View Full Version : Temperature vs. Fuel Density


MD80rookie
28th Oct 2008, 08:52
All,

Of course density changes with temperature. Is there any constant that can be used to find our density with just the temperature available? Jet A1 considered.

Brgds
Rookie



enicalyth
28th Oct 2008, 09:56
You are really asking for the coefficient of thermal expansion of a family of kerosenes. It is given the Greek symbol “Beta” and is 0.95 – 1.00 per degree Celsius.

Unfortunately it does vary with temperature as indeed do the thermal expansion properties of plain old water.

Suppose you had a 1000 cc of kerosene at 15 deg C and it weighed 800gm. If the coefficient of thermal expansion is 0.001 per deg C then the change in volume down to 5 deg C and up to 25 deg C will be 1000 x 0.001 x10 = 10 cc

The weight of the kerosene is still 800gm, only the volume has changed.

So the specific gravity is 800/990 = 0.808 at 5 deg C for 0.800 at 15 deg C and 800/1010 = 0.782 at 25 deg C

Points to note are that a) coefficient of thermal expansion is not a constant over the whole range of temperatures you are likely to meet; b) at very cold temperatures the fuel is no longer purely liquid; c) what are the effects of the additives?

From memory F35 AVTUR is specified within a window of acceptable specific gravity of 0.775 – 0.840 but generally speaking pans out to be 0.803 and with the usual dyestuffs and additives has a coefficient of 0.99 per degree Celsius but I am none too sure about that last figure.

Flambards
28th Oct 2008, 10:07
I see the Airbus fuel readout gives a density adjusted figure. Does this mean that putting in 10 tons of hot fuel, say at 25 degrees, the cockpit guage will actually read slightly less. i.e. fuel at standard 15 degrees?

Or, as I think it does, wil it read 10 tons and will slowly contract to less as the outside temperature drops. In otherwords what we read on the guage is what we get?

Thoughts?

Oilandgasman
28th Oct 2008, 10:46
Jet A1 is a mixture of two hydrocarbon liquids distilled from crude oil. These liquids or "cuts" are kerosene and naphtha. There are slight differences in these cuts depending on the temperatures of the distillation process and the crudes used. The cuts are within a specific range and therfore are not one fixed density. Jet A1 is therefore not a fixed density either but within an allowable range.
In summer Jet A1 is a 50/50 mix of these two liquids and in winter the naphtha proportion is increased by about 5% to allow for the lower temperatures encountered.
If you wish to see the full spec, Goggle ASTM Jet A1 Specification.
In my day we also used to add anti static and an anti icing additives. These are very small amounts and will have little impact on the overall SG.
Sulphur free Jet A1 is normally water white in colour. If there is any water present, which there should not be, the Jet A1 will be a "milky white" colour.
If the Jet A1 is sold as heating oil it is known as paraffin oil. This product has a dye added to it to distinguish it from Aviation quality Jet A1. The dye is usually pink or blue depending on the company selling it. (e.g. In the UK these products were sold as Aladin Pink or Esso Blue paraffin oil.)
Other than the colour paraffin oil is Jet A1.
So including the info in the previous thread, the result is that there is not a simple constant you can apply to temperature to give you density.

BelArgUSA
28th Oct 2008, 14:36
I fly a 747-200, 10 tanks option.
In our books, the max fuel is 166,400 kg for full tanks.
It is a limitation.
xxx
Should it be hot weather, we top the tanks, and barely can put 155,000 kg.
In Siberia, in winter, topping the tanks, it is possible to fill 170,000+ kg...
That is over the weight limitations. Illegal...
xxx
One thing to remember -
Fuel is sold in litres, or gallons... by volume.
If you buy COLD fuel, you get a discount... HOT fuel is... more expensive.
Your jet engines only know weight and mass... not litres.
xxx
So, instruct fuelers to fill the tanks at the time of day fuel is cold.
Stay away from fuel trucks, the sun heats the fuel quickly.
Underground tanks might be better.
But... if you top your tanks with cold fuel, the sun will expand fuel in the tanks.
And your tanks will drip...
xxx
In my little car, I buy cold gasoline... early morning. I do not top the tank.
:ok:
Happy contrails

MD80rookie
16th Nov 2008, 21:42
You are really asking for the coefficient of thermal expansion of a family of kerosenes. It is given the Greek symbol “Beta” and is 0.95 – 1.00 per degree Celsius.


Yes! Thanks!

0.95 - 1.00 per degree celsius is exactly what I'm looking for. But is there any "standard density"? If I only have the temp and a constant I can't calculate my density unless I know what the density is at let's say 15 degrees?!

Any comments apprec.

/Rookie

el #
16th Nov 2008, 23:40
In my little car, I buy cold gasoline... early morning. I do not top the tank.

A sensible proposition, so I made some exact calculation for you, to get a figure of the saving you achieved so far.

First factor to consider, c'mon, you don't use the car that much.
Second, you haven't stayed very long in Argentina, as apparently you cannot keep yourself quiet in your life :)
Third, there is not much thermal excursion in Buenos Aires.
Finally, fuel there is cheap anyway (in western terms).

Without boring you with the math, I've calculated that you saved only AR$ 32.50. A much better saving would have been made by running the car on natural gas, even if like a taxi driver (!!!) told me once, el gas esta para la cocina.

Enough anyway for a decent bife!

galaxy flyer
17th Nov 2008, 04:16
From memory F35 AVTUR is specified within a window of acceptable specific gravity of 0.775 – 0.840 but generally speaking pans out to be 0.803 and with the usual dyestuffs and additives has a coefficient of 0.99 per degree Celsius

There's the answer, MD80rookie. It does vary, fairly widely and is a factor, if filling the tanks is a normal operation. The fueler should be able to provide that fuel's current SG.

Most jet fuel does have an SG of .803, anyway much less than the usual answer of 6.75 lb per US gallon which is 0.81 kg/l, if my conversion is right

GF

Swedish Steve
17th Nov 2008, 10:23
Is there any constant that can be used to find our density with just the temperature available? Jet A1 considered.
I work at ARN. Once upon a time I might have said yes. The density goes up as the OAT goes down. But since the ARN fuel supply was changed to the railway from Gavle the density changes with every load of fuel. We can have 0.801 fuel one day and 0.809 the next. Temp is the same. It depends on which refinery it comes from.
Anyway you call yourself an MD80 driver. One narrow bodies it doesn't make a lot of difference. On a 10000 kg fuel load, the difference between 0.793 (midsummer) and 0.813 (midwinter) is only 200 litres. We don't bother at all on our narrow bodies, we use 0.800 all the time (means I can work it out without a calculator!)

MD80rookie
4th Dec 2008, 16:12
My fellow swede,

Thank you for the answer. Different fuel load from different refinery, then you being the fuel supplier can correct for temperature with a constant. Now I can sleep at night :)

Of course, small aircraft as the MD80 = small difference in weight vs volume. But when departing from warm destinations like egypt, the quantity can change after an hour or two at cruise due to this problem...

See you!

Rookie

Swedish Steve
4th Dec 2008, 21:01
But when departing from warm destinations like egypt, the quantity can change after an hour or two at cruise due to this problem...

Yes the qty, or volume, will decrease as the fuel cools down, but the weight will stay the same. The indications on the flight deck are in kilos, and there is a densiometer in the fuel tank that adjusts the qty in litres that is measured to give you a constant weight. (or linearly reducing weight as you are flying!)

MD80rookie
5th Dec 2008, 17:53
No, the indicated weight of fuel in this aircraft is calculated by means of resistance (I happen to be type rated:8).

You see, the amount of fuel loaded in egypt will be correct on ground. Once airborne, temp decreases and volume will be slightly less due to the problem with MD80's resistance type fuel qty system. It measures the quantity and assumes a temp from the resistance. The allowed error is 270kgs with full tanks and a density of 0.803. Lower density = my margins shrink! Do you see the point?

So, if I could calculate the specific gravity with only a constant and fuel temp, I could disregard any changes in fuel temp/density at cruise.

Swedish Steve
5th Dec 2008, 20:59
Look at this
http://www.pprune.org/rumours-news/211563-careful-your-jet-fuel.html

Also
the indicated weight of fuel in this aircraft is calculated by means of resistance

Are you sure, I have a problem deciding how this works. All older aircraft I can remember have capacitive gauges.

Brian Abraham
6th Dec 2008, 01:10
The specifications for Jet A seems to call for a SG between .775 and .84 at 15°C.
See http://www.exxonmobil.com/AviationGlobal/Files/WorldJetFuelSpecifications2005.pdf

OverRun
8th Dec 2008, 07:18
Viscosity-temperature properties of Jet Fuels; PM me for a copy of the paper.

Wodrick
8th Dec 2008, 11:15
Are you sure, I have a problem deciding how this works. All older aircraft I can remember have capacitive gauges.
Certainly had float operated resistance gauges, or at least that's what I told drivers !
"Right fuel indicator sticks at 4550"
"Ice on the float guv be alright when it melts"

I would the fix it of course after they had gone

RA73
30th Jan 2011, 13:42
I've noticed the questions and answers concerning aviation fuel density and weight.

I've got a bit of a science background (I suppose many of us do) and understand about specific gravity and weight vs volume at differing temps.

(I've searched the internet, in obviously the wrong places) Can anyone offer a website or even a place to write off to, where I could get a copy of whatever chart that into plane fuelers use to give the density for their fuel when delivered at the a/c?

There must be charts for weigh vs temp for each grade of fuel, Jet A, A1 and the mil grades JP5 and 8 that are specific to that fuel with it's additives.

I don't need any slick answers or nifty science I would just like to know where I could get such graphs/charts.

We tend to use more fuel than a 747 so it becomes important and it would be nice to be able to double check what the fueler tells us.

Anybody?

Many thanks...

Swedish Steve
30th Jan 2011, 18:18
No can't be done. Jet A1 has different density from different refineries. The only way to check the delivery SG is to measure it. All the dispensers here have bottles and a little stick that floats in the fuel. The refuellers check the density on request. It is not a constant with temp, but is higher in the winter on average, than in the summer. It will be the same for a few days, and then jump when they change the delivery tank.

RA73
30th Jan 2011, 18:44
That sounds reasonable to me. That's why I always see a small range in SG's for the same temp (ie std day).

I'll stop looking and accept what the fueler shows us on the day, thanks Swedish!

DERG
31st Jan 2011, 13:19
Greeting...have the actually finalised the JP8 formula? Is it in regular use for civil aircraft? Regards

JMW
15th Nov 2011, 00:32
The temperature density relationship of hydrocarbons is defined in the Manual Of Petroleum Measurement Standards.
Originally this was a selection of tables created using hydrometers but these days the standard is not the tables but the calculation.
Hydrocarbons are divided into commodity groups and each group has a defined range of densities and a defined set of constants for the calculation.
Hence aviation fuels form one commodity group, lubricants another and so on.

As has been mentioned, the aviation fuels are blends.
Blending will be designed to deliver a fuel that satisfies a number of target properties which each have a reasonable set of limits. There are limits on density but these are go/no-go limits and hence have quite a wide range (as can be seen from the commodity group itself.) which usually means that all the products in a commodity group have density ranges that overlap to some degree or another.

The refiners run optimisation programs to maximise the profitable conversion of crude which means they will bias the production of the products within the allowable limits to enable them to suit the current crude slate and production call.
It is not unusual to find that certain properties will vary significantly one batch to another even sequential batches from a single refinery.

So, for any batch of aviation fuel you do need to know the density for that specific batch of fuel. This is usually reported by the refiner at 15degC.or can be measured on site.
However, because the temperature can vary in storage or as it is delivered it helps to know the density at the flowing temperature and apply volume correction factors.
There is a spreadsheet at Cheresources that performs all these calculations including volume correction factors. There are variants of this available from RMI (an email address is in the spreadsheet) if required.
Density to Temperature Correlations for Hydrocarbons - Cheresources.com Community (http://www.cheresources.com/invision/files/file/126-density-to-temperature-correlations-for-hydrocarbons)

Slasher
16th Nov 2011, 04:28
In my little car, I buy cold gasoline... early morning.
I do not top the tank.

You do get extra gas BelArg, but unless I'm missing
something a piston engine sucks volume not mass.

jacob5456
11th Mar 2012, 18:21
We fly in Africa and here refilers don't calculate SG so according to our procedure we have to use standard 0,79. In that case in hot conditions we get actual fuel in kg's greater by 300 to 400kg if to refill 2600ltr. So theres extra fuel not included in papers. So to equalize that we have to write down that we consume much less fuel than we do. Which is nonsense:ugh:

JeroenC
13th Mar 2012, 14:39
Here's a copy/paste from Boeings Jet Transport Performance Methods:
Did you notice that LHV decreases as fuel specific gravity increases? It might seem logical to assume that fuel that has a higher specific gravity would also produce more energy per unit of weight than a fuel having a lower specific gravity, and yet you see from the equation above that the opposite is true: lighter fuel has more energy per unit of weight.

This fact arises because denser fuels have a higher ratio of carbon atoms to hydrogen atoms. The energy of combustion of carbon is less than that of hydrogen. Denser fuel, having relatively less hydrogen, therefore produces less energy per unit of weight.

Interestingly, however, denser fuels have higher energy content per unit of volume. This is due to the fact that the higher density fuels, due to their molecular structure, can pack more molecules into a given volume such as a liter or a gallon. Although each molecule has slightly less energy, the number of molecules per unit of volume increases with density more than the energy content of each molecule decreases. The net effect is a greater amount of energy per unit of volume.


Where LHV stands for Lower Heating Value, expressed by Boeing in BTU.

Now my question is: do we wnt to know liters or kilograms ( what I thought and has been described in other posts before)?

jh5speed
14th Mar 2012, 09:05
Slasher - it may suck volume - but only that which is enough to do the job. If you have dense fuel you do not need so much volume flow rate, so you can throttle back ...

Nessus
16th Apr 2012, 02:46
In the POH for the Cessna Caravan, the following is stated in the Weight & Balance section:

Information on the Weight and Moment Tables for different fuel grades is based on average fuel density at fuel temperatures of 60°F. However, fuel weight increases approximately 0.1 pounds per gallon for each 25°F decrease in fuel temperature. Therefore, when environmental conditions are such that the fuel temperature is different than shown in the chart heading, a new fuel weight calculation should be made using the 0.1 pounds per gallon increase in fuel weight for each 25°F decrease in fuel temperature.

The above corresponds quite well with the coefficient of thermal expansion explained by Enicalyth.