X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 18 Jan 2012 10:34:28 -0500 Message-ID: X-Original-Return-Path: Received: from nskntmtas04p.mx.bigpond.com ([61.9.168.146] verified) by logan.com (CommuniGate Pro SMTP 5.4.3) with ESMTP id 5354774 for lml@lancaironline.net; Wed, 18 Jan 2012 07:30:45 -0500 Received-SPF: pass receiver=logan.com; client-ip=61.9.168.146; envelope-from=frederickmoreno@bigpond.com Received: from nskntotgx01p.mx.bigpond.com ([58.165.11.246]) by nskntmtas04p.mx.bigpond.com with ESMTP id <20120118123007.TYVC1385.nskntmtas04p.mx.bigpond.com@nskntotgx01p.mx.bigpond.com> for ; Wed, 18 Jan 2012 12:30:07 +0000 Received: from Razzle ([58.165.11.246]) by nskntotgx01p.mx.bigpond.com with ESMTP id <20120118123005.IVTY23205.nskntotgx01p.mx.bigpond.com@Razzle> for ; Wed, 18 Jan 2012 12:30:05 +0000 MIME-Version: 1.0 X-Original-Message-Id: <4F16BB3E.00015A.01484@RAZZLE> X-Original-Date: Wed, 18 Jan 2012 20:29:50 +0800 Content-Type: Multipart/Alternative; charset="iso-8859-1"; boundary="------------Boundary-00=_QPUZT9JMYHI1VA400000" X-Mailer: IncrediMail (6244788) From: "Frederick Moreno" X-FID: FLAVOR00-NONE-0000-0000-000000000000 X-Priority: 3 X-Original-To: "Lancair Mail (lml@lancaironline.net)" Subject: Fw: Re: Ceramic exhaust coatings X-Authentication-Info: Submitted using SMTP AUTH LOGIN at nskntotgx01p.mx.bigpond.com from [58.165.11.246] using ID frederickmoreno@bigpond.com at Wed, 18 Jan 2012 12:30:04 +0000 X-SIH-MSG-ID: ox86GNP3TFa2kTAvmTy2alorgFm6/gF5uMhSBI0wt0lHEVbGsd/fRc+9cqJfw4rgxFkZYgr/bz8wYqT0XI3bsdm6IbtBWLDY5cI= --------------Boundary-00=_QPUZT9JMYHI1VA400000 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Gary wrote: =0D =0D "So, all those racers out there (motorcycles, quads, drag cars, sand rail= s, drag boats, snowmobiles, etc.) with heat coatings on top of their pistons are only using it to "feel good"?"=0D =0D No. =0D =0D You fail to understand the thermal problem. Ceramic coating piston tops = and cylinder head cavities has been shown to gain 1-2% more horsepower at ful= l power. I had my pistons and cylinder heads coated for this reason, and because it made me feel good. =0D =0D But it works on pistons because the thermal event lasts through the power stroke only, about 180 degrees of rotation, or about 12-15 milliseconds.=20 The peak heating only occurs for about half of this when the pressures an= d temperatures are highest. This is when most of the power is made, and avoiding a bit of heat loss for a few milliseconds is worthwhile. =0D =0D Here is the difference between pistons and exhaust pipes. In case of the piston, the thermal "wave" from the transient heating only penetrates a = few mils into the ceramic coating during the event. Then the gas temperature falls dramatically, falls some more during the exhaust stroke, and then there is a blast of cold air and evaporating avgas taken in and compresse= d.=20 The top few mills of ceramic coating are cooled, a reduced amount of heat reaches the piston or head metal, and the cycle continues. =0D =0D Contrast this very rapid transient piston heating and cooling with the exhaust pipe. Blast of hot gas, then slowing of the hot gas, then some oscillations of hot gas back and forth in the pipe, and then another blas= t of hot gas. A thermocouple buried in this rapidly changing flow can not respond fast enough to report instantaneously, and displays an "average" temperature which we interpret as the EGT. So does the inside of the exhaust pipe. =0D =0D With no cooling event occurring, the thermal coating inside the pipe soak= s up energy, temperature rises and stays high, and the interface between ceramic and metal gets hot. Then the metal gets hot and it stays hot.=20 Everything gets red hot. This is not aluminum piston country. =0D =0D The ceramic coating inside the exhaust pipe reduces the heat flow to the metal a bit, but only a small bit. The metal still gets hot, but its temperature is lowered slightly. Even slight lowering of temperature hel= ps a little bit, so it is up to you to decide if it is worth the cost and effort. If it feels good, then do it. =0D =0D Don't disparage things that feel good. That is why we fly, build nice airplanes, and enjoy sex. Don't knock it. =0D =0D Gary also wrote: "On a side note, I know it sure keeps my chrome motorcyc= le pipes from turning brown or blue. Oh, and they have not shown symptoms o= f failure after years of use. Read below."=0D =0D Come on, Gary, to you seriously consider a motor cycle spending most of i= ts life at low power settings to be comparable to an aircraft engine running 50F lean of peak at 65% power? If you want to make it a good comparison, open the throttle on your motor cycle, accelerate up to about 90% of top speed, back off the throttle to hold this speed, and then continue for 10= 00=20 hours. After that I would like a report on your chrome exhaust pipes. =20 Then we have something to compare and discuss objectively because only th= en will the operating conditions and duration be approximately the same.=0D =0D =2E..Don't do it. It will droop off due to gravity having absolutely no = creep strength, and will drop in a heap in a few hours. And it will rust to du= st in a few cycles....=0D =2E..Mild steel has no capability in this operating regime.=0D =0D Gary wrote further: "Why is it then that there are hundreds, no thousands= , of experimentals out there (several at this airport) with steel [my empha= sis added] exhaust systems that have been flying for years, decades, with no problems or symptoms that you describe?"=0D =0D I am sorry if the context of my comment in italics above evaded you. The question I was responding to was about using mild steel for aircraft exha= ust pipes. Pursuant to earlier emails discussing I noted that even stainless steel had low creep strength at the higher temperatures of interest. Mil= d steel has virtually no creep resistance or oxidation resistance at the sa= me temperatures. Build mild steel headers for your airplane and when they g= et hot, they will get soft, creep, and deform. I will leave it to you to lo= ok up the creep strength and oxidation rates of mild steel in the temperatur= e range of interest for this discussion, namely 1200-1500F. =0D =0D As to your comment about experimental (aircraft ) operating for years wi= th no problems, let me again clarify since it appears my earlier text was unclear in conveying its message. I was referring to mild steel (conside= red to be 1020, 1030, etc. ) while aircraft exhaust pipes are all made with a steel alloy normally referred to as STAINLESS steel, usually 321 stainle= ss, an austenitic alloy with a mix of properties making it attractive for exhaust pipes on airplanes. Unlike mild steel which is almost entirely i= ron (Fe) with a bit of carbon and low quantities of other alloying agents, 32= 1 stainless steel has the following alloying agents: =0D Fe, <0.08% C, 17-19% Cr, 9-12% Ni, <2% Mn, <1% Si, 0.3-0.7% Ti, <0.045% P= , <0.03% S Translation: lots of nickel and chromium and important additio= ns of titanium. What this means is summarized as follows: =0D "Grades 321 and 347 are the basic austenitic 18/8 steel (Grade 304) stabilised by Titanium (321) or Niobium (347) additions. These grades are used because they are not sensitive to intergranular corrosion after heat= ing within the carbide precipitation range of 425-850=B0C. Grade 321 is the g= rade of choice for applications in the temperature range of up to about 900=B0= C, combining high strength, resistance to scaling and phase stability with resistance to subsequent aqueous corrosion." See http://www.azom com/article.aspx?ArticleID=3D967 for more insights. =0D Mild steel it ain't. =0D I hope this helps your understanding. =0D Fred Moreno=0D =20 --------------Boundary-00=_QPUZT9JMYHI1VA400000 Content-Type: Text/HTML; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable
Gary wrote:
 
"So, all those racers out there (motorcycles, quads, drag cars, sand= rails, drag boats, snowmobiles, etc.) with heat coatings on top of = their pistons are only using it to "feel good"?"
 
No.
 
You fail to understand the thermal problem.  Ceramic coating pi= ston tops and cylinder head cavities has been shown to gain 1-2% more hor= sepower at full power.   I  had my pistons and cylind= er heads coated for this reason, and because it made me feel good.  =
 
But it works on pistons because the thermal event lasts through the = power stroke only, about 180 degrees of rotation, or about 12-15 millisec= onds.  The peak heating only occurs for about half of this= when the pressures and temperatures are highest.  This is when= most of the power is made, and avoiding a bit of heat loss for a few mil= liseconds is worthwhile. 
 
Here is the difference between pistons and exhaust pipes.  In c= ase of the piston, the thermal "wave" from the transient  heating on= ly penetrates a few mils into the ceramic coating during the event. = Then the gas temperature falls dramatically, falls some more during the = exhaust stroke, and then there is a blast of cold air and evaporating avg= as taken in and compressed.  The top few mills of ceramic coating ar= e cooled, a reduced amount of heat reaches the piston or head m= etal, and the cycle continues.
 
Contrast this very rapid transient piston heating and cooling with t= he exhaust pipe.  Blast of hot gas, then slowing of the hot gas, the= n some oscillations of hot gas back and forth in the pipe, and then anoth= er blast of hot gas.  A thermocouple buried in this rapidly changing= flow can not respond fast enough to report instantaneously, and displays= an "average" temperature which we interpret as the EGT.  So does th= e inside of the exhaust pipe.
 
With no cooling event occurring, the thermal coating inside the pipe= soaks up energy, temperature rises and stays high, and the interface bet= ween ceramic and metal gets hot.  Then the metal gets hot and it sta= ys hot.  Everything gets red hot. This is not aluminum piston countr= y.
 
The ceramic coating inside the exhaust pipe reduces the heat flow to= the metal a bit, but only a small bit.  The metal still gets hot, b= ut its temperature is lowered slightly.  Even slight lowering o= f temperature helps a little bit, so it is up to you to decide if it is w= orth the cost and effort.  If it feels good, then do it. 
 
Don't  disparage things that feel good.  That is why = we fly, build nice airplanes, and enjoy sex.  Don't knock it.
 
Gary also wrote: "On a side note, I know it sure keeps my chrome mot= orcycle pipes from turning brown or blue.  Oh, and they have not sho= wn symptoms of failure after years of use.  Read below."
 
Come on, Gary, to you seriously consider a motor cycle spending = ;most of its life at low power settings to be comparable to an aircraft e= ngine running 50F lean of peak at 65% power?  If you want to make it= a good comparison, open the throttle on your motor cycle, accelerate up = to about 90% of top speed, back off the throttle to hold this speed, and = then continue for 1000  hours.  After that I would like a repor= t on your chrome exhaust pipes.   Then we have something to com= pare and discuss objectively because only then will the operating conditi= ons and duration be approximately the same.
 
...Don't do it.  It will droop off due to gravity havi= ng absolutely no creep strength, and will drop in a heap in a few hours.&= nbsp; And it will rust to dust in a few cycles....
...Mild steel has no capability in this operating regime.
 
Gary wrote further: "Why is it then that there are hundreds, no thou= sands, of experimentals out there (several at this airport) with = steel [my emphasis added] exhaust systems that have been flying = for years, decades, with no problems or symptoms that you describe?"=
 
I am sorry if the context of my comment in italics above evaded you.=   The question I was responding to was about using mild stee= l for aircraft exhaust pipes.  Pursuant to earlier emails d= iscussing I noted that even stainless steel had low cree= p strength at the higher temperatures of interest.  Mild ste= el has virtually no creep resistance or oxidation resistance at = the same temperatures.  Build mild steel headers fo= r your airplane and when they get hot, they will get soft, creep, and def= orm.  I will leave it to you to look up the creep strength and oxida= tion rates of mild steel in the temperature range of interest for this di= scussion, namely 1200-1500F.
 
As  to your comment about experimental (aircraft ) operating fo= r years with no problems, let me again clarify since it appears my e= arlier text was unclear in conveying its message.  I was referring t= o mild steel (considered to be 1020, 1030, etc. ) while = aircraft exhaust pipes are all made with a steel alloy normally refe= rred to as  STAINLESS steel, usually 321 stainless,= an austenitic alloy with a mix of properties making it attractive f= or exhaust pipes on airplanes.  Unlike mild steel w= hich is almost entirely iron (Fe) with a bit of carbon and low quant= ities of other alloying agents, 321 stainless steel= has the following alloying agents:

Fe, <0.08% C, 17-19% Cr, 9-12% Ni, <2% Mn, <1% Si, 0.3-0.7% T= i, <0.045% P, <0.03% S   Translation: lots of nickel and = chromium and important additions of titanium.   What this means= is summarized as follows:

"Grades 321 and 347 are the basic austenitic 18/8 steel (Grade 304) st= abilised by Titanium (321) or Niobium (347) additions. These grades are u= sed because they are not sensitive to intergranu= lar corrosion after heating within the carbide precipitation range of 425= -850=B0C. Grade 321 is the grade of choice for applications in t= he temperature range of up to about 900=B0C, combining high stren= gth, resistance to scaling and phase stability with resistance t= o subsequent aqueous corrosion."  See  http://www.azom.com/article.aspx?Art= icleID=3D967 for more insights.

Mild steel it ain't.

I hope this helps your understanding.

Fred Moreno

 
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