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carbon bonds (was: mogas vs 100LL)

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brian-1927(at)lloyd.com
Guest

Posted: Tue Nov 13, 2007 9:11 am Post subject: carbon bonds (was: mogas vs 100LL)

I hate it when something sticks in my head overnight. It means I am  

not going to get a good night's sleep. (Yes, I do lose sleep over  

stuff like this. Yes, I probably am crazy.)



The issue was the comment about higher grades of fuel having more  

carbon-carbon bonds and therefore more energy. The Wikipedia article  

I referenced, http://en.wikipedia.org/wiki/Octane_rating, also  

alluded to that. OTOH I figured that if there was an appreciable  

increase in C-C bonds there would be a shift in best stoichiometric  

mixture when measured by mass ratio.



As a mental experiment I decided to trot out my old and rotten  

chemistry memories to compare the two simplest organic compounds with  

single and double carbon-carbon (c-c) bonds: ethane (C2H6) and ethene  

(C2H4). Ethane has a single C-C bond and ethene has a double C=C  

bond. Combusting ethene should release more energy than combusting an  

equivalent mass of ethane. Here is what the two molecules look like:



Ethane:



   H H

   | |

H-C-C-H

   | |

   H H



Ethene:



H     H

  \   /

   C=C

  /   \

H     H

When you have the double carbon bond you no longer have bonds for the  

two extra hydrogens. This changes the combustion reaction from:



2(C2H6) + 7(O2) = 4(CO2) + 6(H2O) + energy



To:



C2H4 + 3(O2) = 2(CO2) + H2O + energy



The mass of ethane is 30gm/Mol. The mass of ethene is 28gm/Mol. The  

mass of O2 is 32gm/Mol. So the oxidizer-to-fuel mass ratios for the  

two reactions are:



7(32)/2(30) = 3.73 (for ethane)



3(32)/28 = 3.42 (for ethene)



This is a 9% difference in mass ratio. (I didn't include the N2 from  

the atmosphere because, while it does change the individual mass  

ratios, it does not effect the percentage difference at the end which  

is what I was looking for.)



My gut feeling is, if "higher quality" gasoline had a lot more C=C  

(double) bonds (and therefore more energy), we would have to readjust  

our carburetors when we switch fuel in order to get a proper mixture.  

Since we don't ...



BTW, I encourage someone to show me where I am wrong as I always am  

looking to learn.



--

Brian Lloyd                         3191 Western Drive

brian HYPHEN 1927 AT lloyd DOT com    Cameron Park, CA 95682

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry



PGP key ID:          12095C52A32A1B6C

PGP key fingerprint: 3B1D BA11 4913 3254 B6E0  CC09 1209 5C52 A32A 1B6C

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l39parts(at)hotmail.com
Guest

Posted: Sun Nov 18, 2007 4:42 pm Post subject: carbon bonds (was: mogas vs 100LL)

You lose sleep over things like that?  Sheesh.  The amount of energy liberated, the temperature produced, and the speed of the deflagration/detonation are three independent characteristics.  Nitroglycerin, for example has a very high speed of combustion, but a rather low BTU content.  Acetylene has a C-C triple bond and produces the highest combustion temperature (aside from the 'observed', but unsubstanciated diatomic hydrogen combustion). 

  

 You are correct that octane is measure of anti-knock characteristics.  It is not a measure of BTU content (energy).  Good luck in convincing people of that though.  Billions have spent on advertising to convince the public otherwise.  Using a higher octane gas than an engine needs is of absolutely no value.  Higher grades of gas may have more additives that do something good for the engine (or may not), but that isn't what octane measures.  There is something called octane creep, wherein an engine needs a higher octane fuel as it gets older, related to the fact that it is more prone to pre-ignition due to deposits in the cylinders.  Marvel Mystery Oil may help... or maybe not.  I believe MMO's usefulness is in preventing varnish in the delicate little parts of the carb.

  

 But I digress.  Your points were all correct in your previous post.

  

 Trivia:  What is the 66 in Phillips 66?  It is the octane rating of straight gasoline from way back in the old days when brewing gasoline was a lot simpler than it is today, before cracking of the heavy ends was possible.



 	  Quote: 	
		   From: brian-1927(at)lloyd.com

 Subject: Yak-List: carbon bonds (was: mogas vs 100LL)

 Date: Tue, 13 Nov 2007 09:09:49 -0800

 To: yak-list(at)matronics.com

 

 --> Yak-List message posted by: Brian Lloyd <brian-1927(at)lloyd.com>

 

 I hate it when something sticks in my head overnight. It means I am 

 not going to get a good night's sleep. (Yes, I do lose sleep over 

 stuff like this. Yes, I probably am crazy.)

 

 The issue was the comment about higher grades of fuel having more 

 carbon-carbon bonds and therefore more energy. The Wikipedia article 

 I referenced, http://en.wikipedia.org/wiki/Octane_rating, also 

 alluded to that. OTOH I figured that if there was an appreciable 

 increase in C-C bonds there would be a shift in best stoichiometric 

 mixture when measured by mass ratio.

 

 As a mental experiment I decided to trot out my old and rotten 

 chemistry memories to compare the two simplest organic compounds with 

 single and double carbon-carbon (c-c) bonds: ethane (C2H6) and ethene 

 (C2H4). Ethane has a single C-C bond and ethene has a double C=C 

 bond. Combusting ethene should release more energy than combusting an 

 equivalent mass of ethane. Here is what the two molecules look like:

 

 Ethane:

 

 H H

 | |

 H-C-C-H

 | |

 H H

 

 Ethene:

 

 H H

 \ /

 C=C

 / \

 H H

 

 

 When you have the double carbon bond you no longer have bonds for the 

 two extra hydrogens. This changes the combustion reaction from:

 

 2(C2H6) + 7(O2) = 4(CO2) + 6(H2O) + energy

 

 To:

 

 C2H4 + 3(O2) = 2(CO2) + H2O + energy

 

 The mass of ethane is 30gm/Mol. The mass of ethene is 28gm/Mol. The 

 mass of O2 is 32gm/Mol. So the oxidizer-to-fuel mass ratios for the 

 two reactions are:

 

 7(32)/2(30) = 3.73 (for ethane)

 

 3(32)/28 = 3.42 (for ethene)

 

 This is a 9% difference in mass ratio. (I didn't include the N2 from 

 the atmosphere because, while it does change the individual mass 

 ratios, it does not effect the percentage difference at the end which 

 is what I was looking for.)

 

 My gut feeling is, if "higher quality" gasoline had a lot more C=C 

 (double) bonds (and therefore more energy), we would have to readjust 

 our carburetors when we switch fuel in order to get a proper mixture. 

 Since we don't ...

 

 BTW, I encourage someone to show me where I am wrong as I always am 

 looking to learn.

 

 --

 Brian Lloyd 3191 Western Drive

 brian HYPHEN 1927 AT lloyd DOT com Cameron Park, CA 95682

 +1.916.367.2131 (voice) +1.270.912.0788 (fax)

 

 I fly because it releases my mind from the tyranny of petty things . . .

 — Antoine de Saint-Exupéry

 

 PGP key ID: 12095C52A32A1B6C

 PGP key fingerprint: 3B1D BA11 4913 3254 B6E0 CC09 1209 5C52 A32A 1B6C

 

&g========================> 
	


 	  Quote: 	
		   

 


	


Share life as it happens with the new Windows Live. Share now!  [quote][b]

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brian-1927(at)lloyd.com
Guest

Posted: Sun Nov 18, 2007 5:58 pm Post subject: carbon bonds (was: mogas vs 100LL)

On Nov 18, 2007, at 4:41 PM, Ron Davis wrote:



 	  Quote: 	
		   You lose sleep over things like that?  Sheesh.


	


Yeah, sometimes. Or maybe I just can't sleep and stuff like that ends  

up grabbing the unused processing neurons; my brain's way of  

twiddling its thumbs. Think of it as counting carbon bonds instead of  

sheep.



 	  Quote: 	
		   The amount of energy liberated, the temperature produced, and the  

 speed of the deflagration/detonation are three independent  

 characteristics.


	


Well, delta-T * mass implies energy to me but you are right in that  

temperature is not heat.



 	  Quote: 	
		   Nitroglycerin, for example has a very high speed of combustion, but  

 a rather low BTU content.  Acetylene has a C-C triple bond and  

 produces the highest combustion temperature (aside from the  

 'observed', but unsubstanciated diatomic hydrogen combustion).


	


Huh. And here I was going to call it Ethyne. I was forgetting that  

was Acetylene.



 	  Quote: 	
		   You are correct that octane is measure of anti-knock  

 characteristics.  It is not a measure of BTU content (energy).   

 Good luck in convincing people of that though.  Billions have spent  

 on advertising to convince the public otherwise.  Using a higher  

 octane gas than an engine needs is of absolutely no value.  Higher  

 grades of gas may have more additives that do something good for  

 the engine (or may not), but that isn't what octane measures.


	


Nope.



 	  Quote: 	
		   There is something called octane creep, wherein an engine needs a  

 higher octane fuel as it gets older, related to the fact that it is  

 more prone to pre-ignition due to deposits in the cylinders.   

 Marvel Mystery Oil may help... or maybe not.  I believe MMO's  

 usefulness is in preventing varnish in the delicate little parts of  

 the carb.


	


OTOH, I suspect that MMO actually reduces the octane rating of the  

fuel. We can certainly get away with it when burning 100LL in our low- 

compression radial engines as we have huge detonation margins but  

that might not be the case when running mogas.



 	  Quote: 	
		   But I digress.  Your points were all correct in your previous post.


	


Thank you. I thought I was but I have been known to be wrong in the  

past.



 	  Quote: 	
		   Trivia:  What is the 66 in Phillips 66?  It is the octane rating of  

 straight gasoline from way back in the old days when brewing  

 gasoline was a lot simpler than it is today, before cracking of the  

 heavy ends was possible.


	


What comes out first is best. 



--

Brian Lloyd                         3191 Western Drive

brian HYPHEN 1927 AT lloyd DOT com    Cameron Park, CA 95682

+1.916.367.2131 (voice)             +1.270.912.0788 (fax)



I fly because it releases my mind from the tyranny of petty things . . .

— Antoine de Saint-Exupéry



PGP key ID:          12095C52A32A1B6C

PGP key fingerprint: 3B1D BA11 4913 3254 B6E0  CC09 1209 5C52 A32A 1B6C

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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