Subj: Turbochargers recommendations.
Date: 4/29/01 4:54:35 AM Eastern Daylight Time
From: rotaryeng@earthlink.net (Paul)
Cliff Manzke wrote:
Paul:
I've been reading all the turbo talk lately and finely got the chance to comment, so here goes:
I did some calculation based on a few assumptions for a 13 B, which are:
160 hp normally aspirated at sea level (29.92 inHg ambient pressure, 85°F)
BSFC of .55 lb/hp·hr
A/F ratio of 12.5 to 1, giving a BSAC (brake specific air consumption) of 6.875 lb/hp·hr
This gives an inlet airflow of 18.3 lb/min or 252.5 cfm at 85°F
Using these numbers and a few more assumptions, I figure 10.0 inHg of boost (giving 39.92 inHg MAP) will give you about 200 hp at sea level. I'm making some
guesstimates here as I don't have a known accurate "hp vs. RPM vs. manifold pressure" map for a 13B. Please provide some better numbers if you have them, but
remember that "desirable" numbers don't do much for turbo matching. Be honest!
So.....based on 200 hp at 39.9 inHg MAP, you'll get a corrected airflow of 22.0 lb/min and a pressure ratio of 1.33. Now, suppose you wish to maintain that
power (200 hp) up to an ambient pressure of 20.0 inHg (just over 10,000 ft). This will result in a corrected airflow of 31.7 lb/min and a pressure ratio of
2.0, which puts you right in the middle of a TO4E-50 trim compressor map....And just about this time I read the post from Paul Yaw and he suggests the same
thing. Thank you Paul for checking my sanity!
Now the other half of the puzzle is the turbine, and here Paul yaw suggests a "P" trim (74.2 mm dia wheel with a .76 trim) and a 1.00 A/R housing. I was
going to suggest the same trim turbine with the next smaller housing (.81 A/R), but Paul may know something about 13B's that I don't.
The real point to all of this is that this is a pretty "big" turbocharger we're talking about, simply because the aircraft requirements are quite different
than the automobile requirements. I can comfortably say that if the stock 13B turbocharger (a T3 of some sort?) was sized correctly for the street, it will be
way too small for the air. Sure, it'll work, but the wastegate will likely be opened from the get-go (sea level), which only means more exhaust pressure and
therefore more exhaust heat to get the desired boost. The desirable scenario is to have the wastegate shut (or better yet, no wastegate) at sea level and max
power with the turbo producing the desired boost. This desired boost can fine tuned with selection of turbine housing, but only if the whole
compressor/turbine assembly is in the right ball park to begin with. Given the low boost requirement at sea level (~10 inHg), the TO4E-50/P turbo efficiency
will improve as altitude increases, hit a "sweet spot" somewhere near 10,000 ft, and then begin to fall off again. By doing this, you MIGHT (big maybe here)
be able to eliminate the wastegate altogether. This is a complicated issue and has a lot to do with how effective your intercooler is. With insufficient
intercooler capacity, you will likely reach a detonation limit due to air charge temp long before you reach your flat rated altitude, in which case you need
to 1) get a bigger intercooler, or 2) open the wastegate, or 3) close the throttle, or 4) use a bigger (less restrictive) turbine housing. Note that the last
three options all produce the same end result, i.e., less boost and therefore less power. The first option is the best but not always practical.
As far as turbo overspeed goes, if you size the turbo such that it is optimum at something like 10,000 ft, then turbo overspeed is unlikely. The T4 turbines
have a maximum speed of 135,000 rpm or so. In the case of the TO4E-50 this means a pressure ratio of at least 3.5, which equates to about 48 inHg MAP at
20,000 feet! On the other hand, high air charge temperature (and detonation) is likely to be a problem with unrestricted boost and a wastegate is a fool proof
way to prevent that.
If a 13B will actually make more than 200 hp with only 10 inHg boost, then an even larger compressor might be in order. I recall 250 hp at 10 inHg coming
up, in which case a TO4E-60 trim or even a TSO4 (84 mm wheel, .49 trim) might be a better choice. If anyone can provide some actual data I can make a better
assessment of this.
As far as the T4 turbocharger hardware goes, the TO4E series is the latest (and most efficient), although all of it is pretty old stuff. The T4-P trim
turbine map I have is dated 1968 and it hasn't changed since! The GT series (GT12, GT15, GT30, 32, 35, 37, 40, 42, 45, and maybe a few more in between) is
newer and would be a better choice but unfortunately design information (compressor and turbine maps) are closely guarded secrets or Garrett/Allied
Signal/Honeywell/General Electric, or whoever they are this year! If someone can get their hands on one, a GT35 or GT37 might be a good starting point for the
13B.
The bad news about Turbonetics is, ah, bad. Do get one of their catalogues if you can, as it is an excellent source for compressor maps and turbo parts. The
folks at Turbonetics were always real helpful, so I hope the people (and knowledge) will carry on somewhere.
I hope this helps more than in confuses everyone. I'll be out of town for the next week and a half, so hold your questions. In the meantime, bug Jeff
Spitzer for some TO4E parts to help "the cause"! Oh, and read the article "Turbo Power" in Kitplanes to get an idea on how not to do it.
Cliff Manzke
Cliff, we are fortunate indeed to have you and Jeff on here. You guys are the experts
in this field having got your airplanes up to 57,000 feet. Thanks a bunch.
I do indeed have the Turbonetics catalog with all the maps. I also have some power
curves for the stock 89-92 205 HP 13B Mazda with 5 psi boost and Paul Yaw's power curves
which I will upload when you get back if you remind me.
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org
Subj: Turbo charger questions.
Date: 4/28/01 7:12:42 PM Eastern Daylight Time
From: rotaryeng@earthlink.net (Paul) Sender: root@gull.mail.pas.earthlink.net
Old message 13 Jan 2000
Don Moncrieff wrote:
Thanks Chris for your 18 Dec. letter. I seem to be in a very similar
place with my 13B and am wondering very similar things about my turbo.
I'll be very interested in the conclusions and solutions you reach.
I'm trying to figure out the best thing to do with both the switching
valve and waste gate. Have you come to any conclusions yet?
You may have noted that Paul Yaw (thanks Paul) told me that I will not
be able to limit the boost because the wastegate and turbine are very
small.
So, if the wastegate is not needed and the switching valve is to help
reduce HC emmissions--what do we need? I suspect I'm displaying a lot of
ignorance.
You could control the boost with an add on wastegate, but I feel that
the stock turbo is VERY inappropriate for your application. The danger
is in overboosting the engine, and overspinning the turbo. Either one
is a bad thing. EVERY stock turbo that I have disassembled has had many
cracks in the turbine housing, and the manifolds usually crack sooner or
later. The aftermarket pieces like a TO4 are less prone to cracking and
are much easier to control because of the larger turbine. The bearing
section is also much more durable. The compressor wheel is bigger which
means lower rpm for a given amount of airflow/boost. You will need a
relatively large turbo if you wish to normalize your manifold pressure.
I don't know at what elevation the stock turbo would overspeed, but it
would be quite low.
If you turbocharge your AC engine, the turbo itself will be the most
highly stressed piece in the system. I don't think anyone knows yet
what the life expectancy is for a turbo on an AC rotary. My opinion is
that using the stock turbo would be dangerous. A TO4E 50 trim
compressor, P trim turbine, 1.0 A/R tangential turbine housing. will
work quite well if you use an aftermarket turbo manifold like the piece
made by HKS. If you build headers you will have problems controlling
the boost, and you will have to step up to a Q trim turbine, and may still
have to modify it to get everything under control. If you use the turbo
to normalize at high elevation, a turbo tachometer is mandatory. If you
spin them too fast ugly things happen. After all this, you may still
need to make a housing swap to get exactly what you want.
While I am on the subject, Bob Keller sold Turbonetics, and Rick Head
has left and formed his own company with Jon Myers and one other guy
from Turbonetics. My dealings have always been with Rick, and so I will
be buying from him in the future. An added benefit is the expertise of
Jon Myers who has been working with turbos since he was at Rajay years
ago. They are good guys, and they know what they are doing. The
company name is ITS, and I will post the phone number tomorrow. (I don't
have it here with me.)
Paul Yaw
Thanks Paul. I was wondering what was going on at Turbonetics as I had
some trouble getting some help there. I was considering Fastrax in
Torrance or Gardena as a source and dropped in yesterday to talk
to them. The main guy was in Japan so no luck so far. Fastrax has been
supplying the Garrett turbo's for Able Ibbara's 800HP 13B.
BTW aircraft turbo's housings are supposed to contain a burst turbine. As such they
are heavier. If your non AC turbine is oriented such that high energy turbine
particles exiting the housing could penetrate the firewall or a critical
part of the engine a SS & Kevelar shield would be a safety feature. You
will probably have to deal with an under the cowl in-flight fire as well.
Keep the turbo out near the side of the cowl with a SS fire shield
between it and the rest of the engine and firewall. The Kevelar
should be on the back side of the SS. Hopefully the SS will be merely
dented and not penetrated. WW II turbo's could explode
and the particles would not penetrate anything as the turbo's were mounted
near the outside of the cowlings with the turbine plane of rotation
tangential to the cowling surface.
Turbo RPM could be another input to the computer that controls
boost by means of a electronic waste gate. This literally would
be an ounce of prevention.
Paul Lamar
An update. The stock turbo's that don't crack are the 89-91. Paul
Yaw was referring to the 87-88 and the dual 1993 and later turbo's.
I am going to try the stock single 89-91 turbo first before I go to all
the trouble and expense of a TO4 and a new exhaust manifold.
Fastrax does not want to deal with you if you are airplane.
Paul Lamar
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
http://home.earthlink.net/~rotaryeng/ http://www.linux.org