The other night I was filling my car with gas and shivering in the sub-zero temperature and it occurred to me that since gasoline is sold by volume, the gallon I was pumping now should have more mass than the gallon I pumped last summer.
What’s the difference in mass between a gallon of gasoline at -5° Fahrenheit and one at +85°?
Bu does outside air temperature really matter for gasoline? I assume the storage tanks at most gas stations are buried well below the frost line. Does the temperature of the gas coming out of the pump actually vary much between seasons?
The volume of the gas is exactly the same while being pumped into your tank no matter the temperature of the fuel. There would be a difference if the outside temperature was to change. Fill your tank to the top on a cool 35 degree morning but the afternoon temperature is 85 degrees, the gas will expand and your gas tank would possibly overflow. It would be just the opposite if you filled up in the heat of the day and the temperature cooled, your gas tank would be less than full. The gas pump could care less about the temperature of the fuel though, it pumps the same amount no matter the temperature of the fuel.
chukhung point was correct, though. Suppose the temperature had indeed some influence on gasoline volume. Then, for the same volume of a more compressed liquid, more molecules of gasoline could be filled, so, more mass would be available at that same volume, since it would be more compressed. But as it was said, temparature in this case wouldn’t affect gasoline that much.
Is that right? I’m too sleepy to think it over to much.
Since gasoline is sold by volume, you get more mass (and more energy) when it’s colder. Thermal expansion coefficient is about 10[sup]-3[/sup]/C so a 40C (70F) temperature difference causes a 4% change in density. (I hope I got that right, anyone want to confirm or correct?)
But remember that gasoline storage tanks are underground. The temperature variation should be much smaller than air temperature.
The standard volume of a gallon of gasoline at 60 degrees F is 231 cubic inches. The coefficient of expansion for gasoline is 950x10-6.
(change in volume)=(.000950)X(initial volume)X(change in temp in degrees celsius)
A gallon of gas at 85 degrees would occupy 234 cubic inches.
A gallon of gas at 5 degrees would occupy 224 cubic inches.
If you have a 20 gallon tank, the volume would be 4620 cubic inches.
At 85 degrees, your tank would hold 19.74 gallons of gas.
At 60 degrees, your tank would hold 20 gallons of gas.
At 5 degrees, your tank would hold 20.63 gallons of gas.
This does not take into account the expansion of your steel tank, or anything else for that matter. I don’t know if gas pumps compensate for temp changes or not.
Also, someone check my math. If I am pathetic enough to do math on a Friday night, I may be pathetic enough to screw it up.
My source shows the expansion coefficient for gasoline as being 950x10[sup]-6[/sup], but I had to look it up online, so it may be wrong. Also, 40C is 104F.
In most States in the US, there is no temperature compensation whatsoever. When the Bureau of Weights and Measures people certify the pumps, they really are typically only concerned with the volume, not the mass.
In other words - they want to certify that when the pump says “1 gallon”, it is pretty close to “1 gallon”. Mass does not (typically) enter into it for typical standard gasoline pumps.
For industrial use, there sometimes is a mass correction on the pumps, but in those cases the pumps read out in terms of “pounds” of fuel, rather than “gallons”.
Gas stations here have a sticker on the pump saying that the gas is volume corrected to 15C. IOW the guys who calibrate the measuring devices or meters use the density of gas at 15 degrees C and let the seasons over the whole year level out the slight differences due to ground temp fluctuations.
I’m not mmmiiikkkeee, but I’m in Canada. Around here there is a sticker, I believe with the Weights and Measures Canada logo, that says ‘Volume Corrected to 15 degrees C’. Of course, the average temperature in Canada isn’t 15 degrees over the year, especially in the North. But apparently (according to From the Ground Up, my pilot training manual) it’s the average tempreature for North America at 40 degrees north lattitude, and the figure used for the ICAO Standard Atmosphere.