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. There are no other options, besides diesel, to power heavy long-haul trucks. This idea is found in this video (25:00), and also other places in this movement.
In particular, 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, not even in theory. Or at least, so goes the claim.
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 passenger 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.
Of course, large diesel engines in heavy trucks often last 650,000 miles or more, compared to 150,000 miles in small vehicles. Using small gasoline engines for SUVs in heavy trucks would result in the engine wearing out more quickly and needing to be replaced more quickly.
However, diesel truck engines last so long because they are heavily built. This is basically a design decision by engineers. Gasoline engines (or natural gas engines) can also be built as heavily. Engines which are built more heavily last far longer and also cost much more. Heavily built engines are not used in small passenger vehicles because consumers would not pay a large additional upfront cost (perhaps more than $20,000 extra) for a car that will last 600,000+ miles. Many people don't drive more than 10,000 miles per year anyway, and nobody keeps a car for 60+ years straight. As a result, it has never made sense to build engines for cars so heavily. However, gasoline engines designed for heavy trucks could certainly be built much more heavily and could have longevity approaching that of large diesel engines. The longevity of gasoline engines still may not match diesel engines, because diesel engines have fewer RPMs and therefore less wear, which is an additional reason for their longevity. However, even this factor could be overcome by using an engine with a larger displacement than necessary and therefore lower RPMs.
In summary, it is quite possible to build large heavy trucks which run on gasoline, and which have torque and longevity similar to large heavy diesel trucks. This could be done by using gasoline engines which are much more heavily built, have larger displacement, and have a greater gear reduction to increase torque. As a result, gasoline could easily replace diesel for long-haul transportation if we had any reason to do that.
This issue is important because EV adoption is growing rapidly and could cause a reduction in gasoline demand. It's at least possible that gasoline demand will drop to low levels over the next 60+ years. If this happened, then there would be more than double the fuel available, in each barrel of oil, for heavy duty trucks. If short-haul trucks and delivery vans are also electrified, it would increase the amount of fuel available for long haul trucking by more than 4x because less fuel is used in other sectors of the economy. This would mean that a decline in oil extraction by 75% would cause no change in fuel available for heavy duty trucks.
As a result, we could easily have enough diesel and gasoline to power heavy-duty trucks for at least 80 years, even if oil peaks in 2030 and then declines in a symmetric fashion, which is extremely pessimistic. Even an imminent peak in 2030 and a symmetric decline would leave 25% of today's production even 80 years from now, which would pose no change in fuel for long-distance trucking if easy and automatic adjustments are made -- the kind of adjustments which are automatically performed in market economies.
These facts contradict one of the main doctrines of this doomsday group. One of the key ideas of this group was that trucks would suddenly stop running because of a shortage of fuel. However, that idea was not correct. There is enough fuel to keep trucks running for a very, very long time, using basic fuel switching, which is easy and routinely carried out by market economies.
There are also other alternative energy sources, besides gasoline, for heavy trucks. Long-haul trucks could easily run off natural gas, electricity, coal, or woody biomass. Coal and woody biomass can be converted into diesel fuel using the fischer-tropsch chemcial process, which has already been in widespread use for many decades. Battery improvements are being implemented (such as solid state batteries) that would enable an 800+ mile range for long-haul trucks, which is more than they're allowed to drive in a day.
The latter two of those options (woody biomass and batteries recharged by renewables) are never running out. As a result of these things, it's not clear that we face a shortage of fuel for trucks over any time period, ever, even millions of years from now. Of course, the truck fleet can only be transitioned slowly to renewable energies, over many decades, but we appear to be transitioning far faster than is necessary to avoid any disruption.
As a result, it's not clear we ever face a shortage of fuel which threatens long distance transportation. The far future is difficult to predict, and I expect humanity will end for other reasons at some point, but there is no inevitable trend, over any time period, which implies that trucks will stop running because of a shortage of fuel.
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