WG 2.7 CRD Inlet Swirl Flaps

[RTB]

I still can't say I a onboard here. One thing that makes a vacuum not a good comparison is that it is a fan, not a compressor. A fan has no stator on the discharge to convert the dynamic pressure (flow) into static pressure. It is just designed to push air from one place to another without compression.

A compressor in a turbo does have a stator (or no less than a diffusor in the case of vaneless turbos) and is designed to convert flow into pressure. Thus the surge/flow maps show lack of back pressure as a bad thing. So while flow is definitely a loading factor, fluid density is also a major factor. Increase the discharge pressure (by choking the discharge) = increased fluid density = increased compressor load = greater power required = lower RPM.

[JeanLuke]

Originally Posted by RTB

One thing that makes a vacuum not a good comparison is that it is a fan, not a compressor.

It's not the best, but both are radial flow impellers. Larger garage vacuums like mine are not fans but definitely radial flow blowers. ASME defines fans, blowers and compressors by pressure ratio. You are correct that the compressor side of a turbocharger is a radial compressor, not a fan or a blower. My garage vacuum is a blower. So, yes, it's not the best analogy but it's all I had.

Moving on...

Originally Posted by RTB

So while flow is definitely a loading factor, fluid density is also a major factor.

As I said, the key is mass flow. As you correctly pointed out, for air mass flow depends on both volume flow and density. These are mathematically related by the universal gas equation - PV=nRT. (Google that one, it will take pages to explain.)

With a radial flow device, reduce the mass flow and the power reduces. That is a fact of how they behave - look up any radial flow device performance curve. Adding pressure differential = reduced mass flow = reduced power. To be 100% clear, this applies only to radial flow devices. It does not apply to axial flow (think of propellers). They behave very differently.

For an example, look at a typical radial-flow compressor performance curve here: https://www.ingersollrand.com/en-us/...turbo-air-2000
Notice how the power decreases as the flow decreases?
That particular model had a vaned diffuser. Our compressors have volute diffusers. They do the same thing, convert kinetic energy into pressure following Bernoulli's equation.

[JeanLuke]

Originally Posted by RTB

One thing I would like to try is playing with boost pressure versus Swirl vane position. Just curious if I can create a small pressure drop across the swirl vanes. The reason being to try and create a JT effect (Joule-Thomson effect). This will result in a corresponding temperature drop at the inlet valve. Large aircraft air conditioning systems use this to cool the air in the cabin by way of an "air cycle machine". It is also used in the oil and gas industry to chill and dehydrate the gas. Even in our cars now in the TX valve in our aircon. The principle is everywhere.

I want to see if a slightly higher loaded turbine will be offset by the cooler air into the cylinder. All in the name of a little efficiency. Obviously this would only be in cruise conditions. Vanes need to be open for higher power times.

The results of this test will go in the newly created ECU thread "Playing around with the 2.7 software (ECU and TCU)"

My gut feeling is that it will be waste of time, but time is something I have right now.

I meant to comment - this would become a zero-sum proposition...

The end game is to maximise the number of oxygen molecules in the intake charge. This is done by two means - increasing the air density and increasing the air pressure. The density means that for a given volume there is more oxygen. The pressure means that in a given time (i.e. the time the intake valve is open) more volume can be "squirted" into the cylinder. As we know, density and pressure are related.

If you use the swirl vanes to reduce temperature, you are doing this by reducing the pressure (i.e. expansion cooling) which means lower density. The reduced pressure means a smaller volume will "squirt" in when the inlet valve opens, and it will be at a lower density despite being at a lower temperature.

[RTB]

Originally Posted by JeanLuke

If you use the swirl vanes to reduce temperature, you are doing this by reducing the pressure (i.e. expansion cooling) which means lower density. The reduced pressure means a smaller volume will "squirt" in when the inlet valve opens, and it will be at a lower density despite being at a lower temperature.

Yep, totally agree. But the experiment will include an increased supply pressure to offset the pressure drop across the vanes. It will be complete trial and error since there is no pressure sensing there.

The question for the success or failure of this is more a ratio of losses from increased exhaust back pressure, to gains from reduced cylinder charge temps.

[RTB]

Originally Posted by JeanLuke

It's not the best, but both are radial flow impellers. Larger garage vacuums like mine are not fans but definitely radial flow blowers. ASME defines fans, blowers and compressors by pressure ratio. You are correct that the compressor side of a turbocharger is a radial compressor, not a fan or a blower. My garage vacuum is a blower. So, yes, it's not the best analogy but it's all I had.

Moving on...



As I said, the key is mass flow. As you correctly pointed out, for air mass flow depends on both volume flow and density. These are mathematically related by the universal gas equation - PV=nRT. (Google that one, it will take pages to explain.)

With a radial flow device, reduce the mass flow and the power reduces. That is a fact of how they behave - look up any radial flow device performance curve. Adding pressure differential = reduced mass flow = reduced power. To be 100% clear, this applies only to radial flow devices. It does not apply to axial flow (think of propellers). They behave very differently.

For an example, look at a typical radial-flow compressor performance curve here: https://www.ingersollrand.com/en-us/...turbo-air-2000
Notice how the power decreases as the flow decreases?
That particular model had a vaned diffuser. Our compressors have volute diffusers. They do the same thing, convert kinetic energy into pressure following Bernoulli's equation.

Below is an example of my old work. This entire scenario is based around constant input power.

This is an engine driving a compressor through a fluid coupling. This allows the compressor speed to do whatever it needs based on its own load.

In this graph, engine speed can be seen to remain constant. So input power is remaining constant. As the discharge pressure is lowered (controlled by people), the compressor speed (NPT) rises (Compressor unloads). As a result the opposite would be true. As the discharge pressure rises, the compressor speed would lower. This was a common and well know occurrence across the fleets I used to analyze.

They used to start these machine in a way I disagreed with. They would have everything in manual. Set the engine speed to a fixed value. Get plenty of distance away from the surge line, then load the compressors by the use of the control valves. The result was a increased discharge pressure, reduced compressor speed, and unit approach to the surge line. Then they would increase the engine speed, resulting in an increased compressor speed, and repeat the process. The system has an auto button which worked well, but the old boys just liked doing it this way. No harm was done.



If input power remain constant, and the discharge is slowly blocked off, the wheel speed will lower. The combination of increased discharge pressure and reduced RPM brings the unit closer to the surge line. At the point of surge, the flow temporarily reverses and the speed falls violently. Now though the discharge pressure is low, the speed increases again, the surge margin increases and the discharge pressure builds. This then causes the wheel to slow down and the surge cycle to continue.

If in a constant input power situation, the wheel speed increased as discharge pressure increased, then the compressor would move further to the right and away from the surge line and be less likely to surge. This doesn't happen.

I am happy to just agree to disagree on this one.

[JeanLuke]

Yep, looks like we're not going to reach a consensus on this. Let's move on.

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[goodies]

What way do they go to open and close