Chem Question

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ive been thinking all this morning about why our cars cant use fuels such as methanol or ethanol.

and it seems my genious work mate seems to think that it is becuase the longer the chain of carbon atoms the more energy is released.

however i dont understand this why does more energy comeout of a longer chain vcan someone clear this up for me itss been bugging me all morning!

*stig
 
Its to do with the structure of them and how many carbon atoms they contain for a given volume i think.
Cars can use the substances you said, just that they combust at lower temperatures which mean that high compression ratios cannot be acheived, therefore it would be a very inefficient engine.
 
The Americans are dedicating a lot to the refinement and production of ethanol i believe.. they obviously think its going to be the replacement fuel of the future..
 
its the branching.

Branched hydrocarbons of the same number release more energy than long chain ones per combustion (simplest way i can describe it)

so for example

c-c-c-c-c-c would produce less energy than

...c
...|
c-c-c-c
......|
......c

ignore the dots :)
 
Brazil has lots of sugar cane growing anyway, so any wastage can be fermented to provide very cheap ethanol as a mere bi-product of something they were already doing. Ethanol itself whilst reasonably viable is not as efficient and provides less "miles per gallon" than other fuels like petroleum or diesel.
 
the energy released on burning really doesn't have much to do with the carbon chain length - thats an over simplification of the burning/explosion process which is a complex radical reaction.

the reason they don't use ethanol/methanol is that engines have to be different - its not as flammable as petrol, has a much lower vapour pressure blah blah blah. i'm not sure how much they need to change on the average engine but certain components will have to be changed and you can't use both methano. and petrol, just like you can't use desiel and petrol cos they have different burning characteristics
 
aardvark said:
the energy released on burning really doesn't have much to do with the carbon chain length - thats an over simplification of the burning/explosion process which is a complex radical reaction.

the reason they don't use ethanol/methanol is that engines have to be different - its not as flammable as petrol, has a much lower vapour pressure blah blah blah. i'm not sure how much they need to change on the average engine but certain components will have to be changed and you can't use both methano. and petrol, just like you can't use desiel and petrol cos they have different burning characteristics

I think it runs on diesel engines with little (if any) modification.
dunno.gif
 
gord said:
The Americans are dedicating a lot to the refinement and production of ethanol i believe.. they obviously think its going to be the replacement fuel of the future..
LOL! Already in production, hoss. :)

http://www.eere.energy.gov/cleancities/vbg/af_available.shtml

Now if only we could get some control over the oil companies that are large and powerful enough to keep this technology from really developing, the effort would really spread. ;)
 
Meridian said:
I suspect the real answer had about a hundred times as much to do with economics as it does with chemistry.


M
bingo. my mates dad is a Major Lawyer for one of the MASSIVE oil companies.

they'd stand to lose billions if all cars suddenly started running on non-crude based hydrocarbons.
 
I think the burn characteristics and oxygen balance are diffferent to normal alkane/air so it would require some serious engine modifications. Has to do with the time that the flame propagates inside the cylinder. Sounds like geek stuff but pretty sure it's true.

One time I accidentally set alight to a beaker of ethanol and it just gave a nice blue lick on the top, nothing dangerous. I'm glad it wasn't heptane or something coz it would have gone up like shot.
 
hehehe, yea, ever burnt a glass of Vodka? same thing.

i'm sure that there is a Hydrocarbon that can be produced in some reaction
that would give similar burn-performance to Octane.
 
as some guy said above its all about the economics - there is no reason that you can't have a fuel efficient engine based on burning ethanol/methanol, one that may even be more efficient that petrol ones, but its all about the money.

there is of course the problem of producing all that ethanol, and we'll need a lot!
 
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