Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Does Naptha (White Gas) have the propensity to lose its volatiles?

ie when the cap is left off the container, pouring some out and then pouring the unused back in over many times with the small amounts that we use etc etc etc

While I cannot claim to be any kind of expert on complex hydrocarbon chemistry, I do believe that any evaporative fuel will lose potency over time, especially if well exposed to the atmosphere, rather than being tightly "bottled" up! It actually loses its potency in at least a couple of three ways. First is simple evaporation of the more volatile vapors. Second is the oxidization of reactive elements, absorbing oxygen from the atmosphere in small doses, thus weakening their ability to combust in a highly oxygenated environment when and where they are intended to "burn". Finally, there is the tendency for fuels to absorb moisture from the atmosphere, again weakening their potential combustion energy.

Generally speaking, if you are not leaving the container open for hours on end, which you should never do around our flaming engines anyway, then there is likely little real loss experienced. But of course, a half empty container holds a bigger portion of atmosphere and more molecules of regular "air" therefore the less fuel in your container the more these issues can react with your fuel supply, so it is likely a good idea to transfer to smaller containers as your fuel volume diminishes, especially if long term storage is considered.

Now if all of the above sounds ominous, let me back up a bit by saying that I have stored regular automotive fuels in less than full containers, for my lawn mower, for a couple of years without it going fully "bad", but it really did seem somewhat weaker.