Like it or not, 2010 trucks will utilize urea in theirselective catalytic reduction (SCR) emissions control systems. So, let’s discuss some facts about urea anddispel a few myths.
The new diesel emissions fluid (DEF) is a mixture of 30%urea in water, so it could conceivably freeze at approximately 10 degrees F.But, since the EPA doesn’t allow these systems to be inoperable, truck OEMshave done two things to assure the DEF tanks won’t freeze. When the vehicle isrunning, enough of the engine’s coolant will circulate through the tanks toassure the fluid won’t freeze. After setting overnight, frozen DEF fluids canbe thawed by electric heaters in the tanks.
Skeptics also fear that urea will evaporate out of the DEFtank at higher temperatures. Urea does become more volatile at approximately120 degrees F, but again the EPA has demanded safeguards. DEF tanks are closedsystems that will allow no evaporation into the atmosphere, much likeevaporative emissions systems that have been used on passenger cars since the’70s.
Urea is not toxic at elevated temperatures as some havereported. Sure, it gets odoriferous, but it’s never any more toxic thanhousehold ammonia.
What about maintenance practices with SCR systems? The DEFtanks I’ve encountered contain between 20 and 25 gallons. Since DEF consumptionis on the order of one gallon every 300 miles, the average DEF tank should beable to go 6,000 miles or more before refueling. That should give drivers ampleopportunity to find urea. I’m also certain that most vehicles will haveflashing lights and alarms on the dashboards so the driver will know in advancewhen the tank gets low. OEMs don’t want to gamble that vehicle horsepower willbe significantly de-rated because the DEF tank is out of urea. Besides, eachdriver could easily carry a gallon or two of DEF on the truck.
I’ve also heard that SCR will be a problem because it’sunproven technology. SCR has been used in trucks in Europe for a decade, so alot of experience is out there for the OEMs to draw upon. At a TMC ExhaustEmissions Forum in Phoenix several years ago, both Daimler and Volvo sharedtheir favorable experiences with SCR. Remember, the EPA would not allow SCRusage in the U.S. until the OEMs developed systems to assure them that aninfrastructure existed and that engines would not operate properly if the DEFtanks contained no urea.
SCR has one significant benefit which makes it an excellentchoice. For once, fuel economy with anew emissions reduction system is improved! Depending on to whom you listen,SCR improves fuel economy 3% to 5%. I did a few calculations assuming Ioperated a truck 100,000 miles per year at 6.5 MPG fuel economy on $3.00 pergallon ULSD. If fuel economy is increased 3% to 5%, Diesel fuel savings isapproximately $1,370 to $2,285 per-truck-per-year. Factoring in the cost of theDEF at $3.00 per gallon (it likely will be less expensive) resulted in a netfuel cost savings of $775 to $1,290 per year per truck. That’s a significantsavings!
You might hear claims out there that EGR-equipped vehiclesget equivalent fuel economy. Increased EGR always has an adverse effect on fueleconomy, and EGR levels had to be increased again to meet 2010 NOx emissionsrequirements. A major reason SCR provides better fuel economy is that enginesutilizing SCR can operate at about 50% of the EGR levels as other engines.
I can’t calculate what it would cost you to trade upto a 2010 model-year truck; you can do these calculations using your fleet’sfinancial variables. But a 2.5% improvement in fuel economy is worthconsidering.
