Wasted thermal energy

[Gerrie]

Having read the very interesting and informative thread about power vs torque, I remembered some heated discussions I've had with friends about the topic of somehow putting the thermal energy generated in internal combustion engines (notably around the exhaust system) to use. It seems so obvious that I can't believe it hasn't been pursued yet; for example: can the energy not be harnessed to get the gas in the air-con moving (like in gas or paraffin fridges) so that the power required to drive the compressor mechanically can be eliminated? C'mon you engineering types, what do you know about it? Maybe we stumble onto something new here.......my fee is 10% of the vast profits!

[alanB]

My old Volksie used to use the heat from the exhaust pipe to heat the car (air was blown over the exhaust and back into the car). The problem being that any leaks in the exhaust pipe was potentially dangerous to the occupants (didnt stop millions of Volksie's being made like that nor do I know of anyone dying due to carbon monoxide poisoning from the heater).

On a related note a Turbo is probably the most famous method of extracting more "free" power from the exhaust. When the exhaust valve opens the pressure inside the combustion chamber is still much higher than ambient. In normally asperated engines that energy is lost as the gas rushes out the exhaust. By putting a turbine in the path of the gas, one improves the efficiency of the engine quite a lot (more use is made of the energy released during combustion).

[Gerrie]

I'm actually referring to the thermal energy (heat) which is lost, whether the exhaust gas is used to drive a turbo or not.

I remember as a student diverting the air from my Volla's fan housing outlets to act as a "blower" directly onto the carburettor, adjusting the fuel/air mix accordingly. Of course it overheated after about 5000 km, but until then it was the fastest Beetle around!

[pretdave]

Having read the very interesting and informative thread about power vs torque, I remembered some heated discussions I've had with friends about the topic of somehow putting the thermal energy generated in internal combustion engines (notably around the exhaust system) to use. It seems so obvious that I can't believe it hasn't been pursued yet; for example: can the energy not be harnessed to get the gas in the air-con moving (like in gas or paraffin fridges) so that the power required to drive the compressor mechanically can be eliminated? C'mon you engineering types, what do you know about it? Maybe we stumble onto something new here.......my fee is 10% of the vast profits!

Hi Gerrie

This is in fact being done - in particular by BMW.

"Now the BMW Group’s engineers are working on a technology able to convert the thermal energy contained in the exhaust gas directly into electric power. This thermoelectric process of recovering energy and generating power by means of semi-conductor elements has already been used for decades by NASA, the US Space Agency, in space probes flying into outer space."

Do a Google search "BMW thermal energy recovery" for a more complete report.

Cheers Dave

[Gerrie]

Damn! Beaten to the post by BMW! Thanks, I'll have a look at it.