wjbell

Need some opinions here... I have a couple small peltier devices out of a water cooler with some nice heat sinks and fans... I was thinking the flat top of the stock air horn would make a good spot to mount one.

My main question is, do you think the heat from the engine transferring up the intake and meeting an extremely cold spot where the peltier is would stress the metal and crack it? I drove the truck around a bunch today then popped the hood and felt the top of the intake and it wasn't too warm, of course today was a cool day. But the cold side of the peltier is very cold. Probably below zero.

Second, do you think a peltier would eventually spread the cold through enough of the intake body to make a difference in the air passing through it?

And what is the intake, cast aluminum?

XLR8R

The intake horn is cast aluminum - an excellent conductor of heat.

Any thermoelectric refrigeration module mounted to it would not be able to create a localized heat sink capable of creating significant thermal stresses in the alloy on an intergranular scale.

Your 2nd question hinges on the BTU equivalent rating of the TEC(s).

Absorbing thermal energy from the intake airhorn would lengthen it's heat-soak interval, though I'm not sure you could measure it in an empirical sense.

Besides, you won't have a closed loop thermal transfer mechanism - where do you think the Peltier will reject heat to?

Also, a CTD achieves highest BSFC at intake air temps of 60-90*F, thus relegating your solid-state scheme to hot weather usage - where it will be least efficient and therefore least effective.

wjbell

Thanks for the reply. I thought that the colder the intake temps - the denser the air - more energy to use. Not true?

XLR8R

Indeed - that's a great rule of thumb for most gassers, but it's a bit of conventional wisdom that doesn't translate perfectly to compression ignition engines... in a Cummins, too cool of an intake charge lowers combustion chamber temps and reduces efficiency.

Dense air is good, but not necessarily cool air - that's one of the reasons why turbochargers & diesels compliment each other so well.

XLR8R

Also, the energy is contained within the fuel, of course - the air just delivers the oxidizer required to release the fuel's thermal energy, and provides a reliable natural ignition mechanism.

wjbell

So do you think there's any room for improvement on cooling the intake air where it will make a difference or is the stock intercooler a perfect match for the engine and couldn't be improved?

XLR8R

For instance, the stock CAC on a 3rd Gen does a great job - keeping differentials pretty small (5-10*F normal driving, 25*F WOT w/no heat soak) - that's with hot side temps that can exceed 350*F.

Quality aftermarket CACs offer a marginal improvement in heat-exchanging efficiency & pressure loss.

Your TEC should fare better on the hot pipe - an ounce of prevention is worth a pound of cure:

wjbell

My intake temps after the intercooler, according to my scangauge2 (which I don't trust farther than I can throw it), are 90-110 degrees F. 110 while sitting fully warmed up at idle and in the 90's while moving. Is this a normal intake air temp?

XLR8R

Again, depends on what the ambient is - on an 85*F day, you could expect to see intake horn air temps anywhere from 5-25* higher depending on how hard you've been working the skinny pedal.

Where does your scan gauge monitor from?

wjbell

This is on a ~60 degree day driving normally. I think the scangauge gets it's temp reading from the IAT sensor... not sure though.

XLR8R

That's what I thought - our numbers are taken from an intake horn-mounted type K.

wjbell

Yeah, I figured to get real measurements I'd have to use a thermocouple in the actual air stream.

So what are the intake temps on the third gen, only 5-10 deg hotter than ambient temp with normal driving?

XLR8R

Precisely!