Turbocharger Compressor Outlet Force

[mellotango]

I am quite new to turbochargers and am researching a project that involves the use of turbochargers. I have a question about the force generated on the compressor outlet. We understand the exhaust gas directed into the turbine side of the turbocharger, which in turn spins the shaft wheel, and the residual exhaust gas exits the outlet of the turbine. So when the shaft spins, it also drives the compressor wheel which sucks in and compresses the air, and pushes it out of the compressor outlet back into the car engine.

My question is, when this compressed air exits the compressor outlet, is the force or thrust of this airflow, same as the force/thrust of the exhaust gas exiting the turbine outlet, since the shaft is working both the turbine and compressor wheel simultaneously? And can the force/thrust at the compressor outlet be adjusted to be less, same or more than the force/thrust generated at the turbine outlet?

[Tim]

That is what boost controllers are for.

[shadow88]

This could be the beginning of quite a pissing match, but I'll throw in my 2 cents.

To equal the force on the turbine (exhaust) and compressor (intake) They would have to matched very well to each other and the engine including housings for both turbine and compressors.

Some people have tried measuring exhaust backpressure in the exhaust manifold and compared it to the boost pressure in the intake manifold, and that seems to get you pretty close, with quite a bit of messing around between wheels and housings and tuning of the engine to acheive that. Not that it's a waste of time, just most people are ok with being a little high on the exhaust side.

It's not instant failure of the turbo to have mismatched wheels and housings and pressures. In fact, most people prefer a responsive turbo to a laggy one for street use, and that generally means higher exhaust pressure than intake pressure.

[Shadow]

I think the simplest answer is....no, the force is not equal. What is happening on either side of a turbo only relates to the point that the turbine wheel/housing needs to be able to generate enough force to create "boost" on the compressor side. In order to do this efficiently the compressor wheel needs to be a proper match to the turbine wheel.

Since there are a number of compressor wheels that can generate boost from the same turbine wheel/housing there will always be varying degrees of boost efficiency/pressure.

[Reaper1]

Agreed. The answer is definitely "no". The biggest reason for that is efficiency.

[tkelly27]

It's a little more complex than force. Torque on the shaft, yes, aside from the tiny amount of bearing lag, the torque applied to the turbine is the same as the amount of torque the compressor applies to the air. If it wasn't the shaft would be twisting. It does twist a little, but the torque is still transferred.

Pressure, it depends. It depends on the turbine, turbine housing, compressor, and compressor housing. With a small turbo you'll typically have turbine drive pressure higher than compressor outlet pressure. With a really big turbine you can get under 1:1 where the drive pressure on the turbine is less than the boost you are making. I prefer big turbos personally.

Flow, no, unfortunately you have to have more flowing out than you're putting in. This just happens naturally because you're injecting fuel and burning it. Now you have the same amount of oxygen molecules, and a bunch of other hot, expanded gasses.

Other than torque, there isn't really a good way to measure force in an operating turbocharger.

[Reaper1]

Correct. There is no good way to measure force in real time on an operating turbo beyond measuring the torque on the shaft.

You could extrapolate it if you measure compressor/turbine inlet, compressor/turbine outlet, and shaft rpm. Basically that will give you the work being done, then knowing the physical dimensions of the parts of the turbo you can figure out the work. That is a VERY basic way of doing it, but it would get you a ballpark number.

[turismolover22]

I vote nocommon sense tells us we want boost. Our cars dont perform well without it. The point which we move the same air in as out would have to be at either the very beginning of turbo spool, or at the very max of any given "matched setup" but in the end, i would think you could never equal the pressures between the two. The only way i could imagine that is if you used a compressor so large it could move more air than the exhaust turbine could use. Because once you add boost, the fuel necessary to run a motor correctly goes up very fast, and with it, the air you push in. So once we push more air into the car, that air burns, expands, and gets expelled. If the air never expanded, then yes you could totally equal the air intake to air expulsion acriss the turbine and compressor.The only way you could even remotely equal air input and exhaust is by knowing these things.What boost is pushed per cfm exhaust pressure across turbineHow much air (cfm) you move with specific compressor sizeThe density of boosted airThe density of burnt, exhaust gassesThats just a starting point, i would assume, for actually calculating what setup truly gives you a 1-1 boost to exhaust rating. But from what i would assume, i would think it would be something along the lines of a large hybrid turbo. Something like a large t4 compressor strapped to a t3 turbine wheel.