Exhaust Driven Alternator

[Viturro]

The turbo-alternator isn't a good idea, if you want more efficiency for a N/A engine you should make it normal turbo, and if your car is turbo the restriction of a high rpm/low force alternator isn't good either at 100%, now if you put the alternator in the turbo, well you could have better efficiency of engine less pressure on exhaust means better performance on engine.
And about BMW i know that in the 2010 m5 there was a electricity generator taking heat form the exhaust.
The temperature idea is cheaper and more efficient i think, but its expensive.

[Varn]

I want to pick your brain about this, oil pan. I know what I am going to ask is a bit off this topic.

So by increasing boost you get lower exhaust temps? You mentioned in another thread that you got something like 3 psi at 60 mph and that gives you several hundred degrees less exhaust manifold temps? How does that work. Besides measuring it do you have a theory about it?

Originally Posted by oil pan 4

If you really want to do something with all the heat going out the exhaust on a typical vehicle get a diesel and put a turbocharger or 2 on it.
Before I turboed I saw EGTs in the 1000'F to 1100'F all the time, now they rarely go above 800'F and normally stay between 400'F and 600'F.
These are all preturbine temperatures too.

[oil pan 4]

The diesel cycle starts off with isentropic compression, then some constant pressure heat addtion followed by isentropic expansion.
With the isentropic compression and expansion and constant pressure heat addition that means the more air you can stuff into the engine the better off the entire cycle is for making both power and effiency.
You can do this with a supercharger to some degree, very well with a turbo and some what with water injection or with a mix of them.

3 psi doesn't sound like much. Where I am the pressure is about 12.5psia.
By adding 3psig at 60mph that is putting almost 25% more air into the cylinders of my air loving diesel engine.

[Varn]

Seems like the ∆p should be proportional to the ∆T. I am not arguing, just looking for clarification.

Am hoping for some analysis as to why there might be 70% reduction in total temperature with only a 24% increase in compression pressure. Does that mean your engine gets 51% more efficient?

Perhaps your thermocouple is a bit skewed? Wouldn't the numbers go from say 1000°F to 650°F?

[oil pan 4]

My results are very typical of what happens anytime a turbo install is done on a non-turbo engine.

[Air-Hybrid]

The attitudes through the thread are that gas sped only really slows when hitting a turbine, but not for a heat-exchanger.
I'm not saying that's wrong, but I just don't get why folks think (or seem to imply) that a heat-exchanger in which the exhaust-gas temperature drops considerably does not also look like a major restriction (hence back-pressure) to the engine? ... what am I missing?

Whether a hot, fast-moving gas stream comes up against a whizzing impeller, or it travels through a tube-boiler (or similar) the gasflow will be diminished as it exits... won't it?

[Nerys]

the biggest problem with any sort of alternative charging methods is POWER demands. most moderns cars simply demand too much power.

I was thinking about and still might try and use the exhaust to charge my car but not in the way you might think (too expensive for my budget right now but working on it theoretically at least)

First low power car. namely my geo metro and my geo tracker. they already only have two pulley driven items. water pump and alternator.

First ditch the water pump in its place an electric water pump (not nearly as power hungry as you think 6amps and you can REALLY cut that back since its made for a V8 engine!!) I bet at 2 amps it would still be more than we need for out little engines.

second alternator. ditch it. now how do you charge. well first of all if you REDUCE Power consumption enough you might not even NEED to worry about charge. just install a second battery both deep cycle and be done with it. plug it it when you get home. in the summer a geo metro I estimate can go a week between charges depending on how much night time driving one does.

that brings up THE LARGEST power draw in the car short of the starter and the regular "keep alive" systems. LIGHTS. a single brake light is 21-27 watts of power !! 2 amps. how many BULBS are in your car again? do the math. its HUGE. so just replacing all your bulbs with LED will bring your total demand lighting down from HUNDREDS of watts to a few watts.

the last don't forget the interior light and all those little but VERY power hungry dash bulbs !! (I am at this stage now working on replacing all the bulbs)

next up HEADLIGHTS. this one is a lot trickier. getting enough lumens from 10w led's to see on the highway is chidishly easy and cheap.

what is NOT so easy is getting the right "optics" to create a usable and SAFE for both you and other drivers BEAM pattern. this is the hard part. once we solve this now your chewing 20watts low beam instead of 100 watts !!!

so how do you replace the charge? well I got 2 30watt amorphous (red) solar panels. these work in low light !! so more charging. one on the roof of each car (easy on the tracker with its flat room have not checked fit on the metro) that takes care of some of the power that panel will make me 300 watts of power every day. in fact it alone might be enough save for the blower motor (big power pig)

so my last thought was MAN all that HEAT going out the exhaust pipe. can't I USE that somehow. and then it hit me.

Peltier Coolers !! we use them overclocking computers. they create temperature gradients when you apply power to them (one side gets hot one side gets cold and you dissipate the hot side to keep the cold side colder)

these ALSO work in REVERSE !! if you HEAT UP one side and "COOL" the other side and create a temperature gradient YOU GET POWER out of them. ie they are generators.

think about making your exhaust pipe SQUARE and lining the bottom with these Peltier's with cooling fins in the air stream below the car. that is one heck of a temperature gradient.

the trick is finding affordable Peltier's that can handle those kinds of temperatures. SO exactly how HOT does the exhaust get ?? As soon as I find my ir thermometer I will find out :-)

now your turning your exhaust heat into power back into the battery WITHOUT blocking or restricting the exhaust at all. don't forget your zener diodes so the battery does not drain down POWERING the Peltier's :-)

that is where I am at in the theoretical department for now.

ideas ?

[Varn]

Trust me you don't want an electric water pump. They are about 10x less reliable. A few seconds without them and you have a toaster.

They work for drag racing but for they do not operate proportional to the the engine speed or power. Just droll along.

I had one on a V8 Fiero and it worked until you really got on it for 30 seconds then the temps came up. Had a terminal fall off the relay and oops I look down and the temp gauge is pegged.

Go for it if you want to re-invent the wheel.

Probably the biggest draw on a more modern car is the computer system and ignition system. Brake lights are on what 5% of the time headlights yeah you have to have them. Starter, use what 2400 watts for 5 seconds. That is not a big deal.

Looking for economy from electricity get an old school diesel.

[Nerys]

its simple really. if the electric pump dies the car does not explode. remember this is a 1l 3cyl engine and a 1.6l 4cyl engine.

I simply get out and put the belt back on. problem solved.

the water pump and alternator from what I understand on a geo metro consume 15-18% of the engines power (less on the larger tracker engine)

thats a pretty big GAIN.

the point of lowering the power is not to increase mpg by reducing alternator drag but to ELIMINATE the alternator and water pump drag all together and make the power consumption low enough that "charging" the battery is convenient and not a hassle.

electric motors DESIGNED right are extremely reliable. if you had reliability issues you had crappy motors.

maybe your race car would be a toaster without its pump for a few seconds but I can go several MILES with no damage in a pump failure scenario in a metro. plenty of time to realize something is wrong stop and fix it.

I was THINKING about dual pumps for redundancy but they are so stinking reliable it should not be needed especially since I can always just put the belt back on as a backup.

[Viturro]

N/A engine exhaust temp... around 700º C and lower close to the exit.
BMW use that thing Nerrys, on the m5 on 2011 i think. but like in the midde of exhaust like at 200º or 100º.
Seedbeck effect.