It's been a year since the third round of emissions controls for diesel engines took effect. After the first two rounds, unintended consequences created problems for truck users, first with higher than expected under-hood temperatures from exhaust gas recirculation (EGR), then from high fuel consumption cleaning out diesel particulate filters (DPF).
The promise of 2010 pollution control strategies is that proven technologies have eliminated potential problems, and the 2010 engines should be problem-free. But after one year of service, what is the reality?
Clearing the air
Emission control technologies have virtually eliminated particulate matter (PM) and nitrogen oxides (NOx) from diesel exhaust. January 2007 restrictions on PM brought us DPFs, and restrictions on NOx increased the use of EGR. To make DPFs work, sulfur in diesel was limited to 15 ppm.
Further NOx restrictions in January 2010 resulted in two different technologies. International's MaxxForce engines use Advanced EGR and credits from the EPA to provide an In-Cylinder Solution that meets EPA requirements. All other on-highway engine manufacturers chose selective catalytic reduction (SCR), a chemical exhaust after-treatment using urea injection to neutralize NOx.
SCR has been used for years in Europe so a great deal of development and field experience went into making our 2010 SCR engines virtually foolproof.
Performance in practice
The addition of SCR is far less a problem for vocational fleets than for long-haul truckers. Mixers can return to plants with a ready supply of diesel exhaust fluid (DEF), the urea solution that creates the reaction with NOx.
Maintenance personnel can fill DEF tanks. Gauges and alert lamps warn when DEF is getting low, and reduce the risk of running out of DEF, having the engine de-rate, and eventually shut down. So for 2010, problems are minimal.
But in the past year, vocational fleets have reported difficulties with the 2007 technology. All 2007 diesels use ceramic porous-wall DPFs to capture solids. Exhaust with soot from combustion and ash from motor oil additives build in the filter's cells, while the gaseous exhaust permeates the walls on its way to the tailpipe.
Engines that run continually at peak temperatures automatically regenerate, sometimes several times daily. Given the stop-and-go duties of concrete mixers and trucks, though, engine temperatures are rarely high enough to trigger regeneration. To avoid loss of power and eventual shut down, the operator must start a manual regeneration that can take up to an hour.
When soot builds in the cells and restricts exhaust flow, a regeneration process clears the filter by burning the soot. The process injects diesel fuel into the exhaust, and it passes over a diesel oxidation catalyst. The catalyst raises the exhaust temperature above 1100 ° F, burning off the soot.
A small amount of ash remains after the regeneration process, which builds up over time and must be cleaned. The process involves removing the DPF and cleaning out accumulated ash with heat, vibration, and compressed air.
DPF cleaning can be outsourced or done with purchased equipment. Prices vary for cleaning machines, but the one year break-even point to clean the filters in-house is generally one filter per day, or about 250 medium- and heavy-duty trucks 2007 or newer in the fleet. Payback becomes less than one year. Light-duty diesels' DPFs are often welded in place and are good for the expected life of the truck.
Ceramic filters can easily crack, when handled outside their canisters. Some fleets have reported up to 15% cracked filters. Soot build-up on exhaust pipes is a sign of a crack.
My report card on the 2010 engines: once you get past the initial price of SCR — as much as $9000 for some trucks — they're not much different from the 2007 models. The DPF equipment on the 2007s seems to need the most maintenance.
Paul Abelson is a former director of the Technology and Maintenance Council of the American Trucking Association and is on the Board of Truckwriters of North America. Efirstname.lastname@example.org.
Read more from Paul Abelson at his Fleet Factors blog.
Greener fleets are coming
Just as Tier 4 engines were being delivered to construction fleets, there was news that more restrictions were coming. In late October 2010, the U.S. Environmental Protection Agency and Department of Transportation announced the first national standards to reduce greenhouse gas and improve fuel efficiency of heavy-duty trucks. The goal is to reduce emissions by about 250 million metric tons and save 500 million barrels of oil over the lives of vehicles produced in the program's first five years.
To update fleet owners on these developments, key partners from CALSTART, America's leading clean transportation consortium, will discuss some of the new and upcoming vehicle and equipment technologies at a special session at World of Concrete.
The 90-minute seminar includes presentations on current product offerings, future technology developments, and regulatory issues that affect the development and deployment of clean, advanced technology vehicles. Topics will include hybrid technology, energy storage configurations, infrastructure needs, and market strategies. This session will also cover effects of the EPA/DOT new fuel efficiency and greenhouse gas standards. For details, visit www.worldofconcrete.com.