expanding gas and fillups
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also... 99% of all gas stations have LARGE UNDERGROUND tanks, it takes a LOT to change the temp of the gas in the storage tanks.... as some of you may have noticed the gas going through the handle cools it off significantly
Jeff |
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As said, fuel is stored underground. And if you're in the United States at a modern station, there's a rather large concrete pad over it. The only differences will occur if your area has longer periods of drastic temp change (such as large summer/winter temp differences). The difference between morning and midday are rather insignificant.
I'm currently in central Florida - when I fuel up, I can feel the metal joints on the nozzle get cold any time during the day/night. The same happens in south Florida ;) If you're in Canada, no worries - there's a fuel density sensor to compensate (or so I've been told) :p |
Around here the air pollution folks have asked us to fuel in the evening. reduces ground level ozone.
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Yes, that is true. Since gas is stored underground, the temperature doesn't fluxuate much, but it should stay under 60F. Gas station owners have been caught warming it up a bit to reduce the actual amount coming out..
There are random screenings where an official will collect samples and test them to find these kinds of things.. |
If you take a reasonable guess at the temperature of the fuel in the tank, and look at the coefficient of expansion of gasoline, you'll likely find that there probably won't be a large enough difference to matter. For instance, over a 100F difference in temperature, 10 gallons of gasoline when cold would be 10.3 gallons when hot. I'm guessing that most underground gas tanks swing over maybe 30-40 degrees, so the difference between 10 gallons at the coldest time in winter and at the warmest in summer is probably no greater than .1 gallon, or 1%. It's more than the pump's supposed maximum margin of error at .5%, but not much more. And if you're comparing fills during the day/night of the same season, probably less than the pump's error.
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Thermal expansion can be a huge factor. Pumping in the morning helps prevent your paid for fuel from evaporating out the tank.
Stations are supposed to be selling 60F gallons but in South Louisiana that happens maybe two months a year... So the gas is normally pumped above 60F. Since the gas pump metering element is a positive displacement meter when the gas is over 60F the station makes money by selling you less fuel than indicated. In Canada I've read the pumps are temperature compensated since the looser would be the station owners due to the ground temp being below 60F. It would be a simple matter for stations to add temp compensation though. In the petroleum industry all sales by volume are also temperature and pressure compensated by published ASTM tables. That or there done by direct mass measurement. Its worth big dollars! |
Morning fillups do yield more, but it's not a whole lot more. 950x10^-6 at 20C for instance. So for every 15F difference in temperature there's about a 1% difference in energy. But, this only a concern from the perspective of the 60F standard, the average consumer won't see anywhere near that difference if they fill in the morning compared to the afternoon.
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With those HUUUUUGE tanks, even a .1% difference could add up real fast.
BTW, this should be extremely easy to test. Get a soda bottle of gas, mark it, put it in the fridge, mark it again, put it in the sun, mark it again. Empty it and figure out the volume... |
Only if you get your gas from a station that stores it in refrigerated plastic bottles at night, then puts 'em in the sun once it rises. ;) I mean, .2% can make a difference, but there are a ton of things to do that'll show much larger gains.
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What the hell are you rambling about? Pump it in a plastic bottle...
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Yer analogy. Putting it in the fridge, then the sun, is going to show a much larger difference than the driver will see at the gas station when filling in the morning compared to afternoon, unless the gas station stores their gas in the same way. :p I suppose you could measure the volume, put it in the fridge for a few minutes until it drops a few degrees, which is the difference you'll see at the station, then measure it again, but I don't think most people have accurate enough equipment to measure a .00095% difference in volume per degree C.
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BUT, the temperature change will also make your bottle shrink or expand. Plus, just on general principles, I don't want any of my pals putting gas in soda bottles.
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In soda bottles or in the fridge either. I think you would need to take a gallon gas tank and fill it at different times to see the difference if any. Good luck on the research project.
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Arrrrr, you guys take everything too literal and straightforward :P.
I was just offering an example how to measure the gas fluxuations. I wasnt saying that the gas actually changes that much, I was just proposing an way to see the drastic changes and how temperature CAN effect expansion.. If you leave the cap loose, the bottle wont change.. And perhaps we are looking at this differently. Seems I am looking at it like "how much the gas station saves by a small variable" as everyone else is thinking "how much I save"....I have a 8 gallon tank, so equals next to nothing..gas stations have 10,000 gallon tanks.. |
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Have you ever seen a sealed gas jug expand? In the afternoon itll look like its about to bust and in the night itll look like someone crushed it like a coke can. Your saying a plastic bottle wont do the same as a platic jug?
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The experimentation has already been done. The ASTM has published tables to correct for the thermal expansion of all types of hydrocarbons. There not all the same and also not linear.
If I remember I'll look up the correction factors that apply to gasoline when I get back to work next week and list a few that cover ambient temps. |
Ok I finally got round to looking up the correction factors today. The volume correction factors are taken from the ASTM book "Petroleum Measurement Tables Volume Correction Factors Volume II Table 6B".
The table requires you to know the API gravity, so I used 60API which is about an average value for gasoline. https://img502.imageshack.us/img502/4...rrectioqj1.jpg |
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