A comparison between in cylinder measurements of soot and NOx patterns and 3D computations of Diesel combustion

In the present paper the status of development of diesel combustion and pollutant formation modelling at Diesel Engines and Fuels Research Division of Istituto Motori is pointed out. The main features of the model are discussed comparing the numerical results with some experimental data. For the experiments two single cylinder direct injection diesel engines were used. In the head of both engines two small quartz windows have been mounted to obtain pictures of the injection and combustion processes by high speed cinematography, and to apply the two colours technique for soot temperature and soot loading measurements. One of the two engines may be also equipped with a second head, in which a fast acting valve allows the direct sampling of the combustion products. To simulate the diesel engine combustion an improved version of the Kiva II code was used . A coupled soot formation and combustion model, assuming acetylene as crucial pyrolitic specie, was also set up. Finally the Zeldovich' mechanism was added to perform computations of NO concentrations . The numerical results were compared with the experimental ones in a number of test cases using Tetradecane and n-Heptane fuels. Numerical results demonstrate that the reduced kinetic soot model can reproduce the right scaling of soot and pyrolitic products locally in the combustion chamber, also if the absolute accuracy of the predictions is not fully satisfactory: the model over predicts both acetylene and soot volume fraction and under predicts NOx. As consequence the numerical fitting of the experimental measurements of the overall exhaust emissions can be obtained only with the introduction of further empirical multiplying factors