Wow!

I have trouble seeing biodiesel as an aircraft fuel for the same
reasons #2 diesel is not suitable: the tendency to gel and/or solidify
at the low temperatures commonly encountered at high altitudes. JetA
would probably be more suitable, particularly if it were heated. The
heat would have to be controlled somehow. Biodiesel, if made from the
right vegetable oil stock, might also be suitable if heated.

The other problems I can see right off the top of my head are that of
low vapor pressure and higher viscosity. If the fuel was sprayed
directly on hot metal, the low vapor pressure might not be a factor,
particularly if special injectors were used. Maybe. The higher
viscosity would require a modified fuel system including injectors.
And probably the fuel map would have to be made temperature aware as
the viscosity of some of these fuels change dramatically with changing
temperature. On the plus side, a lower volume of fuel would have to be
dealt with per cycle for the same power/energy; and range would be
improved.

Looks like a major development effort to me.

Doc Custer
Retired software engineer and sometime Audiologist
Building RV9-A. Fuselage

Doc,

 Cold performance is an issue.  The fuel works well in diesel equipment
with no modifications.  I'd be surprised if we couldn't replace the gas
injectors with some of the new piezoelectric units being used in common-rail
engines as an update to the earlier heavy fuel work?

 Folks have been using waste veggie oil in diesel cars and trucks for
years.  Add a second fuel tank, with either a coolant-fed heater core in the
veggie tank, or by running the veggie oil thru a heat exchanger on the way
to the engine.  Start the engine on diesel fuel until the water warms the
veggie oil (and the viscosity drops) and switch the fuel valve over from the
D2 tank to the veggie oil tank.  Switch back to Diesel to purge the fuel
system before shut-down.

 Maybe reduce the size of the water radiator a bit and direct heat to the
biodiesel in the wing tanks to keep it warm instead.  Maybe a three-tank
system for a biodiesel rotary airplane similar to the veggie oil cars -
start and stop on a small tank of Jet A, switch to warm biodiesel for
cruise, and back to Jet A before landing.

Andy Hecker


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