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 first 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 (NOx) 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 Jan. 1, 2011, and in 2015 Tier 4 final will culminate EPA’s set of emission requirements with additional reductions in NOx 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 precede off-road fleet standards—has made for a smoother process. Advancements in engine technology needed to take place, and fuel consumption has remained a priority for manufacturers. Costs have undoubtedly risen for engines and the equipment that they power, but manufacturers tout the benefits available to their customers as a result of these changes.
New territory
Dave Hahn, a product manager with 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 electronics systems that would help reduce the NOx and particulate matter,” he explains.
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True technologies As with a number of other construction equipment manufacturers, Case Construction Equipment, Racine, Wisconsin, launched its Tier 4 Final compliant wheel loaders at ConExpo-Con/Agg, in Las Vegas March 4-8. Case equipped both 821F and 921F models with a selective catalytic reduction (SCR) solution that treats emissions separately with diesel exhaust fluid (DEF) and does not require the engine to recirculate exhaust gas, the company says. Brad Stemper, solutions marketing manager for Case, says while there are “clear advantages” to both SCR and cooled exhaust gas recirculation (CEGR), “the benefits of one solution can outweigh the other based on the application of the machine.” Stemper describes why there is not a one-size-fits-all solution to address Tier 4 requirements for different C&D equipment: Wheel loaders: These versatile machines tackle a wide variety of tasks, which creates inconsistent engine loads and emissions output. Horsepower output and the ability to create breakout force also have a major impact on performance of the machine. Given these operating characteristics, SCR is well-suited for wheel loaders because it is an aftertreatment system that lets the engine do what it is designed to do: generate power at varied engine loads. The technology doesn’t require the use of regeneration to burn off accumulated particulates for faster throttle response time. The end result is full power and breakout force when needed. Additionally, SCR engines are enhanced to create an efficient combustion process. Readily available DEF fluid is significantly less expensive than diesel fuel and is typically only needed in small amounts. There is no need for a diesel particular filter, which reduces long-term maintenance costs. Excavators: Unlike wheel loaders, excavators are used extensively for digging and lifting. As such, engine loads are more consistent and the engine typically operates at stable speeds. The result is relatively steady combustion temperatures and emissions. Given these characteristics, a CEGR system is befitting because a portion of the exhaust gases can be cooled relatively easily, blended with fresh air and circulated back into the combustion chamber to lower combustion temperature, which in turn, reduces nitrogen oxides (NOx). An aftertreatment DPF system can then be used to reduce particular matter. Crawler dozers: Similar to excavators, dozers rely on brute force and raw power to move material, which would suggest the machines are candidates for CEGR. However, an important distinction is that dozers and excavators tackle the load differently. An excavator’s hydraulics handle the majority of the machine’s lifting and moving, while on a dozer, the transmission is the primary mechanism that exerts the power needed to push the load in the forward direction. As the dozer backs up to prepare for another forward push of material, the load is taken off the machine. The result is inconsistent engine loads and emissions output much like those encountered with a wheel loader. As such, SCR is appropriate for dozers because it lets the engine run at peak performance without compromising power or drawbar pull required to move material when it’s needed most. At the same time, the technology allows for significant gains in fuel efficiency. Loader backhoes: Like wheel loaders, loader backhoes experience inconsistent engine loads and emissions based on the variety of work they perform. This would suggest the use of SCR for emissions control. Yet, an advantage of a backhoe is the agility it offers when digging and lifting heavy loads in tight spaces. Therefore, some manufacturers enlisted electronic controls to develop Tier 4 interim-certified machines with smaller engines that use CEGR technology. Importantly, it also has the power and torque to do what it most often needs to do: facilitate productivity when handling heavy loads in tight spaces¬—all the while conserving fuel and meeting emissions requirements. Skid steer loaders: Skid steers offer a bit of a different wrinkle to the conversation. Operators typically run these machines at consistent speeds, producing consistent combustion heat needed to decrease particulate matter. A skid steer also has a lower purchase price when compared with larger machines, which means the addition of SCR technology has a greater impact on the overall cost of the equipment. CEGR is typically the right technology for this application based on overall value to the user and the machine’s operating characteristics. A catalyst-only solution is a third option for skid steers. |
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 after-treatment to further decrease NOx and particulate matter. After-treatment emissions control technologies for engines include selective catalytic reduction (SCR) to control NOx, 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-Con/Agg, hosted in Las Vegas March 4-8, 2014. All of the engines incorporate SCR systems with DEF, while the D8, D13 and D16 engines also use DPF.
Volvo describes its SCR technology this way, “The Volvo solution incorporates an after-treatment catalyzer that reduces NOx levels by injecting a urea-and-water-based reduction agent. When the reduction agent, known as diesel exhaust fluid (DEF) … is heated by the exhaust, it produces ammonia. This causes a chemical reaction in the catalyzer that converts NOx to nitrogen and carbon dioxide—both of which are found naturally in the air. The system reduces NOx emissions by as much as 95 percent.”
Hahn says meeting Tier 4 interim requirements were actually 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 was ready to tackle Tier 4 final, much of the legwork had been completed, he explains.
Caterpillar, Peoria, Illinois, purposefully added a majority of its advanced engine technology during the Tier 4 interim phase, says Doug Mihelick, commercial manager, industrial power systems division for Caterpillar. Technologies that the diesel and gas engine manufacturer put in its Tier 4-compliant engines, which the company also presented at ConExpo-Con/Agg, include: cooled exhaust gas recirculation (CEGR); after-treatment 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 NOx reduction below Tier 4 interim levels,” Mihelick notes.
Mihelick says Caterpillar added only an SCR system with DEF to cut NOx 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.
Fueled up
Mihelick says fuel consumption in Caterpillar’s engine systems has improved more than 10 percent from Tier 3 to Tier 4 as a result of adding advanced technologies to its engines, including SCR. “In each succeeding generation, we’ve delivered some additional fuel consumption improvements,” Mihelick explains.
He 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.”
Volvo Construction Equipment also has been able to reduce fuel consumption throughout each phase set by EPA, according to Hahn. “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 NOx and particulate matters collectively, because, as he explains, reducing NOx increases particulate matter while reducing particulate matter increases NOx.
“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 after-treatment technologies used. “There is a science to exhaust emissions, and it does include design factors,” Dutcher says. “Fuel economy largely depends on the after-treatment device applied,” he says.
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 additional costs can be expected for new machinery applying Tier 4 engines and exhaust after-treatments. “Certainly the cost to construct the added components and apply them to construction machinery has driven machine prices higher,” Dutcher says.
However, some of the new engine features and technologies are providing cost benefits, he points out. Dutcher says Isuzu expects its customers to see durability and reduced service and maintenance costs arising from these modifications.
“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. “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.”
Hahn says, while the overall cost has increased, fuel use has decreased and productivity has increased. “Those two factors really address the additional cost,” he says.
Hahn adds that costs associated with maintenance have not changed much, until the introduction of Tier 4 interim and its after-treatment technologies, including DPF. Ensuring the DPF is clean and that the exhaust tank does not crystallize or go back to its natural state is important, 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 Construction & Demolition Recycling and can be reached at mworkman@gie.net.
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