High temperature corrosion at urea dosage in heavy-duty trucks
Typ
Examensarbete för masterexamen
Program
Publicerad
2020
Författare
UDHAYAKUMAR, PRANESH
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
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.
Beskrivning
Ämne/nyckelord
High Temperature Corrosion , Ammonia , Austenitic and Ferritic Stainless Steel , Exhaust after-treatment , Oxidation , Nirtiding