Superchargers- how do they work?!?

[seesul]

Wow, thanks for the perfect drawing Micdraw!
So as I can see this is the turbo supercharger so in fact turbocharger!!!
Don´t know why but I was always told that b-17 didn´t have turbocharger but mechanically driven supercharger. This picture shows something else- a pure turbocharger....with a waste gate system for the boost pressure control and intercooler for the power increasing...wow, what a technology back in 40´s...
Thanks again mate!

[HoHun]

Hi Seesul,

>This picture shows something else- a pure turbocharger....

If you have a look at the Supercharger Flow Diagram, you can find a mechanically-driven Supercharger there as well: Follow the intake airstream though A, B and C, and right after the fuel injection, you'll see a part labeled "impeller". This impeller is the wheel of the mechanically-driven supercharger, also called "engine stage" in US terminology since it was part of the basic engine. In the schematic drawing, it's located right on the back of the crankcase and appears to be driven directly by the crankshaft, but I'm not sure this is entirely accurate - I think it might be driven by a geared transmission in order to reach the high speeds usually require for centrifugal superchargers.

Regards,

Henning (HoHun)

[seesul]

Thank you for your note, haven´t noted it.
Yes, you´re right there´s a mechanicaly driven turbine but I can´t see any RPM/pressure control system on it. Should it be a supercharger it would cause overpressure in the air intake at high engine RPM. Maybe stupid thought but it could be device for a better mixture distribution into the cylinders.
But anyway, the main part that is on the lower part of the wing is turbocharger.
Think I´ll print out this drawing and will ask some crew member from one of 3 B-17 beeing displayed in Duxford...I´m leaving for Duxford tomorrow...

[seesul]

Henning,
here is the text I got from Jim Peters, a former engineer of a B-17, WW2 vet, few months ago...that´s an excellent explanation. I´ve forgot I have it and found it now...

Roman :......There are three types of superchargers.... One is belt driven that in effect pumps air at an increased pressure to the carburetor. Second is an internal so-called supercharger that by rotating with the engine distributes the air/fuel mixture to each individual cylinder more or less evenly, which is it's purpose. Third is the exhaust driven turbosupercharger, which consists of two wheels mounted above each other,where both rotate on a common shaft. This third type has the exhaust driving a turbine wheel which , when the exhaust gasses flow through the turbine wheel, causing it to spin...at the same time rotating the compressor section which pumps compressed air to the carburetor, also there is an item called a waste gate, which when open....bypasses the exhaust past the turbine wheel, but when closed causes both the turbine wheel and the compressor to spin...the B-2 type had a top RPM of 23,500 RPM and the B-22 had a top RPM of 26,000 RPM...both were used interchangeably. This waste gate is controlled,so that the exhaust gasses,pass through the turbine wheel in varying pressures, causing the turbine wheel to spin faster and faster as the waste gate is closed gradually. This turbosupercharger is compact....with only about an inch (25cm) seperating the turbine wheel half from the half that compresses the air going to the carburetor, and the turbine wheel which operates at 1500 degrees F,from the air compressor which is drawing in and compressing the up to -60degrees F. going to the carburetor. In efffect, all this does is fool the engine into thinking it is operating at sea level pressure..14.7 Inches Manifold Pressure...(37cm), when it is operating at an altitude of 30,000 ft, where the pressure is down to 1.5 inches of Manifold pressure or 4 cm. Therefore the actual pressure being delivered to the carburetor is at roughly 12 inches of manifold pressure or 30cm. Does this make sense to you ? Control System....the early B-17 through the "F" model was operated by hydraulics where an engine driven hydraulic pump on the two inboard engines, supplied hyd pressure to operate the waste gate, but was troublesome in that the lines and fittiings were subject to damage. With the "G" model (and also the later B-24s) the hydraulic system was replaced by an all electric controlsystem which then had a electric motor closing the waste gate, along with a pressuretrol which sensed the alititude, an overspeed governor which did not allow overspeeding of the turbine wheel, and where the control system had what was known as a Wheatstone Bridge Circuit, whereby any unbalance of an input would cause the system, after making the change to automatically balance itself. The cockpit control was called a TBS for TurBo control, where one control knob controlled all four engines simultaneously. There was also an amplifier for each engine, a junction box for each engine, a waste gate motor for each engine, a pressuretrol for each engine, all conncected by the one circuit called a Wheatstone Bridge, again where either the cockpit control, pressuretrol (altitude) or overspeed governor would automatically maintain the setting of the cockpit control. The WW II aircraft operated on a 24V DC electrical system. and the turbo control system operated on a 400 Cycle 115V AC system...this 400 cycle 115 V was supplied by an Inverter which was an electric motor driving a 115v 400 cycle generator, on the same shaft. The B-17 landing flap position indicator was also operated by this same 115v 400 cycle supplied by the Inverter. My scanner is not working or I would scan a photo of an exhaust driven turbosupercharger. I hope you can understand this explanation. If not, please ask. Jim

_____________________________

James S. Peters Sr. T/Sgt
B-17 Flt Engr, 27 missions
99 BG, 348BS, 5th Wing, 15th AAF
Tortorella, (Foggia#2), Italy
My Tour was from 12/03/44-06/19/45
M/Sgt USAF (Retired)

[Heinz]

Great info guys!

[red admiral]

Figures from Rolls-Royce for Spitfire XIV

Super-chargergear Altitude(ft)Withoutexhaustthrust-Withexhaustthrust

MS 5,000 345 351
13,500FTH 388 400
23,500 373 399
FS
31,500FTH 419 454
40,000 377 424

[vanir]

Race engineering was an earlier hobby of mine, I'd like to add to the description of superchargers. Keep in mind my expertise is more automotive engines than aero engines, which have some different rules due to operating altitudes.

There are a few distinct types.
Roots type and centrifugal (compressor) type.
Exhaust driven and mechanically driven.
Clutched and direct drive.
Multiple stage and multispeed types.

All these can be easily divided into the two groups of roots and centrifugal.
Turbochargers and centrifgual compressors use identical construction, but different drives. They are the same thing and work differently from roots type blowers.

Roots type blowers are inefficient but mechanically uncomplicated.
Centrifugal blowers (including turbochargers) may be highly efficient but must be carefully tuned, set up and maintained.

Centrifugal blowers are the type generally used in aero engines. A turbosupercharger is essentially a two stage blower with the second stage driven by exhaust fumes. Multiple stage superchargers have both (or more) stages mechanically driven. The different stages may be two separate installations or one widened casing with two impeller sizings.
Multiple speed superchargers have one installation with a clutched or synchronised, multiple speed gear drive for it.
Turbochargers have extra piping and equipment and are generally larger, heavier and more complicated than mechanically driven compressors (until you start playing around with multiple stages and speeds, which can make a mechanical installation quite heavy and cumbersome).

Centrifugal superchargers rely upon an impeller to compress intake charge within a spiral casing. Tuning the impeller capacity to casing diameter provides the engine operating parameters at which maximum efficiency is attained. All centrigual blowers have a fairly narrow band of high efficiency, it may be say, 65% at 1000rpm/sea level, 110% at 2000rpm/sea level and 165% at 3000rpm/sea level, then 75% at 3500rpm/sea level. Change altitude you get a different effect. You might get 110% at 3000rpm/4000m and 140% at 3500rpm/4000m, but this is a problem if your motor redlines at 3200rpm.

Hence you have multiple stage superchargers, one small casing say, and one bigger, for high efficiency at low altitudes (roughly speaking), then regained efficiency at higher altitudes. This acts as if you are back at sea level for operating efficiency. At lower altitudes the high altitude impeller just doesn't spool up (ie. operates at something like 5% efficiency if that) so you don't have any detrimental effect from it. But hit the right altitude and it's like a kick in the guts for the motor.

Another way to improve supercharger efficiency is to use charge coolant. Water injection for example might lower the heating effect of compressing intake charge (which is a limiting factor on supercharger efficiency), so you might get a return of 185% at 3000rpm/sea level on your motor. Problem is the air intake being cooled actually reduces manifold pressure. It's a net gain in power, say 80hp in a 1000hp engine but reliability is vastly improved.

With actual boost systems fitted, like water injection there is a combination of wastegate adjustment and charge coolant. The Fw-190A system for example uses a two stop system operated by the pilot, the first stop adjusts the wastegate and the second stop activates a C3 fuel injector in the supercharger exhaust casing (used for charge cooling before MW-50 kits were available from the manufacturer in Jan44).

All centrifugal superchargers (including turbochargers) use a wastegate system to limit boost pressures at maximum power settings and engine speeds, particularly in the case of overspeeding the engine. This may be as simple as a pressure release valve located on the supercharger casing.
Yes I know it is mounted in the exhaust stream on turbochargers. It is on the casing in mechanical types for the same effect. No it is not a blow off valve, they're piped to the intake manifold proper. (just pre-empting arguments here)

So whilst supercharger efficiency at the higher boost pressure drops back a little (metered by the charge coolant), it now functions at 1.58ata instead of 1.42ata and gives a net gain of some 300hp, for a limited duration.

With multiple stage superchargers some sort of charge cooling is necessary, because intake is passing through two compressions and heats up quite a bit, dramatically reducing overall efficiency. Intercoolers and aftercoolers are the preferred method although in some cases water injection either substitutes or supplements.

With particularly light airframe engineering requirements like the Me-109 a few innovations were used to achieve the effects of multiple speed supercharging and aftercooling, in order to keep the weight down. A hydraulic drive system was used on the 605/603 motor impeller which acts like a multiple speed drive and increases best operating altitude by about 2000m, but without the extra mechanicals of a genuine multispeed system. MW-50 charge coolant was introduced in 1944 to also allow wastegate adjustment for higher, limited duration boost pressures in the later 605 motors (1.8ata and 1.92ata), for a net gain of 300-450hp without the weight expense of aftercooling.

For a complete mechanical setup, a high output engine using a turbosupercharger with intercooling just check out the sheer size and complexity of a P-47 engine layout.

A multispeed impeller drive essentially increases the operating altitude of the motor a little. To raise the operating altitude a bit more, you put in another gear. Multiple stages put the intake charge through another process of compression.

[kool kitty89]

A turbosupercharger is essentially a two stage blower with the second stage driven by exhaust fumes.

This isn't necesarily ture. The term turbosupercharger was used simply to refer what is now usualy called just a turbocharger. Turbo-supercharging may refer just to the use of a turbosupercharger, but since in operational WWII US context there was always an "engine supercharger" any turbocharging would have a mechaicaly driven supercharger stage as well.


Something that often gets mixed up is two-stage and two-speed superchargers. (though this has pretty much been adressed here already, these are some pretty common mistakes made in literature which can be confusing)
As mentioned a 2-stage supercharger has 2 impellers with one feeding into the other; there are several configurations of this, usually 2-speed and always multi-speed.
With a multi-speed supercharger (usually 2-speed), it can be single stage. Take the Merlin XX, using a 2-speed supercharger. (single stage is implicit)
There are also cases like the DB 601, 605, and 603 which had variable speed supercharger driven by a fluid coupling and didn't have a finite gear ratio.

With 2-stage supercharger there are several different configurations: the one used on the Merlin had both impellers driven by a common shaft with 2 gear settings. The US engines (partiularly Pratt and Whitney) had the standard single-stage single-speed "engine stage" mounted to the back of the engine, along with a significantly larger external stage with multi-speed gearing. (neutral, low blower, and high blower)

THere were also some cases with both stages of a 2-stage supercharger having individual multi-speed gearing, but I don't know if these saw operational use. (I believe some German engines used this configiration expirementally)

[seesul]

the more posts in this thread the more I learn, thx guys!

[HoHun]

Hi Vanir,

>(used for charge cooling before MW-50 kits were available from the manufacturer in Jan44).

Do you have any source for the January 1944 introduction (or any introduction at all)?

>All centrifugal superchargers (including turbochargers) use a wastegate system to limit boost pressures at maximum power settings and engine speeds

In aero engine applications, mechnically-driven superchargers typically use a throttle instead. I'm aware of wastegate configurations only for turbo-supercharged engines.

>With particularly light airframe engineering requirements like the Me-109 a few innovations were used to achieve the effects of multiple speed supercharging and aftercooling, in order to keep the weight down.

This had nothing to do with weight - the system was already used in the DB 601, and it was later adopted by Allison and used in a fighter as heavy as the F-82.

Regards,

Henning (HoHun)

[vanir]

This isn't necesarily ture. The term turbosupercharger was used simply to refer what is now usualy called just a turbocharger. Turbo-supercharging may refer just to the use of a turbosupercharger, but since in operational WWII US context there was always an "engine supercharger" any turbocharging would have a mechaicaly driven supercharger stage as well.

In engineering a turbocharger is a layman introduced term that appeared somewhere along the way for what is just a supercharger. That said, so is "turbosupercharger" and you are quite correct. As a layman's term it doesn't really describe any particular piece of engineering, it just became a popular term for a particular supercharger setup, like turbocharger did. I appreciate what the common terminology means in the US and thankyou for the input. It makes some American aero publications I've been reading make more sense (about the D-motor for instance).

It's probably a similar thing with turbojet and turbofan, which evolved really as layman's terms for various bypass and whatnot, I wouldn't be surprised if jet/turbine engineers pull their hair out over that. "Turbojets" frequently used bypass too, for cooling purposes. Then you have high bleed, low bypass turbofans and oh my god I don't even know what I'm talking about

Popular use of certain terminology is by no means universal, a good point and one for the reader to keep in mind.

Do you have any source for the January 1944 introduction (or any introduction at all)?

Let's see. Mercedes Benz AG archives, Stuttgart (second hand, cited by the comprehensive DB605 homepage of an enthusiast).
Joe Baugher.
I'll have to look up others. I've read repeatedly the 801D-2 had always been intended to mount MW-50, but production of the kits was delayed unexpectedly. I presume C3 injection was introduced as a stop gap. I've seen no primary source documentation...but for one.

A graph of comparative performance (I can attach) which shows A-8 (801D), A-9 (801TS), Ta-152C-1 (603LA) and Ta-152H-1 (213E) performance curves at sondernotleistung. The A-8 has a very interesting graph showing two different maximum performance settings, one for 1.58ata and one for 1.65ata. The A-9 has just 1.65ata. Keeping in mind C3 injection is not as an effective charge coolant as MW-50...this could be consistent with the two performance curves representing both C3 injection and MW-50 use for the 801D motor in the A-8.

It's a lot of assumptions, isn't it.

Do you have references/documentation to the contrary? I'm open to a qualified correction, as always. I want to know, rather than claim but I do simply speak freely as at the best information at my disposal. No offense is intended.

Another confusing thing about the 801, MW-50 issue is that I've noted recent American sources in particular, even among engineers refer only to MW-50 use and seem completely unaware of the C3 injection system. But at the same time documentation of the use of C3 injection in the 801 is taken from US examination of probably an F-8.

This boost system has caused me more headaches than any other factor about WW2 aircraft. Just trying to figure out exactly what it was, how it worked, what its specifications were, what its particulars are.

Please, by all means, put this one to bed.

In aero engine applications, mechnically-driven superchargers typically use a throttle instead. I'm aware of wastegate configurations only for turbo-supercharged engines.

Safest bet is to look them up at engineering sources but I'll explain amid my own meagre comprehension.
Wastegate is the term describing valves mounted within the supercharger casing to release unusable or dangerous pressures. All superchargers from the roots GM 6:71 diesel type to the turbosupercharger of a P-47 Thunderbolt have them.
Adjusting the wastegate adjusts boost under given conditions, say full throttle and maximum operating speed. On an engine driven supercharger it is mounted to the impeller housing. On an exhaust driven supercharger it is mounted in the exhaust stream driving the impeller. The key point is that by adjusting this valve, you adjust boost pressure at a given condition.
A US document at Luftwaffe experten clearly describes the manual operation of the wastegate in the mechanically driven BMW 801D supercharger, for attaining the higher boost pressures used in conjunction with C3 injection.

This had nothing to do with weight - the system was already used in the DB 601, and it was later adopted by Allison and used in a fighter as heavy as the F-82.

I spent quite a bit of time and argument researching this particular issue. I'm open to correction, but gathered the 601 used a mechanically driven supercharger where the 605 and 603 used a hydraulically driven one. This is consistent with the full throttle heights for these engines in conjunction with altitude performance graphs and low altitude outputs.
It is noteworthy I began with the assumption the hydraulic drive was used on all 600-series engines, but was repeatedly and markedly corrected as I (unsuccessfully) sought a blueprint for the 601 engine/supercharger.

Since the present assumption appears consistent with all available data, naturally I would nevertheless gladly accept any documentation, particularly blueprints of the 600/601 supercharger displaying a hydraulic drive. It is however listed as mechanical at various aero/engineering sites, where the 605 and 603 are specifically stated as hydraulic and innovative.

[vanir]

Just to clear up another potential problem...about wastegates. On a roots type blower these are simply a pressure release valve tapped in. The reason I made the earlier distinction with centrifugal blowers is that on these it is more likely to be a more complicated driver/pilot adjustable valve system termed wastegate. Turbochargers always have complicated wastegates even if automatically controlled, because of the need to vary the release of exhaust pressure at different operating speeds.

[HoHun]

Hi Vanir,

>In engineering a turbocharger is a layman introduced term that appeared somewhere along the way for what is just a supercharger.

What Koolkitty pointed out is that the turbo-supercharger was always used in connection with an engine-driven supercharger stage in US engines of WW2. It was not a terminology remark.

>Let's see. Mercedes Benz AG archives, Stuttgart (second hand, cited by the comprehensive DB605 homepage of an enthusiast).

You were talking about the BMW 801. Re-quoting:

"The Fw-190A system for example uses a two stop system operated by the pilot, the first stop adjusts the wastegate and the second stop activates a C3 fuel injector in the supercharger exhaust casing (used for charge cooling before MW-50 kits were available from the manufacturer in Jan44)."

So it's BMW documentation I'd like to see.

>Do you have references/documentation to the contrary?

You claim MW 50 for the BMW 801, you bring documentation. I'm quite aware of the countless claims for MW 50 in popular books, but haven't seen anything backing it up, ever. There is quite a community of researchers on the various internet fora, and I know they have been looking for information on MW 50 for years - in vain, as far as I'm aware.

>A US document at Luftwaffe experten clearly describes the manual operation of the wastegate in the mechanically driven BMW 801D supercharger, for attaining the higher boost pressures used in conjunction with C3 injection.

Well, bring it here. I believe you must be misreading something as the increased boost ("Erhöhte Notleistung") was invoked by a manually operated valve, but it affected the operation of the BMW's Kommandogerät computer, not simply that of the supercharger.

>I spent quite a bit of time and argument researching this particular issue. I'm open to correction, but gathered the 601 used a mechanically driven supercharger where the 605 and 603 used a hydraulically driven one.

The DB 601 had the same hydraulical supercharger drive as the DB 605. See attached manual page ...

Regards,

Henning (HoHun)

[vanir]

Originally Posted by HoHun

Hi Vanir,

>In engineering a turbocharger is a layman introduced term that appeared somewhere along the way for what is just a supercharger.

What Koolkitty pointed out is that the turbo-supercharger was always used in connection with an engine-driven supercharger stage in US engines of WW2. It was not a terminology remark.

>Let's see. Mercedes Benz AG archives, Stuttgart (second hand, cited by the comprehensive DB605 homepage of an enthusiast).

You were talking about the BMW 801. Re-quoting:

"The Fw-190A system for example uses a two stop system operated by the pilot, the first stop adjusts the wastegate and the second stop activates a C3 fuel injector in the supercharger exhaust casing (used for charge cooling before MW-50 kits were available from the manufacturer in Jan44)."

So it's BMW documentation I'd like to see.

>Do you have references/documentation to the contrary?

You claim MW 50 for the BMW 801, you bring documentation. I'm quite aware of the countless claims for MW 50 in popular books, but haven't seen anything backing it up, ever. There is quite a community of researchers on the various internet fora, and I know they have been looking for information on MW 50 for years - in vain, as far as I'm aware.

>A US document at Luftwaffe experten clearly describes the manual operation of the wastegate in the mechanically driven BMW 801D supercharger, for attaining the higher boost pressures used in conjunction with C3 injection.

Well, bring it here. I believe you must be misreading something as the increased boost ("Erhöhte Notleistung") was invoked by a manually operated valve, but it affected the operation of the BMW's Kommandogerät computer, not simply that of the supercharger.

>I spent quite a bit of time and argument researching this particular issue. I'm open to correction, but gathered the 601 used a mechanically driven supercharger where the 605 and 603 used a hydraulically driven one.

The DB 601 had the same hydraulical supercharger drive as the DB 605. See attached manual page ...

Regards,

Henning (HoHun)

I take it there's some reason you're looking for a fight? Surely a bar brawl would be more satisfying than a web argument with a sincere poster.

I have to go to work in five hours, so I'll answer all your questions tomorrow. You have so very many questions, but it's such a lonely place at the top, yes?

It's alright mate. Take it all in stride. You're being argumentative. Chill.

[HoHun]

Hi Vanir,

>I take it there's some reason you're looking for a fight?

If you can't handle a simple request for sources without taking it as a personal challenge, maybe you should stay on the safe side and don't make any doubtful claims - or better, don't make any claims at all.

>I have to go to work in five hours, so I'll answer all your questions tomorrow.

As far as I'm concerned, no need to - you're going to be on my ignore list by then.

Kind regards,

Henning (HoHun)