Carbon monoxide (CO) is indeed a highly combustible gas. It is an excellent fuel that was once used in heating and lighting of homes but was of course highly dangerous because of its toxicity. Methane or propane are the only kind of gases used for this purpose today.
CO is formed by the partial combustion of a hydrocarbon with insufficient oxygen. If you have a furnace or water heater that needs maintenance it can easily produce large quantities of highly poisonous carbon monoxide. Complete combustion produces CO2 which is not combustible, which is not toxic but can displace oxygen in tight confined areas like a grain silo. In that case the CO2 is generated by bacterial decomposition.
The principle of the wood-gas generator is to restrict the availability of oxygen for the bed of coals inside the kettle and then draw air through the coals. That hot gas will be rich in CO. It is then cooled and sent to a special carburetor where the gas is mixed with air and fed to the engine cylinders.
It is extremely easy to construct a wood-gas generator, also called a producer-gas generator, or in German: Holzgas. The only disadvantage is that you have to keep a fire going in the generator and when you are done driving you cannot pull the car or truck into a garage because the generator will still be producing gas until the fire is cold.
Every licensed driver had to be made aware of cautions in dealing with Holzgas powered equipment. The German Army had about 12 percent of it vehicles operating on Holzgas as early as 1937, but of course liquid fuels like diesel and gasoline are much more convenient for tactical use. So mainly support vehicles and civilian transports used Holzgas during the war until the fuel situation became a crisis in 1944 and even tanks were using them. Hundreds of thousands of these Holzgas generators were made during the war and they can power both diesel and gasoline engines with the proper simple adaptations. A diesel engine with a Holzgas adaptation gets a lot better diesel mileage because some of the fuel is delivered by the CO entering the intake along with air through a special carburetor added to the engine. A gasoline motor can run entirely on gaseous fuel (namely CO) because a spark plug provides the ignition source, whereas the diesel uses an oil injector.
A conventional diesel engine provides more complete than a gasoline engine because of its design. A diesel must swallow excess air to compress to generate the heat for the ignition of the oil injected into the cylinder. A Holzgas modification would have some CO added to the intake air which would be heated by high compression inside the cylinder and then when the diesel oil was injected the mixtures inside would explode. So a diesel with Holzgas might only use as much fuel as though it were idling instead of hauling freight because the Holzgas would add gaseous fuel in the form of carbon monoxide.
A conventional diesel engine has as much as 17 percent oxygen in the exhaust at normal operating speed without any load. Normal air is 21 percent oxygen. So a human could breathe pure diesel exhaust for some time before being overcome by heat, dehydration, and edema caused by the acrid nature of the exhaust and it high carbon particulate content.
In thousands of medical journals I have only found one case of a man who was killed by diesel exhaust, an 85 year old who was overcome not by carbon monoxide but by emphasema from the smoke. For a homicidal gaschamber this would be a fiasco because it would take too long. Experiments with live animals showed that under varying loads and less than ideal engine operation conditions many animals survived a five hour exposure of fumes so thick that they cause pain to human eye.
These scientific papers (Holtz) from 1941 and (Pattle) 1957 are online and completely refute the diesel story. I have a lot more data, including colored charts of gas compositions under various loads to make the science more straightforward.
Btw, producer gas is primarily CO but it also contains some hydrogen. that is why in Germany you could fill a child’s balloon with town-gas and it would float. Nowadays that would be unthinkable because nontoxic and noncombustible helium is available. Hydrogen generated in such a way is called “water gas” because water molecules are disintegrated by the high heat in the generator coal bed, and if a small spray is fed into the firebox there will be a fair amount of hydrogen liberated. The hydrogen is of course combustible along with the CO. Hydrogen produced in this way is useful for various chemical processes, including the production of synthetic oil and gasoline, which involves the “hydrogenation” of carbon from coal to produce different hydrocarbon structures than the ones originally going into the process, including fertilizers, munitions and synthetic dyes. Coal, oil, gasoline, methane, etc. are all hydrocarbons. The German chemical industry has been called “an empire of coal, air, and water” and it was the best in the world. Auschwitz was a massive industrial operation.
To think that the Nazis used Rube Goldberg murder schemes when they were so technically skilled in any other matter speaks volumes about the veracity of the Holocaust stories that have been told and accepted without much skeptical thought.