Abstract: A process is described for producing a diesel fuel/water emulsion for a diesel engine in which, as a function of the operating condition of the engine, water and diesel fuel are mixed at different quantitative proportions and supplied to the engine. The water and the diesel fuel separately are led practically to the intake side of the injection pump and are mixed only in the pump cylinder. The non-injected highly pressurized excess quantity of fuel is stored temporarily in an accumulator and is again supplied to the injection pump during the next intake stroke. The process makes it possible to produce a very fine water/fuel mixture and in addition to keep the volume of the fnished water/fuel mixture low, so that when the quantitative proportion is changed because of the inertia of the system, the new fuel/water mixture is available at the point of consumption (injection nozzle).