[alfa] Manifold heat and cold starting

[C M Smith <cmsmith@xxxxxxxxxxxxxxx>]

Enrichment for cold starting is required because the cold gasoline droplets 
do not vapourize as readily when the engine is cold. In essence, you dump 
more fuel in so that enough of it vapourizes to create an ignitable 
mixture, the rest of the fuel vapourizes and burns during the combustion 
process, but without the extra fuel the mixture would be too lean to ignite.

Heated intake manifolds are beneficial for street cars because the fuel 
droplets in the intake stream (whether fuel injected or drawn through 
carbureter venturis)  tend to land on the intake manifold walls and so lean 
out the mixture much as for a cold engine. Heating the manifold walls 
reduces this tendency without significantly heating the intake air.

With modern port injection you tend not to see much manifold heating, but 
the throttle body is usually still heated to prevent icing issues.

Cheers

Michael


Michael Smith
White 1991 164L
Original owner
--
to be removed from alfa, see /bin/digest-subs.cgi
or email "unsubscribe alfa" to majordomo@domain.elided