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DEF: A New Variable in Managing Truck Fleets

DEF is an acronym for diesel exhaust fluid used by diesel engines incorporating selective catalytic reduction (SCR) technology. As of Jan.1, DEF is now required for SCR-diesels to meet 2010 EPA emission standards.

January 2010, Work Truck - Feature

by Mike Antich - Also by this author

The U.S. Environmental Protection Agency (EPA) mandated all diesel-powered vehicles with engines greater than 3 liters of displacement, manufactured after Jan. 1, 2010, must significantly reduce nitrogen oxide (NOx) emissions. The federal and separate California standards are the strictest exhaust regulations in the world, requiring near-zero emissions of particulates and NOx.

The two technologies designed to comply with EPA 2010 diesel emissions legislation are EGR (exhaust gas recirculation) and SCR (selective catalytic reduction).

About 85 percent of truck and engine manufacturers have chosen SCR to comply with the new regulations. Some of the companies utilizing SCR technology are Cummins, Daimler Trucks (Freightliner & Western Star), General Motors, Hino, Isuzu, PACCAR (Kenworth & Peterbilt), AB Volvo (Volvo & Mack), and John Deere.

One reason most truck manufacturers chose SCR is many are currently using the technology in Europe, Japan, and Australia. For instance, Volvo already has 25 billion miles of experience using SCR technology.

Navistar/International will utilize enhanced EGR technology to comply with the standards. EGR technology reduces the amount of oxygen molecules by introducing cooled exhaust gas, which is lower in oxygen, into the intake system. This reduces the combustion temperature and lowers NOx production.

NOx formation is the byproduct of the high combustion temperature in diesel engines. As the combustion temperature rises, more NOx is exponentially created from oxygen and nitrogen molecules.

"The engine manufacturers that have chosen SCR will continue to use cooled EGR, but at a reduced rate," said Jim Tipka, VP of engineering for the American Trucking Associations (ATA).

DEF Requirements for Use in SCR Diesel Engines

SCR technology uses an ultra pure urea, more commonly known as diesel exhaust fluid (DEF), and a catalytic converter to significantly reduce NOx emissions. SCR works by injecting a very precise amount of DEF into the vehicle's hot exhaust stream. Once inside the SCR catalyst, the ammonia gas forms a chemical reaction with the NOx emitted by the engine. As a result of this chemical reaction, SCR converts NOx into water vapor and harmless nitrogen gas.

With the projected growth in DEF consumption, a nationwide DEF refueling infrastructure is emerging.

A recent milestone occurred when Gilbarco Veeder-Root shipped its first Encore S Diesel Exhaust Fluid dispensers for North America Sept. 2, 2009. The Gilbarco Encore S DEF dispenser was the first of its kind produced specifically for the North American market. Gilbarco Veeder-Root supplies gas pumps, payment systems, point-of-sale systems, and other equipment and services to the retail and commercial petroleum market.

It is anticipated there will be strong competition in the DEF dispensing market in North America. All major truck stops have committed to carrying and selling DEF. Early front-runners in establishing DEF refueling facilities are Pilot and TA Travel Center.

"DEF dispensers will be located at truck stops catering to over-the-road trucks and at high-velocity fuel providers," said Richard Browne, vice president of marketing for North America at Gilbarco Veeder-Root.

In addition, a growing number of public sector fleets are dispensing DEF at on-site fueling facilities, such as the New Hampshire DOT; City of Philadelphia; City of Rockville, Md.; and City of Colorado Springs, Colo., according to Kevin DeVinney, director of dispensers and fleet systems marketing for Gilbarco Veeder-Root.

"Starting Jan. 1, engine NOx emissions must be reduced by 85 percent from current levels. This new level of reduction results in a cumulative NOx reduction of 99 percent from 1974 levels," said Browne.

SCR technology is not limited to medium- and heavy-duty trucks. Passenger cars and light-truck manufacturers around the world are also adopting SCR technology to meet increasingly stringent emission requirements being legislated.

Diesel engines manufactured before Dec. 31, 2009 are not subject to the 2010 EPA diesel emission regulation.

DEF Onboard Technology

Trucks with SCR-diesels are manufactured with onboard tanks to hold DEF, ranging 7-8 gallons for light trucks, up to 23 gallons for a Class 8. "The 7-8 gallons for light trucks was determined by estimating how much DEF would be consumed between oil changes. The minimum size of tank for each type of truck is set by the EPA, as announced in the Nov. 9, 2009 Federal Register," said Tipka. "Heavy work trucks, such as dump trucks and concrete mixers that return to the same location at the end of each work day (centrally fueled), must have a tank with the capacity to hold enough DEF to last at least twice as long as the diesel fuel will last."

The DEF tank is almost always located on the driver side of the vehicle. The DEF nozzle is smaller than nozzles used to dispense diesel fuel.

The average DEF consumption per truck is expected to be approximately 2 percent of fuel consumption, depending on vehicle operation, duty cycle, geography, and load ratings. This works out to 1 gallon of DEF required for every 300 miles traveled (assuming fuel economy of 6 mpg), said Chad Johnson, marketing manager for Gilbarco Veeder-Root. At this rate, a heavy-duty truck traveling 120,000 miles annually would require approximately 400 gallons of DEF per year. Another way to calculate usage is that DEF will be consumed at a 50 to 1 ratio with diesel. (For example, for every 50 gallons of diesel fuel burned, 1 gallon of DEF will be used.)

"A medium-duty truck will probably only have to fill up 10 times a year with DEF," said John Lounsbury, director of marketing for Terra Environmental Technologies in Sioux City, Iowa, which produces nitrogen products as reagents to industrial customers to help them meet local, state, and federal air quality standards.

Failure to refuel the DEF tank will cause the truck to exceed allowable NOx emissions. For this reason, EPA requires OEMs to have a visual or audible warning to alert a driver when  DEF fluid is low - less than 2.5 percent of the DEF tank capacity. However, this alert occurs while the truck is still able to drive hundreds of miles more before the tank is empty. If the driver chooses to ignore the numerous alerts and runs out of DEF, the engine will shift to a performance-restricted mode and eventually no longer restart. However, the engine will not stop running and strand the driver if the vehicle runs out of DEF while moving. Once the DEF tank is empty, a derating of engine power will occur and eventually the truck will be restricted to a maximum speed of 5 mph.

An SCR system requires minimal maintenance. The system has a DEF dosing unit filter, which should be replaced about every 200,000 miles (or every 1-2 years) as part of routine maintenance. This is a simple spin-on cartridge filter. All other vehicle maintenance intervals will be unchanged. For instance, lube filter service intervals will remain unchanged on SCR-equipped vehicles since the SCR process treats exhaust emissions after they are produced by the engine.

"DEF is corrosive to copper and brass, as well as other materials. Only approved materials, such as high-density polyethylene (HDPE), can be used in the DEF tank, packaging, and dispensing equipment," said Johnson.

If DEF is spilled on a vehicle, no damage will occur, and drivers are advised to simply rinse with water.

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