new garrett's (dualboost)
#26
On a standard turbine there is a radius between the inducer and exducer as the flow of exhaust is inserted from the vertical and exits on the horizontal.
On the dualboost design the flow goes from vertical to the horizontal via that heat shield and then it enters the turbine wheel horizontally and exits horizontally.
#38
The axial turbine deal is pretty clever. Compared to radials, axials can't do high expansion ratios (which is why you see multiple axial stages on aircraft) but they can operate with higher efficiency over more of the operating range.
This efficiency advantage of axials is particularly large when the exh gas velocity is high compared to the turbine tip speed, precisely the situation that presents itself during an engine's blowdown period. The axial is simply better able to convert the engine's exh pulse energy into boost.
And compared to radial, the axial is inherently a tidier wheel (lower mass, less inertia). The inertia situation is further improved by the higher rotational speeds, which lets everything get smaller and less inertia-y.
On top of that, there's a big reduction in aero-induced thrust load on the rotating group. Less thrust load = lower bearing losses = more zippier turbo.
To me the coolest part is that the improvement in transient response comes without adding much if any cost. The construction of a dualboost turbo is basically the same as a traditional wastegated turbo.
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