REFLECTOR: Oil Breather Nipple Into Exhaust Pipe
Brian Michalk
michalk at awpi.com
Sun Apr 27 13:40:15 CDT 2008
I was thinking about your question the other day.
Would there be an inherent problem with venting the case to the intake
manifold? It would sure keep oil spray to a minimum.
I would do it before the throttle body, close to ambient air pressure.
Bob Jackson wrote:
> Chuck, Kirk, Brian & All – thanks for all the ideas and suggestions on
> routing the oil breather into the exhaust pipe.
>
>
>
> Thinking more about it based on Brian’s astute observation that although
> there may be fairly high (in our case ~108 ft/sec exhaust gas
> _velocities_ per side at WOT since ours is a twin turbo design) doesn’t
> necessarily mean high exhaust gas _pressures_ at a oil breather nipple
> if it’s located only about a foot from the exhaust pipe outlet (our
> case). If I did my math right, I figured the 108 ft/sec exhaust gas
> velocity from our ~225 cfm per side air flow rates through 2.5 inch
> diameter exhaust pipes. I’m also now thinking that although our
> _intake_ air rate may be ~450 cfm total, the _exhaust_ gas rate will
> probably be considerably higher than that due to the combustion of the
> fuel too, correct?
>
>
>
> What Brian says makes good sense to me – how can you have high pressures
> that close to ambient pressure when it’s only a foot away through a 2.5”
> tube? But my EE background is not strong enough in flow dynamics to
> figure it out exactly. I’m probably splitting hairs, as Brian says!
> Does anyone have the theoretical background to confirm that oil breather
> back pressure (or Venturi ‘vacuum’ affects) should not be an issue,
> depending on the angle of the nipple into the exhaust gas flow?
>
>
>
> From the practical side, I did get a chance to look fairly closely at a
> new Turbo Cirrus TIO-550N (turbo-normalized by Tornado Alley for
> Cirrus). They run their oil breather line into an exhaust pipe nipple
> that enters the pipe at right angles and appears to be cut off flush on
> the inside. There is about two feet of pipe past the nipple to the
> outside end of the exhaust stack…
>
>
>
> My inclination at the moment is to copy the Cirrus approach.
>
>
>
> Chuck – our first plan was to use an air-oil separator, but we’ve gone
> away from it because of stories of the condensed water vapor returning
> to the crankcase with the condensed oil, and the internal corrosion
> problems that may be caused by the water. When you say your oil
> analysis has been good over the years, have you noticed any problems
> that may have been caused by the returned water?
>
>
>
> Thanks for the help!
>
> Bob
>
>
>
> ------------------------------------------------------------------------
>
> *From:* reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]
> *On Behalf Of *Chuck
> *Sent:* Wednesday, April 23, 2008 2:26 PM
> *To:* Velocity Aircraft Owners and Builders list
> *Subject:* Re: REFLECTOR: Oil Breather Nipple Into Exhaust Pipe
>
>
>
> Bob, have you considered an air-oil separator? The turbo's will create
> higher cylinder pressures (temps) and thus more blow-by through the
> rings. This will send more oil/water vapor out the breather and into the
> exhaust/atmosphere. Anytime you weld an exhaust pipe, your adding a
> stress riser which can crack and fail. If you do it, you might want to
> have it normalized (heat treated) afterwards.
>
>
>
> I've had a separator for years and it works well. I'm also finishing my
> add-on turbo and plan to keep the same system. I get very little oil
> through the separator discharge tube and my oil analysis has been fine.
>
>
>
> Chuck H
>
>
>
>
>
> Bob,
>
> A simpler though less aesthetic solution would be to clamp a short
> length of pipe to the leeward side of the current exhaust pipe and
> exiting the cowl through the same opening that you have currently.
> You could attach the oil breather tube to this pipe. If the exit end
> of the pipe is cut diagonally as your exhaust pipe may be, I
> believe that will give the slight negative pressure that you are
> looking for. This solution also may mitigate the freezing over of
> the breather line.
>
>
> Kirk
>
>
> > From: bobj at computer.org
> > To: reflector at tvbf.org
> > Date: Tue, 22 Apr 2008 22:04:35 -0500
> > CC: bobj at JaxTechLLC.com
> > Subject: REFLECTOR: Oil Breather Nipple Into Exhaust Pipe
> >
> > Does anyone have experience or ideas for the best way to weld a
> nipple into
> > the exhaust pipe for the oil breather hose?
> >
> > We want to weld a nipple for our oil breather hose into the short
> exhaust
> > outlet pipe of one of the turbochargers (we've custom-added to our
> IO-550N).
> > We are aware of several issues and concerns. One issue is how far the
> > nipple is extended and/or is angled into the exhaust gas stream.
> If for
> > example on the inside of the pipe, the nipple is extended and
> angled away
> > from the turbocharger, it might create a small Venturi effect and
> help draw
> > moisture and oil 'fumes' out of the crankcase. But if angled away
> too much,
> > this Venturi might be strong enough to excessively de-pressurize the
> > crankcase and cause problems.
> >
> > Or, if the nipple were angled a little too much back into the
> direction of
> > the turbo exhaust, it could positively pressurize the crankcase
> and cause
> > engine seal problems.
> >
> > Hopefully, there is an angle of the nipple that creates no positive
> > crankcase pressure, and with just the proper, small amount of negative
> > pressure to help draw out the oil fumes slightly.
> >
> > Another issue we're concerned about is that this short stub of a
> breather
> > nipple on the inside of the turbo exhaust pipe could eventually
> burn through
> > or break off and strike the prop. This has apparently happened in
> the past
> > with some certified aircraft (not bang into the prop, just break off).
> >
> > Finally, we've also heard that if the nipple enters the exhaust
> pipe at
> > right angles and is flush cut with the wall of the exhaust pipe, not
> > extending into the inside of the breather nipple, it may be slightly
> > pressurized and can become completely clogged with 'soot' over a
> period of
> > time.
> >
> > If anyone has experience or suggestions for how far in to extend
> the oil
> > breather nipple into the exhaust pipe, and which way to angle it,
> we would
> > appreciate the help.
> >
> > Or alternatively, if someone has a (TCM or Lycoming) engine with a
> factory
> > installed oil breather nipple, maybe they could look to see how
> far the
> > nipple extends into the exhaust pipe, and at what angle.
> >
> > Thanks,
> > Bob Jackson
> > N2XF -- Ten years and still working!
> >
>
>
> ------------------------------------------------------------------------
>
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