View the Tier 4 video.
For 12 Long Years, ever since the EPA included off-highway diesel engines on its hit list of polluters, engine makers have been scrambling, reviewing, analyzing, redesigning and refining the science of compression ignition to come up with the world's first smokeless tractor.

And let's just say, they've come a long way, baby. Those black puffs of smoke that once characterized tractor exhaust have been reduced to a few particles on a pinhead, thanks to technologies that better control the burning of fuel.

But one more overhaul is required to get the regulated emissions down to zero. EPA's final regulations for non-road diesel engines, known as Tier 4, are at hand, and engineers say it's the toughest round yet.

“Achieving the first three tiers wasn't too much of a hassle with turbos and electronics,” says Barry O'Shea, product manager for AGCO high-horsepower tractors. “But it got tougher with Tier 4.”

This final tier — which went into effect this year for some engine sizes and continues up to 2015 — applies to all non-road diesel engines, including farm tractors. And it is at the squeaky-clean level. A tractor equipped with a Tier 4 engine driving in a smoggy city like Los Angeles will not only limit pollutants but will actually clean the air.

There's a big cost to Tier 4, though, because it requires treatment of the exhaust gas, which farm tractors today are not designed to do. That has tractor engineers agonizing and stewing over what tractor designs will work with the new engines. “It would be easier to reconfigure the whole tractor, to be honest with you,” O'Shea says.

Tier review
How did the desire for clean air become a dictating factor in a tractor's design?

The war on engine emissions started back in the 1970s when Congress signed the Clean Air Act. At first the focus was on highway vehicles. But by 1994, the EPA widened its scope to include off-highway vehicles used in agriculture and construction. It was discovered that these high-compression engines were a leading producer of particulate matter (PM) and oxides of nitrogen (NOx), the stuff that produces soot and clogs lungs.

As a result, the EPA developed four standards or “tiers” for gradually lowering these by-products of combustion. Each tier set limits on the amount of pollutants allowed in the exhaust. The tiers also required that sulfur be lowered in diesel fuels. Sulfur is added to fuel for lubrication; without it, engines need to be redesigned or face premature wear.

Engine manufacturers went to work and developed a wellspring of technologies to meet the standards, which began going into effect in 1996. Many were borrowed from on-highway trucks, which were already being regulated. Advanced electronic controls, high-pressure common-rail fuel systems, air-to-air intake coolers and advancements in turbochargers are among the technologies used to fine-tune combustion.

The first three tiers for non-road vehicles were completed this year. Now manufacturers are working to meet Tier 4, and, to quote a pack of Carletons, “this is the one they'll have to beat.”

Most stringent yet
The Tier 3 regulations reduced by 60% the emissions of the unregulated engines produced just 12 years ago. Tier 4 requires a 90% reduction in the levels of PM and NOx set by those Tier 3 standards.

“I always think of the white hankie test for carbon,” says Roger Gault, technical director of the Engine Manufacturers Association (EMA). “When you place a hankie over the exhaust, it will remain white if the engine is compliant. Tier 4 engines will be that clean.”

Large engines rated over 174 hp will have the toughest time meeting the requirements. Tractor engines this size will require not only advanced engine technologies but also after-treatment of the exhaust gas.

Because this poses new problems — like how to fit all the new components and plumbing under the narrow nose of a tractor — the EPA has staggered the deadlines for this size category. The interim deadline, which applies mostly to PM, comes up in 2011. The final deadline, which includes the tougher limits on NOx, is set for 2014. All farm vehicles with engine power ratings of 174 hp and above and manufactured beginning on those dates must comply. Smaller tractors (75 to 174 hp) must comply with the interim rules a year later, by 2012.

Interim solutions
Manufacturers are looking at two different methods to make tractor engines burn cleaner. One is to recirculate cooled exhaust gas through the engine to reduce NOx, and then pass the exhaust through a special filter to capture the particulates. This process is called cooled exhaust gas recirculation (EGR) with the use of a diesel oxidation catalyst (DOC) and particulate filter, which together make up the diesel particulate filter (DPF).

Some tractor makers, including John Deere, and engine manufacturers like Cummins have announced they will use this method to meet the interim regulations that go into effect in 2011. Deere says this method lets it use the same engine platform used for its Tier 3 tractors, which are considered very fuel efficient. But the company will use a higher percentage of cooled EGR than what it uses now to meet the new limits on NOx.

“The engines themselves will not change much,” says Doug Laudick, product manager at John Deere Power Systems. “The major difference will be the addition of a DOC/DPF unit to reduce particulates. These devices are similar to a muffler in shape and will likely replace the muffler. The visible differences will be a slightly larger exhaust component and new instrumentation that monitors after-treatment components.”

The second solution is called selective catalyst reduction (SCR), which uses a chemical after-treatment (in conjunction with another after-treatment) to control NOx. A liquid solution, typically urea, is injected in the exhaust gas to neutralize the noxious compounds.

SCR is widely used in Europe, where motorists pull up to a station to fill up with both diesel and urea. Although the technology is not used in the states yet, some truck manufacturers have announced they will use it to meet EPA's on-highway regulations for 2010, says EMA's Gault.

AGCO is considering using this technology in some of its equipment to reach the Tier 4 interim and final requirements. The company owns Sisu Diesel in Finland, which already builds and markets an engine with SCR technology for use in forestry equipment.

In the end, all manufacturers concede they may need both EGR and SCR to meet the final Tier 4 rules, given the technologies known today.

At what cost?
Both solutions will require added components and new design concepts, which will add to production costs. The EPA estimates that the cost for the advanced emission controls will be 2 to 3% of the total cost of the vehicle. So on a $230,000 vehicle, the new equipment and modifications to handle the larger engine would be about $6,900. However, maintenance costs may be lower due to the use of low-sulfur fuel.

To offset the hefty price tag, manufacturers may offer new equipment features to make the costs more palatable and create an incentive to buy. “[The manufacturers] know what they are up against,” Gault says. “If no one buys the equipment, they won't be in business.

“As far as packaging and equipment configuration, there have been a number of discussions on how all the hardware is going to fit,” Gault adds. He says the added complexity and hardware associated with Tier 4-compliant engines will be a challenge for equipment designers.

Meeting the challenge could lead to drastic design changes. O'Shea says some of the concepts being considered, and not necessarily by AGCO, include a forward-mounted cab that sits over the engine components or an engine placed in the rear, like on a combine.

Fuel economy also may suffer once engines reach the Tier 4 final phase. O'Shea says the technology used to achieve each previous tier typically brought a drop in fuel efficiency. This caused farmers to rush to buy tractors before the next new tier was implemented.

“Tractor engines are going through now what the automotive engines did in the 1970s,” adds Dave Morgan, assistant director, the Nebraska Tractor Test Lab. “Manufacturers are adding technology to the engine to control emissions, and typically that has a negative effect on fuel economy.” However, he says, some companies have bypassed the hit and introduced tractors that maintain, and in some cases increase, fuel efficiency. (Go to http://tractortestlab.unl.edu and click on Test Reports.)

Third solution
Because of the difficulty and costs involved in meeting the Tier 4 final standards, manufacturers are still looking for an alternative to using both SCR and cooled EGR. Instead, they hope for a new solution to pull them out of the bind.

“There could be a breakthrough in the morning,” O'Shea suggests. “Someone could come up with new technology to achieve Tier 4 final without using cooled EGR and SCR. That's why a lot of people are trying to come up with a new solution right now. Because without it, there will be huge costs.”

Gary Stanek, manager of engine applications and planning with New Holland, sums it up: “The objective is to provide customers with technologies that will meet the requirements of Tier 4 with minimized fuel consumption and optimized performance, without sacrificing reliability or durability. Anything less than that would be unacceptable.”

YOUR NEXT TRACTOR

Will engines drive your next tractor purchase?
If you’re planning to buy a new tractor, knowing how interim Tier 4 emissions regulations will affect engine design can help you decide which tractor to purchase. “Interim Tier 4 standards for engines 174 hp and greater take effect in 2011, and the availability of these products that year might affect what ag customers buy between now and then,” says Doug Laudick, product manager at John Deere Power Systems.

“Different engine manufacturers are going to make different technology choices that will affect such engine attributes as maintenance costs, fuel consumption and other performance characteristics,” he says.

“Ag customers who stay informed about these technologies and their effect on engine performance and maintenance will be better informed to make smart equipment acquisitions.”

Clint Schroer, off-highway communications manager with Cummins, agrees: “While all engine manufacturers will of course meet the new emissions standards, farmers will need to decide which engine manufacturer will offer the most productive and efficient solution.”

So what should buyers do in the meantime? “Existing ag equipment should not be affected by the interim Tier 4 or final Tier 4 emissions regulations,” Laudick says. “The EPA states that only new equipment must be emissions-compliant by the deadlines. However, local regulating authorities might enact different requirements, so ag customers should be aware of those rules to ensure full compliance.”

See the video
Watch a video about how Tier 4 engines work.