| In the last years, the presence of diesel engines vehicles in the European car fleet has reached all-time levels, being the sale of these cars quite above of the petrol-fuelled ones. The main reason of this fact is the higher efficiency of the diesel engines (that implies a lower CO2 emission), contributing to the development and optimization of such engines. However, the vehicle industry faces up to stringent legislative restrictions on pollutants emission, being the nitrogen oxides (NOx) and the particulate matter (PM) the main regulated diesel emissions. This fact has promoted the development of emissions reduction techniques that affect, not only the combustion process, but also the pollutant emissions once they have formed, that is, acting in the exhaust system. Nevertheless, is necessary to develop theoretical models that allow improving the understanding of the physical and chemical complex phenomena causing the pollutants formation, making possible the establishment of cause-effect relationships between the engine operating conditions and the pollutant emissions level.; In this doctoral thesis, a phenomenological combustion model, which considers the space and time evolutions of a reacting diesel fuel jet, has been developed in order to estimate the instantaneous gaseous concentration (especially NO x) in a diesel engine cylinder from the start of the injection until the exhaust valve opening. The total injected fuel mass has been divided into different fuel packages, through the fuel injection rate file, to take into account the heterogeneous nature of the diesel combustion process. Due to the importance of the kinetics on the formation and destruction mechanisms of the main pollutant species and radicals, the instantaneous composition of each fuel package has been calculated by using a chemical reaction mechanism which considers 38 species and 83 reactions. A single cylinder diesel engine was tested to validate the model and to analyse the influence of the injection parameters (injection pressure, injection timing and injected fuel mass) on the NOx emissions. The model proposed in this work also provides a better knowledge of the local mixing fuel/air processes, which represent one of the most important uncertainties when modelling diesel combustion. |
