In the current campaign I'm running, most internal combustion engines are gas generator-powered. Some communities use alcohol, or biodiesel, or even petrochemicals in a few areas around oil wells. We gathered up some info on the motoring effects.
Gas Generator Notes
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 can be used). Twigs, sticks and bark aren't good, they tend to jam up the hearth; and in fact the charcoal is preferably chopped to specific size pellets. A few places have produced biomass briquettes, mostly for non-military uses. Starting time is usually at least 10 minutes, and the first 5 minutes of startup require a fair amount of user attention; 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 generator is usually mounted in the open. The Imbert-style generator is typically a galvanized steel garbage can, 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 and a cooling radiator.
Diesel engines can be converted to use a gas generator, 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.
- 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
- charcoal is 208 kilograms per cubic meter
- a 200 liter (55 gallon) drum can hold about 42 kg of charcoal ... energy equivalent of 21 liters of gasoline
- a 120 liter (32 gallon) trash can holds about 25 kg of charcoal ... energy equivalent to 12.5 liters of gasoline
- an empty 32 gallon trash can with lid weighs 7 kg
Ethanol and Methanol Notes
Consumption of alcohol, compared to gasoline is 2.2:1, so the distance you can travel with the same gas tank is less than half. Methanol is very corrosive, unlike ethanol.