Talking to a turbo expert

[ringo]

For white blue, this is smikle's calculation a while back in the engine thread. You really need charts or a program to find enthalpies.

First you deal with the compressor work. This comes off the turbine.
After doing all smikle has done, you can look at the quality of the exhuast that's left back to figure out how much load the turbine can take.
This is all limited to the exhaust energy, you can't get more than that, and you can't take it all.
I will try and do a whole calculation, engine and turbine, but it's going to take some time, since i have to refresh my memory.

That calculation applies to the compressor side which I assume needs less power compared to the potential in the exhaust gas. The reason I make this basic assumption is the history of super efficient piston aero engines after WWII and serially turbo charged plus turbo compounded commercial truck engines you find today.

Yes, after you take way the compressor load, you can look at what's left. This varies through the rev range obviously, as the efficiency of turbine and compressor vary.But for simplicity you can use one value for both.
One thing though, you cannot use every drop of energy, the turbine exhaust pressure has a role to play in what's left.
All that matters is that the generator load + compressor load is not more than the energy coming from the exhuast manifold.
I'm gonna do the calculation, gimme a while.

[WhiteBlue]

It is fine if you do that but please consider that the the 2013 engine will have a mass flow of 0.36 and not 0.48 kg/s. The target is reducing the fuel consumption by 25% which will directly impact the air mass flow.

Also the turbine design needs careful consideration. If radial turbines have only 70% efficiency and axial turbines had already 82% in 1950 F1 should not be using inefficient hardware. Please also consider the twin spool design which I proposed. I believe it is essential to a high efficiency of the total design by making the rpm of the compounder and the charger turbines independent of each other. Alternatively one could also avoid the concentric shafts of a twin spool design by exiting the compounder shaft as a free shaft to the other side.

[riff_raff]

WhiteBlue,

At the mass flows and pressure ratios an F1 engine would require, a single stage centrifugal compressor and turbine would be best. Axial flow compressors and turbines are more efficient with larger sizes and lower PR's per stage. But with a 2:1 or 3:1 PR turbo on a 1.6L engine, the dimensions, tip clearances and tolerances very much favor a centrifugal device.

Since turbochargers are dynamic compression devices (as opposed to positive displacement devices like a Rootes supercharger) their performance is affected by intake/exhaust flow densities, pressures and velocities. By nature, a turbocharger should always have a positive work balance between the turbine and compressor. But how efficient that balance of work is becomes a function of how close the turbine and compressors are operating to their best efficiency.

Dynamic turbines (and their compressors) are driven by the transfer of momentum or impulse energy from the exhaust gas flow to the turbine blades. So the more efficiently that exhaust gas flow imparts its energy onto the turbine blades, the more work the turbine can transfer to the compressor. This why variable geometry turbine nozzles can be so effective.

Nice discussion.
riff_raff

[xpensive]

@ Terry;

Swedish technology is usually a safe bet; http://www.lysholm.us/

[WhiteBlue]

WhiteBlue,

At the mass flows and pressure ratios an F1 engine would require, a single stage centrifugal compressor and turbine would be best. Axial flow compressors and turbines are more efficient with larger sizes and lower PR's per stage. But with a 2:1 or 3:1 PR turbo on a 1.6L engine, the dimensions, tip clearances and tolerances very much favor a centrifugal device.

Since turbochargers are dynamic compression devices (as opposed to positive displacement devices like a Rootes supercharger) their performance is affected by intake/exhaust flow densities, pressures and velocities. By nature, a turbocharger should always have a positive work balance between the turbine and compressor. But how efficient that balance of work is becomes a function of how close the turbine and compressors are operating to their best efficiency.

Nice discussion.
riff_raff

If I want to use a single turbine for turbocharging and turbo compounding I would have to go for a hybrid solution and split the two power streams electrically. The compressor would use an electric motor for powering and for the surplus electric energy I would use for my electric front wheel motor.

But I have my doubts that this concept would have the highest efficiency. This is why I would use two turbine stages as the diesel truck engines do.



The turbo machinery is shown in red and the gearbox in green. The compounding power is targeted at 65 bhp. This means that total engine power would be raised to 715 bhp by the HERS compounding system without increase of fuel consumption.

If this system fails I would go straight back to the original R-3350 design and take the compressor power directly off the crankshaft by a supercharger and do the complete turbo compounding with one axial turbine. I actually have my doubts that this would be more efficient than two turbines with dedicated consumers and free rpms.

[ACRO]

the mighty wright 3350TC worked a little different. it was supercharged for boosting the cylinders and turbocharged for power take off to the crankshaft via reduction gear. it had THREE compund turbocharger

btw- a beautiful engine. running in the 50,s it has a two stage mechanical blower, turbo compounding, DIRECT FUEL INJECTION!!!- it represended the very last technology in big radial aero piston engines before the turbine came.

well, turbocompunding is not new, but you have to use two turbochargers and not a spiltshaftdesign.

the reason is that one turbine has to be mechanically conneced to the crankshaft and is so directly dependable on the engine speed where the other stage is dependable on the volume of exhaust gases and not the engine speed. in situations like shifting down with closed throttle the turbocharging stage would spin down where the turbocompunding stage would spin up. it this case you would get surge and stall effects. you cannot build it like a real gasturbine where a two spool design is common.

all designs i know, turbocoumpunding or a two stage turbocharging incorporate two independent chargers and not a two shaft design in one package.

the general idea of turbocompunding is to further increase power when you cannot do it further by higher boosting due to material limits of the internals for a specified engine life.

at f1 when they want to reach a higher power than lets 650hp boost they will simply rise the boost pressure instead of searching horses in compound systems.

nevertheless the turbocompund idea is an interesting technology

[WhiteBlue]

The writhe 3350 TC did not use turbo compounding initially in the B29 and other military installations. TC was added for the civil airlines to reduce the fuel consumption and make transatlantic and South American destinations possible with direct flights. The engine was supercharged from the crank shaft from day one as all applications of that time needed high altitude modes for military purposes.

The turbo compounder is an axial one stage segmented device. Due to packaging considerations it is split into three units.That way it can be sized approximately like the cylinders and does not need a bigger cowl than the non TC engine.

The engine simply shows that by the use of appropriate turbines an additional 25% shaft power can be generated from the exhaust energy. I don't think it will make much difference if you take the compressor power from the crank shaft or from an independent exhaust turbine. In the end it is an issue of weight and cost which way you decide to do it. If you run the compressor directly from an exhaust turbine you have a lot less mechanical gearing to do. Only the residual turbo compound power has to be rpm reduced. I think it is cheaper that way.

Btw, the serial design of a standard turbo charger and a turbo compounder as in the Scania package is no different to what I am proposing except that I think axial turbines would be more compact and efficient. The fact that the Scania design is in commercial use shows that the compounding turbine can run downstream from a turbocharging turbine without negative interference if you run it on an independent shaft and rpm.

[WhiteBlue]

The writhe 3350 TC did not use turbo compounding initially in the B29 and other military installations. TC was added for the civil airlines to reduce the fuel consumption and make transatlantic and South American destinations possible with direct flights. The engine was supercharged from the crank shaft from day one as all applications of that time needed high altitude modes for military purposes.

The turbo compounder is an axial one stage segmented device. Due to packaging considerations it is split into three units.That way it can be sized approximately like the cylinders and does not need a bigger cowl than the non TC engine.

The engine simply shows that by the use of appropriate turbines an additional 25% shaft power can be generated from the exhaust energy. I don't think it will make much difference if you take the compressor power from the crank shaft or from an independent exhaust turbine. In the end it is an issue of weight and cost which way you decide to do it. If you run the compressor directly from an exhaust turbine you have a lot less mechanical gearing to do. Only the residual turbo compound power has to be rpm reduced. I think it is cheaper that way.

Btw, the serial design of a standard turbo charger and a turbo compounder as in the Scania package is no different to what I am proposing except that I think axial turbines would be more compact and efficient. The fact that the Scania design is in commercial use shows that the compounding turbine can run downstream from a turbocharging turbine without negative interference if you run it on an independent shaft and rpm. The axial turbines some companies are now designing for use as range extenders must have very similar sizes. In fact they are probably around 40 hp power and not the 170 we are talking here. So I would not be too concerned that axial turbines would not be available in the size segment.

[timbo]

I don't know why you would want turbo compounding if you'd have option of running generator with the exhaust.
Compounding IMHO would be as lossy as generator and more prone to mechanical failures.

PS it was successful (mildly) on airplanes because they operate at the same revs for the most time.

[ACRO]

@whiteblue: true, the first 3350 double cyclones were not turbo compounded- not even fuel injected. but we talked about the 3350TC (tc for turbo compund). in his last series it was in my eyes a really masterpiece of piston engine for that time.

its also right that nearly all engines used supercharging and not turbocharging- one reason was the poor metallurgy and handling the high exhaust gas temperatures at turbine entry in those days. the 3350 was the first and only engine of that class that used super and turbocharger. btw- this thing achieved for 2 minutes ( max take off) a bmep of far above 250psi 50 years ago...

well, how do in know... ? i,m an airline pilot, of course never had flown a super connie or something like that, but i,m just interested in that kind of engines


regarding the turbocharging: when i understand your picture right you want a turbocharging and compounding turbine in ONE housing. that will give you the problems i wrote above.

running multiple independent chargers downstream really does not seem to be a problem - scania like you said e.g VW runs two chargers downstream ( but both for boost) . but it is a different story if you talk about running two chargers downstream or if you talk about a two shaft exhaust charger in ONE housing where one stage is exhaust gas flow dependant and the other is engine rpm dependant. that will cause surges and stalls at some engine conditions, and nobody builds it thatlike ( as far i know)

you are right that the exhaust turbine is axial flow- all turbochargers turbines are thatlike, and the compressor in a turbocharger is always centrifugal flow.

long story short conclusion : TC is a very interesting story, used in aviation, and scania used it in trucks. but nearly all manufacturers refuse of using it, a more efficient turbocharging with higher and higher boosts seem to be the better way.

in formula i , with quick changing engine loads, it makes no sense for me. and you will see in 2013 that f1 will see nothing of a compund system or a turbo which drives an generator but a solid twin turbo mounted downstream in two housings. the first turbo is small for low engine rpms and quick reaction, the second, bigger turbo will kick in at higher rpms and loads for a sufficient boost.

it today simply seems to be the best and most efficient way to do it.

regards

[WhiteBlue]

I don't know why you would want turbo compounding if you'd have option of running generator with the exhaust. Compounding IMHO would be as lossy as generator and more prone to mechanical failures. PS it was successful (mildly) on airplanes because they operate at the same revs for the most time.

I don't really care which way it is done as long as it is efficient and generates additional power from the exhaust beyond just the power for the compressor. Electric conversions are not at all lossless. The motor, the generator and twice the power electronics are contributing to heat losses when you take the hybrid electric route.

The important thing IMO is not missing out on an opportunity to recover an energy potential that is bigger than KERS and may come with lower weight penalties.

[autogyro]

http://en.wikipedia.org/wiki/Rolls-Royce_Crecy

Sorry fellas it goes full circle and ends up here again.

[ACRO]

I don't really care which way it is done as long as it is efficient and generates additional power from the exhaust beyond just the power for the compressor.

i think you make here a mistake in thinking. the turbocharger is fed by the combustion gases . the more the charger pumps air in the engine the more fuel can be fed in the engine, the more exhaust gases are produced which drive the charger faster and faster giving more boost which allows to even more fuel be combusted. its a circle. at low rpm,s /low throttle instantly there are not enough combustion gases from the engine to fully drive the charger and a turbo lag occours.

when you set a benchmark to 650hp in our 2013 engine and it should be reached by turbo compunding it means that a part of power comes not from boosting but from mechanical assistance of the second charger.

this means that the first charger has too boost lower because the second charger also will do a job. this means that the lower boost give less exhaust gases for driving the second charger. its a circle again.

compunding would make fully sense when our 2013year 1.6 litre would not be able to accept a boost that is sufficient for reaching 650hp alone. then you could in compound systems look for additional power. but our 1.6 litre will accept 650 just from turbocharging and so it makes no sense to put a compound charger behind it only to boost lower or otherwise getting an engine that produces more than 650hp.

compounding is a way to rise overall power of the engine without rising the bmep - but when you can reach the wished power by boosting alone it makes no sense.

thats why all manufacturers go in charging and not charge-compounding with todays better materials of the engine core ( pistons, rods, crankshaft etc...)

[WhiteBlue]

regarding the turbocharging: when i understand your picture right you want a turbocharging and compounding turbine in ONE housing. that will give you the problems i wrote above.

running multiple independent chargers downstream really does not seem to be a problem - scania like you said e.g VW runs two chargers downstream ( but both for boost) . but it is a different story if you talk about running two chargers downstream or if you talk about a two shaft exhaust charger in ONE housing where one stage is exhaust gas flow dependant and the other is engine rpm dependant. that will cause surges and stalls at some engine conditions, and nobody builds it thatlike ( as far i know)

you are right that the exhaust turbine is axial flow- all turbochargers turbines are thatlike, and the compressor in a turbocharger is always centrifugal flow.

long story short conclusion : TC is a very interesting story, used in aviation, and scania used it in trucks. but nearly all manufacturers refuse of using it, a more efficient turbocharging with higher and higher boosts seem to be the better way.

in formula i , with quick changing engine loads, it makes no sense for me. and you will see in 2013 that f1 will see nothing of a compund system or a turbo which drives an generator but a solid twin turbo mounted downstream in two housings. the first turbo is small for low engine rpms and quick reaction, the second, bigger turbo will kick in at higher rpms and loads for a sufficient boost.

it today simply seems to be the best and most efficient way to do it.

regards

What kind of difference should it make to the turbines in what kind of housing they sit? My design is simply a bit more compact. Aerodynamically and thermodynamically it should be a bit more efficient and that should really be the difference because designing two axial stages surely must give you a better air flow with lower losses compared to the way Scania does it. What matters is the technology you use, such as temperature resistance of the exhaust valves in the engine in order to tolerate more heat from the back pressure of a more efficient turbine package. The super Conny engine had a mean time between overhauls of 3500 h. An F1 engine in 2013 has a life expectancy of 12-15h.

You as an airline pilot should appreciate the higher efficiency of axial turbines and compressors. All modern turbofan, turboprop and turboshaft engines use axial technology due to the higher efficiency. Helicopter turboshaft engines and turboprop engines btw use the same design that I propose here. One turbine provides power to the compressor for the engine and the other drives the shaft for propulsion. Chrysler used the design in their automotive turbine in the sixties. The compressor was radial but both turbine stages were axial.



If you think away the monstrous heat regenerators you have a glimpse how compact a 100 kW two stage turbine really is.

To adapt to operating conditions both turbines could be fitted with computer controlled variable vanes. Compared to the engine management complexity of modern direct injection engines without throttle it should not be a big deal to provide good turbine operation over a wide band of primary ICE operating conditions.

Just bolting on the biggest and baddest turbo charger is not the most efficient way to go. Any boost will also increase the exhaust gas flow so that you end up with more wasted exhaust gas potential. Besides boost pressure will be legally limited to 2 bar. So it makes sense to think about how to recover the exhaust gas energy. It can be either done by electric compounding or mechanical compounding which ever way is more efficient.

[WhiteBlue]

http://en.wikipedia.org/wiki/Rolls-Royce_Crecy

Sorry fellas it goes full circle and ends up here again.

I don't see the reference as useful. The Crecy exhaust regeneration was never really successful and thrust from the exhaust is not a feature that F1 cars can use. So I fail to see how this particular engine could educate us on turbo technologies, which is the issue of this thread. The Wright 3350 TC was successfully flown for more than a decade creating huge benefits for the airlines and the people using them. Aircraft with 3350TC engines held the records for long range powered flights for a very long time.