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Development of the advanced combustion system in new Ford Power Stroke

Scorpion1
Several bowl concepts were considered for the combustion system. These bowls are all scaled to the same volume. Styron et al. Click to enlarge.

Ford developed a new 6.7L V-8 turbo diesel, code named “Scorpion,” for the full-size pickup truck and light commercial vehicle markets. At last week’s SAE 2011 World Congress, engineers from Ford and AVL Powertrain presented a paper on the development of the combustion system that delivers a leading 400 hp (298 kW) and 800 lb-ft (1,087 N·m) of torque, up from the previous Power Stroke’s 350 hp and 650 lb-ft along with best-in-class fuel economy.

The combustion system includes the piston bowl, swirl level, number of nozzle holes, fuel spray angle, nozzle tip protrusion, nozzle hydraulic flow, and nozzle-hole taper. Joshua Styron, PhD, and his team used computer simulations to evaluate the piston bowl shapes, precise placement of the fuel spray within the combustion chamber, glow plug positioning and other factors.

While all of these parameters could be explored through extensive hardware testing, Ford used 3-D CFD studies to screen quickly two bowl concepts and assess their sensitivities to a few of the other parameters. A fractional-factorial Designed Experiment (DoE) was developed that assessed three shape parameters in each bowl concept as well as two swirl levels, and three fuel spray angles. The two bowl shapes were selected based on a multi-objective optimization which sought to simultaneously minimize fuel consumption and NOx and soot emissions. The DoE also allowed an assessment of sensitivities to variations in the other parameters which could be important for robustness considering manufacturing variation.

Each piston bowl was built into a single-cylinder engine block. Two cylinder heads, each with a different swirl level, were also prepared. A suite of injectors was built to vary the number of injector holes, fuel spray angle, hydraulic flow, and nozzle-hole taper. For each injector, copper washers of varying thickness were used to fine tune injector targeting. For each hardware combination, EGR sweeps were performed at four different operating conditions to allow a complete assessment of emissions and fuel economy performance.

The two higher load points are critical for dynamometer-certified emissions compliance. The two lower load points are critical to typical driving fuel economy and chassis-certified emissions compliance. Analysis of the EGR sweeps proved useful for selecting all of the combustion system parameters that now form the heart of the 2011 6.7L Power Stroke V-8 Turbo Diesel.

Scorpion2
The chamfered re-entrant bowl allows fuel to interact with the glow plug twice because it directs some of the fuel upwards towards the head. Styron et al. Click to enlarge.

Glow plugs were chosen as the primary cold-starting aid. CFD studies were performed to find an optimum location that could enhance cold-start ability, cylinder head strength, and glow plug durability. The recommended location and several depths shorter and longer were tested in multi-cylinder engines to verify function and provide data for determination of the final glow plug location. The production location, outside of the valve bridge area, maximizes interaction of vapor-phase fuel with the glow plug while minimizing impingement of liquid phase fuel.

The final design features a chamfered re-entrant bowl, with low swirl, and an 8-hole nozzle with a medium included spray angle, a single row of holes, and low hydraulic flow. The bowl shape and all of the optimum parameters remained constant throughout multi-cylinder engine development. The complete combustion system can be experienced in the current production engine.

The production glow plug location, outside of the valve bridge area, maximizes interaction of vapor-phase fuel with the glow plug while minimizing impingement of liquid phase fuel. 3-D CFD, multi-cylinder cold-start tests, and full engine durability tests were used successfully to design, develop, and verify the new glow plug location which is significantly further from the injector than a traditional placement.

Four hundred horsepower was the target. Early in the development program, fuel economy was viewed as much less important to this customer than power and torque. But we believed we could deliver a good combination of both—400 horsepower along with fuel economy that was not only significantly better than the old 6.4, but higher than our competitors’ engines, too.

To deliver class-leading fuel economy and refinement as well as lower emissions, the combustion system had to make the best use of the limited supply of fresh air entering the engine. Combustion systems with the best air utilization extract the most heat from the fuel, produce less soot and NOx, and minimize the energy required to pump fresh air into the engine.

—Joshua Styron

Resources

  • Joshua Styron, Brian Baldwin, Brien Fulton, David Ives, and Subramanian Ramanathan (2011) Ford 2011 6.7L Power Stroke Diesel Engine Combustion System Development (SAE 2011-01-0415)

Comments

HarveyD

Aren't those features something that could have been used decades ago?
It seems that ICE have improved more in the last 10 years than the previous 100+ years.

ai_vin

"Four hundred horsepower was the target. Early in the development program, fuel economy was viewed as much less important to this customer than power and torque."

Sheesh, even with oil at over hundred dollars a barrel people still think this way! Fuel economy is nothing more than an afterthought to too many people.

SJC

Thank goodness they sell no where near as many of these than they sell Prius. They might sell 10,000 of these and 200,000 Prius, so many offset the few that believe that they MUST have this truck or their life is meaningless :)

wintermane2000

sjc think again..they are likely to sell many millions of these as they are work truck engines.

ai vin when your dealing with a job where you can litteraly make enough money on one job to pay for the truck and your house... 5-600 vs say 4-500 bucks for the fuel needed to run it during that job doesnt matter. My friend in the bis explained it all to me and the numbers are just shocking.

harvey.. up until recently they didnt have any of the needed tech to actualy manage to do any of this. A good exmaple is you couldnt get the pumps needed to achive the massive pressures they use in the fuel system nor the fast computers they use to control the injectors.. they also didnt have a zillion other bits of tech they do now... it all just came together and allowed an explosion in progress.

SJC

"for the full-size pickup truck and light commercial vehicle markets"

You think that they will see 1 million of these engines in 10 years like the Prius? I would like to see data to support that claim.

wintermane2000

Do you have any idea how many trucks they sell per year?

Multi-Modal Commuter Dude (formerly known as Bike Commuter Dude)

Ford alone sold 214,956 Super Duty trucks in 2010, including chassis cabs, according to PickUpTrucks.com. The total heavy duty/light commercial truck market consisted of 293,405 trucks. Ford has by far the largest share of this market.
You will see 1 million of these engines on road in as little as five months. With US sales of Prius around 300,000, Ford sells about 2 Super Duty trucks for every 3 Prius sold, for comparison.

Peter_XX

The combustion chamber as a bowl in the piston was invented in the early 1900's by the Swedish inventor Jonas Hesselman. It was revolutionary at its time, since it allowed an increase of (smoke-limited) power by ~50% and also reduced fuel consumption. Since then, development of combustion chambers has been part of engine development. Changes in fuel injection systems, turbocharging, combustion, etc. has necessitated changes also in the combustion chamber. The two combustion chambers exemplified by Ford are already in use on various production engines.

The power and torque of this engine might sound impressive but note that a 3-liter diesel engine for cars can give more than 300 hp and 600 Nm. The specific performance of such an engine is far better than the engine discussed here. Even more extreme is the new 2 143 cc Mercedes engine that has a torque of 500 Nm. Extrapolate that up to 6.7 liters…

globi

The Iveco Ecodaily with a 3 Liter Diesel engine has a payload of 9400 lbs. This is significantly more payload than what the F350 currently offers.

Not sure why American 'workers' require more expensive vehicles with less payload, less space and lower mileage than European 'workers'.

Multi-Modal Commuter Dude (formerly known as Bike Commuter Dude)

The Iveco is indeed a sweet vehicle, and should be praised for its efficiency and capacity. While the Iveco has a greater payload (9400 lbs. vs. ~6000 lbs. for the Super Duty), one must remember that Americans are not afraid of trailers. The Iveco is capable of towing 7700 lbs, while the Super Duty can pull up to 24,400 lbs. Quite the difference. From Ford.com and EcoDaily.Iveco.com, respectively.

globi

Well, European workers typically do not need to tow more than 7000 lbs (not many workers own yachts) and if they need to tow heavy equipment such as a bulldozer or an excavator they just use a dump truck with a flat bed trailer (which there are plenty to choose from: Iveco, Scania, MAN, Renault, Volvo, Mercedes-Benz, DAF).

Stan Peterson

wintermane,

Well spoken. Thanks for your Post.

SJC

Super Duty trucks does not mean it has this engine in it.

SJC

Many of the Super Duty are gasoline engines. They are SO heavy and such gas hogs that they do not even list curb weight nor mileage. God help us if they continue to buy these in great numbers when they really do not need them.

ai_vin

@SJC

Yeah that's the real problem, people buying cars they really don't need. I've got no problem with people driving big trucks if they really need them but too many times it's not need that sells a car - it's image!

Remember the SUV tax loophole? That was put into place to help farmers and tradesman but it wasn't long before the salesmen were showing daytraders how they could own a HUMMER and have the government pay for it. I swear I even saw one ad aimed at housewives.

I've fallen for the image thing myself, when I was younger. I bought a pickup because I was sure I'd be hauling my gear out to the back country every weekend. I used the bed just once, about a week after I got it because a friend heard I had one and needed help moving.

SJC

Here they buy Super Duty trucks because they haul horse trailers, house trailers or boats a few days per year and the other 350 days per year they have one person picking up groceries.

KGC

@SJC & ai vin

Perhaps we can make you both honorary czars and you can decide who gets to drive a big truck and who does not. It appears that you both have extensive knowledge how people use their trucks and the earth is in real need of your expertise. I have a truck, not a big one, but a truck none the less. Sometimes I haul stuff, sometimes not. Quite frankly it's not your business. This world has spent the last 100 years using oil like it's water, now we're all going to die in the next 10 if everyone doesn't go electric? Goodbye cruel world.

I read sites like these because I do care and would like to see more environmentally friendly power sources, but they are not here yet for most people. I promise you the day a BEV is made that produces similar to an ICE, they will sell like hotcakes. Until then, try not to judge everyone else and do your own part.

FYI, most Super Duty buyers are looking for diesel for the towing and better fuel economy.

SJC

It is everyone's business when you use twice as much fuel.

KGC

Okay buddy.

ai_vin

Just for the record I think every true American has a GOD given right to own and drive the biggest darn truck they can buy, I just want to make sure they ARE true Americans. So let's make it a law that they have to proven it - by providing their birth certificates at point of sale. We could even call it the Birther Bill of Sale.

LOL

SJC

If your big truck is not used for business and has no commercial plates, then you are charged a guzzler fee at time of purchase. When you go to register the truck every year, your fee will be much higher because you consume a lot of fuel and do no work.

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