Biodiesel in France - overwinter storage

[DBA Forum (B) - Trevor Glave]

I have heard from a couple of big barge owners that all road diesel in France is now BioDiesel and that it will significantly deteriorate if left in a a barge tank for a few months, certainly over the winter, losing maybe 20% of its energy content and maybe doing other bad things to the engine. It has been our practice in the past to leave the fuel tank topped up over the winter to minimise water condensation in the tank. (Not sure how relevant this actually is.) Would we be better off in the future to run the tank as low as possible before leaving the boat for the winter and then refilling the tank with fresh diesel at the start of the next season? Is this fuel degradation really bad news?

Trevor G. - barge 'Penelope's Ark'

[DBA Forum (B) - Balliol Fowden]

I think the jury is still out on this one and will be for a while, but I think it fairly certain that the combination of bio-diesel content and any water in the tank could prove to be bad news in respect of bug infestations. I have seen the storage life likened to petrol, but for different reasons. With petrol the problem is the evaporation of the more volatile hydrocarbons, thus loss of calorific value. I have not seen any mention of a loss of calorific value in diesel per se, but if you get the bug then there must be some effect.

Big tanks (like ours) seem to be likely to be bad news in the future. If you fill them will you use the fuel before it degrades? If you leave them part full will they gather condensation, hence encourage the bug? My intentions, rightly or wrongly, for the immediate future will be (1) not stock up on fuel, (2) drain any settled water from the tanks before the winter, (3) close off the tank vents when not drawing any significant amount of fuel, and (4), hope.

If I were to add any more fuel before the winter (unlikely now) I would make sure to add some suitable treatment whilst filling, so that it mixes. I can't see there is much point adding it afterwards unless you can stir the tank or rock the boat!

Balliol.

[DBA Forum (B) - Frank Kordbarlag]

"All road diesel is bio diesel" in France. This is wrong. All road diesel in France contains between 3-7% bio diesel is nearer the truth. And this fact should set your mind at rest. All diesel, bio or not, will draw water from the air.

So your choice is between an empty tank which attracts condensation or a full tank in which the diesel attracts moisture. In both cases you may get bugs, but with a full tank your tanks will not rust.

Frank

[DBA Forum (B) - Andy Soper]

There is an article in the Knowedge Base on the effects of bio diesel :

http://www.barges.org/knowledgebase/mechanical/uls-bio-diesel.

There are no reports of loss of calorific value - stored petrol yes.

The bugs like bio - use a additive introduced before fuelling as Balliol advises - worth including one with a cetane improver especially if you have a DAF!

Frank summarises the dichotomy well!

[DBA Forum (B) - Adrian]

On Wed, 13 Aug 2014 09:48:22 +0200, "DBA Forum (B) - Frank Kordbarlag"

Post by DBA Forum (B) - Frank Kordbarlag
All diesel, bio or not, will draw water from the air.
So your choice is between an empty tank which attracts condensation or a full tank in which the diesel attracts moisture. In both cases you may get bugs, but with a full tank your tanks will not rust.

The "condensation in non-full fuel tank" belief is pervasive among
boaters. However, I have recently read a credible (scientific)
analysis of the situation, which concluded that the fullness of the
tank actually makes little difference. And, of course, I now can't
remember where I saw it.

I think the best practice is to have a drain cock right at the bottom
of your tank, and to drain off a little fluid from it occasionally.
Any water in the tank will come out first. I do this once a month,
and with an almost-empty propulsion fuel tank find almost no water.
Much the same as for my almost-full heating fuel tank.

Adrian


Adrian Stott
Tel. UK (0)7956-299966

[DBA Forum (B) - Colin Stone]

Google for Tank Condensation Myth - David Pascoe.

Just opened my tank water drain, probably a good year since the last time and averaging about half full tanks, and not a drop of moisture visible. Also checked with water finding paste - no trace.

Colin Stone
KEI


Sent via BlackBerry® BIS

[DBA Forum (B) - Peter Cawson]

One has to ask "Where can the water come from?" and the answer is surely from the vapour in the void above the fuel. Provided there is no real opportunity for fresh air (with a moisture element) to enter the tank, then the tiny amount held in the vapour will not cause serious problems. So, keep the fuel filling points firmly closed - perhaps with a clingfilm covering over the winter if one thinks the minute breether vent will be a problem - it won't. New air (with natural airbourne moisture) should only enter the tank as the engine draws fuel from it, so in winter, this should effectively be nil - worse perhaps on a wet summer's day when you're cruising and consuming fuel?

Colin's experience should be typical - a few drops of water that should be drained off from time to time, irrespective of season.

Peter

[DBA Forum (B) - Colin Stone]

Post by DBA Forum (B) - Peter Cawson
One has to ask "Where can the water come from?"

With the fuel or a deck flush filler cap leaking. Both probably equally likely.

I take a fuel sample in a glass jar and use PTFE tap on deck filler threads.

Post by DBA Forum (B) - Peter Cawson
Colin's experience should be typical - a few drops of water....

Actually, no few drops!

Colin Stone
KEI
Sent via BlackBerry® BIS

[DBA Forum (B) - Balliol Fowden]

[quote="Peter Cawson" post=56971] if one thinks the minute breether vent will be a problem - it won't.


Peter[/quote]

Not all vents are that minute. TRIWV requires vents 1.25 times the diameter of the filler. I'm not sure why they want them that big, but in practice if filling from a road tanker or bunker ship you need big vents, at least 1" for a 1.5" filler in my opinion to reduce the risk of a blow back, and possibly pollution and probably then a fine. I have specified the same bore vents as fillers in recent years since "Actief's" vents are only about 20mm per tank which is too small.

Balliol.

[DBA Forum (B) - Martin Phillips]

I agree with Peter. Over winter the water content of air is minimal as it's cold: at 10 C, no more than 9 g per kg air or 11 g per cubic metre, and lower at lower temperatures. You'd need a lot of air exchanges to get a substantial water problem in the tank, even if all of the water were to condense out which it won't. It might be argued that there's more potential for condensation in the summer when the water content of the air couldl be higher, and the fuel / tank (if below water level) is likely to be at a lower temperature than the air.

Most air exchange (assuming a single vent and a reasonably well-fitting filler) will be caused by pressure variations: either due to weather systems, or possibly more likely due to the pressure drop from wind blowing over the vent. Even a daily change of 20 mB would only cause an exchange of ~ 2% of the tank's head space.

Martin/