Questions regarding Air/Oil Separators

On Sat, 10 Apr 2004 08:15:25 -0400, "Doodybutch"
wrote:

I am think of having one of these Air/Oil Separators installed on my R182
(Lycoming O-540) at annual this summer.

I have a couple of questions:

1) Do they actually work and keep the oily mess off the bottom of the plane?
2) I think there are at least two different ones available - which is the
best?
3) Are there any problems with them?

Thanks,

DB


The following is an excerpt from Sacramento Skyranch's monthly
newsletter (hopefully not breaking any copyright rules here). Quite an
eye-opener on the whole Air/Oil Separator issue. The Sacramento
Skyranch website is at www.sacskyranch.com and is full of very
interesting info.



Crankcase Distillation of Water by Air Oil Separators

The burning of 40 gallons of fuel during a flight produces 40 gallons
of water. Although most of the water goes out the exhaust as a gas,
some ends up in the engine crankcase as byproducts of combustion. In
cold weather we can sometimes see this crankcase water as droplets on
the oil dipstick or rocker box. Engines, such as the Lycoming
O-235-L2C, often have rust inside the rocker covers where the water
condenses and collects inside the cover. How is water that is
produced as a byproduct of combustion, and finds its way into the
engine crankcase, removed from the engine?

Your engine is a distillery in which we add combustion byproducts,
including water and unburned fuel into a oil bath; agitate and aerate
with the crankshaft and other rotating parts; heat until the more
volatile products, principally water, vaporizes into a gas and flows
thru a pipe called the crankcase breather into the cooler atmosphere.
This is illustrated as such:

[Sorry, I can't paste the picture in here]


Usually we think that we need to raise the temperature of the
distillery to the boiling point of water 212 degrees F. (-2 degrees
per 1,000 feet above sea level) to separate the water from the oil.
However, since the water, oil, and other byproducts are being
thoroughly mixed, the water forms a azetrope (constant boiling
mixture) with some of the other compounds which changes the mixture's
boiling point. We end up with a range of boiling temperatures,
possibly lower and higher.

A contaminate that has a higher boiling temperature than water, when
mixed with water to form a azetrope, lowers the contaminants boiling
temperature so that the distillation of water from our sump also
removes other contaminants from the oil. This is the milky white
mixture you sometimes see on the engine breather, dipstick or other
condensing surface.

Corrosion pitting is the most common reason camshaft lobes and
followers are damaged (2nd might be stuck valves). Making sure your
distillery is functioning properly by removing water from the engine
crankcase is important if you want to prevent corrosion damage to your
engine. Normally, you need not worry; operate the distillery often and
make sure you completely warm it up. Ground running the distillery
just adds water and doesn't produce steam -- you need to fly your
distillery to fully heat it up.

Every distillery has a condenser that turns the distilled vapors back
into liquid form. With engines we prefer that condensation occurs in
the atmosphere or in a vent line that slopes downward. Now lets modify
the distillery and add what is commonly called a "air/oil separator"
to our system. I use the more accurate term "gas/liquid separator"
since our separator cannot tell the difference between air and any
other gas, or oil and any other liquid. If our gas/liquid separator is
cooler than our oil sump, then our gas/liquid separator also becomes a
condenser with a return line back to the engine. Oil, along with any
distilled liquids, are returned to the engine.

Take for example a worst case scenario. You mount our gas/liquid
separator in a cold area of the engine compartment. You attach it to a
large heat sink called the firewall. Everything you have done has
increased your condenser's efficiency at condensing water and other
vapors into a liquid. Now you're engine pumps the condensate back into
the engine along with some engine oil. You couldn't design a better
way of trapping water in your engine.

The warmer our gas/liquid separator, the less efficient our distillery
is at condensing water and pumping it back into the engine.