Recently, the energy decline movement has proposed a new idea: large semi trucks cannot run on any fuel other than diesel. Only diesel offers the combination of high energy density for long hauls, and high torque for heavy loads. Battery electric trucks do not have sufficient range for long hauls, and gasoline engines do not have sufficient torque for heavy loads. Only diesel offers the combination of high torque and high energy density which is required for long haul trucking.
This idea is found in this video (25:00), and also other places in this movement. The idea is part of a broader claim within this movement that long-distance trucking will imminently be disrupted because of energy shortages. This idea means that peak oil will cause a decline or even collapse of supply chains. Heavy trucks cannot be transitioned to batteries or other options as oil declines. Furthermore, driving EVs as personal vehicles would make no difference because the gasoline freed up thereby cannot be used to power heavy trucks. Heavy trucking will decline along with oil regardless of whether passenger cars are EVs or not.
In particular, the video above claims that gasoline is not suitable for heavy trucking because of a lack of torque. Large diesel truck engines often produce 1,500 ft-lb of torque, which is several times higher than even the largest gasoline SUV engines. This amount of torque is necessary to haul heavy loads, so gasoline engines cannot do it. Or at least, so goes the claim.
This idea is not correct. Heavy trucks could easily run on gasoline or many other fuels. The torque of gasoline engines could easily be increased using a simple gear reduction. A simple 3:1 gear reduction would increase the torque of gasoline engines (and decrease the RPMs) so that the torque is far higher than a diesel engine. A gear reduction decreases RPMs and inceases torque, which is one of the main purposes of the transmission in almost every motor vehicle.
No combustion engine has enough torque to carry heavy loads if it's connected directly to the drive shaft. Neither diesel engines nor gasoline engines could do it. For this reason, a transmission is required to increase the torque of the engine, both for diesel and gasoline engines. Gasoline engines simply require more of a gear reduction, that's all. As a result. it’s obviously possible to increase the torque arbitrarily by using gears, after which, gasoline engines could easily be used to power heavy trucks.
Large semi trucks frequently already have 2 (sometimes 3) separate transmissions in series, with 12 or more separate gear combinations. Adding another simple gear reduciton would only modestly increase the complexity and wear of the transmission.
There is also another way (besides gears) for semi trucks to run off gasoline. We could use gasoline-electric trucks, where the engine is not connected to the wheels at all. The gasoline engine drives a generator, which generates electricity, which powers an electric motor and drives the wheels. This kind of setup is already widespread and is used in almost all locomotives, many large articulated city buses, and a few passnger cars (Mazda MX-30 and Honda Clarity). In these vehicles, the torque of the engine is completely unimportant because the engine is not connected mechanically to the wheels. In this case, only the power of the engine is important, and even some big SUV engines have sufficient power to drive a large semi truck.
This issue is important because EV adoption is growing rapidly and could cause a reduction in gasoline demand. This would mean more fuel is available for heavy trucking, if necessary. This could extend the amount of truck fuel we have for decades or centuries. Even after oil has peaked and declined by half, after 80 years or more, the amount of fuel from oil for powering trucks could remain the same or even increase if we switched to EV passenger cars in the mean time, because driving EVs would free up gasoline to be used by heavy trucks if necessary.
In addition to gasoline, there are many other possible fuels for heavy trucks. Natural gas can be used to power heavy trucks, and there are already more than 100,000 heavy trucks in China which are powered by natural gas. Coal could be converted into synthetic diesel, and this has already been done on an industrial scale. Battery-electric trucks could be used for long hauls by stopping to recharge once during the day. Finally, there is even another energy option for trucks. Gasoline could be used in existing turbines for electricity generation at power plants, and the natural gas which is freed up thereby could then be used as a truck fuel. Natural gas heavy trucks are already available and in widespread use.
In summary, there is a vast amount of fuel available for heavy trucks. The diesel they currently use is only a small slice of the total fuel available. There are many fuel substitutions which could be done easily if there were any reason for it.
This issue is important because it has implications for the future of long-haul trucking. Gasoline demand could very easily decline enormously over the next few decades because of EV adoption, which already has a 25% market share globally. Coal and natural gas usage could also decline substantially because of widespread renewable penetration. If usage of gasoline, coal, and natural gas declines to a low level, then the remaining fuel in the ground could be enough to power heavy trucks for many centuries.
Of course, it's possible to power heavy trucks using renewable energy. It could be done using battery-electric trucks and either battery swapping or periodically stopping to recharge. We could also run trucks from renewable energy by manufacturing synthetic fuels using carbon from the air and renewable electricity. And there are other options.
All these renewable options are inferior substitutes to diesel, at present. They are either too expensive or have drawbacks like frequent recharging during long truck hauls.
However, the price of renewable energy continues declining over time. Even synthetic fuels made from renewable electricity, which are currently far more expensive than diesel, may become cheap before we are forced to transition heavy trucks away from fossil fuels.
In any case, this issue poses no threat whatsoever to industrial civilization. Even inferior substitutes will be used if necessary. Even if it were necessary for all heavy trucks to be battery-electric, it would be done. Truckers would simply be paid more to stop and recharge several times per day. Even if we were forced to use synthetic diesel made from renewable electricity, and the price were 3x higher forever than diesel is now, and there were no other options, it would still be done. It would imply a modest reduction in standard of living because of higher shipping costs, and a switch back to rail rather than freeways because of much greater energy efficiency of rail. There are obvious substitutes in all cases, no matter what, and we have vastly more time than is necessary to manage a transition.
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