[elhigh]

I've thought about butanol from time to time. If I remember correctly butanol's strong points are:

- 90% of the chemical energy of regular unleaded - a big improvement over ethanol
- already compatible with gas-safe materials and handling equipment
- comparable octane to gasoline, so it's pretty much a drop-in replacement for gasoline.

NOTABLE DOWNSIDES:

- way more viscous than gas. It's like diesel. Conventional gasoline injectors may not be able to handle it.
- Already partially oxygenated, so it has to run richer than gas. A flex fuel injection computer would adapt to this with no difficulty.
- No octane advantage, so you can't get any power back by raising the compression ratio

As you noted, the yield is low. And when I first read about it several years ago, research was underway to improve output via genetic modification of various organisms.

But right now oil is trading at under $55 per barrel. That kind of thing tends to dry up funding from the sources that provide funding but don't have the necessary long view to realize what the funding is intended to hedge against. I haven't heard much about research into butanol lately, only the occasional glimmer about cellulosic ethanol. And again, even then, not a lot. That cheap oil is blinding a lot of people.