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Fuel Facts by Don Nix former President, GBG Industries, Inc
(The following is a series of articles
exploring all facets of model engine fuel. The writer is Don Nix, former President of GBG Industries, Inc., manufacturers
of POWERMASTER model fuel.)
© Don Nix
No. 3 - Nitromethane, the Mystery Ingredient?
No. 4 - 2-Stroke vs.
4-Stroke Fuels
No. 5 - Storing Fuel for Maximum Shelf Life
FACTS ABOUT FUEL No. 3 - Nitromethane, the Mystery
Ingredient?
(The following is the third in a series of articles exploring all facets of model engine fuel. The writer
is Don Nix, former President of GBG Industries, Inc., manufacturers of POWERMASTER model fuel.)
Nitromethane.....
everybody knows it's there, but few, it seems, really know much about it. Although most seem to know - at least vaguely -
that's its primary purpose is to add power, we still get an occasional call or letter asking, "Why do you use it in model
fuel?" At best, there is much misinformation regarding this somewhat exotic ingredient. Let's see what we can do to clear
some of it up.
Nitromethane is just one of a family of chemicals called "nitroparaffins. " Others are nitroethane
and nitropropane. Nitroethane can be used successfully in small quantities.
(Top fuel drag racers, which generally
run on straight nitromethane, sometimes add a little in hot, humid weather to prevent detonation.) -at one time, nitroethane
was only about half as expensive as nitromethane, but its cost now is so nearly the same, using it to lower cost is hardly
worth the trouble. Neither of the nitropropanes will work in model engine fuel. Incidentally, nitromethane is made of propane,
in case you didn't know (and I'll bet you didn't).
Yes, NITRO = POWER! But.... there are conditions and contingencies.
First of all, it doesn't add power because it's such a "hot" chemical. Not at all. This may come as a surprise to most readers,
but the methanol (methyl alcohol) in the fuel is by far the most flammable ingredient.... nearly twice as flammable as nitromethane.
As a matter of fact, if nitro were only 4 degrees less flammable, it wouldn't even have to carry the red diamond "flammable"
label!
In actuality, nitromethane must be heated to 96 degrees F. before it will begin to emit enough vapors that
they can be ignited by some sort of spark or flame! (I demonstrated this not long ago to a friend by repeatedly putting a
flaming match out in a lid ful of nitro. I might add that he insisted on standing about 20 feet away during the demonstration.)
So.... how does it add power? We all know (I think) that although we think of the liquid part substance we put in
fuel tanks (in our automobiles or model airplanes) as the fuel, in truth, there is another "fuel," without which the liquid
part would be useless. Remember what it is? Right.... just plain old air (in reality, the oxygen in the air).
Every
internal combustion engine mixes air and another fuel of some sort in our case, a liquid glow fuel. The purpose of the carburetor
is to meter those two ingredients in just the' right proportions, and every individual engine has a requirement for a specific
proportion of liquid fuel and air. Try to push in too much liquid without enough air, and the engine won't run at all. That's
the purpose of the turbocharger on full-size engines to cram in a lot more air than a simple carburetor or fuel injection
system can handle.
Now..... suppose we were to find a way to run more liquid through our model engines without increasing
the air supply? That would add power, wouldn't it? Well, guess what.... we can! An internal combustion engine can bum more
than 2 1/2times as much nitromethane to a given volume of air than it can methanol. Voila! More Power! That's how it works,
and it ain't all that complicated. Nor do we have to spend a lot of time thinking about it in the course of a normal day's
sport flying.
However, there are some factors we do need to consider. As a practical matter, virtually all our everyday
sport flying can be done on model fuel containing from 5% to 15% nitromethane. If you're flying something like a trainer or
a Cub or similar model, there's probably no reason why 5% won't work perfectly well. Need a little more power? Move up to
10% or 15%. In most of our sport engines today, I really wouldn't recommend going any higher than that. It probably won't
hurt anything, but it won't do you much good, either.
We sell more 15% fuel than any other single blend, and for good
reason. Most of the popular engines on the market today are built to run on something very near that blend. Typically, European
engines will successfully run on lower nitro blends, because they are built to do so. Why? In Europe, nitro can cost between
$150 to $200 a gallon! Reason enough?
Nitro does more than just add power. It also helps achieve a lower, more reliable
idle. One good rule of thumb for checking to see if a particular engine needs a higher nitro blend is to start the engine,
let it warm up for a few seconds, set throttle to full idle and remove the glow driver. If it drops rpm, move up to a 5% higher
nitro blend. If there is no discernible drop, you should be fine right where you are.
One of the most popular Misconceptions
is that by adding substantial nitro, the user will immediately achieve a huge power jump - Just ain't so. Most will be surprised
to learn that in the 5% - 25% nitro range, you will probably only see an rpm increase of about 100 rpm static (sitting on
the ground or on a test stand) for each 5% nitro increase. In the air, it will unload and achieve a greater increase, and
it will probably idle better, too.
My pet rule is this: If you have a model that's doing well, but just isn't quite
"there" powerwise, go up 5% in nitro. If that doesn't do it, you need a bigger engine, not more nitro!
Most of our
popular sport engines in use today aren't set up to run on much more than 15% or 20% nitro. Increasing the nitro has the effect
of increasing the compression ratio, and each specific engine has an optimum compression level. Exceed it and performance
will probably suffer, not gain, and the engine will become much less "user friendly."
High performance racing engines,
for example, are tuned entirely differently.... Compression ratio, intake and exhaust timing etc.... and are usually intended
to run on much higher nitro. Also, competition (FAI) is ddifferent. By the rules, these engines are not allowed to use any
nitro at all, and they go just as fast as those that run on 60 or 65%! The first question that comes to mind, then, is, "Why
aren't all engines designed to run on no nitro, so we can all save a lot of money?" Ask any of the world-class competitors.
Those engines are a serious bitch to tune and run, and are definitely not user-friendly! In fact, they are well beyond the
skill levels of most average flyers. There's a price to everything.
Another statement we read or hear frequently is
that nitromethane is acidic and causes corrosion in engines. It isn't acidic, and the manufacturers say it doesn't happen.....
can't happen. However, at least one noted engine expert and magazine writer insists that it does. Flip a coin. (I once asked
Dave Shadel, 3 -time World Pylon Champion, and a fellow who works on more high performance engines than anyone I know, how
frequently he encounters rust in engines that have been using high nitro blends. Ms answer? "Never.")
Why does nitro
cost so much? I have no clue as to the cost of manufacturing, other than it takes a multi-million dollar investment in a large
refinery to produce it, there is one pretty good reason: There is only one manufacturer of nitromethane in the Western Hemisphere.
Figure it out for yourself
Also (and this will come as a big surprise), our hobby industry only consumes about 5%
of all the nitromethane produced; and full-size auto racing about another 5% or so. This means we have no "clout" whatever,
and simply must pay the asking price. Where does the rest of it go? Industry. It's used for a variety of things - a solvent
for certain plastics, insecticides, explosives (yes, it was an ingredient in the Oklahoma City bombing) and I'm told it's
an ingredient in Tagamet, a well-known prescription ulcer medication (no wonder that stuff is so expensive!). Please note
that while nitromethane is an ingredient in making some explosives, under normal use, it in itself, is not explosive. (Remember....
the guy used fertilizer, too.)
Hardly a month passes that someone doesn't call to ask, "I hear more nitro will make
my engine run cooler. Is that true?" Nope. The higher the nitro content, the higher the operating temperature. Fortunately,
in most of our sport engines, the difference in operating temps between 5% and 10% is negligible, and there are lot of other
factors (proper lubrication, etc.), that are much more important.
Finally, remember in the beginning of this, we said
that nitro adds power because we can bum more of it than we can methanol, for a given volume of air? This also means that
the higher the nitro content of the fuel, the less "mileage" (or flying time) we will get. In a typical .40 size engine using
15% nitro, we can usually get a minute to a minute and a half flying time for every ounce of fuel. The Formula I guys are
lucky to get 2 minutes out of an 8 oz. tank!
What's the practical side of this? If you go to a higher nitro blend,
be sure to open your needle valve a few clicks and reset before you go flying. Otherwise, you'll be too lean, and could hurt
your engine. Conversely, if you drop to a lower nitro blend, you'll have to crank-er in a little.
FACTS ABOUT FUEL
No. 4
2-Stroke vs. 4-Stroke Fuels. Is There Really A Difference?
(The following is the fourth in a series
of articles exploring all facets of model engine fuel. The writer is Don Nix, former President of GBG Industries, Inc. Readers
are invited to contact Don directly via e-mail - FLYERDON@aol.com.)
Well, what do you think? Is there really a difference,
or is this merely a big hype by the fuel manufacturers to sell more products? Let's see a show of hands…..ah, yes…about
evenly divided. Well, let's explore the facts.
Fact: Most 4-stroke model fuels contain less oil than comparable 2-stroke
fuels.
The most common response to this is, "But 4-stroke engines have more moving parts….they should need more
oil, not less!" Well, that sounds reasonable, but it doesn't stand up under close examination. The number of moving parts
has nothing to do with it. What is important? Think about it.
Fact: With rare exceptions, 4-stroke engines run at
substantially slower rpms than a comparable 2-stroke engine…most in the under-10,000 rpm range vs. 12,000, 13,000 or
more for a typical 2-stroke of the same size. They are engineered to deliver maximum power at slower rpms, with bigger props.
What does this have to do with it? One of the main factors used in determining the proper oil content of fuel is heat. To
use the well-worn term, it doesn't take a rocket scientist to figure out that the more slowly an engine turns, the less heat
it generates from friction. If you don't believe that, rub your palms together slowly, then as fast as you can.
So….lower
rpms = less heat = less need for oil.
Fact: 4-stroke engines only fire every other stroke, vs. every stroke by a 2-stroke
engine. Firing, or combustion, burns fuel, which creates heat. Logically, it may be deduced that if there is fire in the chamber
only every other stroke, the engine has time to cool off a bit between combustion cycles. Let's take that a little further:
Using a hypothetical 4-stroke engine turning 10,000 rpm = 5,000 combustion cycles per minute, vs. a hypothetical 2-stroker
turning 13,000 rpm…with the same number of combustion cycles per minute….the gap widens.
The 2-stroker
has 160% more combustion cycles than the 4-stroker. Even though this is partially offset by the fact that at least some 4-strokers
have a higher exhaust gas temperature, the message is clear: 4-strokers remain cooler, and need less oil.
Fact: Oil
doesn't burn (or shouldn't) - methanol does. Using a little logic, we arrive at the conclusion that a properly made 4-stroke
fuel will deliver better performance than a 2-stroke fuel in the same engine.
Why? Remember…the 4-stroker is
only firing every other stroke. This results in the plug element wanting to cool down between strokes, resulting in a "colder"
plug. Excess or unnecessary oil, constantly dousing the element, is going to make it more difficult to achieve a slow, smooth
idle. Those who contend that, "Well, using too much oil can't hurt anything" are wrong. In addition to causing undue friction
in the engine, keeping the metal parts from properly mating, etc., too much oil in 4-stroke fuel is constantly trying to cool
a plug element that is already having problems. Sort of like pouring a bucket of cold water on a poor guy who is already shivering.
Again, since oil doesn't burn, it's doing nothing to help us develop power….it simply lubricates and goes right
out the exhaust and all over everything. However, suppose we don't put unnecessary oil in the fuel, and replace it with methanol,
which does burn. Well, what do you know…greater top end power! Hey, I think we're on to something here! Remove unnecessary
oil from 4-stroke fuel, and we get a "twofer" - two benefits for the price of one….a slower, more reliable idle plus
greater top end power!
Conclusion: For reasons that should be clear above, a properly blended 4-stroke fuel should
deliver better all-around performance in a 4-stroke engine than a regular 2-stroke fuel in the same engine.
While
it's not going to actually harm anything to run 2-stroke fuel in a 4-stroke engine, never, ever run 4-stroke fuel in a 2-stroke
engine. It's not going to have enough oil. Now, for those of you will say that you have done it with no problems, I'll agree…..if
you have a real good ear and keep the needle valve "fat" (rich), it will probably work just fine…but the official word
is DON'T! It reduces your margin of error unacceptably.
Finally: Because engine manufacturers have been burned in
recent years by some fuel makers' attempt to lower the cost of their products by using either too little oil or a cheap grade,
most manufacturers today are recommending that you run a 2-stroke fuel only in their 4-stroke engines, or will specify what
would seem to be an abnormally high oil content (and it probably is). Who could blame them? Since they know they have no control
over the oil used in someone else's fuel, they're just trying to cover their fannies. So would I.
Note: I believe
it's commonly known that the manufacturers of YS engines…among the most powerful 4-stroke engines available….mandate
that only fuels containing oil contents in the normal 2-stroke range be used. Their engines are unique, and the manufacturer's
recommendations should be followed, although, as with anything, there are exceptions.
FACTS ABOUT FUEL No. 5
Storing
Fuel for Maximum Shelf Life
(The following is the fifth in a series of articles exploring all facets of model engine
fuel. The writer is Don Nix, former President of GBG Industries, Inc.Readers are invited to contact Don directly via e-mail
- FLYERDON@aol.com.)
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 unusable.
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
© Don Nix
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