Today I got a little brainstorm and thought of turbocharged cars and how turbos reuse the otherwise wasted exhaust gases increasing the engine's efficiency. After that I thought of belt-driven alternators and ACs and so on and got an idea: why not use exhaust turbines to power the alternator and AC ? I mean, it would work perfectly, right?

Clearly, I can't be the first one to think of that so maybe someone can explain me why hasn't anyone done that? It would save tons of fuel and never again would we need to compromise economy.

You can only introduce so much back pressure into the exhaust gas stream before serious engine damage and efficiency drop happens. It takes a fair bit of power to drive the alternator when it is really loaded, even more so the air con pump.

You would also have the problem of reduced energy at idle, similar to the old dynamos.

It'd probably make more sense to supplement the electrics by using renegerative braking, once the technology has matured and come down in cost enough.

or how about cats in hamster wheels chasing the hamsters?

How about running the turbocharger directly off the engine pulleys rather than using exhaust gasses??

oh,,,,, hang on.

Quite a lot has been done over the last few years to make alternators and air con pumps more efficient. Alternators often have freewheel clutches, and air con pumps have really improved to the tune of being about 70% more efficient with regards to the power needed to drive them.

There is also the option to 'underdrive' the alternator and air con, by fitting a smaller crankshaft pulley.

Reclaiming energy under braking is possible, and will probably be standard a few years down the road.

Biggest MPG saver has to be your right foot though, and if you learn to 'create a safety zone' around your car, that means less braking and even more MPG.

A decent dash mounted solar cell charge panel helps as well.

Cats chasing hamsters = pulled over by RSPCA

Right... Well, thank you for your replies. I thought of low power while idle aswell. Still, it seems like a good idea. But I still wonder if anyone has ever tried that method?

How about running the turbocharger directly off the engine pulleys rather than using exhaust gasses??

oh,,,,, hang on.

Has anyone done electrically driven forced induction?

That should mean almost no lag , and the amount of boost could be mapped independently of the engine speed?

I'm sure there must be a reason why this wouldn't work , but what is it?

or how about cats in hamster wheels chasing the hamsters?

there is a paper shredder in the paper the other day that is powered by a dynamo attached to the hamsters wheel, when it runs enough fresh bedding for the hamster is created with the paper that has been shredded.

Has anyone done electrically driven forced induction?

That should mean almost no lag , and the amount of boost could be mapped independently of the engine speed?

I'm sure there must be a reason why this wouldn't work , but what is it?

they use too much power to pump the required amount of air.

Has anyone done electrically driven forced induction?

Yeah, there are quite a few different bits of kit out there:

Autospeed article

No idea how they stack up compared to traditional methods though.