Condensation in fuel tank

GrahamM376 said:
So you know better than the CAA and FAA? Checking for water in tanks is part of DI on all aircraft and there are various circulars advising operators to leave tanks full to help avoid the problem. I don't think there's much difference between aircraft and uninsulated tanks in boats and shore storage.
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As I said, we've been through all this before ..... and totally discounted aircraft as a suitable comparator because, as LW says, those tanks experience a change of temperature of, say 80 degrees C in 10 minutes. A boat tank experiences a change of, say 10 degrees C in 10 hours. :)

Richard
 
RichardS said:
I'm sure that there wouldn't be a concern if they were permanently operating at ground level like a boat or a car. Having said that, 1ml of water in an aircraft might be a cause for concern if it was sufficient to stop the engine ..... for obvious reasons. :)

Richard
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Any fuel system needs to be designed to cope with a certain amount of water.
When I fill my bike first thing in the morning, I look at the dew on the petrol pump nozzle and wonder how much of that the filter can cope with.
 
Thank you JumbleDuck for doing the sums in post 17.
It prompted me to look up how much water diesel will hold. At 20 deg it seems to be about 50mg/kg for petrodiesel (but up to 1200 for biodiesel). This is true solution that will not settle out.
Petrodiesel will go hazy at about 100mg/kg and given time will settle out back to 50mg/kg.
So your 1ml (cc if you prefer!) of condensation would saturate over 20 litres of dry petrodiesel or make it hazy (or lie in the bottom of the tank providing a nice water interface for the bugs) if it was already saturated. That's half your postulated tank!
 
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Plevier said:
So your 1ml (cc if you prefer!) of condensation would saturate over 20 litres of dry petrodiesel or make it hazy (or lie in the bottom of the tank providing a nice water interface for the bugs) if it was already saturated. That's half your postulated tank!
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Good point. That's why I use one of those additives which emulsifies any water which does get in.
 
JumbleDuck said:
Good point. That's why I use one of those additives which emulsifies any water which does get in.
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Which additives do that? I use Marine 16 but that's just biocide isn't it?

Edit - on Marine 16s website there is a paper explaining why (in their view) it's a bad thing to emulsify it, better to precipitate it and treat it!
 
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Plevier said:
Thank you JumbleDuck for doing the sums in post 17.
It prompted me to look up how much water diesel will hold. At 20 deg it seems to be about 50mg/kg for petrodiesel (but up to 1200 for biodiesel). This is true solution that will not settle out.
Petrodiesel will go hazy at about 100mg/kg and given time will settle out back to 50mg/kg.
So your 1ml (cc if you prefer!) of condensation would saturate over 20 litres of dry petrodiesel or make it hazy (or lie in the bottom of the tank providing a nice water interface for the bugs) if it was already saturated. That's half your postulated tank!
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and of course if the temperature drops the ability for fuel to hold saturated water is reduced hence this becomes free water. and if anybody wants to know the maximum allowed free water level in Jet A1 for aircraft its <15 ppm for commercial aircraft and <5 ppm for military aircraft . the levels are different due to the opinions of the different governing bodies. meanwhile as the temperature drops in the airspace above the fuel and the tank walls become cold, moisture droplets will form on the inside the tank which will fall into the fuel adding to the amount of free water at the bottom of the tank.

The reason fuel may be delivered from the kerbside pump with water in it is that fuel is delivered from road tankers that are at ambient or warmer (solar heating of the bowser) and often goes straight under ground where it is much cooler hence free water comes out of solution. kerbside pumps tanks that run low may suck water bottoms if they are present.
 
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There are surprising effects due to differences in temperature. A friend who has long been in the oil business and until recently owned a filling station tells me that he had a long running dispute with the vat bods about the difference in bought and sold volumes. Fuel arrives hot from the refinery and therefore less dense than when it is sold cold to the consumer. There is therefore a difference in the quantity bought and sold, this is not understood by the pencil heads who inhabit HMRC.
 
PaulRainbow said:
Not sure how one mans opinion becomes a "myth buster", when there is plenty of evidence elsewhere that water enters diesel via ambient moisture and condensation.
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But that is a different issue, surely? The 'myth' is that the air alone, in an empty or near empty tank, is the cause of condensation in tanks. The link says otherwise, as does Maine Sail in a practical test. It may well be that moisture contained in the fuel when it enters the tank settles out or, as seems most likely, water enters via a poorly sealed filler cap.
 
vyv_cox said:
But that is a different issue, surely? The 'myth' is that the air alone, in an empty or near empty tank, is the cause of condensation in tanks. The link says otherwise, as does Maine Sail in a practical test. It may well be that moisture contained in the fuel when it enters the tank settles out or, as seems most likely, water enters via a poorly sealed filler cap.
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I agree that moisture in the fuel can settle out, differences in temperature will cause that and poorly sealed filler caps and certainly known to cause problems. But moisture in the air can and will be absorbed by diesel. It surely follows that the more air in a tank, the more moisture that the fuel can absorb. This can be repeated over and over and add up to a measurable amount of water. Same with condensation, if you have half a tank of cold diesel (cooled over night for instance) and you warm the boat up it is possible to have condensation form on the inside of the tank.
 
PaulRainbow said:
I agree that moisture in the fuel can settle out, differences in temperature will cause that and poorly sealed filler caps and certainly known to cause problems. But moisture in the air can and will be absorbed by diesel. It surely follows that the more air in a tank, the more moisture that the fuel can absorb.
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Diesel can absorb very, very little water, unless you add something to it to promote emulsification. Another poster gave the figures upthread. If diesel did absorb water, there wouldn't be a problem. If condensation mattered, the streets would be littered with cars stopped by water in the fuel.
 
JumbleDuck said:
Diesel can absorb very, very little water, unless you add something to it to promote emulsification. Another poster gave the figures upthread. If diesel did absorb water, there wouldn't be a problem. If condensation mattered, the streets would be littered with cars stopped by water in the fuel.
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That's wrong. Diesel can absorb water, the saturation point depends on temperature. Once it reaches saturation point it settles in the bottom of the tank. If your diesel contains less water than the ambient air it will absorb water, diesel is hygroscopic. So you can have times when the diesel will absorb water from the air and times when the temperature drops and that water is released to fall to the bottom of the tank.
 
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