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Diesel costs


Dunworkin

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6 hours ago, Chewbacka said:

In this weather don't fill the tank to the top you need about 10% empty as the diesel is cold and when the sun beats down onto you boat and heats the tank the fuel will expand and you don't want it overflowing into the canal.

 

Twaddle.

 

Please show your calculations if you disagree. 

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15 minutes ago, Wanderer Vagabond said:

 

  The last fill up I had was at Hawne Basin which I think was selling at 66p Domestic/£1.13 propulsion so an 80/20 split on 100 litres would cost £75.40

You will not find anyone to match them and today I think he will do well at 80P

6 minutes ago, Mike the Boilerman said:

 

Twaddle.

 

Please show your calculations if you disagree. 

I have seen boats that were filled to the brim in autumn spewing out of the vent on a warm spring afternoon, I cant be ***** to look up the coefficient of expansion for diesel

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2 minutes ago, Mike the Boilerman said:

 

Twaddle.

 

Please show your calculations if you disagree. 

Can you explain why on my last two refillings, despite leaving a gap of at least 5 litres (probably more) below the filler pipe, within half an hour I've had to come out and syphon another 5 litres out of the tank to stop the diesel coming out of the fuel tank vent and into the cut? 10 litres might not be 10% of a 160 litre tank (6.25%), but that is sort of splitting hairs.

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4 minutes ago, ditchcrawler said:

You will not find anyone to match them and today I think he will do well at 80P

I have seen boats that were filled to the brim in autumn spewing out of the vent on a warm spring afternoon, I cant be ***** to look up the coefficient of expansion for diesel

 

That's because if you could, you'd find the assertion I quoted was twaddle, and you know it.

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3 minutes ago, ditchcrawler said:

You will not find anyone to match them and today I think he will do well at 80P

 

It was only on 2nd June that I filled up. I agree that where I am at the moment (Worcester) I wont get anywhere near matching the Hawne Basin (or Turners on the Shroppie) price.

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7 minutes ago, Mike the Boilerman said:

 

That's because if you could, you'd find the assertion I quoted was twaddle, and you know it.

Why did you say that,it made me look it up, cold diesel on a hot day, 160 lts could make an extra couple of lts but if the boat trim changes then the level could be nearer the vent to start with maybe.

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1 minute ago, ditchcrawler said:

Why did you say that,it made me look it up, cold diesel on a hot day, 160 lts could make an extra couple of lts but if the boat trim changes then the level could be nearer the vent to start with maybe.

That may well be the issue with my boat, not having the inclination to dismantle the vent, I don't know how close to the fuel surface it is when the fuel is about 5 litres below the filler tube. What I do know however is that in hot weather (and with a warm engine since that also heats up the diesel tank) if I don't leave a substantial gap several litres will either go into the cut or if I notice beforehand, get syphoned out into a 5 litre canister I carry for exactly that purpose. I suppose that next time it happens I could just ignore it and tell myself that I'm imagining it:unsure:

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Perfect reply... Spot on as to what I was trying to get some context around. I had overlooked the point you make about topping up when it gets down to around 60 litres or so... Just goes to underline the learning curve ahead but hopefully one that will be such good fun. ??

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THERMAL EXPANSION Like all liquids, diesel fuel expands slightly in volume as its temperature increases. The coefficient of thermal expansion measures the rate of the expansion. A typical value of the coefficient of thermal expansion for diesel fuel is 0.00083 per degree Celsius (0.00046 per degree Fahrenheit). Using this value, 1.000 gallon of diesel fuel at - 7 °C (2 0°F) will expand to 1.037 gallons at 3 8°C (100°F).

... meaning if your tank has a capacity rated at 25 gallons it is possible for it to expand up to 25.925 gallons in the described scenario. Meanwhile, a tank designed to hold 25 gallons of fuel must be designed to be at 95% capacity maximum, which means a tank that can hold 25 gallons will actually be a 26.31579 gallon tank to allow 5% for expansion. That means that in the above scenario there would be 0.39079 gallons of empty space left after expansion.

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36 minutes ago, Mike Hurley said:

THERMAL EXPANSION Like all liquids, diesel fuel expands slightly in volume as its temperature increases. The coefficient of thermal expansion measures the rate of the expansion. A typical value of the coefficient of thermal expansion for diesel fuel is 0.00083 per degree Celsius (0.00046 per degree Fahrenheit). Using this value, 1.000 gallon of diesel fuel at - 7 °C (2 0°F) will expand to 1.037 gallons at 3 8°C (100°F).

... meaning if your tank has a capacity rated at 25 gallons it is possible for it to expand up to 25.925 gallons in the described scenario. Meanwhile, a tank designed to hold 25 gallons of fuel must be designed to be at 95% capacity maximum, which means a tank that can hold 25 gallons will actually be a 26.31579 gallon tank to allow 5% for expansion. That means that in the above scenario there would be 0.39079 gallons of empty space left after expansion.

 

I am not arguing that that is the theoretical / 'legal' (?) requirement but in the real world no one knows to within a few litres how much is in their tank, and I guess few even know what their tank is 'rated' to hold.

 

With the car and boats, I just put the fuel nozzle in and fill until the nozzle 'clicks' and stops dispensing, pay the man and toddle off - after the first few minutes (car) or hour (boat) the fuel used ensure the level has dropped below the filler.

 

I certainly don't start doing mental arithmetic :

 

Tank is rated at 210 litres

I have 45 litres in the tank

So if I put in 165 litres it will be full, 

But - I must leave a 5% 'expansion space', so if I fill it then I'll need to siphon out about 10 litres.

 

Or :

 

I put 155 litres in .

 

ALL ASSUMING I KNOW EXACTLY WHAT I HAVE LEFT IN THE TANK TO START WITH

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Just looking at the figures quoted for the split.  I'm pretty certain that the "60/40" split often quoted is 60% propulsion, 40% domestic, i.e. the propulsion percentage is first.

 

A lot of people seem to be quoting figures where the propulsion percentage is first (do you really want to claim 80% propulsion?).

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2 hours ago, Mike Hurley said:

THERMAL EXPANSION Like all liquids, diesel fuel expands slightly in volume as its temperature increases. The coefficient of thermal expansion measures the rate of the expansion. A typical value of the coefficient of thermal expansion for diesel fuel is 0.00083 per degree Celsius (0.00046 per degree Fahrenheit). Using this value, 1.000 gallon of diesel fuel at - 7 °C (2 0°F) will expand to 1.037 gallons at 3 8°C (100°F).

... meaning if your tank has a capacity rated at 25 gallons it is possible for it to expand up to 25.925 gallons in the described scenario. Meanwhile, a tank designed to hold 25 gallons of fuel must be designed to be at 95% capacity maximum, which means a tank that can hold 25 gallons will actually be a 26.31579 gallon tank to allow 5% for expansion. That means that in the above scenario there would be 0.39079 gallons of empty space left after expansion.

This is pre-supposing that all the expansion that is taking place is just from the fuel. Not having dismantled it I don't know the workings of the fuel tank vent (contained in the port side mooring bollard) but if there is any pipe from it going into the fuel tank then if the pipe goes below the level of fuel in the tank once filled it would be the expansion of the air above the fuel that is driving the diesel out of the vent when overfilled. All that I do know is that without a significant gap between the bottom of the filler tube and the top of the diesel in the tank, in hot weather, several litres will come up out of the vent and into the cut (and how do I know that?:unsure:).

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3 hours ago, Robbo said:

200 litres of diesel will expand by about 2litres of a increase of 10°C.  - Source JFGI

 

So as I said, the initial assertion that 10% increase in volume would occur is wrong by a factor of 10.

 

Another factor overlooked is the tank itself will be the same temperature as the diesel, and when the diesel warms up on a hot day, so will the tank. So the tank itself will expand in volume and capacity when warming up too. 

 

So the calculation will need to use the difference between the volumetric coefficients of expansions of diesel and of steel.

 

And there is a third major factor still being overlooked in this argument!

Edited by Mike the Boilerman
For clarity
  • Greenie 1
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I don't know much about diesel and I hadn't heard that it can expand.  Now I don't know who to believe.  I usually fill right to the top and never had a problem.  How much space should I be leaving?

20 minutes ago, Mike the Boilerman said:

 

So as I said, the initial assertion that 10% increase in volume would occur is wrong by a factor of 10.

 

Another factor overlooked is the tank itself will be the same temperature as the diesel, and when the diesel warms up on a hot day, so will the tank. So the tank itself will expand in volume and capacity when warming up too. 

 

So the calculation will need to use the difference between the volumetric coefficients of expansions of diesel and of steel.

 

And there is a third major factor still being overlooked in this argument!

What's the third factor?

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3 hours ago, Mike Hurley said:

THERMAL EXPANSION Like all liquids, diesel fuel expands slightly in volume as its temperature increases. The coefficient of thermal expansion measures the rate of the expansion. A typical value of the coefficient of thermal expansion for diesel fuel is 0.00083 per degree Celsius (0.00046 per degree Fahrenheit). Using this value, 1.000 gallon of diesel fuel at - 7 °C (2 0°F) will expand to 1.037 gallons at 3 8°C (100°F).

... meaning if your tank has a capacity rated at 25 gallons it is possible for it to expand up to 25.925 gallons in the described scenario. Meanwhile, a tank designed to hold 25 gallons of fuel must be designed to be at 95% capacity maximum, which means a tank that can hold 25 gallons will actually be a 26.31579 gallon tank to allow 5% for expansion. That means that in the above scenario there would be 0.39079 gallons of empty space left after expansion.

But you dont run the tank empty and they buy 25 gallons, you just fill it up so if you had 10 gallons left you could put another 16.3 in to fill it.

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1 hour ago, doratheexplorer said:

 

What's the third factor?

 

The temperatures of the tanks on my boats are largely governed by the canal water temperature, with them all being in the bilges. I know some tanks are in the counter block but even these have a significant surface area exposed to the uxter plate, which is normally in the water.

 

There is a forth factor too ;)

Edited by Mike the Boilerman
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6 minutes ago, Mike the Boilerman said:

 

The temperatures of the tanks on my boats are largely governed by the canal water temperature, with them all being in the bilges. I know some tanks are in the counter block but even these have a significant surface area exposed to the uxter plate, which is normally in the water.

 

There is a forth factor too ;)

I don't know about the canals where you are, but round here the water is much warmer right now than it was in February.

 

What's the forth factor?

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5 minutes ago, doratheexplorer said:

I don't know about the canals where you are, but round here the water is much warmer right now than it was in February.

 

What's the forth factor?

If you filled up in February and not used a drop since then you need to cruise more!

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9 minutes ago, doratheexplorer said:

I don't know about the canals where you are, but round here the water is much warmer right now than it was in February.

 

 

I don't see what that has to do with the price of eggs. We are considering the rise in the temp of the diesel between dispensing it into the tank at say 8.30am (when it might have cooled overnight in the yard tank) and later afternoon when the sun might have warmed it up in the boat tank.

 

The forth factor is the rate at which the sun can transmit heat energy into the diesel raising its temperature, through the limited surface area of steel.

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10 minutes ago, Mike the Boilerman said:

 

I don't see what that has to do with the price of eggs. We are considering the rise in the temp of the diesel between dispensing it into the tank at say 8.30am (when it might have cooled overnight in the yard tank) and later afternoon when the sun might have warmed it up in the boat tank.

 

The forth factor is the rate at which the sun can transmit heat energy into the diesel raising its temperature, through the limited surface area of steel.

So it's best to buy diesel in the afternoon?

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In my part of the world it gets to 40c in the summer and our trucks would leak from the tanks if they were filled up and parked in the sun. I can only go by experience, no problem in the cooler days but the hot ones would result in puddles of diesel under most of the trucks.

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