silverx8

There is a way to increase the charge density and reduce the tendency to detonate through chargecooling. I did not get straight A's in thermodynamics, but I I remeber the fundamentals of pressure and temperature. As the pressure rises, the temperature rises. As the pressure falls, so does the temperature.

Any boosted engine has to deal with high temperature gas coming in. That is unless there is some sort of active cooling. Way back wehn somebody tried this using the air conditioner. It worked and increased horsepower a little bit (5%). Turbomoters use intercoolers to reduce the gas temperature by transfering the heat to the ambient air before the high pressure air goes to the motor. These intercoolers transfer the heat better given a larger temperature differential, and at best can only get close to a temperature well above ambient.

This is where the RX8 gets into trouble. the high pressure high temp mixture is volatile and tends to knock and rip up the motor. This is where chargecooling could help.

By raising gas pressure before it goes through the intercooler, the intercooler gets hotter, allowing it to transfer more heat out. After the intercooler, a pressure regulator brings the pressure back down to a tolerable 7 to 10 PSI, but the lower temperature allows a charge density of an equivalent 14 PSI.

O.K. for all of you math junkies.

PV=NRT, or pressure times volume is proportional to temperature in Kelvin.

PV at room temp is is 14 psi 1 cubic foot, and temp is 291 degrees Kelvin (65 degeees Farenheit). Going to 14 psi shoves this into 1/2 cubic foot. Temperature doubles to 482 degrees K, or 589 F. If the intercooler can transfer heat down to 210 deegrees F (boiling water) 372 K, then when the gas is expanded by reducing pressure to 7 PSI, the temperature will fall to 21/28 of 372 K. That is 279 degrees K, or 42 degrees F. The air is actually colder than the inlet temperature.

Compared to the aforementioned intercooled setup that implies a charge density that is 30% greater than with the intercooled setup. That means the 240 RWHP, could jump to over 320 RWHP without detonation.

Of course these are calculations given the capabilities of the current turbo setups, and the addition of a 7 psi post intercooler pressure regulator. Your results may vary.

army_rx8

hmmmm well it seems plausible..but i dont' really feel liek researchign to see if you crossed all your t's and doted your i's...hehe i'll let rotary god or teh other rotarys whizz's do that:p hehe. i've never heard of this being done before..which really only means that if it was done it wasn't super duper mainstream as i am no tup to date on history or evolution of said things..as i am not a car mechanic/thermodynamics whiz kid. ah well i'm sure someone will figure out something way befor i have the monies to get a turbo

hmm well that was a good amount of useless babbling on my part lol

Imidazole

Call me a dumbass... but...

A lot of **** into squished into an intercooler, made hot, then really cool - and then coming out of the intercooler, into a regulator...

Is it just me or does that sound like a traffic jam in the intercooler, with lots of **** trying to get in, and something not letting it get out... Defeating the purpose?

I'm not physics nut, hell... But, sounds like it wouldnt last for long.

army_rx8

^^ture...haha probable why i hav enever heard of it on a production (or any) car...it isn't really cost effective to get parts that can go the distance maybe.

Richard Paul

iTrader: (5)

Oh boy, haven't we been here before???? Yes a few times. I commend you for thinking out of the box. Also for using your education as applied to a given problem.

But your lack of experience prevented you from seeing the real world problems. First you have to pay to make the extra pressure. The use of exhaust to drive the compressor is not free, regardless of what some say. Where are you going to put the extra heat generated making the extra boost?

Wait, I have a better way of showing it. You are proposing to make the turbo put out say 14 psi but only use 7 of it, right. You are going to force the air through an orfice to build the heat and then when it is hot reject said heat so whenit is expanded the lower pressure has lower temp.

You just invented the airconditioner. So you only need to look at how much power is used to cool a very small amount of CFM for the passenger cabin to realize that you will need a enormous compressor using large amounts power to drive to make this system function. In the AC system you have an outside power supply (the engine) to drive the compressor and the results are not trying to gain power but sacrificing some.

In order to give you an idea of the kind of volume we are talking about our resident female expert has suggested that you should disconect the hose of a turbo at idle and hold your hand in front of it. Now this is less than idle for turbo as it is hardly turning. Now think if it were making pressure and flow. Next go to your AC unit and see how much air comes from it at ***** to the wall full on double speed.
Nothing in the relm of what an engine requires.

Now see how much power is consumed by the AC compressor and get an idea of what it takes to lower temps below ambiant. The only way to really do this is with a liquid to air cooler that has an unlimited water supply. As in marine operation.

Now that is said you must realize that just because you have cooler air doesn't stop it from detonating. You will still have the extra mass to expand and produce extra pressure. That is why we did this right? The pressure can only go to the limit of the fuel we use. To simplify this I will point out that the IC is only used to reduce the temp so it will not exceed the thermal limit of the internals.

If you have X coming out of the blower (in mass) that is what will go in, no more. So in order to get the engine to except this mass without melting we cool it. We don't cool it so we can get more in than the engine can handle.

You seem to understand expantion, so apply that to forcing the rotor around or piston down. If it wasn't for the thermal loads on the engine you could increase this at will. Additionally and not the last item but the most important is the detonation limit of the fuel. When compressed to the point of autoignition you get detonation. But that is not the only thing that will cause detonation. Combustion chamber shape and a bunch of other items.

The rotary seems to have a unique problem of combustion chamber shape and the flow into and out of it. It is inferior to the piston engine here. This can be seen in the fuel milage. Inefficency. The extra surface area to volume ratio is a negative to keeping the air/fuel in mix. Getting the turbulence and/or tumble of the standard engine is not happening.

"You just keep thinking, Butch"

guitarjunkie28

oh hell, just run a water to air intercooler with dry ice and acetone freeze-your-***** intake temps.

Ajax

how bout we not freeze my ***** and just make it really cold.. thanks :b

Richard Paul

iTrader: (5)

I did that once with methenol. Just doesn't last forever. You can see how many BTU's a system can take when a run at Bonniville is over and the alcohol is warm.

Only in a boat with an unlimited heat sink under you can you get free lunch.

Ajax

if we wanna have real fun, what we'd do is add a second battery and alternator, strap a really big TEC (thermo electric cooler) to the intercooler to cool it down (when you run current through it, one side gets ice cold, the other gets hotter than hell) and we'll strap the other side of it to the catalytic converter (now don't ask me how the **** i plan to orient that TEC).. there we go.. CARB legal turbo + super intercooler...

haha..

Richard Paul

iTrader: (5)

Again we have a vision problem or should I say size problem. You would need a generator set from Catepillar to get enough heat rejection for the amount of airflow you need. Now if the Cat needs to be turbo'd or not we'll have to see.

Ajax, "you just keep thinking, Butch"

rotarygod

I'm glad Richard posted already. It saves me alot of time. Wasn't this exact same thread question asked a couple of months ago?

Why heat up the air by making say 14 psi and then bleeding off half of it to get a cooler charge temperature when you could just boost to 7 psi which wouldn't raise the temperature near as high to begin with? This is far easier and still more efficient.

Ajax

Richard,
It wasn't meant to be realistic.

A TEC large enough to cool a computer processor to freezing temps draws too much power. I'd need to pull the 30kw fuel cell off the ford explorer at school to power a TEC big enough to cool the intercooler enough to be useful. And like I said, how the hell would you position the thing so it would be even useful? If you dont dissipate that heat somehow, it's just gonna smoke everything in the vehicle.

Richard Paul

iTrader: (5)

But RG, you are a much better wordsmith then I.
You're probably pretty glib in a bar with the girls too.

Richard Paul

iTrader: (5)

I know it was a joke Ajax. I just wanted to keep it going. :D

Ajax

Blah!

I'm gonna go hit something with a large hammer... excuse me.

Richard Paul

iTrader: (5)

Talk about big hammers. Here's a nubee with 10 posts tring to present something usefull and all we can do is hammer him.

Really Silver, we like you or we wouldn't be THIS nice. It's just that this gets brought up every so often and we have all the arguments in inventory.
Now you have been baptised. keep thinking. We are here until you teach US something. We can all learn.

You can be proud! You got two pages in an hour and a half. Not many posts do that.

silverx8

Well, the turbos used for the currently offered systems (Greddy, etc...) are capable of the relatively modest 14 PSI at the flow rates of the 9K RPM 2.6 L motor, they just don't dare to go that high due to the fragility of the rotary. Air conditioner units are not made for these kinds of loads, turbochargers are.

Air to water chargecoolers are probably better capable of shedding the heat than air to air intercoolers. But the radiator ends up shedding all of the heat.


As for the extra heat. The heat is from pressure. It matters not whether the air goes to 14 PSI outside the motor, and then 19 times that inside the motor, or 7 PSI outside and then 13.75 times that inside the motor, the total heat is the same. Therefore this setup sheds the same amount of heat as a 14 PSI motor.

The difference is that less heat is shed in the motor and more is shed outside. This cools the combustion chamber and heats the intercooler, or radiator directly.

Again, this is just a trick to get more from the rotary. You could get the same result by restricting the airflow out of the intercooler, and increasing boost at high RPM. The airflow restriction will keep motor pressure down, boost up, and the intercooler hot.

silverx8

Here are some chargecooling links:

http://www.driftworks.co.uk/forum/showthread.php?t=191
http://people.msoe.edu/~cohenm/espritse.htm
http://www.superchargersonline.com/content.asp?ID=7
http://www.mustang50magazine.com/techarticles/65218/

Here is an excerpt from the last link

"Conclusions
Our day with the instrumented aftercooler-equipped car was most instructive. When we left we had reached several general conclusions.
• This sort of testing is easily done with a digital thermometer. If you can beg or borrow such a thermometer, the time spent documenting your system’s temperatures will be well spent.
• Most blower heat can be correlated directly with engine/supercharger rpm. The higher the rpm, the higher the discharge air temperature. This is true even when free-revving the engine while the car is motionless.
• The engine oil blower lubricant does not heat the supercharger.
• Aftercooling water gets to 10 degrees greater than ambient, then stabilizes.
• It takes tremendous heat to raise the cooling water 5 degrees.
• A 65-mph cruise cools the water compared to around-town driving.
• Blower discharge temperature varies widely; an aftercooler goes a long way to even out these fluctuations. This is a huge tuning advantage over a non-cooled blower installation.
• Deceleration rapidly heats the discharge air. Larger bypass valves would probably help this situation somewhat.
• It takes all-out, continuous racing—i.e. open-road racing, road racing—to put more heat into the cooling system than it can reject under any normal atmospheric conditions. After all that, the bottom line is, if it’s blown and has more than 6 pounds of boost, we’d cool the discharge air."

rotarygod

Not true at all. The rotary is FAR and away capable of handling more than 14 psi of boost. It all depends how it was tuned. My friend Ari at Rotary Performance ran 26 psi of boost PLUS a 75 shot of nitrous on a stock block 13B for an entire season of drag racing. Total power output was 620+ rwhp.

rotarygod

We all understand the benefits of charge cooling. No one is arguing against it. It's your way of doing it that we don't believe in. You want to add more boost which will add far more heat than just simply running less boost. Then you want to run it through an intercooler (nothing wrong with that), then you want to bleed some pressure off so that there is a further temperature drop in the system. This remaining cooler air will then arrive at the engine. The problem with this is that while you will get some temperature drop with this setup, the total overall temperature still isn't going to be as low as if you had just run lower boost and therefore made less heat to begin with. You are also working your turbo harder. You're talking about doing it the hard way.

Richard Paul

iTrader: (5)

Can you tell me how I know from reading this that they were running a roots blower??? That's just something I want to see.

But on top of that where in this "expert" conclutions do you gain an argument for your style system. At best you are arguing for intercooling. No one here is against that under all conditions, just some. My favorate observation here is the magic 6psi limit. This you will find this is not gospel.

Clue" look up the Eaton webb site and check the incuded plots and see if something jumps out at you. Or you could find them already posted on this forum by "search" there you will also find the answer to my question. Like I first said this is a road we have driven before.

rotarygod

Actually they were running a Vortec centrifugal.

Richard Paul

iTrader: (5)

[QUOTE=silverx8]Air conditioner units are not made for these kinds of loads, turbochargers are.

Have you ever serviced an AC system?? Do you know the spec for highside/low side? There are difference but you can bet around 280 psi on the high side. These sort of presssures are not done with centrifugal compressors. They require piston compression. And talk about heavy duty these things can exist for us because of scale. Like a model airplane engine small scale gives alot of strength for given job.
They run even the four strokes up to 10,000 with 20% nitro. I know of one soul who runs 25%. Me.

Richard Paul

iTrader: (5)

Then why, oops I just thought the answer. They run blow through. I was going to ask why they got temp increse when off power decreasing rpm. And why cruise temp was same at given rpm as WOT.

Engage brain before opening big mouth

But then why the 6psi barrier?

silverx8

For a noob, I seem to have put my foot in it. But to continue:

The A/C compressor gets great pressure, but flow through is low. It just gets people cool. It does not make power.

Nitro cools the charge through expansion of the high pressure gas (that is good).

Chargecoolers have a long duration thermal lag. The article quoted is to illustrate that they are well up to the thermal load.

Given the tight confines, a chargecooler could be a better solution anyway.