The environmental impact of exhaust air pollution from ships has attracted great public attention. The world's naval fleet releases a significant amount of nitric oxides NOx into the atmosphere due to the characteristics of the combustion process typical for two-stroke marine diesel engines and the use of heavy fuels. Knowing the process of generating exhaust emissions and determination of influential parameters are important factors in improving the two-stroke slow-speed marine engines, particulary for further fuel consumption reduction and stringent regulations on the limitation of nitrogen oxide emissions. So far, researches in techniques and emissions reduction methods have revealed that there are economic and technical problems with the application of the developed technologies to marine propulsion engines, which calls implementation and fullfilment of strict legal regulations into questions. In this doctoral thesis, a model of a marine slow-speed two-stroke diesel engine has been developed. Experimental and numerical analyses of the nitrogen monoxide formations were carried out. When measuring the concentration of nitrogen oxides in the exhaust emissions, the amount of nitrogen dioxide (NO2) is usually measured, since nitrogen monoxide is very unstable and due to the large amount of oxygen in the exhaust gases it is rapidly converted into nitrogen dioxide and its amount is included in the total emission of nitrogen oxides. The model fuels and combustion stoichiometry, kinematics of the piston mechanism, developed temperature in the cylinder, change release heat and formation of nitrogen monoxide have been thoroughly elaborated. The most significant parameters for the formation of nitrogen monoxide have been determined. Model validation was performed based on measured combustion pressures, engine power and concentrations of nitrogen oxides at 25%, 50%, 75%, 100% and 110% of maximum continuous engine load. The posibilities of fuel consumption optimization and reduction of nitrogen monoxide emissions by correcting the injection timing and changing the compression ratio were examined. The results of the study indicate that by optimizing the injection timing and compression ratio parameters fuel oil consumption can be reduced and nitrogen monoxide emissions can be successfully corrected to comply with the exhaust emissions standards.