|6.7-liter Power Stroke V-8 turbocharged diesel engine. Click to enlarge.|
Ford has provided initial details on the new Ford-engineered, -tested and-manufactured 6.7-liter Power Stroke V-8 turbo diesel engine. Debuting in the next-generation F-Series Super Duty truck, the new diesel engine will deliver improvements in torque, horsepower and fuel economy while adding more fueling flexibility—the engine is sanctioned for up to B20 biodiesel blends—and meeting 2010 emissions requirements.
The diesel engine team made improvements and changes throughout the engine architecture—including the use of an “inboard exhaust” design, a first for a modern production diesel engine—to deliver on aggressive horsepower, torque, emissions and fuel economy targets.
In January, Ford and Navistar, Ford’s long-time diesel supplier, agreed to end several years of litigation. Among the terms of the agreement was the end of the current diesel engine supply agreement effective 31 Dec 2009. The new Ford diesel steps fully into the opening.
All-new design. 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 layout 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.—Adam Gryglak, Lead Engineering Manager
The volume of the exhaust system feeding the turbocharger is smaller by about 50% because of the inboard architecture.
Turbocharger. The single-sequential Honeywell 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.
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 compact unit 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. To help reduce NOx emissions to required 2010 levels, the new Power Stroke reduces engine-out emissions. 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 runs the exhaust gas recirculation (EGR) through a two-step process utilizing separate cooling sources. 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.
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.
The high-pressure Bosch fuel system injects fuel at up to 30,000 psi (2,000 bar) and 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. 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.—Adam Gryglak
The new 6.7-liter Power Stroke V-8 turbocharged engine features instant-start glow plugs, allowing quick start even in extremely cold temperatures.
Emissions. 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% compared with the previous standard. The Ford aftertreatment system is a three-stage process.
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 °C. 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.
Urea SCR. Before the exhaust gas enters the SCR chamber, it is dosed with DEF, an aqueous solution that is approximately 67.5% water and 32.5% pure urea. Dosing occurs between 200 and 500 °C.
Diesel Particulate Filter (DPF). Periodic regeneration occurs at temperatures in excess of 600 °C.
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.
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.