Compare Fuels Chemically

[Curbie]

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:
http://i825.photobucket.com/albums/zz177/Curbie_Pics/FuelSS.jpg
....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.

Thanks,

Curbie

 

[Curbie]

Jim,

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.

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

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.

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
economics.

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.

Curbie

 

[steamer]

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.

(SNIP)
--Just as he says. FWIW I once did a 'fractional distillation' of
kerosene and graphed the results. It was just a little amateur science: no
expert me. I was trying to find out why my steam boiler's kerosene burners
coked up so quickly and I found that the stuff starts to turn to carbon
at very low temperatures.

 

[Curbie]

Jim,

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

No big loss, electronic and mechanical projects show more results anyway.

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".

Thanks,

Curbie

 

[Curbie]

Jim,

I think I understand your Lear point, he was getting results but
mischaracterize HOW those results where achieved and when people
followed the mischaracterizations their results where random and a lot
effort was wasted.

My interest is in following tried and true technologies and to that
end I was half-settled on ethanol for no other reason then it's what I
know best (racing with methanol), but in talking with people on-line
about DIY production of ethanol people suggest alternatives like SVO
or bio-diesel as being a better option, but their reasons for their
selection was kind of the same as mine, what they knew best.

In thinking about their reason for their choice it seemed silly, but
occurred to me that I had the same silly reason for my choice and had
better study all three processes to base my choice on something of
substance.

That was the reason for starting my spread-sheet, just compile all the
information I've accumulated on fuels over the years into one
spread-sheet for comparison, simple. In doing that the numbers were
not jiving and that lead to my attempt to calculate for the numbers,
not so simple.

I've never worried too much about a "wild goose chase" because I
always seem to learn something of value in the process, I know that
two of these three technologies will turn out to be wild goose chases,
but I expect the effort to narrow my focus on the one technology that
best suits my needs.

I know the calculations in my spread-sheet are close, but since this
is the start (or foundation) they better be right here or they will
become progressively inaccurate as I build on them. I talk on-line in
a lot of different places and sometimes find people who have knowledge
I don't, but are interested in the same results, and I've found it
never hurts to ask.

I'm retired too, so a have time new to play with things I'm interested
in, and I'm not inventing any new wheels, just trying to determine the
best beaten path to follow.

Thanks,

Curbie

 

[Curbie]

Michael,

Thanks, it is interesting but like I said in other posts, I like
technologies with a well defined and well beaten path; I wouldn't even
know where to begin with this.

Curbie

 

[Curbie]

Wouldn't be better just experiment with SVO (straight veggie oil) and avoid everything but growing the crop and pressing the Oil?

Exactly my point! I don't know the answer, but I better find it out
before I select an option. I can see where the mostly mechanical
process of SVO would have some advantages for someone from the view
point of simplicity, but I believe given a little time and practice,
I'll be able to follow the beaten path for any one of the three
options, so in my view the "Best" question becomes which option gives
the best return of investment.

From the stand point of crop yields ethanol has a clear advantage, but
then considering energy density of yielded units, oil crops narrow the
gap. When I look at time, material, and energy costs for all three
options the clarity goes away.

Curbie

 

[Curbie]

Jim,

I think your right with the leaky joint analogy, but I want to focus
on building or fixing leaky joints with the commitment that for me
comes from the knowledge that I chosen the best option. Just because
the spread-sheet says one option has a better energy density, doesn't
mean that option will be the most cost effective path, although I
think a spread-sheet will help there too.

One step at a time.

Curbie

 

[Curbie]

Harry,

Well, after a couple days of chasing my tail (nothing new), I think
I've finally tracked down my trouble, the numbers I remembered for
gasoline (14.7:1) and methanol (6.5:1) are Stoichiometric ratios and
my spread-sheet calculates air/fuel ratios and there mot exactly the
same thing.

It seems Stoichiometric ratio considers air as just nitrogen and
oxygen where I was also considering the argon and CO2 present in air,
also I read somewhere on-line that the Stoichiometric ratio for
gasoline (petrol) is based on a different chemical mixture.

Anyway, it seems I was remembering Stoichiometric ratios and
calculating air/fuel ratios, but I'm pretty confident now that the
calculations are proper for my purposes.

Thanks for the link though, densities and specific gravities are next,
but at some point I'll go after heat values.

I'm old enough to have learned the imperial system in school and have
no clue what they teach these days, but I do use wikipedia a lot, so
over the last year or so I've been writing a series of conversion
routines for my spread-sheets so I have less and less trouble
understanding the results of metric equations.

Curbie

 

[Curbie]

Yes.

 

[Curbie]

Harry,

Well I was unfortunate enough to have been to school when we were
converting from one to the other.

When I was a kid I didn't know what I was going to learn before I
learned it, let along any other options. It is what it is, I just
accept it and deal with it.

Curbie

 

[Curbie]

Harry,

I agree some fuels are mixtures; I'm using ideal chemistry for
Gasoline (octane), #2 diesel (cetane), SVO (I think canola/rapeseed),
and bio-diesel (don't know yet). The point isn't prefect accuracy, but
rather a mathematical equivalence between the fuels.

Curbie

 

[daestrom]

Harry,

Well, after a couple days of chasing my tail (nothing new), I think
I've finally tracked down my trouble, the numbers I remembered for
gasoline (14.7:1) and methanol (6.5:1) are Stoichiometric ratios and
my spread-sheet calculates air/fuel ratios and there mot exactly the
same thing.

It seems Stoichiometric ratio considers air as just nitrogen and
oxygen where I was also considering the argon and CO2 present in air,
also I read somewhere on-line that the Stoichiometric ratio for
gasoline (petrol) is based on a different chemical mixture.

Not to throw too many variables into your calculations, but you have to
be careful of your percentages for 'standard air'. A common number you
might run across is 21% of air as O2, but that is by volume, not by
weight/mass.

So if you have 78% N2, 21% O2 and 1% Ar by volume, that works out to
about 75.4% N2, 23.2% O2 and 1.4% Ar by weight.

And of course the chemical reactions are mass balances, not volume, so
you might check this part.

daestrom

 

[Curbie]

Jim,

The spread-sheet is nothing more than a way to objectively calculate
heat values for different alternative fuels in comparison to standard
fossil fuels (gasoline and diesel). I'm looking at DIY home-scale
alternative fuels, mainly ethanol vs SVO or bio-diesel.

I feel it isn't good enough for comparison purposes to just look at
crop yields per acre and then energy values per yielded unit of oil or
ethanol. There is also the issue of processing costs both in terms of
initial equipment costs and then per unit processing costs.

I think that crop yields per acre are pretty well known and energy
values per yielded unit of oil or ethanol are less well known in an
"apples to apples" sense, and not well known in an "apples to oranges"
sense, especially when you start trying to consider the energy
required for processing.

SVO seems to have oil pressing and filtering processing costs.

Bio-diesel has all of SVO's initial cost plus the transesterification.

Ethanol has the cooking, fermenting, and distilling costs.

All have planting, fertilizer, and harvesting costs.

The devil is in the details and I'm just starting to sort through all
the details and their associated costs in order to choose the best
path for me.

Curbie

 

[Curbie]

daestrom,

The components of air are by volume:
Nitrogen Component of Air by volume (Pn) 78.084%
Oxygen Component of Air by volume (Po) 20.946%
Argon Component of Air by volume (Pa) 0.934%
Carbon Dioxide Component of Air by volume (PCo2) 0.033%

.... but I also have the mass of each component:
Atomic Mass of Carbon (MaC) 12.0107
Atomic Mass of Nitrogen, (MaN) 14.0067
Atomic Mass of Oxygen (MaO) 15.9994
Atomic Mass of Argon (MaA) 39.9480
Atomic Mass of Carbon Dioxide (MaCo2) 44.0095

.... then I tried to convert volume to mass by:
Atomic Mass of Air (MaAir) 14.6759 =(MaN * Pn) + (MaO * Po) +
(MaA * Pa) + (MaCo2 * PCo2)

=((Hydrogen - (Oxygen * 2)) / 2) + (Carbon * 2)
was used to calculate oxidation required for combustion.

Air mass for oxidation:
oxidation required for combustion * MaAir

I know fuels are not chemically monolithic, but in order to try an
objective "apples to oranges" comparison, it seemed that ideal
chemicals may get me close.

Curbie

 

[Steve Ackman]

In <[email protected]>, on
Thu, 11 Feb 2010 04:21:30 -0800 (PST), Neo,

The nice thing about
running a car on diesel is that one does not have to
consider that it might be dilluted with ethanol
so it is guaranteed to have an energy density
of 46.4 MJ/kg all the the time. .

You think anti-gel ingredients have the same energy
as diesel? Or you just don't live in a climate where
they're used?

 

[Curbie]

Jim,

The more I think about this, the more I think that small scale testing
from planting to final product seems in order. Getting a jump on
growing a small feed-stock of several varieties seems valuable in and
of itself just to have seed for production planting.

I'm not too sure how scaleable things like screw presses are, but I
think the literature is pretty clear on most of the mechanical stuff.
For the stills I think I would be better off building a small one,
need the practice with these smaller and newer designs anyway.

Curbie

 

[Curbie]

Jim,

I'm studying the notion of a small continuous still (~.5 liter/h) to
be primarily solar heated, with heat augmented as needed by a
secondary source, to run 24/7 120-150 days per year. Using your
concern which I have considered, the solar would supply all the heat
when it can, and when it can't, it would supply as much as it can,
augmented by something dependable, maybe electric.

Curbie

 

[Curbie]

Jim,

For a test press I've been looking at a small bottle jack with a jig
along the lines of an auto-shop press, from my reading that seems to
be a dual benefit to heating the feedstock in terms of both increased
oil (small, but significant) and the energy required to press the oil
from the feedstock.

The issue is, I can test yield per acre with this idea but not energy
per process and the whole idea of testing is to figure out which
process (oil or ethanol) has the best return of investment.

I think I'll get closer to an answer by small scale testing of
ethanol, SVO is such a mechanical process that I think I can get close
numbers from people that are using the system and there doesn't seem
to be an obvious way to improve on what's already being done.

The current home-scale ethanol process on the other hand appears at
first blush seems to have room for significant improvement in terms of
energy input, not the amount, but source. The current home-scale
producers seem to using large output (gallons per hour) batch stills
with their associated large input energy requirements, and then
balking at the size of solar heating equipment needed to run them. No
wonder.

Curbie

 

[Curbie]

Jim,

I've thought about (but haven't tried) a small flash boiler with an
automotive thermostat to let the depleted liquid pass on and bring
more in from the reservoir. If it works it should respond quickly and
self-regulate the flow. It might need a separate water flow control in
the fractionating column to allow higher temperature and more complete
separation in the boiler.

I like this idea and will have to toss it around some, THANKS.

You could preheat the incoming liquid with condensate.

I talked with a guy who is doing just that, like i said, I think there
is some room to improve on enthanol production.

Curbie