About Wood Gas
"Wood Gas" is the term used to refer to the collective combustible gasses released from wood when burned in a low-oxygen atmosphere. Most commonly the fuel in use is wood, but other substances can be used, such as corn cobs, coal, cow manure, peach-pits, and other well-dried biomasses.
Instead of burning hot and bright like a campfire, the fuel in the gasifier is choked and may be better equated to smoldering than burning. The lack of oxygen and slow burn rate encourages the fuel to release gasses like Hydrogen, Methane, and Carbon Monoxide in the smoke. The woodsmoke is pulled by the natural vaccuum of the truck's engine through a condenser, which also filters and cools the gasses before they reach the engine.
Gasifier Types
There are four main types of Gasifiers:
-Downdraft or Imbert
-Updraft
-Fluidized bed
-Cross Draft
There have been many variations on these designs, some with very surprising results. The main reason for these gasifier modifications is the need for optimal results with a particular fuel or gas requirement.
For internal combustion use, the Imbert gasifier is ideal, as it produces the least amount of tar and particulates. The operation of the Imbert will be described in detail here, although other gasifier types work on similar principles.
Efficiency
Efficiency:
A well designed and fueled gasifier will have efficiencies ranging from 40-80%, which is a good value, but this percentage only factors "energy-in versus energy-out" of the gasifier itself. The device which combusts the syngas for its end use has its own efficiency, and combining this efficiency with that of the gasifier results in a lower overall efficiency number. Evaluating the energy-in versus energy-out of your total system is very important, especially when searching for areas in need of improvement. A common technique to improve efficiency is cogeneration (CHP, or "combined heat and power"). Cogeneration is the reclamation of what would otherwise be wasted heat, taking the excess heat from one or more of the following components: the gasifier itself, cooling components, the internal combustion engine, the gas turbine, or the electric generator. This reclaimed thermal energy can then be used to dry the fuel, for space heating, or even for cooling and refrigeration.
Casey's Woodgas Truck
Over one year ago, I began my first woodgas project, the Mazda truck that ran on gasified wood chunks. I spent thousands of hours on this project and learned a lot about wood gas and different types of gasifiers. We built two separate experimental cooling systems for the gasifier and drove over 90 miles on wood gas.
I'm actually planning another experimental vehicle as a future project. Now that I am a little wiser on the subject, I am looking for a vehicle that has easily adjustable ignition timing and I will design a simpified gasifier that can be easily modified. Along with it, I would like to implement a more basic, lighter weight, and convection-style cooler /condenser.
The engine itself runs on the gasses produced in a greatly choked fire. The flammable gasses are Hydrogen, Methane and Carbon Monoxide. To get a suitable amount of these gasses requires specific conditions in the combustion chamber.
The basic premise of using woodgas in automobiles is well known and was most popular during World War II, when petroleum fuel shortage was always a concern. There are many different designs for gasification systems, however, and if you are considering modifying your own vehicle, you will possibly have to pay someone for his or her plans.
My design is a modification of other plans I had found, and almost the entire system is made from recycled or salvaged materials. The only byproducts of woodgas are water, soot, and creosote, which are the same as using a woodstove in your home. Also, the carbon released in the burning process is the same amount the wood would naturally release as it decomposed, meaning woodgas fuel is nearly carbon neutral as far as atmospheric pollution is concerned. And let's not forget, you can always grow more trees, whereas oil takes millions of years and conditions that are just right.