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This work describes an experimental and numerical investigation of the thermal transient of i.c. engine exhaust systems. A prototype of exhaust system has been investigated during a NEDC cycle in two different configurations. Firstly an uncoated catalyst has been adopted to consider only the effect of the gas-wall heat transfer. The measurements have been repeated on the same exhaust system equipped with a coated catalyst to point out the contribution of the chemical reactions to the thermal transient of the system. The measured values have been compared to the predicted results carried out with a 1D thermo fluid dynamic code, developed in-house to account for the thermal transient of the system and the chemical reactions occurring in the catalyst.

To identify the most significant parameters influencing the cosmetic corrosion of cold-rolled and coated steel sheets, stretch deformed panels were phosphated, painted and exposed in real time on an experimental car for 5 years. Based on advanced microanalysis techniques, the morphologies and the chemical composition of the corrosion salts are characterized. Comparisons between accelerated tests and natural exposures are made and corrosion mechanisms are identified. On that basis, a 3-step cyclic model of cosmetic corrosion is presented. Combined with the experimental results, this model outlines the importance of the coating characteristics, the compositions of the corrosion products, the humidity and temperature cycles during the exposure tests (natural or accelerated) and the environmental conditions (salts and polluting gases) on the corrosion mechanisms and the resistance of painted coated steels.