Quote:
Originally Posted by ForcedInduction
Heat is only what is making the gasses expand. Its the aerodynamic flow of the gasses across the turbine that does the work, not the heat.
A turbine is a turbine, they all work by the push of gasses flowing over the work surfaces, the temperature makes very little difference. Thats why a turbo will make the same boost just as easily with 600*f exhaust as it can with 1600*f exhaust.
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No offense intended by the following wording FI....I just want to be very clear:
The above is flat-out incorrect.
I think that by insisting on that 'windmill' view, you're holding yourself back from even greater turbo-mastery than you already have.
The turbine absolutely will NOT "make the same boost just as easily" with 600F gas as with 1,600F gas.
In fact, it will require -considerably- more mass-flow at 600F than at 1600F; to produce the same shaft-power (psi x cfm of boost, or compressor-massflow)
Again, a turbo-turbine is NOT just a windmill....NOT just a simple propeller...it IS a HEAT ENGINE.
....so you gotta remember your Carnot...
I sense that you're (reasonably) resisting changing your view of how turbos work just on my word....so I urge you to look it up in any turbomachinery textbook, and verify for yourself that what I'm saying here is true.
It's clear that you already know a ton of good stuff about turbos from the practical/usage side; so I think that if you give yourself the advantage of correctly viewing them as heat-engines instead of as simple 'fans', you'll find the use and tuning of them more intuitive, and even more rewarding.
PS; the Carnot numbers also imply that not only can more shaft-power be extracted from hotter gas, but also that a higher -percentage- of that higher energy can be extracted. (i.e. higher efficiency too)
That's why the output-power of heat-engines (including turbos) tends to rise NON-linearly with input temp. Double the temp, get four times the power....roughly that sort of relationship....and with much higher efficiency at the same time.
That first-order relationship between temp and both power and efficiency is why the jet-turbine guys are always pushing the limits of materials so they can raise the turbine-inlet temp just another 100 degrees.
It's also a partial factor in why adding an intercooler tends to reduce the boost a few psi at the same engine conditions as before.
It's not just the added flow-resistance of the IC....it's also the lower energy-content of the cooler exhaust, plus the reduced efficiency of the turbine at that new lower temp....it's a double-whammy on the turbine power output.
The same factor is why it's an advantage to wrap the headers....i.e., to maintain the gases as hot as possible going into the turbine.