Welcome to European Tribune. It's gone a bit quiet around here these days, but it's still going.
Hm-m, I did some read-up. Branson wants ethanol, not biodiesel. Of ethanol, this study, says:

Ethanol, being an alcohol with similar properties to methanol, is also unsuitable as a jet fuel for similar reasons. Ethanol's energy density and specific energy are too low, and would thus limit aircraft range and maximum payload.

At low power settings ethanol jet engines would emit acetaldehyde (C2H4O) again bringing localised health problems around airports, especially for ground support staff.

Ethanol's flash point of 12°C is even lower than methanol's, so it would not meet jet fuel specification requirements, and would present major safety dangers.

So Monbiot was right for the worng reasons.

The study evaluates other possibilities, too. I summarise:

  • Biodiesel: as additive, it raises the cloud point (Monbiot directly lifted a sentence from the study here) as well as the freezing point, but there is research into refined biodiesel blends for which the effects are less. Fatty acids in biodiesel can be oxydised, but the resulting storage problem is minimal when it is a 10% additive. Production cost is significantly above that for oil-derived jet fuel even at the lower limit, potentially multiple times of it. There is also the issue of conflict with the needs of road traffic (which as afew et al calculated already can't be supplied from domestic biodiesel production).

  • Methanol: problems as for ethanol.

  • Synthetic kerosene: poor lubricity due to lack of sulphur and low aromatic content, but this can be mitigated with additives. Effect of lack of aromatic stuff on turbines must be investigated with tests. Somewhat lower energy density, impacts long-range flights. Too small domestic capacity for biofuel production (they calculate 10% of present demand). This is a very expensive option.

  • Liquefied methane: needs special engines, expensive, methane leeaks during the production chain or in the air have greenhouse effect [and for lack of a 'methane cycle', like the carbon cycle for CO2, this can't be ignored for biogas-methane].

  • They speak of liquefied H2 too. Significant aircraft modification needed. No solution yet for reducing nitrogen oxide emissions (solutions for kerosene-burning engines not applicable). Very expensive.

*Lunatic*, n.
One whose delusions are out of fashion.
by DoDo on Wed Sep 27th, 2006 at 09:59:48 AM EST

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