Honda just dropped a bit of a bombshell on the world with its announcement that their heat-harnessing hybrids recapture more lost energy than even Toyota's hybrid drive during highway driving. This is fantastic news, since about half of American passenger vehicle driving happens at 65 MPH or faster, and mileage at those speeds has been almost completely unaffected by hybrid engines thus far.
The project uses Rankine cycle engine to capture waste heat from the car's exhaust and turn it into work. The system is fairly simple, though the thermodynamics are not. Basically water is heated, converted to steam, and the steam's expansion is used to turn a generator. Of course, that's a very basic explanation. For a more technical analysis, Green Car Congress always has the scoop.
The system was installed in a hybridized Honda Stream (only available in Japan). It is currently about 13% efficient and generates 3 times as much energy as a regenerative braking system in the EPA highway cycle. While highway mileages have been largely unaffected by regenerative braking, heat capture could assist in mileage increases in both highway and city driving.
Honda has decided that, at current efficiencies (and gas prices), it will not be cost-effective to include heat-capturing devices in production cars. Similar projects have come to the same conclusion. But with rising energy costs, and better engine designs, this could be a huge possible source of energy as more than 30% of a fuel's energy is immediately lost as heat in an internal combustion engine.
It's a promising new frontier, one with applications beyond vehicles everywhere from large-scale power generation to microprocessor cooling. Way to go, Honda.
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