With the possible exception of those who lived through the oil shortages of the early 1970s, we take the availability of petroleum fuels for granted. But it has not always been that way everywhere – especially if you lived outside the U.S. during World War II.
Going into the second world war, the U.S. supplied 80 percent of the world’s petroleum needs. Thus, although gasoline was rationed in this country during World War II, relatively speaking, it was still available. Elsewhere in the world, and especially across the pond, it was a different story.
At the beginning of World War II, after the U.S., Europe was probably the biggest petrol user as it had progressed toward increased mechanization. When Germany started World War II, that country had domestic fuel production for just 25 percent of their needs, and some of that was derived from coal.
Germans vexed by fuel shortages
Before the war started and in anticipation of their needs, the Germans started stockpiling petrol. As German leaders believed they would win the war in a few months, and in the process take over the Caucasus (and other) oil fields, they judged domestic fuel stockpiles to be adequate. As history shows, it was not that simple.
For one thing, the German military’s thirst for fuel was enormous. As an example, the big German Tiger tank consumed 3 gallons per mile (not miles per gallon) on the open road and 6 gallons per mile off-road. When Germany invaded Russia, the situation was compounded by very poor roads and the approach of winter weather.
Almost immediately, Germany began rationing fuel at home and confiscating fuel wherever their troops invaded. Civilian populations, especially those in occupied countries, were hard hit at the war’s outset. Occupied countries typically reserved their meager petrol supplies for first responders, physicians and other occupations where vehicle startup time and acceleration were most important. According to my father-in-law (a World War II veteran), toward the end of the war, German mechanized troops carried hoses to siphon fuel from any disabled vehicles they found.
A larger-than-life character leads the Danish resistance
At this point in the story, we switch to an on-the-ground expert, Dr. Harry LaFontaine, now deceased. I first met Harry in the late 1980s. To say that he was a colorful individual would be a vast understatement. One of his claims was that he handled the special effects scenes in the movie Thunderball.
According to Harry, he grew up in Denmark near the German border, where he became fluent in a German dialect. Partially as a result of that skill, at some point in World War II, he became a leader of the Danish resistance.
During that time, he claimed that the resistance got wind of a high-level German officer’s plan to meet in Denmark with the leader of German occupation forces there. The resistance intercepted the German staff car and captured the officer in it. It turned out that the German officer had about the same build as Harry. So, Harry put on the German uniform and drove to the German occupation headquarters in Denmark.
Unfortunately, I cannot embellish the story like Harry did, relating how he bluffed his way into the German occupation headquarters. Once inside the headquarters, and in control, he demanded to see a list of all informers who were working with the Germans. He took the list, looked it over, and informed the Germans that those listed were all double agents and should be rounded up and executed (I told you he was colorful).
Dropping back to early technology
When the Germans invaded Denmark, they took all the petrol supplies they could find, assuring the populace that the conservation period would be short-lived, because the war would be over in five months. Within days, however, the people of Denmark faced mass starvation. Harry was put on a committee chaired by famed physicist Niels Bohr to find a substitute fuel.
In a crisis, one often drops back to what he knows will work. In this case, Plan B happened to be small producer gas plants (gasifiers) that were used in the early 1900s to fuel internal combustion engines. Based on well-established science, producer gas plants were widely used before good liquid fuels became broadly available.
The decision was made to focus on gasifiers. As a cover for his underground nighttime resistance activities, during the day Harry operated a factory to produce gasifiers.
The science of the pegasus system
In operation, gasifiers heat solid organic materials rich in volatile gases (such as wood) to drive off the gases in them. These volatile gases are then piped to spark-ignition engines to fuel the engines. These systems are also sometimes referred to as petroleum/gasoline substitute systems (pegasus).
The principle used to produce fuel by producer gas plants can be shown with a burning match. As the match burns, the heat drives off volatile gases in the head and body of the match. These gases float upward before they ignite. Initially, the gases are too rich to ignite (leaving a gap between the match and the flame), but after rising into the air a little way, the gases mix with air and burst into flame.
Gas composition is typically heavy in carbon monoxide with hydrogen, carbon dioxide, hydrocarbons and small amounts of other gases. Because air is roughly 80 percent nitrogen, the gas also contains significant amounts of nitrogen. Of course, the nitrogen and carbon dioxide are not combustible. Because as much as 34 percent of the gas could be carbon monoxide, gasifiers could not be operated indoors; even an idling vehicle outdoors could be dangerous.
Simpler engines a good fit for gasifiers
Different kinds of gasifiers are based on different concepts. One common kind, known as a down-draft gasifier (for the direction of the air flow in the gasifier), is pictured at left below. Others include the up-draft and cross-draft. One advantage of the down-draft is that the vapors produced must pass through the hot bed of coals at the bottom of the gasifier. The high temperatures of the hot bed of coals serve to break down tar molecules into lighter hydrocarbons that can be used by the engine.
In operation, a solid fuel that contains volatiles is placed in the gasifier and sealed, and the contents allowed to partially combust by carefully limiting the air supply into the gasifier. Just enough air is allowed into the gasifier to allow enough burning to occur to provide enough heat to drive off the volatile gases, but not enough air to allow most of the volatile gases to burn. The heat supplied by partial combustion drives off the volatile gases, which become the fuel that can be used to fuel spark internal combustion engines.
Engines back then were much simpler and used some form of carburetor. The producer gas line was fed into the carburetor through the air intake. This points out one key disadvantage of gasifier systems: They had to be located relatively close to the engine that they were fueling since the gas could not be stored.
Alternate fuel requires special handling
For gasifier start-up, a small blower is used to pull a slight vacuum on the gasifier to draw the combustion air into the gasifier. Once gas is being produced, the gas is fed to the engine and the vacuum produced by the pistons in the engine provides the necessary suction on the gasifier.
A cubic foot of producer gas contains roughly 150 British thermal units (Btu). In comparison, natural gas is roughly 1,000 Btu per cubic foot and propane vapor is about 2,500 Btu per cubic foot. Producer gas has a relatively low energy content, but if that is all you have, you take it because you now have some way to obtain fuel and mechanical power from available materials.
Unfortunately, in addition to having a low energy content, the fuel is also dirty and must be cleaned before feeding to an engine. A typical gas clean-up train is pictured below right. It consists of a filtration step to remove particulates and a cooling step (similar to a car radiator) to condense and remove tar and water vapor. The cooling step is also necessary to increase the density of the gas, and thus increase the amount of gas and energy into the engine. Failure to properly clean the gas results in coking in the engine and eventually, damage to the engine.
“Bulky, cranky and dangerous” -But they (mostly) worked
Because green wood produces a greater proportion of volatiles in the form of tar (creosote), the wood should be dried first. Hardwoods will also produce less tar. And in order to get adequate air and gas flow through the fuel bed, the wood needs to be of a specific particle size that encourages air and gas flow.
The fuel had to be prepared in a special way. Bark-free wood particles that were roughly 3 inches long by 1-1/4 to 2 inches in diameter were considered ideal in that they “flowed” when poured into the gasifier, and, once inside the gasifier, allowed air and gas to pass through. Special wood “chunkers” were commercially available and tree branches in the 1-1/4- to 2-inch diameter range were highly sought. Vehicles such as cars, which did not have space to carry bulky bags of extra fuel, were equipped with roof-top racks for this purpose.
As can be imagined, operating a vehicle or tractor fueled with producer gas is a lot different than simply turning on an engine fueled with petrol. For one thing, one cannot start up as quickly as with a petrol engine. However, once warm, for idling, the air supply to the gasifier can be turned down to allow just enough air to maintain some combustion and heat, but conserve the fuel in the gasifier. Usually, this allows the gasifier to be started and the engine operable within a few minutes even after setting for a while.
Another problem is slow acceleration and load following capability (such as going up a hill). To some degree, an increase in gas generation can be accomplished by feeding more air into the gasifier, which increases the rate of combustion and thus increases the temperature in the gasifier, increasing the gas generation rate. Operating and maintaining a gasifier-fueled vehicle required special skills and training. Special drivers’ licenses were issued to those qualified to operate such vehicles.
Gasifier systems were described as bulky, often unattractive, cranky and dangerous. Gasifiers were built into car trunks or into trailers towed behind cars, onto the beds of trucks, or onto the sides or fronts of farm tractors, and in a few cases, onto military vehicles. The advantage for tractors was that the ducting to feed gas into the carburetor could be extremely short. A big disadvantage of this mounting arrangement was that the gasifier interfered with the tractor operator’s view.
Gasifiers soon returned to dust heap of history
Despite their downsides, gasifiers were widely used in Europe, Japan, China, Brazil, Australia and elsewhere during World War II. By 1942, Denmark had more than 20,000 vehicles and fishing boats running on wood, charcoal, coal, peat and compressed seaweed.
Most people were glad to get back to petrol fuels as soon as the war was over. However, agriculture was an exception and some gasifier-fueled vehicles continued to be operated into the 1960s.
As evidence of Dr. LaFontaine’s expertise, the Federal Emergency Management Agency hired him to design a gasifier system for emergency use in the U.S. This design was published as a booklet titled “Construction of a Simplified Wood Gas Generator for Fueling Internal Combustion Engines in a Petroleum Emergency.”
Today, a few gasifier systems can be seen in some European museums. Preppers and others build, research and play with these systems. FC
A. This is the actual gas-producing heater unit, with a sealed top and air admitted selectively at the bottom through controlled vents. Note the uniform nature of the wood fuel.
B. Filter. Usually filled with oiled cork or wood chips soaked with oil, to collect any ash or other particles from burner. In some units, this element contained charcoal or wood, which, when heated, contributed more flammable gas and still filtered the overall product.
C. “Extra” radiator, through which gases were passed prior to combustion in the carburetor. Two gas channels provided greater surface area, thus two sealed filling caps. Acid from the wood heating had to be regularly removed from this unit to avoid pitting. This radiator was not connected to the ordinary auto cooling system.
D. An electric blower, powered by the vehicle battery, was needed to start the unit under ordinary circumstances. The “second exhaust” from this blower was used to determine whether gas production was adequate prior to start-up. In very cold weather, or when the battery was low, the vehicle was started with gasoline.
E. Hot gasses were baffled through water in this unit, providing both cooling and filtering. Acid collection required frequent flushing.
The author gratefully acknowledges Schiffer Publishing and author John Fuller Ryan for permission to use pictures and other information for this article from the book Wartime Woodburners: Gas Producer Vehicles in World War II.
A semi-retired agricultural engineer, Phil Badger has worked in bioenergy research, development, tech transfer, and consulting most of his life. He managed the U.S. Department of Energy’s SE Regional Biomass Energy Program for 15 years. Raised in the Midwest, he currently lives in Florence, Alabama. He is interested in hearing from anyone having knowledge or experience with gasifiers during World War II. Email him at email@example.com.