I scored 5 :-(
Detention for me...
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5 too.
8-(
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7, more by luck than judgement
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I read often, only post occasionally
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6.
Imagine my surprise given the only one I knew was why aluminium wasn't used. The rest were complete gue....
...I mean....ahem. Er... - 6 - yes 6. I knew all the answers to those 6.
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Adam
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Let just say I got a "needs improvement"
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I'd quarrel with the answer to No. 2 - how does the turbo derive its energy source from the temperature of the exhaust gas?
(7/n, need improvement).
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Yes, and when has a supercharger been the same thing as a turbo? i thought a supercharger was mechanically driven off the crankshaft?
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I got 11!
Oh and Turbocharging is Supercharging.
A super charger is a pressure pump driven by the engine generally these days meaning mechanically but Supercharging is pressurising the incoming gases however its done. Turbo charging is specifically driven by the exhaust gases.
Jim
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7 (needs improvement) here
Stargazer
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I'd quarrel with the answer to No. 2 - how does the turbo derive its energy source from the temperature of the exhaust gas? (7/n, need improvement).
Because the hot gasses are expanding.
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>> I'd quarrel with the answer to No. 2 - how does the >> turbo derive its energy source from the temperature of >> the exhaust gas? Because the hot gasses are expanding.
Surely immediately after combustion, the gasses start to cool?
Anyway, surely it's only gas pressure that drives the turbo -
isn't the fact that a gas, heated, expands, a red herring?
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"Surely immediately after combustion, the gasses start to cool?"
What do you class as immediately? Distance between cumbustion and turbo is probably about 4 feet, all enclosed in heated ducting unable to expand. Its hits turbo plenum where it can expand, microseconds after combustion, probably having lost about 1% of its heat energy. Ever seen a glowing red hot turbo?
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In what way does anything but gas pressure make a difference?
"Surely immediately after combustion, the gasses start to cool?" What do you class as immediately?
After the fuel/air mix has gone "BANG"!
Distance between cumbustion and turbo is probably about 4 feet, all enclosed in heated ducting unable to expand. Its hits turbo plenum where it can expand, microseconds
Microseconds? I'd have to work out the volume of the gas, the volume of the pipe, etc.
after combustion, probably having lost about 1% of its heat energy.
So it has lost heat and started to reduce in volume...
Ever seen a glowing red hot turbo?
No.
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after combustion, probably having lost about 1% of its heat energy.
>So it has lost heat and started to reduce in volume...
No because its never had the chance to fully expand since it went bang.
If there was no more expansion going on there would be no pressure.
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>> after combustion, probably having lost about 1% of its heat >> energy. >So it has lost heat and started to reduce in volume... No because its never had the chance to fully expand since it went bang.
"The potential for volume increase due to temperature has reduced" - better?
If there was no more expansion going on there would be no pressure.
Eh? Can't work that out at all.
Anyway, here's the nub:
In what way does anything but gas pressure make a difference?
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Distance between cumbustion and turbo is probably about 4 feet, all enclosed in heated ducting unable to expand.
4 feet, in what engine?
Its hits turbo plenum where it can expand, microseconds after combustion, probably having lost about 1% of its heat energy. Ever seen a glowing red hot turbo?
It could lose 25% of it's heat and still be red hot.
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7 for me.
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7, of which approx 6 were complete guesses.
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6. And I can't see how a turbo derives it's energy from the temperature of the exhaust gas.
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6 and like the rest of you I disagree with some of the answers that are supposedly correct. We can't all be wrong can we?
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Espada III - well if you have a family and need a Lamborghini, what else do you drive?
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I agree with the supercharger thing. Its not a turbo. That is, not a turbo driven by exhaust gasses. Its a compressor not a turbo.. Assuming a turbo is driven by gasses, but then a Turbo compresses.... DOH!
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I scored 11 (smug mode off..)
Now, back to the temperature / pressure thing. The gas expands through the turbo, and as it does so its temperature goes down - not because it it is losing heat to the atmosphere, but simply because it is expanding, and temperature and pressure are inextricable linked by Boyle's law, and hence the power from the turbo comes both from the pressure and the temperature. When the air is compressed by the other end of the turbo, not only its pressure but also its temperature rises (which is why there's all that stuff about charge cooling) - which is just the opposite effect.
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RichardW
Is it illogical? It must be Citroen....
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I scored 11 (smug mode off..) Now, back to the temperature / pressure thing. The gas expands through the turbo, and as it does so its temperature goes down - not because it it is losing heat to the atmosphere, but simply because it is expanding, and temperature and pressure are inextricable linked by Boyle's law, and hence the power
Sorry Richard, Boyles Law relates pressure and volume, I think you mean Charles' Law or the combination of the two in the Ideal Gas Law.
StarGazer
from the turbo comes both from the pressure and the temperature. When the air is compressed by the other end of the turbo, not only its pressure but also its temperature rises (which is why there's all that stuff about charge cooling) - which is just the opposite effect. -- RichardW Is it illogical? It must be Citroen....
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See, I wrote that in there and then was about to backtrack and write words to the effect of "Smug mode now in the back of the cupboard", but then submitted it anyway. And I was wrong. Well half wrong anyway - Boyle's law is P1V1 = P2V2
Anyway, P1V1/T1 = P2V2/T2 was what I was getting at, which is part of the ideal gas law. Of course, exhaust gas is likely to be far from ideal, but it's a start....
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RichardW
Is it illogical? It must be Citroen....
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Another point re the heat loss of the exhaust gasses:
For instance on a 4 cyl turbo the turbo is getting 2 dollops of red hot gas every revolution where as each individual cylinder is only pumping exhaust gas every other revolution and is therefore cooled by the induction stroke, accordingly where the gas itself will cool a fair bit from combustion to turbine the turbo it'self may run at very near combustion chamber temps.
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I got a not too good 6.
I also got question 2 wrong for thinking too far into it: the energy is not sourced from the pressure and temperature of the exhaust gas, but from the difference between those and the ambient temperature and pressure.
I wasn't trusting them to ask me a truthful question after they said a turbo and a supercharge were the same thing!
Also I'm dubious as to the answer of question 4. Surely oil can cool?
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Mike Farrow
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"Also I'm dubious as to the answer of question 4. Surely oil can cool?"
Yes it can and does in other applications. When things are very hot however oil is not used, it has a tendency to catch fire.
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I would imagine that all turbos which are lubricated by oil are also cooled by the oil to some extent.
Like some others above, I have some concerns about the validity of some of the given answers.
I scored a lamentable 9 points!
Number_Cruncher
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Turbine bearings are cooled by oil and can also, additionally, be cooled by water, however IIRC the point was the cooling of the charge air not the turbocharger it'self.
I suggest that the questions/answers may appear ambiguous when viewed from, a motoring perspective because the refer to the wide gamut of turbocharging applications such as aero engines, commercial engines etc.
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I scored 9 points and thought I did well, you're too hard on yourself.
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Well, I got 11; but I cheated, I read the info on the site first.
Perhaps I am a little more expert now! I shall read Toad's nice new electronic boost gauge (installed by my own fair hand - first auto job in years, and one requiring some thought which would have been expensive bought by the hour) with even more interest.
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What's a turbosupercharger then ? They were used in some WW11 aircraft by the Americans .....
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The Luftwaffe was very fond of using them too.
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IIRC the RR Merlin had a twin stage supercharger and was cooled using glycol (an oil based compound).
I scored 7. Some of my answers were based on ignorance of questions on specifics but I thought some of the general answers were wrong.
I'm not losing any sleep on it as I did not bother reading the blurb at all:-).
madf
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