High temperature corrosion at urea dosage in heavy-duty trucks

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Examensarbete för masterexamen
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2020
Författare
UDHAYAKUMAR, PRANESH
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Sammanfattning
Increasing strict norms of emission control for automotive makes the manufacturers to reduce the unwanted emissions.This can be possible by improving the engine efficiency which eventually increases the engine operating temperature particularly in exhaust line where the higher temperature may lead to varying thermal load on the materials of the exhaust line.The increase in temperature may gradually increase the concentration of NOx as well.However,to reduce NOx emission from heavy duty trucks can be done by the most promising technology called selective catalytic reduction,a state-of-the-art technique which is being used in the exhaust system of the truck.Aqueous solution of urea (32.5% of Urea and 67.5% of water) is injected into the SCR system to reduce the NOx into nitrogen,water and oxygen by reduction reaction.But in this thesis work urea is not used whereas the ammonia is used in the simulated gas.As mentioned earlier,when the material is exposed to exhaust gas mixture (with urea) and higher operating temperature in exhaust line may have a severe effect on the materials used in terms of material degradation like lowering the mechanical properties, spallation into the downstream of the engine which is a very serious issue.The currently used SiMo51 for exhaust manifold and 1.4509 for silencer are showing certain drawbacks such as lacking reliable behaviour in higher temperatures over a long thermal load cycles and material degradation.In this study,different materials are exposed in the simulated exhaust gas atmosphere at 700°C and 550°C for 168h.Two atmospheres were used ,one as without ammonia (taken as a reference) and the other with ammonia (aqueous urea).Both ferritic and austenitic grade materials of wrought and cast group were used.Corrosion resistant behavior of stainless steels are complicated with oxygen and water present together in the environment.The materials developed iron rich oxide and Cr rich oxide on the surface, but some materials developed internal oxidation which might degrade the mechanical properties of a material as discussed earlier.
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High Temperature Corrosion, Ammonia, Austenitic and Ferritic Stainless Steel, Exhaust after-treatment, Oxidation, Nirtiding
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