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Corn Gas - Auto Fuel

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ddsyverson(at)comcast.net
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Posted: Mon May 29, 2006 8:29 am Post subject: Corn Gas - Auto Fuel

There probably is a lot more to be said about yet about this subject; I see no 

one has talked much about the energy content, but we have touched a bit on 

the vapor presasure issue.



Corn gas (what we call ethanol in the US - Midwest - probably need to change 

that to "cane gas" where it is made from sugar cane) has a couple 

characteristics that make it unique in addition to the structural effects on 

our equipment.



1) Energy content: 

Pure ethanol has approximately 60% of the BTUs of non-ethanol gasoline. A car 

which gets 20 MPG on gasoline, will get 12 MPG if recalibrated to run on pure 

ethanol (approximately) - everything else being equal (its not actually 

equal, but it is close enough to equal for government work). If we use 10% 

ethanol/90% gasoline, doing the math says we will get 94% of the energy out 

of the 10% corn gas mix compared to non-corn gas. IT ALSO MEANS - we are 

running lean by that same amount..... the larger percentage of ethanol, the 

leaner we run; and, while a small addition of ethanol might go by unnoticed, 

particularily if we have a mixture adjustment on our engine, more than a 

little ethanol will mean that a carbureted engine will have to be re-jetted 

if it is going to live and run on higher percentages of ethanol. Electronic 

fuel injected engines have the ability to fine tune the mixture on our cars 

to some degree; and, what we call "flex fuel" EFI cars can run on anything 

from 100% gasoline to 85% ethanol by making the rather dramatic mixture 

adjustments necessary for this - you could not do that with a carburetor - it 

would need to be rejetted. 



The Variable venturi carburetors on rotax engines, as I understand it, can 

adjust the mixture automatically according to ambient pressure (as with 

changes in altitude) But I don't believe they can make the adjustments for 

energy content of the fuel - it works differently than the leaning adjustment 

on a continental or lycoming which controls the fuel flow - not the air flow.



So.... maybe a rotax can get along on small admixtures of ethanol, but I would 

be inclined to take the factory's recommendations since they are the best 

source of what works and what doesn't.



2) Vapor pressure: Gasoline and ethanol are not the same. Ethanol, by itself, 

is more volatile than gasoline and vaporizes more easily at low pressures, 

particularily if it is warm (like at 12,000 feet in New Mexico in August).



Ethanol is a single chemical compound of fairly short structure. Gasoline is a 

generous mixture of short and long chain hydrocarbons (heptane, hexane, 

octane, nanotane, etc, etc; as well as isomers of each) - causing it to have 

both low vapor pressure components and high vapor pressure components - as a 

matter of fact in Minne-snowta, the oil companies are kind enough to change 

the porportions of short chain to long chain ratios in gasoline seasonally so 

the dumb stuff won't vapor lock in the summer and your car will actually 

start in the winter - seems the gas has to vaporize a little in order to burn 

at all.  Basically, you can't change the ratios of short chain to long chain 

hydrocarbons with ethanol, because, ethanol, by definition, is a single 

compound, not a mixture of compounds like gasoline. 



Some parts of the world. Like Brazil, have had a lot of experience (20 + 

years) with ethanol in their cars and there has to be a body of information 

out there about what works and what doesn't. 



Really hoping that EAA will have some updates to their auto gas information.



Later,



Dave S.

St Paul, MN

Do Not Archive



On Monday 29 May 2006 10:08 am, Randy Daughenbaugh wrote:

 	  Quote: 	
		   

 <rjdaugh(at)rapidnet.com>





 Ignorant question here...why is Ethanol harmful to run in our motors

 again??

 Andrew



 Andrew,

 I will take a whack at this one.



 A.  It is corrosive to some materials

 B.  It attacks some elastomers.

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morid(at)northland.lib.mi
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Posted: Tue May 30, 2006 6:40 am Post subject: Corn Gas - Auto Fuel

Great post Dave.

Thanks,

Deke



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smokey_bear_40220(at)yaho
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Posted: Tue May 30, 2006 9:57 am Post subject: Corn Gas - Auto Fuel

Great post Dave!



I am in Brazil today.  The pure alcohol price is about

50% of gas, but there is still a mix of gas, diesel,

alcohol and even propane in use on the roads here. 

Feelings are mixed on which is best too.  Wish I could

find a fuels expert to ask.



I mostly travel up to 10 miles a day on burger power

when not working.   Good milage, but occasionally

stalls and sputters when running.  Clogged carb. 

Certainly not lean..... Slow climb rate too.  Do you

think 10% alcohol might help?  



Kurt S.



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rjdaugh(at)rapidnet.com
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Posted: Tue May 30, 2006 12:48 pm Post subject: Corn Gas - Auto Fuel

While it is true that energy density in alcohol is not as great in

hydrocarbons, one of the mileage problems with running alcohol in engines

designed for gasoline is that the engine is not taking advantage of the

properties of the alcohol.  Alcohol (ethanol or methanol) has much higher

octane rating than petroleum.  Thus engines could be designed with much

higher compression ratios and we could get much higher mileage from lighter

engines than what results when we burn ethanol in engines designed for

gasoline.



I don't mean to defend the ethanol fuel industry.  I am not sure it is fuel

efficient.  It takes a lot of energy to grow corn (fertilizer, tractor fuel,

refining the ethanol, etc) but it is paving the way for ethanol from

cellulose.   And they are burning it at Indy next year!



Randy



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smokey_bear_40220(at)yaho
Guest

Posted: Tue May 30, 2006 3:10 pm Post subject: Corn Gas - Auto Fuel

Randy,



I think I saw recently where someone is developing an

alcohol designed engine.  Higher compression and more

turbo will make it get about the same MPG as gas.



Kurt S.



--- Randy  Daughenbaugh <rjdaugh(at)rapidnet.com> wrote:



 	  Quote: 	
		   While it is true that energy density in alcohol is

 not as great in

 hydrocarbons, one of the mileage problems with

 running alcohol in engines

 designed for gasoline is that the engine is not

 taking advantage of the

 properties of the alcohol.  Alcohol (ethanol or

 methanol) has much higher

 octane rating than petroleum.  Thus engines could be

 designed with much

 higher compression ratios and we could get much

 higher mileage from lighter

 engines than what results when we burn ethanol in

 engines designed for

 gasoline.

 

 I don't mean to defend the ethanol fuel industry.  I

 am not sure it is fuel

 efficient.  It takes a lot of energy to grow corn

 (fertilizer, tractor fuel,

 refining the ethanol, etc) but it is paving the way

 for ethanol from

 cellulose.   And they are burning it at Indy next

 year!

 

 Randy


	


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