PPRuNe Forums - Temperature vs. Fuel Density

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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

Quote:

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.

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:

Here's a copy/paste from Boeings Jet Transport Performance Methods:

Quote:

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)?

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 ...

In the POH for the Cessna Caravan, the following is stated in the Weight & Balance section:

Quote:

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.