A friend of mine postulated about adding an STS blower to the intake of an ATI blower. This may seem absurd, but blown diesels are now doing just that, supercharging turbo systems and mixing with propane for unbelievable power. I presented an alternative to my ATI supercharger, with an STS and he said I should keep the ATI, but add the STS.

After looking at the plumbing of an STS, it would not be too far-fetched to consider such an alternative.

What sort of issues and performance outcomes would be possible? Just a wild topic to dicuss...

UD

 

you'll need to do some math to get the rite turbo...

 

The book I am reading has a Blower-turbo set up (gas engine in a hot rod). At high turbo boost there is positive torque to the front of the crank through the blower belt.

 

i cant imagine that, unless you are talking about VERY high boost pressures, that boosting the supercharger would help. Turbos already heat up the air charge, and then to run the air through a supercharger (which heats up the air even more than a turbo does) I would question how dense the air charge making it into the motor would relaly be. Why not just run a high boost supercharger or a high boost turbo?

 

theoretically, if the pressure from the turbo was greater then the superchargers to make boost, the supercharger would become a restriction. at the same token, if the supercharger was no longer the main compressor in the system, the air should not be heated by the superchargers compressor side. now.. the correct style for this setup would be the roots style blower as this is a positive dispacement compressor meaning that if you put in already compressed air, the roots style blower should compress it even fuirther increasing boost pressure. serious intercooling would be a MUST on this system. I know volvopenta uses a dual system on there marine engine, but with an infinite amount of cooler then ambient air temperature water available for intercooling purpose, it work very nicely!

Chris

 

What, exactly, do you think is the advantage to a blower + turbo combination? More boost???

 

engineermike,

I don't know that it would be a route i chose to go in a car.. unless it was just for Wow appeal.. and uniqueness, but for marine use where motors are run at mid to high rpm throughout the day, the supercharger helps to make torque way down low for immediate response for planing, and the turbo generates power exactly where its needed, the point just before plane out when the hull is plowing through the water and has the most resistance.

but i agree, I think one or the other is plenty on a car, adding that many systems for power sounds like a very expensive, experimental, and problem prone setup!

Chris

 

I thought under the same boost, turbos heated the air more due to the extra heat coming from the exhaust?

 

depends on a few things, smaller turbos yield igher intake air temps.

Im not sure about centrifugal blowers, but i knw roots type are someting like 50% efficient, whereas most turbos are ~75% efficient. The heating is not due to the turbine housing, the heating is the thermodynamic product of compressing the intake charge.

 

The heat from the turbine housing is minor. Turbo's typically have peak efficiencies around 77% while centrifugals run around 72% max. Higher efficiencies have lower discharge temps. I had a B&M 144 at 7 psi that was running 38% efficient.

Mike

 

Also, when you put 2 compressors of the same size in series, regardless of type, the 2nd one increases the pressure much more than the first.

At my work, we use multi-stage recip (PD) as well as centrifugal compressors. The latter stages are always sized smaller, but supply the same dP as the earlier stages.

 

Correct, we are doing this on our cummins turbo diesel customers. Its compound turbocharging....doesn't necessarily add hp, but allows you to run much higher pressure ratios, which diesels do. On a gasoline engine, this would be a waste of time. I doubt any of you will be running 100psi of boost anytime soon on a V8....hehe

Jose

 

Mike,

I don't see it... if you have a belt driven compressor, and a turbo which is going to be capable of moving more airflow at lower RPM due to the fact thats its gas driven... you will actually be pushing on the face of the blades of the supercharger compressor creating a condition where the compressor is the restriction... its the same effect as cooling fans running while at a 70 mph cruise.. they become restrictive to cooling air trying to cross through. if both compressors are of equal size, and spinning at equal speeds, then yes.. the second compressor has to work much less to inhale the charge and will be compressing an already compressed charge from the first compressor. so for your work experience, yes you are correct, but in this instance, the supercharger would have to be sized properly, and the turbo would need to be controlled via VNT or other means to maintain a beneficial compressor wheel speed or else there would be points where the supercharger is in the way. the best approach would be to have a bypass with check valves in place and a gate to transfer the charge air from the supercharger at low rpm for torque off idle, and then open to the turbo at boost threshold where the turbo begine to create higher pressure then the supercharger. opening the supercharger to atmosphere would also eliminate a very large percentage of the crank shaft parasitic loss from the compression process, this would equate to a linear power curve gaining both at the bottom end and top end of the operating range.

Chris

 

It works like this. . . the air is compressed as it enters the supercharger. Compressed air is more dense than atmospheric pressure air. So, since the air is more dense, it also has more weight for centrifugal force to act upon. Therefore, the centrifugal supercharger will cause a greater pressure increase when fed already-compressed air.

Don't believe it? Look at a compressor map (either supercharger or turbo - doesn't matter). The Y axis of the chart is pressure RATIO. That is, the absolute discharge pressure divided by the absolute inlet pressure.

If you run a Vortech S-trim at a typical 40 lb/min and 25000 rpm, the pressure ratio is 1.3, which, if pulling from atmosphere, will supply 4.41 psi boost.

Now. . . supply the same S-trim at 40 lb/min and 25000 rpm with 10 psi from a turbocharger. Now, at the same 1.3/1 pressure ratio, the discharge pressure (boost) becomes 17.4 psig.

You see, supplying the supercharger with pressurized air only makes it boost the pressure by a greater amount. It will not get in the way or restrict flow unless you reach sonic velocity, or choke, somewhere in the housing. You would have to make somewhere around 1000 hp to get there, which I don't think is going to happen "at a lower RPM".

 

Actually, opening the supercharger discharger to atmosphere would add parasitic loss to the crank. This is also counter-intuitive, but when you open the discharge of a centrifugal machine (pumps or compressors), the flow rate goes through the roof. You wind up doing more total work (and taking more power to do it) even though there is no discharge pressure.