Return-Path: Received: from sccrmhc12.comcast.net ([204.127.202.56] verified) by logan.com (CommuniGate Pro SMTP 4.2.8) with ESMTP id 616128 for flyrotary@lancaironline.net; Fri, 21 Jan 2005 11:02:37 -0500 Received-SPF: none receiver=logan.com; client-ip=204.127.202.56; envelope-from=kenpowell@comcast.net Received: from 204.127.205.150 ([204.127.205.150]) by comcast.net (sccrmhc12) with SMTP id <200501211602070120012mj2e>; Fri, 21 Jan 2005 16:02:07 +0000 Received: from [166.102.160.133] by 204.127.205.150; Fri, 21 Jan 2005 16:02:06 +0000 From: kenpowell@comcast.net To: "Rotary motors in aircraft" Subject: Re: [FlyRotary] changed to Octane Date: Fri, 21 Jan 2005 16:02:06 +0000 Message-Id: <012120051602.14119.41F1277C000F038900003727220075115004040A99019F020A05@comcast.net> X-Mailer: AT&T Message Center Version 1 (Dec 17 2004) X-Authenticated-Sender: a2VucG93ZWxsQGNvbWNhc3QubmV0 MIME-Version: 1.0 Content-Type: multipart/alternative; boundary="NextPart_Webmail_9m3u9jl4l_14119_1106323326_0" --NextPart_Webmail_9m3u9jl4l_14119_1106323326_0 Content-Type: text/plain Content-Transfer-Encoding: 8bit Ernest, absolutely the best explanation I have ever heard. I was trying to explain this to a friend recently and just couldn't seem to present it in a manner that he could visualize. I'll try again using your explanation. Ken Powell Bryant, Arkansas 501-847-4721 snip....... > It's entirely plausible, Ed. > > First consider gasoline. Being a organic substance, it is not a nice > even mixture of identical molecules. It is a random and often chaotic > mixture of carbon compounds. These compounds are mostly chains of > carbon atoms with hydrogen hanging off the unused bonds. Sometimes the > chains hook back on themselves, but mostly they just intertwine like > strands in a cotton ball. The shorter strands evaporate and burn easier > and faster. If I can get the order correct, the number of carbon atoms > in each molecule goes: > > 1)methane > 2)butane > 3)propane > . > . > 8)octane (this one's important) > 12)hexane > > Now the way organic material burns is important. When exposed to oxygen > and energy (we usually use heat, but other methods are possible), the > oxidation process removes a carborn from the END of the chain, reacts it > with the oxygen to give up carbon dioxide and water. It's very > important to consider that the center carbons are safe till all the ends > are burned off, and none will burn till the ends are exposed to oxygen. > > Now, how does that apply to us. > > First, liquid gas does not burn except for the very surface...the part > exposed to oxygen. In the few milliseconds that a molecule will be in > the combustion chamber of an engine, it has to be exposed to air and > burn completely. If it has to wait for 1000 neighboring molecules to > burn away first, it will be halfway down the exhaust before it can even > get started. > > Second, if you let the gas distill, you seperate out the short chains > from the long chains. Think of dried wheat chaff, stick, and logs. The > chaff will flash and be gone. The sticks will keep an nice fire going, > and the logs will burn all night...IF you can get them lit. For a nice > campfire, you'd want some of all of it. What Mistral experienced was > the chaff getting sucked in quickly and being burned off with some of > the sticks, and then the logs clumping up and being sucked in as a tree > trunk. > > Third, the magical 'octane'. The original test for octane was to > compare the burning of a sample of a fuel in a calibrated engine. The > engine was calibrate with pure OCTANE, exactly 8 carbon atoms in every > molecule. You can burn any fuel in an internal combustion engine, you > just have to get the mixture and spark timing correct. If the fuel > burns fast like propane, you want to spark later. You'd want to spark > diesel earlier. A mixture that is either lean or rich of peak will want > an earlier spark. Higher compression calls for a later spark. In all > cases, what you're doing is compensating for how quickly the fuel burns > so that you can get maximum pressure in the cylinder at the right time. > The problem that was found with the long runners was that it screwed the > mixture up. Instead of a nice clean flame front that could be > compensated for, you got a hodgepodge mixture of wheat chaff and oak > tree trunks. > > This is courtesy of an overzealous organic chemistry professor from > 1987. I may have forgotten a thing or two since then. > > >> Homepage: http://www.flyrotary.com/ > >> Archive: http://lancaironline.net/lists/flyrotary/List.html --NextPart_Webmail_9m3u9jl4l_14119_1106323326_0 Content-Type: text/html Content-Transfer-Encoding: 8bit
Ernest, absolutely the best explanation I have ever heard.  I was trying to explain this to a friend recently and just couldn't seem to present it in a manner that he could visualize.  I'll try again using your explanation.

Ken Powell
Bryant, Arkansas
501-847-4721
 
snip.......
> It's entirely plausible, Ed.
>
> First consider gasoline. Being a organic substance, it is not a nice
> even mixture of identical molecules. It is a random and often chaotic
> mixture of carbon compounds. These compounds are mostly chains of
> carbon atoms with hydrogen hanging off the unused bonds. Sometimes the
> chains hook back on themselves, but mostly they just intertwine like
> strands in a cotton ball. The shorter strands evaporate and burn easier
> and faster. If I can get the order correct, the number of carbon atoms
> in each molecule goes:
>
> 1)methane
> 2)butane
> 3)propane
> .
> .
> 8)octane (this one's important)
> 12)hexane
>
> Now the way organic material burns is important. When exposed to oxygen
> and energy (we usually use heat, but other methods are possible), the
> oxidation process removes a carborn from the END of the chain, reacts it
> with the oxygen to give up carbon dioxide and water. It's very
> important to consider that the center carbons are safe till all the ends
> are burned off, and none will burn till the ends are exposed to oxygen.
>
> Now, how does that apply to us.
>
> First, liquid gas does not burn except for the very surface...the part
> exposed to oxygen. In the few milliseconds that a molecule will be in
> the combustion chamber of an engine, it has to be exposed to air and
> burn completely. If it has to wait for 1000 neighboring molecules to
> burn away first, it will be halfway down the exhaust before it can even
> get started.
>
> Second, if you let the gas distill, you seperate out the short chains
> from the long chains. Think of dried wheat chaff, stick, and logs. The
> chaff will flash and be gone. The sticks will keep an nice fire going,
> and the logs will burn all night...IF you can get them lit. For a nice
> campfire, you'd want some of all of it. What Mistral experienced was
> the chaff getting sucked in quickly and being burned off with some of
> the sticks, and then the logs clumping up and being sucked in as a tree
> trunk.
>
> Third, the magical 'octane'. The original test for octane was to
> compare the burning of a sample of a fuel in a calibrated engine. The
> engine was calibrate with pure OCTANE, exactly 8 carbon atoms in every
> molecule. You can burn any fuel in an internal combustion engine, you
> just have to get the mixture and spark timing correct. If the fuel
> burns fast like propane, you want to spark later. You'd want to spark
> diesel earlier. A mixture that is either lean or rich of peak will want
> an earlier spark. Higher compression calls for a later spark. In all
> cases, what you're doing is compensating for how quickly the fuel burns
> so that you can get maximum pressure in the cylinder at the right time.
> The problem that was found with the long runners was that it screwed the
> mixture up. Instead of a nice clean flame front that could be
> compensated for, you got a hodgepodge mixture of wheat chaff and oak
> tree trunks.
>
> This is courtesy of an overzealous organic chemistry professor from
> 1987. I may have forgotten a thing or two since then.
>
> >> Homepage: http://www.flyrotary.com/
> >> Archive: http://lancaironline.net/lists/flyrotary/List.html
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