Stirling engine in lieu of radiator

[aspera]

I was reading an article in Racecar Engineering and thought I'd pass along the clever idea that I read. One of the racecar engineers (speaking about a prototype Ricardo diesel engine) mentioned the idea of using a Stirling engine to power some accessories instead of wasting all that heat with a radiator. The key thing about the idea was that the intent was to decrease aerodynamic drag.

I thought this was a clever bit. First, you'd get an immediate gain from blocking the grill and then you'd get a secondary efficiency gain by recovering wasted energy to power to run accessories like an electric water pump, alternator, etc.

The only thing that I'd add to the idea is a water jacketed turbo. If you want lots of heat...that's a good place to find it!

[Piwoslaw]

There are a few threads on thermoelectrically recovering waste heat from the exhaust, for example VW Golf with exhaust thermoelectric power: +5% MPG . But maybe putting thermoelectrics on the radiator might be a good idea. I'd think it's at least as hot as the tailpipe. And aspera is right: maybe the best place to recover waste heat from is the turbo or intercooler.

[FastPlastic]

Interesting idea. You may still want some cooling, but not nearly as much. Stirling engines work off the temperature difference, so the cooler you can get the cold side, the more power you can generate.

[Big Dave]

Even a Stirling needs a heat sink. Since the heat rejection will presumably be at a lower delta-T the "radiator" would have to be even bigger.

Stirlings are awfully heavy/bulky for the power you get. They may be of value in stationary or even marine applications, but I doubt they would be worth the space/weight/cost on a land vehicle that rarely operates at over 50% of rated power.

Again, a technology that has not been widely used for good reason.

[Frank Lee]

Where does one get a Stirling engine?

[FastPlastic]

Can't say I've seen anyone selling a big one. Only ones I've found were little models like this one "The Stirling Design External Combustion Engine". For the most part they are relatively simple machines. So I'm guessing it's more of a, you need a big one, you build it.

[aspera]

Originally Posted by Piwoslaw

There are a few threads on thermoelectrically recovering waste heat from the exhaust, for example VW Golf with exhaust thermoelectric power: +5% MPG . But maybe putting thermoelectrics on the radiator might be a good idea. I'd think it's at least as hot as the tailpipe. And aspera is right: maybe the best place to recover waste heat from is the turbo or intercooler.

Thanks for the link. It looks like engineers are all working on ways to delete alternators and/or recover waste heat energy. Thermoelectrics on the radiator sounds like a good way to get a relatively constant difference in temperature, but much smaller than the difference between EGT and ambient temp.

One thing that came to mind in the other thread was the cost of the parts. Manufacturers would save loads of money if they didn't have to put alternators on engines. That's a lot of weight off the nose of the car, too.

[Christ]

I don't know about alot of weight... most alternators are in the <20# range, aren't they?

I can see how it would save money, because of the "complex" electronics that are used with alternators, and of course, it would save drag on the engine, and make the "total package" more compact, so there is really no reason to *not* get rid of the alternator.

[ConnClark]

A Stirling engine won't be a good replacement for a radiator. There are several reasons why. First it will act as a layer of thermal resistance to the cooling system of your other engine which can lead to over heating. Secondly your thermostat isn't open all the time and tends to release hot coolant in pulses (Stirling engines are only efficient with a constant supply of heat). The problem with the extra cooling area has already been mentioned.

Stirling engines work best with constant heat supply and a constant load at a constant speed. The best place for a Stirling engine to recover heat energy from would be the exhaust.

This company makes a Stirling engine however I doubt you can afford it. Infinia Corporation
I applied there for a job last year.

[Bicycle Bob]

The Stirling was much improved, but rendered more mysterious, in the free-piston type. Now, the latest development is the thermoacoustic Stirling, in which the only moving part is a magnet, and efficiencies are up to 30% - close to the Carnot limit using normal burners. It would not do that well on exhaust, already cooled by expansion, but it looks better than many other techniques. The motors consist of heavy tubing with heat exchangers at each end, with careful shaping and a magnet and pickup coil in the middle.