Honda Looks Into Recycling Engine Waste Heat

Honda Ranking heat recovery system

Honda engineers are trying to make the old internal combustion engine more efficient by recapturing energy that is usually lost as heat through the exhaust. There's lots of room for improvement: According to Amory Lovins from the Rocky Mountain Institute, only about 1% of the energy contained in a gallon of gasoline moves the driver of a car (if that's not shocking, we don't know what is). The rest is partly used to move the vehicle's weight, but it is mostly just lost as heat.

What Honda is trying to do is turn some of that heat into electricity via the Rankine cycle co-generation. In a hybrid, that electricity could then be used to power the car via the electric motor. The big benefit would be better fuel economy on the highway, where traditional hybrids show smaller gains (very little regenerative braking).But lets not get too excited yet. So far, the system is not efficient enough to be cost-effective and implemented in production vehicles. Maybe that will change if oil prices keep going up, the technology is refined and demand for more efficient vehicles keeps climbing (there are good signs on that front).

Test results showed that in 100 kph (62 miles/hour) constant-speed driving, the use of the Rankine cycle improved the thermal efficiency of the engine by 3.8%. In the US highway cycle, the Rankine cycle system regenerated three times as much energy as the vehicle's regenerative braking system. [...]

Maximum power available from the volumetric expander is as much as 32kW (43hp), and maximum thermal efficiency of the unit is 13% at 23kW (30hp).

We can wonder, though, if simply down-sizing cars and engines, using more carbon fibers and advanced materials, improving aerodynamics, reducing rolling resistance in tires, etc, might not be an easier way to gain efficiency. Of course, it's possible to do all these things with heat recovery, but it does add weight, complexity and cost, and so it might not be the best bang for the buck while we wait for the next step, which will probably be plug-in hybrids and electric vehicles.

In the meantime, you can always hop on your bike!

::Honda Researching Advanced Hybrid Drive with Rankine Cycle Co-Generation

We wrote about a similar technology a couple of years ago: ::Creating Electricity With Exhaust Gas

See also: ::Honda to Introduce an "Entry Level" Hybrid in 2009, ::Honda Bringing 62.8 MPG Diesel to the US by 2010, ::Honda Shows Off FCX Fuel Cell Concept Car, ::More Details on Honda's 2006 FCX Fuel Cell Car

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