Two stage Superchargers

[icepac]

Better not be too rude to others, either; if Rolls-Royce refer to compression ratio, in their engines, then who are we, following on behind, to put ourselves above them? Note that compression ratio and pressure ratio are not the same thing, either. CR measures the decrease in volume, while PR measures the increase in pressure; the two figures are never the same.

And it was called an intercooler (again by the manufacturers) because it was interposed between the compressor and the engine.

Edgar

So you call the charger cooler that sits after all supercharging stages the same name as the charge cooler that sits between stages of supercharging?

Hint: they use different names to indentify thier location on the engine.

This makes it easier to order the proper part.

All of the catalogs I have for marine and aero engines specify the charge cooler naming by where it sits in the induction system.

Nice spin attempt by using the mechanical compression of the engine as one of the "stages" of supercharging but you are as wrong as the multitude of others who parrot incorrect information so often than it becomes accepted.

 

[Tradewind]

Anyone here actually pumped 2 centifugal fan units in a staged arrangement to find out what actually occurs?

 

[Shortround6]

Not with air

The old fire pumps I used to work with had two centrifugal impellers that were piped to allow for both parallel or series use. It's been about 20 years since we got rid of them but as I recall the 1000gpm (gallons per minute) pump was rated at it's 1000gpm at 150 psi discharge (from draft) in parallel and 500gpm at 250psi in series.

 

[Zipper730]

Firstly: Aren't pretty much all twin-stage superchargers also twin-speed designs (if not more)?

Secondly: Are there any inherent advantage in weight, compression, some practical variable by having two compressors with individual cases, or two in one case?

Third: With the Merlin III having a pressure ratio of 3.5-to-1, the Merlin 25 at 4.5-to-1, and the Merlin 61 at 6.5-to-1 on two stages: I'm just trying to figure out how it didn't end up like 12.25-to-1 or 20.25-to-1?

I figure that there was some kind of loss by either

• Forcing the airflow through a a torturous path
• Some kind of effect of forcing the air through the after-cooler (drag)

Fourth: German Superchargers

• Hydraulic Clutching: If you have two speed hydraulic clutching, does that mean the gearing system has two ranges of speeds to operate within?
  
• Pressurized Cooling: I guess the advantage is the ability to more rapidly force coolant through the engine and carry away heat more rapidly?

 

[Shortround6]

The Merlin III didn't really have a pressure ratio of 3.5 to 1. it was more like 2.6-2.7 in service. You also have to know at what efficiency they pressure ratio is claimed. The Merlin III may have reached 3.5 but as the efficiency falls it requires more power to get the same compression and a larger amount of the power is converted to heating the intake charge vs actually compressing it. This becomes self defeating as the hotter charge is both actually less dense and more likely to suffer from detonation which limits the amount of boost you can actually use.

Part of the reason the two stage superchargers were more efficient is that each stage operated at a lower pressure level than single stage superchargers.
The Early Merlin 61 operated at about 5.25 to 1 and to reach that each stage only needed to operate at 2.3 or some combination that would reach 5.25. (12lbs boost at 22-23,000ft?)
with a given type of fuel there is only so much boost you can use and the more boost the higher the temperature which has to be reduced.

Power required for a supercharger goes up with the square of the impeller speed (tip speed) as a generality, number of impeller blades and size/shape of the blades also matter, so running superchargers at very high speeds increases power required and temperature rise very quickly.

For the Germans the DB hydraulic coupling (NOT clutch) worked like a torque converter on an automatic transmission. The more oil in the casing the closer the output shaft matched the input shaft in rpm. For the DB the coupling at max slip drove the supercharger (though a gear set) at about 7 times crankshaft speed. as the plane climbed a control feed more oil into the coupling and the output shaft progressively gained rpm until it maxed out at about 10 times the crankshaft speed. This eliminated the need for different gears.

You can only drive a supercharger impeller so fast. Once the tip speed exceeds the speed of sound at the pressure/temperature inside the supercharger you get shockwaves which disrupt the airflow though the supercharger. That is you upper limit. Likewise there is a lower limit at which the airflow tends to breakdown or surge. Aircraft superchargers are not positive displacement pumps. You don't get X amount of air moved per revolution of the impeller. At too low an airflow you get the air backflowing around the impeller at the outer limits of the casing. you need a certain volume of air moving through the supercharger to make sure all the air is going in the same direction (even if not at the same speed, there is a lot of turbulence in a supercharger)

It doesn't matter how many speeds you use in the drive system to the supercharger, the supercharger it self has an upper and lower limit of the rpm it operates at.

 

[Zipper730]

The Merlin III didn't really have a pressure ratio of 3.5 to 1. it was more like 2.6-2.7 in service. You also have to know at what efficiency they pressure ratio is claimed.

So above a point, the amount of compression requires disproportionate amounts of energy to do it?

The Merlin III may have reached 3.5 but as the efficiency falls it requires more power to get the same compression and a larger amount of the power is converted to heating the intake charge vs actually compressing it.

I thought if heat went up, pressure went up?

This becomes self defeating as the hotter charge is both actually less dense and more likely to suffer from detonation which limits the amount of boost you can actually use.

I know heat would cause detonation, but I'm not an expert on the subject of heat on pressure and density: Heat seems to increase pressure, but reduce density; the opposite for cold.

Part of the reason the two stage superchargers were more efficient is that each stage operated at a lower pressure level than single stage superchargers.
The Early Merlin 61 operated at about 5.25 to 1 and to reach that each stage only needed to operate at 2.3 or some combination that would reach 5.25. (12lbs boost at 22-23,000ft?)

So basically, the idea is to distribute the pressurization across two stages, with each doing enough compression efficiently and avoiding excessive engine work, and heat to do it?

Power required for a supercharger goes up with the square of the impeller speed (tip speed) as a generality

I'm curious why it increases to the square? It sounds like a simple/silly question, but I honestly don't have an answer: I merely memorize the rule, but honestly, I would have figured it'd gone up to the cube (length/width/height)...

For the Germans the DB hydraulic coupling (NOT clutch) worked like a torque converter on an automatic transmission. The more oil in the casing the closer the output shaft matched the input shaft in rpm.

Because the oil is slippery & lubricating...

For the DB the coupling at max slip drove the supercharger (though a gear set) at about 7 times crankshaft speed. as the plane climbed a control feed more oil into the coupling and the output shaft progressively gained rpm until it maxed out at about 10 times the crankshaft speed. This eliminated the need for different gears.

It seemed bizarre to me too! I didn't know exactly how it worked until now, but I did understand the variable-speed quality to it.

You can only drive a supercharger impeller so fast. Once the tip speed exceeds the speed of sound at the pressure/temperature inside the supercharger you get shockwaves which disrupt the airflow though the supercharger. That is you upper limit. Likewise there is a lower limit at which the airflow tends to breakdown or surge.

Is this similar to how a wing stalls?

Aircraft superchargers are not positive displacement pumps.

So a positive displacement pump is a pump that gets x-amount of air moved for a given number of rpm?

 

[Zipper730]

I don't know much about Roots superchargers, but I believe they are generally less efficient, or maybe less effficient at high pressure ratios.

They need more energy to pressurize the air?

In any case, in 1939 Mercedes-Benz improved their W154 Grand Prix car by changing from the M154 V12 with two parallel Rootes type superchargers to the M163 with a two stage system with two Rootes type superchargers in series.

So, it had some uses!

 

[Deleted member 68059]

If one makes a chart of compressor efficiency, you can start with one blade, then you can work upwards - where the eventual maximum efficiency is gained with an infinite number of blades (of infinitely small thickness).

A roots blower is (in some respects) a bit like having a centrifugal blower with 4 blades (an absurdly low number) - strictly looking at things from a compression efficiency standpoint. The fact its also positive displacement (flow = volume x rpm), means you get gigantic pressure pulses, this is why on clever roots "style" blowers, you see people putting in angled entry and exit passages such that the rotor opens out into the port gradually, and also why you get people using screw designs to try to even out these pulses. Pressure pulses create flow unsteadiness and other undesirable characteristics which all create inefficiency, this inefficiency is mostly manifested in the form of frictional losses (in viscous form within the flow and from the fluid to the walls), this heats up the fluid, which makes it expand. Somewhat the reverse of the purpose of a compressor.

In reality the number of blades in centrifugal blowers is limited by manufacturing, weight, area-blockage and skin-friction losses. However people try to get in as many as reasonably possible. The more you have, the less freedom the air has to do unwanted things in the flow channels, like recirculate and so on.

Roots blowers only really work acceptably by having a tiny clearance at the tips, which is virtually impossible to maintain, as the thing starts off cold then gets hot - and then it eventually starts to wear out as bits of dirt and grit get in and get ground up between the rotors, and makes any sort of very high compression impossible, as the stuff just tries to flow back through the tip clearances, and very high pressures distort the casing around the rotors.

However its interesting to reflect that the roots blower by itself does not actually compress anything at all anyway ! Its only moving a blob of something from A > B. So it will only add pressure when the inlet passage is appreciably bigger than the outlet, which is another way of saying its sized to supply more air than the thing using it at the other end needs. Whereas a centrifugal blower generates a pressure difference even sitting in free air at both ends spinning, as the difference in pressure is purely a factor of the outer radius minis the inner radius of the impeller.

Once nice thing about roots blowers (like axial compressors) is that in a long & thin rotor format, they do lend themselves to being packaged conveniently in small spaces around engines. Wheras a sodding great big centrifugal blower, which needs a big diffuser to work well, is a very large package problem unless the entire car/plane has been designed around it in the first place. They are also used sometimes by very lazy engine designers who want to make a "hot-rod" engine, without doing any hard design work. for which a positive displacement pump is ideal as it works the second it starts spinning, and hence has no "lag". The fact its about 25% less efficient than a proper compressor is something they decide they dont care about, as often a sufficient performance boost can still be reached on the available fuel without detonation occuring. Hence pathetically one or two car-makers are still selling cars with roots blowers on, which is pretty embarrassing.

Generally, except for very low pressure oil pumps for oil-mist scavenging, where it is useful to have a positive displacement action (which works at low speeds), nobody with any sense uses roots blowers for anything these days. Numerous people do for historical reasons (top fuel dragsters etc), but from a thermodynamics perspective they are horrid useless things for pumping compressible fluids (like air).

I would expect to receive various incredulous replies to this comment from any American friends reading, but sadly the fact is they are just not very good, but easy to use....

The earliest report I`ve read where all the above was definitively stated regarding the two methods was 1931, although it is very likely that reports are available saying the same thing going back well into WW1.

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Sadly the earlier comment that two-stage centrifugal superchargers are more efficient than single-stage because they can operate each stage at lower tip speeds, is not the case. Up to the limit of the single-stage compressor, in terms of pressure ratio, it is always considerably more efficient to achieve the compression in a single stage, as the air-path between stages is invariably convoluted and causes significant dynamic pressure head losses. A two stage is simply needed above a certain pressure ratio, as you just cant get a single stage to do it. This is one reason the German engines in WW2 stuck to single-stage SC`s too long, as certain of their top scientists in compressors were obsessed with things being as efficient as possible (Others decided on more power ! - with a less "efficient" solution...)

You also cannot lower the tip speed of a two stage blower for a given flow rate relative to a single-stage SC of the same overall size , because the flow rate is limited by choke at the inlet eye diameter of whatever the first stage is. So for a given throughput, added stages only add pressure - not flow, because if the compressor was designed to be as small as possible in the first place, the flow the engine needs will already result in the first stage eye being supersonic just above whatever the max performance was designed to be anyway. (I`ve sort of explained that backwards, sorry....). This is because there are fairly strict design guidelines on the ratio of the inlet eye to the impeller tip diameter in order for the compressor to work well, and so if you have run out of packaging space, you basically cannot increase the diameter of the inlet pipe to the supercharger. Of course real life is a bit more complicated, because some compressors will be designed (by accident or otherwise) to choke at the outlet first, or be totally under or oversized in the first place anyway - in which case lots of tweaks can be made.

But essentially in "maths-world" that is the limit to it.

 

[rinkol]

They need more energy to pressurize the air?
So, it had some uses!

Positive displacement superchargers, such as the Roots supercharger, were of interest on automotive applications since the availability of useful boost at low engine speeds avoided problems with throttle lag and helped maintain the available engine power over a broad speed range. The BRM V16 racing car from the 1950s was unusual for the time in using a centrifugal supercharger. This experiment was unsuccessful - while the engine could achieve high power levels at high rpm levels, the power fell off badly as engine speed decreased. As a result, the unfortunate drivers often ended up having to frequently shift gears in order to maintain a reasonably optimal engine speed.

 

[MiTasol]

Secondly: Are there any inherent advantage in weight, compression, some practical variable by having two compressors with individual cases, or two in one case?

See Engine design as related to airplane power : with particular reference to performance at varying alt for a discussion on all the various options in use or consideration in 1943

 

[wuzak]

With the Merlin III having a pressure ratio of 3.5-to-1, the Merlin 25 at 4.5-to-1, and the Merlin 61 at 6.5-to-1 on two stages: I'm just trying to figure out how it didn't end up like 12.25-to-1 or 20.25-to-1?

I figure that there was some kind of loss by either

• Forcing the airflow through a a torturous path
• Some kind of effect of forcing the air through the after-cooler (drag)

Looking at the gear ratios, the two stage engines had lower ratios than the single stage engines.

The Merlin 45 had a ratio of 9.1:1.
The Merlin XX had ratios of 8.15:1 and 9.49:1.
The Merlin 61 had ratios of 6.39:1 and 8.03:1
The Merlin 66 had ratios of 5.79:1 and 7.01:1
The V-1650-1 had ratios of 8.15:1 and 9.49:1.
The V-1650-3 had ratios of 6.391:1 and 8.095:1
The V-1650-7 had ratios of 5.80:1 and 7.35:1

So the superchargers of the 2 stage engines ran at slower rpm than the single stage engines. The S/Hi gear on the 2 stage was a lower ratio (slower speed) than the M/Lo gear on the single stage engines.

It made no sense to run them at the higher speed, as that would cost power and the engine could not take the boost, so it would have to be throttled.

Firstly: Aren't pretty much all twin-stage superchargers also twin-speed designs (if not more)?

No. There were different designs.

Pratt & Whitney 2 stage engines had Lo, Hi and Neutral for the auxiliary (1st stage) supercharger, which was driven independently of the main/engine stage supercharger.

Allison's auxiliary stage was driven by a fluid coupling, so had a variable ratio.

 

[Zipper730]

The earliest report I`ve read where all the above was definitively stated regarding the two methods was 1931, although it is very likely that reports are available saying the same thing going back well into WW1.

View media item 25548

I thought thrust loss was considerable for a turbocharger over a supercharger?

As I understand it, the turbo is either bypassed at low-speed with the exhaust exiting an alternate pathway; then the exhaust is not bypassed and goes through the turbine: As this happens, the RPM of the turbo goes from either zero RPM or wind-milling RPM to a higher figure, which starts compressing the air; as the air gets thinner, the backpressure lowers and the turbine is able to spin faster until the turbine limit is reached.

I'm curious if as back-pressure drops, thrust increases (however little) as the energy to drive the turbine still leaves some surplus that can expand reasonably well against the airflow, or stays about the same?

Sadly the earlier comment that two-stage centrifugal superchargers are more efficient than single-stage because they can operate each stage at lower tip speeds, is not the case.

That's good to know...

You also cannot lower the tip speed of a two stage blower for a given flow rate relative to a single-stage SC of the same overall size , because the flow rate is limited by choke at the inlet eye diameter of whatever the first stage is.

When you say "choke" do you mean the air-pressure dams up?

 

[GregP]

The terminology has also changed over time. What we know now as a turbocharger started life as a turbo-supercharger. Hence, some people maintain the Allison has no supercharger because they heard that somewhere, have never seen a diagram of it, or else don't know what they are seeing when they look at it.

The charge-cooling radiator in a Merlin was called an intercooler when it was developed, and today we know an intercooler as the thing that goes between two boost stages and an aftercooler as the thing that goes between the last stage and the engine. That is with 80 years language "development," or "recession," depending on your age.

The correct terminology depends on when you talking, and seems to change whenever marketing comes up with a new catch-name to charge more for it since it now seems "new." The kids today think that 4 valves per cylinder are a new development that came with the Japanese small cars and motorcycles, but the Allison had them as-designed in 1929. What they apparently didn't have was a great marketing department.

 

[wuzak]

The charge-cooling radiator in a Merlin was called an intercooler when it was developed, and today we know an intercooler as the thing that goes between two boost stages and an aftercooler as the thing that goes between the last stage and the engine. That is with 80 years language "development," or "recession," depending on your age.

It is still called an intercooler in the turbocharged cars of today.

But in multi-stage compressors they are aftercoolers, with intercoolers between stages.

I think there was also a difference in terminology from country to country.

 

[Deleted member 68059]

I thought thrust loss was considerable for a turbocharger over a supercharger?

The graph is brake horsepower - not airspeed. Its to show you the difference in engine power due to the different methods of efficiency in compression between roots, centrifugal mechanical and turbocharging. Ram and thrust effects are important but are a whole other thing to explain and cloud the issue of which method is the better compression method.

As I understand it, the turbo is either bypassed at low-speed with the exhaust exiting an alternate pathway

There is no generic way Turbos are installed. Its not very common to have a bypass to try to get thust - because the thrust only works well with short exhaust stacks with very carefully shaped outlets which converge to increase the gas speed. Simply dumping it into the airstream out of a tube before the turbo with a big butterfly valve is not going to get you anywhere fast. People certainly did it - but for the reasons stated it does not work very well.

I'm curious if as back-pressure drops, thrust increases (however little) as the energy to drive the turbine still leaves some surplus that can expand reasonably well against the airflow, or stays about the same?

Backpressure reduces of course with altitude, this basically increases the pressure-ratio across the turbine, which is more or less free power. This helps the turbo the higher you go, sadly there is a limit to all this, which is usually that you cease being able to do much extra as the turbine shaft speed has definite limits before it flies apart/the bearings "go". So eventually you need to open a wastgate to dump exhaust gas to slow the turbine down. When this happens depends on how the whole thing is sized in the first place/the desired boost/the mechanical limits - also possible that the compressor wheel flies apart before the turbine wheel does ! - This is why on a real power/altitude graph on a Turbocharged plane you`ll see almost flat power up to a very high altitude, then a rapid fall off - thats when the turbine & compressor shaft has reached max rpm. Which has much the same effect as running out of gears in a crank driven supercharger.

Eventually you`ll also fall off the egde of the compressor map as well.......

This shows you the compressor map from a turbocharged German aero-engine. You can see that the "consumption curve" starts bottom left and goes topwards top right as you climb, because it needs to have a higher compression ratio as you go up. Eventually you`ll "fall off" the edge of the map because you`ll either run out of shaft speed, or the efficiency will drop so low you`ll detonate (as it will get insanely hot).

View media item 25561
This shows you how air mass flow varies against altiutude at several different boost levels. Once you reach the limit for flow at max shaft speed - power falls away drastically. Just like hitting your full throttle point in your top gear in a mech. driven SC.

View media item 25560
I declare this to still be on-topic, because these charts are from a two-stage compressor !

 

[Zipper730]

The terminology has also changed over time. What we know now as a turbocharger started life as a turbo-supercharger. Hence, some people maintain the Allison has no supercharger because they heard that somewhere, have never seen a diagram of it, or else don't know what they are seeing when they look at it.

I suppose that could be either corrected or simply pointed out "sometimes simply called a turbocharger"...

The graph is brake horsepower - not airspeed.

I wasn't talking about speed either, I was talking about altitude (there was a mention of exhaust thrust).

Ram and thrust effects are important but are a whole other thing to explain

It depends on the carburetor intake and the airflow pathways

There is no generic way Turbos are installed.

Now, that's something useful to know

Its not very common to have a bypass to try to get thust

I didn't know that, I just thought they bypassed all the turbo's at low-speed to avoid an over-boost.

thrust only works well with short exhaust stacks with very carefully shaped outlets which converge to increase the gas speed.

Straight forward enough

Backpressure reduces of course with altitude, this basically increases the pressure-ratio across the turbine, which is more or less free power. This helps the turbo the higher you go, sadly there is a limit to all this, which is usually that you cease being able to do much extra as the turbine shaft speed has definite limits before it flies apart/the bearings "go". So eventually you need to open a wastgate to dump exhaust gas to slow the turbine down.

The limiting factor usually seems to be the turbine, sometimes the compressor is the limit, regardless above 1,300 fps you usually would see a fall-off (not sure what you could do with modern aerodynamics: Some fan-blades on jets can reach up to Mach 1.4 -- 1,610 fps at sea-level and 32F -- before efficiency fades) even if.

This is why on a real power/altitude graph on a Turbocharged plane you`ll see almost flat power up to a very high altitude, then a rapid fall off - thats when the turbine & compressor shaft has reached max rpm.

Logical

Eventually you`ll also fall off the egde of the compressor map as well.......

So basically it won't be able to continue to compress the air as efficiently at the minimum, it will produce disproportionate heat in the process, or actual pressure will lower to a point that it'll be impractical for use (even if above atmospheric) even if heat was not factored?

This shows you the compressor map from a turbocharged German aero-engine.

So Y-axis is fuel burn, and X-axis is rotational velocity?

Regardless what does "mGS", "Had", as well as V sub I, M^3/S all mean? I have a feeling I should know what it does but I have no idea.

This shows you how air mass flow varies against altiutude at several different boost levels.

So, the Y axis shows mass-flow?

BTW: What's ATA mean? I know the germans used it for engine power, but I have no idea if it means atm's or something different...

Once you reach the limit for flow at max shaft speed - power falls away drastically. Just like hitting your full throttle point in your top gear in a mech. driven SC.

 

[Deleted member 68059]

I suppose that could be either corrected or simply pointed out "sometimes simply called a turbocharger".

I have never seen it called a turbocharger in the English language during ww2, in a survey of thousands of archive documents. The term has a definite chronological impact - and is therefore not a "sometimes". 1965 is the first date it was used in any aerospace context in America (NASA-SP-7016, REV. 2) & the earliest UK refence to the term "turbocharger" is 1947 and the first appearance of it on https://www.flightglobal.com/FlightPDFArchive is 1970. So it is misleading to say it is "sometimes called a turbocharger". It was called turbosupercharger before the end of ww2, and the terms faded into one another after that. In present times, the term turbosupercharger is never used except in historical discussion. Sadly I do not know of the specific date it WAS first used, maybe some knows that here?

It depends on the carburetor intake and the airflow pathways

I suspect I`m overcomplicating what you are trying to say here but for your information German engines didnt have carburettors - and hence had NO chokes, so comparing any ram effects between Allied and German aircraft engines is impossible without correcting for pressure drop across the choke, which is worth a jump from 3:1 to 3.3:1 in compressor pressure ratio on a Merlin 45 for example (October 1942 Royal Aircraft Establishment Report#3958). This sort of thing makes it very difficult to compare performance of the actual compressors....

The limiting factor usually seems to be the turbine

References required.


Had mGS = Pressure Head Adiabatic (Had) in meters of gas column (mGS) (this axis would be labelled Pressure Ratio in Allied compressor maps, which is a totally different way of representing the pressure generation capacity of the compressor - but basically you can look at it as in y+ axis = more pressure).
ata = "technical atmospheres" absolute manifold pressure ~ more or less 1 Bar (0.98)
m^3/s = cubic meters per second (aka volumetric flow rate of the compressor)

 

[Zipper730]

I have never seen it called a turbocharger in the English language during ww2, in a survey of thousands of archive documents. The term has a definite chronological impact - and is therefore not a "sometimes". 1965 is the first date it was used in any aerospace context in America (NASA-SP-7016, REV. 2) & the earliest UK refence to the term "turbocharger" is 1947 and the first appearance of it on https://www.flightglobal.com/FlightPDFArchive is 1970.

It was never referred to as a turbocharger in slang prior to that?

So it is misleading to say it is "sometimes called a turbocharger". It was called turbosupercharger before the end of ww2

So, I could say "in modern days, turbosuperchargers are now called turbochargers", correct?

I suspect I`m overcomplicating what you are trying to say here but for your information German engines didnt have carburettors - and hence had NO chokes

What's a choke exactly?

correcting for pressure drop across the choke

That would mean the change in velocity -- I have trouble grasping that one. With radiators, if I recall the goal is to decelerate the airflow to exploit pressure; then run it through the radiator where it heats up and expands, with a reducing velocity and a pressure drop across the rear-side?

Had mGS = Pressure Head Adiabatic (Had) in meters of gas column (mGS) (this axis would be labelled Pressure Ratio in Allied compressor maps, which is a totally different way of representing the pressure generation capacity of the compressor - but basically you can look at it as in y+ axis = more flow).

Okay, but to be clear, adiabatic means a closed system where heat does not exit the system?

ata = "technical atmospheres" absolute manifold pressure ~ more or less 1 Bar (0.98)

So either 1.00 or 0.98 atms?

m^3/s = cubic meters per second (aka volumetric flow rate of the compressor)

Okay

 

[Deleted member 68059]

So, I could say "in modern days, turbosuperchargers are now called turbochargers", correct?

I think so yes.

View media item 25565
Without a choke (another case of changing nomenclature, its known now more often as the carburettor venturi, and choke is now typically known as the cold start assist enrichment valve) - a carburettor doesnt work, as you need a pressure difference to suck fuel out the float-bowl. Hence a venturi (which chokes the flow a bit) is inserted to increase the flow velocity where the main jet emerges. Which is the significant power potential advantage of injection, in that this "restrictor" no longer exists.

View media item 25564
The equation used to calculate Adiabatic pressure head by German compressor designers was this ^

Where gamma = 1.4, the P term is pressure ratio, T0 is entry temp and R=gas constant. You need to be a bit careful with the term adiabatic, its a "closed" process in as far as we assume that the actual physical compressor housing does not transfer its heat to the outside air, BUT - we are certainly saying with it that its non-reversible. In that to change the volume (eg compress the air) it DOES take energy away to do so, which IS removed from the process (and hence needs to be put IN for it to be done), as mechanical work.

One technical atmosphere (ata) = 0.98 Bar.

I would add (respectfully), that the last three points above can be google-searched quite easily,....so I hope you might try to do so from now on - and keep the questions to things you need the specific knowlege of the forum to answer..Its not very fair to ask me to spend time writing all this out saving you from typing "adiabatic", "choke" or "air pressure ata" into google..

 

[pbehn]

We may live in a binary society as far as "chokes" go in cars. The last car I owned with a manual choke and a button on the dash with a "C" on it was a Mini I sold in 1983. I just asked my daughter and she has never heard of or seen a choke in a car, though they obviously do have some sort of cold start mechanism built in.