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outside air temperature and mpg
I have been logging the fuel economy and outside air temperature for a month or so; and thought I'd try to make sense of it. There's a nice trend, a linear fit gives mpg = (0.4*temperature) +70. Nice mix of imperial mpg and degrees centigrade - that's just what we use in the UK!
I found some figures for the "dynamic viscosity" of air and so compared figures for 10 degrees C and 20 degrees C. Air - Absolute and Kinematic Viscosity The effect on economy is 6% (78.5 and 74mpg (imp) at 20C and 10C respectively) ... and the viscosity changes by 5.3% (3.44 and 3.5). Convincing - provided I've chosen the right type of viscosity... |
The benefits are more than just aero. There's faster warmup times, warmer tires, hotter air charge, and less frequent rain.
It is not necessary to concern yourself with viscosity. Aerodynamic drag varies linearly with air density. Without a datalogger, it's difficult to know how much energy you spend overcoming aerodynamic drag, versus inertia and rolling resistance, but you can use the Tools -> Calculator link at the top of the page to concoct an estimate for steady-state driving (zero inertial loads). |
I concur that there is a linear relationship between temperature and mpg. Here are my results. This is 3 years of daily commuting, so it's as consistent as the real world can be. mpg is averaged at each point.
http://mcguckin.us/files/car/mpg_temp_2010_08.png |
...FWIW, I have 8-months worth of AM (to work) and PM (to home) mpg-vs-temperature data showing similar results.
...there's a definite trendline difference: • AM is cooler with slightly less traffic (at 0600 AM). • PM is hotter with more traffic (at 1700-1800 PM). ...overall altitude difference is 220-feet over 26.2 miles, all freeway at 65 mph. |
ecoxantia -
I agree that IAT is an important component of MPG. Here is what I found : ElmScan + Customized Scantool Software = data logging! http://ecomodder.com/forum/187883-post20.html Quote:
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I know this was from a while ago, but would you be able to post the data for your graph, in a spreadsheet or equivalent? |
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