Top tier

The U.S. Environmental Protection Agency (EPA) has implemented its national regulations program to reduce emissions from off-road diesel engines in phases over the last nearly two decades. Since the introduction of the initial Tier requirement—what EPA refers to each emissions reduction phase—engine manufacturers have produced new diesel engines with advanced emission control technologies. EPA’s central goal of these regulations is to diminish exhaust gases from diesel-powered machinery.

Tier 4, the most recent and final mandatory phase of EPA’s emission standards, requires a 90 percent reduction in both particulate matter and nitrogen oxides (NO_X) over Tier 3’s standards for off-road engines and equipment, resulting in near-zero levels.

EPA split Tier 4 requirements into two parts: Tier 4 interim and Tier 4 final, which went into effect at the beginning of this year. EPA began enforcing Tier 4 interim requirements Jan. 1, 2011, and in 2015 Tier 4 final will conclude EPA’s set of emission requirements with additional reductions in NO_X and hydrocarbon emissions.

Meeting these multiple tiers of emissions regulations has been quite a challenge for some manufacturers, while others, like Anaheim, California-based Isuzu Motors America, say working with on-road applications—with clean air initiatives that typically exceed off-road fleet standards—has made for a smoother process. Advancements in engine technology have had to happen, and fuel consumption has remained a priority, manufacturers say. Costs have undoubtedly risen for engines and the equipment they power, but manufacturers tout the benefits available to their customers as a result of these changes.
 

New territory

Dave Hahn, equipment manager of powertrain PST for Volvo Construction Equipment, Shippensburg, Pennsylvania, says meeting Tier 4’s requirements was a “technological challenge” for the manufacturer of 4- to 16-liter engines for its line of equipment. He says as EPA established new standards, engine manufacturers asked questions such as: What technology was available? When manufacturers realized they had to create the technology, “That drove everything,” Hahn says.

“All engine manufacturers had to develop the systems, not only physical engine systems but [also] electronics systems that would help reduce the NO_X and particulate matter,” he explains.

Hahn adds, “Advancements were made with sensors, injection issues and fuel systems, and that’s where we, and all engine manufacturers, had to work to develop that technology as it just wasn’t out there.”

While in-engine modifications helped engine manufacturers reach Tier 2 and Tier 3 regulations, Tier 4 interim and Tier 4 final standards require exhaust aftertreatment to further decrease NO_X and particulate matter. Aftertreatment emissions control technologies for engines include selective catalytic reduction (SCR) to control NO_X, diesel particulate filters (DPF) to capture the lingering particulate matter and exhaust gas recirculation (EGR), which recirculates some of the exhaust gases back into the combustion chamber.

Volvo introduced its lines of Tier 4 final-compliant D4, D6, D8, D11, D13 and D16 diesel engines at ConExpo/ConAgg, held in Las Vegas March 4-8, 2014. All of the engines incorporate SCR systems with diesel exhaust fluid (DEF), while the D8, D13 and D16 engines also use DPF.

According to Volvo, its SCR technology “incorporates an aftertreatment catalyzer that reduces NO_X levels by injecting a urea-and-water-based reduction agent. When the reduction agent, known as DEF, … is heated by the exhaust, it produces ammonia. This causes a chemical reaction in the catalyzer that converts NO_X to nitrogen and carbon dioxide—both of which are found naturally in the air. The system reduces NO_X emissions by as much as 95 percent.”

Hahn says meeting the Tier 4 interim requirements was much harder than complying with those of Tier 4 final. “Tier 4 interim was all new territory; we were breaking new ground,” Hahn says. By the time Volvo Construction Equipment went to tackle Tier 4 final, much of the legwork had been completed, he adds.

Caterpillar, based in Peoria, Illinois, purposefully added a majority of its advanced engine technology during the Tier 4 interim phase, says Doug Mihelick, the company’s commercial manager, industrial power systems division. Technologies that the diesel and gas engine manufacturer put into its Tier 4-compliant engines, which Caterpillar also presented at ConExpo/ConAgg, include cooled exhaust gas recirculation (CEGR), aftertreatment systems with supporting cradles, exhaust filters consisting of a diesel oxidation catalyst (DOC) and DPFs, new turbochargers and software to run the engines and regeneration devices.

“Tier 4 final regulations required additional NO_X reduction below Tier 4 interim levels,” Mihelick notes.

To meet these stricter standards, Mihelick says Caterpillar added only an SCR system with DEF to cut NO_X levels from Tier 4 interim’s 2 grams (g) per kilowatt-hour (kWh) to just 0.4 g/kWh for 130- to 560-kilowatt engines under Tier 4 final requirements.
 

Fueled up

Mihelick says that as a result of adding advanced technologies to its engines, including SCR, fuel consumption in Caterpillar’s engine systems has improved more than 10 percent from Tier 3 to Tier 4. “In each succeeding generation, we’ve delivered some additional fuel consumption improvements,” he explains.

Mihelick adds, “The most impressive achievement: Our Tier 4 final products are up to a 12 percent improvement in diesel fuel consumption over the prior Tier 3 product generation, depending on load factor and application.”

Hahn says Volvo Construction Equipment also has been able to reduce fuel consumption throughout each phase set by EPA. “I would guess our fuel consumption is 10 to 20 percent less than it was with Tier 2,” he says of the company’s Tier 4-final engines.

To meet Tier 4 standards, Hahn says it was all about the fuel. The company set out to find a balance between reducing NO_X and particulate matters collectively, because, as he explains, reducing NO_X increases particulate matter while reducing particulate matter increases NO_X.

“To find a balance between the two, it all had to deal with fuel. Fuel injections, timing, air flow, you name it, and all of those things had to come together to meet those emissions standards,” Hahn says.

Also new with Tier 4 is the use of ultra-low-sulfur diesel fuel (ULSD), with a maximum sulfur concentration of 15 parts per million. EPA says it adopted these “cleaner diesel fuel” requirements for in-use diesel fuel to decrease sulfur levels by more than 99 percent.

John Dutcher, director of sales and marketing for Isuzu Motors America, says fuel efficiency ultimately depends on the aftertreatment technologies used. “There is a science to exhaust emissions, and it does include design factors,” Dutcher says. “Fuel economy largely depends on the aftertreatment device applied.”

He continues, “An Isuzu advantage is the compactness of the exhaust aftertreatment device and simplicity in which we can employ it. Our focus is on the end user and how they will benefit from our design changes.”
 

Cost benefits

Dutcher says higher costs can be expected for new machinery applying Tier 4 engines and exhaust aftertreatments. “Certainly the cost to construct the added components and apply them to construction machinery has driven machine prices higher,” he says.

However, some of the new engine features and technologies are providing customers with cost benefits, he points out. Dutcher says Isuzu expects its customers to see durability and reduced service and maintenance costs arising from these modifications to its engines.

“Technology has a cost, and our industry had to pass this cost on to society in the form of price increases,” Caterpillar’s Mihelick says.

However, operators may see saving in other areas that help to offset this initial higher cost. “Based on the fuel consumption improvements we’ve implemented through our Tier 4 journey, we expect our customers to enjoy lower operating costs compared to prior machine and engine generations,” he adds.

Hahn says, while the overall cost has increased, Volvo equipment’s fuel use has reduced and productivity has increased. “Those two factors really address the additional cost,” he says.

Hahn adds that maintenance costs had not changed much, until the introduction of Tier 4 interim and its aftertreatment technologies, including DPF. Ensuring the DPF is clean and that the exhaust tank does not crystallize or revert to its natural state is an important step, he says.

“We like to show that on the new machines you can walk up to the exhaust, wipe your hand [across it] with a white glove, and it is clean. The air coming into the air cleaner is dirtier than the exhaust coming out of the exhaust pipe,” Hahn says.

The author is associate editor of Recycling Today and can be contacted at mworkman@gie.net.