Naked Science Forum
Non Life Sciences => Technology => Topic started by: evan_au on 17/01/2020 20:04:39
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On the Naked Scientists podcast this week, I heard about the the dangers of heavy-metal pollution caused by brake-pad wear.
In stop/start traffic, electric vehicles and hybrids use regenerative braking to turn the car's momentum into stored electricity, which is then reused when the car accelerates.
This is much more efficient than traditional internal combustion engines, which use the car's momentum to produce heavy-metal pollution from the brakes.
Would hybrids & electric vehicles be a solution to this heavy metal pollution?
See: https://www.thenakedscientists.com/articles/interviews/car-brakes-contribute-air-pollution
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And yet, life expectancy, house prices, and the number of first-class degrees, increase every year. Who is kidding whom?
But hybrid vehicles with regen braking obviously make sense from any aspect.
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And yet, life expectancy, house prices, and the number of first-class degrees, increase every year. Who is kidding whom?
And life expectancy would be very slightly better if, all other things being equal, we dropped the levels of heavy metal pollution in our cities. So, it plainly makes sense to consider doing it- especially if there are sid benefits.
The people who don't recognise that have been kidded by those who want "business as usual" so they can keep making short term profits.
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The only way I can visualise the mechanical reclaiming of energy is either by a flywheel or by the compression of gas neither of which are really applicable to a vehicle, by generating electricity and storing it in a battery is the only way that has had any success.
When regenerative braking was introduced for F1 cars some attempt was made to use flywheels but it was soon abandoned
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Don't all the worn out batteries count towards heavy metals in the environment?
Yes, scientifically, but no, politically, because mining, refining, manufacturing and scrap reclamation are all done in places like India and China, where toxicity has no effect on the re-election of European politicians, or in the USA where public health comes second to Greatness.
Best of all, people who live in countries where such things are not made, will be required to scrap all their simple, reliable old piston-engined vehicles and buy new ones they can't repair, or be accused of poisoning their children and drowning polar bears. Thus the "developing" world becomes ever more impoverished and selfrighteousness rules.
Liza - Yeah, you're right. My colleagues at Kings College have looked at vaping and they've measured metals inside of it. That means it is a cause for concern.
And there, children, is modern environmental science in a nutshell. As soon as an academic can measure anything, it's a Cause for Concern. The scientific breakthrough in the published paper was using BAD as an acronym for brake abrasion dust, thus guaranteeing headlines and funding in the absence of actual epidemiology.
Halc's suggestion of mechanical regeneration is interesting. I remember drawing a torsion spring hybrid bus when I was about 8 years old, but https://worldbuilding.stackexchange.com/questions/163428/maximum-theoretical-energy-density-of-clockwork has a neat discussion which shows that the best hypothetical carbon-fiber spring has an energy density just 3 orders of magnitude lower than diesel fuel and about 1/100 that of a battery. Flywheels are great until you try to change direction, when all the saved BAD turns into tyre dust (or mangled corpses) instead!
But here's an idea. Go back to James Joule's honeymoon experiments. If you use a paddle wheel in water as a brake, it has comparable energy density (as liquid) to the best batteries, and outperforms batteries if you turn it into steam. So a hybrid diesel/steam vehicle would bring some romance back to the roads and save the planet!
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Who not use a hydrogen fuel source instead of diesel?
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Because diesel engines already exist, along with a worldwide standard of fuel, fuel distribution and maintenance, and have a proven record of safety and reliability, plus the high energy density of petroleum-derived fuels that are conveniently liquid at ambient temperature, vaporise easily, have a very narrow explosive range and a defined ignition temperature, are easy to manufacture, and are no use for anything else. Remember, when heavy oil was used for lubricating steam engines and paraffin for lighting, the lighter fractions were flared off to get rid of hazardous waste!
Hydrogen gas has a poor volumetric energy density, and liquid hydrogen, though having unbeatable gravimetric energy density, is volatile and hazardous under all conditions. Diesel is preferred for engines running at constant speed because it can give a more complete burn than gasoline. A small constant-speed diesel driving an electric transmission with intermediate storage should be capable of the "100 mph 100 mpg" goal for a family car with a very clean exhaust.
The ultimate use of a waste product would be to use the heat of spent nuclear fuel to drive a Stirling engine: free fuel (we'll pay you to take it away!), phenomenal energy density (about a million times that of liquid fuels) and no gaseous or particulate emissions, but I don't think homo is quite sapiens enough for that product yet.
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Who not use a hydrogen fuel source instead of diesel?
Energy density and a lack of hydrogen mines/ wells.
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Hydrogen can be generated from surplus voltaic and wind energy but energy density and distribution will always be a problem the, future is diesel
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Flywheels are great until you try to change direction, when all the saved BAD turns into tyre dust (or mangled corpses) instead!
For this reason, they should be mounted with a vertical axis. The thing spins fast when the vehicle (they've implemented busses with it) is going slow. It resists being reoriented as it crests hills and troughs, but the flywheel probably isn't moving much on the former.
The point of mechanical hybrid drives is to reduce cost and weight. I don't think they're particularly more efficient than batteries, but they're good for more stops and starts.
Anybody know what the battery capacity is for something like a Prius? The dealer salesman acted like nobody ever asks that. I live in mountains, and I floor my Prius up a steed grade. How far do I get before its just that little 3-banger getting me the rest of the way up that hill? Can I give the car intelligent input so it doesn't charge the batter with the engine just before I know I'm about to go back down that same grade? No, it cannot do that.
OK, so no Prius. I get better fuel economy with my 2-liter with a stick. I can get 50 mpg on public roads and over 60 on a track, and I don't use my brakes much, driving instead on the principle that it costs money to press either pedal.
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"The ultimate use of a waste product would be to use the heat of spent nuclear fuel to drive a Stirling engine"
The amount of energy that can be derived from the heat output of spent fuel is tiny (that's why it is called spent!) it would be hopelessly uneconomic to try and build a power station using it
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The difference between power and energy is important! You can get plenty of power from fissionable fuel with a high neutron capture cross-section because the chain reaction involves plenty of nuclei per second, but the total energy produced is the same whether you extract it all at once in a bomb, over a few years in a controlled reactor, or over the lifetime of the universe by natural decay.
The question is whether a "hot" source of non-controllable waste could drive a useful engine. It turns out that NASA had already contracted prototype studies but cancelled the project after a mere 30% cost overrun on $200,000,000 (wouldn't it be good to have NASA manage the HS2 project? It would have been scrapped by the third week!). A purely terrestrial version wold be a lot cheaper and in production, would go some way to offsetting the cost of nuclear waste disposal by generating electricity instead of using electricity to circulate the cooling ponds.....