Alcohol fuel is permitted in most categories of speedway and dirt flat-track racing. 117
Two Stroke Performance Tuning
Both methanol (methyl alcohol) and ethanol (ethyl alcohol) have an octane rating by the Research method of 140-160, depending on mixture richness. Therefore these fuels can be used with very high compression ratios. Methanol and ethanol have a very high latent heat of vaporisation, i.e., it takes a lot of heat to convert them from liquid form into vapour. Petrol has a latent heat of evaporation of 135 Btu/lb., methanol 472 Btu/lb. and ethanol 410 Btu/lb. This heat, required for proper atomisation, is removed from the piston crown, combustion chamber and the cylinder, resulting in an internally cooler engine. An engine burning methanol will usually show a 6-8% power increase over one running on Avgas 100/130 (i.e., Racing Fuel 100), without any change in compression ratio. With the compression ratio increased to its maximum, power can rise as much as 15-17%. Where does the power increase come from? The two cycle engine is a type of heat engine, i.e., one that burns fuel to cause the expansion of gas, and the subsequent movement of the piston. The more heat produced by the combustion fire, the more pressure there will be exerted on the piston, which gives us a power increase. Using petrol, the fuel/air ratio for best power (i.e., the strongest force on the piston) is 1:12.5. With methanol, for example, we can increase the fuel/air ratio to 1:4.5, although I usually prefer a ratio of 1:5.5; less than 1:7 is too lean. One pound of petrol has the energy potential of about 19,000 Btu (one British Thermal Unit is the amount of energy required to raise the temperature of one pound of water one degree Fahrenheit.). In comparison, methanol delivers around 9,800 Btu/lb., which means that it produces less than 52% of the heat energy of lib of petrol. However, because we are mixing more methanol with each pound of air (1:5.5) than petrol (1:12.5), we are actually producing more heat energy by burning methanol. To work out how much more heat energy is produced, we have to divide 12.5 by 5.5, which equals 2.27. Next we multiply 9800 by 2.27, which gives us 22,246. This indicates that methanol, in the correct fuel/air proportions, will produce 17% more heat energy than petrol at the correct fuel/air ratio.
By comparison, the maximum increase we can obtain using ethanol is about 10%, although it does have anti-knock and cooling properties very nearly the same as methanol. In coming years, I expect we will see a marked increase in the useage of ethanol in both racing and road engines. As the world's oil supply dries up, more racing organisations and governments will encourage the production and use of ethanol derived from grain and sugar producing plants. Strong public opinion against all forms of motor sport using valuable reserves of crude based fuels will, I expect, soon force many sanctioning bodies to ban the use of petrol in motor racing, with the obvious alternatives being ethanol or ethanol/toluol, ethanol/acetone blends. From the above calculation, you can see that an engine running on straight methanol will burn more than twice as much fuel (1.8 times as much for ethanol) as one burning petrol. Therefore you must be careful to ensure that the fuel tap, fuel lines and needle valve will flow the required amount of fuel. This can present some problems, as many carburettors will not flow the required
amount of fuel through the standard needle and seat. Often a larger replacement is not available, so you will have to enlarge the discharge holes to increase flow by the amount necessary. At times you will find it impossible to get main jets large enough, so again you will have to resort to some drilling. Most Mikuni carburettor jets (the hex head type) are classified with regard to their fuel flow rate, the number stamped on the jet standing for the ccs of fuel the jet is capable of flowing in a certain time. If you are changing from petrol to methanol, then you should start testing with jets at least 2.3 times as large, eg: change 210 jet to a 480. The round head Mikuni jets are rated according to their nominal bore diameter in millimetres, eg: a round head 250 jet has a nominal aperture of 2.5mm. Again, when changing from petrol to methanol you will have to begin with jets with an aperture area 2.3 times as large. (Aperture area = nr2). Keep in mind also when you convert to an alcohol fuel, either neat or blended, that the fuel/oil ratio may have need of adjustment. Straight methanol would require only 80% as much oil, or a 25:1 ratio in many applications, although some engines will require a 16:1 mix. It is always best to start testing at 20:1 and work from there. There are other problems involved in the change to alcohol, some of which will affect you and some your engine. Since your life is the most important, we will deal with you first. Methanol is extremely poisonous and, as it is an accumulative poison, it can build up over a period of time and oxidise to form formaldehyde, eventually causing blindness or even insanity. It is absorbed through the skin and lungs, either by direct contact or from the vapours. Inhalation of the exhaust gas can also be dangerous as vaporised methanol is usually present, especially when rich mixtures are being used. Alcohols are a very effective paint stripper, and they may attack some fibreglass resins. They have a scouring effect on fuel tanks and lines so these should be soaked in alcohol and then drained so that the residue does not find its way into the carburettor when you switch from petrol to alcohol. Methanol and ethanol will absorb huge amounts of water out of the air, so they must always be kept in an air-tight container. The fuel will also have to be completely drained from the tank and the carburettor to prevent the formation of water-induced corrosion and oxidization. This can be particularly damaging to a carburettor and usually results in blocked metering passages. After burning alcohol in a two-stroke engine it is most important to run a petrol/oil mix rich in oil through the engine each time you put your machine away after a day's running. If this is not done, you v,'ill soon find corrosion and etching of the cylinder wall, crank and piston pin, needle and ball bearings that will lead to premature failure. To prevent this occurrence, I would suggest that you run a half pint of 16:1 petrol/oil mixture through the engine. In colder climates, starting difficulties may be encountered when pure alcohol is being burned. Some use other more volatile fuels blended in, to help overcome this problem. Usually 5% acetone or a maximum of 3% ether is used. I do not recommend starting aerosols containing ether, due to the possibility of engine damage being caused by detonation. Personally I feel the best method is to remove the spark plug and pour about a half teaspoon of either petrol or neat acetone into the cylinder before you attempt to start the engine. Alcohol burners demand a good ignition system. Not only does the ignition have to cope with much higher compression pressures, it may also be called on to fire plugs
Two Stroke Performance Tuning
wetted by the very rich mixture being inducted. Alcohol fuels burn much more slowly than petrol, so it will be necessary to experiment with more ignition advance. It is not possible to predict just how much additional advance will be required as there are so many variables involved, but you should begin testing with about an extra 3-5° advance. Before you advance the spark lead, do make sure that the carburation is fully sorted out. If the engine runs just slightly lean, with added spark lead you could very easily hole a piston. As well as a much larger main jet, it is probable that a different needle profile and a larger needle jet will be required. To correct off idle leanness, a bigger pilot jet and a small 1.0 to 1.5mm slide cutaway may be needed.
Originally Posted by jbiplane
Thank Norman, Frits and others. I found here many interesting ideas. We are small company which works like "engine atelier" for small aircrafts, UAV and other applicarion where weight and fuel economy are vital. To the moment numerous codes like ~bimotion ~mota ~Ricardo Wave ~Lotus concept.
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. is this happen to be one of your saws ?
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