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  • 6.7L Cummins Diesel Engine - The Future Of The Cummins 6.7L

6.7L Cummins Diesel Engine - The Future Of The Cummins 6.7L

More Power And Fewer Emissions By 2016

Jason Thompson
Feb 1, 2010
Photographers: Courtesy of the Department Of Energy, Courtesy of Cummins, Courtesy of Fiat
The Cummins B-Series engine has been used in Dodge Ram trucks for more than 20 years. The engine's architecture has carried over for the most part since 1989, but the 6.7L version found in the current Ram uses many technologies that were unheard of in the mainstream diesel market only a few years ago. Substantial changes for the B-Series came in 2007 with the introduction of the 6.7L Cummins, which included digital common-rail injection, variable geometry turbocharging, exhaust gas recirculation (EGR), a closed crankcase (with coalescing filter), lean-operating catalytic converters, NOx absorbers, and diesel particulate filters.
Photo 2/10   |   6 7L Cummins Diesel Engine top View
Built On A Proven Design
If you took a diesel mechanic from 1936, he would recognize and be able to repair any Cummins B-Series engine until roughly 1997, when the 24-valve VP44-injected ISB engine debuted. If you showed that same mechanic an '08 common-rail-injected 6.7L, he'd understand how the long-block went together, but beyond that, he'd be lost. While the future Cummins B-Series engines will continue to build on its proven design, over the next decade, we expect to see some major updates to this platform. Here's what the Cummins mechanic of 2016 will need to know.
Cummins' Goals For the Future
Cummins' light-duty diesel program has a goal of 10 percent better brake thermal efficiency over its current lineup of engines. This is a massive jump in efficiency for diesel engines. At the same time, Cummins plans to meet Tier 2, Bin 5 emissions requirements while maintaining the same power density it has today. In addition, Cummins plans to make its next engines work with cutting-edge biofuels. To help Cummins achieve this, the Department of Energy has supplied funds and a forum of scientists, engineers, chemists, industrialists, and researchers.
Future Strategies
With all the talk about exhaust aftertreatments, we sometimes forget to focus on ways to eliminate the incomplete combustion where it's formed: inside the combustion chamber. If engineers are able to control the production of particulate matter and NOx in the engine-there will be no need for external exhaust aftertreaments such as catalytic converters, urea injection, and diesel particulate filters.
1. Premixed Controlled Compression Ignition (PCCI)
One technology in this group has to do with fuel injection strategies. A diesel engine produces an uneven flame, and in the different areas there are various air-fuel ratios and flame types (diffusion flame equals traditional diesel, and homogenous explosion equals Otto gasoline). To control this, engineers manipulate how fuel is injected and in what kind of air it is injected into. With early and late premixed controlled compression ignition (PCCI), multiple injections (up to seven) of 20 to 50 percent of the total amount of fuel injected is fired 30 to 40 degrees before the piston reaches top dead center (TDC). This technology goes far beyond traditional pilot injection. The PCCI process works to decrease NOx and particulate matter (PM) during mid-to-high loads, and there is very little part of the flame that's a traditional diffusion type. During this touchy fueling technique, efficiency stays the same while emissions drastically decrease. The hurdle to overcome here is controlling the timing of the explosion flame, which is similar to the homogenous combustion of a gasoline engine.
2. Low-Temperature Combustion (LTC)
Another strategy is low-temperature combustion (LTC), which involves manipulating the turbo(s) and increasing EGR up to 60 percent. This works while in low-to-mid load operation, and future Cummins engines are projected to feature dual-loop EGR systems similar to those found in the new Volkswagens. The high-pressure loop (used during low loads) is a more traditional EGR setup. The new, low-pressure loop is used during mid-loads and its air supply is routed from after the DPF and then goes through the turbo's compressor side.
3. Sequential Turbos, SOHC Or DOHC With Variable Valve Actuation
Another hint of things to come is the promise of variable valve actuation (VVA) with either single or dual overhead (SOHC or DOHC) camshafts. This, incorporated with fast-response intake valves, might solely solve diesel's NOx and PM problem. To further control the air, future 6.7L engine plans show a two-stage variable geometry sequential-turbo setup that features a variable geometry turbine housing on the low-pressure stage. All of these in-cylinder techniques are types of high-efficiency clean combustion (HECC).
4. Electronics
New Cummins diesel engines will feature onboard diagnostics, a fuel quality sensing ability, and robust in-cylinder pressure sensors. The fuel injection pressures will be high (31,900 psi) and the injectors will be able to control smaller quantities of fuel, and up to seven injection events per stroke. All of these in-cylinder techniques will need to communicate with the exhaust aftertreament strategies, and this will be the job of the electronics. Another interesting hint of things to come is electrically driven components (fan, water pump, and power steering pump), and exhaust energy recovery.
5. Aftertreatment
The biggest feature of future Cummins' exhaust aftertreament is its absence, although SCR or urea injection is still on the table. If the in-cylinder techniques fail or are too expensive to bring into production, we'll see a more refined version of the exhaust treatment than what is currently available.
Current 6.7L Technology
The current 6.7L meets 2010 emissions without the need for selective catalyst reduction (SCR), also known as urea. Cummins groups its future plans for the B-Series engine into two categories: in-cylinder techniques and aftertreatment solutions. In-cylinder modifications include a new Bosch common-rail injection system, advanced combustion through changes in the combustion chamber, EGR, and variable geometry turbocharging.
Exhaust aftertreatment equipment includes a 2.1L close-coupled catalyst made by Emitec. It has elliptical metallic guts arranged at 300 cells per square inch (cpsi). It works by taking oxygen, hydrocarbons, and carbon monoxide from the exhaust and converting them to water and CO2 by means of a chemical reaction. Next down the exhaust pipe is a 5.2L NOx absorber catalyst made by Corning. It has a cordierite and barium oxide substrate arranged at 300 cpsi. Since a diesel engine usually operates in an excess-air mode, it is impossible to control NOx with a traditional three-way catalytic converter, which only works in a rich-fuel mode. So instead, under lean conditions, a NOx absorber turns NOx into barium nitrate, which sticks to the surface of the substrate inside the absorber. When all the surface area is covered, the computer tells the engine to go into rich mode, eliminating all the oxygen in the exhaust system. This releases the barium nitrate and turns it into nitrogen gas and water vapor as it reacts with the precious metals.
Another job of the NOx absorber is to deal with sulfur, which can poison the catalyst. Sulfur is a reason why the exhaust system needs to generate high temperatures during regeneration. Finally, there is the (9.4L) catalyzed diesel particulate filter made by NGK. It has a cordierite substrate at 200 cpsi. Its job is to filter all the engine's particulate matter and then burn it up during regeneration.

Sources

Cummins Inc.
Columbus, IN 47201
812-377-5000
www.cummins.com
U.S. Department Of Energy
Washington, DC 20585
202-586-4403
www.fueleconomy.gov

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