The Department of Internal Combustion Engines and Vehicles, Technical University of Bielsko-Biala has carried out work on alternative fuels in the area of dual-fueling of SI engines. The paper presents the concept of dual fuel (alcohol and gasoline) MPI injected spark-ignition engine using a fuel mixing device. The solution consists in mixing the fuel (gasoline and alcohol) before or in the fuel rail, which ensures a variable share of alcohol in the mixture in the range from 0÷100%, depending on the engine operating conditions (engine revolutions and load), and its thermal state. The fuels are delivered to the mixing chamber through the solenoid valves that allow a proper selection of the proportion of alcohol and gasoline. The pre-prepared mixture is injected through the original injectors to the intake manifold, around the intake valve. This paper presents the prototype of the mixer that allows mixing of the gasoline and alcohol in any proportion using a PWM.