Can anyone tell me?
18 years ago
Can anyone tell me?
refer to = Storing Fuel for Maximum shelf life and many other articles under "Fuel" at
(The following is the fifth in a series of articles exploring all facets of model engine fuel. The writer is Don Nix, Past owner of Powermaster, Inc.
During the Q&A part of countless "Dog & Pony Shows" at hobby clubs all over the U.S., one of the frequently asked questions is, "What's the shelf life of fuel?" The answer if both simple and easy: Properly stored, model engine fuel will last almost indefinitely. So..what constitutes "properly stored"? Let's take a look.
Contrary to many things you might have read or heard, just about the only thing that adversely affects model fuel is the absorption of moisture from the air. Keep the air away from it, and your fuel will likely be potent longer than you are! Methanol - the major ingredient in model fuel - is hygroscopic. This means it's virtually 100% soluble in water, and absorbs moisture from the air like a vacuum cleaner sucking up dirt.
Most modelers have no idea how rapidly this can - and does - happen, and tend to be rather skeptical about the idea. Let me paint a picture for you: Almost everyone has spilled a little fuel on the top of their fuel can in their flight box. If so, you've no doubt noticed that the shallow film of raw fuel takes on a cloudy, milky look. What you are seeing is the methanol sucking moisture right out of the air. Since the quantity of fuel is thin with a lot of surface area, the absorption is rapid, the water won't mix with the oil and the fuel turns cloudy. Just remember how quickly this happens...almost immediately..and it might give you an idea of just how quickly your fuel can be ruined if you leave the cap off, allow a vent tube to remain open, etc.
The wide surface area relative to the quantity of the fuel exposed is disproportionate, of course, to leaving the cap off the fuel jug, but I think you get the idea. In a humid condition such as exists in parts of the U.S., it doesn't take very long at all to adversely affect your fuel. And it doesn't take a large opening..a cross-threaded cap, a small vent line, etc. is all that's needed to do the damage.
The solution is simple, of course..just keep it tightly sealed. And yet, sometimes that's not enough. Most of us have seen small droplets condensed inside our fuel jugs after it's become partially empty. This is the result of condensation of moisture as the air trapped inside the jug cools. Until about a year ago, there was little we could do about this, but there is now a method to take care of this problem. Since it's not the purpose of this column to commercially promote our own products, those interested are invited to contact the writer at the e-mail address above, and we'll be happy to tell you about the product that will solve the problem.
For the reasons above, it's our opinion that it is rarely a good idea to buy model fuel in 55 gallon drums. Unless all the fuel is poured up the first time the drum is opened, a substantial volume of air is trapped inside the drum each time it's opened. Steel containers of any kind warm and cool much more readily and rapidly than plastic, and condensation is much more evident in this type container. The result is that the last portion of the drum of fuel is quite likely to be contaminated with moisture, sometimes to the point of being unusuable.
There is another downside to buying fuel in drums, especially if more than one person is using it. With no control over the type container the fuel is dispensed into..perhaps not bearing sufficient or proper warnings, etc., the liability is incredibly high if an accident of any sort should occur. Model clubs considering this type of fuel purchase for their members should be particularly aware of the potential liability..which is huge!
While it's true that the UV in sunlight (or in fluorescent lights, for that matter) will cause pure nitromethane to deteriorate over time, it's our experience that once the nitro is in solution and substantially diluted, the deteriorative effect is relatively minor.
To test this, some years ago we put a gallon of 10% fuel out in direct sunlight (in sunny Southern California) for a month. At the end of that time, we tested that fuel in an engine vs. fresh product and could see no difference. While it certainly won't hurt anything to store fuel away from direct sunlight, etc., it's our personal opinion that the adverse effect of sunlight on fuel under normal operating conditions is too little to worry about regards Alan T. Alan's Hobby, Model & RC Web Links
Ted shuffled out of his cave and grunted these great (and sometimes not so great) words of knowledge:
I have about 4 gallons of fuel left that were given to me 2 years ago. The fuel is kept in a cool basement. A jug I just opened this year is perfectly fine. I estimate this fuel is about 3 - 4 years old as the gentleman who gave it to me had it for a year or so.
Very informative, Alan. Would it help to store fuel with something other than air in the container, like nitrogen, maybe? I only ask this for those who buy fuel in large quantities and keep it a long time. I buy mine by the gallon, keep it tightly closed, and use it fairly rapidly. I've never had any noticeable problems.
I've got about 16 gallons left of a 54 gallon tank of methanol in the back shed. The tank's now over 11/2 years old, opened only to mix fuel of course.
Now, I don't know how you are meant to tell that fuel is going "off" but my RPM readings from recently-mixed fuel are the same as they were when I got the stuff, and the idle and transition behaviour is the same too. The only variations I get seem to relate more to ambient temperature.
I hadn't intended to spend so long using up the fuel, but as far as I can tell there hasn't been any downside.
In fact, I reckon my "barrel aged" methanol is giving me flatter spins, lower knife-edges and cleaner stall-turns. It does seem to cause the odd rough landing though...
----------------------------------------------------------------------- slovensko's Profile:
When I was working in a laboratory, we regularly got many of our chemicals in "Cubitainers", sturdy cardboard boxes with a plastic bladder inside that collapsed as the liquid was dispensed through a spigot. It's a wonder to me that the fuel makers don't use these, as they would minimize the fuel's exposure to air. I'd love to buy my fuel in say, a 5-gallon Cubitainer.
"Morris Lee" schreef in bericht news:48b47$4294a4f3$d818628c$ snipped-for-privacy@NAXS.COM...
Yes, cubitainer is the answer : I always buy wine in cubitainer nowadays because it's cheap and easy to handle. And the wine doesn't turn to vinegar. But that's probably because a gallon is finished in 4 days by my wife and me. I surely consume more wine than glow fuel these days...
Olivier, who, as a foreigner, loves "la douce France", their wine and food
The reason you don't have any problems is because even at 100% humidity the air contains far less moisture than you might think. It is unlikely the air contains more than about .04 pounds of water per cubic foot. So you would only get an ounce or two of water in a 55 gallon drum. It would take a couple of ounces of water per gallon to notice the effects, and initally the effects may actually be good. A small amount of water in the fuel will prevent detonation.
Unlike the above artical methanol will not suck water out of the air like a vacume cleaner, it will only asorb what it is in contact with. However an open or poorly sealed container is in contact with an almost infinate supply of air and water.
Yeah, way back when it was half full I sat down and worked out, given the average relative humidity, how much water could be absorbed into the remaining methanol. Basically *very* little, partially helped by the low humidity of where I am, but even in a high-humidity climate the amount absorbed would be trivial.
Another thing you should remember, is that with the use of muffler pressure, water is introduced into the fuel, even as you fly- and this exhaust gas does have quite a bit of water in it. However, I've never noticed any real difference in engine performance at the end of the tank or end of the day- so it would seem that we needn't worry too much about a little water in the fuel, even while trying to prevent it. It's just about inevitable. -Paul
And the air we breathe is 80 percent nitrogen anyways. The rest , about19 percent is what we use and the balance are rare gases, pollution. Use dry air and it should be ok if you sweat the moisture. You could put a moisture trap on the vent bung.
One other thing, moisture is sucked into the 'air' intake when the engine is running so I wouldnt sweat the fuel.
I do not know much about glow fuel but, reading this thread I will point out that the discussion of water content in the fuel is not nearly as "simple" as several folks are making it out to be. You cannot get the answer by simply looking at a psychometric chart to determine the amount of water in the air at a given temperature, pressure, and relative humidity; that won't work.
To actually answer the question, you need to dive into phase-diagrams for non-ideal mixtures. Start with Raoult's Law which is where I think a few people were coming from. BUT, that only applies to ideal fluids and these are definitely ideal fluids. Ethanol and Water has a large positive deviation from Raoult's Law.
Glow fuel is more than a binary mixture and I won't even begin to pretend that I remember enough thermodynamics to begin to tackle this problem except to say that I am confident that you could end up with a lot more water in your fuel than you think. However, I also believe that the fuel will burn with a fair amount of water in it.
The major concern is a leaky container. If your container is tightly sealed and vapor cannot transfer between the inside and outside you are pretty safe from water contamination. Yes, air in the head space will exchange but if it is limited to that small volume and not many many cycles of that, you should be free from significant water contamination. An open container, even in relatively low humidity will exchange an awful lot of water.
The other consideration besides water contamination is the breakdown of other constituents that may be unstable compounds.
Acetone Benzole Ethanol Ether Methanol NitroMethane Petrol Propylene Oxide
Here is something I found rather quickly:
A couple of points. First if you expose the fuel to enough air to gain moisture you are also going to evaporate a LOT of the volitiles. So if you stored a half gallon for a year or so and it was still a half gallon it would be ok. Second, last fall I stored roughly a tenth of a gallon in my flight box in a plastic gallon jug for the winter. It was in my shop where the temp ranges from 45 when I am not there to 70 some when I am there. I heat my shop with a kerosene heater. LOTS of water vapor produced. I often burn a gallon of kerosene over a day of working out there and by evening the air feels wet. That tenth gallon of fuel had a lid that only sort of seals. If you turn the bottle upside down fuel runs out at a pretty good rate. I suppose in five minutes the bottle would be empty inverted. So not much of a seal. The fuel worked just fine this spring. I did not even have to reset the needle valve.
The fuel still was clear with no evidence of any separation of oil. This alone tells me it did not pick up much water as it only takes a few % of water in fuel to start knocking the oil out into a separate phase. And there have been good tests reported in the model mags in the last couple of years to show that a few % of water does no harm.
By the way, this was five year old fuel that had not been opened until about Oct of last fall. Got a bunch cheap and still flying it. I have enough for maybe two more years.
Not a Chem E but I am a PhD Chemist so know a little about water pickup from the atmosphere. You have to know about these things when you are doing micro chemistry with things like lithium aluminum hydride that have a real affinity for water unlike methanol which has at best a mild affinity for water.
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