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07-17-2014, 05:07 AM
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Join Date: Sep 2007
Location: Central IL
Posts: 5,516
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Quote:
Originally Posted by Toobuilder
Newer diesel powered light trucks have exhaust tip augmentors that draw in fresh air to dilute the particulates. Any reason the same concept could not be applied to an aircraft engine? Exhaust flow combined with cowl exit airflow should be able to generate negative pressure in this venturi. Benefits include no need for the reed check valve, and the temperature of the stub pipe will be well below the coking temperature.
Might not have quite the "sucking power" of the reed valve tapped into the primary tube, but should still pull some, and keep the belly clean.
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The reason for the augmenters is to cool the exhaust during regeneration of the particulate trap. The trap is a ceramic filter that collects the carbon particulates and then uses 740 C to burn them off. This must be done at high mass flows out the exhaust or the trap will overheat during the burn off. They can get over 1000 if over loaded. In the early testing of this system the exhaust burn off paint of nearby objects and the temperatures ignited fence posts and other combustable materials nearby (pants legs). That is what the augmenter is for, temperature dilution.
Almost nothing is free, tapping pulse energy with a check valve is. Higher velocity ( to operate a venturi) comes at a price of exhaust back pressure. AND, it won't help the more frequent issue of carbon collection. Non-starter I think.
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Bill
RV-7
Lord Kelvin:
“I often say that when you can measure what you are speaking about,
and express it in numbers, you know something about it; but when you
cannot measure it, when you cannot express it in numbers, your knowledge
is of a meager and unsatisfactory kind.”
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07-17-2014, 06:58 AM
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Join Date: Jul 2009
Location: Mojave
Posts: 4,652
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If the exhaust augmentor (venturi) is not a smaller OD than the exhaust pipe, it won't create any back pressure. You are simply are introducing high velocity, expanding gasses into the back end of a diffuser, which will create low pressure at the front and draw in air. This is how exhaust augmentors work for engine cooling.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.
Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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07-17-2014, 07:14 AM
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Join Date: Nov 2005
Location: Asheville, NC
Posts: 2,692
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Taking Toolbuilders thought further, maybe complete disassociation from the exhaust is the path via installation of a venturi in the cowl exit airflow.
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Bill Pendergrass
ME/AE '82
RV-7A: Flying since April 15, 2012. 850 hrs
YIO-360-M1B, mags, CS, GRT EX and WS H1s & A/P, Navworx
Unpainted, polished....kinda'... Eyeballin' vinyl really hard.
Yeah. The boss got a Silhouette Cameo 4 Xmas 2019.
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07-17-2014, 08:39 AM
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Senior Curmudgeon
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Join Date: Sep 2005
Location: Dayton Airpark, NV A34
Posts: 15,420
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Most of us are flying with all electric panels, there is a vacuum pump pad blocked off on the engine that could be put to use.............
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Mike Starkey
VAF 909
Rv-10, N210LM.
Flying as of 12/4/2010
Phase 1 done, 2/4/2011 
Sold after 240+ wonderful hours of flight.
"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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07-18-2014, 08:47 AM
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Join Date: Nov 2008
Location: Missoula, MT
Posts: 714
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Little coke
I flew about 10 hours Sunday/Monday which brought me to about 75 hours since installing the ASA separator. I had checked the discharge tube in the exhaust with a borescope a couple times and saw nothing - absolutely nothing.
After the flights I checked it again with borescope and could just see a tiny bit of the black stuff but it was farther up the tube - slightly above where it penetrates the exhaust pipe - so I couldn't get a real good angle with the borescope. So I removed the top cowl, disconnected the discharge hose from the separator and blew/sucked on it - fine, no noticeable restriction.
I then removed the reed valve from the exhaust pipe so I could look down into the tube welded to the exhaust. There was the slightest amount of the black stuff accumulated around the inside of the tube so I cleaned it out with a screwdriver the right size but there wasn't even enough for me to see when I looked up the exhaust pipe.
I bought the second reed valve and will be installing it anyway. And, I'll be checking the exhaust discharge every 10-20 hours until I see a pattern.
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Bryan Douglass
=VAF= 2020 dues paid
RV-10 N242BD
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07-20-2014, 05:34 PM
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Join Date: Apr 2005
Location: Indepenence, Oregon
Posts: 342
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Yes, Allen has a coke problem
Just checked my -10 for coke. Was almost identical to JCHANG10 photo, a little more than Dan H. My photo turned out bad or it would be posted. Perhaps 50% blocked about 1/2" up the tube. My bracket is upon the right exhaust on the 45 just behind the heater. Total time since new is 50.8 hours with the first 40.5 using mineral oil and Aeroshell 100 since. (Engine was slow to break in)
I strapped my engine compartment thermocouple to the outside of the pipe right about where the coke formed. Unfortunately it was too late for a flight, but will try to get up tomorrow before some visitors arrive. If not, it could be a few days.
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Bruce Patton
Rans S-20 Raven 796S flying since 2019 (slowly)
RV-6A 596S flying since '99 (Sold)
HP-18 5596S flying since '89
RV-10 996S flying since 2014, quick build wing and slow build fues., - dual Skyviews with complete system, two radio and not much else. Interior completely finished with Zolatone. CF plenum. 1624 lbs, FLYING after a 21.5 month build.
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07-20-2014, 10:40 PM
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Join Date: Oct 2005
Posts: 1,516
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Second Reed installed
Installed a second Reed valve today.
Like Dan Horton, I do like the idea of negative pressure in the crankcase and I am not quite ready to do away with the idea of the crankcase breather line plumbed into the exhaust. However, there is enough evidence at this time that stubs welded into the exhaust tubes will coke up and create a potential for a crankshaft gasket to blow out.
Here is my install, I pointed the valve up so as not to have an oil drip after shut down.

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Ernst Freitag
RV-8 finished (sold)
RV-10 Flyer 600 plus hours
Running on E10 mogas
Don't believe everything you know.
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07-20-2014, 11:04 PM
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Join Date: Nov 2010
Location: West Linn, Oregon
Posts: 1,351
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As a result of the other posts, I made a point to check my exhaust stem during my annual inspection today. I too have coke in my stem, and a good deal of it. The separator and valve were added prior to the first flight and the Hobbs currently shows about 91 hours.
I have decided to remove the valve and stem. I am going to keep the separator and will run the line to drip on the exhaust like the stock setup, so I will still benefit from having the separator and clean belly.
I used Mineral oil for the first 20/25 hours and then Aeroshell 15W-50 since.

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CharlieWaffles - But you can call me " Mark"
RV-10
N928MT
Flying - AKA Still Tinkering
Build Project Site
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07-21-2014, 08:21 AM
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Join Date: Oct 2005
Posts: 1,516
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Wow Mark
I hope people pay attention to this issues before someone plugs up completely.
Good catch
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Ernst Freitag
RV-8 finished (sold)
RV-10 Flyer 600 plus hours
Running on E10 mogas
Don't believe everything you know.
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07-21-2014, 09:27 AM
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Join Date: Nov 2005
Location: San Francisco, CA
Posts: 525
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Quote:
Originally Posted by CharlieWaffles
I have decided to remove the valve and stem. I am going to keep the separator and will run the line to drip on the exhaust like the stock setup, so I will still benefit from having the separator and clean belly.
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I ran this way for a while until the saddle version became available. I say it cut down on the oily belly maybe 50% at best. I still had an oily belly, oily engine mount, oily firewall, etc.
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#40533 RV-10 Builder and CFI
1/2006 Started build
10/19/2011 First flight
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