Abstract: A piston engine is operated by pressurizing combustion air to a pressure above ambient pressure and adding water to the combustion air, and supplying the pressurized combustion air to which water has been added to a combustion chamber. An emulsion of fuel and water is sprayed into the combustion chamber. A desired rate of supply of water to the combustion chamber is determined and, in the event that the desired rate of supply of water changes, the rate of supply of water to the combustion chamber is adjusted by regulating the addition of water to the combustion air.

Abstract: Method of reducing nitrogen oxide (NOx) emissions in a supercharged piston engine, in which the pressure of the combustion air is increased to a level higher than that of the ambient pressure by means of a supercharger equipment and in which water is sprayed as an emulsion into the engine's combustion space with the same injection equipment as in connection with the fuel injection and, further, the water content of the combustion air is increased before bringing the combustion air into the engine's combustion space.