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What a light off activity test is?
A kind of engine test, to measure the catalyst activity @ equilibrium conversion through increasing T experiment + decreasing T experiment .
possible variation of light-off test, the effect?画图
- static procedure:↑ and ↓ T stepwise, ➭ conversion(%) vary follow T with a little delay.
- dynamic procedure:↑ and ↓ T continuously (through N & load variation).
- light-off temperature:(T 50 -value) the temperature at which 50% conversions of ex gas is achieved.
what is lambda sweep tests?
A kind of engine test, to measure the catalyst activity @ constant T(above light off) through increasing λ (<1 ~ >1) .
possible variation and effects of λ sweep activity test? 画图
- static procedure: ↑ λ stepwise :
- NOx conversion ↓ and suddenly 0,
- CO, HC conversion ↑, when λ=1 suddenly increase over NOx%.
- pseudo-dynamic procedure: ↑ λ average stepwise, high amplitude:
- same conversion as static.
- dynamic prodcedure: continues λ variation 三角波
- λ = 1 conversion & X- ove conversion: HC,CO conversion = NOx conversion
*What parameters will increase CO conversion?
- increase temperature
- Increase lambda
constituents of a typical 3-way catalyst(E4 level)? and Oxidation catalyst or SCR catalyst for diesel?
- 3-way catalyst: 1)washcoat constituents: Al2O3>CeO2>ZrO2>alkaline earth (20~100g/L) 2)precious metals: Pt,Pd>Rh(全称） (15~100 g/cu.ft)
- oxidation catalyst: Al2O3>SiO2>TiO2, Zeolites>V2O5>Pt>Pd
- SCR catalyst: Al2O3, TiO2, Zeolites>V2O5
elaborate mechanical deactivation:
- Destruction of insulating mat;
- Breaking of substrate;
- Erosion & Plugging of substrate;
example of catalyst mechanical deactivation:
- 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.
- constituents: Ce2O3
- engine: gasoline engine
- catalyst: three-way catalyst
*How does Oxygen storage/desorption of CeO2 enable OBD of TWC by 2 lambda sensor?
ceramic wall thickness
washcoat secondary particle
washcoat meso- & micropores
washcoat primary particle
precious metal particle
primary particle micropores
- inlet hole
- ceramic wall thickness
- layer thickness
- washcoat macropore
- washcoat secondary particle
- washcoat meso- & micropores
- washcoat primary particle
- precious metal particle
- primary particle micropores