Re: [Phys-l] Hybrid mileage

["Bob Sciamanda" <treborsci@verizon.net>]

I don't drive a hybrid, but I have pondered this question of summer vs 
winter mpg values for a gas-powered car.
I come up with two (seemingly) competing effects:

1) In summer, the drive wheels typically roll without slipping.  In winter, 
rolling with significant slipping is read by the odometer as an inflated 
value for the distance traveled and so yields an inflated value for an mpg 
value calculated from odometer readings.  Of course this is an erroneous 
value of the mpg; the actual miles *travelled* per gallon is less with the 
slipping.

2.) In winter the engine runs at lower start and warmup  temperatures, and 
for a longer time than in summer.  In response, the computer feeds a richer 
gasoline mixture to the engine, during the (longer) warmup time. And even 
after warmup the lower temperature of the intake air prompts a richer 
gasoline mixture from the computer during winter  These lower air 
temperature effects  result in a diminished mpg value during the winter.

My experience is that, even using the inflated mpg values given by effect 
1), effect 2) wins.   Winter mpg readings based on odometer readings are 
typically less than summer mpg readings.

If you wish to enhance the fictitious 1) effect, run your car on blocks - 
travel zero miles per gallon but read fantastic mpg values from your 
odometer ;>)

Bob Sciamanda
Physics, Edinboro Univ of PA (Em)
treborsci@verizon.net
http://mysite.verizon.net/res12merh/

--------------------------------------------------
From: "Robert Yeend" <ryeend@sbcglobal.net>
Sent: Tuesday, January 05, 2010 3:16 PM
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Cc: "Nancy Seese" <nancyseese@redshift.com>
Subject: [Phys-l] Hybrid mileage

> A colleague asked me why it is that she consistently gets 6-8 mpg
> less in the winter than summer with her Prius Hybrid. Her mechanic
> said that that was "normal," but gave no explanation. Nor can I. She
> said that she uses the heater in the winter about as much as the air
> conditioner in the summer.
>
> Ideas?
>
> Bob Yeend
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