NOVELTY - Preparing a fuel for automotive applications, stationary engines and marine applications, comprises: heating alcohol by passage through a heat exchanger; treating heated alcohol by passage through a catalyst bed, where the alcohol is partly converted to the corresponding ether, resulting in a fuel mixture containing alcohol and ether and also containing water; and cooling the resultant water-containing mixture of alcohol and ether by passing it through the above heat exchanger and optionally adding selected additives to the mixture.    USE - The process is useful for preparing a fuel for automotive applications, stationary engines and marine applications.    ADVANTAGE - The process: provides conversion in liquid phase, so there is no need to evaporate reactants or to condense the products; can be carried out using a cheap, compact integrated device, which is a quasi-autothermal converter, which upgrades lower-grade bio fuels (containing alcohol) to effective fuels for use in diesel engines, and enables the conversion in an auto-thermal mode; does not require to remove water from the produced fuel mixture prior to use, which further enables a compact design; stores only fuel containing alcohol in the primary fuel tank; utilizing buffer tank which enables handling of an uneven or unsteady fuel consumption and return flow from the common-rail of the engine, handling of unsteady fuel consumption when used with unit injectors, and allows starting the engine without operating the reactor, hence one may use the engine to produce electricity for start-up (heating) of the fuel upgrade reactor i.e. start-up without using the battery of the vehicle; requires a moderate heat input for start-up, which is compatible with electric heating using the battery of the vehicle and the operation is auto-thermal the rest of the time; and provides efficient and easy control of the dehydration reaction using the electric heater and adjusting the flow through the reactor.    DETAILED DESCRIPTION - Preparing a fuel for automotive applications, stationary engines and marine applications by catalytic liquid phase conversion of alcohol of an alcohol-containing primary fuel to the corresponding ether, comprises: heating alcohol by passage through a heat exchanger; treating heated alcohol by passage through a catalyst bed under an adjusted temperature and at a controlled flow rate, where the alcohol is partly converted to the corresponding ether, resulting in a fuel mixture containing alcohol and ether in the desired proportions and also containing water; cooling the resultant water-containing mixture of alcohol and ether by passing it through the above heat exchanger in the opposite direction of the primary fuel flow and optionally adding selected additives to the mixture, thus obtaining a water-containing fuel mixture of alcohol and ether under auto-thermal operation conditions, the fuel mixture having specific features for a given application. An INDEPENDENT CLAIM is also included for a device for carrying out the process, comprises an inlet for an alcohol-containing fuel from the primary tank, a start-up heater initially heating up the catalyst bed or alternatively the flow downstream of the heat exchanger, a heat exchanger, which heats up the cold alcohol to a suitable temperature prior to reaction, a reactor, a catalytic bed within the reactor, where the alcohol is partly converted to ether and water, a pressure reduction valve, inlet means for adding additives and a buffer tank, where the resulting fuel mixture of alcohol, ether and water is stored after passing back through the heat exchanger for suitable cooling, the heater only being used during start-up and the process thus being conducted under auto-thermal operation conditions.