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Old 12-12-2017, 04:58 AM   #1 (permalink)
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Energy in 1 liter of biogas @ 1 bar

I've been looking for how much energy is in 1 liter of bio- (or natural) gas, so I can work out how far 1 can drive with a 3 gallon (=11,35 l) tank (natural or biogas compressed herein to 250 bar).

These sources have some useful info:
deepresource
ct.gov

Anyway, here are some of my calculations, let me know if they're correct (I'm not sure, since the difference with hydrogen is HUGE. In comparison, hydrogen has 0,003 kwh/l whereas natural or biogas has 5,42 kwh per liter, so 1806x more)

1 cu foot of natural gas = 0,012 gallons natural gas @14,73 psi (=1,0155 bar) = 0,045424941 liter natural gas @14,73 psi (=1,0155 bar)
1 cubic metre of natural gas = 8,8 kwh
0,0283168 cubic metre = 1 cubic foot
1 cubic metre = 35,31472 cubic foot
8,8 kwh / 35,1472 = 0,25037 kwh per cubic foot
1 cu foot of natural gas = 0,012 gallons natural gas @14,73 psi, so 0,25037 kwh is in 0,012 gallons natural gas @14,73 psi or 0,25037 kwh is in 0,045424941 liter natural gas @14,73 psi
0,25037 kwh X 22,0143 = 5,51 kwh is in 1 liter of natural gas @1,0155 bar
5,42 kwh is in 1 liter of natural gas @ 1 bar
135,64 kwh is in 11,35 liter of natural gas @250 bar

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Old 12-12-2017, 06:06 AM   #2 (permalink)
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Thats a lot of extra math...and I can say right off the bat that 1 litre is not equal to 2/3rds of a cubic meter, as your 5.5kwh/litre vs 8.8kwh/cubic meter suggests. 1 cubic meter is 1000 litres, so it would be 0.0088 kwh/litre.

Quote:
One GGE of natural gas is 126.67 cubic feet (3.587 m3) at standard conditions. This volume of natural gas has the same energy content as one US gallon of gasoline (based on lower heating values: 900 BTU/cu ft of natural gas and 115,000 BTU/gal of gasoline).[16]

One GGE of CNG pressurized at 2,400 psi (17 MPa) is 0.77 cubic foot (21.8 liters or 5.75 Gallons). This volume of CNG at 2,400 psi has the same energy content as one US gallon of gasoline (based on lower heating values: 148,144 BTU/cu ft of CNG and 115,000 BTU/gal of gasoline.[16] Using Boyle's law, the equivalent GGE at 3,600 psi (25 MPa) is 0.51 cubic foot (14.4 L or 3.82 actual US gal).
and 1 US gallon of gasoline contains 33.40 kwh of energy.

250 bar is pretty close to the 3600 psi mentioned (3625), at which it takes 3.82 gallons of CNG to equal the 33.40 kwh. You have "only" 3 gallons, so 3.82/3 = 0.78534 multiply that by 33.40 kwh and you have 26.23 kwh in your tank. (~2.3kwh/litre @ 250 bar - or 9.2 watt-hours per litre at 1 bar vs the 8.8 watt-hours per litre of our original math. The 0.4 difference is either from using a different value per litre, or from rounding too much in the math)

Now you see why CNG vehicles have such big tanks...
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Old 12-12-2017, 10:48 AM   #3 (permalink)
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Quote:
Originally Posted by Stubby79 View Post
3.82 gallons of CNG @250 bar to equal the 33.40 kwh.
Where did you get that data from ?

Quote:
Originally Posted by Stubby79 View Post
you have 26.23 kwh in your tank. (~2.3kwh/litre @ 250 bar - or 9.2 watt-hours per litre at 1 bar vs the 8.8 watt-hours per litre of our original math.
Your equation is thus:
26,23 kWh = 11,35 litre x 2,3 kWh/litre @ 250 bar
26,23 kWh = 11,35 litre x 0,0092 kWh/litre (@1 bar) x 250 bar
26,23 kWh = 26,105 kWh so doesn't match, but it's close

Calculating it another way:
1 GGE = 3,587 m @ "standard conditions" (=250 bar ?)
33,4 kWh = 3,587 m @ 250 bar
33,4 kWh = 3587 liter @ 250 bar
33,4 kWh = 11,35 liter @ 250 bar x 316,0352
33,4 kWh/316,0352 = 11,35 liter @ 250 bar
0,1056 kWh = 11,35 liter @ 250 bar
11,35 liter x 0,0093 kWh/l @ 250 bar

That last calculation seems wrong (perhaps because standard conditions doesn't mean 250 bar ?) but I got a number of 0,0093 kWh which seems to be close to the 0,0092 kWh I got from the above calculation, so that may be the right number (it also almost matches the 9,2 watt you also calculated).

Recalculating:
11,35 litre x 0,0093 kWh/litre (@1 bar) x 250 bar = 26,388 kWh
So that's even worse than with 0,0092 kWh; with 0,00925 it gives:
11,35 litre x 0,00925 kWh/litre (@1 bar) x 250 bar = 26,246 kWh
That seems to be about the right figure ?
It would mean that natural/bio gas is about 3,083x more energy rich than hydrogen.

Last edited by smallscaleH2; 12-12-2017 at 10:56 AM..
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Old 12-12-2017, 01:32 PM   #4 (permalink)
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Quote:
1 cubic metre of natural gas = 8,8 kwh
Just divide that by 1000 you boob!

And multiply by 250 to get the energy density @250 bar.
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Old 12-12-2017, 02:30 PM   #5 (permalink)
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Quote:
Originally Posted by smallscaleH2 View Post
Where did you get that data from ?
All my data came from wikipedia's entry on gasoline gallon equivalent. https://en.wikipedia.org/wiki/Gasoli...lon_equivalent

Any bad math came from me.
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Old 12-12-2017, 03:46 PM   #6 (permalink)
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Depends on how much CO2 is contaminating your bio gas.

Probably should get a diesel and run bio gas intake fumigation. That way when your roughly 2/3 of a gallon equivalent worth of bio gas runs out you're not stuck on the side of the road with no fuel.
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Old 12-13-2017, 08:27 AM   #7 (permalink)
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Quote:
Originally Posted by jakobnev View Post
1 cubic metre of natural gas = 8,8 kwh
Just divide that by 1000 you boob!
And multiply by 250 to get the energy density @250 bar.
8,8x250/1000= 2,2 kwh = 1 liter natural gas @ 250 bar x 11,35 liter = 24,97 kwh
That's pretty close to the 26,23 kWh Stubby79 calculated out.
8,8/1000= 0,0088 kwh per liter natural gas. We got a figure of 0,0092 - 0,0093 so pretty close to that too.

I doubt any of us is really wrong, rather some differences can be explained by the fact that natural gas varies in its make-up (gases) so energy ratings can fluctuate a bit.

Let's round it off and say its 0,009 kwh per liter
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Old 12-13-2017, 08:53 AM   #8 (permalink)
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So what kind of vehicle is going to be cursed with less than 1 gallon worth of liquid fuel range?
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Old 12-26-2017, 08:55 AM   #9 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
So what kind of vehicle is going to be cursed with less than 1 gallon worth of liquid fuel range?
I don't know who would want to do that if that's the only fuel source taken along (that said, it does allow for a 50 km range with modern cars, so not too bad when compared to older electric cars). Multiple 3 gallon tanks could be taken along if someone would like to use natural gas as the only fuel (the benefit of the small 3 gallon tanks is that less fuel could explode in a single go, so it's safer than to take along say one 9 gallon tank. In any case, I just wanted to calculate it out to compare it to hydrogen.
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Old 12-26-2017, 09:37 AM   #10 (permalink)
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I have the equivalent of 2 gallons in the ranger

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