3 ms·

Let me make an analogy: Your petrol car has a heat engine. It converts about 20% of the heat energy released by combustion into mechanical energy. The rest goes

Let me make an analogy: Your petrol car has a heat engine. It converts about 20% of the heat energy released by combustion into mechanical energy. The rest goes out the tailpipe. Yet harnessing that remaining energy is not so simple because the temperature gradient is (relatively) small. The thermoelectric effect also requires large temperature gradients, and efficiency is proportional to the gradient.

eloff 5y ago
I think the car is a bad example because the temperature gradient is high and it should be possible to harness some of that waste heat. We just don't try. With hybrids we could definitely put that electricity to use, so I'm surprised no attempt is made to harness it. Especially for long haul trucking it could be worth it, but they're aren't diesel electric hybrid trucks that I'm aware of. Or at least they're not common. I do understand your point though.
- stickfigure 5y ago
  We do try! Some power plants and ships pipe turbine exhaust through a boiler and steam engine to increase fuel efficiency: https://en.wikipedia.org/wiki/Combined_cycle_power_plant https://en.wikipedia.org/wiki/Combined_cycle_power_plant Might be tough to fit all that under the hood though.
  - eloff 5y ago
    I was talking about in cars specifically. It would seem to me that adding some kind of TEG around the engine and part of the exhaust system might be worth it on a hybrid vehicle. https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator I guess it would depend on if you can make it cheaply enough.
    - stickfigure 5y ago
      Sounds like folks are working on it: https://en.wikipedia.org/wiki/Automotive_thermoelectric_generator https://en.wikipedia.org/wiki/Automotive_thermoelectric_gene... The numbers being floated about seem to be 4-5% fuel efficiency gain. Significant, but as you say it depends on the price.

eloff 5y ago

I think the car is a bad example because the temperature gradient is high and it should be possible to harness some of that waste heat. We just don't try. With hybrids we could definitely put that electricity to use, so I'm surprised no attempt is made to harness it. Especially for long haul trucking it could be worth it, but they're aren't diesel electric hybrid trucks that I'm aware of. Or at least they're not common. I do understand your point though.

stickfigure 5y ago
We do try! Some power plants and ships pipe turbine exhaust through a boiler and steam engine to increase fuel efficiency: https://en.wikipedia.org/wiki/Combined_cycle_power_plant https://en.wikipedia.org/wiki/Combined_cycle_power_plant Might be tough to fit all that under the hood though.
- eloff 5y ago
  I was talking about in cars specifically. It would seem to me that adding some kind of TEG around the engine and part of the exhaust system might be worth it on a hybrid vehicle. https://en.wikipedia.org/wiki/Thermoelectric_generator https://en.wikipedia.org/wiki/Thermoelectric_generator I guess it would depend on if you can make it cheaply enough.
  - stickfigure 5y ago
    Sounds like folks are working on it: https://en.wikipedia.org/wiki/Automotive_thermoelectric_generator https://en.wikipedia.org/wiki/Automotive_thermoelectric_gene... The numbers being floated about seem to be 4-5% fuel efficiency gain. Significant, but as you say it depends on the price.