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Topic: Why are hydrocarbons effective fuels?  (Read 31390 times)

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Offline zcami2

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Why are hydrocarbons effective fuels?
« on: March 28, 2012, 08:55:20 AM »
Hi all,
I would like to know why it is that hydrocarbon chains (specifically alkane groups) are effective fuels?  What is it about their chemical structures that enable them to rapidly ignite in such a way that they are compatible with the modern combustion engine?  Also could it potentially be possible for a member of the alcohol group (specifically ethanol) to be capable of running an engine without combination with a separate alkane based fuel source?

Thanks,
Z.C.

Offline Arkcon

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Re: Why are hydrocarbons effective fuels?
« Reply #1 on: March 28, 2012, 09:34:16 AM »
Ethanol fuel (E100 -- meaning 100 % ethanol) is pretty common in Brazil.  There's a model of automobile pictured to use E100 in this article here. http://en.wikipedia.org/wiki/Ethanol_fuel_in_Brazil The feasibility of ethanol fuel gets a pretty through explanation in that article.
Hey, I'm not judging.  I just like to shoot straight.  I'm a man of science.

Offline fledarmus

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Re: Why are hydrocarbons effective fuels?
« Reply #2 on: March 28, 2012, 12:26:26 PM »
There are a lot of things that make hydrocarbons good fuels - high energy density, large increase in pressure on combustion, easily controlled combustion, relatively safe to store and transport, not particularly volatile, doesn't absorb water, wide range of combustion conditions, easily vaporized, stay liquid under a wide range of conditions of temperature and pressure, and many many more.

But I think the major thing that makes hydrocarbons effective fuels is that the technology of transportation has evolved with hydrocarbon fuel usage. Early cars, it didn't make a lot of difference what you put in the gas tank, as long as it was liquid and would burn. As the cars were engineered to use fuel more and more efficiently, they became specialized for very specific blends of hydrocarbons. Now with all the regulations on efficiency in both emissions and energy conservation, very small changes in fuels can lead to large losses in energy available.

The two major problems that alcohol fuels have are that they absorb water and that alcohol fueled vehicles are hard to start in cold weather. Almost everything else can be taken care of using current technology. However, to bring alcohol fuels up to the same level of efficiency we get from hydrocarbon fuels will require a new set of engineering improvements based on a consistent supply of standardized fuels, with a distribution network for both vehicles and their fuels, and people willing to buy and use them.

Offline typhoon2028

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Re: Why are hydrocarbons effective fuels?
« Reply #3 on: March 28, 2012, 12:35:03 PM »
also cost and availablity

Offline zcami2

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Re: Why are hydrocarbons effective fuels?
« Reply #4 on: March 29, 2012, 03:51:46 AM »
Thank you all for your replies :)
I must say that the E100 article was particularly interesting and helped a lot.
Thanks again,
Z.C


Offline Sadi Carnot

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Re: Why are hydrocarbons effective fuels?
« Reply #5 on: March 29, 2012, 12:07:49 PM »
There is no reason that an alcohol (such as ethanol) couldn't be used as a fuel source, but it is worth noting that the hydrocarbons in gasoline have a higher heat of combustion than ethanol (compare 47.0 kJ/g for gasoline vs. 29.7 kJ/g for ethanol).  So to put that in perspective, if gasoline's density is somewhere in the neighborhood of 750 g/L, and ethanol's density is right around 790 g/L, then 1 L of gasoline could perform 35,250 kJ of work, whereas 1 L of ethanol coud only perform 23,463 kJ of work.

Just something to think about:P

Offline juanrga

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Re: Why are hydrocarbons effective fuels?
« Reply #6 on: March 31, 2012, 08:36:32 AM »
Hi all,
I would like to know why it is that hydrocarbon chains (specifically alkane groups) are effective fuels?  What is it about their chemical structures that enable them to rapidly ignite in such a way that they are compatible with the modern combustion engine?  Also could it potentially be possible for a member of the alcohol group (specifically ethanol) to be capable of running an engine without combination with a separate alkane based fuel source?

Thanks,
Z.C.

The use of alcohols in engines is not anything new. In page http://www.ethanolontap.com you must find info about use of ethanol in vehicles of several kind. There is a category of dragster races (Top alcohol) which uses methanol as fuel.
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Offline Corporeus

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Re: Why are hydrocarbons effective fuels?
« Reply #7 on: June 15, 2012, 10:34:36 PM »
The reason hydrocarbons are effective for combustion is because combustion always releases water, and carbon dioxide. That's why engines require oxygen to be able to combust. Engines use octane as a fuel, but not a simple 8 carbon chain, with a methane group on each end, and 6 methylene groups in the middle. they use something called 2, 2, 4 - trimethylpentane. which is still the same C8H18 but its arranged differently, its an isomer of octane.

Another reason hydrocarbons, more specifically alkanes, are a better source of fuel, is because of the large amout of weak bonds. The more bonds, the more energy, and the weaker the bonds, the less energy needed to seperate those bonds.

In conclusion, hydrocarbons are ideal for fuel because of their combustible structure, and the ideal elements needed for combustion.

Offline Borek

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Re: Why are hydrocarbons effective fuels?
« Reply #8 on: June 16, 2012, 04:16:19 AM »
The reason hydrocarbons are effective for combustion is because combustion always releases water, and carbon dioxide.

In a very convoluted way it can be right, but in general it is incorrect.

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That's why engines require oxygen to be able to combust.

Again, there is grain of truth in what you wrote, but it is more confusing than helping for someone not understanding what it is all about.

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Engines use octane as a fuel

This is simply wrong. n-Octane and iso-octane are reference fuels, but they are not used as a fuel.

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Another reason hydrocarbons, more specifically alkanes, are a better source of fuel, is because of the large amout of weak bonds. The more bonds, the more energy, and the weaker the bonds, the less energy needed to seperate those bonds.

Again, half truth at best.

I am afraid your answer suggests you understand only 25% of the problem, but you pretend to know it all.
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Offline Corporeus

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Re: Why are hydrocarbons effective fuels?
« Reply #9 on: July 03, 2012, 04:11:20 PM »
Im not going to fight with you, but I am in highschool, about to take Chemistry 2 AP. I dont know all, but from reading around on Wikipedia, and these forums, its what i've learned. The thread starter is also posting in the highschool section, so we may have similar minds being that we are both in highschool. Im new to this forum, so it would be nice if instead you dont down me because you might have more experience, but instead teach me. Thanks.

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