Explain intercoolers to me

Factual Questions
1

More to the point, explain air-water intercoolers to me. I understand the basic concept behind an intercooler, that of taking air from the turbo, and routing it through a radiator-type thing prior to feeding the engine, so as to reduce the temperature and give the engine more dense air.

Incorporating water seems like a logical way to help lower the temperature, but since no water can get into the engine, how is this accomplished? From what I’ve been able to find online, it seems like the intercooler itself has a case built around it, and water is circulated through this case. Is that even close to correct? Any good sites with descriptions or diagrams?

As long as I’m on the turbo topic, how bad is it for a turbocharged vehicle to drive through a few inches of water? I know turbo’d cars should be left at idle for a little while before shutting them off so the turbo can cool more evenly, and it seems like firing water up on it would be worse than immediately turning it off.

2

Okay, an intercooler is just a small radiator, just like what cools the engine itself. There’s a “manifold”, or “plenum” at each end, connected by a row of a bunch of small tubes (to give greater surface area) through which the water flows.

Water flows through the tube, the air passing over it carries off some of the heat, cooling it. The cooler water leaving the other end then goes on to cool the engine, and it carries that heat back to the radiator to start it all over again.

Now, take that same radiator- basically-and put a water-tight duct around the tubes, so you can run water through where the air used to go. Then just run your turbo-air through where the water used to go.

It really is just that simple.

The act of compressing the air- as in the turbocharger compressor stage- heats it up, and that heat reduces the intake charge density (which is exactly opposite to what the turbo is trying to do in the first place.)

The intercooler takes away that excess heat, making the charge air denser, providing more power.

As for letting the car idle for a while, the “cooling down” has to do with the impeller bearings in the turbo housing. The impeller is force-fed pressurized oil that both lubricates the shaft (which can be turning 100,000 rpm at full scream) as well as cools it.

If you blew right in from the freeway at sustained 80MPH speed, power-slid into the driveway and then immediately shut the car off, the turbo would still be smokin’ hot, but has now lost that cooling oil in the bearings.

The oil that’s in there basically cooks- it breaks down and carbonizes from the heat (1,200 degrees F isn’t impossible.) And naturally, this carbon “coke” is not good for either the turbo or engine- when you go to start it up next time, the bearings are scored by the debris, and then flushed into the engine.

Do this for a couple of weeks during your commute and the bearings get rapidly destroyed- the turbo begins to leak oil into the exhaust and pressure stages, the impeller won’t spin as well, reducing power, and could simply seize up. Impeller seizures tend to be catastrophic failures, by the way. :smiley:

3

This true for a standard engine set-up, but on a side-note,(and nothing to do with your question) the extreme demands of WWII piston-engine planes led to the introduction of injecting a methanol/water “anti-detonant fluid” mix directly into the intercooler - only used for short bursts of power, like take-off or combat. (The methanol stopped the water freezing)

Some of the planes from that era are still being raced today at places like Reno. The races are short enough for the planes to carry sufficient anti-detonant mix for the entire flight, so many have the standard intercooler matrix removed and all the cooling done by dumping huge amounts of ADI fluid in via a spray bar. This means less restriction in the intake flow, and no need for the drag of an external radiator. IIRC these are called “Tube” intercoolers, and it leads to the planes leaving a trail of stream in their wake (water may also be sprayed onto radiators, oil-coolers and even directly onto the cylinders of air-cooled motors!)

4

the purpose of cooling the intake air is not only to increase air density and thus power, but also to prevent detonation.

detonation occurs when the air/fuel mixture in cylinder gets so hot it ignites spontaneously before the spark plug fires.

detonation is BAD. it lowers power, it sounds nasty and it is damaging to the engine i believe. higher octane number ( 93 vs 87 etc ) fuel is less likely to detonate, thats the purpose of having these numbers.

this is the reason ( among other things ) why you can’t just slap as much PSI compression as you want on an engine, because more PSI means more extra temeprature and you’re getting closer to detonation.

5

i have also read that air-water intercoolers are not as good as ones that just use air, and no water.

but i have absolutely no way to verify this claim :slight_smile: