The Knowledge: How to Rebuild Our World From Scratch (21 page)

TRANSPORT

A gasoline engine is sheer magic. . . . Just imagine being able to take a thousand different bits of metal—and if you fit them all together in a certain way—and then if you feed them a little oil and gasoline—and if you press a little switch—suddenly those bits of metal will all come to life—and they will purr and hum and roar—they will make the wheels of a motor car go whizzing round at fantastic speeds.

R
OALD
D
AHL,
Danny, the Champion of the World
(1975)

MAINTENANCE OF A NATION’S ROAD NETWORK
is enormously expensive and time-consuming, and in the post-apocalyptic world roads would deteriorate surprisingly quickly, even though the heavy traffic pummeling along them will have ceased. In temperate regions, the punishing cycle of freeze-thaw will steadily widen small gaps and cracks, and seeds blown into crevices will soon grow into stout shrubs and trees, their roots further crumbling the thin skin of asphalt on the surface.

In fact, our modern asphalt thoroughfares, although beautifully smooth for bombing along the highway at 70 miles per hour, have a surface actually less durable than the robust construction of ancient Roman roads. Many
viae publicae
, crowned with a thick layer of hard
paving stones, were still passable a millennium after the destruction of the civilization that laid them. The same will not be true of our own transport network. Before too long even major highways, the arteries of the old civilization, will become all but impassable. You’ll need rugged off-road vehicles even for exploring the dead cities—for the first time SUVs will become necessary to get around urbanized areas.

After the Fall, the solid steel tracks of railways will be far more resilient than roads, but they will eventually succumb to the cancer of rust. Still, over the first few decades long-distance travel over land will probably be easiest along the old train lines, provided you keep them clear of vegetation.

The contraption that underlies much of modern transport is the internal combustion engine: it drives the family car as well as trains and light aircraft. But mechanized vehicles also serve in some of the most crucial roles for supporting society—the tractor, combine harvester, fishing boat, and delivery truck—and you will want to keep these running for as long as possible after the apocalypse. So let’s take a look first at how to provide the basic consumables required by mechanized vehicles—fuel and rubber—before exploring what the fallback options might be if society is not able to maintain mechanization and regresses even further after the apocalypse.

We’ll come back in a bit to the slightly different functioning modes of gasoline and diesel engines, but for the moment it is sufficient to understand that they require different liquid fuels. Both gasoline and diesel are liquid mixtures of hydrocarbons—similar molecules to the vegetable oils described in Chapter 5. Gasoline or petrol is a blend of hydrocarbons mostly with backbones 5 to 10 carbon atoms long,
whereas diesel is a slightly heavier, more viscous fuel made up of longer compounds of between 10 and 20 carbons. As we saw earlier, substantial reservoirs of these liquid fuels will remain behind after the collapse, in gas stations, depots, and the tanks of abandoned vehicles. But before long the surviving society will need to begin producing its own to sustain mechanized farming and transport.

Today these fuels are made by the processing of crude oil. The methods needed to treat crude oil to yield gasoline and diesel are relatively straightforward, and could be conducted on a small scale by a recovering civilization. Fractional distillation is used to separate out the component liquids, working on the same basic principle as distilling alcohol from water after fermentation. The larger hydrocarbon fractions can be “cracked” to break them down into the more useful smaller-molecule fuels by heating with a catalyst of alumina (such as crushed pumice rock).

So the problem in maintaining a supply of fuels for transport and driving agricultural machinery in the aftermath won’t be so much in the difficulty of the chemical processing, but in acquiring crude oil from the bowels of the Earth without sophisticated drilling equipment or offshore rigs. It is possible, though, to make automobile fuel without using oil as the feedstock, and a post-apocalyptic society may learn a lot from the green movement today.
Rudolf Diesel himself already noted in the early 1900s that “power can be produced from the heat of the sun, which is always available for agricultural purposes, even when all natural stores of solid and liquid fuels are exhausted.”

A viable substitute for gasoline-powered vehicles is ethanol (which we saw in Chapter 5 can be produced by fermentation). Brazil is the world leader in booze-fueled vehicles: every car on its roads runs on an ethanol blend, from 20 percent mixed with gasoline up to 100 percent ethanol-fueled. Even in the United States, many states require that all gasoline contain up to 10 percent alcohol, a blend that can be
used without modification to the engine. Indeed, the very first mass-produced car, the Ford Model T, was designed to run on either fossil-fuel gasoline or alcohol, and several distilleries in the US converted crops into car fuel until Prohibition killed the practice.

The problem with large-scale production of ethanol for fueling the transport system of a recovering civilization is sourcing enough refined sugar to feed the fermenting microbes. Crops like sugarcane that underpin Brazil’s sustainable biofuels economy cannot be grown outside the tropics. And while sugars are present in all vegetation, making up the strands of cellulose that plants use for structural support, the cellulose is so tough and chemically stable that the vital sugars are locked tightly away and inaccessible. After the Fall, therefore, rather than trying to process such biomass into refined fuel suitable for motor engines, it may be much more feasible to rot it in a biodigester to produce methane gas (see
here
), or simply burn it to fire a boiler in a static power station.

The rumble of diesel engines, on the other hand, will almost certainly still be heard in the post-apocalyptic world. A diesel engine is pretty versatile and can be run on vegetable oil processed into
biodiesel by reacting the oil with the simplest alcohol, methanol, under alkaline conditions (by adding lye—either sodium or potassium hydroxide, as we saw in Chapter 5). Methanol, also called wood alcohol, can be produced by dry distillation of lumber (see
here
), but ethanol from fermentation will also do. Any leftover methanol or lye, as well as the undesired side products glycerol and soap, can be cleansed out by dissolving them in water bubbled through the biodiesel, which finally needs to be thoroughly dried by heating to drive off the water before use.

Practically any vegetable oil can be used. Oilseed rape is a good crop as rapeseed yields a great deal of oil per acre (more than other sources such as sunflowers or soybeans), the oil can be easily pressed
from the seeds, and the leftover stems make nutritious animal fodder. If need be, animal fats can also be used. Tallow is rendered from scrap meat or carcasses by simmering in water to melt the fat, which then separates and floats, and can be scraped off after cooling. Tallow is processed into biodiesel just like vegetable oils, but the longer hydrocarbons that are present mean that it is liable to congeal in the fuel tank in colder weather.

The issue with these biofuels is that they rely on the transformation of crops into fuel, and keeping even a small car on the road would consume the agricultural output of at least half an acre. Depending on the circumstances of the recovery, it may be that food is scarce for the surviving population. In that case, can vehicles be powered from nonedible sources?

All internal combustion engines actually run on gas (not to be confused with the abbreviation of “gasoline”), rather than liquid fuels. A fine mist of gasoline or diesel is created, which vaporizes before combusting in the cylinder. So another option for keeping mechanized transport going is to deliver combustible gas directly into the engine from a pressurized gas cylinder. This is how modern compressed natural gas (CNG; methane) or liquefied petroleum gas (LPG; a mixture of propane and butane) vehicles are fueled.

A low-tech alternative suitable for the aftermath, when pumping gases into canisters at a pressure of hundreds of atmospheres may prove too challenging, would be to fit vehicles with gas storage bags. Common during the fuel shortages of the First and Second World Wars, these hold coal gas or methane in rubber-sealed fabric balloons, with two to three cubic meters of gas the equivalent of a liter of gasoline.

A slightly less unwieldy option is to build a wood-powered car and generate the fuel gas as you drive.

The key principle is known as gasification. To understand this, light a match and peer in closely. You’ll notice that the yellow luminous
flame actually dances clear of the blackening wooden stick, separated by a clear gap. The flame is not in fact predominantly fueled by the matchstick itself, but by combustible gases produced as the complex organic molecules of wood are broken down in the heat, gases that ignite as the hearty flame only when they meet oxygen in the air. This is the same process of pyrolysis we explored in the context of the dry distillation of wood and condensation of the vapors into a variety of useful fluids, but for powering an engine we want to maximize the conversion to flammable “producer” gases and separate the pyrolyzing wood and the flame much farther than in the match. These gases must be prevented from igniting until they can be piped into the engine, where they are finally allowed to mix with oxygen and explode usefully in the cylinders.

A LONDON BUS FUELED BY A GAS BAG DURING THE FIRST WORLD WAR.

During the Second World War, nearly a million gasifier-powered
vehicles kept essential civilian transportation running throughout Europe. Germany produced a version of the Volkswagen Beetle with all the wood gasification equipment installed smartly within the body, with a hole in the hood for loading more wood the only giveaway to its extraordinary power source; and the German army even deployed more than fifty Tiger tanks propelled by
wood gasifiers in 1944.

A gasifier is essentially an airtight column with a lid on top, and can be constructed from salvaged materials such as a galvanized trash can atop a steel drum, and common plumbing fittings. New wood is piled in at the top, and as it slowly progresses down it is first dried, then pyrolyzed by the contained heat, and partially combusted in the limited oxygen to generate the necessary operating temperature. Most important, a bed of hot charcoal forms at the bottom of the column and reacts with the vapors and gases given off by the pyrolysis to complete their chemical conversion. The final producer gas is then drawn out of the bottom, rich in flammable hydrogen, methane, and carbon monoxide—which is poisonous, so make sure you operate only in a well-ventilated area—along with up to 60 percent inert nitrogen. Cool the producer gas to condense any vapors that could otherwise gunk up the engine, and then feed it into the cylinders.

Around 3 kilograms of wood (depending on its density and dryness) is equivalent to a liter of gasoline, and so the fuel consumption of producer gas cars is measured not in miles per gallon, but miles per kilogram—wartime gasifiers achieved around 1.5 miles per kilogram.

Fuel is not the only consumable needed to keep an automobile rolling. Rubber is required to manufacture the tires that are constantly worn down by driving, as well as the inner tubes that are inflated like doughnut-shaped balloons to cushion the journey.

To be of practical use, the material properties of raw rubber need to be tweaked by vulcanization: it is melted with a sprinkling of sulfur and then poured into a mold to set. In the process the rubber’s coiled
molecular chains become interlinked into a tough, resilient mesh by bridges of sulfur. This produces an almost indestructible substance, more elastic than native latex, which doesn’t become sticky when warm or brittle when cold.

VEHICLE POWERED BY WOOD GASIFIER.

The trouble with rubber is that once it has been vulcanized, it cannot be simply melted down and re-formed into new products. To provide an adequate supply of tires with crisp treads, as well as providing for all the other uses of rubber, such as valves and tubes, a post-apocalyptic society won’t be able to recycle leftovers: it is going to need to find a fresh supply of rubber.

Rubber has been traditionally produced from latex tapped out of the
Hevea
rubber tree, which grows only under humid tropical conditions within a narrow strip around the equator. An alternative source is provided by the stems, branches, and roots of
guayule. In contrast to
Hevea
, this small shrub is native to the semiarid plateaus of Texas and Mexico. Guayule achieved prominence during the Second World War when the Allies lost 90 percent of their rubber supply with the Japanese invasion of Southeast Asia. The chemistry behind making synthetic rubber will be fiendishly tricky in the early stages of recovery, so once preexisting rubber supplies have deteriorated after the grace period, reestablishing long-distance trade will be one of your top priorities if you don’t live near a natural source.

Even if you are able to provide for your fuel and rubber demands, you won’t be able to keep vehicles going indefinitely. The components of any remnant machinery will inexorably wear out and deteriorate, and although you will be able to cannibalize spare parts for a certain period, you will inevitably have to begin making your own. Manufacturing replacements for modern engines will demand a high level of metallurgical know-how to blend appropriate alloys and machine tools able to create parts to exacting tolerances—topics that we covered in Chapter 6. And so if the post-apocalyptic civilization does not reattain these capabilities before the last working engine seizes and fails, it will lose mechanization, and the surviving society will regress even further. So in this situation, what backups are available to you to keep the vital functions of transport and agriculture running?