We all know that avgas expands when it warms up outside, as can be seen from fuel dripping out of the fuel vent. Based on this principle, wouldnt it be to our advantage, as consumers, to go to the gas station and fill up our cars when its the coolest part of day?? In doing so we would get the same amount of fuel in mass, but pay less because the gallons would be less. :rawk:
Go to gas station when its cool??
- Thread starter pkrgod
- Start date
Chris_Ford
Well-Known Member
TV Stations in Phoenix were advising that during the great gas shortage of '03... But wouldn't you have to burn some excess to leave room for when the gas expanded once it warmed up?
Oh God, I've started another physics debate
/worst physics guy ever.
Oh God, I've started another physics debate
/worst physics guy ever.
Bigey
Well-Known Member
Chris_Ford said:TV Stations in Phoenix were advising that during the great gas shortage of '03... But wouldn't you have to burn some excess to leave room for when the gas expanded once it warmed up?
Oh God, I've started another physics debate
/worst physics guy ever.
Geez chris, cant believe you care that much about my :rawk: smiley.
At least i dont repeat the same word like "cowabunga" or something.:rawk:
moxiepilot
Well-Known Member
funny that I have though about this since I started flying.
the only other part of the equation that I can bring to this thread is that temperature effects the density of the liquid and the machine measures the volume.
the question now becomes, how signifigant is that with a compresable liquid?
the only other part of the equation that I can bring to this thread is that temperature effects the density of the liquid and the machine measures the volume.
the question now becomes, how signifigant is that with a compresable liquid?
ananoman
New Member
"the question now becomes, how signifigant is that with a compresable liquid?
"
The last I checked, gasoline was not compressable, but 100/130 avgas will vary from 6.14 lb/gal at -4 F to 5.73 lb/gal at 104 F. If you are fueling a large aircraft the fuel temperature can make a noticable difference due to the quantities involved. In a car it is not much of a factor due to the fact that most stations don't have tanks that are above ground. Once you get 3-4 ft underground it is usually a pretty constant 55 F.
"
The last I checked, gasoline was not compressable, but 100/130 avgas will vary from 6.14 lb/gal at -4 F to 5.73 lb/gal at 104 F. If you are fueling a large aircraft the fuel temperature can make a noticable difference due to the quantities involved. In a car it is not much of a factor due to the fact that most stations don't have tanks that are above ground. Once you get 3-4 ft underground it is usually a pretty constant 55 F.
moxiepilot
Well-Known Member
brain fart, of course liquids are incompressible. I was thinking about density...go ahead, just ignore me.
OldTownPilot
Well-Known Member
here is the engineer coming out in me, be warned.
The coeficient of thermal volumetric expansion (beta) of gasoline is 950 X 10 ^ 6 (1/C) or .00095 in english units it is .000538 (1/F) as per http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Thermal/ThermExpan.html we can assume this number is constant through the temp. ranges that we are dealing with.
The temperature in the tanks may vary seasonally (in Maine anyway) from 50F to 58F causing a .43% change in volume.
On a bitter cold day say 0F the temperature of the gas bay dip to 48F before the meter, remember the moving gas creates heat internally so the dip is rather small, on a warm winter day the temp will stay near 50F causing a .11% change in volume. I would assume that the differences in the summer would be simmilar.
Here is a chart comparing the change in temperature to change in volume:
1 .05%
2 .11%
3 .16%
4 .22%
5 .27%
8 .43%
10 .54%
15 .81%
18.6 1%
20 1.08%
30 1.61%
One can interpret these percentages as "sale" percentages based on the temperature change. Remember the most you may get is 3-5 degrees or so within the time period that you need to fill 'er up. resulting in a net savings of .2% or so. For example on a $30 dollar purchase you are saving 6 cents for freezing yo' a** off. However on a 20 gallon tank you would be loseing .04 gallons (about 1 cup) out of the fuel vent.
Clear as mud, right?
The coeficient of thermal volumetric expansion (beta) of gasoline is 950 X 10 ^ 6 (1/C) or .00095 in english units it is .000538 (1/F) as per http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Thermal/ThermExpan.html we can assume this number is constant through the temp. ranges that we are dealing with.
The temperature in the tanks may vary seasonally (in Maine anyway) from 50F to 58F causing a .43% change in volume.
On a bitter cold day say 0F the temperature of the gas bay dip to 48F before the meter, remember the moving gas creates heat internally so the dip is rather small, on a warm winter day the temp will stay near 50F causing a .11% change in volume. I would assume that the differences in the summer would be simmilar.
Here is a chart comparing the change in temperature to change in volume:
1 .05%
2 .11%
3 .16%
4 .22%
5 .27%
8 .43%
10 .54%
15 .81%
18.6 1%
20 1.08%
30 1.61%
One can interpret these percentages as "sale" percentages based on the temperature change. Remember the most you may get is 3-5 degrees or so within the time period that you need to fill 'er up. resulting in a net savings of .2% or so. For example on a $30 dollar purchase you are saving 6 cents for freezing yo' a** off. However on a 20 gallon tank you would be loseing .04 gallons (about 1 cup) out of the fuel vent.
Clear as mud, right?
OldTownPilot
Well-Known Member
Sorry guys to bore you with the details, but as a 3rd year Mechanical Engineering student, the thermal expansioan stuff was pretty easy. Just dont get me started on fluid flows, pi terms and partial differential equations.
Actually I am getting quite burnt out with the engineering stuff, and the more I get into it, the less I want to do. Hence coming here and learning to fly.
Actually I am getting quite burnt out with the engineering stuff, and the more I get into it, the less I want to do. Hence coming here and learning to fly.