**4. Conclusions**

In the present chapter, the problem of the 1-D simulation the fluid-dynamics, combustion and performance of SI engines has been analyzed in detail. Among the different aspects that have to be faced when approaching this problem, the discussion has been focused on the incylinder pressure evolution versus crank angle, paying specific attention to the closed-valve phase, and on the turbocharger modelling. An accurate model tuning procedure has been outlined for both topics, and indications have been given on how the model could be made predictive, even in the presence of variable coefficients (such as, for example, the in-cylinder heat-transfer coefficient and the turbine efficiency multiplier).

Although quite good results can be obtained adopting of the Wiebe approach for the simulation of combustion, provided lookup tables can be built from combustion experimental data for its coefficients, the reliability of the 1-D approach can be improved to a great extent if a predictive combustion model is used for the heat-release calculations. In this case, the researcher has different options, within the fractal or non-fractal frameworks. Attention has mainly been focused on the authors' combustion model, but acceptable results can also be obtained with any model from the literature. In general, the accuracy of the overall simulation model depends on how the various sub-model results are combined.
