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Re: [Phys-l] Hybrid mileage

In order to meet emission requirements the cc has to be at a certain minimum temperature. A sensor monitors the cc temp and tells the car's computer to run the engine at high enough rpms to bring the cc up to temp. For a hybrid that may mean going from zero rpms to finite rpms. For a non-hybrid that may mean increasing the idle speed.

(These days you don't "drive" a car, you just point it. The computer drives it!)

From: [] On Behalf Of Stefan Jeglinski []
Sent: Tuesday, January 05, 2010 1:22 PM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Hybrid mileage

Part of the loss of mpg in the winter for a hybrid (and all other
cars) is that the engine has to run longer to bring the catalytic
converter up to temperature to meet emission reduction requirements.
And the engine has to run more to keep the converter up to


In a non-hybrid anyway, you run the engine for however long you want,
whether the CC is up to temp or not. Are you saying the temp of the
CC affects the gas useage? And/or, are engines tuned to run at
slightly higher rpm to provide extra energy to keep the CC at temp?

I don't quite get the full extent of your description. If you could
describe things in terms of energy generated/expended rather that
"engine running longer/more" it would help.

Stefan Jeglinski
Forum for Physics Educators