In article .com,
" wrote:

On-Condition wrote:
wrote:
I'd be interested in reading anything on the practice of using diesel
and biodiesel in turbines your refering too. Did you read this
somewhere, or is that from experience? Have you actually heard of
Biodiesel being used in jets? Or is your reference to biodiesel gelling
related to cars?

The first time I heard of biodiesel was in a documentary about some
Halifax buses. They use fisheries byproducts. They have had to deal
with gelling, though Halifax winters are not all that cold.


To get a little OT, there is a lot of neat stuff being done right now
with biomass hydrocarbons. (veggie oil, fish oil etc.) The bugaboo
seems to be injector coking in direct injection engines, though actual
experienced rate of coking from one motor to the next is a point of
huge debate in the alternative fuel crowd these days. Indirect
piston-pump injected engines will apparently run on straight veggie oil
reasonably well with few ill effects or modifications.

These guys are heating the oil and running straight to the motor.
Apparently the added energy causes the long stranded molecules to burn
cleaner which is what averts the coking. I'd be highly interested in
seeing somebody do that with an allison 250 and what the results were.

No knowledge or experience involving biodiesel in turbines, but winter
diesel is/was being used by DHC6's in the artic about half of the time
since turbine fuel is only available at the main bases. Their PT6's
are in fact derated to 600 shp as suggested
for another airplane type. I never saw any technical documentation
on this, it being common practice.

Regarding Hydraulic lock I was thinking more preventatively. Like going
to the hanger once a week and walking through a few blades regardless
of whether you were actually going flying. Though I would figure at
15/1 it would require much less oil to frag the engine than at 7.5/1.

No doubt, but I think either ratio will suffice as soon as you start,
especially with one of the inertial starters that just won't stop
once engaged. Walking the props used to be mandatory in the military
where even a desk gets a walkaround twice a day ;-)

My point was that diesels start at 15/1 and gas engines are around 7/1
or 8/1 So oil leakage in a diesel should increase cylinder pressure
way faster than it would in a gas engine. For example: an ounce of
excess oil in a gas engine my increase the cylinder pressure by 10% or
so, the same ounce in a diesel of the same displacement would increase
the pressure by much more than 10%. At a higher pressure the mass of
the air displaced by a constant uncompressable volume (the oil)
increases.

Obviously you don't have to fill the cylinder completely with oil to do
a lot of damage. Just increase the pressure in the jug to the point
were rings crack or bolts become fatigued. With the four strokes you
walk the blades, the valves open and the oil that leaked past the lower
rings dribbles into the exhaust stack. With the Zoche there is no
valve, so once oil dribbles into the cylinders past the rings, how do
you get it out? I would guess the only way to clear a lock or to
prevent an over-pressure from a partial hydraulic lock would be to
remove the injector and cycle the engine. Or perhaps the porting design
prevents it? I don't know.

Zoche is a 2-cycle engine, so there is no oil in the crankcase to leak
into the cylinder. Actually, there is no airplane that has ever flown a
Zoche, either, for that matter. He has been around since at least 1980
and has never flown the engine!


I saw that there is a diesel CH701 flying with the engine out of a
Mercedes Smart. I'd love to read more about that bird but haven't been
able to find any good info.

-Matt