Following the Trail of Tiers

Sept. 28, 2010

The off-road engine market has come out of its corner to go another round with the Environmental Protection Agency (EPA) in a fight that started in the late 1990s. It all has to do with reducing engine emissions by phasing in increasingly demanding regulations.

Engine manufacturers who want to market to North America, Western Europe and Japan must have a development strategy to move from non-regulated Tier 1 and 2 engines to Tier 3 and another to achieve Tier 4, which begins in 2012 or 2014, depending on the output side.

Two paths to the goal

"For International products, Tier 3 is in effect now," says Steven Hyde, director of international business development for International Engine Group. "Like other manufacturers, we are taking a dual approach to meeting Tier 3 regulations."

International engines in the lower output ranges can meet Tier 3 — at the sacrifice of some output — with the traditional mechanical fuel system. Beyond that point, International will use the same emissions formula it used for EPA 2004, namely the exhaust gas recirculation (EGR) engine with electronic fuel system. The company is looking at two paths to reach Tier 4.

"Some of our engines will have a common rail system and others will have our proprietary G2 fuel system, increased EGR, variable geometry turbocharging (VGT) and other technical changes," says Hyde. "We think there is going to be some resistance to selected catalytic reduction (SCR) systems, particularly in North America. SCR requires fleet managers to maintain one more fluid in their machines. That means extra cost and an extra preventive maintenance step. We are developing to that standard, but our primary path for North America is to use an EGR system with a diesel particulate filter. That said, if our customers tell us they want SCR, we are prepared to respond to what they want."

SCR is used to reduce NOx levels in the emission system. It works very efficiently in stationary applications, such as power plants, and has been around for years. The main advantage of SCR is improved fuel consumption.

With the convergence of on- and off-road emissions requirements, International says it is well positioned for the 2010 off-road market and beyond.

"There is going to be a transition and not all ranges of engines will be converted at the same time," says Hyde. "In construction and agriculture equipment, the life of the machines on the ground is very long. Therefore, International's goal is to allow its OEM customers to have the lowest cost solution we can develop and solutions that will help the end user make a decision to buy a new machine."

The question, of course, is how much of the on-road technology is transferable to off-road. Hyde says most technology in International's approach will work in both markets.

"The EGR, VGT, and particulate filter and associated controls are all transferable," he says. "On-road is a little tougher to meet because of complicated rules that have to do with transient test cycles and the like. We feel what we have developed for the on-road market will translate well for the off-road business."

By the time Tier 4 becomes fully effective in a few years, International will have a line of Tier 3- and Tier 4-compliant engines for the off-road market that ranges from 80 to 400 hp.

"The regulatory evolution is worldwide, and that regulation-driven environment demands modern engine designs encompass the off-road markets in North America, Western Europe and the Far East," says Hyde. "In the future, countries such as Brazil and Russia, will adopt some form of off-road regulations. It probably won't be the full EPA standards, but over the next several years, there will be a worldwide regulated environment."

Without exception, Tier 3 and Tier 4 technology will cost more than older technology, which has customers concerned. They also question the durability and reliability of the technology.

"The turbocharging system must be very robust," says Hyde. "By putting hundreds of thousands of these systems on the road, we've gained experience that can be transferred from on-road to off-road for Tier 4."

The multi-platform approach

John Deere Power Systems uses a multi-platform approach to meeting Tier 3 and Tier 4.

"Our PowerTech M is designed for 48 to 99 hp engines, our PowerTech E is for 60 to 200 hp, and PowerTech Plus is designed for 145 to 600 hp," says Doug Laudick, product manager. "This approach was necessary, because there is no one-size-fits-all solution to Tier 3 requirements."

Deere says its engines are tailored to the power requirements of OEMs.

"They know their power requirements, so we offer PowerTech Plus for those applications where high performance and fuel economy are a must," says Laudick. "PowerTech E and M are for applications where electronic controls without VGT and EGR satisfy customer needs."

Like other manufacturers, Deere plans to leverage its Tier 3 technology to meet future emissions regulations. The company has been exploring various technology options, including advanced in-cylinder and aftertreatment solutions.

According to Laudick, Deere plans to continue with the multiple-platform approach for Tier 4.

"An optimized combustion system plays a crucial role in reducing emissions," he says. "This includes the use of multiple injections, increased fuel injection pressure, and modified aftertreatment technologies. Possible alternative solutions include diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) systems, NOx absorbers, lean NOx catalysts, SCR, and homogeneous charge compression ignition (HCCI)."

Deere's PowerTech M engines are the simplest in the PowerTech family. The engines have two-valve heads, fixed geometry turbochargers, and mechanical fuel systems; come in 2.4- and 4.5-liter models; and are designed for less demanding applications.

"Their mechanical controls are simple to operate and maintain," says Laudick. "The PowerTech M 2.4-liter engine is Interim Tier 4/Stage III A compliant. They are either turbocharged or air-to-air aftercooled, and when compared to Tier 2/Stage 2 counterparts, they have improved or maintained peak torque, improved low-speed torque, and improved or maintained transient response time."

Although PowerTech E engines also have a two-valve head and fixed geometry turbochargers, they also have electronic control and more sophisticated fuel delivery. The smaller, 2.4- and 3.0-liter engines use electronic unit pumps. The larger 4.5- and 6.8-liter engines use a high-pressure common-rail fuel system.

"The PowerTech E 2.4-liter engines also meets Interim Tier 4/Stage III A standards and are turbocharged or air-to-air aftercooled," says Laudick. "They differ from their Tier 2/Stage ll counterparts in that they have a new power bulge feature and higher peak torque. They also have low-speed torque (4.5- and 6.8-liter), as well as improved or maintained transient response time and cold-weather starting."

Similar solutions

Volvo Construction Equipment has already met EPA Tier 3 regulations with its current line of engines and expects to meet Tier 4 with the addition of diesel particulate filters, technology that was used to meet on-road 2007 regulations.

"Although similar, there are some unique challenges moving to off-road, such as operating environment and duty cycles that impact the technology used," says John C. Bartz, product planning manager for wheel loaders and articulated haulers at Volvo.

In meeting Tier 3, Volvo designed the Volvo D16E diesel engine with V-ALT, which the company says creates an optimized match between engine, machine systems and operator controls.

The D16E heavy-duty engine is a 16.1-liter in-line four-stroke water-cooled six-cylinder diesel with turbo and intercooler. It has an integrated single-cylinder head, four valves per cylinder, overhead camshaft, electronically controlled unit injectors and Volvo's electronic engine management system.

"We are also actively exploring alternative fuels and hybrid technology to address tightening energy and air-quality requirements," says Bartz.

A tough row

All of these many changes have been a response to meeting tighter emissions regulations.

"It started for us in 1996 with EPA Tier 1 non-road emissions regulations," says Chris Maifield, engine applications program manager at John Deere Construction and Forestry. "The result was more-capable fuel systems and retarded injection timing, basically to reduce NOx and particulate matter (PM) levels. Electronic engine controls were only necessary in our largest engines. When we got to Tier 2, engine controls were added to many more applications. High-pressure common-rail fuel systems were introduced in some applications to give us more control over injection timing and rate. We also added turbocharging, charge-air cooling, four-valve cylinder heads, and higher capacity cooling systems to many applications."

Electronic controls, turbocharging and charge-air cooling have become almost standard on today's off-road equipment, although some smaller machines can use less-complex emissions control.

From 2006 to 2008, EPA regulations tightened up even more to drive down NOx levels for engines above 50 hp.

As the industry moved into this Tier 3 time frame, engines became more complex. More efficient electronic fuel system controls and air systems were necessary. For example, the Deere Tier 3 PowerTech Plus engine family uses VGT, EGR and a four-valve cylinder head. High-pressure common rail fuel systems have been added to many more applications for Tier 3.

"High-pressure common rail is a fuel system that is very common in the automobile industry, but until recently was rarely used in our industry," says Maifield. "Basically, it involves a pumping element that pumps fuel to a very high pressure in an accumulator that we call the 'rail.' This provides high pressure independent of engine speed — critical for PM reduction. The injector controls the start and end of injection, the rate of injection, and, in some cases, multiple injections."

Not every Tier requires reduction of each emissions element. For example, Tier 3 only requires NOx reduction, not PM reduction. Tier 4 will require reductions of both NOx and PM in phases. Tier 4 has an interim emissions reduction, which starts in 2011 for many Deere applications.

"We will see a huge PM reduction — at least 90 percent in most applications," says Maifield. "That will require aftertreatment because you can't get that kind of reduction with the engine alone."

Final Tier 4 emissions reductions will begin in 2014 for many applications. This will bring about another very significant emissions reduction, but this time on the NOx side (80 percent plus), which will also require additional aftertreatment in many applications.

"In addition, changes may have to be made to the cooling system, exhaust system, air intake system, and even the vehicle structure and sheet metal to accommodate the engine changes," says Maifield. "Tier 4 will bring the new challenge of aftertreatment."

The on-road market has already gone through some of these Tier 4 changes, and some of them can be transferred to the off-road industry.

"For instance, some aftertreatment concepts are transferable, but you have to make sure these components can live and perform well in the off-road environment under a totally different duty cycle," says Maifield.

Although EPA regulations include provisions that allow phased-in introductions, Tier 4 is going to be a significant development challenge for engine and vehicle manufacturers.

"Disregarding phase-in and flexibility provisions in the regulations, we essentially have two separate, two-year windows in which to update our vehicles above 75 hp, and these two windows are only three years apart," says Maifield. "Previous Tiers allowed three- to four-year windows to introduce the same range of machines and the emissions Tiers were four to six years apart in most power classes. Clearly, Tier 4 is going to be the greatest challenge we've faced in the emissions era."