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WARREN, Michigan (AP) -- The stinky, steaming air that escapes from a car's tailpipe could help us use less gas.

A thermoelectric generator like this could be used to convert exhaust heat into energy.

Researchers are competing to meet a challenge from the U.S. Department of Energy: Improve fuel economy 10 percent by converting wasted exhaust heat into energy that can help power the vehicle.

General Motors Corp. is close to reaching the goal, as is a BMW AG supplier working with Ohio State University. Their research into thermoelectrics -- the science of using temperature differences to create electricity -- couldn't come at a better time as high gas prices accelerate efforts to make vehicles as efficient as possible.

GM researcher Jihui Yang said a metal-plated device that surrounds an exhaust pipe could increase fuel economy in a Chevrolet Suburban by about 5 percent, a 1-mile-per-gallon improvement that would be even greater in a smaller vehicle.

More... (http://www.cnn.com/2008/TECH/science/08/10/tailpipe.power.ap/index.html)

As I understand it, exhaust fumes contain a decent amount of unburnt fuel too. Why can't we just build engines that are 10% more efficient? Maybe more horsepower isn't always the answer?

... A thermoelectric generator like this could be used to convert exhaust heat into energy....

I want a wood pellet stove with this TEG to power the fans and auger, so that the stove can run during electric power outages or even off-grid. There is a paper demonstrating the concept with a modified stove, but I have found no indication that it was ever turned into a retail product.

If it's this durable then why wouldn't it work on the roof of a house?

If it's this durable then why wouldn't it work on the roof of a house?

Neither the temperature difference available at the roof, nor the power density (sunlight is about 1kw/(meter^2), is high enough to get anything significant out of this. Solar photovoltaics and solar thermal water collectors are far more efficient and practical for roof use.

Didn't even glance at the article, but using a Stirling engine to generate electricity from engine waste heat has been in my mind, as many others, for a while.

Unfortunately, most hypermilers use the engine so sparingly that we need to *keep* waste heat in the engine to keep it warmed up and running efficiently!

Maybe we could use exhaust heat to turn a turbo, then use that to turn an air compressor, then pump that air back into the intake. Oh, sorry, already been done.

Heat is energy. Realize that trying to harvest it could cause excessive backpressure and negate the increase in fuel economy.

I think they need to reinvent the ICE. This is way old technology and all we've done is make it more efficient than the original design.

I looked up those TEG's before and are quite expensive to get them with a decent output. Definitely worth tinkering with though! I also looked up turbo alternators and they are only in their infancy. As far as i can see, getting an alternator to spin as fast as a turbo is a stumbling block. I would imagine the electronic end of it is more or less the same as an existing alternator. Can you imagine one of these in a prius, providing permanent power to the IMA......three figures mpg all day! With some tinkering with the software of course...

ollie

As I understand it, exhaust fumes contain a decent amount of unburnt fuel too.I thought the EGR was supposed to take care of that...maybe the EGRs need improvement?

Presumably they would just coat the outside of an exhaugst pipe to capture some of the energy that would have just been wasted. No additional backpressure, doesn't cool the engine, and produces some electrical power after the engine has shut down. Could be useful in a hybrid/PHEV situation.

THe egr reduces NOx emissions and re-introduces some of the combusted mixture back into the air stream. It doesnt reintroduce all of the unburnt fuel but only a percentage. I have a feeling you could improve efficiency somewhat if this amount that is reintroduced could be increased. Of course that reduces overall power but it increases economy and emissions.

...I think they need to reinvent the ICE. This is way old technology and all we've done is make it more efficient than the original design.

A few years ago I saw some discussion about abolishing the cam shaft and running the valves electrically. The research was starting with large truck engines, and gave no indication when it might migrate to our cars.

If this were to be combined with abolishing the throttle valve (power control would move to the cylinder valves) and some taller transmission gears, then we could get all the benefits of P&G with ordinary constant-speed driving.

A few years ago I saw some discussion about abolishing the cam shaft and running the valves electrically.

The problem with that is that it's a marginal improvement to a fundamentally inefficient engine. (Which, to make matters worse, is usually running at less than its optimum efficiency.) IC engines are limited by their basic thermodynamics (see Carnot cycle), so to get major efficiency improvements, you have to go to either a Stirling engine or a gas turbine.

The problem with that is that it's a marginal improvement to a fundamentally inefficient engine. (Which, to make matters worse, is usually running at less than its optimum efficiency.) IC engines are limited by their basic thermodynamics (see Carnot cycle), so to get major efficiency improvements, you have to go to either a Stirling engine or a gas turbine.

You also periodically hear about research into using a modified Stirling engine to tap power from the exhaust heat, but practical implementation is always just around the corner. The Stirling engine powered fan we have for our wood stove doesn't seem particularly efficient. I hope this development pans out, but I'm not holding my breath.

Does anyone know if there's any kind of like... video rental store but for books? Amazon is getting way too expensive for my book habit.

Oh yeah, doesn't a turbo already use the cars exhaust for power?

The problem with that is that it's a marginal improvement to a fundamentally inefficient engine. (Which, to make matters worse, is usually running at less than its optimum efficiency.) ...

And that "less than optimum efficiency" is part of the reason for going to electric valves. It would allow nearly infinite variable valve timing.

I'm imagining that electric valves, combined with wider transmission gearing, direct fuel injection, and no throttle restriction, Pulse&Glide-like efficiency could be built into the automatic engine controls. Atkinson cycle / variable displacement becomes a software matter, so the sweet spot of the BSFC (brake specific fuel consumption) graph used in Pulse mode could be moved around and geared to match the current steady-state load, and Presto! Automatic P&G efficiency without user intervention, and no Glide needed.

Those nasty part-throttle pumping losses would be gone too. On my Subaru, that is 4 kilowatts (5+ horsepower) at 60 mph, doing nothing except create manifold vacuum.

Of course, the public might have to get rid of its normal expectation of lots of extra power or torque instantly available even in the highest possible gear. My imagined control scheme may require downshifting several gears in order to get high power.

Stirling engines are more efficient, but have they reached the power densities that we need for automotive use?

And that "less than optimum efficiency" is part of the reason for going to electric valves. It would allow nearly infinite variable valve timing.

But it still amounts to putting lipstick on a pig :-) The IC engine is limited in its efficiency by the laws of thermodynamics: nothing you do can improve it beyond that limit.

The idea of capturing energy from exhaust gas isn't new: it was used on some WWII aircraft engines: http://en.wikipedia.org/wiki/Turbo-compound_engine Never went very far because, as the article points out, it was more efficient to eliminate the IC engine and just run the turbine.

IC engines aren't used in cars because of their fuel efficiency: it's because they have the torque & acceleration needed. Once you have an electric-drive hybrid, you can replace the IC engine with a more efficient type, and greatly increase mpg even before you take into account things like regen and grid charging.

Stirling engines are more efficient, but have they reached the power densities that we need for automotive use?

Ford had Stirling engine powered cars running in the '70s: http://www.time.com/time/magazine/article/0,9171,904117,00.html Chrysler also had gas turbines in cars, but they weren't designed for fuel economy.

PS: It's interesting what you can find out there in cyberspace. Seems like GM had experimental prototypes of the Stirling engine hybrid I described - in 1969! http://www.cheersandgears.com/forums/index.php?showtopic=19742

jamesqf: But it still amounts to putting lipstick on a pig :-) The IC engine is limited in its efficiency by the laws of thermodynamics: nothing you do can improve it beyond that limit.
----

But that limit is still much higher than we are achieving now in ordinary automotive use.

Wikipedia answered my question with this line: "The main difficulties involved in using the Stirling engine in an automotive application are start-up time, acceleration response, shut-down time, and weight, not all of which have ready-made solutions." Some successes are listed, but it is clear than Stirling engines are not yet good enough for us to abandon other lines of improvements to the pigs we know as Internal Combustion Engines.

At least free air con should be an easy product of this waste heat...
Instead of venting engine bay and losing heat from exhaust to atmosphere it could all be hermetically sealed and 'collected' via something like a exhaust heat exchanger like on a boat... and passed along a surface at/below the front bumper experiencing high windage/cooling...where the temperature differences would be at a maximum?

Is lightning a thermoelectric charge?

Is lightning a thermoelectric charge?

No

"The main difficulties involved in using the Stirling engine in an automotive application are start-up time, acceleration response, shut-down time, and weight, not all of which have ready-made solutions."

Sure they do - the solution I described, and which GM was working on 40 years ago. Electric drive, with the engine driving a generator. That way the Stirling engine's startup & shutdown time and acceleration no longer matter, while weight reduction is just a matter of engineering.

... while weight reduction is just a matter of engineering.

I am an engineer. I've heard this phrase many times. It is often used to hide serious obstacles, including economic obstacles (cost) that render elegant or technically feasible solutions dead-on-arrival.

I am an engineer. I've heard this phrase many times. It is often used to hide serious obstacles, including economic obstacles (cost) that render elegant or technically feasible solutions dead-on-arrival.

C'mon you know its true, you are all just lazy , next time you design a car make its entire chasis out of carbon fiber and magnesium wheels and small titanium block. oh , and make it for less than $20K , you lazy lazy engineer :p:rolleyes:

ICE can be improved tremendously, car design can be made smarter, safer, engines can last longer, but what would be the profit there ? what car manufacturer will spend 1 billion dollars to make a car that will run forever, no one, because that means they will not make money anymore by having new models to replace those ageing 10 year old cars.

HUMANITY IS UNITED, GREED ABOVE ALL. don't you all forget that. :(

ICE can be improved tremendously...

No, it can't. Just like computer chips can't be made smaller forever. At some point you run up against the laws of nature.


...what car manufacturer will spend 1 billion dollars to make a car that will run forever...

Honda? Toyota? Maybe not "forever", but for a lot longer than what comes out of Detroit.

HUMANITY IS UNITED, GREED ABOVE ALL. don't you all forget that. :(

Nothing wrong with greed. The problem is short-sightedness. The greedy but far-sighted manufacturer will invest in making quality products, because that generates customer satisfaction and more business. For a real world example, compare the past business practices and current income of US vs Japanese automakers.

Nothing wrong with greed?
I think its one of the deadly sins along with gluttony, vanity, jealousy, sloth etc etc
The movie who killed the electric cars shows the link between oil companies, manufacturers and state. Our green party leader till last year drove a mid 80's mitsubishi mirage on cng (compressed natural gas) which has since been phased out because of pressure from above. It was half the cost of petroleum, and free loans were available to get it installed...And our cars in NZ got bigger since the 70's.

Buckminster Fuller did a way cool car in the 50's that trashed all comers for ecomony and performance. It looked like a falling water drop and was a 3 wheeler.

The car is fundamentally the buggy without the horse, and often even now still looks the same.

Andre Citroen, the pioneer of the front wheel drive car and making serious MPG initiatives, got into financial problems.

Greed has got a lot to answer for.

fullers 1933 dymaxion car here: http://en.wikipedia.org/wiki/Dymaxion_Car

Nothing wrong with greed?
I think its one of the deadly sins along with gluttony, vanity, jealousy, sloth etc etc

That's your religion, not mine.

Greed has got a lot to answer for.

In all those examples, the root problem is not greed, but short-sightedness. Take for instance GM and the EV1. Suppose that instead of killing the project (for whatever reason), they had instead kept working it, and started selling electric & hybrid vehicles. Would the company be on the verge of bankruptcy today? Suppose even that they had put some thought into ways of making decent profits off small, fuel efficient cars, instead of short-sightedly tying their company to gas-guzzling SUVs and pickups? Wouldn't they now be making a lot more money? If they were really motivated by pure greed, wouldn't they have wanted to do this?

That is actually one of the characteristics of greed -- short sightedness. At least that has been my observation. Pure greed just can't see that far ahead -- it is an overwhelming urge to go after what is seen here and now.