A Leaner, Cleaner Machine: Engineers Cut 4,000 Pounds of Exhaust-Scrubbing Gear from New Locomotive

October 1, 2013

Over the last decade the U.S. government has enacted a number of rules designed to reduce smog and air pollution in cities and towns. Many of the regulations focus on two culprits: nitrogen oxide (NOx) and particulate matter (PM) like tiny chemical, metal, soil and dust particles.

The most stringent of these rules, called Tier 4 emission standards, will kick in for locomotives on January 1, 2015. They will slash particulates by 70 percent and NOx by 76 percent from the current Tier 3 emission levels for every new engine. “The demands on the industry have grown exponentially,” says Len Baran, heavy-haul platform leader at the locomotive maker GE Transportation. GE has built the world’s first locomotive that solves the problem in an ingenious way.


The Tier 4 standards, which were announced in 2004, put industry engineers in a tight spot. One of the easiest ways out involved adding a large filter and a 4,000-pound catalytic converter, as heavy as a passenger car, on top of the engine. The converter uses many gallons of urea, a chemical compound first discovered in urine, to break up NOx in diesel exhaust into nitrogen and water.

But the solution has a big downside. The converter hampers access to the engine and adds extra maintenance. Railroads would also have to invest an estimated $1.5 billion in urea distribution infrastructure. “We took a different track,” Baran says. “We decided to solve the problem inside the engine and cut out the need for urea, converters and PM filters altogether.”

Since 2005, GE has invested $600 million in the development of a Tier 4 locomotive that eliminates the need for any NOx and PM exhaust “after-treatment,” the catch-all industry term for filters, converters and similar technology. Engineers from GE Transportation and GE Global Research spent several years in the lab, building and experimenting with a new engine design. The team built a single cylinder engine for testing, gathered detailed measurements of the exhaust and plugged the information into custom software models designed to simulate a full-scale engine. “We realized early on that we had to keep the temperature inside the cylinder at an optimal level to reduce NOx and PM,” Baran says. “So we devised an ingenious system that pipes in some of the hot exhaust gas. That’s the simple explanation.”

Today, GE’s new Tier 4 Evolution Series Advance Power 4, which is ecomagination certified, locomotive is the only engine that meets the EPA’s Tier 4 requirements without any after-treatment technology. GE has already built and started testing two of the locomotives on a track in Pennsylvania. Another set of Tier 4 diesel engines is going through endurance tests inside a GE locomotive plant.

“We don’t need a filter and we don’t need a converter,” Baran says. “It’s a game-changer.”