Supercharging and aftercooling...

[mgithens]

I searched for previous posts and didn't find what I was looking for, so I bring my question.

After reading up on supercharging and noticing that some cars and systems use an aftercooler to reduce inlet temperatures, I am wondering if an intercooler will reduce horsepower??

AS I UNDERSTAND IT --> The example system used 6.5 lbs of boost with just a supercharger and with intercooling it drops to 4 or so. This will provide the same amount of air (maybe slightly more), but at a lower temperature and therefore lower cylinder pressure. I don't have the inlet temperatures, but the system without intercooling produces nearly 50% more HP and compression ratio was kept to 10.5:1.

 

[TheBlacksmith]

When you compress air, it gets hot because of the work done on it. Use a hand tire pump and you'll notice the pump cylinder gets warm. Turbochargers aggravate this effect, because they use a turbine driven by hot exhaust gases close coupled to the air pump. All things being equal, the intercooler/aftercooler results in a cooler denser charge. Your engine uses pounds (weight)/cubic feet (volume) of air to burn fuel - the actual pressure of the air is less important. Cooling the air, while reducing the pressure, makes it denser and easier to pack into the engine. Some engines are less affected by intake restrictions, so the density doesn't matter so much and the cooler does cause a restriction. This may explain your results. Trivia - some diesel engines have both a turbo and a mechanical supercharger in series - the term intercooling refers to a cooler between the turbo and the supercharger, the term aftercooling refers to a cooler "after" all the compression, prior to the engine. The terms are used somewhat interchangeably today.


Blacksmith

 

[EMc]

Hello again,

More trivia: reducing the temperature of the air with an intercooler before it hits the cylinder helps eliminate predetonation, which is apparently a fair-sized problem in the performance compact sector.

So, if I ran a "precooler", cooling the air before it ever hit my supercharger, and then either ran the charger at a slightly higher ratio of engine speed than normal, or slapped a bigger charger on, would I increase the air density going into the engine? And even if I did, would it help me, or just mess up my air-to-fuel ratio and drive my ECU insane as it tried vainly to compensate?

AND... What about carrying a bottle of pure oxygen onboard for use like a NOS system, to give me extra zoom when I need it? Or is that just risking a huge explosion?

EMc

 

[evelrod]

A "precooler" by definition would be impractical, indeed illogical what with all the attendant pump and refrigeration components.

O2 has been tried many times (we die it on a drag bike back in the 50's) but it ,too, is impractical with the high pressure delivery system involved. Nitrus is still the most practical method of introducing more O2 into the combustion process.

Try a web search as all these nitrus and turbo kits are well tested and readily available from several sources, particularly the import drag segment of the market.


Rod

 

[JayMaechtlen]

hey, EMc

here's another take-

the supercharger is sucking atmosphere - at outside temperature. It would take refrigeration to get it colder.

after going through the supercharger, it is hotter. You can then run it through a simple heat exchanger, and cool it somewhat (transferring heat to atmosphere - it won't get as cool as outside air, but it will be cooler than what comes out of the compressor/supercharger)

the simple heat exchanger is called an "intercooler" or "aftercooler". No refrigeration required, fairly cheap, etc. That's why it is semi-commonly used on highly supercharged engines. Also because you really need to keep the charge temp down to avoid detonation under high boost...

- right, Rod?

(you're really having fun with the graphics, eh, Rod?)
cheers
Jay

 

[mgithens]

Well, I am considering adding a supercharger to my car. My concern is that I already run 10.5:1, so even though people are running this setup, the engineer in me won't let me bolt on what I don't fully understand. I have seen systems with 6psi and some of them have aftercoolers. I am wondering if an aftercooler at 4psi is equal to 6psi without. My logic being that there are equal amounts of air, they are both denser, but for different reasons. The 6psi setup will be dense due to pressure, but the 4psi w/aftercooler will be dense due to pressure and lower temps (lower than 6psi temps, not less than ambient). I guess the simplified question is does power generate only due to oxygen content(provided there is fuel to match)?? Or is there a relationship to power that is tied to the actual cylinder pressure??

I don't want to see 1400 degree exhaust temps, I want my daily driver to be just that.. I just want more kick, and bragging rights...

(btw.. the 6psi is an actual figure, the 4psi is my estimate with losses due to the restriction of the aftercooler)

 

[NickB]

With a good intercooler you will see very little pressure drop.As an example, my chrysler 2.2 runs at 18 psi of boost, and even at high rpm/high boost, where airflow is the highest, there is still less than 1psi pressure drop across the intercooler. My cooler is monstrous however, as it's part of an intercooler from a freightliner 18 wheeler. The stock cooler would see 1.5-2 psi pressure drop running at 15 psi in the manifold.

In almost every case, the intercooled engine will make more power than a non-intercooled engine running at the same boost pressure, because of the higher density of the air. The non-intercooled engine will also be more prone to detonation because of the higher inlet temperatures.

 

[evelrod]

on a parrallel note, daily drivers should by all rights be just that---daily drivers! Build your rod for the show or go, but NOT your daily driver. I tell my kids, that jusst because I did it back then, they don't necessarily have to be as stupid as I was. I also had 35 speeding and racing tickets in 1959!!! You can't get by with that now.




Rod [flush]

 

[JayMaechtlen]

well, this is theorising on my part, but:

I'll rephrase the question as "given a constant mass flow rate of air, (same number of molecules per minute) and the fuel to match- will increasing the temperature of the mix increase or reduce the power output?"

seems to me the following:
A lower inlet charge temp will cost less power to compress, and permit more optimum timing perhaps

oh, yes- depending on the type of blower, reducing the back-pressure in the inlet tract should either:
1- permit higher flow (in the case of turbocharger) or
2- reduce the horsepower cost of driving it (any mechanically driven device)

if the charge temp were too low (Alaska in winter?) you could get poor combustion?

common use for performance is to go for max charge density at minimum temperature.
comments?

jay

 

[Whittey]

I've always thought the same. Then I read this REAL interesting article about a Smokey Yunick Fiero that had a heated intake charge. Using a device similar to a turbo, but that doesn't compress on its own but mixes and heats(a 'homogenizer'). They bring the air/fuel up to 400-440F and, due to the expansion of the liquid fuel to gas, to about 15psi (limited). 250hp, 230ft-lbs, 151cid, 50mpg. I've got a PDF of the article here, though it you are concerned with the legality of having it you should go and buy it from

http://www.hotrodarchives.com

(June 1984 Hot Rod Magazine).


-=Whittey=-

 

[evelrod]

Whittey, put you last in the form of a new post. I am sure it will get a few people thinking again. I remember the article, now that you remind me. A good example of "thinking outside the box". Smoky wasn't exactly cut from a bolt of silk, but his ability as an inovator was never in question. His writings SHOULD be , but probably will never be, required reading!!!


Rod

 

[JayMaechtlen]

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**********
bummer
I wonder how Smokey's widow/estate would feel about it?

regards
Jay