When the Tier rating program started in the U.S. in 1996, the goal was to reduce nitrogen oxide and particulate matter from the exhaust of diesel engines. Since then, engine technology has been getting more complex and costly in the drive to meet emission requirements. Tier 4 has been implemented in two stages since 2011 with the Tier 4 Final rule being a requirement for the majority of new diesel engines manufactured as of Jan. 1, 2014.
What does this mean for sweeper manufacturers and sweeping contractors?
“All sweepers using ‘non-road diesel engines’ (the auxiliary engines that are commonly used to power the sweeping equipment on truck-mounted sweepers) must now meet Tier 4 emission requirements,” says Steve Douglas, product manager at Johnston Sweepers.
This essentially means that the two worlds of on-road and off-road EPA standards need to collide. “It’s two different engines and two different pieces of legislation,” adds Douglas.
Sweeper manufacturers that produce units with just one diesel truck engine will focus their attention on on-road emission standards and adapting their cabs to a new chassis. And those manufacturers that also use an auxiliary engine for the sweeping unit will encounter different challenges when selecting an engine that meets their standards and also complies.
And since no single technology enables an engine to meet the stringent emissions standards, sweeper manufacturers have been challenged with designing equipment that delivers maximum power and productivity, while also dramatically reducing particulate matter and nitrogen oxide emissions. As you can imagine it’s been no easy task.
Complicating the challenge is that many of the engines available from engine manufacturers usually will not bring a piece of equipment into compliance with Tier 4 standards on its own. Instead, the engine manufacturer will give their buyers, in this case sweeper equipment manufacturers, application standards that are needed to bring the sweeper, into compliance with Tier 4.
“The engines come from the manufacturer completely certified,” says Brian Giles, sweeper products manager at Elgin Sweeper. “Different manufacturers achieve compliance through various after-treatment options, but all these come as part of the engine assembly package. The sweeper manufacturer must install the loose pieces where and how the engine manufacturer instructs them.”
Manufacturers say there are few main “after-treatments” that can be used on machines to assist the engines in meeting the Tier 4 emission standards. “It’s basically a whole new engine,” says Jim Adair, product manager at Schwarze Industries. “It’s not just adding components to an existing engine and then you have a Tier 4. That Tier 4 engine is certified by the manufacturer and you follow those parameters of its application.”
The technology being used to reduce emissions in combination with the new engines is:
Particulate Filter: A diesel particulate filter is used to collect the particulate matter generated by combustion. Often called a particulate trap, it does just that - traps the particulate matter. As more and more material is collected, backpressures increase and the filter must be cleaned. Normally, the filter cleans itself by oxidizing the material in a process called regeneration.
Regeneration: As stated above, the cleaning of the particulate filter is accomplished by regeneration. Regeneration of the filter cleans by converting particulate matter to nitrogen oxide and water. The temperature within the filter must be at a certain level to make this happen. Regeneration can happen passively, actively or a combination of both.
“A regeneration on the chassis of a sweeper is probably one of the worst-case scenarios,” Adair says. “Sweepers do not get up to the speeds needed to regenerate and burn off the soot that the particulate filter collects. When you’re running at such a low speed, you never get the RPMs up to regenerate while sweeping. A forced regen is needed where the sweeper has to sit for a full 30 minutes to incinerate the collected soot.”