There has been and is hydrogen cars from car makers
BMW have over 100 running
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Honda have hydrogen fuel cell cars runnIng
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Mazda have even had a rotary engine hydrogen car
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The reason that they don't build them for general public is again simple:
They cost a fortune Eg the Honda is supposed to cost $140k per car to build
Hydrogen fuel economy is very poor as it has less Engery in it
It takes massive amounts of energy to create hydrogen so it's not very green
It has to be stored at −253 °C (−423.4 °F) to remain liquid or it leaks creating some difficult storage problems
There is no infastructure network for them
People aren't very keen on driving around with a tank of explosive hydrogen under massive pressure in the boot..think Hindenburg Zeplin "oh the humanity" etc etc daft I know as they happily drive around with a tank of rather flammable petrol :crazy:
Regenerative braking (called KERS in F1) is already used in the petrol hybrid road cars like Prius , the electric cars like Peuegot iOn use it , as will the PSA hybrid4 products.
The veyron is a fantastic automotive irrelevance that was built simply because it could be ,it has 10 radiators :
3 heat exchangers for the air-to-liquid intercoolers.
3 engine radiators.
1 for the air conditioning system.
1 transmission oil radiator.
1 differential oil radiator.
1 engine oil radiator.
This is what it takes to control the heat generated by a power plant designed to deliver the 1001 bhp required to overcome the friction of air on the way to 267mph. The engine is a monster, it "eats" 45,000 litres of air per minute when running flat out..that's 4 or 5 days breathing for you or me
A modern road car doesnt generate anything like that level of heat and have very efficient cooling/heating systems that dont waste anything like as much heat. The concept of heat exchange have been tried and dismissed by the automotive market exactly because of systems like the vw beetle which the public decided was crap of the 1st grade as it just didn't supply the amounts of heat required or when the exhaust leaked a bit delivered a healthy slug of carbon monoxide :!: It also means you still have to have a second system for cabin cooling in the form of an air con system as this is what the public expectation has led to demand for. It won't work with diesel engines which are very thermally efficient ( think about how long it takes a diesel car to get upto temp on cold days) so would require additional systems. It also requires additional under bonnet packaging that does not fit with modern car design. So far the water system offers the best packaged system capable of meeting consumer expectations.
At the end of the day It all comes down to cost...the cheapest way to provide people with a personal mobility solution is the internal combustion engine and until the black stuff runs out or legislation is changed to force a movement away from it that will always be the way.