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The use of state of the art simulation tools for effective front-loading of the calibration process is essential to support the additional efforts required by the new Real Driving Emission (RDE) legislation. The process needs a critical model validation where the correlation in dynamic conditions is used as a preliminary insight into the bounds of the representation domain of engine mean values. This paper focuses on the methodologies for correlating dynamic simulations with emissions data measured during dynamic vehicle operation (fundamental engine parameters and gaseous emissions) obtained using dedicated instrumentation on a diesel vehicle, with a particular attention for oxides of nitrogen NOx specie. This correlation is performed using simulated tests run within AVL’s mean value engine and engine aftertreatment (EAS) model MoBEO (Model Based Engine Optimization).

CFD (computational fluid dynamics) theory such as equations of conservation and of the turbulent kinetic energy are explained along with their numerical solution and the FIRE solution algorithm. The techniques are applied to different areas of four-stroke and two-stroke engines such as to a small 4-valve engine with moving piston and moving valves and different intake ports to show the in-cylinder charge movement, followed by the flow calculation and heat transfer in the water jacket and applied also to detect the velocity pattern on the front face of the catalyst, all in the same 150cc engine. One of the CFD applications to different two-stroke engines deals with the variation of manifold-diffuser-catalyst layouts to obtain an evenly distributed velocity in the catalyst. Second a fan cooling system with rotating fan indicates the weaknesses of the original layout in terms of cylinder temperature distribution and improvement steps are shown.