Ford's issues with its long-time heavy duty diesel engine supplier Navistar will soon be coming to an end. The 2011 edition of the Ford Super Duty pickup will get an all-new diesel V8 designed in-house code-named Scorpion. So now, if Ford has any durability issues with its big diesels, it will have no one to blame but itself.
Officially the Scorpion retains the Power Stroke badge, but that and eight cylinders in a V-configuration are all that is carried over. The Scorpion engine picks up a variety of technologies that have been appearing on other recent engines, both gas- and diesel-fueled, as well as adding a few new tricks, particularly the turbocharger. The biggest change for the architecture is the move to an inside-out layout. Since the early days of the V-engine configuration, most examples have had the intake system mounted in the valley between the banks with the exhaust on the outside. Like BMW's new turbocharged gas V8 and GM's current on-the-shelf Duramax 4500, the Scorpion switches this around. Read on after the jump to learn more.
A turbocharger uses the engine's exhaust gases to spin up a turbine that in turn drives a compressor to push more air into the engine, thus making more power. The beauty of the system is that it consumes very little energy under light load conditions and allows smaller engine displacements with equal power to larger ones for improved efficiency most of the time. When extra power is needed, the turbo helps expand the engine's operating range on-demand. Therein lies the rub, the on-demand part.
Turbos of course are not immune to physics and most people have heard of turbo-lag. That's the time delta between when the driver pushes the accelerator and all that "on-demand" power actually becomes available. There are two main causes of lag. One is the time it takes for the exhaust gases to actually get from the cylinder to the turbocharger and apply pressure to the turbine. Over the years, engine designers have attempted to address this by moving the turbo physically closer to the exhaust ports. This is problematic on a V engine with two sets of exhaust ports so the exhaust has to be plumbed around the engine to the turbo. One solution is to mount two turbos, one on each cylinder bank with very short exhaust manifolds. This however, adds cost, weight and complexity.
The alternative is the inside-out layout. By essentially reversing the flow direction through the cylinder heads with the exhaust exiting in the valley, extremely short manifolds can be used to feed a single turbo mounted on top of the engine. In this way the turbo spins up much more quickly, delivering compressed air to the intake runners, which wrap around the ends of the cylinder heads to the outboard-mounted intake ports.
The other source of lag is the turbo itself. Any device that rotates at speeds up to 100,000 rpm will be subject to the limits of inertia. The larger the rotating mass, the more energy it takes to spin it up to speed. The radius of the mass also impacts the inertia. The previously mentioned sequential turbo systems combat this by using a smaller turbo for light load, low speed conditions. As the exhaust flow energy increases it is diverted to a larger turbo with more capacity. Another solution has been to use a variable vane turbo where adjustable venturis in the inlet tract are used to increase the velocity of the exhaust stream. helps to spin up the turbo faster.
The Scorpion features a brand new turbocharger design from Honeywell that we will likely see in many more applications in the coming years. It combines the principle of the sequential turbo approach with the variable vane system. However, instead of two separate turbochargers, two smaller diameter ones are mounted in one housing on a common shaft. The smaller diameter reduces the rotational inertia of the system while still allowing for sufficient flow capacity at higher speeds. It also eliminates the extra plumbing complexity of a dual turbo setup.
Besides performance, the new architecture affords a number of other benefits. The turbo plumbing on the current Navistar supplied PowerStroke engine means that the cab has to be removed from the frame to access the turbocharger. With the turbo now sitting directly on top of the engine, that is no longer an issue and assorted other components are also now more accessible.
Beyond the new turbo technology and layout, most of the rest of the engine is becoming increasingly common place. In order to meet the latest emissions standards, the Scorpion features many of the same technologies found on the latest light duty diesels. The Bosch common rail fuel injection system operates at 30,000 psi and the piezo-electric injectors can provide up to five pulses per power cycle. The multiple fuel pulses spread the power delivery and reduce the combustion temperature. The effect is that the engine runs cleaner, producing less soot and NOx, while using less fuel and producing more power at the same time.
However, the engine still needs extra help down stream. The after-treatment system kicks off with the usual oxidation catalyst that eliminates unburned hydrocarbons and also increases the exhaust temperature. The increased temperature helps improve the efficiency of the selective catalytic reduction (SCR) system. The SCR is the increasingly common urea injection. A solution of 2/3 water and 1/3 urea is injected into the exhaust stream where the urea decomposes into ammonia that reacts in a second catalyst to turn NOx into nitrogen and water. Lastly the exhaust passes through a particulate filter to trap most of the remaining soot.
Finally Ford has sought to reduce the mass and improve the durability of the new diesel. Ford and Peugeot were the first automakers to use compacted graphite iron for diesel engine blocks for their jointly designed 2.7-liter V6 that debuted back in 2003. Since then Audi has also used the material for some of its diesels including the V12 used in the R10 TDI race car. The CGI block has double the strength of typical gray iron and better fatigue resistance. This allows Ford to make the block lighter with thinner walls without sacrificing durability. Ford claims the engines have been run continuously on the dynamometer for the equivalent of 250,000 miles without problems.
The aluminum cylinder heads have dual water jackets to ensure they stay cool enough to withstand 2,600 psi combustion pressures. Also aiding the weight reduction measures is the use of a push-rod valve-train. In spite of the cam in block layout, the Scorpion still has four valves per cylinder as we saw in a Ford patent filing several months ago.
So far Ford isn't releasing much in the way of specifications for either power or efficiency of the new engine other than to say that it is both more powerful and more efficient than the engine it replaces. It will be debuting on the refreshed 2011 Super Duty pickups that we will learn more about soon.
There is one last little tidbit that fleet users will be happy to learn about. Like the 2010 version of GM's 6.6-liter Duramax, the 6.7-liter Power Stroke will be fully compatible with B20 biodiesel blends, addressing one of the issues some current Power Stroke operators have had. Because the current engine injects some fuel into the exhaust stream for particulate filter regeneration, the use of B20 has caused damage to some engines. This will no longer be true for the new engine.
All-new Ford-engineered, Ford-tested, Ford-built diesel maximizes 2011 Super Duty's productivity
* An all-new 6.7-liter Power Stroke® V-8 turbocharged diesel engine – debuting in the
2011 Ford F-Series Super Duty® – will deliver significant improvement in torque, horsepower and fuel economy, enhancing productivity and further strengthening its
position as the class leader for towing and payload
* Extensive durability testing put the new Power Stroke diesel engine through the equivalent
of 250,000 miles
* Industry-first single-sequential turbocharger with double-sided compressor wheel delivers fast throttle response along with the volume of air boost needed for maximum power; new engine also is biodiesel compatible up to B20
dearborn, Mich., Aug. 31, 2009 – A new era in Ford diesel technology arrives with the Ford-engineered, Ford-tested and Ford-manufactured 6.7-liter Power Stroke V-8 turbocharged diesel engine.
Debuting in the next-generation F-Series Super Duty truck, the new diesel engine will deliver significant improvements in torque, horsepower and fuel economy while adding more fueling flexibility and easily meeting stringent new emissions requirements.
The new diesel 6.7-liter engine also shares the Super Duty's legendary reliability and durability while delivering best-in-class towing and payload.
"This all-new diesel engine has been so extensively tested both in the lab and in the real world that we're confident we're giving our customers the most reliable and productive powertrain available today," said Derrick Kuzak, group vice president of Global Product Development. "Our Super Duty customers demand reliability and durability in their trucks so they can deliver the best results for their business and their customers. That's exactly what this engine delivers."
The diesel engine team made improvements and changes throughout the engine architecture to deliver on aggressive horsepower, torque, emissions and fuel economy targets. The 6.7-liter Power Stroke uses an "inboard exhaust" architecture, an automotive-industry first for a modern production diesel engine. It combines the best of proven technology with new, patented approaches backed by an extensive laboratory and real-world testing regimen to assure customer satisfaction.
Benefits of the new 6.7-liter Power Stroke V-8 turbocharged diesel engine include:
o First use of a compacted graphite iron (CGI) engine block in a Super Duty-class vehicle in North America; stronger than regular gray cast iron, Ford has successfully used CGI in engine blocks in products around the world. The block structure was optimized for reduced weight and maximum strength to meet the demands of higher torque and horsepower
o Unique inboard exhaust and outboard intake architecture, an automotive-industry first for a modern production diesel engine, reduces overall exhaust system volume, which leads to better throttle response for the customer; additionally, reduced exhaust system surface area minimizes heat transfer to the engine compartment and improves NVH (noise, vibration, harshness)
o The new engine architecture enables easier service work for all major engine components, potentially reducing down time. On turbocharger service, for example, the body/cab no longer has to be removed from the frame to access the turbo; also, the high-pressure fuel pump, EGR (exhaust gas recirculation) components and thermostats are directly accessible from the front of the vehicle
o Honeywell's single-sequential turbocharger features an industry-first double-sided compressor wheel mounted on a single shaft. The unit is uniquely center-mounted on a pedestal low in the back of the valley for improved NVH. This turbocharger design allows the single unit to deliver the benefits of a twin-turbocharger system in a smaller, more efficient package, combining the benefits of a small turbocharger (faster response) and a large turbocharger (ability to compress and force more air into the engine for more power) in one unit
o The high-pressure Bosch fuel system injects fuel at up to 30,000 psi. The system delivers up to five injection events per cylinder per cycle using eight-hole piezo injectors to spray fuel into the piston bowl. The direct-injection system is calibrated and phased for optimum power, fuel efficiency and NVH
o Aluminum cylinder heads for reduced weight; the mid-deck construction with dual water jackets provides increased strength and optimal cooling; also, six head bolts, instead of four as found on other engines, help improve sealing and maintain cylinder integrity even with the higher firing pressures; overall the engine is about 160 pounds lighter
o Compatible up to B20 fuel, allowing greener fueling options of up to 20 percent biodiesel and 80 percent petroleum diesel
"Our Super Duty customers are no-nonsense, no-compromise individuals," said Barb Samardzich, vice president, Global Powertrain Engineering. "Those are the attributes our team took to heart when engineering this all-new diesel engine so we can deliver 'Built Ford Tough' capability, reliability and enhanced productivity."
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."