5.7 Why are "cold start" emissions so important?
Description
This article is from the Gasoline FAQ, by Bruce Hamilton with numerous contributions by others.
5.7 Why are "cold start" emissions so important?
The catalyst requires heat to reach the temperature ( >300-350C ) where it
functions most efficiently, and the delay until it reaches operating
temperature can produce more hydrocarbons than would be produced during
the remainder of many typical urban short trips. It has been estimated that
70-80% of the non-methane HCs that escape conversion by the catalysts
are emitted during the first two minutes after a cold start. As exhaust
emissions have been reduced, the significance of the evaporative emissions
increases. Several engineering techniques are being developed, including the
Ford Exhaust Gas Igniter ( uses a flame to heat the catalyst - lots of
potential problems ), zeolite hydrocarbon traps, and relocation of the
catalyst closer to the engine [76].
Reduced gasoline volatility and composition changes, along with cleanliness
additives and engine management systems, can help minimise cold start
emissions, but currently the most effective technique appears to be rapid,
deliberate heating of the catalyst, and the new generation of low thermal
inertia "fast light-up" catalysts reduce the problem, but further research
is necessary [76,82].
As the evaporative emissions are also starting to be reduced, the emphasis
has shifted to the refuelling emissions. These will be mainly controlled
on the vehicle, and larger canisters may be used to trap the vapours emitted
during refuelling.
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