Reinventing the engine

Aug 1, 2008 12:00 PM, By Jodie Wehrspann

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.