destruction by erosion: erosion begin from the surface of entrance of catalyst, eat and break catalyst. When it become small, it will slip into exhaust pipe and hit back and forth, and finally become small and round.
obstruction of inlet molten iron & local melting of substrate: molten piston ring plug the inlet, and make the nearby inlet also melting(cordierite).
DIESEL-blocking or inlet surface area: soot cover alomost all the surface of entrance, if you see the crooss section may know that the channels were blocked only a few mm behind the entrance. the real origin is iron oxide from corrosion of exhaust gas collector & pipe (after remiving soottreat the samples for 2h @ 800˚C, will see red colored depoists)
thermal deactivation phenomena
stintering of PGM & WC -Particles
formation of inactive modifications
melting of the substrate
example of thermal deactivation
600˚C: washcoat reaction, sintering of Platinum(highly dispersed, ↓ active surface, irreversible), diffusion of Rhodium oxide in isomorphic Aluminium oxide
1000˚C: fase change of Aluminium oxide, formation of ἀ-Aluminum oxide, washcoat destruction
1450˚C: cordierite substrate melts
chemical deactivation phenomena
poisoning by inorganic fuel additive（S,Mn, Pb)
poisoning by inorganic oil additive ashes(P,Zn...)
poisoning by other inorganic components (Si)
examples of chemical deactivation and effects
poisoning elements distribute macroscopicly
deposits on Pt, clogging, ↓surface, partially reversible
3 methods to study the durability of catalyst:
laboratory oven ageing;
durability run on engine bench;
durability run with vehicle.
*explain if and how they constitute an abstraction of reality:
main feature of precious metal, why they are commonly used in catalyst despite their high price?
1)high melting point; 2)prefer metal state--[not easy to oxidize,when lack of O2, back to metal state]
the exhaust gas temperature of diesel engine, MPI gasoline engine and DI gasoline engine.
diesel: mostly 150~280˚C.
gasoline-DI: mostly 300~450˚C.
gasoline-MPI: mostly 330~450˚C.
New European Driving Cycle
a driving cycle consisting of four repeated ECE-15 driving cycles and an Extra-Urban driving cycle, or EUDC
is supposed to represent the typical usage of a car in Europe
is used to assess the emission levels of car engines
What the oxygen storage effect is?
What constituent performs the effect?
Which type of engine & catalyst is relevant?
effect: balance oxygen partial P, stabilize PGM dispersion, adsorption of NOx.
engine: gasoline engine
catalyst: three-way catalyst
*How does Oxygen storage/desorption of CeO2 enable OBD of TWC by 2 lambda sensor?