I recall a demonstration in 5th or 6th grade. Wood was heated in a closed container; gas was emitted through a tube, and it was flammable. Not surprising, as a normal wood fire works by heating wood and having the emitted gases burn. Note that solids cannot burn; only gasses can burn. A wood (or any combustible solid) fire is really the combustion of the gasses that are emitted when wood (or other solid) is heated. Thus, you can heat it in a closed container, and burn the gas elsewhere – as in an engine; you are merely separating the gassification from the combustion. By the way, there is another name for that gas that is emitted: smoke.
(Actually, it is a mixture of gasses – possibly including methane – and some finely-divided solids plus substances that are liquid at room temprature. I was told that you can precipitate the liquid components; you get creosote. There may be alcohols and oils – e.g. turpentine, in the case of pine. One respondent suggested there is hydrogen in there; I’m not sure that that would be the case; seems unlikely, but i’m not qualified to say definitively.)
Related topic is coal gas, which one gets by heating coal the same way:
I see them every year when I go to North Korea. Photos here:
They are retrofitted to older trucks and are seen more frequently on the east coast of North Korea.
My wife, Taimi, was a child in Finland during World War II. She remembers wood-powered vehicles well. Her Uncle Jani (“Yanni”), a farmer, no mechanical genius, rigged up his farm truck to run on wood chips. She remembers buses having power limitations, so passengers would get out and push on the hills.
Bob
This is a process called pyrolysis and involves the partial oxidation (burning) of the wood chips. Because the process occurs with an insufficient amount of air actually burn the wood, the pyrolysis of the wood produces a gaseous product that contains CO and partially oxidized organic compounds. This gas if fed to the engine where it finishes the combustion in the cylinders. A very inefficient and dirty process, but practical when there is no fossil fuels available.
A Dutch ‘leading adventurer’ recently traveled trough Eastern Europe in a wooden car powered by wood. Check out this TED-video, nice shots of the car at the 12:00 minute mark.
here’s the link http://www.youtube.com/watch?v=f8FisM59BfQ
Find it hard to believe you two MIT grads did not know about these cars and trucks running on wood as fuel. I’ve seen many photo and films of “gasifiers” over the years.
Wood chips? Before natural gas was available, in England they used goal gas. Apparently one of the combustables in coal gas is carbon monoxide. It combines exothermically with oxygen
CO + 1/2 O2 = CO2 Delta H -238 Kcal/mole
Compare this with methane combustion of -802 Kcal/mole
So it wouldn’t work as good as methane, but it would still pack a kick enough to power a car I imagine.
Perhaps the wood chips were used the same way, roast 'em up in other words and collect the combustable gas. I think it might work in a pinch.
There’s a rather famous mystery short story – forget if it is Agatha Chrisie or AC Doyal – about a murder comitted with coal gas, the killer simply let the unburned gas into the bedroom, and the cause of death was carbon monoxide.
I swear that I have heard this clip several years ago on Car Talk. I remember many of the details. And then, I remember the subsequent week Geena Davis (I think!) called up and said that her father had had this contraption or something, and the guys at that point had received the correct answer, and imparted it at the same time as she called. I vaguely remember that this clip was even online for a while as a “best of” kind of thing. So, is this a recorded clip?
Hans is talking about could be a Holzbrenners.
A picture is here : http://www.shorey.net/Auto/German/VolksWagon/Beetle/1942%20VW%20Kommandeur-Wagen%20Holzbrenner%20Fossil%20Fuel%20Type%2082E%20f3q%20B&W.jpg
It could also be a Holzgas (wood gas), Holzgasvergaser, and Imbert (the inventor).
Basically, you load the cooker with wood chips (or charcoal, or even coal), light it on fire, deprive the fire of oxygen so the combustion is incomplete, and the incomplete combustion creates a gas which can be burned by the engine. Basically it’s a pressure cooker. The wood burns then goes through a cooler and a filter and gets piped back to the engine where’s there’s a special adapter for the carb. Oh, and you need a fan to keep the combustion going.
They set up special “Holzgas Fueling Stations” in Germany where they sold pre-cut wood chips (matchstick sized), and they told drivers on the Autobahn to take every exit and then get back on since the exits back then were paved with cobblestones and the vibration of the cobblestones would stir the ashes and keep the fire burning.
There you have it
Maybe not so efficient for running a car, but it works awesome for home heating up here in Maine. Check out this site http://hotandcold.tv/wood%20furnace.html for good info on the efficiency and concept as well as data on the output from the gasification process. These furnaces have been in use since the 70s and can increase the efficiency of a wood burning appliance by 40%
There is a wood burning truck on display in the Mercedes Benz Museum in Stuttgart, Germany. A MB truck was converted after WWII due to the severe shortage of fuel and the need for trucks for the post war era. The display described the process, but I can’t remember the details. So, Hans is right, there were such vehicles back then.
The gasification guys are right. In addition, I guess that part of the wood chips were burned conventionally to produce heat to the chamber where chips were placed for the actual gasification. This would all be consistent with the details Hans gave about the cleaning out the soot, etc. My question now is how did they feed the chips into the fire and the chamber? I would bet that it was done something like a firebox on a steam engine where coal is shoveled in by hand to replace that which had burned. But the same question applies to the gasification chamber. It sounds like it may have been big enough to get some miles out of a single batch of wood chips that would have to be cleaned out and reloaded when all the gas had been extracted from one batch and the truck would have to stop to be refilled. It sounds like pollution-wise it was a brush fire on wheels!
There was a show on Science Channel last year called ‘Stuck with Hackett’. He made a pretty decent wood gasifier, and used it to provide fuel for a rail car he built out of junk. Here is the link: http://science.discovery.com/videos/stuck-with-hackett-jet-train/
I don’t want to read about German “inventiveness” during WWII. Too clever for their own good and got what they deserved.
As so many others have pointed out, one runs an automobile on wood via “wood gasification”. After hearing your lame pathetic attempt to answer the question on your show, I am glad I decided to attend Harvey Mudd and not MIT.
I doubt that the front-line Germans created anything a sophisticated as a plant that would extract flammable gasses from wood chips. They just burned the chips.
I think it was like the old science-teacher trick of starting a fire in a milk bottle and putting a hard-boiled egg on the opening. As the fire removed the oxygen, the egg got sucked into the bottle.
Hans said they were fleeing the Russians, which meant they had to come up with something FAST. He also mentioned a flap that would pop open periodically. I think they “Jerry-rigged” a drum to the exhaust pipe, filled it with wood chips, started the chips on fire and sealed it as best they could. The suction on the exhaust pipe then turned the engine by creating a partial vacuum that pulled up on the piston of whichever cylinder had the exhaust valve open. When the oxygen was diminished and the fire in the drum started going out, the amount of suction would decrease which allowed the flap to open, allowing a fresh blast of air to fill the drum and rekindle the fire. They needed wood chips rather than sawdust or logs because they needed good kindling that would ignite and burn fast.
Nope, it’s a very old technology, pre WWII, and it involves using combustion to heat the wood chips to create and extract flammable gasses, not just burning the wood chips.
In more detail (from somebody who works on the design of coal gasifiers):
“The simplest gasifier is basically one vertical tank full of wood chips. The bottom layer is ignited and continuously fed air (or O2 in an industrial setting for purer syn-gas). The O2 is restricted to maximize CO and H2 concentration. You can continuously add wood to the top of the bed and remove ash from the bottom of the bed. The heat rising through the bed dries then partially oxidizes the slowly descending wood bed. There is a narrow layer where the actual gasification takes place. The gas also contains significant methane and methanol.”
I think this is the actual truck Hans was referring to… Opal Blitz with Oval tank and Imbert burning gas unit!!