VW Golf with exhaust thermoelectric power: +5% MPG

[Big Dave]

Just another scheme to separate the rubes from their money.

You'd be able to give your vehicle the "basjoos treatment" for less money and you know the "basjoos treatment" works.

[ConnClark]

Originally Posted by jjackstone

Actually if I recall, from MetroMPG's and other's posts, the alternator disconnect has been showing about a ten percent gain in overall FE. Please correct me if I'm wrong.

MetroMPG's car is so optimized he could go on a diet and loose 5 pounds and get a 10% improvement. His results in magnitude of improvement are not typical gains for an average car.

The TE generators do work but as has been stated are highly inefficient-- unless a newer technology has been released, they are generally between 3-5% efficient.
Doesn't matter what gear the vehicle is in, just the temperature differential between the "cold" side and the "hot " side of the junction.

Driving in first at high rpm is the best way to heat up the exhaust. The car is burning the most fuel it can in a given time and the engine is under the least load, hence the pistons are extracting the least power from the combustion gases and the hotter the exhaust gases.

Actually winding a car up in neutral at full throttle would be better for heating the exhaust but you would probably throw a rod.

[jjackstone]

Does this mean thermoelectric exhaust generators as these, work better in cold climates?

Probably not a whole lot unless that cold air is directed to the TE junction. We're talking about temperature differentials of a few hundred degrees C in general(once the car is warmed up).

Driving in first at high rpm is the best way to heat up the exhaust. The car is burning the most fuel it can in a given time and the engine is under the least load, hence the pistons are extracting the least power from the combustion gases and the hotter the exhaust gases.

Alright, I'll give you that one, but I sure wouldn't want to be driving around in first gear all day
JJ

[roflwaffle]

Originally Posted by MetroMPG

Tim: you're right, their figures don't add up. 600w production in highway use, yet they're claiming that offsets 30% of power needs. Which means the car needs 2000 watts to drive down the highway? Don't think so. Their figures need explaining.

Maybe the clue is "600 W(e)". What's (e)? I haven't seen that before.

The thing is that the output in city driving is probably a lot less due to lower average power output and a small difference in temperature. The 600W is probably max output on the highway with the average output around 100-200W.

Originally Posted by ConnClark

MetroMPG's car is so optimized he could go on a diet and loose 5 pounds and get a 10% improvement. His results in magnitude of improvement are not typical gains for an average car.

The thing is alternator energy efficiency, like ICE energy efficiency, isn't linear AFAIK, which is why we're seeing things like dual-speed alternators, and the like. If this thermoelectric system can replace lightly loaded and inefficient alternator operation, then it could very well increase fuel efficiency by ~5% since the other 5% is when the alt is more heavily loaded and more efficient. It also depends on the manufacturer's alt operating parameters, which may be more efficient for a compact car that's focusing on efficiency light a Metro or Civic CX/VX as opposed to a car that focuses more on other stuff.

[rmay635703]

Originally Posted by ConnClark

I don't buy it. It may get 600 Watts running flat out

This is just sensationalistic marketing hype.

What happened to this guys idea.
Johnson Electro Mechanical Systems

Anyway, There are already Chinese 250 watt per sq. foot thermjunctions for sale although they need a temp difference of about 400C & 25C to operate near that (never bought one, maybe they lie)

I agree with roflwaffle...
I would not doubt a 5% mileage gain, many alternators are not real efficient across their range; couple the belt and frictional losses that should be childs play to get a 5% increase with smarter alternator management.

[ConnClark]

Okay here is the smell test on the 5% mileage improvement.

600W = 0.805HP

If it takes less than 17HP to operate a car the claims might be valid.

Note: This system only supplements the alternator and doesn't remove it.

[Daox]

Keep in mind the alternator is only roughly 50% efficient. So, in order to generate 600W, you need to generate 1.6hp.

[beatr911]

Nice work VW.
It always amazes me how these brilliant engineers pull a rabbit out of the hat every few years. Vehicles have come such a long way.

[ConnClark]

Originally Posted by Daox

Keep in mind the alternator is only roughly 50% efficient. So, in order to generate 600W, you need to generate 1.6hp.

Good catch. So that would raise the bar to 34 HP. However it forces the alternator to operate in its lower efficiency range which would reduce the net savings.

[rmay635703]

Originally Posted by ConnClark

Good catch. So that would raise the bar to 34 HP. However it forces the alternator to operate in its lower efficiency range which would reduce the net savings.

I have often wondered why the alternator isn't just cycled on when it would be at its most efficient range then cycled off when it won't be. Sure your battery would experience some small discharge/recharge cycles but I would think the efficiency gain would be enough to justify slightly lower battery life.

Perhaps its time for battery management on cars?