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Period aircraft engines run on avgas, 100 octane gasoline. They might run on gas as low as 80 octane. Water contamination in avgas can destroy an engine in one flight!
Alcohol does not lubricate valves and moving parts, and destroys a lot of gaskets, hoses, etc.. Modifying an engine to run on alcohol can be done, but you'd need to take the engine completely apart, fabricate non-rubber substitutes for various synthetic materials (fuel hoses, seals, gaskets), adjust fuel systems, ignition systems, etc. Valve systems especially rely on lead in fuel to keep lubricated. Modern (21st Century) American cars operate on up to 10% alcohol, normally, but of course they're designed for that.
Alcohol burns most efficiently at a 9:1 ratio with air (whereas gasoline is 14:1 to 16:1, depending on the engine and fuel); hence the alteration to the engine's fuel injection system. Alcohol has about 34% less energy per gallon than gasoline, but can produce a bit more power; range will be reduced about 10% if the engine runs otherwise. More improvement in fuel efficiency would require changing the compression ratio of the cylinders -- unlikely in the field with minimal tools!
Alcohol will loosen dirt; good fuel filters are even more important in an alcohol-fuel engine. Charcoal can be used to pre-filter the alcohol before it's put into the plane. Alcohol-fuel engines don't start well in cold weather -- ethanol doesn't vaporize sufficiently below about 60 degrees fahrenheit. Using a bit of gasoline, propane or ether for starting is common in older, simpler alcohol-fuel engines.
The engine will still need regular lubricants -- oil, basically. Probably some very nice animal oils -- whale oil or dinosaur oil, anyone? -- could be handwaved as good enough to substitute for motor oil. Remember, the engine weighs 1068 lbs. dry! Just taking it off the aircraft is a chore. And the sort of home-made conversion we're talking about here would have to be partly un-done if the plane ever is to run on gasoline again.
Ethanol is the best choice; produced by the fermentation of sugars -- wheat, corn, rice, beets and cane are examples of vegetation with high sugar content; they give a high yield when fermented and distilled. A basic fermenter takes 50 gallons of water, 130 pounds of sugar, and some yeast to produce basic alcohol in about 24 to 48 hours (varies by temperature). Then you'd need to run it through a reflux still ... the basic pot still only makes about 70% alcohol. The output from that water-sugar fermenter + a reflux still is about a gallon of reasonably-pure ethanol in a day or so. Of course, more or bigger fermenters, and bigger stills, gives more output.
In a general way, using sorta-woody, sorta-sugary "feed" in a fermentation-distillation process, 1 ton of "dried plant matter" will produce 20 to 40 gallons of ethanol -- at best.
The construction of fermenter tanks and reflux stills calls for some effort, too -- nothing Doc Apache's gang can't do, but still a chore. The body of the still and the tubing needed for the actual distillation coils will be the hardest part to build. Salvaging tubing from a crashed Duck is probably the best source of tubing.
"We haul in a ton of chopped sugar-knobs from the antediluvian jungle, chop them up and feed them to the big fermenter tanks (made like large enclosed wooden vats). Drawing off the raw alcohol after a day, we run it though the reflux still -- burning plant debris and sugar-knob stalks keep the still hot and bubbling along. Out the other end of the still dribbles hot, pure alcohol, to be filtered through charcoal and poured into the plane. In about 8 or 9 days, we will have filled the Duck's tanks. Meanwhile, 'Skippy' and Bob are laboring over the dismantled engine, cursing and sweating."
Whale oil, dinosaur oil and vegetable oils need to have their wax components removed before being useful in this kind of motor. However, some sort of super-peanut could be imagined, that, when pressed and filtered, produced something that could be used in the engine -- again, at least some adjustment of the fuel pumps and fuel injectors would be needed, but (with some hand-waving) perhaps less than for ethanol conversion. A biological-derived oil would probably need more cleaning and de-gunking of the engines -- they're not a happy in the high temperatures of an internal combustion engine, and produce a lot of gunky deposits (compared to gasoline or ethanol). Peanut oil, butter, animal fat, deep-fryer oil (used in "frybrid" engines), algae oils, etc. have been used to operate internal combustion engines -- especially diesel engines (in fact Rudolf Diesel's first engines ran on peanut oil). You need to add a pre-heater to the fuel feed system -- natural oils of this sort need to be heated to reduce their viscosity.
"King Bobo tells us that the oil of the giant macrola nut is burned by their people in stoves and forges. 'Skippy' says it might be purified and filtered enough to run the Duck's engine -- but it's gonna run very rough and smoky, and we're gonna have to fiddle with the injectors, and add an electrical heater to the fuel system."
From the Experimental Aircraft Association, regarding partially-alcohol "gasoline" in modern aircraft:
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Alcohol in autogas when used in aircraft has caused numerous problems such as fuel leaks and fires due to rapid deterioration and swelling of rubber gaskets and seals. Fuel tank quantity floats made of cork and/or composite materials are attacked by the alcohol in fuel and allow particles to float in the fuel, clogging fuel screens, plugging carburetors, etc. Sloshing compound used in many fuel tanks to seal leaks also reacts with the alcohol, causing fuel leaks and fuel system contamination.
Marvel Schebler carburetors that have the old composite floats are damaged by 100LL fuel as well as autogas and are particularly sensitive to alcohol in the fuel. Aircraft owners should have the newest metal float installed. Stromberg carbs such as used in the TCM-C and A 65/75/85 models that have an old style of neoprene-tipped float needle in the carburetor is attacked equally by 100LL and autogas and should be replaced with the newest style needle. Swollen float needle tips cause a lean mixture and eventual engine damage. Cessna aircraft with rubbertipped fuel strainer plungers are also damaged by the use of autogas with alcohol and frequently leak after a short time of use with an autogas/alcohol mix.
Most recently a “malfunction” appeared in the FAA alerts describing a Piper aircraft that caught fire in flight due to a leaking fuel strainer gasket that was swollen by the use of alcohol mixed with autogas. The pilot was able to turn off the fuel to stop the fire and save himself but he was forced into becoming a glider pilot.
Any rubber part such as fuel lines, fuel cells, and 0-rings in fuel selectors are subject to damage from alcohol mixed in the fuel. In addition to problems associated with alcohol in autogas, oxygenated fuels have been tested and shown to provide 3 to 5 percent less BTU output than avgas, thus decreasing range somewhat. |