a 40-80% ethanol conversion to diethyl ether for the cold-starting and cold operation of a spark ignition engine. A few selected solid acid materials are evaluated as potential ethanol dehydration catalysts. Resin-based catalysts, such as cross-linked sulfonated polystyrene, fail to satisfy the on-board conversion requirements while gamma-alumina material gives a better performance.