It can be done, however, it won’t solve the energy crisis. You still need to spend more energy to make and transport the ethanol than you’ll ever get out of it. Until it’s made using 100% renewable means (wind, solar, etc…) then it’s not going to be any kind of fix.
Additionally, cars can be converted to run on ethanol , but emissions certification becomes a major problem. From a technical standpoint, you just pretty much just have to change the timing and fuel/air settings for an engine, and then make sure all of parts in the fuel system play nicely with ethanol. I.e., you can’t have seals that absorb the ethanol and eventually fail.
I can’t think of this topic without getting a picture of the Simpsons treatment of it: Homer at the ethanol bowser alternating the nozzle between the fuel tank and his mouth: “One for you and one for me…”
Technically, a big hurdle is that alcohol-powered cars are very hard to start in cold weather. This is why they’re selling E85 (85% ethanol, 15% gasoline) for use in “flex-fuel” vehicles. The gasoline makes sure that you can actually start the thing in the middle of winter.
As for making ethanol efficiently, there are some people who think that switchgrass might be much better suited for ethanol production than corn is.
Ok, even if alcohol production does give back more energy than it takes to produce it, where are you going to grow all these additional crops? I find it difficult to imagine that there is so much arable land just sitting around in the world. Isn’t it already being used to grow food?