|
|
Colyn writes:
<<<< say more about the turbo stall issue?
>>>>>
You will have to pardon my sloppy vernacular. Supercharged or
supercharging is the general case where there is some kind of
compressor ahead of the intake valve. Turbo supercharging is the
specific case of the turbine driven centrifugal compressor. TSIO = Turbo
Supercharged Injected Opposed
When I wrote to "turbo stall" I should have said Turbocharger
Compressor Stall. Compressor stall happens when the mass flow /
pressure ratio is too high for for a given shaft speed (high boost at
high altitude). One of the things that controls shaft speed is the A/R
ratio (Discharge Area over Radius to the centroid) of the Compressor,
where the higher the A/R the slower the speed.
When I designed the Lycoming installation I hired a retired Garrett
engineer, Paul Uitti, as a consultant to make specific component
selection recommendations. Paul had designed the TIO540-AE2A turbo
system for the Malibu Mirage. His turbo recommendation was for the T04
with a compressor A/R of 0.50 and a M13 A/R 0.58 on the turbine. This,
combined with running higher compression pistons (8.7:1) and low
maximum MAP of 35" kept me on the right side of the surge line.
Paul was the one that told me that the original TSIO550 had evolved
from a turbo normalized 520 and that the compressor selection was
marginal so to limit the pressure ratio of the compressor they limited
the pressure drop across the turbine with a restrictor. Remember that
the turbine and the compressor share a shaft and so their torque must
match and the mass flow doesn't change (except for the addition of a
little fuel).
One other observation. A few hundred hours ago I put insulating wrap on
the crossover tube that balances exhaust manifold pressure by allowing
exhaust flow from the left bank to the right bank, where the wastegate
is located. At the 1,000 hour inspection I was disturbed to see that
the crossover tube had significant thermal deterioration. This
indicated lots of flow at high temperature. This also indicated that
there was plenty of reserve turbocharger "margin" as the wastegate had
to be open at high power settings.
I resolved the crossover damage issue by fabricating a new tube and
making a radiant shield that would allow airflow over the tube. Moral
of the story, don't wrap your headers.
I hope this clarifies things.
Regards
Brent Regan
|
|