Exhaust Driven Alternator
 

Reading over this article, Browser Warning

It dawned on me, why not drive the alternator with exhaust gas instead..
Similar concept to a turbo charger, except just use the velocity of the exhaust in a carefully designed generator system to drive charge.

For mainstream use it'd have to be able to recover the entire starting current draw within some short time of idle..

not sure it would be wise to have the electronics near something that hot, so you'd have to have a turbo belt system that connected the "exhaust to rotational velocity" piece to the alternator which adds complication and cost to the system.

Not sure why this is in the Unicorn Corral. It has been discussed in other forums on this site as well.

I'm not sure how useful it would be, but it at least has potential to help. It would be interesting to see how the efficiency of the engine is affected by the exhaust restriction, and how quickly it could help recharge the battery.

-soD

I can't imagine how it would help. You'd have to put such restriction on the exhaust to build up enough pressure that the engine would start burning a fair amount of fuel just to compress/pump the exhaust. Energy is energy. Maybe rethinking the alternator efficiency is a better idea?

Yes I did pose the question of what is the most efficient new alternator last month.

ps the best ive found was on a scca car and its belt ran off the rear axle of a mustang.
Not sure about water intrusion issues would just blow the diode im sure.

FYI I have seen one working off the turbocharger on a big rig a one off 10 years ago

Turbocharged cars seem to be able to use the compressor to stuff more air in without prohibitive amounts of restriction on the exhaust. I could see there might be a way to make it work.

The biggest problems would be heat, and gearing the 100K RPM of a compressor wheel down to something that a standard alternator or generator would work reasonably with.

Could be insurmountable problems, sure. But I don't think that warrants including this in with all the other unicorn poop.

-soD

Cars need [in many cases, for optimum use] back pressure. And as soD said, turbo charged cars do fine with it. Well, more than fine lol

As efficient as the driveline/axle alternator would work, it still slows the car down. This seems pretty brilliant, since the exhaust happens when the engine is on.

actually thats not a bad idea use a system like the volt, hybrid tech not drive. have an I4 turbo diesel powering two HI output "exhaust driven" alternators. The alternators then power the electric drive of the vehicle. the obvious problem is heat to help this issue 2 generators would be used if more power would be needed the rpm of the diesel motor would be ramped up

no, back pressure is bad almost always
 

..."Cars need [in many cases, for optimum use] back pressure"...

engines ?
do not need back pressure in the exhaust , less back pressure is always better (except during decel)
which is one reason some users of
engines
use
headers , to minimize and or completely eliminate exhaust back pressure at certain
designed for rpm / load conditions

but
on decel
back pressure in the exhaust is irrelevant OR desired for braking purposes
and the engine intake has high vacuum during decel , so it would be easy to use vacuum to switch a valve to direct exhaust flow to spin an alternator
during decel only

actually how about the absence of pressure to spin the alternator, use the vacuum from the intake to spin the generator there would be no lag because there would be no restriction on the exhuast side. once it overcomes the restriction it operates like a normal motor.

That would put some large pumping losses into the intake. I'd say probably not worthwhile.

-soD

only during decel
 

An alternator doesn't produce a constant power. It varies according to demand.
So it would create a varying restriction in the exhaust, which would impact the engine's power.. and probably noise output.

A few years ago BMW was developing a steam-driven alternator to be heated by the exhaust as an attempt to recover some energy. That might work in a hybrid...

This idea has been discussed, quite rationally on the main boards already...

Does-tigers-turbogenerator Work?

The main issue is this:

exhaust turbine=expensive
alternator belt= cheap

Wouldn't even say that's the main issue. The main issue is that for anything other than a hybrid, it's going to generate way more electric power than the car can use. A typical alternator might put out a maximum of around half a kW, but only a small fraction of that most of the time. Even with lights on, a car might only use a couple of hundred watts, if that.

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.

Popular Science - Google Books page 82

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.

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?

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.

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?

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

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?

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 ?

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.

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.

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.

Whether a manufacturer decides to install Seebeck devices, a 'turbosteamer' setup or a turbo-generator, there will be some increase in back-pressure as heat is turned into work during the exhaust gases' journey to the tailpipe.
The TIGERS system utilises a bypass valve for when the motor is at part-load operation, so the back-pressure is not strangling the engine.

I think any vehicle design would need to be at least a 'mild hybrid' for a turbo-gen to make sense, but it would have to be seen how much additional cost it would be incurred relative to the lifetimes fuel savings. ... it seems to me that it could somewhat improve a hybrid's highway economy; and the same may be true for large trucks (without being hybrid, even) as they are pulling under load for much of their operation.

At what temperature is a catalytic converter designed to work?

True, but electrical connections and components multiply the number of failure points, and anything that moves or vibrates is liable to problems from that (e.g., fatigue). There is pretty much just one failure point for the drive on a conventional water pump--the belt. There can be quite a few for an electrical pump; every connection, the relays, the switches (if any), whatever controls you have on the system, etc.

You won't damage the engine if you notice that the pump is no longer working. Most people (including me!) are going to miss that for a while at least. So you need to rig up some sort of very unambiguous signal, like a loud chime or a big light, when the temp gets to a certain point. If you rely on a gauge, the one time you will need to pay attention to it you will miss it. (Murphy's law.)

An electric pump could be a win, but you would need to make the system at least somewhat fail-safe. And you'd need to pay close attention to the design and fabrication of the electrics.

IMHO.

-soD

Several hundred degrees Celsius, I imagine.
But (and I assume this is where the question is leading), the ability once hot of the Cat' to remain in the "light-off" temperature zone is dependant on how the levels of incompletely burnt HCs in the exhaust gas as well as it's overall temperature.
With a correctly designed system that includes a bypass valve, a turbo-generator should be perfectly capable of operating effectively without overly cooling the cat' downstream.

I run electric pumps and don't see much benifet over belt driven ones.
The only time the electric pump would shine is if you had an alternatorless power system that provided all the free electrical power you needed.

So unless you have a really good alt delete setup already well tested, up and running don't bother with an electric pump.

It's usually quoted to be from 500 to 650.

I'm not totally certain on whether a cat' is cable of being able to work to the best of its ability once it passes the 'light-off' temperature, but 'several hundred degrees Celsius' is not a bad fit for most vehicles' light-off point.
Unless there are practically no COs or HCs present in the exhaust I believe the cat' temperature is self-sustaining; plus if adding an exhaust turbine presents problems in holding the heat up enough, can't exhaust wrap be fitted?

...er, new 5 years ago based on the article date.
BMW did a similar experiment, but neither system is very near being fitted to production vehicles so far as I know. ~ Steam system are heavier and more complex than a turbo-generator; nothing that I've seen seems to point to them being of any greater efficiency either... ??

Just adding a turbo charger will add 30 to over 80 pounds depending on the application.
Adding a Rankine cycle would add much more weight for small gains.

For example classical boiler design calls for 10 to 12 square feet surface for each horsepower you hope to generate with a Rankine engine.
My turbocharger and added piping weighs about 60 pounds and generates about 40 horsepower worth of compressed air the way I use it, but I only use about 1/3 its max rated output.
The turbocharged diesel has no problem producing 2 to 3 times the horsepower and 10%-20% better fuel economy over an N/A diesel.