Conclusively proving that technology is indeed cyclical, BMW has successfully integrated a small steam turbine into a prototype 5 series that converts waste engine heat into electricity, resulting in a solid 10% increase in miles per gallon.
Cars waste a stupidly large amount of fuel (about 60% of what you put in the tank) heating themselves up for no reason, and unless you live in North Dakota or Scotland or Soviet Russia where a hot car is a good thing, most of the time all that heat just escapes uselessly into the atmosphere. BMW is fighting back against the tyranny of inefficiency with its Turbosteamer Project, which uses brand-new old-fashioned steam engine technology to harvest electricity from heat.
A steam engine is one of the simplest forms of engines. Heat boils water into steam, and then the steam pushes on a piston or drives a turbine or whatever to do work. Since you can use any source of heat to boil water, in theory you can just duct tape a steam engine onto anything that warms up to a couple hundred degrees and harvest energy from it while cooling it down at the same time. This is all that BMW is doing: the company is adding a small, steam-powered electric generator to an automotive exhaust system that sucks heat out of exhaust gases, boils a fluid into steam, and uses the steam to run an electric generator.
Implementing this kind of thing isn't easy, and BMW says that the steam mod won't reach the production line for years yet. The automaker did stick one in a Series 5 Saloon, and it was apparently able to provide 100% of the electricity used by the car, reducing fuel consumption by a not-too-shabby 10%. This means that CO2 emissions are reduced as well, so as long as the generator itself isn't made of baby seals and solid gold, it's a win-win for everyone.