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CHEE 323

28.12

TWC Catalyst Design: The Start-up Problem

A poorly adjusted vehicle can fail

a modern emissions test within

the first 100 seconds of operation,

especially if the choke is needed

for starting.

In region I shown at right, the

catalyst is at too low a temperature

to be effective.  The “light-off” temp

of today’s catalysts is 250 to 300°C,

shown here as the end of region II

where kinetic control is observed.

Various technologies are being developed to deal with this problem

exhaust gas igniter in the exhaust line

air-pumps to promote catalytic HC oxidation and light-off

electrically heated catalyst beds

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