Seeking a healthier life leads to new measures to regulate emissions of pollutants that cause environmental problems. A significant amount of CO2 is released into the atmosphere by burning fossil fuels. Allowed emissions of pollutants from diesel engines have been regulated over the past few decades, and new, stricter regulations are expected in the coming years. These rules include European emission standards resulting from government policies as a means to reduce environmental pollution. Harmful emissions from internal combustion engines depend on the spray process, fuel atomization and the fuel-air mixing process. It can therefore be concluded that a detailed understanding of the spray process is of paramount importance for engine development. This thesis describes the spray process formed by high pressure injection of fuel through a small-diameter nozzle. It is for ecological reasons that great resources are invested in the development of new mathematical models that would sufficiently describe the spray process. Furthermore, a comparison of two spray modelling approaches, namely Euler-Lagrange and Euler-Eulerian, is presented and described. Understanding of the complex nature of spray fuels formed under high pressure in expressional research is limited and this understanding can be significantly improved by numerical simulations. At the end of the paper an analysis of spray process simulation results is presented and conclusion of the need for computation simulations of fuel injection is made.