103TDI Range display

[Corey_R]

www.ocba.sa.gov.au/assets/files/volume.pdf

Oh thanks Highlander, that's an example of exactly what I'm talking about. So my points were correct. Cheers.

Good to see that this fuel act protects the distributors and retailers, but not the consumer

[logger]

We can't deny the laws of physics. ALL liquids expand when heated and contract when cooled.

Indeed they do..

For the purpose of fuel measurement there is an Australian standard which is set at 15 degrees celsius. There are regulations and procedures for volume corrections.
Here is one link for example
www.ocba.sa.gov.au/assets/files/volume.pdf

Yep?? Essentially just says liquids expand and contract. We know that.

Sorry to spoil a good argument. You even refer to hot expanded fuel and cold dense fuel, in your statement, apparently interchanging volume and mass. Some merit there though as wouldn't hot fuel be less dense as density is defined as mass divided by volume.

Yes, thats correct. Your not spoiling anything.

Mass the same, volume greater at higher temperature resulting in lower density.

Yes, I agree....and the law as of physics will no doubt also state that the volume does not vary with temp.
Which is the point I am making.. A 55 litre fuel tank fits 55 litres of hot fuel and 55 litres of cold fuel. But if you honestly think you can fit more litres into your tank on a cold day as compared to a hot day, fill your your car on a cold day. But that is rubbish and that is what I was pointing out to Coreying. The meters on the bowser will not be telling you a lie just because temperature changes, which is what he was inferring. If bowsers were to meter out fuel by weight you would fit a greater weight into your tank on a cold day that on a hot one. But this is not the case.

I hope we can agree that if two vessels contain identical volumes of the same fuel differing only by one being relatively hot fuel and the other cold, the cold fuel would be more dense and contain more energy. The latter will drive your car further all else being equal.


Now back onto the MFD range display. I find it takes quite a distance for the range to empty to change after changing driving style. I wonder if it is a time or distance algorithm that the MFD uses to make the calculation. Drove 30km somewhat briskly today @ 120~140 and range was only 450km. Return journey over same 30km trip at ~ 65kph took a full 20kph of tiddling along before the MFD range started to climb back up and over the last 10km it rose about 50km to 500km so range increase 80 km over the trip.

[logger]

The sensor system that tells you litres/100 on the MFD jumps around a fair bit even when driving at a steady state. If my maths are correct every 0.1 it changes, could represent a change in fuel use of less than a couple of Millilitres per minute which is bugger all. A jump of 1.0, from 6.0 to 7.0 l/100 when doing 100kph is difference of 16mls per minute.

[Frankenstrat]

Yes, I agree....and the law as of physics will no doubt also state that the volume does not vary with temp.

For a change in volume vs change in temperature:

Delta V= B x Vi x delta T

Delta V = change in volume
B = beta (coefficient of volume expansion of the fluid)
Vi = initial volume
delta T = change in temperature

However, as we probably all know, the tanks are situated some distance below ground where to all intents and purposes, the temperature can be regarded as stable. The fluid in the tanker delivering the fuel is quite likely to be subject to ambient temperature.

[pologti18t]

We can't deny the laws of physics. ALL liquids expand when heated and contract when cooled.

How about water?

[logger]

For a change in volume vs change in temperature:.....

You are talking about a liquid, I was talking about a container as in the fuel tank which maintains a constant volume regardless of temperature.

[gregozedobe]

Good to see that this fuel act protects the distributors and retailers, but not the consumer

Yes, it is interesting that the service stations adjust the delivery "volume" according to the delivery temperature. This is because if the fuel a tanker unloads is literally "hot from the refinery"; it will shrink in volume as it cools back to "undergound tank ambient" temp, and the servo doesn't want to pay for fuel they can't sell (the shrinkage from hot to cool).

Once it has been in the underground tank for a while it will have cooled down a bit, and that is the best time for us retail consumers to buy it.

Some people believe they are being ripped off by an inaccurate bowser because their container (jerry can or fuel tank) accepts more than its "rated" capacity, but in fact the rated capacity may be incorrect, or it may have an extra volume designed in for air to allow for fuel expansion.

In the US the "longest distance on a tankful" enthusiasts all do a "ventectomy" to their golfs so they can fill up the vent voulume with extra fuel.

[Frankenstrat]

You are talking about a liquid, I was talking about a container as in the fuel tank which maintains a constant volume regardless of temperature.

The material from which the fuel tank is made would have a coefficient of linear expansion, and therefore the volume of the container would would vary with temperature change.

By way of simple explanation, most substances expand when heated, the amplitude of vibration of the atoms increases moving the atoms further apart. The coefficient of linear expansion of stainless steel is 17 x 10^-6m/°C (assuming the fuel tank is made from stainless steel)

[hoi polloi]

How about water?

It contracts 'till 4°C - then from 4°C to zero it goes haywire..



Regards,
- Anthony.

[Frankenstrat]

The fuel tank is plastic!

I didn't know that Dermot, we pedants prefer the term polymer. It's still subject to the laws of physics though. As Scottie used to say in Star Trek, "Ach, ye canna change the laws of physics, Captain". If it gets warm it expands, if it cools it contracts.

I suppose there is a bonus, on a really hot day you get more Golf for your money!