| Fuels | - Fuels |
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Above: an InView four stroke engine.
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- from http://www.waltercedric.com/rc-helicopter-mainmenu-65/141-techniques/198-why-using-nitromethan-.html
Nitromethane ("nitro") is manufactured in production volumes by mixing nitric acid and natural gas (or other hydrocarbon base) under high temperature and pressure. It can be made in the laboratory by some complicated mixing and distilling of acetic acid, sodium carbonate, and sodium nitrate which is rather hazardous. The element that is most important is the oxygen which "disassociates" from the liquid at high temperatures.
While Methanol has almost the same amount of oxygen (50%) by weight, it is the overall "mix" that contributes to the unique nature of nitro, allowing a much higher fuel flow and the typically inert nitrogen which can serve to "soften" the shock of the combustion process and inhibit pre-ignition (this is not to say using nitro prevents pre-ignition).
All fuels, whether gasoline, methanol or nitro (which incidentally can be burnt at 100% mix like most fuels) have a "stoichiometric" or chemically correct air to fuel ratio, at which they theoretically (as calculated by chemists on paper) burn the most efficiently in air.
With gasoline it is 14.9:1 (air to fuel) with best power at 12.7 and best fuel consumption at 15-16:1. Gas puts out 2.78 kJ of energy per kg.
Stoichiometric methanol burns best at 6.5:1 or twice the liquid (by volume) for the same amount of air as gas and produces 2.67 kJ per kg, slightly less than petrol, but typically produces 10% more power due to the temperature drop of the mixture as it vaporizes, which produces a more dense mixture (higher density = more power). Methanol burns twice as much liquid as gasoline because it carries its own oxygen supply along with it (50% by weight). Methanol can also run 40% rich and still make good power because of this. This excess fuel contributes to cooler operating temperatures.
Nitro burns at a big 1.7:1, or 37% liquid, 63% air, or nearly three times as much liquid as methanol. Energy at stoichiometric = 4.05 kJ per kg or 1.5 times that of methanol. This is where the effects of nitro become important. Getting fuel into an engine is never a problem. The problem with producing power from a given engine is getting the air in! Hence, the use of superchargers, turbochargers, special manifolding, porting and valving arrangements on modern car engines. With model engines in general, we don't have the luxury of supercharges, etc. So Nitromethane actually provides "chemical" supercharging, introducing up to 3.8 times more liquid overall or 5.5 times more oxygen per liter at 100% "stoichiometric" mix, meaning more fuel (methanol) can be burnt, because of all the extra oxygen (the oxidizing agent).
For example, a methanol only mix provides 400 grams / liter of oxygen (gasoline has zero oxygen). At 20% nitro, there is 3.14 kJ/kg of energy and 436 g/l of oxygen, and because at 20% nitro the correct mixture or air / fuel ratio is about 4.2:1, a 35% increase in fuel flow will occur, which means around 47% more oxygen ends up in the engine when tuned correctly.
This increase in oxygen availability and fuel flow amounts to richer running. For example, the main needle has to be opened further to flow the correct amount of liquid to match the incoming air (which is pretty constant at any given throttle opening / rpm level). This also means that the tank may last up to 35% less than with straight methanol fuel. If you get 20 minutes with "straight" fuel, 20% nitro could only last 15 or so minutes. (In practice this is not a linear relationship. With more nitro, typically a smaller throttle opening is needed for the same amount of power, i.e. at hover. So it's generally more than 15 minutes mentioned here but less than the original 20 minutes.) With all this extra oxygen and fuel going into the engine, more power is available, as mentioned before, up to 50% at 80% nitro has been measured. So for every 5% nitro, a power increase of about 3-4% might occur if everything is adjusted correctly.
Of course 3% is not much, but at 30% nitro which is common in the USA and Japan in choppers 15% to 20% power increases are easily within reach. More power equals a higher combustion pressure which equals more heat! Cooling: Of course with 42% more liquid going through the engine at 30% nitro much more heat can be soaked up - liquid absorbs heat much better than air. There is also 42% more oil going into the engine, almost flushing the internals continuously, which also helps take out more heat. So we have internal liquid cooling! All this extra liquid keeps the metal surface temperatures down and eliminates the burning of oil to carbon. So there are usually little or no carbon deposits in nitro fueled engines above 10% nitro. The cooling effect of nitro is further born out by the increased usage of high nitro fuels in fuselaged models which are almost totally enclosed for drag minimization. The nitro is used just as much for cooling as it is for good power!
| Energy density of some fuels |
|
storage type |
energy density |
|
|---|---|---|
|
by mass |
by volume |
|
|
MJ/kg |
MJ/L |
|
|
compressed gaseous hydrogen at 700 bar [1] |
120 |
4.7 |
|
compressed natural gas at 200 bar |
53.6 |
10 |
|
46.9 |
34.6 |
|
|
diesel fuel / residential heating oil [5] |
45.8 |
38.7 |
|
gasohol (10% ethanol 90% gasoline) |
43.54 |
28.06 |
|
42.8 |
33 |
|
|
biodiesel oil (vegetable oil) |
42.20 |
30.53 |
|
34.39 |
22.16 |
|
|
30 |
24 |
|
|
19.7 |
15.6 |
|
|
hydrazine (toxic) combusted to N2+H2O |
19.5 |
19.3 |
|
liquid ammonia (combusted to N2+H2O) |
18.6 |
11.5 |
|
liquid hydrogen + oxygen (as oxidizer ) (1:8 (w/w), 14.1:7.0 (v/v)) |
13.333 |
5.7 |
|
11.3 |
12.9 |
|
|
6.9 |
12.7 |
|
|
hydrazine (toxic) decomposition (as monopropellant ) |
1.6 |
1.6 |
|
ammonium nitrate decomposition (as monopropellant ) |
1.4 |
2.5 |
|
0.54–0.72 |
0.9–1.9 |
|
|
0.40 to 0.72 |
? |
|
|
compressed air at 20 bar |
0.27 |
|
|
0.22[27] |
0.36 |
|
|
0.14-0.22 |
? |
|
|
0.09–0.11[30] |
0.14–0.17 |
|
|
0.0206 [35] |
? |
|
|
ultracapacitor by EEStor (claimed capacity) |
1.0 [36] |
? |
|
0.002 |
? |
|
- from http://en.wikipedia.org/wiki/Energy_density
| Energy Density of Methanol (Wood Alcohol) |
Edited by Glenn Elert -- Written by his students, an educational, Fair Use website.
topic index | author index | special index
| Bibliographic Entry |
Result (w/surrounding text) |
Standardized Result |
||||||||
|---|---|---|---|---|---|---|---|---|---|---|
| Caretto, Larry. September 11 Homework Solutions [doc]. Mechanical Engineering 694C Seminar in Energy Resources and Technology. California State University, Northridge. Fall 2002. | " In a fuel cell, the maximum work is given by the change in the Gibbs function for the oxidation of methanol is 22.034 MJ/kg." | 22.034 MJ/kg | ||||||||
| Zittel, Werner & Reinhold Wurster. Advantages and Disadvantages of Hydrogen . HyWeb – the Hydrogen and Fuel Cell Information System in the Internet. 1996. |
|
20.16 MJ/kg | ||||||||
| Thomas, George. Overview of Storage Development DOE Hydrogen Program . Sandia National Laboratories. May 2000. |
|
19.9 MJ/kg | ||||||||
| Bossel, Ulf. The Physics of the Hydrogen Economy [pdf]. European Fuel Cell News, Vol. 10, No. 2, July 2003. | " The Higher Heating Values are 22.7, 29.7 or 31.7 MJ/kg for methanol, ethanol and DME, respectively, while gasoline contains about 45 MJ per kg." | 22.7 MJ/kg |
Methanol, also called carbinol, methyl alcohol, wood spirit, or wood alcohol, is a colorless, poisonous liquid with very little taste. Its lack of color is an important hazard and often the strong smell of wood alcohol or kerosene is added so that workers will become aware of leaks and spills. Methanol is miscible with water and most organic liquids, including gasoline. It is extremely flammable, burning with a nearly invisible blue flame. Methanol has become a major feedstock for the synthesis of acetic acid and large amounts of methanol are consumed in the production of methyl esters. Methanol itself is employed as an extractant and solvent for many substances, and is sometimes blended with gasoline in cold weather to reduce condensation problems. It was formerly obtained from wood as a co product of charcoal production.
Ever thought what would happen if you drank a dose of methanol? You probably think no one would do it but if it happened for prolonged periods, methanol can cause blindness or death. It can also be absorbed through the skin.
Methanol's chemical formula is CH 3 OH. It has a molecular weight of 32.04 and boils at 64.7 °C and freezes at -97 °C. Energy density is measured by the amount of energy per mass. The standard unit for energy density is megajoules per kilogram (MJ/kg). The energy density for methanol is around 22 MJ/kg.
Jenny Hua -- 2005
- from http://hypertextbook.com/facts/2005/JennyHua.shtml
| Energy Density of Gasoline |
Edited by Glenn Elert -- Written by his students, an educational, Fair Use website.
topic index | author index | special index
| Bibliographic Entry |
Result (w/surrounding text) |
Standardized Result |
||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Zittel, Werner & Reinhold Wurster (Ludwig-Blkow-Systemtechnik). Hydrogen in the Energy Sector. Chapter 2: Physical Properties . HyWeb. |
|
45.7 MJ/kg | ||||||||||||
| Caldirola, Manuela. Physics of High Energy Densities . Amsterdam: Academic Press, 1961. |
|
47.5 MJ/kg | ||||||||||||
| Thomas, George. Overview of Storage Development DOE Hydrogen Program [pdf]. Livermore, CA. Sandia National Laboratories. 2000. |
|
44.4 MJ/kg | ||||||||||||
| Nommensen, Arthur. List of common conversion factors (Engineering conversion factors). IOR Energy. |
|
36.4-49.6 MJ/kg | ||||||||||||
| Harrison, Reid R. Low Power Circuit Design, Lecture 1: Why is Low Power Circuit Design Important ?[pdf]. Spring 2001. |
|
44 MJ/kg |
Energy density is the amount of energy stored in a given system or region of space per unit volume or mass. It therefore has units of energy per length cubed or energy per mass. Gasoline has an energy density of about 45 megajoules per kilogram (MJ/kg).
Gasoline is a mixture of the lighter liquid hydrocarbons used chiefly as a fuel for internal-combustion engines. It is produced by the incomplete refinement of petroleum by condensation or adsorption from natural gas by thermal or catalytic decomposition of petroleum or its fractions by the hydrogenation of producer gas or coal or by the polymerization of hydrocarbons of lower molecular weight.
Gasoline is one of the most important fuels used in the transportation industry. Most gasoline is used in engines that move automobiles and light trucks. Gasoline engines also power other vehicles and machines, including airplanes (aviation), motorboats, tractors, and lawn mowers.
Arthur Golnik -- 2003
- from http://hypertextbook.com/facts/2003/ArthurGolnik.shtml
| Lubricants |
Among the polyalkylenes polybutylene, a copolymer formed by the polymerization of isobutylene and butene, is preferred. Typically polybutylenes will have an average molecular weight of from about 300 to about 2000 and a viscosity index of from about 70 to about 122 (ASTM D2270). Various grades, corresponding to different average molecular weights, are commercially available from Amoco Chemical Company (Chicago, Ill.) under the name Indopol.RTM. Thus by way of example only, Indopol L-50.RTM. has an average molecular weight of 420 and a viscosity index of about 90 when measured by ASTM D2270 whereas Indopol H-100.RTM. has an average molecular weight of 920 and a viscosity index of about 109. Suitable polybutylenes include:
|
Ave. Mol Wt. |
Viscosity Index |
|
320 |
69 |
|
420 |
90 |
|
460 |
95 |
|
560 |
96 |
|
610 |
97 |
|
660 |
100 |
|
750 |
104 |
|
920 |
109 |
|
1290 |
117 |
|
2060 |
122 |
|
2300 |
122 |