the fastest diesel locomotives usually have a speed around the low 200kph range, while the fastest electric locomotive can go over 300kph, and up to 574 kph. what is the difference? what makes it not currently possible to design a diesel locomotive that can go over 300kph?
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High speed rail requires a metric ass-load of power to continuously fight wind resistance and keep the train moving. Diesels aren’t as efficient as they’d need to be to produce enough power to run a HSR train in the size we want those trains to be.
We absolutely could design a diesel-electric HSR locomotive. It’d be a fuck-off huge landwhale of a train with a generator that would make an ocean-going supercarrier blush guzzling enough fuel to run a thousand traditional diesel trains, but it’d run!
But using the track gauge and vehicle length restrictions we have, diesel just can’t make the power needs required for high speeds.
There are a few reasons. Firstly high speed trains run on new expensive railway lines. The cost of the smooth rails and the advanced signalling system required is so great that adding the catinaries and transformers to allow electric trains is a minor cost and well worth the expense.
But in addition to this a big issue with high speed rail is the time it takes to accelerate up to those speeds. There is not much time accelerating from one station up to high speed before you need to slow down for the next stop when going at these high speeds. In addition to stations there are also corners with slower speeds and other obstacles which demand lower speeds. So while weight is generally not an issue for trains that go slow and steady for hours between stops it is a big deal for passenger traffic, especially high speed trains. The diesel engine in the locomotive is basically too heavy for the high speed train. It will add a lot of distance and time for both accelerating and slowing down because it is so heavy.
It’s likely the “tyranny of the rocket” problem.
Carrying fuel is not free. Diesel has mass and a diesel locomotive must expend fuel in order to accelerate that fuel. The more fuel you carry the more fuel you must carry to move that fuel.
Moving faster costs more fuel for the same mass, which means you must carry more fuel to move that extra fuel, which requires more fuel to move.
Eventually you reach the point where you have to carry more mass in fuel+vehicle than the total mass you can move with that fuel. I’m sure trains, even going 574 kph, aren’t nearly to that point, but they’ll still reach the point where the train is more fuel is a high enough percent of the total payload that it’s simply not economical to do so.
Electric trains, on the other hand, don’t carry their own fuel and so aren’t limited in that way. It still costs more energy to move fast than to move slow but since they aren’t carrying their own fuel the energy costs don’t ramp up nearly as fast, allowing for higher speeds to still be economical.
High speed rail requires a metric ass-load of power to continuously fight wind resistance and keep the train moving. Diesels aren’t as efficient as they’d need to be to produce enough power to run a HSR train in the size we want those trains to be.
We absolutely could design a diesel-electric HSR locomotive. It’d be a fuck-off huge landwhale of a train with a generator that would make an ocean-going supercarrier blush guzzling enough fuel to run a thousand traditional diesel trains, but it’d run!
But using the track gauge and vehicle length restrictions we have, diesel just can’t make the power needs required for high speeds.
It’s likely the “tyranny of the rocket” problem.
Carrying fuel is not free. Diesel has mass and a diesel locomotive must expend fuel in order to accelerate that fuel. The more fuel you carry the more fuel you must carry to move that fuel.
Moving faster costs more fuel for the same mass, which means you must carry more fuel to move that extra fuel, which requires more fuel to move.
Eventually you reach the point where you have to carry more mass in fuel+vehicle than the total mass you can move with that fuel. I’m sure trains, even going 574 kph, aren’t nearly to that point, but they’ll still reach the point where the train is more fuel is a high enough percent of the total payload that it’s simply not economical to do so.
Electric trains, on the other hand, don’t carry their own fuel and so aren’t limited in that way. It still costs more energy to move fast than to move slow but since they aren’t carrying their own fuel the energy costs don’t ramp up nearly as fast, allowing for higher speeds to still be economical.
There are a few reasons. Firstly high speed trains run on new expensive railway lines. The cost of the smooth rails and the advanced signalling system required is so great that adding the catinaries and transformers to allow electric trains is a minor cost and well worth the expense.
But in addition to this a big issue with high speed rail is the time it takes to accelerate up to those speeds. There is not much time accelerating from one station up to high speed before you need to slow down for the next stop when going at these high speeds. In addition to stations there are also corners with slower speeds and other obstacles which demand lower speeds. So while weight is generally not an issue for trains that go slow and steady for hours between stops it is a big deal for passenger traffic, especially high speed trains. The diesel engine in the locomotive is basically too heavy for the high speed train. It will add a lot of distance and time for both accelerating and slowing down because it is so heavy.
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