Ford Super Duty Pickups To Offer Clever PowerStroke Turbodiesel V8 Page 2

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Ford 6.7-liter Power Stroke V-8 diesel engine, to be fitted to 2011 F-Series Super Duty pickups

Eureka! Let's flip it around!

The innovation came in where the turbo was mounted: in the engine's vee, between the two banks of cylinders. This reduces the distance the exhaust gases must travel through the exhaust manifolds from each bank before they reach the turbo, meaning more heat can be scavenged for more power.

But that requires that the airflow in the engine be flipped completely round, with intake manifolds on the outside and the exhaust exiting toward the engine's vee. And that meant designing a brand-new engine from scratch. Which is exactly what Ford has done.

Ford is not the only maker to design a diesel with its airflow reversed. General Motors used the same approach for its now-shelved new 4.5-liter Duramax diesel. That GM engine may still reappear in the future, but for now, Ford has exclusive bragging rights.

One tough turbo

The turbocharger itself was a custom design with Garrett, replacing the twin turbos used on earlier Power Stroke turbodiesels. The new design uses a single turbine--that's the part driven by the exhaust gases--with variable vanes, driving two back-to-back compressors. Ford calls it a "single sequential turbo."

For a sense of how tough the turbo has to be, consider that it produces up to 30 pounds per square inch of boost while running at speeds well in excess of 100,000 revolutions per minute.

Alphabet soup for emissions:  EGR, DOC, SCR, DPF

Among the alphabet soup of modern emissions control techniques, Ford knew it would use exhaust-gas recirculation (EGR), which feeds some of the exhaust back into the cylinder to be burned again. This lowers the temperatures inside the cylinder, and reduces formation of NOx.

Ford's innovation in the new Power Stroke EGR system was to take the exhaust gas it recirculates only from a single bank of the V8 engine, which makes the plumbing and piping far less complex.

After recirculation, the remaining exhaust enters a diesel oxidation catalyst (DOC) that converts hydrocarbons (HC) into water (H2O) and carbon dioxide (CO2).

It continues on to a selective catalytic reduction (SCR) system, used for the first time in a Ford diesel, that injects a urea solution into the exhaust gases. Their heat converts the urea into ammonia, which chemically converts the NOx into nitrogen and water vapor in its own, dedicated catalytic converter.

The SCR concept was pioneered by Mercedes-Benz for its passenger-car diesels, under the name BlueTec. In cars, the urea solution is refilled by the dealer at every 12,000-mile service; for Ford trucks, some owners may have to add it themselves based on usage.

Finally, the remaining exhaust passes through a diesel particulate filter (DPF) that traps any remaining soot. The accumulated particulates are periodically burned once the trap has filled.

Adam Gryglak, lead engineering manager for Ford's new 6.7-liter PowerStroke V-8 turbocharged diesel

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[Ford Motor Company, PickupTrucks.com]