On Feb 26, 2:06 pm, Ed Huntress <
huntre...@optonline.net> wrote:
> On Tue, 26 Feb 2013 14:02:10 -0800,
e...@whidbey.com wrote:
> >On Tue, 26 Feb 2013 15:26:19 -0500, Ed Huntress
> ><
huntre...@optonline.net> wrote:
http://en.wikipedia.org/wiki/Glow_fuel
"Ingredients
Glow fuel is a mixture of methanol, nitromethane, and oil.
Methanol is the primary ingredient as it provides the bulk of the
fuel, and is needed as a solvent for the other ingredients. The
presence of methanol causes the glow plug found in model engines to
heat via a catalytic reaction with the platinum metal wire element
which glows in the presence of methanol vapor.
Nitromethane is added to the methanol to increase power and to make
the engine easier to tune. Typically glow fuel is about 0-30%
nitromethane. While higher concentrations can result in better engine
performance, usage of highly concentrated nitromethane is rare due to
its cost. Although a given amount of nitromethane contains less energy
than the same amount of methanol, it increases the amount of available
oxygen in the combustion chamber per every intake stroke, which allows
the engine to draw in more fuel while still maintaining a favorable
mixture setting. The increased amount of fuel entering the engine
increases power output, and also aids in cooling. For racing use, the
nitromethane content can be increased to the range of 30%-65%.
Nitromethane is often difficult to obtain in many countries, so in
these countries glow fuel typically has no nitromethane at all.
Lubrication
Most model engines require oil to be included with the fuel as a
lubricant since the engine has no independent oiling capability. Model
engine fuel is typically 8-22% oil, with the higher percentages run in
older design two-stroke glow engines that use bushings for the
crankshaft bearings. The most commonly used lubricants are castor oil
and synthetic oils, and many glow fuels include a mixture of the two.
The oils included in glow fuel generally are not burned by the engine,
and are expelled out the exhaust of the engine. This also helps the
engine dissipate heat, as the oil emitted is generally hot.
Four stroke model engines, since they are generally designed to be
simple powerplants while still incorporating the usual camshaft,
rocker arms and poppet valves of larger sized four stroke engines, are
generally meant to use glow ignition and their fuel. Often, the oil
percentage for four stroke glow fuel can be lowered from the 18-20%
figure used for some two-stroke engines, down to as low as a 12-15%
percentage per unit of blended glow fuel, but use of such low-
percentage lubricant fuel can also mandate the need for a small
percentage of castor oil in the mix to avoid having too little oil in
the mix, and also mandates setting the high-speed fuel mixture
carefully by using a handheld digital tachometer to check engine speed
to avoid over-leaning of the fuel mixture.
Glow engines generally have to be run slightly rich with a higher fuel/
air ratio than is ideal to keep the engine cool as the fuel going out
the exhaust also takes heat with it, and so vehicles with glow engines
generally get coated with lots of oil. Almost all the oil comes out
the exhaust, and some nitromethane and methanol as well (as it's not
all burned) requiring some cleaning when one is done using the model.
The nitromethane that exists in many glow fuel blends can cause
corrosion of metal parts in model engines, especially four-stroke
designs, due to the nitric acid residue formed from combustion of
nitromethane-content glow fuel, making the use of a so-called "after-
run oil" a common practice after a model flying session with a four-
stroke glow engine-powered model.
Glow fuel is not difficult to make, and so many modelers mix their own
to save money, but some of the ingredients are flammable and/or
explosive and so can be dangerous, especially in large quantities.
Most modelers buy their glow fuel premixed from such manufacturers
such as Byron, Blue Thunder, FHS Supply, Model Technics, Morgan,
Powermaster, Tornado, Wildcat, and many others.
"Typically glow fuel is about 0-30% nitromethane."