When the Operating Engineers’ Local 150 recently hosted a “Tier 4 Seminar” at its Wilmington, Ill., training center, an impressive number of machine owners and operators took time on a balmy October Saturday (a perfect work day) to hear a number of engine manufacturers explain the details of the latest emissions-reduction technology. Judging from questions asked, equipment users are extremely interested in the technology, which, as they learned, is not applied in a one-size-fits-all manner.
Having progressed since 1996 through five, successively more-stringent phases (Tiers) to reduce exhaust emissions, off-highway diesels in many horsepower categories are now officially subject to the most-stringent standard, Tier 4-Final, except for those in the 75-to-174 horsepower band and those with more than 750 horsepower, which are subject to Tier 4-Final regulation in January 2015.
Retrofitting for PM Control
In nonattainment areas, where air-pollution levels consistently exceed National Air Quality Standards, state regulations may require that existing equipment used on publicly funded projects (or any project) meet standards for PM.
According to Glen Chrusciel, project manager, retrofit, John Deere Power Systems, a machine owner in this situation might find an actively regenerated DPF a cost-effective way to keep the machine working, since the device can reduce PM by a minimum of 85 percent.
He reminds owners that in many instances, passively regenerated systems might not perform well, and that each application must be data-logged to record exhaust temperatures and duty cycles to assure the EPA and CARB (California Air Resources Board) that the DPF can be passively cleaned.
In his experience, says Chrusciel, only about a third of candidate machines can support a passive DPF. Plus, he says, machines that move from job to job will encounter differing duty cycles, some of which might not support passive regeneration.
In these situations, says Chrusciel, he typically advises an actively regenerated DPF system that uses an integral diesel-fueled heater. An active system is more expensive, he says, “but in the long run, it provides valuable flexibility.”
Although the regulations do address emissions of carbon monoxide and hydrocarbons (unburned fuel), the two pollutants of primary concern are particulate matter (PM) and nitrogen oxides (NOx).
PM includes tiny particles of solid carbon, carbon particles saturated with unburned fuel and oil residue, and compounds of sulfur—in short, black smoke with the potential to harm lungs. NOx includes NO (nitrogen monoxide or nitric oxide) and NO2 (nitrogen dioxide)—gases that are toxic by inhalation. NO2 also is a suspected contributor to smog and acid rain.
Controlling PM and NOx, however, is complicated by the so-called “NOx/PM trade-off,” which means that measures taken to reduce NOx tend to increase PM, and vice versa. Nevertheless, engine manufacturers have continued to develop techniques for reducing these pollutants, both during the combustion process (“in-cylinder”) and after they leave the combustion chamber (“after-treatment”).
In-cylinder techniques include: modification of the combustion chamber; variable-geometry turbocharging and charge-air cooling to precisely control intake-air volume and temperature; cooled exhaust gas recirculation (CEGR); and fuel-system refinement, including electronic control of fuel injection and high-pressure common-rail (HPCR) fuel systems, which routinely operate at pressures exceeding 30,000 psi and allow multiple injections of fuel during a single combustion cycle to improve the efficiency of the burn and to reduce emissions.
CEGR involves recycling a portion of the exhaust to the cylinders in order to reduce the oxygen available for combustion, thus subsequently reducing cylinder temperatures and retarding NOx formation. Recycled gases typically are cooled via an external cooler before combining with fresh intake air, says Doug Laudick, manager of product planning, John Deere Power Systems, in order to maximize the benefit of charge-air cooling.
But that said, a few engines do employ either “warm” EGR systems, which do not use an external cooler, or “internal” EGR systems, which adjust engine-valve timing to retain a certain volume of exhaust in the cylinder to be mixed with intake air.
Because Tier 4-Interim and Tier 4-Final regulations demand huge reductions in PM and NOx, respectively, after-treatment is now supplementing in-cylinder technology. For example, selective-catalytic-reduction (SCR) systems are now frequently used to deal with NOx exiting the cylinder—either working alone or in conjunction with CEGR.
Undoing Tier 4 Technology
Used machines from North America historically have found ready markets in lesser-developed areas of the world, but ultra-low-sulfur diesel fuel might be in short supply in many of these areas. Operating a machine equipped with Tier 4 after-treatment devices on high-sulfur-content fuel can “poison” catalysts and debilitate sophisticated fuel systems.
This has machine owners questioning if the resale value of their Tier 4 models will be jeopardized if markets with poor-quality fuel will now be closed to these technically advanced machines.
Engine manufacturers, however, are addressing this issue—or already have solutions—among them JCB, Caterpillar, Cummins, and John Deere. In some instances, only an authorized dealer in the country where the machine will be used can perform the “de-tiering” or “de-emissionizing” process.
The SCR system injects small amounts of diesel exhaust fluid (DEF)—a 67.5:32.5 mix of water and urea—into the exhaust stream just ahead of the catalyst. Using this reactant, the catalyst converts NOx to safe elemental nitrogen and water. An ammonia-oxidation (“ammonia-slip”) catalyst neutralizes any excess ammonia formed in the reduction process.
“As we go to Tier 4-Final, taking CEGR to a higher level to deal with an 80- to 90-percent reduction in NOx would have prevented us from providing the level of performance and fluid economy [total fuel and DEF used] that our customers demand,” says Laudick. “To reach that next level, we integrated SCR into our emissions-control strategy.”
Likewise, drastic reductions in PM for Tier 4 engines has prompted routine use—at least on some engine platforms—of the diesel oxidation catalyst (DOC) and diesel particulate filter (DPF).
The DOC is a no-maintenance catalyst that serves to reduce certain pollutants and, when required, to raise exhaust temperatures. The DOC converts carbon monoxide to carbon dioxide and converts hydrocarbons to carbon dioxide and water. Also, depending on its design, the DOC can provide a degree (perhaps up to 30 percent) of PM control. It does so by converting NO in the exhaust to NO2, thus creating a volatile gas that assists in oxidizing (and thereby eliminating) PM at relatively low exhaust temperatures.
The DPF is a filter that traps virtually all remaining PM, which then accumulates in the filter and must be periodically (or continuously) oxidized, a process called regeneration. If the DPF substrate (the filter body, often ceramic) uses a catalyst to produce NO2 (adding to that produced by the DOC), then the DPF can “passively” or “continually” regenerate (oxidize PM with no outside intervention) at moderate exhaust temperatures. Passive regeneration assumes that the engine will produce enough NO in typical use to support the process.
A DPF not using a catalyst must be “actively” regenerated, a process often initiated when exhaust backpressure, caused by accumulated PM, reaches a certain level. A common technique for actively regenerating the DPF is to inject diesel fuel into the exhaust stream just ahead of the DOC. The fuel serves as a reactant to make the DOC function as a “flameless” heater to raise exhaust temperatures upwards of 1,200F, high enough to oxidize PM in the DPF.
Systems not using a DOC, or not using the DOC for this purpose, might instead use a diesel-fueled burner to elevate temperature—or might use the burner to create a primary flame to vaporize added fuel serving as a reactant in the DOC. Whatever the method, manufacturers strive to make active regeneration as transparent as possible, that is, to allow the machine to function normally during DPF cleaning.
Some PM after-treatment systems, although using a “catalyzed,” passively regenerated DPF, are designed to actively regenerate at specific intervals (perhaps every 500 hours). These systems might also use the engine to assist in raising exhaust temperatures during active regeneration by restricting intake air, restricting exhaust flow, changing injection timing, and shutting down the CEGR system. Some engines might rely solely on these adjustments to effect active regeneration.
Peter Engdahl, engine performance engineering manager, Volvo Construction Equipment, makes the point that controlling exhaust temperatures is important both for the DPF system and the SCR system.
“Exhaust-gas heat management plays an important role in the functionality of the after-treatment system,” says Engdahl. “Besides controlling the particulate load in the DPF, heat management also is required to secure high NOx-conversion efficiency in the SCR system over time. The need and method to create additional heat, for example, by adjusting engine parameters and injecting HC [fuel] into the DOC, depend on ambient conditions, machine usage, and application.”
The DPF still must be periodically removed, however, and cleaned of accumulated ash deposits, left mostly by engine-oil additives. The interval varies with engine and DPF design and can range from perhaps 3,000 hours to as long as to the first engine overhaul.
What to use where?
The Tier 4-Final technology applied to various classes of equipment can vary significantly, influenced by a number of considerations: the specific regulations that apply to a horsepower category; engine design, size, and power rating; equipment application (will it run at a steady state or constantly be accelerating and decelerating?); and limitations on after-treatment packaging—whether space constraints or preserving sight lines.
The primary consideration, however, might be user expectations for performance. For example, how important are such factors as transient response (quickly building power to handle loads), maintaining peak power at high altitudes, and fluid (fuel and DEF) economy.
“There’s a wide [technology] expanse in what individual manufacturers are delivering, based on customer needs they want to address,” says Andrew Kahler, product marketing manager, John Deere Construction & Forestry. “Each solution has its benefits.”
As an example, Kahler says that Deere has chosen in some construction and forestry applications to control PM outside the cylinder, because it allows the engine to deliver better acceleration and lugging ability, a critical consideration for many applications.
“To accelerate an engine under load quickly, sufficient fuel is added to the combustion process in a short period of time,” says Kahler, “and the result is that the engine rapidly creates the torque required. Particulate matter might result, but the diesel particulate filter will capture it. Using the DPF gives the flexibility to fuel the engine as quickly as torque is required and to deliver peak performance in demanding applications.”
Emissions-control strategies, then, can differ manufacturer to manufacturer, engine to engine, and machine category to machine category, depending on the specific approach chosen to address the application and perceived user needs. DEUTZ perhaps has most concisely summed up the situation: “As much technology as necessary, and not as much as possible.”
Following is a brief overview of strategies being employed by a number of engine manufacturers. In addition, Diesel Progress has given us permission to share its graphic representation of what each engine builder is doing.
“Since all customer applications are not the same,” says Caterpillar’s Doug Mihelick, commercial engine manager, “Caterpillar has chosen scaleable, integrated systems that allow us to deliver solutions specifically tailored to meet our customers’ needs. We recognize that one technology does not fit all applications, and this fundamental realization leads to designing and utilizing a comprehensive technology portfolio.”
Building on its ACERT combustion technology developed nearly a decade ago, Caterpillar’s Tier 4-Final technology ranges from that of the C32 (800 to 1,200 horsepower) using CEGR (Cat NOx Reduction System) and dual DOCs—to the smallest models (7.6 to 28.2 horsepower) that control NOx and PM in-cylinder. Between, for example, are the C7.1—using HPCR, CEGR, SCR, DOC, and a “service-free” DPF—and the C9.3, similarly equipped, but with a Cat Regeneration System (burner) for actively cleaning the DPF.
According to Cummins, the emissions strategy for specific engines is determined by power output, displacement, and emissions levels to be met. For example, the new QSG12 (335 to 512 horsepower) meets Tier 4-Final by using the Cummins Xtra-High Pressure Injection system, DPF, and SCR—without CEGR. Overall, says Cummins, the goal is to balance in-cylinder and after-treatment techniques for optimum emissions control at all loads and exhaust temperatures, while also optimizing engine response and fuel efficiency.
Cummins’ Tier 4-Final strategy ranges from that of the QSF2.8 (49-74 horsepower) using HPCR, CEGR, and the Cummins Compact Catalyst (a DOC manufactured by Cummins Emission Solutions)—to the 19-to-78-liter QSK Series that uses “a combination of clean in-cylinder combustion and integrated SCR.” In the mid-range, the new QSF3.8 (85 to 132 horsepower) uses only HPCR, SCR, and reduced CEGR, and the QSB4.5 (121 to 173 horsepower), QSB6.7 (155-310 horsepower), and QSL9 (250 to 400 horsepower) use HPCR, CEGR, SCR, and a DOC.
Bobcat, when planning its new 1.8-, 2.4-, and 3.4-liter engines, worked with its sister company, Doosan Engine Group, to develop an “ultra-low particulate matter combustion” (ULPC) system. All three engines use HPCR, CEGR, and a DOC; the 3.4-liter adds SCR. The goal, says Bobcat, was to eliminate the necessity for after-treatment service. According to Chris Knipfer, segment application marketing manager, Doosan Infracore Construction Equipment, the engines are designed to vary combustion pressures with the load, thus optimizing performance, fuel economy, and emissions control.
When JCB developed its Dieselmax engine in 2004, it was designed with Tier 4 regulations in mind, incorporating an innovative “clean-combustion” system, says Chris Giorgianni, vice president, product, JCB North America. Today, the new JCB Ecomax engine, the Tier 4 derivative of the Dieselmax with even further refined combustion characteristics, is being used in the company’s equipment for applications in the 75-to-174-horsepower range.
The Ecomax meets Tier 4-Final regulations using CEGR and a compact SCR system that JCB calls a “one-can solution,” designed to simplify packaging challenges. A proprietary system for mixing urea with exhaust gases just ahead of the catalyst, says JCB, keeps piping runs short to further accommodate installation.
For JCB applications requiring 42 to 73 horsepower, JCB has partnered with the Kohler Global Power Group to supply three- and four-cylinder engines that will be identified as JCB Diesel by Kohler. The Kohler engines use CEGR and a DOC, in combination with HPCR. Kohler’s Tier 4-Final solution in this power band is aligned with that of JCB, says Giorgianni, that is, no-maintenance after-treatment.
“Isuzu engines with ratings of 49, 63, and 70 horsepower,” says John Dutcher, director, sales/marketing, Isuzu Motors America, “use only a compact diesel oxidation catalyst in the emissions-reduction strategy.” A compact SCR system is used for larger diesels, and in many applications, he says, exhaust-related components are installed on the engine to simplify machine installation.
For its Tier 4-Final D4, D6, D8, D13, and D16 engines (the number is displacement in liters), Volvo combines its V-ACT (Volvo Advanced Combustion Technology) system with CEGR and a full complement of after-treatment (DOC, DPF, and SCR). This concept, says the company’s Engdahl, “provides the best combination of high performance with low consumption of fuel and DEF in the range of machines using these engines.” The company’s D11 engine, installed in A25 and A30 articulated haulers, uses warm EGR and SCR—but no DPF. (Volvo Trucks, of course, has been using SCR systems for on-highway diesels since 2005.)
John Deere Power Systems
According to Deere’s Kahler, the company has progressed through the emissions Tiers by employing a “building-block” (Integrated Emissions Control) approach to optimize engine performance and operating efficiency, while maintaining reliability and long-term durability.
Deere uses a range of in-cylinder and after-treatment technology, from lower-horsepower engines using only a DOC/DPF package (no CEGR, no SCR), to higher-horsepower models that employ CEGR, SCR, DOC and DPF. For the PowerTech PWL 4.5L engine, however, Deere chose an SCR/CEGR/DOC solution (no DPF), saying that this approach strikes a balance between packaging, performance, and operating costs.
Case Construction Equipment was an early adopter of SCR technology, using the technique for certain of its Tier 4-Interim wheel loaders and new M Series dozers. Considering that these machines take on a variety of tasks that create inconsistent engine loads and emissions output, says Brad Stemper, solutions marketing manager, SCR is well suited, because “SCR engines are optimized for efficient combustion.”
Case recently announced Tier 4-Final technology for certain of its skidsteer loaders: two medium-frame models meet compliance with new engine technology and a DOC, while two compact-frame models use CEGR and a DPF. The medium-frame units, says Tim O’Brien, brand marketing manager, are used in fleets and the rental market, and subsequently, have many operators and are frequently moved from application to application. Therefore, the maintenance-free, “DOC-only” solution, he says, made the most sense for these models.
According to Kubota Tractor, Tier 4-Final strategy includes “further optimization of existing technologies that satisfy both emission standards, as well as a wide range of market demands.” Technologies include HPCR, CEGR, and the DPF. Kubota also has developed a new 25-to-50-horsepower engine that uses the company’s proprietary Three Vortex Combustion System.
MTU America’s goal for Tier 4-Final has been to develop a range of engines not requiring a DPF, thus more easily accommodating space and weight constraints of equipment builders. To that end, MTU has developed its own Amplified Pressure Common Rail fuel system, simplified SCR system, and a clean-combustion system that provides unaided cold starts to minus 22F.
MTU Series 1000, 1100, 1300, and 1500 engines (134 to 616 horsepower) use only SCR; Series 1600 (up to 980 horsepower) employs only in-cylinder technology, HPCR, two-stage turbocharging, and CEGR. Series 2000 units (1,050-1,300 horsepower) and Series 4000 models (2,350-4,025 horsepower), available in 2015, follow the no-after-treatment design of the Series 1600.
The basic features of its Tier 4-Interim models, says Perkins, are carried over to Tier 4-Final models, with 3.4- to 7.1-liter models (850, 1100, and 1200 Series engines) using a “tailored” SCR system. For six-cylinder 1200 Series models, the DOC, DPF, and SCR system are in one module, allowing either engine or chassis mounting; four-cylinder models feature a compact DPF/SCR module. The four-cylinder 850 range packages the SCR and the DOC separately for installation flexibility. Perkins’ Technology Integration Workshop helps machine manufacturers integrate after-treatment technology.
According to a recent Komatsu press release, the company’s Tier 4-Final solution builds on the technologies used for Tier 4-Interim engines (including HPCR, “high-efficiency” EGR, and DPF) with the addition of a Komatsu-designed SCR system. The overall design, says Komatsu, “provides a high amount of passive regeneration of the Komatsu DPF with minimal impact on machine operation and production.”
DEUTZ’s Variable Emissions Reduction Technology (DEVERT) is a “modularly structured system, which is incorporated into different engine configurations.” The flexibility of the DEVERT “kit,” says the company, avoids “over-engineering” by ensuring that “only as much technology as is necessary and useful is used.” DEVERT technology includes HPCR, CEGR, DOC, DPF, SCR, and “heat management” systems that include a burner and “engine internal measures,” used singly or in combination. Small engines (25.8-75.3 horsepower) employ only HPCR and CEGR.
The latest generation of Liebherr’s inline four- and six-cylinder engines and its V8 and V12 models (11 basic engines with ratings from 174 to 1,005 horsepower) apparently comply with Tier 4-Final standards using only SCR, in conjunction with a Liebherr-designed HPCR fuel system and combustion-chamber refinements—requiring no DOC, DPF, or CEGR.