Ethanol...biodiesel? Funny you should ask. In the current issue of CAR and DRIVER Magazine, columnist Pat Bedard discusses this issue. Let's distill (if you'll pardon the pun) some of what he says.
This is not to say that running cars on ethanol, the alcohol from fermented vegetable matter, is an entirely bad idea... Ethanol packs a large amount of energy into a gallon compared with alternatives such as natural gas, LPG, and hydrogen. It's not as good as gasoline, however; you need about 1.5 gallons of ethanol to drive the same distance as on one gallon of gasoline...
This has always been the problem with ethanol. We pilots are always performing our delicate balancing act, trying to bring along enough fuel with the particular payload. Requiring that we carry more fuel is not going to go over well, except for perhaps flight school ships that stay fairly local.
Ethanol has other problems, too. To ensure good engine starting, it needs to be mixed with gasoline... Moreover, ethanol can't be shipped in pipelines because it picks up water.
Yikes! Will the effect of water in the ethanol be the same as water in the gasoline (i.e. silence from the engine compartment)?
The usually skeptical Bedard hedges a little on biodiesel:
However, used restaurant "grease," known in the recycling trade as yellow grease, or any vegetable oil, can be transformed into a substitute for diesel fuel by a chemical process known as transesterification. It's a good substitute, too, much closer to diesel than ethanol is to gasoline.
Diesels for airplanes simply have not caught on here in the U.S. But I wonder how biodiesel would work in a turbine engine? It would be interesting to find out.
Of course, whichever alternate fuel we use, we're going to have to have a distribution system for it. You sure wouldn't want to take off on a cross-country in an airplane for which there was limited availability of fuel. You might as well have an aircraft powered by an electric motor with a long, long extension cord.
Right now, it would be pretty hard to replace the current distribution system, or even augment it, which is why gasoline is going to be around for a long time for cars. Whether or not
we'llbe able to use car gas in our airplanes is the question, especially if the manufacturers want to stop producing avgas. And you know that there are many airplanes that cannot use auto fuel due to their high compression ratios.
"Alternate fuels" is a great theory. The reality of actually implementing them is a whole 'nother subject.