I thought I read somewhere that this device was called a "gasogen",
though I'm informed that that's the name of a seltzer bottle. Anyway
what I'm discussing here is a device for adapting solid combustibles for
use in an internal combustion engine. It works by burning the fuel in
an oxygen-starved environment, producing exhaust gases that may be burned
further.

    I don't know what the rules are for wood, though I had a list of the
gas composition once when I first looked into this around 1980 or so.
However, for coal and charcoal I can make a few guesses based on the
chemistry.

    Basically, we have

    C + 0.5 O2 + 2 N2 -> CO + 2 N2                   4341 BTU/lb-C

  { CO + 2N2 } + { 0.5 O2 + 2 N2 } -> CO2 + 4 N2     4344 BTU/lb-CO
                                                  = 10136 BTU/lb-C

    This delivers, in theory, 70% of the total chemical energy into
the cylinders, yielding 780 BTUs per pound of all reactants, and
950 BTUs per pound of air used in both gas generator and engine.

    Now some preliminary guesses:

* The gas-generating step increases the molar fraction of the air by
  20% - from 2.5 units to 3 units. Consequently the pressure-volume
  product should likewise increase. Immediately upon startup the device
  should become pressurized (no pumps needed).

* This step must needs also raise the temperature of the gas. Fortunately
  the nitrogen can be expected to take up the bulk of it.

  4341 BTU/lb-C = 620 BTU/lb (1442 kJ/kg) of combustion gasses, which
  are close enough in composition to air, for our purposes, to use the
  air specific heat. This raises the temperature from, say, 300K to
  1736K (1463C, 2667F). The gasses will need to be cooled before they
  get to the intake manifold.

* Assuming that the air and combustion gasses are brought to the same
  temperature, the proper mix ratio is 6 parts coal-gas to 5 parts air
  at the engine intake. This calls for the coal-gas opening in the air
  intake passages to be 20% larger in area (10% or so larger in diameter
  if applicable) than the air passage itself.

* For the engine part, we have 321 BTUs per cubic foot of CO, which
  comes out to 58 BTUs per cubic foot of total air-fuel mix. The rating
  for hydrocarbons increases with molecular weight, but the BTUs per
  pound are all pretty close to 20000. (This is ~ 120000 BTU/gallon of
  liquid gasoline). Using hexane, we get a lower heating value of 4414
  BTU for a cubic foot of fuel vapor plus the 45.2 cubic feet of air
  required to burn it, or 95.5 BTU/ft^3. For the same intake manifold area,
  we get 60% of the power that we would get on gasoline.

* The density of carbon is given as 2500 kg/m^2 or 2.5 kg/L which is
  20.8 lb/gal, about 3.5 times the density of gasoline. One gallon of
  pure compacted carbon would yield 211000 BTUs for propulsion (300K BTUs
  total). Even given impurities and air spaces between the chunks of
  coal, a coal burner need be no larger than the gasoline tank that it
  would replace. The mass would be 3.5 times higher, of course. This
  is about the same as taking on two or three extra passengers.

    I priced coal last year. I forgot the raw cost but remember it coming
out to about 80 cents per gallon-equivalent. This is for getting *all*
the BTUs. With only the coal-gas energy recovered it comes out to around
$1.14/gal-Eq.

    The best price for charcoal that I've found was for 20 lb bags at
K-mart, at around 23 cents a pound. This is $1.91/galEq for all the
energy, and $2.72/galEq for just the coal-gas portion. Sam's Club might
have it cheaper; I'll have to check. At any rate, those 20 lb bags of
charcoal took up considerably more than a gallon of space.

    Wood is, of course, free for the taking, given a remote enough area.
Again, I don't know what the numbers are for wood, though I did find
a web site that claims that an engine would have 85% of its gasoline-
fuelled power. One of the things I wanted from the Mother Earth manual
was a figure for how much of different types of wood made up a gallon-
equivalent.


   (Trivia note: Woodgas generators make a brief appearance in the
1974 sci-fi movie _Planet Earth_.)

24 responses total.

Trees nowhere are "free for the taking". All trees are owned, and
many trees are in protected preserves. 

A lot of wood is sent to the dump.  Drew, how do you plan to deal with the
pollutants generated by your process?  Would it not make more sense to gasify
the coal in some stationary plant where the result can be purified?

The wood better be sent to processing, not to the dump. Many of these
"alternative" processes become uneconomical because of transportation
costs. It is generally true that a manufacturing process *dilutes*
a resource. For example, concentrated iron ores and other ingredients
are used to make steel in bulk, which is then *diluted* be being
used to make a lot of small appliances that are spread all of the
nation (world). Pulling them back together to obtain bulk steel
again is expensive. (This can also be expressed by noting that 
civilization is driven by increasing entropy, and it is expensive to
decrease entropy.)

Re #1:  Fallen wood is free for the taking on much public land.
However, the fuel-cost of retrieving the "free" fuel must be taken
into account.

Re #0:  I've read that power from an engine running on wood or coal gas
can be as little as 50% of the power available when running on gasoline.
Your figure showing > 50% of the net inlet volume would be used by the
fuel gas backs this up.  You'd probably need changes in spark timing to
get the most out of the fuel; for one thing, a gas mix with so much inert
gas is going to burn more slowly and work best with more spark advance.

You're not going to get a pressure bump.  You've got to have a pressure
drop through the system or you get no airflow.

Wood decomposes by destructive distillation.  I have no figures handy,
but the gas mix is going to be a lot more complex than what you get by
incomplete combustion of charcoal.  The general composition of carbohydrates
(including cellulose) is (CH2O)n; if some of it breaks down to CO + H2
you'll have a richer fuel than you'd get from charcoal.  The excess heat
you noted from 2C + O2 -> 2 CO should be more than enough to do this.

Keeping the gas generator clean is going to be a huge problem.  If you
are using coal or wood, you are going to generate a large amount of
highly toxic tars.  Coal tar is nasty crap, you don't want to mess with it.

Doing this in a fuel-injected vehicle is another issue.  You've got a
computer which controls the fuel injectors and spark; it would have to
be re-calibrated to do the spark for producer gas and you'd need some
sort of modification to shut off the fuel injectors.  The mechanics of
this vary quite a bit depending on the design of the system.

If your car has a mass-air (as opposed to speed-density) system, you've
got a possibility for going halfway.  If you can admit a fuel gas/air
mixture into the manifold through e.g. a manifold vacuum port, you would
admit less air through the throttle plate and reduce the airflow measured
at the sensor.  This would automagically cut back the gasoline flow.  You'd
also have a reduction in the fuel-gas flow when you hit the throttle,
switching you over to gasoline for acceleration.  This appears desirable.

I get the feeling that this would be much better suited for a tree-service
work truck than a personal vehicle.  You could run on sawdust, which is
certainly "free" at that point.

My take on this is that you'd have a lot of work to do to solve some of
the problems relating to particulates, tars and condensible gases in the
mix.  Unless you want to handle a lot of toxic goo (and maybe have to
dispose of it as hazmat) you are going to have to engineer something
which can recycle it internally and is self-cleaning.  Good luck; you'll
need it.

The Germans tried this during WWII.  One of the major problems (other than
having to carry all that wood around to fuel your car -- consider the size
of a steam locomotive tender) was that tars and other byproducts tended to
gum up the inside of the engine, giving a short life between rebuilds.  It
was a very 'dirty' motor fuel.

Incidentally, materials used to clean cyanide and other impurities out of
coal gas at coal gas plants are now creating a major clean-up problem. 
They're highly toxic and corrosive because of what they absorbed.

The cars I have to work with are (1) an old station wagon with a normal
carbeurator system, and (2) a _Grand Am_ with individual fuel injectors for
each of four cylinders (I heard this called "throttle body", but was later
informed that that was the wrong term.)

I had deemed the smaller car unsuitable because the air intake ducting was
all plastic, which I supposed would be prone to melting in spite of cooling
the exhaust gases. I'm not sure that there is a vacuum port anywhere past the
plastic that's big enough to carry enough fuelgas-air mix.

The station wagon seems suitable (might as well; it's becoming effectively
useless due to fuel costs anyway) as at least the air cleaner housing is
metal, and it's a normal carbeurator system. I'd need a valve in the fuel
line, preferably one that can be worked remotely. As for the spark timing
issue, there should be no more inert gas in the system than there would be
with gasoline; and certainly no more than if it were somehow possible to burn
the wood or coal directly inside the cylinder. (Half of the allotment goes
through the gasogen, the other half goes into the engine's air intake.)

I have an idea for cleaning the fuel-gas; not sure just how it will work. It
involves liquid filtering. The gas would go through a run of pipe with
radiator fins to cool it as much as possible, then would be bubbled through
one or more sealed 5 gallon buckets of water. What remains should be stopped
by the air filter, which might have to be changed (or cleaned) more often.

Re #6:  All gasoline fuel-injection systems have a throttle body.  If there
is one central injector at the throttle body, it is called "throttle-body
injection".  If there are separate fuel injectors at each cylinder,
then it is "multipoint fuel injection".  Your Grand Am has the latter.

(Multi-point FI has a relatively short distance between the fuel
injector and cylinder, and eliminates a lot of issues relating to
fuel-transport delays down the manifold walls and sudden fuel vapor
condensation/evaporation on tip in/tip out events.  It's more
expensive than TBI, but vastly superior.)

My impression of the Grand Am is that its intake manifold was
aluminum.  You've got a plastic air cleaner and rubber duct from
that to the throttle body (and a mass-air meter between? look for
a sensor with wires in that air path), but from the throttle body
on it looked like metal to me.  You don't necessarily need a really
big opening into the manifold; the brake-booster port might be
sufficient to offset a lot of airflow.  You'd want to separately
carburete a fuel gas/air mixture and run it through the port,

Remember, most of these easy schemes only work if it's a mass-air
system; if the engine uses a speed-density system (calculating manifold air
density by v=RT/P and using that and engine speed to estimate airflow)
you will not have any automatic offset for the fuel gas/air mix you 
admit through the alternate pathway.  The system will inject gasoline
as if the entire manifold gas mix was air; you'll go way rich, pollute
like mad and save nothing.  This isn't in line with your goals.  (This
would work just fine on the carbureted car; a carburetor is just a
crude mass-air meter with integral fuel injector.)

You shouldn't have a problem with hot gases melting your manifold,
for two reasons:  one, you've got a long run of pipe from the back
end of the car to the engine, and two, you need to pre-chill that
gas anyway in order to get decent air density and condense the tars.

The idea of a car breathing through a bong is just too much.... but
if you don't aggressively cool the water you'll just wind up with
steam instead of fuel.  Steam burns no better than nitrogen.

>As for the spark timing issue, there should be no more inert gas in the
>system than there would be with gasoline....

Not so.  On a per-volume basis, you've got about half as much oxygen
with the gasogene product/air mix as you do with gasoline/air.  The
CO takes up a lot more volume than hydrocarbons do, displacing air
and reducing the total BTU value of a fuel/air charge.  You're adding
nitrogen along with the CO, so the inert fraction goes up too.

The issue of pollution controls also rears its ugly head.  You probably
have an EGR system to control NOx, but on a CO/N2 fuel mix you'd almost
certainly have no need for it.  No idea what this would do to performance
or efficiency at part throttle (you want gasoline for full-throttle
operation).

I think your best bet is probably to trick out the car for maximum
aerodynamic efficiency and drive with a feather foot.  If you decide
to play with this on either car, I'd treat it as a hobby and not as
a serious cost-reduction program.

My grandfather reportedly had such a delivery vehicle for his bicycle business
in Germany during WWII.  I saw one on display in the Museum of Science and
Technology in Munich when I was there 15 years ago.  It looked more like a
small locomotive than it did a car.

Your water-cleaning scheme sounds highly restrictive.  This will tend to 
greatly reduce the power available, and will make you run very rich if 
you don't bypass it when running on gasoline.

I would try this on a carburated car.  Doing it on a fuel-injected car 
would greatly complicate it, and there are enough issues to work out 
already.  I'd also try it on a car that isn't worth overly much, so that 
if you damage the engine somehow with this scheme you won't be out much 
money.

Oh, and I'd use wood for this.  Don't mess with doing it with coal.  
Among the byproducts of generating coal gas are sulfuric acid and 
cyanide.  These aren't things you want in air you or your engine are 
breathing.

Byproducts of generating wood gas are methanol, formaldehyde, acetone,
acetic acid, acrolein... and many other nasties. Ever tried to breath
immersed in wood smoke?

From the BBC, here's an article about a car that runs on a gas produced 
by fermenting vegetable matter: 
http://news.bbc.co.uk/hi/english/sci/tech/newsid_1309000/1309201.stm

Apparently it takes 220 pounds of rubbish to produce enough to power 
the car for 60 miles, though, so this doesn't seem like something 
that'll we widely useful.  City sanitation departments might be able to 
reduce their fuel costs, though...

(Heck, many landfills already have vents to release methane gas.  It's 
just allowed to vent into the atmosphere, currently, except when 
vandals light it on fire.  Why not capture it and use it as a fuel gas?)

That's done in some places. However if the value of the product over
time does not exceed the depreciation of the capital investment and
operating costs over time - it isn't a good deal. The is usually the
case. 

There is a greenhouse in Ypsilanti powered by methane gas from the local dump.
Most of the workers there are deaf.  A very admirable business overall,
assuming they are still in business.  We knew a Hungarian student doing
practical training there, who would bring us their gourmet salad vegetables
and herbs, which sold well in local stores.
By powered, I mean heated when the sun is not available.  The crops were grown
hydroponically all winter.  The workers seemed rather content and were
carrying on lots of interesting conversations that I could not understand.
Not a bad place to be on a drear day in January.

Re #12:  I've long advocated the use of digesters to remove the
biodegradable components of trash before landfilling it.  It looks
like someone's found a way to sell the idea.  Good for them.

Re #14:  If you couldn't understand the conversations, how do you
know if they were interesting or not? ;-)

I *like* the concept of using landfill gas as heating fuel for
greenhouses.  I would like it even more if the "furnace" was an
engine which co-generated electricity.  If I had any kind of head
for business, I would think about trying to run with that idea.

My brother just sent me a little tid-bit about a sports car that runs on
rotting gabbage.  0 to 60 in under nder 6 seconds.  Interesting...  I'l

The gas from landfills (and from rotting garbage) has lots of carbon
dioxide in it, as well as methane. It burns, but not as well as
purer methane. The CO2 can be scrubbed out, but that adds to cost.

While looking for something else, I stumbled across a table of
compositions for various fuels.  Here's what it's got for a
selection of likely things:

%Vol    H2      N2      O2      CH4     CO      CO2     C2H4    C6H6

Blast furnace gas
        1.0     60.0    --      --      27.5    11.5    --      --

Blue water gas
        47.3    8.3     0.7     1.3     37.0    5.4     --      --

Carbureted water gas
        40.5    2.9     0.5     10.2    34.0    3.0     6.1     2.8

Coal gas
        54.5    5.5     0.2     24.2    10.9    3.0     1.5     1.3

Coke-oven gas
        46.5    8.1     0.8     32.1    6.3     2.2     3.5     0.5

Producer gas
        14.0    50.9    0.6     3.0     27.0    4.5     --      --

It looks like coal gas is made by destructive distillation of coal;
it's much closer to the composition of coke-oven gas than anything
else.  The output of a gasifier would probably be much closer to
producer gas, of which about 56% is non-fuel.  Producer gas would
displace a lot of air in the intake(1), leading to a lot less energy
per volume of charge(2) and low engine torque.

(1)     A molecule of octane, C8H18, requires 12.5 molecules of
        oxygen for stoichiometric combustion.  A stoichiometric 
mixture of octane and air would thus be about 1.6% fuel, balance
air.  A volume of producer gas requires about (14%/2 + 3% * 2 +
27% / 2) = 26.5% its volume of oxygen to burn, or 1.26 volumes of
air.  The total fuel-air mix would be about 44% fuel gas and 56%
air, compared to 98.4% air for octane.

(2)     Density of air @ 77 F and 14.7 PSIA = 0.0740 lbm/ft^3.  At an
        air/fuel ratio of 15.093:1 and 20770 BTU/lbm of octane, the
air/octane mixture would have an energy of 100 BTU/ft^3.  The producer
gas mixture contains three combustible species:  H2, CH4 and CO.  These
have a heat of combustion of 320 BTU/ft^3, 958 BTU/ft^3 and 310 BTU/ft^3
respectively.  Multiplying these figures by their total volume in a
44% gas/56% air mixture, the total combustion energy of the mixture
is 69 BTU/ft^3.  In practice the density differences caused by the
evaporative cooling of gasoline vs. the heat from the gas generator
would increase the difference further.

Austin Energy is receiving electricity now, or will be soon, from landfill
biogas projects. This is part of the renewable "GreenChoice" program,
combining wind, solar, and biogas sources. There is a simplistic description
here:
http://www.austinenergy.com/greenchoice/biogas.htm
The utility has contracted for 20MW from landfill methane projects, the last
figure I read.

Re #18:
    I don't see a heading for water vapor in that table. Certainly producer
gas has *some*, even with dry wood?

    And what sort of wood are these figures for? Or is it an average?

Gas compositions are always reported on a "bone dry" (!?) basis. Water
vapor continually varies depending upon temperature and pressure
and other system conditions. Certainly most formed in any one of
those processes condenses out soon after. 

There's no heading in the table for water vapor.  (I'll bet that
the raw material for producer gas is coal, not wood.)

That said, water is probably not included for several reasons.
My guesses are:

1.)     It's one of the inputs for several of the processes, and
        the amount of vapor in the product gas depends on the amount
        of excess reactant.

2.)     It's condensible (the only other potentially condensible
        compound in the table is benzene), so the amount of water
        in the final product is likely to be determined by the
        temperature; below a certain temperature the relative
        humidity will always be 100%.

That said, which says much that was said in #21, it is still a
*convention* to omit water from general gas compositions, although it will
be included in a chemical process calculations. 

Re #23:  I wrote #22 off-line, after I'd downloaded #20 and before
I'd seen #21.  That's my usual modus operandi.

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