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Many Diesel-Electric locomotives apply a technology known as dynamic braking to run the motors in reverse instead of using regular brakes. The electricity from this is dissipated as heat through large banks of resistors.
While regenerative braking systems do exist for trains, I do not know if these
are cost or power efficient for freight trains.
I imagine it would be relatively cheap to outfit these vehicle with electrolysis systems that split water into hydrogen and oxygen and then sell the resulting gases to wherever they are needed. This system can reside in its own traincar and (depending on where the need is) might provide (almost) free storage and transportation for the product.
Electrolysis of water may be an inefficient method of making hydrogen, but it's a heck of a lot more efficient than dissipating the energy as heat!!
Flywheel energy recovery
http://www.flybridsystems.com/
High power energy recovery [Twizz, Aug 16 2010]
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Better, capture the gases and then recombine them in a fuel cell; or inject them (in small amounts) into the Diesel's intake airstream and re-burn them to water. |
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I think the general reason for the current method is that they need to do something with the electricity quite quickly, so they heat coils and run fans to blow the heat off the coils into the air. They probably have people looking for ways to store the power, because they'd love to have a way to get it back into the motors. |
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If you want to use the juice to electrolyse water, you need a way to do so in quick bursts, at a high rate, and then lug the equipment around for the rest of the time, waiting. (Weight is not an issue, by the weigh/way, as the locomotives need all the traction they can get.) In my experience, electrolysis is very slow. Have you a plan for speeding up the process? |
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It occurs that they could be heating up tanks of water instead, which would add weight ... |
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Lithium metal would be better - it has a large specific heat capacity. |
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I think the speed of the electrolysis is going to depend on the surface area of the electrodes. As far as I'm aware the electrodes have to be made of very expensive materials such as platinum in order for them not to corrode. |
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// have to be made of ... platinum // |
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Not true; the surface in contact with the water needs to be Platinum, or a similarly inert noble metal. |
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Copper or Iron with a suitably thick Platinum "plating" would suffice - it needs to be dense enough to prevent ion exchange occuring at the substrate. |
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Graphite or semiconductor materials can also be usefully employed. |
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True, you'd have to be mad to make *solid* platinum electrodes... |
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Which brings up the fact that you could be electrolysing, so to speak, the common metal called "lead". Which is to say they could be charging lead-acid batteries off the power, and using them to assist in running the motors a while later. That seems pretty damn obvious, so if they aren't doing it they must have a reason. |
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So I'm thinking that unless this idea has some great advantages, it isn't worth it to the train folks, as fun as it might be for the HB. |
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I do like [8th]'s suggestion about feeding the hydrogen and oxygen back into the engines. That would be elegant. |
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//could be charging lead-acid batteries// sp. "blowing up": batteries have a pretty crappy recharge density. |
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// they must have a reason // |
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Lead-Acid batteries don't appreciate being charged faster then their C/10 rate (50 AHr battery, max charge rate 5 Amps). Charge them too fast and all sorts of bad things happen. |
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Capacitors can charge ultrafast, but their power density isn't spectaculalrly good. |
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Lead acid batteries would add a lot of inertia. Aluminimum alloy cylinders for storing hydrogen and oxygen would be bulky, but not heavy. |
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There are many ways to recover and store energy from braking. Electrolysis is not among the best suited. |
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Most effective would be to feed electric power through brushes and rails to the grid system. For non electrified railways, this would require only short sections of power rails either side of stations, allowing a train to feed power to the grid as it slows into a station, and draw power to accelerate away. |
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Another alternative is a high speed flywheel (see link) |
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Two words: George Westinghouse. |
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Well over a century ago, there was a prize for the best brakes on trains. George Westinghouse won, and later blew a sizable portion of his fortune on Nikola Tesla's Alternating Current idea. (AC: what whac!?!) We still use those brakes today. So, why don't locomotives have regenerative braking? |
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Because EVERY car must be braking at the same time. Westinghouses' brake system was pneumatic. Next time you see a flat car, look by the wheels and see if you notice a pressure 'sphere'. Or, next time you are near a locomotive just about to take off, listen for strange whishing noises. That is the engine topping off each car's pressure spheres one at a time. Or notice that weird thick hose that connects between every car. All of the pressurized air goes through it. If a car's connection disconnects, then EVERY set of wheels, two per car, pneumatically brake: no runaway trains. |
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But ... what if there is a way to harvest the braking energy on every car, and maybe store it? Just saying... |
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How about they use the electricty to convert the nitrogen in the air into fertilizer, then blow that up into the air? I think that process needs water, though. |
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Wily: electric trains often have motors on many if not all the axles. This gives improved traction and would also provide braking from all the motorised axles. |
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It may be beneficial at this juncture to review the differences between loco-hauled freight trains, and multiple-unit passenger trains. |
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A freight train will have, as per [WP]'s excellent exposition, braking on all the cars and the loco, but only the loco(s) will have traction systems. The preferred mode of operation is to get the train rolling at a steady speed and keep it at that speed, avoiding stops (and therefore wasted energy and time) as much as possible. |
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An express passenger train will acclerate to a high speed, and - if all goes to plan - declerate just once, at the end of its journey. It may possibly make one or two stops in a distance of several hundred kilometres. |
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The issue of energy recovery is best considered in the case of a "commuter" or "local" train, which wishes to travel at high speed between frequnet stops. These typically have powered bogies on several of the component cars and are the foremost candidate for a short-term high-power energy recovery braking system which can stop the train efficiently at a station and then smoothly re-accelerate it on departure. |
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