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Compare Fuels Chemically

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Posted by Curbie on February 5, 2010, 7:02 am

Lately, I've trying to compare fuels chemically; I didn't take
chemistry in high school back in the Stone Age so this effort has
involved a lot of ramp-up work. So, I put all the data I've collected
into a spread-sheet:
...and tried to calculate something I was familiar with, the Air Fuel
Ratio, as I remember, for gasoline it is 14.7:1 and methanol 6.5:1, my
sheet is close but not correct, 15.33:1 and 6.67 respectively.

I'm hoping someone could find some time to look at the sheet and show
me where I goofed-up, it is fine if you're too busy, but I thought it
couldn't hurt to ask.

Post or email if you can help.



Posted by Jim Wilkins on February 5, 2010, 7:11 pm

The important numbers are the high and low heats of combustion, the
cost of the raw materials and the investment to manufacture and store
the fuel.

Chemical reactions rarely run only one way exclusively. In the hot gas
there is some incomplete combustion to CO or even CO + H2 <=> C + H20,
thus some extra air is needed to consume all of the fuel. The C is
soot in the exhaust.

I do have a degree in chemistry and don't see any reasonable,
dependable and economical way to manufacture liquid fuel at home
unless you have a surplus of fermentables from your farm. Biodiesel
suffers from an unreliable source. You can get simple plastic tanks
cheaply but distillation and handling equipment is nearly impossible
to find and can be quite difficult to make.


Posted by Curbie on February 5, 2010, 9:12 pm


These "liquid fuel-liquid water" and "liquid fuel-water vapor" heat

I obviously don't have a degree in chemistry, but I'm still studying
two small-scale DIY paths to liquid fuels and will pursue the best one
of them Straight Vegetable Oil (SVO) or bio-diesel and ethanol.

I am not considering Waste Vegetable Oil (WVO) for dependable
feedstock reasons, but if you have enough land (.5 to 1 acre, crop
dependant) to grow your own feedstock, it seems that both paths are
reasonable (the technology has been around for decades) and
dependable, the reason I'm studying them is to determine the

I am much more familiar with DIY ethanol from the 80's, so my
knee-jerk has been to go with what I know, but at a home-scale DIY
levels the net energy margin is thin enough to warrant some research
as to which process is better.

SVO on its face seems easier, screw-press, heat exchanger, and
diesels, but diesels are getting harder to come by, parts and engines.

To be dependable, bio-diesel will need to have two different
feedstock(s), one for the SVO and one for the ethanol. SVO, ethanol,
and potassium hydrate (wood ash and water) = bio-diesel and SVO,
methanol (fossil fuel derivative), and sodium hydrate = a home-made
fuel which depends on fossil fuel supplies.

Ethanol has been produced for over 100 years in one from or other and
there is a large hobby interest in producing ethanol for drinking
spirits, so there is a lot of good information about making DIY
equipment and it runs in modified gasoline engines which are easier to
obtain and get parts for. The first-blush draw bach here is amount of
equipment and its costs required to process 195 proof fuel.


Posted by Jim Wilkins on February 5, 2010, 11:52 pm

Yes, the difference is the energy recovered by condensing the steam.
European articles may assume the high value without saying so.

My point exactly.

I just read the Wiki and a few issues jumped out:

Wood ashes absorb CO2 from the air (if not the fire) quickly and turn
into potassium carbonate K2CO3, which isn't the same as potassium
hydroxide KOH (not hydrate). Obviously it will saponify the
triglycerides into soap as it has for centuries but I don't think it
will perform the competing esterification reaction. If you dissolve it
in water, add slaked lime, remove the precipitate and boil it very dry
you'll have KOH by a slow, energy-intensive process. You have to keep
it sealed from the air afterwards because it absorbs water very

Search for "carbonate". They are discussing the acid process there.
Notice that much can go wrong and you need to analyze the product and
understand and correct the problems.

A big concern is lab work and safe handling, neither of which is
simple or obvious. When instructions say to titrate the free acid
concentration with a standard base they assume you've had a lot of
hands-on training in wet chemistry. Like welding and machining they
are skills best learned in person, a textbook won't notice your

Chemistry is both intensively and extensively complex with plenty of
small but important details to remember, and fairly dangerous. In this
instance lye in methanol is very poisonous and the alternative,
sulphuric acid, is NASTY.

Then you have the enormous problem of hazardous waste disposal, which
has kept me from doing any chemistry at home. No big loss, electronic
and mechanical projects show more results anyway.


Posted by Curbie on February 7, 2010, 1:07 am


Thanks for correcting my mistake; I wouldn't have wanted that to

I know of no electronic or mechanical projects that produce a higher
energy density than liquid fuels which leads me back to SVO or
bio-diesel or ethanol.

SVO can be purely a mechanical process, bio-diesel, and ethanols are
both processes that have been preformed on a DIY home-scale for
decades, and on the other side of the coin, there are risks involved
with both the handling and dependence on fossil fuels to consider in
the over-all risk reward issue.

Your welding and machining analogy is good, but in my view not
complete; learning either way (books or tutor) doesn't guarantee
success on the first attempt, the skills will have to be developed no
matter how you start.

I was just looking for help with a spread-sheet to better understand
the options, but if you or anyone else is uncomfortable with what may
result, "no harm, no foul".



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