12

Why do we mostly use fossil fuel instead of something like... Alcohol? We used it in a portion of our gas, so why don't we use it in greater quantities?

Obviously there's a reason.

My guess is alcohol does not contain enough oxygen to allow for a smooth combustion. Does fossil fuel?

  • 10
    What is this "more reliable and larger sum" that you speak of? I'm not sure what that means? – JPhi1618 Apr 11 '16 at 14:54
  • 7
    If such a thing existed, we would use it. Finding something that really does work better than fossil fuels is extremely difficult because they are just so good. – JPhi1618 Apr 11 '16 at 14:59
  • 7
    I'm not aware that we currently have the technology or resources to make alcohol or any other fuel in sufficient quantities to replace gasoline at a comparable price. What makes you think that we do? – Nate Eldredge Apr 11 '16 at 15:59
  • 5
    Oxygen content of the fuel is not relevant; air-breathing engines extract the oxygen they need from the air, not from the fuel. What you want in a complete combustion is oxygen gas comes in, the fuel is hydrogen and carbon, and water and carbon dioxide comes out the back. If you're carrying around oxygen, that's just adding weight. You get it for free from the atmosphere, so use it. – Eric Lippert Apr 11 '16 at 17:35
  • 3
    Alcohol contains more oxygen than fuels baed on mineral oils, i.e., some rather than essentially none. – David Richerby Apr 12 '16 at 4:49
27

What you really want to look into is Energy Density. So called "Fossil Fuels" have a very high energy density, which is very important for a vehicle fuel since you have to load it and carry it around with you.

This chart shows fuels listed in order of their energy density:

enter image description here

So, the main reason we don't use X for fuel and everyone seems to be so in love with gasoline and diesel is because for our current technology, they are just really, really efficient and packing a lot of power in a small space. Combine that with the fact that it's easy to store and distribute, and you've got a combo that's very hard to beat.

  • Thank you. Also big help with the chart. I found that using something like alcohol don't have a large good mix of energy and we would need double to go half the distance – LostPecti Apr 11 '16 at 15:03
  • 1
    @LostPecti you mean, double to go the same distance. – DrewJordan Apr 11 '16 at 17:02
  • 4
    @LostPecti: Also, consider the costs of production, which is not reflected in this chart. Oil you can just dig out of the ground, which can be expensive, yes. But the total energy cost of turning corn into ethanol is also really high. Also not factored in are the external costs like dealing with pollution. It is very difficult to see the big picture here; it is complicated. – Eric Lippert Apr 11 '16 at 17:33
  • 1
    Another factor, along the lines of what @EricLippert is saying, is that Ethanol from corn also drives up peripheral costs as well. In the US, the increase in food prices is directly related to the cost of fuel, not only due to gasoline prices going up (though at the time of this comment, that price has come down dramatically), but also due to the mandate of using ethanol in gasoline. Since corn is the primary source for ethanol, all of the excess is being diverted to fuel production, which drives up prices everywhere. No more surplus; higher prices. – Pᴀᴜʟsᴛᴇʀ2 Apr 11 '16 at 18:22
  • 1
    @DeanMacGregor Those buses stay near refueling stations. Range anxiety is real. Why don't Toyota and Tesla use biodiesel series-hybrids? – Cees Timmerman Apr 12 '16 at 11:34
23

While energy density is a rather nice property of gasoline and diesel, it's not the primary driver of their use. Instead, the primary driver is a rather practical one: they're cheaper.

On the consumer side of things, we don't tend to notice this, as most places price things volumetricly — so much per gallon. In order to see the "true" price, you have to account for things like energy density and engine efficiency. In the end the price which matters is dollars per mile, not dollars per gallon. If you do the conversion, you see that ethanol (E85) is consistently around 20% more expensive (on a per mile basis) in the United States.

But the lower energy density of ethanol doesn't automatically kill the calculation. You can see this in places like Brazil. Brazil has a substantial number of ethanol-powered vehicles. There isn't anything special about the ethanol in Brazil which increases its energy density. The main thing that's changed is that due to the large number of sugarcane plantations in Brazil, ethanol is much, much cheaper than elsewhere. Price of a fuel is a complex mix of the cost of production, the cost of transportation, and the local tax policy. What's the cheapest option in one place is not the cheapest in another, and people will gravitate towards whatever is cheapest locally.

If the cost per mile of ethanol were to become cheaper in the United States or Europe, then you'd see people switch over there too — even if that means they have to increase the size of their fuel tanks or fill up more often. (As evidenced by people switching over to electric cars, despite the comparatively horrible energy density of batteries. Electricity is much less expensive per mile than gasoline and diesel, so it can make sense to switch over if you can bear the more frequent re-fueling.)

  • the price is actually a symptom, not the driver. Electric batteries for cars are only becoming viable now (with high subsidies) because the increasing cost of obtaining ever more scarce oil is getting closer to the price that makes electric cars the cheaper option. And as @EricLippert mentioned in comments on JPhi's answer, the associated costs make electric cars still very expensive (hence the subsidies) – Rory Alsop Apr 11 '16 at 19:03
  • I just checked and the price difference is small. If ethanol was produced massively, the price would drop. – Tomáš Zato Apr 12 '16 at 8:23
  • 1
    @TomášZato, If you read about the US experiment of trying to produce Ethanol on a large scale you'll see how so much foodcrop or crop land was devoted to corn for the production, that other everyday items have increased in cost. Chicken, beef, and related products (eggs, milk) saw a noticeable increase in price. And that's not even considering the ecological cost of farming and deforestation. I guess my point is that we can't just "make more!" without affecting something else that we also need. – JPhi1618 Apr 12 '16 at 13:20
  • @TomášZato what are you basing that on? Ethanol is already made at an industrial scale so it's hard to believe there are economics of scale that aren't already being captured. At this point increasing production would get into diminishing marginal returns and hence the price would go up not down. – Dean MacGregor Apr 12 '16 at 14:05
  • If all costs including mitigating environmental effects are factored in, then it is doubtful that fossil is still cheaper. The tragedy of this time is that only part of the real cost of burning fossil fuel is part of the price users pay, and the rest is invisibly spread out over all of society and our descendants. – RemcoGerlich Apr 13 '16 at 11:59
7

You absolutely can use ethanol instead of gasoline and disregarding some fairly minor technical issues they are more or less interchangeable.

The issue is one of supply. We have the capacity to produce a reliable supply of gasoline from petroleum extraction which has a well established infrastructure for production and processing.

In a fuel context 'alcohol' generally means 'bioethanol' produced by the fermentation (or an equivalent industrial process) of plant products. The problem is that this puts fuel production potentially in direct competition with food production and the same applies to 'bio diesel' from vegetable oils.

There is also an energy requirement in turning the low concentration alcohol produced by fermentation (equivalent to beer) into a useful fuel by distillation.

  • Thank you. I see the biggest problem is energy density and cost not only to make it but to give the fuel a high density that can be used in modern vehicles. This information that everyone have been very valuable in my research. Thank you All :) – LostPecti Apr 12 '16 at 0:32
  • The day they invent a car that can run on beer, things are going to get much more complicated for the cops. "Sir, I smell beer. Have you been drinking?" "No, officer, honestly, that's from the car..." – Darrel Hoffman Apr 12 '16 at 19:08
  • @DarrelHoffman In London there was (maybe still is) a program whereby all the chip shops, etc, could recycle their used cooking oil - guys would come around in a lorry with some barrels and collect it, bring it back to a processing depot where it was cleaned up and converted for use as fuel in diesel engines. The biggest consumer seemed to be the black London cabs, one driver I recall saying that he rather liked the arrangement, not just because it made economic sense but also because it made his exhaust smell a bit like chips. – J... Apr 13 '16 at 13:12
2

One thing that has not been mentioned here is not only the density but also how efficient the combustion engine is.

For instance--why do we not use electric heaters for entire homes? Because it's 4 to 10 times as expensive as using some form of gas. Electricity is 'cheap' for appliances like a computer--but it's very inefficient in terms of cost when it comes to cooling/heating. Hence why we usually only use electricity to cool, since combustion doesn't exactly cool off things :).

For the most part the main driver of why we use a certain type of energy source for any application is it's a) cheap based on cost + efficiency of engine involved b) convenient and safe given the application.

But it's really important to consider the engine. Efficiency is a measure of say you put in 1.00 units of fuel in, and you get only .80 or so units of work worth of that fuel out of the engine. And nobody's really come up with anything that beats the combustion engine for small-scale applications.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.