Blowdown turbines

[trinidefender]

So we have been talking about blowdown turbines recently.

Here is an 11 page NACA report on blowdown turbines which I think at least a few will find interesting.

http://naca.central.cranfield.ac.uk/rep ... rt-786.pdf

While we are here I think we should include impulse turbines, reaction turbines and combination impulse reaction turbines (the most common type of turbine used in modern gas turbines). Should be a good place to discuss how all three types can be relevant to F1 and speculation on what types we think that teams use. If I am correct, I believe that most automotive turbocharger turbines are impulse turbines.

[trinidefender]

Haven't started reading this one yet but may be of interest as well.

http://www.dtic.mil/get-tr-doc/pdf?AD=ADB806068

An interesting point to note in the first document is that they separated the turbine with 4 different inlet, each covering 90 degrees of the turbine and helping to not mix pressure pulses from each piston. Is this viable in F1?

[wuzak]

Haven't read either yet, but isn't the term "blowdown turbine" specific to the installation in turbo-compounds? ie not a seprate type of turbine - the blowdown turbine will still be either an impulse or reaction turbine.

[gruntguru]

There is no doubt in my mind that all the F1 PU's are utilising blowdown energy as well as pressure energy.

Blowdown energy is "free" in that it can be utilised without increasing backpressure on the engine. Blowdown energy is contained in a brief high pressure, high velocity pulse ejected from the cylinder when the exhasut valve opens and the cylinder pressure is still much higher than the exhaust manifold pressure. To harness this energy, the pressure pulse must be piped to the turbine without adding pressure to the exhaust of any cylinder that is executing its exhaust stroke. If that happened, the pumping work of that cylinder would be increased by the higher back pressure. To ensure this happens, each exhaust header must service a maximum of three cylinders and those cylinders must be evenly spaced in the firing order. The headers must then be kept seperate all the way to the turbine and the turbine must be designed so the blowdown pulses from one header cannot communicate with another header. One look at any of the F1 PUs shows that they are all utilising blowdown energy (including Merc). The clue is the turbine itself having two seperate entries with three cylinders plumbed to each entry.

In addition to blowdown energy, the turbine can extract additional energy (pressure energy) if the pressure in the header is higher than atmospheric during the "non-blowdown" period. This will require the pistons to work harder during the exhaust stroke - robbing the recip' of some power. This lost power will however be less than the power gained from compressed intake air pushing the pistons down during the intake stroke (MAP will be greater than BP in a F1 engine). I believe F1 PUs are using pressure energy in addition to blowdown energy for the following reasons.

1. The airflow required to achieve the most efficient AFR cannot be flowed by the 1.6 litre engine without significant boost pressure. This boost pressure cannot be generated using the turbine power generated by blowdown alone - especially if some turbine power is to be harvested in the MGUK.
2. The most efficient combination of expansion in the cylinder followed by expansion in the turbine occurs at a significant turbine pressure ratio combined with a moderate recip' compression ratio - probably between 9:1 and 12:1. I explained this in more detail here http://www.f1technical.net/forum/viewto ... 73#p536873

[trinidefender]

Haven't read either yet, but isn't the term "blowdown turbine" specific to the installation in turbo-compounds? ie not a seprate type of turbine - the blowdown turbine will still be either an impulse or reaction turbine.

Not according to the link as I mentioned it there. They call it a blowdown turbine and throughout their tests it is run without the aid of a "turbo supercharger" as they called it or exhaust gas driven supercharger or simply turbocharger as we know it. From the article they seem to define a blowdown turbine as a turbine that harvests the kinetic energy of the pressure pulses in the exhaust gas from each cylinder separately.

[Tommy Cookers]

from searching the many NACA reports and technical notes of relevance, I nominate these .....

best for recovery turbines at various exhaust pressures try this, there is sea level data
http://naca.central.cranfield.ac.uk/rep ... rt-822.pdf

and this
http://naca.central.cranfield.ac.uk/rep ... n-1602.pdf


best for recovery by blowdown turbine try this
http://www.enginehistory.org/Wright/TC%20Facts.pdf

[gruntguru]

best for recovery turbines at various exhaust pressures try this, there is sea level data
http://naca.central.cranfield.ac.uk/rep ... rt-822.pdf

"The nett brake specificfuel consumption with a geared turbine is a minimum for exhaust pressures approximately 25% above inlet-manifold pressure and varies only slightly from the minimum for a range of exhaust pressures from 5% - 45% above inlet-manifold pressure"

At first sight this is a surprising result, but is most likely due to the fact that the engine was carburetted. The higher exhaust BP eliminates scavenge during valve overlap and the resulting fuel loss to the exhaust system. Of course the Wright Turbo Compound was direct injected which permited a positive pressure differential across the engine and beneficial scavenging of air without fuel loss.

[Tommy Cookers]

IMO the result should not be surprising - in your terms the turbine PR is greater, in mine the blowdown pressure loss is less

what you call scavenge is surely 'over-scavenge' - for cooling the exhaust valve but wasting fuel and maybe supercharger work
high overlap (really, later EV closure) ie tending to 'OS' was used quite early in WW2 by DB, later by RR
but not here
the R2800 (Pratt & Whitney) NACA engines were low overlap EVC 20 deg
even the V1710 (Allison) NACA engine was only 37 deg EVC
true, scavenge is a compromise, but .... (shall try to check the Wright TC EVC anyway)

to me the significant thing is how happy the 2800 was on real backpressure, and how unhappy the Allison was
so I have been suggesting for about 2 years that EVC must be matched to exhaust pressure
VVT would be nice but the F1 rules intend the matching to be done by modulating the mgu-h rpm

[trinidefender]

IMO the result should not be surprising - in your terms the turbine PR is greater, in mine the blowdown pressure loss is less

what you call scavenge is surely 'over-scavenge' - for cooling the exhaust valve but wasting fuel and maybe supercharger work
high overlap (really, later EV closure) ie tending to 'OS' was used quite early in WW2 by DB, later by RR
but not here
the R2800 (Pratt & Whitney) NACA engines were low overlap EVC 20 deg
even the V1710 (Allison) NACA engine was only 37 deg EVC
true, scavenge is a compromise, but .... (shall try to check the Wright TC EVC anyway)

to me the significant thing is how happy the 2800 was on real backpressure, and how unhappy the Allison was
so I have been suggesting for about 2 years that EVC must be matched to exhaust pressure
VVT would be nice but the F1 rules intend the matching to be done by modulating the mgu-h rpm

I also hold the opinion that EVC has to be matched to exhaust back pressure and toward this goal VVT is really idea. Direct injection does change it up quite a bit though, eliminating the over-scavenge problem.

Actually now that I think about it, variable turbine stators (or as they are termed in the automotive world, variable turbine nozzles) would make the whole controlling back pressure and throttling be achieved much easier vs having the mgu-h act as a throttle. It would also make the whole system much more efficient. Highly doubt it would be implemented on this generation of F1 engines though. Why won't they? I really don't know, it wouldn't cost too much as much of the work on variable valve systems and variable turbos has already been done in the automotive road car and segment for both technologies while gas turbines have been using variable stators for quite some time. I would imagine both technologies would broaden the powerbands, reduce fuel consumption and generally tie F1 back to road car technology and look green, what I thought they were trying to do.

[gruntguru]

Variable Nozzle Turbines ar not permitted. Personally, I think that VNT, along with VVT should be permitted as they are mature, inexpensive technologies and relevant to road cars. If the current F1 engine rules are genuinely aimed at developing transferrable technology, development in combination with VNT and VVT could only be beneficial.

[trinidefender]

Variable Nozzle Turbines ar not permitted. Personally, I think that VNT, along with VVT should be permitted as they are mature, inexpensive technologies and relevant to road cars. If the current F1 engine rules are genuinely aimed at developing transferrable technology, development in combination with VNT and VVT could only be beneficial.

I know neither are permitted. That is why I used the word "would." That's what I was saying, would be great if they shifted these technologies across from road car use to racing use.

On the topic of variable length intakes. They were slated to be legal for 2015 onwards. Is that still the case? I wonder how variable length intakes would interact with the turbo setup.

[gruntguru]

On the topic of variable length intakes. They were slated to be legal for 2015 onwards. Is that still the case? I wonder how variable length intakes would interact with the turbo setup.

That sounds dumb to me! Can anyone suggest how variable intakes would be of particular benefit or relevance? Remember these are fuel flow limited engines with the potential for massive oversupply of air.

[trinidefender]

On the topic of variable length intakes. They were slated to be legal for 2015 onwards. Is that still the case? I wonder how variable length intakes would interact with the turbo setup.

That sounds dumb to me! Can anyone suggest how variable intakes would be of particular benefit or relevance? Remember these are fuel flow limited engines with the potential for massive oversupply of air.

As dumb as it sounds it is true. They were supposed to be legal for 2015 onwards. If the FIA is still going to allow it I am not sure. I guess if an engine manufacturer can work out how to make a continuously variable system compact and light enough to be viable then it can be used to pulse tune the intake tract. With the current regulations and fuel limits I can't see how variable length intakes can help on the issue of power but maybe pulse tuning can help on the fuel efficiency issue.

[J.A.W.]

The arbitrary, 'Luddite' seeming.. F1 engine development restrictions are indeed vexing..
..Given that Honda was utilizing variable length intakes on its F1 cars ~1/2 a century ago..