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Prompted by this comment.

Different hydrocarbon-based fuels have different stability characteristics when left to sit unused for long periods of time. Avgas (and mogas too, for that matter) generally only stay good for about 6 months or so; in sharp contrast, kerosene-type (narrow-cut) jet fuels generally remain usable for around 2 years as-is, and about 10 years if treated with an antioxidant.

In very cold climates (places like Alaska, northern Canada, and [formerly] northern Russia), jets are often given wide-cut fuels, which trade the low vapor pressure (and resultant low high-temperature explosion hazard) of straight kerosenes for a much lower freezing point, as these sorts of places often get cold enough to freeze narrow-cut fuels, which is bad if it happens while the aircraft is in use.[citation needed] In order to get this very-low freezing point, wide-cut fuels mix a lot of gasoline into the kerosene (Jet B, the predominant wide-cut fuel in North America, is an approximately-70:30 gasoline:kerosene mix). As such, one might expect that the storage-stability characteristics of wide-cut jet fuels would be intermediate between those of straight gasolines and straight kerosenes.

What are the actual stability characteristics of wide-cut fuels in long-term storage?

Vikki
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    Note: Russia, CIS, and China normally use TS1 fuel, which is still kerosene based, but with lighter fractions. Northern Europe runs Jet-A-1. Wide-cut Jet-B/JP-4 (almost the same) is mostly used in North America. – Therac Apr 01 '23 at 14:57
  • Avgas keeps a lot longer than autogas. I would avoid using autogas more than 6 months old, but would have no problem flying with 2 year old avgas. – John K Apr 01 '23 at 16:17
  • @JohnK: Interesting. Does the TEL in avgas slow down the deterioration process? – Vikki Apr 01 '23 at 16:33
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    I don't think it's the lead. It's just the base compound formulations are less volatile. Modern auto gas keeps quite along time as well. It takes years to get gum formation, and the octane level of car gas doesn't drop that much over time, a bit more than avgas. Ppl are still very conservative with it tho. It's so clean these days, got car gas all over my shirt a couple of years ago, and hours later my wife couldn't detect any smell. – John K Apr 01 '23 at 17:37
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    Also, turbines may be way more tolerant of off fuel because they do not require more precise ratios like piston engines do. Wider cuts may be more prone to absorbing water, but if it burns, a jet can use it. – Robert DiGiovanni Apr 01 '23 at 18:27
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    The problem with fuels for turbine aircraft is that they can partially oxidize and form solid deposits, which then clog the fuel system. – Therac Apr 02 '23 at 13:56
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    Oxygenated mogas should be used in under 3 months, straight hydrocarbon fuel will last a year+, straight hydrocarbon with antioxidants(100ll) will last a couple of years. Depending on your cutoff and storage. Gums and varnish are caused by oxidation polymerization. Alcohols and ethers are added to mogas to increase oxidation (slightly more complete combustion, up to about 5 or 10% alcohol) but they kill the storage life so are kept separate at the refinery and blended when filling the delivery truck. Alcohol blends also have H2O issues that cause severe degradation in antiknock, +icing hazard – Max Power Apr 05 '23 at 01:36
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    "alcohol free" mogas is still a "reformulated gasoline" by EPA standards it just substitutes an ether like MTBE for alcohol as the oxidant. It is slightly better than alcohol when it comes to moisture problems, but it still does not store like a straight hydrocarbon fuel. The stabilizer additives are very dilute antioxidant, but they are up against a 10% blend of oxygenator so it's kind of a lost cause, they might get you an extra month or two. – Max Power Apr 05 '23 at 01:43

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