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Meaner, Cleaner, Leaner Engines

09/21/2010 @ 9:14am

Last February, Caterpillar president Stu Levenick put impending EPA Tier 4 pollution restrictions in perspective. He said they’d caused his company to take on “the most aggressive and expensive product development initiative in Caterpillar history.”

This comes from the firm that innovated the crawler tractor.

Modifications made to diesels since emissions restrictions took hold in 1996 rival any advance made to machinery since Rudolph Diesel’s introduction of a compression-ignition engine in 1892. “Deere & Company spends about $2.5 million a day on research and development,” says Steve Meinzen of that firm. “In recent years, a significant share of that enormous investment has gone to developing Tier 4 interim engines.”

The environmental payoff is stunning. By EPA estimates, modifications made to diesel to date have cut nitrous oxide (NOx) smog by 1 million tons per year. That is the equivalent of taking 35 million cars off the road.

This is just the beginning. Come January 2011, diesels 175 hp. and larger must meet new Tier 4 interim standards. When the Tier 4 final level is completed in 2015, all diesels, regardless of horsepower, must eject 90% less NOx and 90% less particulate matter (PM). This challenges engineers as never before. In their tightrope walk between the Tier 3 and Tier 4 platforms, designers have a delicate balancing act between NOx and PM. That is where the latest postcombustion treatments now installed on diesels come into play.

One path used to meet Tier 4 interim standards employs exhaust gas recirculation (EGR) to control NOx. This approach still turns out unacceptable levels (by Tier 4 interim levels) of PM. But that soot (unburned fuel) is captured and burned off in a catalytic filter that is part of the engine’s exhaust system.

An alternative technology meeting Tier 4 final rules is selective catalytic reduction (SCR). This approach injects diesel exhaust fluid (DEF) into the engine’s exhaust stream to neutralize excessive NOx. PM output is slashed by tuning the engine to thoroughly combust fuel.

Farmers will literally be able to breathe easier thanks to these advances – but at a cost. Only Caterpillar has estimated its price tag to meet Tier 4, calculating it will add 12% to engine costs over the next three years. Other manufacturers hint at price hikes for whole machines in the 3% to 5% range.

Yet there is a payoff for this extra cost. Cleaner burning engines are more efficient; they drink 15% to 20% less fuel than pre-Tier power plants built 12 years ago. New efficiency records are set at the Nebraska Tractor Test every year. The latest mark breached is 20 hp. hours per gallon. A Massey Ferguson 8680 exceeded that output last year. Indeed, today’s diesels churn out torque levels not possible a decade ago and leap to grow more power in a split second.  

The Brain Box

There isn’t a function on today’s diesels that isn’t regulated by the electronic control unit (ECU). Also called the electronic engine control (EEC) or electronic control module (ECM), these brain boxes constantly regulate all aspects of engine performance like injection pressures and timing, turbocharger operation, combustion chamber temperature, levels of nitrous oxide (NOx) or particulate matter (PM), and even engine timing. This breakthrough has made it possible for engines to burn less fuel and eject fewer pollutants while spurring them on to generate surprisingly tall and long torque curves.

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