I mixed my first batch of fuel yesterday, very easy and works great so far. I purchased Klotz synthetic and racing castor from Tower Hobbies. Found some methanol locally from someone that supplies fuel to local race tracks. I calculated how much methanol I needed to add to a quart of oil to produce the oil content I wanted. Basically I mixed some FAI (no Nitro) fuel, put an ordered quart of high nitro fuel (nitro without hazmat fee) in a gallon bottle, topped off with my mix for a gallon of fuel. We've only ran a couple of tanks due to weather but so far it runs great.
The quart I added was 35% Nitro, don't know the oil content (Trinity fuel from Tower Hobbies). The fuel I mixed was 16% Oil (too low for aircraft, supposed to be on the high sided for cars). If my calculations are correct, my end product was 8.25% nitro (if I used 96 oz of my own mix, I used 100 oz plus 32 oz of 35% nitro fuel). The oil I used was Klotz KL-100 from Tower Hobbies, supposed to be 20% Castor, 80% Synthetic. I used a quart of oil to mix 200oz fuel, calculates to 16% oil if I'm figuring correctly.
I plan to use 16% oil fuel for cars (recommended for my car) and learn what is recommended for airplanes and helicopters ( I still have 5 gallons of Heli fuel left though). The LHS sells racing fuel for $29 per gallon for
30% nitro, 9% Oil, I plan to use 2/3rds gallon of 0% nitro, 16% oil mixed with 1/3 gallon of their fuel to make a gallon of 10% nitro fuel.
The bottom line is that it's just like mixing 2 cycle oil for the weed eater or chain saw except with more expensive ingredients :-( The up side is that I can save a few dollars for very little trouble and have fuel as good as any I have ever bought.
Molecular sieves work by having a hole in the chemical structure that water fits nicely. Bigger molecules like oils or alcohols are too big to fit into the hole in 3A so are not absorbed.
Regeneration by driving the water out with heat is easy enough. Put them on a tray on your kitchen oven and heat to 450 or 500 deg F for a couple of hours. Be sure to rinse them well with alcohol to get rid of all the oils and nitro first. Then dry them in air spread thinnly on a tray for 48 hours or so to get rid of the methanol before you put them in the oven. If you skip the rinse and dry be prepared for a lot of bad odor in the kitchen and perhaps a fire. With a little luck you might even be able to blow the door off the oven if you do it wrong. If that happens you will probably blow out every window in the kitchen too.
Drying ethanol and methanol are two entirely different issues. Ethanol (95%) and water (5%) form something called an azeotrope. An azeotrope is simply the mixture of two compounds that boils at some minimum temperature below the boiling points of any of the ingredients. The result is you can only purify ethanol to about 95% by simple distillation. There are a variety of tricks you can pull to get that last 5% of water out of ethanol by distillation. One is to add benzene as benzene, ethanol and water form a tertiary azeotrope that boils below the ethanol-water azeotrope. But that leaves you with ethanol containing small amounts of benzene and the benzene is not always an acceptable ingredient. So if you want pure ethanol mole sieves is a decent way to dry out that last 5% of water without adding any other organic compounds to your final ethanol.
Methanol on the other hand does not form an azeotrope with water so you can simply distill it in a good still with 20 or 30 theoretical plates and get dry methanol right from the still.
Either methanol or ethanol will tend to pick up water vapor from the atmosphere. However, the amount of water you pick up is so small it is irrelevant for a model engine if you take the slightest care to at least keep a loose lid on the containers. If the containers are sealed well enough that you do not see significant evaporation of the fuel over a six month period you have them more than adequately sealed to prevent significant water absorbtion. After all 1 or 2% water in your fuel does no harm at all in terms of engine performance. If the oil is staying in solution and the fuel is not becoming cloudy or forming a separate layer due to oil being forced out of solution by large amounts of water you are just fine. All the fuss about a small amount of water in fuel by a few in the model community is simply mindless drivel by those who have no clue. In fact there was a published report in one of the model mags several years ago that showed that a few % of water in fuel actually upped the RPMs in static tests. Water injection systems have even been installed on a variety of internal combustion engines over the years to enhance power output.
If you buy a decent grade of methanol to start with it will not have enough water in it to wrorry about. With the most modest efforts to keep it sealed it will never pick up enough water to cause a problem. Thus there really is no reason to bother fooling around drying it to some super dry condition with Mole Sieves. On the other hand if you want to burn ethanol, which if legally sold without all of the government subsidies for fuel ethanol for on the road fuels, you will pay more than you pay for methanol unless it is 95% stuff. If it is
95% stuff you probably do need to dry it to get something that will allow the oil to stay in solution.
If you skip the rinse and dry be prepared for a lot of bad odor in the kitchen and perhaps a fire. With a little luck you might even be able to blow the door off the oven if you do it wrong. If that happens you will probably blow out every window in the kitchen too.
Now this thread get intresting.
All the fuss about a small amount of water in fuel by a few in the model community is simply mindless drivel by those who have no clue. In fact there was a published report in one of the model mags several years ago that showed that a few % of water in fuel actually upped the RPMs in static tests. Water injection systems have even been installed on a variety of internal combustion engines over the years to enhance power output.
Some high altitude warcraft of WWII utilized a water injection system to up the compression ratio resulting in more power.
Fuel will tolerate a bit of water before spoiling the fuel (things no longer mix well after too much water). I wouldn't add water, but I wouldn't panic if the watery fuel is running fine in your engines.
The water injection allows higher power output by cooling the fuel-air charge, which prevents detonation. The blower can compress the mixture more and the water keeps it cooler. Without the water, the amount of boost pressure has to be limited to prevent the engine from self destructing.
The engines that use water injections are engines that will be running at near constant high power outputs. Generators and pumps are frequent users of water injection. If the engine is going to have frequent large throttle movements, the water will not be used, as it causes rough running at lower power settings, plus the fact that the water is not needed to cool the engine.
An airplane engine fits the bill, perfectly. High power settings are what they use in war power output selections. Most of the time, they will not be run that hard, because they carry a limited supply of water. The higher power available with water injection saved more than a few's bacon, for sure.
Sort of an update, I've had a chance to run almost a gallon of the fuel through the model cars and it runs great with only 8.25% nitro. The only difference I notice is I needed to adjust the mixture settings and my fuel makes a little more smoke. I think the difference is my fuel mix has more oil.
I'm paying $11 per quart of oil from Tower hobbies, this makes the fuel somewhat expensive. If you figure a gallon of fuel containing 10% nitro,
20% oil, and 70% methanol, the expenses are $5-$7 for the nitro, $8-$9 for oil, and ~$3 for methanol. I guess that could explain why a gallon of car racing fuel with 30% Nitro and 9% oil is $3-$4 cheaper (at LHS) than car sport fuel with 20% nitro and a higher oil content.
Anyway, $11 per quart seems a little high for oil, not sure. I'm hoping to see if I can find some cheaper, maybe by the gallon or a 5 gallon bucket. I don't want lower quality, just a better price for buying a larger quantity. I did see that Sig sells Baker AA castor for less than $25 per gallon, less expensive than the $7 per PINT for Klotz racing castor from Tower.
Tower Hobbies does have their Klotz with quantity discounts, that combined with free shipping and discount codes I might be able to get it down to $9 per quart or so.
Maybe next I'll see if I can get 4 gallons of 7.5% nitro out of a gallon of
30% nitro heli fuel that I've had for a few years.
Check with the same guy you bought the methanol from -- racing go-karts and motorcycles use castor and Klotz, too, or else they wouldn't be available for us modeling folks to play with.
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