to: fanglers@xephic.dynip.com
subject: alternative fuels I

 Tom Leone was kind enough to send me a copy of "Gas Producers For 
Motor Vehicles: A Historical Review" done by the government of New 
Zealand.  It outlines the basic design and use of gas "producers" for 
use for motor vehicles.

 The gas producer is instantly familiar to anyone who has ever done 
any metal casting - it's a ringer for Dave Gingery's charcoal furnace 
in his metalcasting book, or any solid fuel burning furnace, for that 
matter.  Rather than heating a payload of metal, the produced gas is 
bled off as motor fuel.

 The critical factors for thorough combustion of most fuels are time 
and heat.  The solid fuel bed allows both; temperatures for gas 
producers run 900 to 1000C, though a little tweaking would easily 
allow them to melt iron.

 How can you do this by burning animal dung, charcoal, or firewood?  
The trick is the use of heat to partly burn the fuel in a "reducing", 
or low-air, environment.  The rich combustion short-circuits a number 
of potential reactions and leaves you with mostly carbon monoxide, 
CO.  Robert Harris had lent me his copy of Glassman's "Combustion" 
recently; the chemical reactions outlined in the report matched what 
Glassman had stated.

 The basic reactions are:

       C + O2         -> CO2   =  +97   Kcal
       C + 1/2 O2     -> CO    =  +29   Kcal
       CO + 1/2 O2    -> CO2   =  +68   Kcal
       1/2 CO + 1/2 C -> CO    =  -19.5 Kcal
       CO             -> 1/2 C =  +19.5 Kcal
 
 CO is a very nice fuel.  We normally see it as an end product in 
ordinary gasoline combustion because a stoichiometric gasoline/air 
mixture doesn't burn hot enough during most of the cycle to react much 
of the CO produced.  When the temperature drops below 500C or so (I 
don't remember exactly) the CO reactions "freeze" and combustion 
stops.

 If your CO percentage is high enough - as in what is made by the gas 
producer - you can burn the CO directly and bypass all the 
intermediate reactions.  It's a fairly decent motor fuel, resistant 
to knock, with all the advantages of a gaseous fuel.  On the flip 
side, combustion temperatures are high, which can cause problems in 
some engines.

 You can introduce water or steam into the firebox of the gas 
producer.  

 Now for more magic:

       H2O + C  -> CO + H2   = -31.2 Kcal  (1000 C)
       2H2O + C -> CO2 + 2H2 = -21.4 Kcal  (500-600 C)
       H2O + CO -> CO2 + H2  = +9.8  Kcal

 There are some other reactions here, some of them reversible, but 
the upshot is "something for nothing" - the temperatures are high 
enough to dissociate water into hydrogen and oxygen.  They're 
endothermic reactions, which means the dissociation takes more energy 
than you can recover by recombining them... but remember, we're 
talking two-stage combustion here - we're burning plenty of cheap 
fuel to *make* fuel to feed a separate combustor, in this case a car 
engine.

 What's the deal with hydrogen?  Hydrogen, basically, can be 
considered as a combustion accelerator.  Hydrazine is a good example 
of a compound with lots of easily-available hydrogen - a dash added 
to a slow-burning fuel like nitromethane will perk it right up.  
Fuels with some amount of available hydrogen burn very well; hydrogen 
exchange is the key to a whole group of potential chemical reactions.

 Depending on the fuel used to charge the gas producer you can get 
some other resultants, like methane, some free H2, or even ammonia.
(Yes, Virginia, you can burn ammonia.  It's loaded with hydrogen and 
therefore is of very low octane, but as an additive it works much 
like hydrazine as a combustion accelerant - something slow-burning 
fuels like methane or CNG can benefit from)

 Okay, all this stuff sounds great.  What's the catch?

 Remember all the weird plumbing festooning some of the vehicles in 
"The Road Warrior," or Cabbie's taxi in "Escape From New York?"  
Well, now we know what all that ironmongery was supposed to be, or at 
least represent.  Making producer gas isn't all that difficult, but 
it requires a lot of *stuff*. 

 To start with you need the "producer", which is a solid fuel 
furnace.  The size of the producer depends on how much gaseous fuel 
it's supposed to make.  Figure anything from a trash can to an oil 
drum in size.  It has to have a blower to add air.

 After the gas is produced, it goes through a cooler, like an 
intercooler.  This is usually just a bunch of pipe.

 Next, depending on the type of fuel used, the gas has to be 
filtered.  Some fuels leave abrasive ash as they burn, which is 
entrained by the air flow through the fuel bed.  Fiber or centrifugal 
filters or both are used to remove as much crap as possible; figure 
something wastebasket-sized at least.

 The very last step is the admission of the producer gas into the air 
stream of the driving engine.  The NZ report showed a primitive air-
valve type carburetor, though a modern demand valve arrangement would 
probably work fine. 

 The output of producer gas is, fortunately, largely dependent on 
draw by the car's engine.  Rev the engine up, it pulls more gas from 
the producer, which admits more air, etc.  There's likely a fair 
amount of lag in the gas production process, but given the use of 
these systems for a full century now, it seems to be manageable.

 The producer is a solid fuel furnace.  When the fuel is exhausted, 
you have to scrape out the clinkers and recharge it, just like a wood 
burning stove.  The filter(s) must be cleaned regularly.  You have to 
build up a fire before you can go anywhere - a fire very much like 
the one in the charcoal grill you'd use to grill hamburgers.  
Building up steam in a steam engine would be very fast in comparison, 
and a lot less maintenance too.  Not to mention you have to find some 
place to dump hot clinkers when you recharge the producer.  And once 
you stop you have to shut the thing down somehow.  It's not really 
practical for a 2AM burrito run, but for vehicles which run all day 
it works well enough.

 You also have to have room for all this stuff.  You can strap the 
bits all over a car or tractor, or hang them off the back of a bus, 
or even package them relatively conveniently in the back of a pickup 
truck, but it's still bulky.

 The producers will let you run your car on anything that will burn, 
just like the steam engine guys brag about, but they're a hassle.  
They're only practical when gasoline or Diesel are too expensive to 
afford or not available at all.

 Okay, that wraps up Part I.  Part II coming up...