Turbo from Space, The Porsche 997 Turbo

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Turbo from Space, The Porsche 997 Turbo

Christophorus Magazine 318, Feb/March 2006

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The Porsche 997 Turbo

Porsche Turbo Technology

variable-turbine geometry turbocharger

In the new Porsche 997 911 Turbo, everything is much more Precise and More mature, thanks to the- variable-turbine -geometry. "We have high rotational Speeds at the turhine wheel

Porsche turbo technology for model Porsche 997

The new Porsche 997, 911 Turbo has added power once again. A new Porsche technological advance has made that possible: For the first time in a Porsche, a Porsche turbocharger with variable-turbine geometry is to be used in a gasoline engine.

Porsche's Variable-Turbine Geometry (VTG) turbocharger system

Again and again, Thomas Krickclhcrg Picks LIP the dull-silvery shining part. "With this Porsche turbocharger, Porsche will reinforce its position as the forerunner in turbo technology," says the engineer, project manager for the Porsche Carrera drivetrain at the Development Center in Weissach. And he adds: "Like its predecessors, the Porsche 911 Turbo will become a technology pioneer, and a milestone." And the seven-kilogram (15-Ib.) part that elberg so lovingly rocks in his hands is a major reason for that. For the first time worldwide, the sports car maker is building a porsche turbocharger with variable-turbine geometry (VTG) into an Otto engine. The turbocharger blades onto which the hot exhaust gas impacts are aligned variably in the gas flow at the optimal degree of effectiveness, depending on the operating point.

This technology has been used in turbocharged diesel engines for ten years. Although the engineers at an early stage addressed the issue for gasoline engines too, there were apparently invincible fundamental hurdles to production. For at around 1000 C (1850 F), the exhaust-gas temperatures are significantly higher than with the diesel engine (700-750 C/ 1300-1400 F). The materials that can withstand these temperatures had already been in use for particular purposes
such as jet engine construction and space travel; however, they were not only very expensive, but also very difficult to obtain and also to process. And the various materials must moreover be coordinated with one other in such a way that they aren't warped-or even destroyed-in the 1000 C turbocharger, despite differing thermal expansion characteristics. Ultra-modern calculation and simulation methods helped in making the right choices.

Now Porsche will be taking its space-age material mix to the road-in a Porsche 911 Turbo for terrestrial travel. Eleven adjustable turbocharger blades, each some 21 millimeters long and 7 millimeters wide (13/16 x 1/4 inch) and shaped to a gentle wing profile, will be waiting in the turbocharger exhaust for that hot exhaust gas to flow past. For this to happen as effectively as possible, they are almost closed at the full load of low engine speeds. The higher the speed climbs, the more it turns a servomotor, thus permitting more exhaust gases to flow past unhindered. "For every operational point, we can adjust the optimal impact angle and the optimal cross-section," Krickelberg explains the high-effort coordination process. The exact adjustment is accomplished via the Porsche Engine Control.

Solving the porsche turbocharger problem

"In solving this problem, we have oriented ourselves StrongIy toward the innovative character of the curtting-edge Porsche 959," Krickelberg explains. Porsche borrowed the register charging from the 1987 super sports car, to ensure as homogeneous as possible a power development across the entire engine-speed range. At that time, the engine therefore had two equally large turbochargers. One already provided good response behavior at low engine speeds, while the second took oil additional Compressor tasks Liter, and was responsible for top performance (45O hp/330 kW). A disadvantage was the long expensive pipe system, and the difficult synchronization of the control valves, injection, and ignition.

Porsche turbocharger... the "turbo gap" is virtually a thing Of the Past.

In the new Porsche 911 Turbo (model 997), everything is much more Precise and More mature, thanks to the- variable-turbine -geometry. "We have high rotational Speeds at the turhine wheel shaft, even at low engine speeds," explains krickelberg. On the other side of the turbocharger shaft, a compressor wheel turns at the same Speed, and pros ides a kind Of forced aspiration. That makes maximum torque available, even at low rotation speeds. The "turbo gap" is virtually a thing Of the Past.

At nominal power, the turbocharger shaft rotates at up to 150,000 rpm. The blades move up to 1.2 million liters (43,000 cubic feet) Of air an hour into the cylinders, or 333 liters (12 cubic feet) a second, at a maximum pressure Of 1.1 bar ( 17.4 psi). The formula that engine builder Krickelberg presents is not only generally applicable, but also quite simple: "More air means that more fuel can he injected, which increases the output." In the new Turbo, that's fully 480 hp, and the torque is a hefty 620 newton meters (457 lb.-ft.) at 1950 rpm.

Porsche Turbocharger Art

And so this little work of art, with its fifty-seven delicate components that together spell variable turbine geometry, means another gigantic step forward in Porsche turbo technology. For Krickelberg and the Weissach development team, the introduction of the new 911 Turbo means the conclusion of three exciting but also very busy years. Soon, this powerhouse, this muscle-packed speedster, will be openly displaying its anything-but-everyday energy.

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