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The following article was taken from the June 2009 edition of Light and
Medium Truck magazine
SCR: Some Care Required
By Jim Galligan
Most light-duty and medium-duty commercial
trucks will use selective catalytic reduction to control diesel emissions
beginning in January. Here is a glimpse of what to expect.
Diesel emission standards change again in January 2010, but unlike the previous
changes when the emission-controlling technology was essentially the same, truck
buyers will have a choice this time. The buyer’s decision will affect the
vehicle’s operation and costs throughout its life.
The choice next year will be between an expanded version of the current exhaust
gas recirculation process, which will be used on International trucks and
MaxxForce-brand engines built by Navistar Inc., and selective catalytic
reduction, which will be used by all other commercial truck and diesel engine
suppliers.
The Environmental Protection Agency’s goal for 2010 is to reduce nitrogen oxide
emissions to 0.2 grams per brake horsepower-hour, or about 90% of pre-2004
levels.
All current emission-compliant diesel truck models reduce NOx in the combustion
chamber with exhaust gas recirculation. EGR cools the exhaust gas and
recirculates a portion back into the chamber. This process lowers the combustion
temperature and, as a result, reduces NOx levels in the exhaust.
Executives from Navistar and truck makers planning to use SCR in 2010, most
notably Freightliner Trucks, have engaged in a war of words over the past year.
Representatives from each side accused the other of promoting misleading
information while also seeking to explain why its technological strategy was
best.
SCR proponents contend it is better and easier to reach the EPA’s new levels by
treating NOx in the exhaust pipe rather than adding larger EGR systems to the
engine. SCR proponents have said that the lower combustion temperature in an EGR
system robs the engine of power and, in some cases, fuel economy. However, this
is likely more of a concern for the big-bore, high mileage over-the-road engines
than it is for lower-mileage diesels used in light and medium trucks.
The 2010-compliant trucks using SCR will still have EGR systems, but they may
have slight changes in the hardware and EGR performance.
The SCR Process
SCR systems work by injecting a urea/water mixture, which truck and engine
makers are calling diesel exhaust fluid, into the exhaust stream just before it
enters a catalytic converter.
SCR systems need the DEF to clean the NOx, so the EPA is requiring that 2010
models include a consequence for running out of the urea/water mixture. The
2010-compliant trucks will include signals and/or gauges to alert drivers when
the DEF is running low. The trucks also will have controls to deter drivers from
operating the trucks without DEF. These controls may range from simply reducing
engine power so the truck can operate only in a slow, “limp” mode to preventing
the truck from starting once it has stopped if the DEF is not refilled.
SCR-equipped trucks also will some require training for drivers and technicians,
such as the meaning of the signals and how and when to fill the containers.
Proponents contend this will be a minor issue for truck users.
“Since most Class 7 and smaller trucks come home each night, mechanics can look
at DEF levels the same they do with any fluids,” said Alex LaBrie, principal of
Air Blue Fluids, Brea, Calif., a DEF distribution company.
DEF Usage Rate
DEF will be fed into the exhaust stream at rates controlled by onboard sensors
and computers. The dosing rate will be based on engine size and activity, but
the general consensus from several SCR engine representatives is that the rate
of DEF use will be about 1½% to 2% of diesel fuel use.
The refill frequency for the onboard DEF containers will vary, depending on
container size, the truck and other factors. For example, a Freightliner Custom
Chassis walk-in van with a 10-gallon DEF container getting 10 miles per gallon,
running about 15,000 miles a year with an SCR dosing rate of about 2% will
require about three DEF container fill-ups a year, said Michael Stark, senior
technical sales manager.
Todd Bloom, vice president of marketing for Isuzu Commercial Truck of America,
said DEF use in the Isuzu N-Series truck for a typical customer would be about
one gallon a week, and one tankful of DEF will last six to 10 tanks of fuel.
Performance and Fuel Economy
SCR proponents have said that, in general, the technology will improve fuel
economy, but most of those claims relate to Class 8 over-the-road trucks and the
typical light- and medium-duty truck user may not see much of a change.
Christy Nycz, Cummins spokeswoman, said the fuel economy for Cummins’
medium-duty engines will “remain constant with the 2007-compliant products”.
Rob Cadle, product planning manager with ICTA, said the company expects fuel
economy in Isuzu trucks to improve, but he did not have performance figures at
press time.
“We are working with vehicle testing to quantify how much of what we see on the
[dynamometer] will transfer into fuel efficiency,” he said.
Alan Treasure, director of marketing for Paccar, the parent company for Kenworth
Trucks and Peterbilt Motors, said Paccar’s testing indicated that fuel economy
would improve over 2007-compliant engines, but he did not offer details. Paccar
will use Cummins’ engines and aftertreatment system in its medium-duty trucks.
Maintenance
Maintenance will be minimal for SCR systems, suppliers said. Cummins’ SCR
catalyst, the largest component, will not require periodic cleaning, Nycz said.
Most SCR systems will have a filter for the DEF, either in or near the DEF
container or near the SCR canister. Cummins said the maintenance interval for
its filter will be about 200,000 miles.
Cadle said Isuzu’s SCR filter will have a replacement cycle, somewhere between
one and two years of use, but he said he could not be more definite.
“We’re determining that now,” he said.
Heavy-duty trucks may see fewer regeneration cycles of the diesel particulate
filters but midrange trucks with Cummins engines should operate the same as
current models, said Ginger Lirette, Cummins’ account executive for Daimler
Trucks North America.
“[The] regen duty cycle will remain about the same between 2007 and 2010
products as the approach on [medium duty] has been to keep the engine the same
base structure. EGR will be the same in 2010 as 2007, or very close,” she told
L&MT.
Cost
The only thing that can be said for certain at this time about price is that
2010-compliant trucks will cost more, regardless of which technology is used.
By press time, only Volvo Trucks North America had released a cost — $9,600 —
for the SCR technology on its trucks. The typical cost premiums for medium-duty
trucks likely will be less, in the range of $4,000 to $6,000, said Glenn Ellis,
vice president of marketing and dealer operations for Hino Motor Sales.
While not citing a cost figure, Isuzu’s Cadle said the company was trying to
“bring it in as low-cost as possible. We do know that the truck will be more
expensive to buy, so we’re focusing on offsetting that higher initial cost with
lower operating costs.”
Routing Considerations
As was the case when diesel particulate filters were introduced with 2007
emissions-compliant diesels, the exhaust system up to and including the SCR
components cannot be modified. That should not be a problem for truck chassis
with horizontal exhausts under the frame, but some configurations may require
additional engineering.
FCC’s Stark said short-wheelbase models will require the most challenging
applications, especially for truck users who typically place additional
equipment, such as a generator or other auxiliary power supply, under the frame.
“We’ll have two different configurations, depending on what the customer
requires,” he said.
Weight Considerations
A complete SCR system, including the catalytic canister and the DEF system,
could add considerable weight, again depending on the size of the engine and the
truck. DEF weighs 12 pounds a gallon. The SCR system in the Dodge 3500/4500/5500
chassis cabs, for example, will weigh about 250 pounds, a company spokesman said
at the National Truck Equipment Associations’ Work Truck Show in March.
Freightliner’s SCR system in the Business Class M2 model, with a 6-gallon DEF
tank, will weigh 200 pounds, said Stephen Morelli, sales and marketing manager
for EPA 2010 with Diesel Trucks North America.
Vehicle Availability
Some 2010-compliant models will be available later this year, and some may not
show up on dealer lots until well into 2010.
The Japanese brands will be the last to arrive. Transit time from Japan for
Mitsubishi Fuso trucks, for example, could take three months or more, Michael
Rumsey, vice president of sales, told L&MT. Add time in the ports and shipping,
and it could be late summer before 2010-compliant trucks show up on dealer lots.
Trucks produced in North America will have shorter shipping dates. And for those
buyers who want to get a jump-start, Cummins will have some production models
ready before Jan. 1, Lirette said.
“We will conduct limited product builds in the last quarter,” she said. “If
there are some customers out there who want to get an early taste of the
product, we will have engines available early, toward the end of ’09.”
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