The U.S. Environmental Protection Agency (EPA) rang in the New Year with more stringent emissions requirements for new on-highway diesel powered vehicles. While older vehicles are not held to the higher standards, voluntary retrofit programs utilizing new clean diesel technologies to reduce harmful exhaust pollutants have been made possible through a variety of funding sources.

In April of 2006, the New York Department of Sanitation (DSNY), in partnership with the non-profit, Boston-based Clean Air Communities (CAC) and the New York Power Authority, announced a $422,000 diesel retrofit program encompassing 65 refuse collection trucks currently operating in Queens.

Project manager Jennifer Kain of Columbus, Ind.-based Cummins Emission Solutions (formerly Fleetguard Emission Solutions) says the department's project, begun in the fall of 2005, resulted in three different technologies being installed on the department's refuse collection fleet. More than 50 trucks were outfitted with a high-performing diesel oxidation catalyst (DOC), which reduces harmful particulate matter (PM) from exhaust by a minimum of 50 percent. Another 10 trucks received a Cleaire Lonestar lean nitrogen oxide (NOx) catalyst and DOC combination that reduces PM by a minimum of 50 percent and removes NOx by a minimum of 25 percent. Five remaining trucks were installed with Cleaire Longview lean NOx catalysts and diesel particulate filter (DPF) combinations that reduce PM by 85 percent and NOx by 25 percent. All three devices, which are manufactured by Cummins, were usually mounted vertically behind the vehicle cab, replacing the existing muffler and exhaust systems.

Several factors must be considered to determine the appropriate technology for each retrofit project, including the age and condition of the vehicles to be retrofitted, and the goals of the project, be it reducing PM, NOx or both.

Another factor to consider is access to special fuel sources. Prior to October 2006, the availability of ultra low sulfur diesel (ULSD) fuel was limited. However, it is now available nationally at the retail level and is required in all new on-highway diesel-powered vehicles. “New York City Sanitation has been using ULSD fuel for several years, so [fuel availability] was not a constraint for them,” Kain says.

A primary concern for the project manager was the fact that each of the three technologies installed on the DSNY fleet were passive devices, meaning no heat or energy is added to achieve the PM and NOx reduction. “The duty-cycle on sanitation trucks is sometimes challenging,” Kain says. She says passive systems rely on existing exhaust temperatures of the engine and duty-cycles to initiate the process of regeneration, converting the sticky carbon soot particles from exhaust into carbon dioxide (CO₂) and nitrogen dioxide (NO₂), and leaving behind ash. As refuse trucks typically make frequent starts and stops, they don't often get hot enough to create that chemical reaction for regeneration to occur, putting the engine at risk of shutting down or failing outright. In some cases, refuse trucks will run long enough at the end of the day while driving to the dump to initiate regeneration. If they do not, failsafe controls alert the operator that soot should be cleaned from the device.

Kain says the DSNY fleet may see a small degradation in fuel economy with the Lonestar and Longview lean NOx catalysts because the devices inject fuel on the NOx catalyst to enable NOx reduction. The trade-off comes with a 25 percent reduction of NOx, contributing to healthier air quality.

“The beauty of this particular program, besides getting the grant money and having a hand in cleaning up the environment, is that two out of three of the technologies, the high performance DOC's, require virtually no maintenance,” says DSNY Assistant Commissioner Rocky DiRico, adding that filters on the five remaining trucks require cleaning only once a year.

“We feel this project is a complete success,” DiRico concludes.
— Annie Gentile is a freelance writer based in Vernon, Conn.