Rugged block and proven components

The capability and reliability found in the new 6.7-liter diesel engine starts with the engine block. The new Power Stroke’s block is made from compacted graphite iron (CGI), which is about twice as strong as regular gray cast iron. While this is the first use of a CGI block in North America in this class of vehicle, Ford has successfully used the material in engine blocks in other products around the world.

“Using a CGI block is the perfect solution for the new 6.7-liter Power Stroke,” said Adam Gryglak, lead 6.7-liter diesel engineering manager. “It provides the strength necessary for the increased torque and horsepower produced by our new engine, and it also offers significant weight savings.”

The diesel engine’s deep-skirted block and main bearing caps are cross-bolted for additional stiffness and to aid NVH. The cylinder heads mirror the engine’s attributes as a whole, with lighter weight combined with increased robustness: The cylinder heads are made of aluminum to save weight and, for improved sealing, feature six head bolts per cylinder versus the four head bolts found on other engines.

The cylinder heads, which feature dual water jackets, are capable of firing pressures approaching 2,600 psi. The tall water jacket works as a manifold, flowing high-velocity water for cooling and adding to the structural robustness in the head to handle the higher firing pressures. Crankshaft durability is improved through Ford’s unique undercut and fillet roll treatment to relieve stress.

The valvetrain features patented dual hydraulic lash adjustors, which improves the performance and reliability of the valvetrain by using two pushrods per cylinder instead of the conventional single pushrod, with individual rocker arms. Other proven components round out the engine hardware, including fractured-split connecting rods and a fuel system capable of generating 30,000 psi to feed the common-rail direct-injection fuel system.

The oil pan, which bolts to the transmission, also acts as a structural member for improved powertrain stiffness and adds to Ford’s legacy of virtually bulletproof lower-engine architecture.

‘Built Ford Tough’ testing protocol to ensure durability

The testing protocol developed for the 6.7-liter Power Stroke V-8 turbocharged diesel incorporates the most rigorous engine tests found in Ford globally to ensure 250,000-mile durability. Extensive CAD (computer-aided design) and CAE (computer-aided engineering) work was completed to identify any potential challenges before hardware was created, which not only is time efficient but also helps ensure quality at the outset. Further, a comprehensive examination of warranty and quality tools was used to determine the expected failure modes for every component and system.

Customer data, including driving styles, road types and vehicle usage (towing and payload), also played a key role in developing the testing program that best replicated Super Duty use.

Components were torture-tested in the laboratory with a regimen designed to exceed what even the harshest user might dish out. Engines literally ran continuously for hundreds of hours. Finally, a battery of in-vehicle, real-world tests validated the work done in the laboratories.

The strict testing work also ensured the new engine is B20 compatible, which allows customers an environmentally responsible fueling option of using blends up to 20 percent biodiesel and 80 percent petroleum diesel. Durability cycles were run on multiple blends of diesel fuel to ensure the robustness of the system.

“These cross-functional tests give us the full spectrum of Super Duty customers – from those who run their trucks at maximum power with a maximum load for long periods to those who use them more in a start-stop mode,” said Ed Waszczenko, lead engine durability engineer.

All-new design for all-new engine

One of the obvious visual differences in the new 6.7-liter Power Stroke V-8 turbocharged diesel engine is the layout of the pipes. The exhaust manifolds, for example, reside in the valley of the engine instead of outboard, while the intake is outboard of the engine. The cylinder heads are essentially flipped around in comparison with previous V-8 engine architectures.

This unique layout – an automotive-industry first for a modern production diesel engine – has several advantages. First, the overall exhaust system volume is reduced, meaning air can be fed to the single turbocharger quicker for faster spool up and reduced lag, resulting in improved throttle response for the customer. The improved packaging also places components that need to be in cooler air away from hot exhaust pipes, resulting in better thermal management and, by extension, better fuel economy.

“The physical size of the system is smaller, but more importantly, the air-handling part of the system is considerably smaller and that translates directly into the responsiveness of the engine,” said Gryglak, noting that the volume of the exhaust system feeding the turbocharger is smaller by about 50 percent because of the inboard architecture.

Combining two turbochargers in one package

The single-sequential turbocharger – an industry first – is key to the new diesel engine’s performance. The unit has two compressor wheels driven off one turbine impeller. This approach combines the benefits of a single inertia wheel – faster response without lag – with the thrust of a larger turbocharger, with the ability to force more compressed air into the engine for more power.

The engine’s smaller exhaust volume combined with a corresponding smaller intake volume and smaller turbocharger creates a system that is quicker to boost, more responsive and better able to deliver horsepower and torque, especially at the low end, when the customer demands it.

The turbocharger includes an advanced variable nozzle turbine, which enables variable vane pitch angles, driving optimal turbine power to achieve optimal boosting levels for all operating conditions. The single shaft ensures the transition is seamless. The unit – compact in dimensions – is uniquely center-mounted on a patented pedestal low in the back of the valley instead of hung off the block, which helps balance the system and aids NVH characteristics.

Combustion system clean and powerful

The combustion system is the heart of the new 6.7-liter Power Stroke V-8 turbocharged diesel engine and in many ways encapsulates the careful balancing act the Ford team achieved in terms of power, fuel economy and reduced emissions. The key factor in the next round of federal emissions standards, which begin in 2010, is the reduction of oxides of nitrogen (NOx). To help reduce NOx, the new Power Stroke burns cleaner, thanks to an innovative way Ford developed to cool the exhaust gas recirculation (EGR) to efficiently recycle the combustion gases in the system.

Ford’s system runs the engine with the least amount of oxygen possible in order to reduce NOx without degrading performance and fuel economy. Ford’s solution runs the EGR through a two-step process utilizing separate cooling sources, something not typically seen. The end result is the EGR is brought into the intake at a lower temperature, which means more of it can be utilized, creating greater efficiency throughout the system.

A unique piston bowl design and the high-pressure fuel-injection equipment are huge enablers in achieving the balance of power and lower emissions. The system can deliver up to five injection events per cylinder per cycle, while eight holes in the injector spray fuel into the bowl.

The compressed-air ignition unique to diesels is aided by pilot fuel injections before the piston reaches the top, allowing the charge to heat up even hotter than what you get under normal compression.

“Then when the main injection occurs, we can mitigate NVH because we have a slower ignition process,” said Gryglak. “When the fuel burns, it doesn’t burn with a traditional pop or bang. The direct-injection system is calibrated and phased for optimum power, fuel efficiency and NVH.”

The new 6.7-liter Power Stroke V-8 turbocharged engine features instant-start glow plugs, allowing quick start even in extremely cold temperatures.

How the new Power Stroke meets new emissions standards:

The new 6.7-liter Power Stroke V-8 turbocharged diesel will employ an aftertreatment system to help comply with 2010 federal regulations to reduce nitrogen-oxide levels in diesel emissions by more than 80 percent compared with the previous standard. The Ford aftertreatment system is a three-stage process; a key component is the use of Diesel Exhaust Fluid (DEF).

Injection of DEF to reduce NOx is a proven technology that’s been used throughout the automotive industry. Unlike other solutions used to control NOx, the DEF system allows the diesel engine to run at its optimum range in terms of fuel mixture. Some systems require the engine to run richer – which can be harmful to diesel engines – in order to control the NOx.

Step One: Cleaning and Heating – The first step in cleaning the diesel exhaust occurs when the exhaust stream enters the Diesel Oxidation Catalyst (DOC). The role of the DOC is twofold. First, it converts and oxidizes hydrocarbons into water and carbon dioxide. This conversion happens at about 250 degrees Celsius.

Second, the DOC is used to provide and promote heat, using specific engine management strategies, into the exhaust system. Through appropriate thermal management, this heat increases the conversion efficiency of the downstream subsystem(s) in reducing emissions.

Step Two: Knocking Out the NOx – The next step in the process is what’s known as Selective Catalytic Reduction (SCR). In this process, the NOx in the exhaust stream is converted into water and inert nitrogen, which is present in the atmosphere and harmless. Before the exhaust gas enters the SCR chamber, it is dosed with DEF, an aqueous solution that is approximately 67.5 percent water and 32.5 percent pure urea.

When heated, the DEF splits into ammonia and carbon dioxide. These molecules are atomized, and vaporized, then enter a mixer that resembles a corkscrew. This twist mixer evenly distributes the ammonia within the exhaust flow. The ammonia enters the SCR module, which contains a catalyzed substrate, and through chemical reactions combines and converts the NOx and ammonia into the harmless inert nitrogen and water. Dosing occurs between 200 and 500 degrees Celsius.

Step Three: Scrubbing Away the Soot – The final part of the cleansing system for the diesel exhaust gas involves the Diesel Particulate Filter (DPF). The DPF traps any remaining soot, which is then periodically burned away, known as regenerating, when sensors detect the trap is full. The regeneration process sees temperatures in excess of 600 degrees Celsius to burn away soot.

Quieter, more refined diesel sound for improved NVH

Customers of the 6.7-liter Power Stroke turbocharged diesel engine will notice a quieter, more refined sound. Improvements to the combustion system, structural integrity of the compacted graphite iron block and the single turbocharger mounted to the engine block account for many of the NVH improvements.

Specific design upgrades were made to both the piston and the piston bowl to optimize the combustion process, which features a two-stage combustion event instead of a single-injection event, causing harsh, sudden and loud combustion. Instead, a starter or pilot injection of fuel begins the compression process before the main injection.

The result is smoother combustion and a more refined sound for the customer. When at idle, two pilot injection events are used to make the firing process even smoother and aid in quietness. The “ticking” of the high-speed injectors also is masked by specially designed covers on the engine.

Mounting the turbocharger from the center housing directly to the block provided several advantages as well in terms of NVH.

“When turbochargers vibrate, it can lead to other parts of the vehicle vibrating,” said Scott DeRaad, engine NVH engineer. “The exhaust system, for example, is directly attached to the turbocharger. So when the turbocharger vibrates a lot, the exhaust system vibrates too and that’s disturbing to the customer. Bolting the turbocharger directly to the block eliminates that concern.”

Using one turbocharger, instead of two operating in series or sequentially, helped solve some NVH challenges as well.

“Having one turbocharger eliminates the air-handling noises – the whooshes – as the engine switches from one turbo to the next turbo,” DeRaad said. “Our turbocharger also has ball bearings that pilot the shaft in the turbo, which helps eliminate the potential for the shaft of the turbocharger to gyrate in its housing, which can create noise.”

Other improvements include the addition of two resonators in the intake system as well as a third resonator near the air cleaner.

“We’ve been able to tune the diesel intake system to give us the sound we wanted,” DeRaad said. “It’s now a nice complement to the engine.”

Just as the new 6.7-liter Power Stroke V-8 turbocharged diesel engine is the perfect complement to the 2011 Ford Super Duty, delivering both capability and reliability.

“Developing the new 6.7-liter Power Stroke V-8 turbocharged diesel engine was an awesome endeavor,” Gryglak said. “After all the engineering and testing, we’re confident this engine will ensure the new Super Duty continues its leadership in capability, reliability and productivity.”