Will diesel ever be usurped by electric?

OK, most of my train experience is with the Philadelphia-Pittsburgh route. We had to switch over from catenary to diesel in Harrisburg, but I’m pretty sure that that was the same locomotive, just taking some time to winch up the contact bar. I hadn’t realized that that wasn’t the norm.

EDIT: Oh, and supercapacitors might not be good enough for racecars right now, but they’re one area where the technology is currently advancing at insane speeds. If they’re at “in the right ballpark but not there yet” levels right now, then they might be there in ten or fifteen years. And you can compensate a lot for the dropping voltage as they discharge using switching power supplies.

How about building the electric dragster without the battery? Run it off overhead lines like a train, or in-ground conductors like a slot car track. Or even better, ditch the motor and launch it from a railgun.

However the Tesla has a range of over 600km. The dragster only needs to go 300m. That is a 2000:1 difference. In principle you only need a battery weighing about 250g for the Tesla to go 300m. “The best in existence” isn’t the metric you need. Very arguable that it is the best anyway. It is the best for a mix of power range, price, mass.

This is the problem with working the numbers. The energy needed for a top fuel dragster was worked out above. It isn’t all that much.* A lot less than a Tesla S’s battery holds. But the problem is is that a Li Ion battery won’t deliver the power, and a super-capacitor that can weights too much.

The dragster has about 25MJ of kinetic energy in it at the end of the run. Based upon an estimate of 10MW engine, I had estimated 50MJ of input power. (An overestimate, really 40MJ would be closer). So the efficiency is about 60%. Sticking with 40MJ, that is a heck of a lot of energy, but about 1/9 of the energy in a Tesla S 100 S battery. (Which is a pretty insane comparison no matter what. The dragster goes 300m, the Tesla goes 65km.)

but range has nothing to do with it. Drag racing is all about acceleration (and traction.) the more mass you add, the more power you need to accelerate it, which means you need more battery (more mass,) and so on. There’s also a limit to how fast you can draw current from even high-power cells. And the other thing is you carry all of that mass with you down the entire length of track and you still need to bring it to a stop. Top Fuelers burn off all of their (admittedly small quantity) nitromethane before they reach the trap.

It is about energy. Power is energy per unit time. The energy needed for a drag run is about 40MJ. The capacity of a battery is measured in energy. Range of a conventional electric car is dependant upon the energy content of its battery. A Tesla model S has a range of 600km, with a battery of 100kWh = 360MJ. Thus a Tesla model S 100 D battery contains the energy needed for about 9 drags. Or, a battery 1/9 the size of a Tesla model S can run one drag. This should not be hard, it has been covered above.

If we’re talking about racing it is about power. A 1/9th-size Tesla battery has sufficient energy, but that’s useless unless it can supply it fast enough.

Its both, hence the preceding set of posts. If you don’t have the energy you can’t deliver power for long enough. Equally useless.

Every few years a few articles come out touting the potential benefits of lithium-air battery technology while completely glossing over the issues that have consistently plagued this and other rechargeable air-breathing batteries and proton exchange membrane fuel cells, to wit issues with water vapor, air pollutants, low specific power delivery, and sensitivity to cold air and ambient temperatures. Lithium-air also has specific issues with CO[SUB]2[/SUB] sensitivity and the buildup of lithium peroxide films that drastically reduce the cell’s energy storage capacity and power delivery rates. A practical lithium-air battery would likely require highly filtered and compressed air to achieve anywhere near the theoretical energy density of 13 kW-h/kg, and some elaborate self-cleaning mechanism to prevent peroxide film buildup.

The practical near tem “game changer” in electrochemical batteries is lithium-sulfur which offers a theoretical improvement of up to three times the specific energy capacity of lithium-ion, has good specific power and cold temperature operation performance, and actually offers a significant reduction of manufacturing and end-of-life disposal costs. The major issues with Li-S is longevity, which at best is still short of 100 charge/discharge cycles and a propensity for runaway discharge and rupture at high temperatures or extended operation, which are problems that can be addressed by refining processing, active cooling, and finely controlled power management. However, while even conventional Li-ion are suitable for commuter applications (and may become more so with utilization and operational efficiency gains of autonomous operation vehicles) I remain unconvinced that battery electric power will be suitable for regional or continential range aircraft or long range driving though it is possible that sufficient efficiency gains may make it viable for automated long haul transportation.


Yeah, Li-Air has some pretty nasty issues currently. There does seem to be some useful progress, but the issues with water vapour and CO[sub]2[/sub] are so far only solved with things that wreck the mass advantages. I suspect that when the game changer happens, it won’t be Li air. But I do have hopes that there will be one. No matter, I deeply suspect my next car purchase will be electric.

And the current cars won’t go if you don’t add fuel. That’s not informative. Range isn’t the problem because very little range is needed. So the battery weight required is not determined by range, but by power.

Is “propensity for runaway discharge” another way of saying “catches on fire”?

Seems it’ll be awhile before any of these metal-air batteries will be economically viable at the consumer level. Might come into play for say a semi or something. There’s more space and a greater weight allowance for the necessary support items for the metal-air batteries.

A gasoline-electric like a Volt or simply a hybrid is best in the near-term.

Runaway discharge causes a rapid spontaneous breakdown of electrolyte that can build up and rupture the battery casing and emit toxic and caustic gases, and in severe cases, can result in fire or explosion. I was tangentially involved in a test of a battery system recently in which runaway discharge resulted in a reaction so violent that the door of the test cell was blown off. This was a Ag-Zn thermal battery that has inadequate load and some other issues that led to the rupture and explosion, but lithium batteries in particular will burn energetically and cannot be extinguished by water or ordinary ABC chemical fire suppression systems, requiring dry salt or graphite extinguishing systems.


“Energy density” has mostly to do with range. Given that gasoline and diesel have similar energy densities, and that Tesla is already producing electric vehicles with a range not too different from gasoline/diesel passenger cars, it would seem your question has already been answered in the affirmative.

If you’re thinking of bigger vehicles, like city buses, it’s worth noting that there are already many cities with electric buses powered by overhead wires. In addition, there are already a number of battery-electric bus manufacturers out there; they don’t have the range of diesel buses, and they’re more expensive, but they are attractive because they don’t pollute the air in their immediate vicinity (maybe not at all, depending on the source of the electricity for charging), and they don’t require expensive and unsightly overhead wires. They also reduce national dependence on oil imports. The type of driving done by city buses (low speeds, lots of starts/stops) makes best use of the battery and regenerative braking. Expect to see this technology more and more on other urban vehicles like UPS trucks, garbage trucks, and mail trucks.

For rail, we already know that electric passenger trains for urban service are in common use, but these trains generally aren’t that massive, and therefore don’t require a shit-ton of power to accelerate/brake them. They’re usually on the order of half a kilometer long, 15-20 cars, and only carry a couple thousand pounds of living meat in each car. Contrast this with cross-country freight trains, which can be as much as 4 kilometers long, 100+ cars, with maybe a couple hundred thousand pounds of cargo on each car. Powering such a beast with electric, especially cross-country, is impractical and probably will be for a long time.

You have read the previous comments? Both I and Dr Strangelove covered this in detail. The energy needed is about 40MJ. That is for the 300m drag. The drag car has about 25MJ of energy in it at the end of the drag. Simple physics. You have to get that energy from somewhere. The Tesla equivalent battery to get the drag car going that fast over the 300m is about 1/9 of the entire battery. If you use a battery. But you can’t get enough power (that is energy per unit time) out of the battery. So, if you look at other technologies, such as supercapacitors, which can deliver the power, you find that they can’t hold enough energy to do the job without ending up weighing many times the weight of the drag car.

You seem to agree with this, but somehow have a problem with it as well. I don’t quite get what the question is.

The energy needed is irrelevant in a power-limited scenario. Let’s walk you through the previous comments.
jz78817 states that batteries are too heavy:

You respond that only 1/9th the weight is required based on energy:

But that’s the wrong analysis because the minimum battery weight is not determined by the energy requirements in a power-limited scenario.

We need over 7 MW*. The Tesla battery is 2100 kg at 516 W/kg**. If those numbers are right***, seven will do the job.

*FORGET 8,000 HORSEPOWER ... TOP FUEL IS NOW OVER 10,000 HORSEPOWER! [National Dragster]
***Probably not without adjustment for efficiency and weight changes

The Tesla battery is completely irrelevant; I don’t know why anyone is talking about it. 0.5 kW/kg is completely insufficient for a Top Fuel equivalent. The Tesla is optimized for completely different parameters (cost, longevity, etc.).

Look at li-poly cells for RC applications instead. They have extremely high burst power: at least 7.5 kW/kg right now. That’s on the edge of good enough. They have more than enough energy density.

Supercaps are even better with 40-100 kW/kg, but their energy density is on the edge–barely enough to reach the necessary 150 m/s.

In both cases, rapid progress is being made. Another factor of 2 improvement for either (energy density for supercaps, or power density for li-poly) would probably make it possible.

Addressing Ruken’s comments.

You are missing the point of my initial post about the Tesla battery. I was pointing out that since we only needed 1/9 of “the best” battery, the mass of that battery was not the issue, and thus not the limiting problem. Again you are agreeing with me. I went on to say exactly what you are saying, that the power delivery would not be adequate even though it was not energy limited. I went on to find a power capable solution but could not make it meet the energy needs. You can’t have power without the energy needed, and you cant use the energy if you can’t deliver the power. Again, we agree. I don’t see the issue.

I have the answer: multi-stage dragsters.

The supercaps have incredible power density but won’t quite make it down the track. But why carry that mass the whole way? Eject the depleted caps along the way and you’re reduced the mass you need to accelerate further.

I have not worked out the numbers yet but it should be a simple matter of plugging the parameters into the Tsiolkovsky dragster equation.

This also addresses another complaint about electric dragsters; that their low noise makes the event less exciting. Ejected power cells moving at 100+ mph could make things very exciting for the bystanders.

That “in the right ballpark but not there yet” applies to batteries and super capacitors for all-electric or hybrid electric aircraft as well.

The most recent Aviation Week had a fascinating series of articles on how quickly all the relevant tech is moving and how tantalizingly close much of it is. And how far out of reach some other things are and are likely to stay.

We’re several decades from an electric 737, if ever. We’re maybe 20 years from an electric equivalent to a current turboprop regional 40- or 50-seat aircraft. We’re just a few years from mostly- or fully-electric lightplanes or aerial hover-taxis.

Exciting times in aviation. These novel powertrains enable novel designs in many different directions.