Glow fuel
Encyclopedia
Glow fuel is a generic term used to describe a fuel
source used in model engine
s -- generally the same or similar fuels can be used in model
airplanes
, helicopters
, cars
and boats. Glow fuel can be burned by very simple two stroke engines or by more complicated four stroke engines and these engines can provide impressive amounts of power for their very small size. Glow fuel is primarily for two stroke engines with the need for oil mixed in the fuel and limited exhaust and fuel/air between cycles. Top Fuel
race cars with 4-cycle engines also use methanol nitromethane mixtures but do not contain appreciable oil.
is usually not the primary ingredient, and in fact many glow fuels, especially the so-called "FAI" type, named for the Fédération Aéronautique Internationale
, which requires such fuel in some forms of aeromodeling competition, contain no nitromethane at all.
, nitromethane
, and oil
.
Methanol is usually the primary ingredient, as it provides the bulk of the fuel and is also needed as a solvent for the other ingredients. Its presence is also required for the glow plug generally found in model engines to burn via a catalytic reaction from the platinum metal in the glow plug's wire element glowing in the presence of methanol vapor, to keep the ignition going between strokes.
Nitromethane is generally added to the methanol to increase power and to make the engine easier to tune. Typically glow fuel is about 0-30% nitromethane, with higher percentages of nitromethane generally giving better performance but costing more as nitromethane is considerably more expensive than methanol
. A given amount of nitromethane contains less energy than the same amount of methanol, but it requires less oxygen to burn approximately half, so more of it can be put into an engine during each stroke and this leads to a higher power output.
For racing use, the nitromethane content can be increased well above 30% with a corresponding increase in cost, but some methanol is still required as it's needed to allow the glow plug to ignite the fuel in the first place, and as a solvent to allow the lubricants and nitromethane to mix, so the nitromethane content usually doesn't go any higher than 65%.
Nitromethane is often difficult to obtain in many countries since it is known as an explosive, so in these countries glow fuel generally has no nitromethane at all. Without at least a small amount of nitromethane, glow engines are harder to tune (get the correct fuel/air mixture) correctly and generally provide less power for a given displacement.
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.
. Propylene oxide
is sometimes added in small percentages.
Another form of model fuel, for small compression ignition engines, is called "Diesel Fuel", which generally consists of kerosene
, ether
, oil and some sort of ignition improver, usually amyl nitrate
or isopropyl nitrate
, it is in no way related to the automotive fuel of the same name.
Fuel
Fuel is any material that stores energy that can later be extracted to perform mechanical work in a controlled manner. Most fuels used by humans undergo combustion, a redox reaction in which a combustible substance releases energy after it ignites and reacts with the oxygen in the air...
source used in model engine
Model engine
In radio-controlled modeling, a model engine is an internal combustion engine used to power a radio-controlled aircraft, radio-controlled car, radio-controlled boat, free flight and control line aircraft, and tether car models also use these engines....
s -- generally the same or similar fuels can be used in model
Model (physical)
A physical model is a smaller or larger physical copy of an object...
airplanes
Model aircraft
Model aircraft are flying or non-flying models of existing or imaginary aircraft using a variety of materials including plastic, diecast metal, polystyrene, balsa wood, foam and fibreglass...
, helicopters
Radio-controlled helicopter
Radio-controlled helicopters are model aircraft which are distinct from RC airplanes because of the differences in construction, aerodynamics, and flight training...
, cars
Radio-controlled car
Radio-controlled cars are self-powered model cars or trucks that can be controlled from a distance using a specialized transmitter...
and boats. Glow fuel can be burned by very simple two stroke engines or by more complicated four stroke engines and these engines can provide impressive amounts of power for their very small size. Glow fuel is primarily for two stroke engines with the need for oil mixed in the fuel and limited exhaust and fuel/air between cycles. Top Fuel
Top Fuel
Top Fuel racing is a class of drag racing in which the cars are run on a mix of approximately 90% nitromethane and 10% methanol rather than gasoline or simply methanol. The cars are purpose-built for drag racing, with an exaggerated layout that in some ways resembles open-wheel circuit racing...
race cars with 4-cycle engines also use methanol nitromethane mixtures but do not contain appreciable oil.
Name
Other commonly used names are nitro or just model fuel. Note that the nitro name is generally inaccurate, as nitromethaneNitromethane
Nitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...
is usually not the primary ingredient, and in fact many glow fuels, especially the so-called "FAI" type, named for the Fédération Aéronautique Internationale
Fédération Aéronautique Internationale
The Fédération Aéronautique Internationale is the world governing body for air sports and aeronautics and astronautics world records. Its head office is in Lausanne, Switzerland. This includes man-carrying aerospace vehicles from balloons to spacecraft, and unmanned aerial vehicles...
, which requires such fuel in some forms of aeromodeling competition, contain no nitromethane at all.
Ingredients
Glow fuel is generally a mixture of methanolMethanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
, nitromethane
Nitromethane
Nitromethane is an organic compound with the chemical formula . It is the simplest organic nitro compound. It is a slightly viscous, highly polar liquid commonly used as a solvent in a variety of industrial applications such as in extractions, as a reaction medium, and as a cleaning solvent...
, and oil
Oil
An oil is any substance that is liquid at ambient temperatures and does not mix with water but may mix with other oils and organic solvents. This general definition includes vegetable oils, volatile essential oils, petrochemical oils, and synthetic oils....
.
Methanol is usually the primary ingredient, as it provides the bulk of the fuel and is also needed as a solvent for the other ingredients. Its presence is also required for the glow plug generally found in model engines to burn via a catalytic reaction from the platinum metal in the glow plug's wire element glowing in the presence of methanol vapor, to keep the ignition going between strokes.
Nitromethane is generally added to the methanol to increase power and to make the engine easier to tune. Typically glow fuel is about 0-30% nitromethane, with higher percentages of nitromethane generally giving better performance but costing more as nitromethane is considerably more expensive than methanol
Methanol
Methanol, also known as methyl alcohol, wood alcohol, wood naphtha or wood spirits, is a chemical with the formula CH3OH . It is the simplest alcohol, and is a light, volatile, colorless, flammable liquid with a distinctive odor very similar to, but slightly sweeter than, ethanol...
. A given amount of nitromethane contains less energy than the same amount of methanol, but it requires less oxygen to burn approximately half, so more of it can be put into an engine during each stroke and this leads to a higher power output.
For racing use, the nitromethane content can be increased well above 30% with a corresponding increase in cost, but some methanol is still required as it's needed to allow the glow plug to ignite the fuel in the first place, and as a solvent to allow the lubricants and nitromethane to mix, so the nitromethane content usually doesn't go any higher than 65%.
Nitromethane is often difficult to obtain in many countries since it is known as an explosive, so in these countries glow fuel generally has no nitromethane at all. Without at least a small amount of nitromethane, glow engines are harder to tune (get the correct fuel/air mixture) correctly and generally provide less power for a given displacement.
Lubrication
Most model engines require oil to be included with the fuel as a lubricant, as it's not provided by the engine itself, and so 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 oilCastor oil
Castor oil is a vegetable oil obtained from the castor bean . Castor oil is a colorless to very pale yellow liquid with mild or no odor or taste. Its boiling point is and its density is 961 kg/m3...
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
Exhaust system
An exhaust system is usually tubing used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes...
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
Tachometer
A tachometer is an instrument measuring the rotation speed of a shaft or disk, as in a motor or other machine. The device usually displays the revolutions per minute on a calibrated analogue dial, but digital displays are increasingly common...
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
Nitric acid
Nitric acid , also known as aqua fortis and spirit of nitre, is a highly corrosive and toxic strong acid.Colorless when pure, older samples tend to acquire a yellow cast due to the accumulation of oxides of nitrogen. If the solution contains more than 86% nitric acid, it is referred to as fuming...
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.
Alternatives
Nitromethane is sometimes replaced or supplemented by nitroethaneNitroethane
Nitroethane is an organic compound having the chemical formula C2H5NO2. Similar in many regards to nitromethane, nitroethane is an oily liquid at standard temperature and pressure. Pure nitroethane is colourless and has a fruity odor.- Preparation :...
. Propylene oxide
Propylene oxide
Propylene oxide is an organic compound with the molecular formula CH3CHCH2O. This colourless volatile liquid is produced on a large scale industrially, its major application being its use for the production of polyether polyols for use in making polyurethane plastics...
is sometimes added in small percentages.
Another form of model fuel, for small compression ignition engines, is called "Diesel Fuel", which generally consists of kerosene
Kerosene
Kerosene, sometimes spelled kerosine in scientific and industrial usage, also known as paraffin or paraffin oil in the United Kingdom, Hong Kong, Ireland and South Africa, is a combustible hydrocarbon liquid. The name is derived from Greek keros...
, ether
Ether
Ethers are a class of organic compounds that contain an ether group — an oxygen atom connected to two alkyl or aryl groups — of general formula R–O–R'. A typical example is the solvent and anesthetic diethyl ether, commonly referred to simply as "ether"...
, oil and some sort of ignition improver, usually amyl nitrate
Amyl nitrate
Amyl nitrate is the chemical compound with the formula CH34ONO2. This molecule consists of the 5-carbon amyl group attached to a nitrate functional group. It is the ester of amyl alcohol and nitric acid.-Applications:...
or isopropyl nitrate
Isopropyl nitrate
Isopropyl nitrate is a colorless liquid monopropellant. It is used as a diesel cetane improver. IPN is a low-sensitivity explosive, with a detonation velocity of approximately 5400 m/s....
, it is in no way related to the automotive fuel of the same name.