I did a fair amount of research on gas generator engines for my Morrow Project campaign. They're very useful post-apocalyptic devices, but have some drawbacks, especially for tactical or armored vehicles.
Charcoal is preferred - wood chunks and chips can be used, but are less efficient, make much more tar, smoke and steam, and must be less than 20% moisture content (which means no green wood should be used). Twigs, sticks and bark aren't good, they tend to jam up the hearth; and in fact charcoal is preferably chopped to specific size pellets. A few places might produce biomass briquettes, mostly for non-military uses. Coal can be used, but the mines may not be in operation. High-quality coal is about the same fuel characteristics as good charcoal; low quality coal is about like regular ol' wood.
Starting time is usually at least 10 minutes, and the first 5 minutes of startup are sort of involved, with the operator fiddling with the machinery; and the gasifier continues to operate for another 20 minutes after stopping. You can restart pretty fast if you've only stopped for less than 2 hours. There's a real danger from the large amounts of carbon monoxide produced.
The Imbert-style generator for a military truck is usually a galvanized steel garbage can, or a section of steel culvert, mounted atop a 55 gallon drum (the gasifier unit); the can and drum have to be kept sealed, but are opened to refuel (releasing hot, toxic smoke). The gas generator needs its own precipitating tank (gas bubbling through water) and a cooling radiator (pretty much the same kind of radiator that the vehicle uses for engine cooling).
Diesel engines can be converted, but either need to input a small amount of diesel fuel with each stroke, or (more commonly) replace their glow plugs with spark plugs, and adjust timing, spark etc. like a gasoline engine. Cylinder heads can be reshaped for greater efficiency. Multifuel engines are of course easier to convert.
Energy content: 1 liter of gasoline (0.75 kg) =1.25 kg of charcoal = 2 kg of oven-dried wood or biomass briquets = 2.5 kg 20% moisture wood. This all presumes you have a reasonably efficient gasifier. Other fuels might include corn cobs, nuts, straw, peat, walnut shells, coffee grounds ... Here's a list of possible fuels and their energy content:
http://physics.info/energy-chemical/
The density of charcoal is 208 kilograms per cubic meter. Denser fuel is better, since it reduces the size of your fuel bin, and also means you don't have to stop and refill the gasifier as often.
Transport:
- 200 liter (55 gallon) drum can hold about 42 kg of charcoal ... energy equivalent of 21 liters of gasoline
- 120 liter (32 gallon) trash can holds about 25 kg of charcoal ... energy equivalent to 12.5 liters of gasoline. An empty trash can of this size weighs 7 kg including lid.
Hauling along a wood chipper would make a "traveling convoy" much more self-sufficient.
http://2.bp.blogspot.com/-bmD_6VmcTq...2BGasifier.jpg
Issues for military vehicles: large, bulky size per horsepower; the gasifier itself gets very hot, and is a lot of the "extra" bulk -- so it should be outside the armor, which makes it vulnerable to damage. If the gasifier and the actual engine are at different ends of the vehicle, some rather vulnerable (and hot) plumbing is needed to carry the gas between the ends. When you run out of fuel, you have to wait at least 10 minutes before adding another batch of fuel. Continuous-feed systems are possible, but much more complicated than the basic "open the lid, throw in another batch of fuel" system.
This page talks about some of the issues on power reduction, RPMs, etc.
http://woodgas.nl/GB/woodgasification.html
Here are some pages with pics and info:
http://www.gekgasifier.com/info/intro
http://www.build-a-gasifier.com/Gas-Producer-Cars.html
http://www.ush2.com/978-1-60322-027-9_detail_page.htm
- huh, that one has a gas-generator motorcycle, hadn't seen that before.
http://en.wikipedia.org/wiki/File:Wo...pa_tractor.jpg
http://en.wikipedia.org/wiki/File:99woodgas.jpg
- you don't have to have the gasifier on the same vehicle even. This would work pretty well for converting a diesel locomotive.
http://www.build-a-gasifier.com/Gas-Producer-Cars.html
- info on WW2 German gasifier Volkswagens
http://www.panoramio.com/photo/90117364
http://jimayson.wordpress.com/2008/0...y-were-smokin/
http://www.lowtechmagazine.com/2010/...-gas-cars.html
http://www.shutterstock.com/pic-6294...e-borg-on.html
http://www.robertsarmory.com/gas.htm
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Michael B