Twin screw turbos?

[g-force_addict]

Would a twin screw turbo work?
For the air compressor stage.

Twin screw superchargers are more effective than their centrifugal counterparts.
Of course their gearing will have to withstand higher rpms to work in a turbo.

[Brian Coat]

"Twin screw superchargers are more effective than their centrifugal counterparts."

Ah well that depends what we mean by "effective": breadth of useful operating range? best polytropic efficiency? performance vs. weight? package space? etc. etc.

When it comes to air squeezing there are many horses and many courses.

When well optimized around the required operating conditions a centrifugal compressor might take some beating for a small machine like this, given the various design considerations/constraints.

[strad]

A supercharger works less well as the rpm increases and in general a turbo works best at higher rpms.

[xpensive]

What is a twin screw turbo, I googled it but I only found something which must be totally impertinent here?

[Holm86]

The twin screw supercharger if effective at creating boost at low rpm's.
So it would be completely pointless to create a turbo with a twin screw compressor stage as the turbo first needs to spool up. A supercharger is driven by the crank thats why they create boost so early.

And other than that you would need a gearing of some sort which instantly removes som efficiensy compared to a ordenary turbo that only have a direct drive axle.

[Holm86]

What is a twin screw turbo, I googled it but I only found something which must be totally impertinent here?

It dosnt exist. Its an idea from the thread starter?

[xpensive]

Aha, SRM, a Swedish invention that!

http://www.opcon.se/web/SRM_EN.aspx

[pgfpro]

Would a twin screw turbo work?
For the air compressor stage.

Twin screw superchargers are more effective than their centrifugal counterparts.
Of course their gearing will have to withstand higher rpms to work in a turbo.

I think I see your thought process on this?
To have the compress air efficiency of the screw compressor with the advantage of the turbine for less parasitic losses?

I think the hold up would be the mass of the screw compressor itself. The new turbo forged-machined aluminum compressor wheel's weight is next to nothing and is design to match the new Gamma-Ti turbine wheel's that is so light it's nearly the same weight as the forged-machined aluminum compressor wheel. This is approximately 1:1 ratio that they keep making improvements on every year. The compressor/turbine ratio plays a huge role in longevity at speeds of over 100k rpm.

[g-force_addict]

What is a twin screw turbo, I googled it but I only found something which must be totally impertinent here?

http://en.wikipedia.org/wiki/Rotary_screw_compressor
http://auto.howstuffworks.com/supercharger3.htm

[riff_raff]

Would a twin screw turbo work?
For the air compressor stage.Twin screw superchargers are more effective than their centrifugal counterparts.
Of course their gearing will have to withstand higher rpms to work in a turbo.

g-force_addict-

The simple answer is yes, the Lysholm compressor would function fairly well as an engine supercharger. This fact is made obvious by the numerous successful applications where Lysholm compressors have been used as engine superchargers. However, it would not be correct to unequivocally state that a Lysholm compressor is more "effective" than a typical turbocharger centrifugal compressor. While both devices are compressors, and they both can have very good efficiency, they actually function quite differently. The Lysholm is a positive displacement device with internal compression. It creates pressure by gradually squeezing the air mass into a smaller volume within the screw spaces. The turbocharger centrifugal compressor is a dynamic device that imparts momentum to the passing air mass, and that momentum is converted to pressure within the compressor diffuser housing.

The more complicated answer to your question is a Lysholm compressor is probably not a better choice for F1 than a turbo. The design of any engine is an exercise in compromise. The best choice of a particular subsystem device will depend upon many factors. For a pure race engine, the turbocharger gives the best combination of weight, size and performance.

Regards,
slider

[Tommy Cookers]

Thanks for that !

I'm thinking that the Lysholm is sold in part on durability

Other positive displacement designs were theoretically better, but had poor durability with sliding vanes and/or seals etc ?
Perhaps they should be redone with modern design and materials ?

The Wankel 'engine' is one such, NSU used it as a very efficient supercharger of a piston engine in a 1956? record motorcycle

Also the Comprex ?

[DaveKillens]

This type of forced induction is used a lot in dragsters, in the form of the Roots type blower. The reason why they are not used in Formula One engines is evident in these graphs, comparing a roots blower against a turbo. In a turbo, efficiency is higher at higher RPM.




Fundamentally, in a Roots type blower, as RPM and boost increase efficiency drops off. In a turbo, it gets better as RPM and boost increase.

[Holm86]

Does anybody know of the francis turbine??

How about replacing the standard turbine compressor wheel with a francis turbine wheel. I guess it would work but would efficiency be any better than a regular turbo?

[Tommy Cookers]

I think the OP had in mind road or 2014 F1 application, quite a low pressure ratio
and the basically poor speed/delivery characteristic of the centrifugal compressor

the Roots and centrifugal characteristics were all known 60-80 years ago to those who chose to work on raising the pr of positive displacement types

[DaveKillens]

There are some disadvantages of the Roots type blower. First, it requires power from the crankshaft. Secondly, it delivers pulses downstream. The straight lobes evolved into multiple screw lobes, all in an effort to reduce pulses. And additionally, they are efficient at low RPM or boost, but suffer as RPM and boost increase. Turbos are the opposite, they have terrible lag, but as boost and RPM increase, that's where they come alive.




For those delicate Formula One engines that have to live at high RPM for many races, having pulses travel down the intake is a nightmare. The helical screws help, but the pulses are still there. It's OK to have that happening in a Top Fuel dragster where you just dump huge quantities of fuel into the cylinders and pray they hold up for six seconds, but in a Formula One engine where efficiency and reliability is becoming more and more relevant, it becomes a liability.