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Cummins progressing toward ATLAS Tier 2 Bin 2 fuel-efficient diesel for light-duty pickups

10 May 2013

In a US Department of Energy (DOE)-sponsored project, engineers at Cummins are developing a Tier 2 Bin 2 emissions compliant diesel for application in a light duty pickup (ATLAS, Advanced Technology Light Automotive Systems, earlier post). Tier 2 Bin 2 requirements are only slightly less stringent than the CARB LEVIII-SULEV20 requirements. (Earlier post.) Fuel economy targets for the vehicle are 22.4 mpg US (10.5 l/100km) city and 34.3 mpg US (6.9 l/100 km) highway.

At the recent 2103 SAE World Congress, Cummins discussed key engine technology enablers—including air-handling, fuel system, and base engine design— and development of the combustion system that will help in achieving the target emission levels and fuel economy.

US Light Duty Diesel Emission Standards
(full useful life: 150,000 miles)
Tailpipe emissions [g/mile] US EPA Tier 2 Bin 2 CARB LEVIII-SULEV20
NOx + NMOG 0.03 0.02
NOx 0.02
PM 0.01 0.01
CO 2.1 1.0
HCHO 0.004 0.004

The baseline engine for the work is a Euro IV-compliant inline 4-cylinder 2.8L diesel equipped witha single-stage wastegate turbocharger and generating 160 hp (119 kW) of power and 265 lb-ft (359 N·m) of torque, with a compression ratio of 16.9:1. Emission control is via high pressure cooled EGR with a diesel oxidation catalyst.

The test vehicle is a MY2010 Nissan Titan crew cab 2x4; the truck’s 5.6L V8 was replaced with the 2.8L. The upfitted Titan was tested on a chassis dyno to establish baseline emissions, performance and fuel economy for FTP-75, LA-4 and HFET drive cycles.

Based on the baseline emissions profile, the Cummins team determined that they had to reduce NOx by 99%, PM by 90%, and NMHCs by 67% to meet the design target.

The team started by upgrading the 1600 bar injector system to a 2000 bar system, using 8-hole injectors rather the original 7-hole injectors. The concept architecture calls for upgrading the original single-stage turbocharger to a more efficient variable geometry turbine and a larger compressor wheel/housing to meet requirements for power density and lowered fuel consumption.

To achieve the emissions targets, higher levels of EGR are needed. (Increased EGR rates results in decreased oxygen concentration in the intake manifold, resulting in reduced engine-out NOx.)

The EGR circuit has both high pressure (HP) and low pressure (LP) loops. (LP EGR has an advantage compared to HP in lowering intake oxygen concentration.) The HP loop recirculate exhaust from exhaust manifold to intake manifold via an HP EGR valve; there is no physical EGR cooler in the HP loop. The LP loop runs from downstream of an integrated DOC-SCRF aftertreatment system. AN exhaust throttle and LP EGR valve work together to control mass flow rate. An EGR cooler in the LP loop helps reduce gas temperature before mixing with fresh air upstream of the turbo.

The team found that by optimizing LP EGR, they could reduce fuel consumption by approximately 16% compared to the optimal HP EGR solution. Their work also showed the need for dual loop EGR in certain areas of the drive cycle to help improve fuel economy.

...the dynamics of dual loop EGR varies over the engine operating map driven by duty cycle and emission requirements. There is no single strategy that will work consistently across the engine map and hence several iterations of optimization will be required both analytically and experimentally to arrive at the best possible solution. Several factors like air-handling thermodynamics, turbocharger selection, emission requirements during drive cycle and cold start have a significant effect on calibration development and optimization.

—Suresh et al.

To select the variable geometry turbine, they ran through multiple hardware combinations and duty cycle optimizations.

Other studies have shown that lowering compression ratio can help to reduce engine-out smoke levels along with enabling premixed combustion modes favoring low NOxformation. To confirm this experimentally, the Cummins team made two combustion bowls with 16.5 CR and 15.3 CR. These were installed on two different engines with 8-hole injectors.

With higher EGR, they found a reduction in oxygen concentration for the 15.3 CR down to 15.1%, resulting in a significant reduction in NOxemissions. The additional piston bowl volume also helps to achieve better in-cylinder charge-fuel mixing resulting in lower smoke emissions when compared to the 16.5 CR bowl.

The improved turbine match with the 15.3 CR engine further helped in reducing fuel consumption by 3% when compared to 16.5 CR and this can be attributed towards reduced pumping losses resulting in an improvement in open cycle efficiency.

—Suresh et al.

The Cummins team found a significant reduction in smoke emissions via the combination of lower CR, 8-hole nozzles and high in-cylinder swirl. The team is also exploring the concept of generating variable swirl through the use of variable valve timing as a possible future design feature.

Running a version of the hardware (ATLAS 1.7) in a testbed, they reported finding:

  • 0.40 g/mile engine-out NOx based on a modal roll-up LA-4 cycle. The reduction in NOxwas more than a factor of 4 when compared to the baseline engine.

  • PM emissions were <0.04 g/mile—“stellar”, due to advancements in air-handling and combustion systems.

  • Calibration optimization helped bring down the engine-out unburned HC to 0.27 g/mile. Improved injector nozzle technology and optimization around combustion bowl-nozzle matching may result in further engine-out HC reductions.

  • Fuel economy for a modal rollup LA-4 cycle was 25.4 mpg (9.3 l/100 km), exceeding the city target.

  • Fuel economy for a modal rollup based on HFET was 32.6 mpg (7.2 l/100 km)—falling short of the target. The engineers said that optimization involving engine hardware, calibration, controls and aftertreatment integration will help in bridging the gap.

Mule testing showed a multi-fold reduction in NOxemissions by 36%, 55% and 28% for FTP_75, LA-4 and HFET cycle respectively, compared to the baseline. Equipped with an 8-speed automatic, the mule delivered fuel economy of 24.8, 26.7 and 34.4 mpg US (9.5, 8.8 and 9.1 l/100 km) for FTP-75, LA-4 and HFET cycles, respectively.

The ultimate goal would be to integrated ATLAS 1.7 technologies and 8-speed automatic transmission in the test vehicle with appropriate refinements around design, packaging ,performance, power management and reliability for meeting Tier 2 Bine 2 emissions. Vehicle noise and vibration will be an area of concern for 4-cylinder light duty diesels. Advanced technologies related to engine design as well as challenges around combustion noise improvements need to be addressed in the future.

—Suresh et al.

Resources

  • Suresh, A., Langenderfer, D., Arnett, C., and Ruth, M. (2013) “Thermodynamic Systems for Tier 2 Bin 2 Diesel Engines,” SAE Int. J. Engines 6 (1): 167-183 doi: 10.4271/2013-01-0282

May 10, 2013 in Diesel, Emissions, Engines, Fuel Efficiency | Permalink | Comments (6) | TrackBack (0)

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Comments

There are a lot of people driving trucks in the US.
May as well make them efficient and clean.

Next up - barbecues.

A question for the team:

Is it better to remove the worst polluters from the roads, or try to improve the fleet over time and hope for a trickle down effect ?

1 - this funny team research a developes what Mazda already launched on Japanese, European and recently to US market. SKY-D does all what they want to achieve. There is one difference - Mazda did not ask for any money to develop this kind of clean diesel.
And, parameters of mazda´s SKY-D under 2,2 volume are the same or better than Cummins´s planned 2,8.
Cummins discovers the world !!!!!!!!
(I am pretty sure that Cummins does not need any money for a research and developement, but why not to také if everybody takes???)

Peter, I rather see some of my taxes going to american car companies that probably do not need the money than to continue watching a huge amount of our money being given to oil countries that use the very money we pay them to wage war against us.

Peter: I think the there is a big difference between Mazda's Sky-D and the Cummins engine... Tier 2 Bin 5 compliance vs. Tier 2 Bin 2 compliance. No small hurdle.

Sometimes you have to step back and see how far we have come since the 1970s. Tier 2 Bin 2 and Lev III SULEV II are emissions regulations patterned after the synthetic emission levels needed to propagandize and broadcast the benefits of EVs back when. Back then and even today, the ICE was condemned as the Devil Incarnate and poisoners of us all, and of course the dear "little children". The same sort of propaganda used to describe the Hun bayoneting Belgian mothers and children.

IOW, these emission regulations codify a ZERO EMISSIONS VEHICLE. If an ICE and in this case an Evil Pickup truck can equal the emissions of a TESLA, the entire concern for emissions and dirty air simply goes away.

The US has already achieved EPA Air Quality compliance over the entire country, with minor exceptions, merely employing more lax, Tier 2 Bin 5 emissions levels. Lax rules that are tougher thna anywhere else on the Planet.

Yet we are inexplicably reticent in broadcasting the good news. Just as we are reticent in broadcasting that auto accident death rates have been halved; or that teenage motherhood have been reduced by a similar amount.

When and not if, the vehicles meeting this level of emissions are available, we can afford to call off the war, and demobilize the expensive regulation army created to fight it.

We can spend the money on other needful things. Call it a "Peace Dividend" if you like.

But of course, no governmental organization will easily accept demobilization. There WILL BE political wars to be fought as the demobilizers will cetainly be denounced as wanting dirty Air and Dirty Water.

Isn't it wonderful how American society can solve "intractable problems" that other countries say must simply be endured? Wasn't there a reference to the glorious "City on the Hill" in our literature that accomplished wonders?

" Tier 2 Bin 2 requirements are only slightly less stringent than the CARB LEVIII-SULEV20 requirements"

Really? Is this serious???

AFAIK, to come up with an affordable solution meeting the CARB LEV III- SULEV 20 requirement is a serious challenge to many engineers.

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