This thesis describes the importance and the influence of optimization of geometrical and working characteristics of diesel engine on exhaust emissions and performances of the engine. The marine diesel engine is a complex machine which contributes to polluting of the environment. To control exhaust gas emissions, MARPOL has introduced Annex VI. which limits sulfur in the fuel and the amount of nitrogen oxide in the exhaust gasses. The combustion process is a complex process in which the chemical energy of the fuel is converted to heat energy. It consists of four phases whish are described in the third part of this thesis. In the combustion process inside the cylinders, exhaust gasses are created, which is shown in the fourth chapter. The bad elements of the exhaust gasses are: nitrogen oxides, sulfur oxides, carbon monoxide, carbon dioxide and fine particles. The fifth chapter is dedicated to four stroke diesel engines and the working principle of the some engine is also shown. Since this thesis is dedicated to analysis of the exhaust gasses which are measured on four stroke diesel engine, sixth chapter described this engine with all its systems. The seventh chapter describes the characteristics of the exhaust gasses measuring device. The eight part of the thesis is dedicated to exhaust gasses parameters analysis. The measuring was done two times and compared to the manufactured's date and with the rules of the IMO-MARPOL Convention. By analysing parameters, we have established that the engine was running in an unoptimized area during harbour arrival and departure manoeuvres. To avoid adverse effects from the exhaust gasses which have a bad influence to the animals and plants, the manufactures have designed primary and secondary methods which are described in the ninth chapter. The tenth chapter is dedicated to alternative fuels, it describes the working principle of the dial fuel engine and composition of the liquefied natural gas. One of the innovations un the ship propulsion are hybrid systems that combine internal combustion engine and electromotors. One of the hybrid systems is shown and described in the eleventh chapter.