It is boat oriented because often there is less tank renewal than in a car but it is quite interesting to know how an oil essence is aging.
We talked about engine additives a few days ago: new-transport / view-on-the-products cleaning-de-slagging engine BARDHAL-facom-t16183-20.html
An older subject: new-transport / the-benefits-of-a-additive motor-t12347.html
Well aging is certainly also related to the presence (or not) of additives (so the quality of gasoline pump) ...
Be careful, some images may shock the most meticulous in mechanics!
Aging of species, causes, consequences and remedies
The gasolines used in our engines, whether they operate in two or four-stroke engines, undergo, over time, alterations that modify their characteristics. What are these phenomena and how to avoid them?
The essences
Who has never tried to use, without success, the contents of an old gasoline can in an explosion-engined machine?
The additives present in the essences sold in the trade do not have vocation to make them usable over a long period. Indeed, the species are refined to the main destination of the automotive market, known for its daily use.
The fuel, sold at the pump, is "guaranteed" stable only a few months, at most.
The phenomena of degradation of species
The essences undergo four types of degradation of their chemical qualities rendering them unfit for their use in the absence of some precautions.
Additives help to delay some of these effects and prolong the life of the fuel.
Volatility
Volatility refers to the ability of the fuel to evaporate into the air.
This phenomenon, which allows their use in combustion engines, also leads to deterioration.
Volatility depends on the storage conditions (temperature) as well as the fuel formulation. Thus, the species are made more volatile in winter mixes to facilitate cold-season starts.
Although the notion of octane does not directly characterize volatility, it can be conceived as an indicator.
Over time, the octane rating of a gasoline fuel drops slowly, day after day, leaving the mixture less and less volatile.
evaporation
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It is easy to see on an "inflated" plastic tank that gasoline has a tendency to evaporate when the temperature rises.
For this reason, fuel tanks are always "vented" to allow, on the one hand, an air intake, but also to offer the possibility of evaporation gases to evacuate.
In the tanks, alternating alternating cycles day and night during which the temperatures vary. These temperature variations cause the production of -volatiles vapors evacuated by the vents of the tank.
The volume of the fuel decreases with the evaporation as well as its volatility.
On the other hand, the nature having horror of the void, the volume of missing fuel will inevitably be replaced by air more or less loaded with moisture (the air "dry" comprises 40% humidity). During the "night" cycles, the temperature drops in the tank and this temperature difference then causes some of the water trapped in the tank air to condense. Indeed, the capacity of the air to keep the water vapor in gaseous form decreases with the temperature (effect of Mollier).
The ultimate consequence of this condensation leads to a slow dilution, with the condensation water, of the fuel present in the tank.
It is the presence of this water that will generate the last consequence, the oxidation, reason why the tanks are designed in inert materials (plastics or stainless steels).
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oxidation
Inside a tank, the fuel comes into contact with the oxygen in the air.
This contact causes oxidation of components from the superficial layer of gasoline. The product of this reaction (polymerization of olefins) is a solid, a kind of gum, present in the fuel in the form of particles.
This rubber, heated during engine explosion cycles will solidify cooling can even stick the valve on their seats, or even cause their deformation and then that of the camshaft ...
In addition, in cases where the tank is not made of inert material, but steel, for example, iron oxide particles, detached from the walls thereof, will also end up in the fuel.
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The cocktail effect or the case of E95 SP10
This fuel replaces the SP95 (lead-free 95) by incorporating 10% ethanol (alcohol) of plant origin. This alcohol is present in the fresh mixture in a homogeneous way.
Unlike automotive engines, nautical gasoline engines are rarely used on a daily basis. Long periods of rest between uses allow the mixture to dissociate. Ethanol (alcohol) thus dissociated, is deemed to have a harmful action on certain engine seals.
The effect of ethanol is sensitive when using 2 mixture time or, once dissociated, it may, in addition, to degrade the oil!
Additives for species
Stabilizers
Star Tron Enzyme Fuel Treatment, Motorex Ethanol Treatment or Quicksilver Quickstore, these products offer common benefits allowing the use of fuel over a longer period that should never exceed 12 months (to say nothing at all!)
These products act mainly against the formation of gums, the oxidation and the dissociation of ethanol.
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Lead substitutes What does it still exist ??
Old engines (usually before 1990) are equipped with valve seats that are not compatible with unleaded gasoline. The lead in petrol lubricates them and prevents their rise in the seats.
Specific additives correct the composition of modern fuels, but, in the case of 2 times, do not replace the oil to be blended with fuel.
To optimize the performance and life of a gasoline engine, it is best to organize to avoid having to keep fuel from one season to the next. If you need to overwinter a tank with fuel, top up (to reduce the oxidation surface) and remember the stabilizer.
Source: http://www.actunautique.com/2019/11/car ... ences.html