Motorists Sue Over 'Hot' Fuel

i_like_spam writes "Motorists in 13 states have filed lawsuits against big oil companies and gas retailers alleging unfair pricing practices related to fuel-pumping temperatures. From an industry standard developed in the 1920's, the price for a gallon of gasoline is based on the density of the fuel at a temperature of 60 degress F. A gallon of gas at higher temperatures is less dense, and therefore contains less energy. The lawsuits claim additional costs of 3 to 9 cents per gallon without temperature adjustments. The fuel industry claims that the costs of installing temerature-adjustment sensors on every pump would be prohibitively high. These sensors are already installed in Canada, however, where the colder temperatures favor consumers."

Comments

Coefficient of expansion

[mdsolar]

This site give the coefficient of thermal expaansion for gasoline: http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Th ermal/ThermExpan.html. For a 20 C increase in temperature I get about a 2% increase in volume or a 6 cent difference for $3/gal gas. So the article seems about right.
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Re:Congressional testimony on Hot Fuels

[Graff]

You are probably spot-on here. I calculate that if the temperature of the fuel is 100 degrees Fahrenheit then we are talking about a 2.11% increase in volume. This is calculated by the following formula:

Vf = Vi x (1 + 950 x 10^-6 x (Tf - Ti))

Vf is final volume, Vi is initial volume, Tf is final temperature in Celsius, Ti is initial temperature in Celsius

However, as you said, the fuel is stored underground and in the time it takes for it to get pumped up and metered out it probably changes very little in temperature. The worst case is a 2.11% increase in volume but the reality is probably a minute fraction of that.

The best thing would be to have meters that measured by mass or by density and rate of flow instead of by volume. I'm not sure what sort of metering they are using for their measurement but it's probably a simple flow rate meter which assumes a certain density to calculate volume. That's one of the more simple and least costly designs to use.

Dipsticks

[DynaSoar]

... And I say with with vehement disgust in lieu of stronger words. I like stronger words, but those to whom they'd refer have their heads someplace where they couldn't hear them clearly, so I'll save them.

When I was crawling in and out of underground fuel tanks in a space suit (not really, but we called it that; the air supply was via a hose, not an air tank) I picked up more than a couple pertinent details. And after reading this article I went and looked up a couple more.

The underground temperature at the depth most tanks must reside is between 54 and 58 F depending on location (and varying 1 to 2 F over a year), not 64.7. That figured was arrived at by a company that sells the same kind of equipment this article talks about. They have a vested interest in the data. Not stated is when the measurement is taken -- just after a 5,000 gal. tanker dumps its load into a 20,000 gal tank?

Tanks need to be more than just under the surface. They need to have enough ground covering them so they don't float up out of the ground through bouyancy. Many are tied down by steel straps to a concrete cradle for this reason, but the depth underground is a fail-safe and still adhered to. They also have to be well underground anywhere a vehicle has to drive over them, or a concrete apron will cover them, so the weight above will be spread out and not collapse the tank. Thus, they're almost invariably below the level where variations will be more than a degree or two.

The average annual temperature temperature where I am, Dallas-Fort Worth, is 64.5 F. The expansion of gasoline from 60 to 64.5 is ~0.3% (0.00069 per degree F; diesel is less, 0.00050 per). The amount of gas above the ground in a piping and pump system is the only part of a fill up that'll be affected by air temperature, and then only if it sits long enough to equalize. The volume involved is from 0.5 to 1.5 gallons depending on distance from riser and style of pump+hose. The rest of what's pumped will come right from underground and will be at or less than 60 F.

If this passes, the average US driver will lose the benefit they're already getting due to the average temperature being less than 60 F. The average temperature from 1900 to 2000 is less than 60 over almost all the US (according to plots from data at NOAA's Earth Systems Research Lab http://www.cdc.noaa.gov/USclimate/USclimdivs.html) . The expansion of the small portion of gas above the riser will be negative for more people than not, more of the time than not. It'll be a contraction.

They'll also pay even more because they'll foot the bill for these devices and their installation; the big oil producers will just plow these costs into the price, and it'll never be noticed, because they can raise the price 10 times that amount, then drop it 9 of that 10, and people will think the price is so close to what it started at that they won't think about it twice.

I had more than a passing familiarity with the issue. Besides going into tanks to inspect them, I also did the annual volumetric testing of gas pumps. I had to apply the correction factor. Where I was, the upper peninsula of Michigan, the average air temperature was very much less than 60. It was 32 F when I moved there in 1976. However, we applied the correction, or rather tried to, based on measuring the temperature of the fuel in the testing can. There was a thermometer built into the glass tube on the side of the can's neck where we also measured the gas level in 0.1 in^3 increments (one part on over 10,000 for the 5 gallon testing can). The temperature was never, as far as I can recall, ever outside the 50s F range.

I'd like to hear from someone up in the Great White as to exactly why they have those temperature sensing devices installed. Whose idea was it, the gas companies' or the peoples'? The article(s; I've looked at several elsewhere) seems to imply the former, but I can't find anything explicit on it.

As a Former Service Station Owner...

[doradox]

I can tell you we received the "correction" and it went both ways. We'd break about even spring/fall (very little correction)with summer/winter( making a little more in summer vs. winter) giving us an small overall gain. For the whole year it was on the order of about $.005 US/gallon. Our market would have have adjusted retail prices to compensate had we not received the correction. When one makes 5 cents per gallon 1/2 cent can be the difference between staying in business or not. This is a non issue.

Steve