Intercooler: What is it? What does it do? How does it do it?
 

I had a vague notion of what it does. So I Googled for some info and found this site which offers a pretty good explanation. Hope it helps you, it worked for me.

Bot


http://www.gnttype.org/techarea/turbo/intercooler.html

You located just about the most informative site out there for turbocharged vehicles.

I didn't check the site, but my simple mind is under the impression that cooler air is denser with more o2 molecules hence more 'oomph'.

It took a lot of math and graphs to explain that to me. Now I finally got it.

It really is a detailed look at the why and how of it all.

You aeroplane guys, is that why fancy-schmancy fighter jets squirt water to boost speed? Somebody told me that one time and I thought he was FOS. Maybe not?

B

Some engines squirt water into the intake, older Corvettes could be set up for this due to the fact high octane gas is no longer available. I never heard of a turbo squirting water. There are however, water to air intercoolers in addition to the normal air to air type. To go full hog, use an a/c evaporator coil in your intercooler setup (with the a/c working of course)

Here's an account of a conversion of a Travco 440 to a Cummins turbodiesel. Instead of a 'traditional' intercooler, he snaked 22' of tubing under the front bumper where the air would flow over it. I'm inclined to think that the reduction in temperature of the air would not be that significant with that setup. Other opinions? I'd be inclined to think that an intercooler like Z's would be much more effective.

http://community.webshots.com/album/232660691ZBdqUT/4

I always thought that the reason intercooled engines had better performance is that cool air takes less energy to compress than does hot air. An intercooled engine, therefore, consumes less energy on the compression stroke. I'm pretty sure that is why multi-stage air compressors benefit from intercoolers between stages.

Colder air makes more power since there are more molecules of oxygen in a smaller space. In laymans terms, it makes a bigger boom when mixed with fuel and spark so more power is made. I'm running 50% methanol & 50% water mix as well as an air to air intercooler on my SEC to prevent detonation and to further cool the intake charge.

I belive the Subaru STI has a air to air intercooler that has a water mister device that cools down the intercooler a few degrees when it's hot out or you're really into the loud pedal. I am curious to know it's effectiveness. My WRX had a small hood mounted intercooler which was apparently efficient enough to squeeze 113.5hp per liter out of that motor. :)

Intercoolers are very common on forced induction engines for two reasons: it gives more power/efficiency as earlier explained, and it prevents detonation as the charging increases the temp of the air/fuel mixture going into the cylinders, which the IC cools. Running a turbo without an intercooler will very likely melt down the pistons.

One of the guys over on the diesel section was talking about fabricating an inter cooler for the 617 several months back. I forget his name but I think he was the fellow who wrote the good piece on putting a 2.43 rear end from an SEL into the back end of a 300D with a 3.05 rear (numbers close).

Here is some technical background about intercoolers. When you compress air or any gas for that matter it heats. There are relationships in classical thermodynamics that mathematically describe this. The one that comes to mind is the isentropic compression. If you compress air from 14.7 psia to 29.4 psia, the temperature would rise from 70 F to 186 F. You cannot let 186 F air go into your engine because it will cause the engine to knock. So you cool it through a heat exchanger. The cooling also increases the density of the charge allowing more oxygen to enter the engine and hence more power to be developed. The intercooler is an air to air heat exchanger.

Expressed mathematically, the relationship is

t2 = t1 * (p2/p1) ** 0.286

where t2 is the final temperature, t1 is the initial temperature expressed in degrees Rankine.

p2/p1 is the pressure ratio of absolute pressure

0.286 is a constant derived from the ratios of specific heat of air which happens to be 1.4. The ratio is the specific heat for constant pressure divided by the specific heat for constant volume.

So at 70 F which is 530 Rankine and a 2/1 absolute compression

t2 = 530 * (2) ** 0.286 = 646

Expressed in Fahrenheit degrees, t2 = 646 - 460 = 186 F

Note that if you use 100 F ambient air, you would get

t2 = 560 * (2) ** 0.286 = 683

t2 = 683 - 460 = 223 F

So a 30 F rise in ambient temperature causes a 37 F rise in pre intercooler temperature.

Damn, I knew I shouldn't have dropped that thermodynamics class. One thing that puzzles me, and I have no idea how to pursue an answer for this, is:

If you deposited a cylinder full of air in a 617 and it was say, twice normal atmospheric pressure but had been cooled down to ambient temperature -- would that quantity of air yield the same or greater temperature after being compressed by a merciless piston as would a cylinder full of air at the same temp but at normal atmospheric pressure?

I want to say it would be a greater temperature because the increased density of air molecules in the first case would cause a greater increase in temp than the more sparse concentration of air which is, nonetheless, perfectly good for breathing.

The change in absolute pressure in the case of a standard 617 is 21:1. The air is compressed to a volume that is 1/21 of the original volume. The temperature goes up accordingly.

In the case of this hypothetical 617, the change in absolute pressure is the same 21:1. The final pressure in the cylinder would be 609 psi, which would have blown the head right off the engine. However, if it remained intact, the change in pressure remains at 21:1. So, the temperature rise would be the same as the standard 617 if they both started at the same temperature.

I always thought it had to with an inter-office waterfountain....whodda thunk?

Water injection in a jet engine increases performance in two ways. One is the reduction in compressor outlet temperature allows for more fuel to be burned without melting the turbine. Two, the increased mass flow from the weight of the water will boosts the thrust.

I was thinking it could go either way. I'm surprised that an air density twice normal would be more pressure than the heads could handle. Don't the pressures during combustion get pretty high? Of course, there's a piston waiting to be moved downwardly by those pressures whereas duing the compression stroke, the heads can only sit there and take it.

What is the ideal level of compressed air (turbo or super) that a 617 can take? This might be toughy to answer. Then again, it is no doubt known what sort of air pressure a 617 turbo is dispensing.

After thinking it over again, I believe you are correct. When the turbo is running, the absolute pressure in the cylinder can get up to 26.5 psi, which is very close to twice the normal density. I'm quite sure that you could dial up the boost to enable 29 psi without any consequences to the head gasket.

As for "ideal level" of compressed air, I don't think there is an answer to that.
The more air you give a diesel, the more fuel you can give it and the more power it will give you. The risk is too much heat and a melted piston.

So, the ideal level of air would be the amount of air that would be just shy of melting the piston when a proper amount of fuel is delivered to that air. It's a delicate balance, one that the manufacturer must stay safely away from, because the conditions are highly variable and he must protect the engine from the worst possible condition.

There are several fellows who have bumped up the boost and the fuel on the 617, without an intercooler, and have had no issues. Of course, watching the exhaust temperature becomes a vital task when maximum power is utilized.

Interesting stuff. Part of why I ask is that I have a fantasy invention that will provide cold, compressed air for combustion and the level of compression would have to be controlled of course. Since a cooler initial temp of the air being sent to the cylinder will lower combustion heat and protect the piston, I'm thinking that if you could deliver air at say 0 Fahrenheit that was also, say, double atmospheric pressure like we're talking about, you would have nifty power considering that air that cold is going to have more oxygen per cc than hotter compressed air.

It's an ambitious idea, maybe too ambitious, I don't know. If you want to hear more, I'll e-mail you. I don't want to let this million dollar idea out to the general public. ;) (yeah, right)

It's a fabulous idea. The current crop of intercoolers will deliver air at temperatures that are about 40°F. above ambient, so the cylinder gets 120°F. air on an 80°F. day. The engine makes good power with this air.

Now, if you could deliver 0°F. air to the engine, you could really dial up the fuel and make some serious power.

But, short of taking dry ice on board with you, how are you going to get the air (lots of it) down to 0°F? Remember, it has to be useable for daily driving.
Runs at the racetrack for 1/4 mile don't count. ;)

I believe it's conceivable for a liquid to air intercooler (L2A) to [under the correct circumstances, e.g. running in a bath of ice water] deliver ambient or slightly sub-ambient charge air temps, but that's not practical for daily driving, just the track.

Hey, you could always plumb an A/C evaporator into the intake manifold...

..........damn condenser can't even keep up with the air inside the cabin..............imagine trying to keep up with 4500 litres/minute. :eek:

Ain't it the troof?

A couple of years ago somebody (I thought it was Zeitgeist) posted a link to a website in which a vortex was used to separate hot gas molecules from cold ones. Darned if I can remember what it was called.

If somebody doesn't name that device, I'll have to resort to an internet search.

B

Twasn't me, I disavow all knowledge and discourse regarding such shameful alchemy and snakeoil.

Sorry H2O2, didn't mean to imply snake-oil-manship. It may not have been this Forum. May have been one of my kuh-razy brothers.


Bot

It's called the Hilsch Vortex. I remember a lab experiment when I was an undergraduate involving one.....many years ago.

Hilsch Vortex, eh?

http://www.visi.com/~darus/hilsch/
http://www.montagar.com/~patj/hilmnu.htm
http://www.airtxinternational.com/how_vortex_tubes_work.php

I know it seems crazy -- that is, how could I possibly hope to get that much cold, compressed air on board and have it at the engine's beck and call? It would use a process different than an air conditioner, but also involving compression and expansion.

I'll put together a thumbnail sketch of the idea soon.

Bot,
Thanks for the links.
I remember a Popular Science cover story from the mid to late 1960s that trumpeted, " Air Conditioner with No Moving Parts".
The article went on to explain the obvious benefits of a such a simple mechanism, and predicted its universal use in auto air conditioners in a few years. Well, I'm still waiting.
Forget the R12 vs R134a controvery, just hook me up with a vortex tube!

OK, Carl, we all will be waiting. Try not to violate the laws of physics too badly. :D

Hah! They all laughed when he sat down at the drawing table with his second hand drafting tools.

All right then, the gauntlet has been thrown down! I don't think I could patent an idea like this anyway, so why not let it slip out (as if it was something worth stealing). More importantly, the only way my device will work is if another technology is first perfected: solenoid powered valves.

I read that those are a long sought breakthrough in conventional, gas engines, one that would enable infinitely variable valve timing. Solenoid valves are scary to me, because imagine the software burps -- if you have an interference engine, goodbye major $$. Bonehead and I discussed this once, he's not sure if you could have a diesel that wasn't interference -- that is, with that high of a compression ratio, no room for the luxury of valve indents (there's a term for that) in the pistons.

I've heard of port valves, sort of like a port hole in a boat that is shut by sliding a pocket door like device. These would eliminate the possibility of bent valves and broken pistons, but how well do they work? I've read that they were formerly used in 2 stroke engines.

Anyway, trust me, I think you'll be surprised.

Two stroke diesel engines have been around for years and they don't have valves, only ports on the side of the cylinder. There is a valve called an "aspen valve" that was conical shaped and had a hole or port on one side. The valve rotated and when the port lined up with a hole in the head, the gases could enter or exhaust the combustion chamber.

Most of them have exhaust valves (Detroit Diesels).

Oh man, that's a cute bit of junk science. If that device worked at all like the first link stated, our energy needs would be over forever and several billionaires, at least, would hoist glasses of brandy every Christmas to the good Mr. Hilsch.

I would guess that at any instant in time, some molecules are moving slower than others in a body of air. However, I imagine that any one molecule would stay in that state for a nano-second of two before being agitated by it's fellow molecules to a more ambient speed.

The auto air conditioner with no moving parts that I'd like to see exists already: the propane refrigerator. I traded for an old one out of a converted camper and it works just fine on 120 AC down at my shop/warehouse.

(BTW Brian, this is NOT the foundation of my ground-breaking invention in the sky I referred to earlier. I'm not THAT naive. ;))

Add heat -- harvest ice. What a miracle of science, and it requires only ammonia, water, and hydrogen gas, I believe. I'll need to refer to howstuffworks.com again. Oh, here 'tis:

http://home.howstuffworks.com/refrigerator5.htm

I mean, every car has waste heat. Why not use that to power one of these coolers? Actually, I may know the answer to that. I've read that this type of cooler does not move thermal mass as quickly as more conventional compressor type coolers. Perhaps there's no way it could work in an auto.

Sure seems like it would be worth a try. Mine is old and rusty but it works fine: a sealed sysem w/ no moving parts and it's totally silent!

The link you provided gave the following link, which is a lot more detailed.

Bot

http://www.nh3tech.org/absorption.html

Carl, the device does work, exactly as advertised. The units are sold and are in use at the various airline facilities that I deal with. They do provide air that is about 40 degrees colder than ambient.

But, nothing is for free. To function, they need a steady supply of compressed air. You don't get the compressed air for free. In fact, it's a rather costly way to get the cold air. But, it's readily available and convenient to use.

So guys, what about using the vortex as a source for an intercooler using the compressor off the turbine?

Bot

Nice try. :D

The device dumps most of the air that it receives as warmer air, so, you would need a huge amount of air to get a much smaller amount of cold air.

The compressor is not able to provide anywhere near enough airflow to allow this device to provide sufficient airflow to the engine.

Additionally, the air from the compressor is about 200°F. The discharge air would then be 160°F. A small benefit, but, nothing like an intercooler, which can probably get down to 120°F. in 80°F. ambients.

Whale Oil Beef Hooked. (Say phrase really fast, over and over). I stand corrected. These lines from the first link gave me pause:

"When the device is properly adjusted, the hot pipe will deliver air at about 100 degrees Fahrenheit and the cold pipe air at about -70 degrees (a temperature substantially below the freezing point of mercury and approaching that of "dry ice"). When the tube is adjusted for maximum temperature on the hot side, air is delivered at about 350 degrees F. It must be mentioned, however, that few amateurs have succeeded in achieving these performance extremes. Most report minimums on the order of -10 degrees and maximums of about + 140 on the first try."

From this, I jumped to the conclusion that refrigeration and heating could be had for far less energy than that required by conventional means. That it works at all is interesting. Sure sounds implausible, that is, seperating one class of molecules from another.

Your subsequent description sounds more realistic.

You're right, that's a good one. I may have clicked on it once, months ago, it looks familiar, but I didn't study it and had forgotten it.

I've read here and there that the propane style is not nearly as efficient as the comressor type. Wish I had better information. More searching is needed. I've lived in small places where the damn refrigerator cycle would wake me up now and then. I hate the damn humm/buzz combination. My propane/elec./no moving parts model is an incredible luxury: SILENCE!