In fact, BMW has found that re-purposing the otherwise wasted exhaust heat to power a thermoelectric generator generating up to 1kW could be used to reduce real-world fuel consumption by as much as 5%. The benefit comes from storing the electricity and using it to pre-heat the engine or power the air-conditioning systems. The illustration below shows the approximate location of the proposed system.
Honda's similar work on the Rankine Cycle, which uses exhaust gas to heat water, creating steam that spins a turbine to generate electricity, has found as much as 32kW can be generated by the method, though the weight penalty for the device reduces fuel efficiency benefits to 3.8% at a 100km/h (62mph) cruise in a 2.0L direct-injection petrol four-cylinder.
BMW is also working on employing solar panels in the sun/moon roof sections of some of its cars. Prototypes have achieved 200W output levels, enough to improve efficiency by about 1%. Expanding solar panel coverage to the entire roof surface could generate up to 1kW, the same output as the exhaust-powered thermoelectric generator, and could benefit efficiency by the same amount, around 5%.
Other future technologies BMW is working on include regenerative braking, stop-start operation, variable frontal aerodynamics, electric power steering and a satellite-aided traffic management system that helps improve efficiency by anticipating when acceleration or braking will be necessary, and smoothing out the transitions between the two, resulting in better fuel economy. In Germany alone, BMW estimates that up to 12 billion liters (3.17 billion gallons) of fuel are wasted annually in traffic jams and other road hindrances.
The individual technologies are part of the overarching EfficientDynamics campaign to create more environmentally-aware cars while maintaining the driving dynamics that have made BMW famous.
Reader Comments
Thu May 15 2008 5:17 AM
kafkef says
Those pics of the guys driving look fake for some reason.. maybe it's just me.
Thu May 15 2008 7:17 AM
chris says
to hell with exhaust gasses, why not use that same technology on the cooling system. theres a hell of a lot more waste heat sitting in the coolant than there is in the exhaust gasses.
I like the idea of it though. we've got so much electronic and electrical equipment on today's cars that the electrical systems need to be beefed up. with electric steering, and almost certainly electric brake boost (if not just electric brakes), the electricity bill adds up. and the alternator is a huge sink for torque off the engine.
the ideal of the heat recovery sounds great to me. thats where 70% of your energy goes: heat. even if you can recover 10% of it, you'll improve mileage quite a bit.
Thu May 15 2008 10:32 AM
Gus says
Cool, I'd never thought of that, using a turbo to make electricity basically. I'm surprised the Prius doesn't use it.
Thu May 15 2008 12:42 PM
Tonto says
The talented people at Los Alamos National Laboratory have come up with a better solution IMO. They need a major automotive manufactures to help fund the research and adaptation of their “Acoustic Stirling Heat engineâ€
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