DEARBORN, Mich., Sept. 23, 2009 – People who know diesel engines are familiar with, and expect, the noisy clatter generally associated with diesels. That is, until now. When Ford's new 6.7-liter Power Stroke® diesel engine debuts in the 2011 Super Duty lineup, it's expected to be the quietest, smoothest diesel on the market, outperforming its closest competitors by several decibels.
Engineering and design improvements to the all-new Ford-engineered, Ford-tested and Ford-built 6.7-liter Power Stroke® turbocharged diesel engine – debuting in the 2011 F-Series Super Duty – eliminate the harsh sounds of the typical diesel to make it one of the quietest and smoothest diesels on the market. Significantly quieter than its toughest competitor, the 6.7-liter diesel challenges traditional views about how diesels should sound.
"Historically, consumer perception has been that diesels should sound rough and tough, but from a sound quality perspective they were actually loud and unrefined," said Scott DeRaad, engine NVH (noise, vibration and harshness) engineer. "At Ford, we approached the new diesel development as though it was more than a work truck and something that people wanted to drive, making ‘quieter' a reason to buy."
Most of the improvement in NVH comes from changes made to the combustion system and the structural integrity of the compacted graphite iron block, as well as from mounting one turbocharger on the engine block instead of two.
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 a 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 performance.
"When turbochargers vibrate, it can lead to other parts of the vehicle vibrating," said DeRaad. "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."
The new diesel will also deliver other significant improvements including better torque and horsepower, class-leading fuel economy and best-in-class towing and payload for unparalleled performance.
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