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Effect of Three Modifications on Performance of Auxiliary Stage Supercharger for V-1710-93 Engine

Three modifications of the auxiliary-stage supercharger for the
V-l’llO—QS engine were designed. and tested as part of an investigation
to improve the power output and the altitude performance of the engine.
A 12-.vane diffuser was substituted for the standard ill—vane diffuser,
and a vaneless discharge passage and a modified scroll were designed
to increase the flow capacity of the supercharger and thereby to
increase the performance at the high volume flows required by the
engine.

With the lZ-vane diffuser installed and the carburetor replaced
by an adapter, the equivalent volume flow at the peak efficiency point
was increased 25 percent at the lowest speed investigated and 9.5 per-
cent at the highest speed. When the carburetor was usgd, anyr increase
in equivalent volume flow was masked by choking in the carburetor. A
small decrease in the peak adiabatic efficiency resulted from using
the 12 —vane diffuser. At the high volume flows where the supercharger
is required to operate, the performance was improved by the lZ-vane
diffuser.

With the vaneless discharge passage, the surge—free range of the
supercharger was increased 35 percent at the lowest tip speed investi-
gated by increasing the maximum air flow. The maximum air flow at
high tip speeds was again limited by choking in the carburetor, which
masked the effect of the vaneless discharge passage on the maximum
air flow.

At the high volume flows near the operating point of the
supercharger, the performance with the vaneless discharge passage was
better than that with the standard ll-vane diffuser. At the low
volume flows the standard ll-vane diffuser gave better performance.
The modified scroll gave performance characteristics that were prac-
tically the same as those of the standard scroll except at high tip
speeds, where the peak performance was improved.