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#1
02-02-2006, 10:53 AM
 Unregistered Guest Posts: n/a
Ethanol btu's per gallon

Does anyone have the gross BTU's per gallon of ethanol from corn? Any difference between this ethanol and that from cellulosic material? How about methanol?
#2
02-06-2006, 10:00 AM
 Robert Fogt Administrator Join Date: Dec 2005 Location: Seattle, WA Posts: 3,467 Rep Power: 13
Re: Ethanol btu's per gallon

I found some information.

Energy density of ethanol
http://hypertextbook.com/facts/2003/RoxanneGarcia.shtml

Various fuels compared.
http://xtronics.com/reference/energy_density.htm

Though if you are asking if ethanol from corn has a different energy density then ethanol from some other substance, I do not know. I would guess they would be the same in its purest form.

I can help convert energy density in megajoules/kilogram to Btu/gallon if you need that.
#3
04-20-2007, 01:44 AM
 Unregistered Guest Posts: n/a
Re: Ethanol btu's per gallon

ethanol is 76000 btu per gallon.
it does not matter what the source was .
#4
05-23-2007, 10:43 AM
 Unregistered Guest Posts: n/a
Ethanol btu's per gallon -- That's not the only question

It would appear that the energy density of ethanol is somewhere between 23-27 megajoules per kilogram depending on the different levels of purity that can be achieved during the distillation process (e.g. it is the same as for vodka or gin, which can be produced at different strenghts).

I understand that greater purity can be achieved by mainly removing water and CO2 from ethanol. The less water and CO2, the purer and the higher the BTUs.

However, let me open the question, by stating that the key is not just the "amount of energy dispensed" by ethanol but, like with any other source of energy, the "net energy dispensed", which is what is commonly called the well-to-wheel impact. In simple terms, how much energy ethanol produces minus how much it uses for production, distillation, distribution, storage, etc.

This is where the type of raw material used for producing ethanol (sugar cane, sugar beet, wheat, corn, cellulose, etc.) makes a significant difference. Corn is a very poor raw material: research varies but, overall, all reports seem to conclude that the "net energy dispensed" by corn-based ethanol is either marginally positive or marginally negative. On the other hand, sugar cane has a highly positive net energy balance (since alcohol results from fermented sugars, it should make sense, all things being equal), in addition to producing more than twice as much ethanol per acre cultivated vs. corn.

Therefore, thinking simply in terms of BTUs can be correct or incorrect depending on the question that you need to answer.

I hope this helps.

PS: a gallon of ethanol contains approx. 80,000 BTUs. A gallons of unleaded regular contains about 119,000 BTUs. As a result, a standard barrel (42 gallons) of ethanol is worth about 28 gallons of gasoline.

Metric tonne ethanol = 7.94 petroleum barrels = 1262 liters
ethanol energy content (LHV) = 11,500 Btu/lb = 75,700 Btu/gallon = 26.7 GJ/t = 21.1 MJ/liter. HHV for ethanol = 84,000 Btu/gallon = 89 MJ/gallon = 23.4 MJ/liter

LHV = Lower Heating Value; HHV = Higher Heating Value.

(Extract from a website): "Energy contents are expressed here as Lower Heating Value (LHV - also known as "net CV" or net calorific value) unless otherwise stated (this is closest to the actual energy yield in most cases). Higher Heating Value (HHV, including condensation of combustion products - also known as "gross CV" or gross calorific value) is greater by between 5% (in the case of coal) and 10% (for natural gas), depending mainly on the hydrogen content of the fuel. For most biomass feedstocks this difference appears to be 6-7%. The appropriateness of using LHV or HHV when comparing fuels, calculating thermal efficiencies, etc. really depends upon the application. For stationary combustion where exhaust gases are cooled before discharging (e.g. certain power stations using condensed gases for pre-heat), HHV may be more appropriate. Where little or no attempt is made to extract useful work from hot exhaust gases (e.g. motor vehicles, small heating boilers), LHV is more suitable. In practice, many European publications report LHV, whereas North American publications use HHV."
#5
12-05-2007, 05:34 PM
 Unregistered Guest Posts: n/a
Re: Ethanol btu's per gallon

I am considering buying an ethanol fireplace. I would like to compare the btus of a gas fireplace vs. an ethanol one. A gas fireplace gives off approximately 40,000-45,000 btus. Can anyone do a direct comparison of ethanol btus (other than for a gallon of ethanol which was already stated).

Thanks.
#6
12-06-2007, 02:54 PM
 Robert Fogt Administrator Join Date: Dec 2005 Location: Seattle, WA Posts: 3,467 Rep Power: 13
Re: Ethanol btu's per gallon

Quote:
 Originally Posted by Unregistered I am considering buying an ethanol fireplace. I would like to compare the btus of a gas fireplace vs. an ethanol one. A gas fireplace gives off approximately 40,000-45,000 btus. Can anyone do a direct comparison of ethanol btus (other than for a gallon of ethanol which was already stated). Thanks.
Not sure I understand your question completly.

40,000 Btus from gas fireplace would need 40,000 Btus from an ethanol fireplace. It wont matter what the source is, a Btu is a Btu.
#7
12-17-2007, 11:08 PM
 Unregistered Guest Posts: n/a
Re: Ethanol btu's per gallon

So how does Ethanol increase octane by 2 to 3 points.?
#8
12-18-2007, 09:39 AM
 Unregistered Guest Posts: n/a
Re: Ethanol btu's per gallon

Octane rating is not about more energy per gallon, it is about tolerating higher compression ratio. Compressing any gas heats it. In the case of an air-fuel charge, it can reach a temperature at which it spontaneously combusts from the heat; this leads to the engine knocking. Diesel engines are designed to operate in this mode, spark ignited engines are not.

Like octane, an ethanol air-fuel charge needs a higher ignition temperature. If the fuel tolerates the compression ratio, higher compression ratios produce more power from a given weight engine and convert a larger portion of the thermal energy to mechanical. Since the fuel is typically more expensive, it may not lead to more economical operation.
#9
12-22-2007, 08:00 AM
 Unregistered Guest Posts: n/a
Re: Ethanol btu's per gallon

Octane in gasoline is not a measurement of energy, but is a measurement of resistance to pre-ignition. Gasoline is made up of HC (Hydrocarbon) molecule chains and those HC chains having 7 carbon atoms are called Heptane and those that have 8 carbon atoms are called Octane. Gasoline fuel rated @ 87 Octane contains 13% Heptane HC chains and 87% Octane HC chains.

Octane can be (and has been by practice) increased by artifical means (addition of special additives and/or improved refinement technologies) and is today (by the American Petroleum Institute or API) more a measurement of fuel rapid oxidation rate @ a specific temperature and pressure (as determined by the API and American Society of Testing Materials or ASTM test procedures) rather than the actual percentage of Octane HC chains.

The reaction in an internal combustion engine is that the higher the Octane rating, the slower the fuel burns and the greater the resistance to pre-ignition. Using a fuel of a higher Octane (on the modern computer controlled engine), higher than what the manufacturer designed their engine for, will not only reduce that engine's fuel economy, but it will also reduce that engine's performance.

As far as fuel for heating, most home heating fuel suppliers will rate their fuel in BTUs based on what appears the most advantagous to their fuel sales. For example: 1 BTU is the heat required to raise 1 lb of water 1ºF. Gasoline has a BTU rating of 18,400 BTUs/lb, whereas ethanol is actually 47% less @ 9,750 BTUs/lb. Because of this, ethanol fuel suppliers display their fuel BTU ratings as BTUs per gallon (giving the consumer a perceived higher heat value). For comparison; heating oil has a BTU rating of 20,400 BTUs/lb and diesel (#2) has a rating of 24,840 BTUs/lb.

For those considering ethanol as an alternative due to enviornmental concerns (ethanol has near zero greenhouse gas emissions when burned), it should be noted that between 0.5 and 1.5 gallons of fossil fuel (depending on who you talk to) is used to produce a single gallon of ethanol.

Steve C.
#10
12-22-2007, 12:35 PM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,534 Rep Power: 19
Re: Ethanol btu's per gallon

I have to take issue with a few of the numbers in post #9.
It is unclear whether they are higher or lower heating values or the source.

Not sure if this link will post www . eere . energy . gov/afdc/pdfs/fueltable . pdf
but source is a Department of Energy table. Qutoing from it. lower heating values (LHV) are given for several fuels in format:
Fuel, BTU/lb, BTU/gallon
Gasoline, 18676, 116090
#2 diesel, 18394, 129050
Ethanol, 11585, 76330
Propane, 19900, 84500
Methane, 20263, 19800
Hydrogen, 52217, N/A

LHVs are clearly the right choice for a motor vehicle fuel as present technology has no way to recover the heat in the water vapor as mechanical energy. For high efficiency furnaces to heat homes, the correct choice is debatable.

#2 diesel has a higher energy content ONLY on a per gallon basis; it is less per pound. Ethanol is a highly oxygenated fuel which is the reason for its lower energy content. In general fuels with higher C/H ratio have higher energy content per gallon. less per pound.

Of course for economy, what really matters is the BTU/\$.

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