Al Gietzen wrote:
I was considering getting my manifold coated on the inside in an effort to reduce wall temps and
heating in the cowl. Before committing to the cost I want to know how much it will really help;
seemed suspicious to me that the very thin coatings (.005-.010") would provide anywhere near the
temp reductions claimed by Jet-Hot.
I estimated the heat flux from a 1600F wall by conduction, natural convection, and radiation to
total about about 5 watts/sq-cm. Most of this is by radiation. If you have air blowing over the
surface it might go up by a few W/sq cm.
I called Jet-Hot to get the thermal conductivity of the coating. They refuse to provide any
engineering data of any kind. They did tell me that the coating on the inside would only be about
0.001"; and about .005" on the outside.
It is hard to imagine that the thermal conductivity could be less than a ceramic, so using that, a
.001" coating gives a temp drop of a whopping 6 C, or about 10 F drop in wall temp. Adding
another .005-.010" on the outside may drop the temp a total of about 100F.
So unless you're doing it to make your manifold and pipes look nice (or I've made an error in my
calcs - entirely possible) these coatings are a waste of money; especially a .001" coat on the
inside. No wonder they don't give out any engineering info.
Al Gietzen
Except for one thing Al and I am not saying this because I necessarily think its true.
I am just saying it is a possibility. Steel and SS tends to oxidize at high temp.
If you can keep the oxygen away from the surface they might not corrode so badly
and perhaps last longer. Mild steel flakes off in large chunks when used for
rotary engine exhaust.
Paul Lamar
Doug Mueller wrote:
Hi Al, I can tell you that the claims are true. They have been in recip engines for years. The claim is
that for every 10 degrees you can cool under hood or cowl temperatures, you will gain almost 1% power.
The reason being is because the under cowl temperatures decrease the density of the intake air before it
goes into the engine. If you were able to scavange the air from an outside source you would only get
radiant heat transfer through the runners to the engine. Also in turbo applications, the heat will
incrimentally raise the temperature over the intercooler their by decreasing the efficiency as well. I
hope this helps. Al unless you are a performance engineer or a very serious motor head, you may not
recognize the benefits and there by conclude that it is a waste of money. BUT if you see things as I do,
you will want every once of performance you can get that basically does not have a price tag. Paul is
also correct, in that it is a good corrosion inhibitor if anything but that is a pricey avenue. If
anyone would like more info, please email me directly. ROTARYRX6@LVCM.COM. This has been covered on the
site in the past so I do not want to rehash this, but I welcome any inquiries. I have done a lot of
research with use in recips, but I will be the first to admit, that I have never done it on any of my
rotary engines with long term statistics. The coatings that I am refering to will handle 2000 degrees
making it perfect for Turbos to.
Anybody wishing to continue the research without my assistance can go to
http://www.techlinecoatings.com.
This is one of the 2 suppliers that I made mention in a previous string.
Doug Mueller
RV-6 13BT
N900DM
Henderson,Nevada
The AirCraft Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site. http://home.earthlink.net/~rotaryeng/
Copyright 1998-2002 All world wide rights reserved.