George's Gas Class
In this article, I'll try to shed some light regarding the variety of fuels available and their applications. I'm not a chemist, so I'm going to focus on fuel from a mechanic's point of view. I don't necessarily believe you have to know the composition of fuels to properly use them.
Above all else, remember rule number one: SAFETY FIRST! Your life is the most important thing here, so great care must always be observed in when handling fuel. Methanol is extremely poisonous. It's an accumulative poison, one that builds up over time, and it can oxidize to form formaldehyde. This can cause blindness, or worse. It can be absorbed through the skin and lungs by either direct exposure or inhalation of fumes. Also, inhalation of the exhaust can be very dangerous. Be careful and use your head.
Methanol and ethanol will absorb large amounts of water from exposure to air, so they must be kept in airtight containers. After burning methanol or ethanol in a two-stroke engine, it's most important to run a petroleum/oil mix through the engine. If you don't do this, the alcohol will corrode the cylinder wall, crank bearings, etc., which will lead to premature engine failure. I recommend that you run a half-quart of 16:1 petroleum/oil mixture through the engine. In most brands of fuel, higher octane ratings are achieved by adding tetra-ethyl-lead and ethylene dibromite. The decomposition of these additives may cause problems in two-stroke engines. The use of higher octane should be limited to blending additives such as acetone, methyl benzene, benzol, ethanol, or methanol. Such fuels will not cause problems in two-stroke engines, but they are more expensive.
Both methanol and ethanol have an octane rating of 140 to 160, so they can be used with very high compression ratios. This can result in an increase of up to 15 percent in horsepower. Where does the power increase come from? The two-stroke engine is a heat-type engine which burns fuel to cause expansion of gases, which propels the piston. The more heat produced by combustion fire, the more pressure will be exerted on the piston resulting in a power increase.
The fuel/air ratio for best power is 1:12.5 for petroleum, and 1:5.5 for methanol. One pound of petrol has an energy potential of 19,000 BTU; methanol has 9800 BTU. However, when these are mixed together, more heat energy is produced.
12. 5 / 5. 5 = 2. 2 7 * 9 8 0 0 = 2 2, 2 4 6
{(22,256/19,000)*100}-100=17%
A 17 percent heat energy increase is very desirable, but there is a catch. With this mixture, you will bum 1.8 times as much fuel as with petrol alone. When using exotic fuels, make sure to increase fuel flow accordingly, or engine life will be shortened.
Also, the oil/fuel ratio needs to be changed. Start with 20:1 and work from there. An alcohol burner requires a strong ignition system, due to the much higher compression ratios, as well.
There is much confusion about what octane ratings are. Most people realize that we can get extra power with a high-octane fuel because of the higher compression ratio and spark advance. However, changing from, say, 97 octane to 110 octane will not give an increase in power. In fact, you could lose power if the engine is not modified accordingly. To combat this problem, I have developed my own method of finding the correct combination of octane and compression After the engine is built, proper carburetion is established. I begin to mix two brands of gasoline, for example, 93 octane pump and 116 octane racing fuel, in small increments. Take two gallons of 93 and add one quart of 116. Now take a speed run verified by radar gun. You should see a speed increase. Now, increase the 116 octane and make another run. Keep doing this until you notice a decrease in speed. You are now running too high an octane rating. Record the mixture that achieved the highest speed. This is the octane requirement for that particular engine setup.
The anti-knock properties of hydrocarbon fuels are related to their molecular structures. The paraffin's heptain and kerosene are long chains of carbon and hydrogen held together by weak molecular bonds which are easily broken down with heat. Iso-octane is a member of the iso-paraffin- fin family, which forms stronger bonds to resist detonation better. The cyclo-paraffin's (napthens) also have good anti-detonation properties. The aromatic fuels such as toluol also have very strong bonds. They also have good anti-knock characteristics. The chemical composition of the fuel determines just how rapidly the fuel will bum and how well it will resist detonations at high compressions and temperatures. For this reason, a high octane fuel will not increase engine power unless the engine actually needs fuel which is chemically stable at high temperature and pressure. Obviously, if the engine does not have proper compression to provide high combustion and temperature, then the octane fuel will not burn completely, resulting in power losses.
Nitromethane is not a good fuel, but it can provide two-stroke engines with a useful power burst. Nitrous contains approximately 53% oxygen by weight, so it is a chemical supercharger. In drag racing car engines, nitro is blended up to 15%, but in two-stroke engines it creates serious problems. I don't recommend its use in anything but small single-cylinder engines.
As mentioned before, an engine could waste power if it is mismatched with the octane requirement of a fuel. If the octane level is too high, only wasted energy and money are produced. However, if the octane level is too low, then we are faced with serious problems. An engine will run on one batch of bad fuel (too low octane), but it will burn holes in the pistons. Another batch of bad fuel can cause engine destruction through detonation.
So you can see how it's important to both the engine manufacturers and consumers to know the octane characteristics of each batch of fuel. To determine this, a special research engine was constructed, by the U.S. government utilizing variable compression features to evaluate and grade fuels. The test engine was a single cylinder, which was operated at standard temperature under full load at standard rpm. The compression was increased until the test fuel produced engine knock. The fuel's anti-knock quality would be specified as Highest Useable Compression Ratio (HUCR). In order to attain reliable tests, the high reference fuel chosen was iso-octane, and the lowest reference fuel was normal heptane. A series of tests were run, using various mixtures of those two fuels, until the blend was found which produced anti-knock behavior identical to that of the test fuel. So if the mixture of 75% iso-octane and 25% heptane produced the same anti-knock characteristics as the test fuel, the test fuel would receive an octane rating of 75.
Recently, a motor-test method, employing a greater engine speed and higher inlet temperature than the research test has come into use. Since the motor test is more severe, it yields ratings 6-12 octane lower than the research test. This is important, since it informs us that the Motor Octane Number (MON) is more relevant to racing engines than the Research Octane Number (RON). The number shown at the pumps is the Pump Octane Number (PON), the average of the RON and MON: (RON+ MON)/2=PON. This yields a credible rating of a fuel's performance under actual load conditions. I sincerely hope that this information will produce better racing engines and add to your enjoyment of our sport.
George Grabowski HPT Sport USA