Re: [Phys-L] cars, gas, and mileage

[Bernard Cleyet <bernardcleyet@redshift.com>]

On 2013, May 16, , at 20:41, marx@phy.ilstu.edu wrote:

> It's not about freezing...
>
> http://www.bellperformance.com/blog/bid/49483/Fuel-Mileage-Dropping-Blame-The-Winter-Blend-Gasoline


That's only part of it -- Tother is the tire pressure unless one reduces the P. to compensate.   One may experience a 7% seasonal pressure increase, especially in the unpleasant areas of the country, i.e. sno then desert.  And there's the density of the air and humidity.  With zero humidity the diff. from zero to 30 C is - ~10% and w/ 50% humidity a further decrease to - ~ 11%.    Since the drag is directly proportional to the density ......     


Air Density Calculator

http://www.denysschen.com/catalogue/density.aspx


Not incidentally petrol is a mixture, so you'll have fractional freezing, but you'll get viscosity sufficient for non operation at, my guess,   -30C.   Octane freezes at -56 C.  Methanol -98 C.  This is only one of the probs. in Antarctica.


bc lives where it rarely is < 10c and > 25C (mid-day)

p.s. I do notice a diff. summer and winter when traveling to Si Valley -- often  12 C vs. > 30 C.