In response to federal emission standards in the United States and Canada, engine manufacturers selected one of two choices to achieve a reduction in emissions of oxides of nitrogen (NOx).
Clearing the Air
In response to federal emission standards in the United States and Canada, engine manufacturers selected one of two choices to achieve a reduction in emissions of oxides of nitrogen (NOx). They either provide an in-cylinder approach through increased exhaust gas recirculation (EGR) only, or an engine aftertreatment approach using selective catalytic reduction (SCR) technology, in combination with EGR.
“The choices in engine technology available to truck and private fleet operators have never been so different,” said Olen Hunter, director of sales for PACCAR Leasing, (PacLease). “And making the right choice has never been so important for companies to control their fleet operating costs, get more mileage out of the engines, and gain a competitive edge.”
Engines manufactured after Jan. 1, 2010 meet the emission standards set by the U.S. Environmental Protection Agency (EPA). The EPA last set new emission standards in 2004 and 2007. Last year, the Obama Administration announced plans to draft regulations for minimum fuel economy and limited carbon dioxide emissions that will go into effect in 2014. Those fuel economy and CO2 standards are being finalized by the EPA and the National Highway Traffic Safety Administration. They’re anticipated to rely on the use of existing products and technology, including 2010 engines, to achieve those goals.
According to Hunter, new engine emission control standards offer one reason why companies should consider full-service leasing from a company that understands the 2010 U.S. EPA-compliant engines.
“Leasing can help take the guesswork out of specifying and servicing 2010 engines,” said Hunter. “Plus, the leasing company can handle any warranty issues and take over any risk associated with truck resale values.”
By choosing the right 2010 engine emissions reduction technology, companies can realize some reductions in operating expenses over the life of the truck, he said. For example, the 2010 engine in medium-duty trucks using SCR technology can offer a net 3 to 5 percent improvement in fuel economy when compared to 2007 EPA-compliant engines.
Hunter said extrapolating a conservative estimate of a 3 percent net improvement, a fleet can help offset the additional cost of the engine — but not completely.
“Consider a fleet running a medium-duty truck with a 2010 SCR engine 35,000 miles per year and getting 7.5 mpg fuel economy,” he said. “With diesel at $3.50 per gallon, when you factor in the 3 percent net fuel economy savings over a typical 6-1/2-year lease term, the company can expect to save $3,156 — or $40 per month.
“Whether you decide to lease or buy a medium-duty truck with 2010 engine technology, even at a net 3 percent improvement in fuel economy, the fuel savings doesn’t completely offset the additional cost,” Hunter added. “However, full-service leasing can make it easier to acquire the new engine technology. You’re not having to deal with a large upfront cost or maintenance of the truck, and you can spread the additional cost of the engine in monthly payments over several years.”
But how does SCR technology deliver a net 3 percent improvement in fuel economy?
To fully understand, truck operators should become more familiar with SCR technology and the increased EGR approaches to emission reduction, said Hunter.
SCR versus EGR
Both the SCR technology and the increased EGR approaches use EGR to circulate a portion of an engine’s exhaust gas back to the engine cylinders to achieve a reduction in emissions. Also, both methods use a diesel particulate filter to remove particulate matter from the engine exhaust.
The SCR technology approach uses a reductant and a catalytic converter to achieve the NOx emission reduction now required by the U.S. EPA and Environment Canada. The increased EGR approach recirculates a significantly larger portion of the engine’s exhaust gas back to the engine, where the NOx emission reduction occurs. The increased EGR approach is often referred to as an “in-cylinder” approach.
SCR accomplishes NOx reduction by mixing the oxides of nitrogen in the exhaust gases with a reductant, most commonly a solution of urea and de-ionized water also known as diesel exhaust fluid (DEF). The exhaust passes through a decomposition tube, where the DEF is introduced through a dosing valve. The exhaust then passes through a cylindrical chamber, also known as the SCR catalyst. Here the DEF reacts with the NOx, breaks it down, producing oxidizing ammonia. The oxidizing ammonia chemically reacts with the NOx, converting the pollutants into nitrogen, water and tiny amounts of carbon dioxide. The SCR catalyst contains a honeycomb-like substrate, which also reacts with the pollutant, converting it into nitrogen and water.
Increased EGR accomplishes NOx emission reduction by increasing the amount of engine exhaust gases into the engine cylinder, slowing and cooling the combustion process. Increased EGR doesn’t require introducing DEF into the exhaust stream to reduce NOx, but it does require more fuel to be injected into the diesel particulate filter for active regenerations. The increased heat created with the enhanced EGR approach also requires greater cooling capacity for the engine.
“Although it’s new to North America, SCR technology is currently used in more than 600,000 trucks around the world,” said Hunter. “SCR has proven its ability to meet European Union emission reduction requirements for many years.”
From an engine performance standpoint, because the SCR aftertreatment system handles the NOx reduction downstream from the engine, Hunter said SCR allows manufacturers to develop engines that last longer and work more efficiently.
According to Hunter, in the development phase of the PACCAR PX line of engines, engineers looked at both high-flow EGR systems as well as SCR to attain emission reductions. “PACCAR engineers believe SCR, in conjunction with moderate EGR, provides the most efficient and effective way to meet the strict EPA 2010 emission regulations,” Hunter added.
Not all SCRs built the same
Operators looking at different SCR engine choices should also consider that even among different SCR engines, there are two major choices that have emerged. One common SCR engine platform uses iron zeolite in the aftertreatment system catalyst while the other uses copper zeolite.
“PACCAR engineers found copper zeolite is much more efficient at reducing oxides of nitrogen at normal engine operating temperatures than iron zeolite,” said Hunter, “This means that engines using copper zeolite as the aftertreatment catalyst are expected to enjoy a fuel economy improvement. That’s because the SCR catalyst is doing the work, and not the engine, to get nitrogen oxide levels down below the EPA threshold.
“We believe that trucks with engines that are less complex and offer longer life, better fuel economy, greater reliability, improved driveablity, and higher power density for better throttle performance, will retain higher resale values,” Hunter added.
“While full-service leasing offers benefits, including the ability to preserve lines of credit for core business projects or other revenue-generating endeavors, it can also help make choosing a truck with 2010 engine technology easier and more affordable. If you’re considering acquiring trucks with 2010 engines for your fleet operation, consider your two choices in emission control, and know full-service leasing may offer the best way to go about it.”
Article provided by PACCAR Leasing Company (PacLease), one of the fastest-growing commercial truck leasing companies in the transportation industry. PacLease is a part of the financial services group of PACCAR Inc, a global technology leader in the design, manufacture and customer support of high-quality light-, medium- and heavy-duty trucks under the Kenworth, Peterbilt and DAF nameplates. PACCAR also designs and manufactures advanced diesel engines, and has conducted extensive testing of 2010 U.S. EPA-compliant engines in many applications, climates and duty cycles. For more information, visit www.paclease.comorwww.paccarengines.com