Richard Paul

iTrader: (5)

To a certain extent it could be done. But in reality it cannot cover a large range. In both the cent and the afs you will get into a minimum of low efficency and worst a surge condition. This occurs because you are relieving pressure while letting the flow go up. If you look at a compressor map for one of these compressors you can easily see why this happens. These compressors want the pressure to go up with the flow.

zoom44

DAMN AND I THOUGHT I WAS A VORACIOUS READER! WELCOME ABOARD

zoom44

is that 8 stages on that particular blower?

Richard Paul

iTrader: (5)

Damn it, I didn't even notice that! Actually it is 7 stages and I'm really stumped now. I can't remember making that blower. To much alcohol I guess.

Let that be a warning to you Fred, brewing and distilling at home? Now that's a serious student of the art.

Hymee

iTrader: (1)

How is this for a few axial flow compressors on a vehicle



Cheers,
Hymee.

zoom44

i counted 7 i can see but thought there might be one more at the near end that is just hidden because of the angle of the photo...

Richard Paul

iTrader: (5)

Now what keeps THAT from flying??

But I hear you guys have a dry lake down under that can be used for this purpose.

Yes that's it, the guys who run there are known as drylakeracingbastards, right?

LarryA

I don't intend to argue with the expert here... just thinking out loud and trying to learn.

It's very easy to visualize that internal compression takes place in a vane type blower... air at atmospheric pressure fills a chamber, the chamber is closed off from the inlet, the chamber gets smaller and smaller, actually compressing the air. It's harder to visualize in a screw type, but I assume that once a given lump of air gets in it gets sealed off from both the inlet and outlet, and the cavity it's trapped in gets smaller throughout rotation, actually compressing the trapped air before the the outlet is uncovered. You should be able to feel pulses if you turn either of these types by hand, because no matter how slow you turn it you are compressing pockets of air.

The axial on the other hand, does not trap air in cavities, it's only pushing it against the air ahead of it... if the air ahead (say, in the manifold) is at 8psi, doesn't the SC take less power than if the air ahead is at 12psi?

You said the rotor will spin as you drive with the belt off, i.e. the air is driving the rotor rather than the rotor driving the air. Obviously the belt is carrying no load; it's not there.

Take a unit that is pressurizing the RX8 manifold to 8psi at 8000 RPM... the drive belt is working hard. Pull it off of there and put it on a 502 Chevy... same pulleys and all... and run the Chevy up to 8000 RPM (hey, it has good parts in it, but we'll stand over here behind the blast wall just in case). The manifold pressure will not be 8psi, of course... let's say it happens to be ~zero, same as it would be at WOT if the SC wasn't even there. It seems to me there would be no load on the drive belt at this point, 'cause there is no higher pressure air ahead of the SC. Will the air be heated as it passes through the SC? Very little... it's only seeing a temporary constriction as it passes through the SC, no difference than air flowing through a carb venturi... it's not being compressed.

If you're still with me at this point... if lowering the manifold pressure by "absorbing" it with a bigger engine unloaded the belt, wouldn't lowering the manifold pressure by leaking air (back to the inlet) also unload the belt?

EDIT: I posted this before seeing your post 1259

davefzr

uhh.. how is the project coming?

Richard Paul

iTrader: (5)

Larry, The axial flow compressor gets it's internal compression via aerodynamics.
Using the same theorys as flying a plane. Each "winglet" creates a high pressure area underneath it and a low pressure above it. In addition to this some energy is put into deflection of the charge. This deflection is redirected by the stationary blade converting that energy to pressure. Then this operation is repeated through the next stage. Since the following stage does not know it is starting with higher pressure it will increase the pressure by a like percentage.

The trick is to know the angles of the deviation in and out. Thus being able to design the following componant. This deviation does not stay constant through out the range. The axial speed vs the tip speed is critical in the pressure rise. It is the higher axial speed that is responsable for the high compression ratio of modern gas turbines.

However we have not the luxury of a fairly constant speed range. We as users of this instrument in lock step with the Otto cycle engine have a new problem, getting it to work throughout a wide RPM band. That has been my work for 20 years now. I'm currently still working on the aerodynamics for the Rx 8 blower. Not having the design and test equipment of GE or RR it takes longer by trial and error.

The positive displacment blowers have a luxtury of being adjustable by slowing or speeding them up. With the AFS it has to be sized for the aprox size of the host engine.

I have to go now, might get back and finish later but a dinner date is yelling at me.
So I'll leave you with this much babble.

rotarygod

When the clutch disengages the supercharger on the Mercedes systems, the blower does not stop turning. As with Richard's unit, the blower does free spin. I've seen it on my friend's supercharged Grand Am. Mercedes also uses a bypass valve. Eaton claims that it only takes about a third of a horsepower to turn their blower when the bypass is open. Even though it freespins, it doesn't quite freespin as fast as it would if the belt were still engaged. This is partially due to the bypass valve but mostly due to the small amount of leakage between blower rotors. Mercedes didn't need to add the complexity since they got very little out of it but they did.

FWIW: Mercedes announced a few months ago that they will be completely phasing out superchargers from their lineup over the next 2 years. The reasons for such were that turbos have gotten very cheap in comparison to superchargers and technology is allowing them to still get the emissions results they need.

bureau13

STOP THE PRESSES! Are you saying the Mercedes blower is a positive displacement blower, AND they use a clutch on it so it can disengage? Do you know what this means? The last of the V8 interceptors could actually work People used to swear up and down that Mad Max's car wouldn't work because it showed what looked like a roots blower with a clutch. I believed 'em, but what do I know!

jds

rotarygod

Too bad Mad Max's car was a prop turned by an electric motor! (I know, we're supposed to pretend) There wasn't even a carb on top of that engine. It was just a scoop on a blower. I did always think it would be really cool though.

Here you go.

http://cgi.ebay.com/ebaymotors/ws/eB...spagename=WDVW

Richard Paul

iTrader: (5)

The clutch in your Rx8 isn't strong enough to hold one of those drag race blowers. much less one of those for an AC unit.

ModMech

In Reply to RPs posts about "modern dynos", post #1162.

The "Dyno Jet" brand that I am familiar with are chassis dynomometers that are used for vehicles. They have a small "weather station" at the facility, and it monitors conditions as the dyno operates, providing real-time correction data.

As he suggested, results are either STD or SAE. I too only deal with SAE, HOWEVER a friend in the tuning business (who does Mazda stuff as well as his Ford specialty) informed me that there are literally DOZENS of "SAE" standards for dyno measurements. If you look carefully, there *should* be a "J-" number listed after the SAE (SAE J-xxxx for example), the ONLY way to compare results and have them mean anything is to use either the SAME DYNO, or the SAME "J" standard, and even then you get back to "different dyno, different day". But in short, that is how you get "inflated" performance numbers.

There is also the question of Wheel or Flywheel HP. Unless you KNOW the calculation for a specific vehicle (and they are ALL different, and no, 80% is not "close enough") to get from measured Whp to Fwhp, you really cannot know your flywheel Hp. For cars that I am familiar with (Fords) the correction is Measured Whp/0.8557 = Crank Hp (FlyWheel actually).

They dynojet uses a fixed mass drum, and the acceleration rate of the drum over time along with the RPM signal will give you HP. You really measure the Tq input as discussed, but with the RPM you can calculate HP at any point, or all points.

Richard Paul

iTrader: (5)

Damn, Jon's blown by me in both replies and views. Goodby cruel world. I'm moving to the S2k forum.

Photic

You can get ahead of him, just promise something rediculously high but give footnotes like drug companies.

THE AFSC Offers the following*:
300+ HP GAINED from the AFSC!
Women will drop down on their knees and praise you. Don't like women? NO PROBLEM! Men will also drop to their knees as well!
Will make you preform better on the track and in the sack!
Unit acutally makes money!
Now with a ultra low APR!









*Actual results may vary. None of this has been proven as scientific fact. Side effects may include heart burn, shortness of breath, hives, and or death.

Richard Paul

iTrader: (5)

Way cool, Photic.

But might I be sceptic, your name starts with "Ph" just like his???

patrick_andraste

I am very interested. How are you doing with it?

globi

But doesn't that automatically mean that the faster one accelerates that drum, the bigger the torque measurement error unless someone knows the rotational masses of the engine, drivetrain and wheels?
Shouldn't an ideal dyno brake the engine according to the torque it generates, so it accelerates slower and rotational masses can be neglected?

Richard Paul

iTrader: (5)

Correct. That is the way engine dynos work and we call it "Brake HP".
The correct way is to hold it at a given RPM and read the torque.
Modern computer controlled dynos can give you step tests at 250 or 500 RPM points. They also can give you acceleration test with so many RPM per sec rise. I used to run my engine with the RPM rise at 200 or 300 per sec for the development work. Then run a 500 RPM step test for the records.
The step test will give you a little higher reading then the RPM tests. But since this is the standard you must fun the step test to compare your readings to others.

Now engine dynos can compare to each other with a reasonable amount of accuracy. The chassis dynos are not that close. The rising rate heavy drum readouts vary. There is no way to get a direct test of the numbers. On an engine yno you just hang a weight off of it at a given distance and read the gauge for torque. Say you hung 50 lbs of center 2 ft. you will get 100 lbs readout. you do this with several weights and check your curve. Then correct it if it is wrong.

Engine dynos will compare within 1% or better. I think chassis dynos cannot be used for comparison to each other. It now comes out that operators are using different correction factors. I have seen numbers for turboed Hondas that are not quite belevable. The numbers for Rx8 owners seem to be belivable.

Also there is no standard for figuring engine hp to wheel hp loss. You can't take a fraction and assume it to be accurate. This will vary even from car to car of the same type. There are just to many mech parts between them.
Remember if it makes heat it took power. So don't go telling me it's direct drive. If the parts got hot they took power. If they didn't you would have as RG says Cold Fussion or perpetual motion. Call the patent office not me.

davefzr

How about some information related to the project? Hows that coming?

Dont make me sick Omi on you again jk

RotorWheeee

Get back here ...were not done with you yet:D

Labop

Man this thread has gotten huge.

RP, are you still looking for a test engine for your SC? Found one on eBay if you need it.

http://cgi.ebay.com/ebaymotors/ws/eB...category=33615

ModMech

The larger error comes from the shorter time you can draw data from, not the driveline, as you are NOT attempting to get to Flywheel HP/Tq, but only to WHEEL Hp/Tq, which is very accurately calculated.

With this type of dyno, yes lighter driveline parts (tires, wheels, d/s, flywheels) DO absolutely change the measured wheel HP/Tq as compared to the exact same vehicle with heavier parts (higher inertias), but the measurement is still valid. The engine made no more Hp from one to the other, but the vehicle will definaely be quicker with the lighter parts, so you could say more of the engine's available power is making it to the ground, which is exactly what you are attempting to measure in the first place, WHEEL Hp/Tq.