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Emission Control
Capturing the Particulates Behind Tier 4
Diesel Engine Regulations
By Keith Gribbins
 The 21st century will be defined as the green generation. In nearly every social and industrial sector, a growing global self-awareness can be found, focused on balancing sustainability with the way human society works and lives within the Earth’s ecosystem.
With a keen eye on a cleaner future, the construction manufacturing industry is also pushing forward with producing eco-friendly machines — especially cleaner burning diesel engines for the construction, landscape and agricultural industries. From compact skid steers to enormous haul trucks, government-issued Tier emission standards are mandating that machine engines (from OEMs like Cummins and Caterpillar) produce far less pollution — particulate matter (PM), oxides of nitrogen (NOx) and carbon monoxide (CO) and hydrocarbons (HC).
These emission regulations — called Tier standards — were created by the Environmental Protection Agency (EPA) more than a decade ago for both off- and on-highway diesel engines; each sector has similar standards and deadlines. For the construction industry, off-highway diesel engine Tiers are coming to a head as the final and most stringent set of regulations (called Tier 4) are already here for small diesel engines. The 25- to 74-hp power band hit Interim Tier 4 in 2008 and the Final Tier 4 standards for all horsepower ranges are fast approaching in 2013 through 2015.
Luckily, diesel designers are already prepared to achieve these new emission standards today — taking the opportunity to not only tweak the way that engines expel pollutants, but also how they can increase efficiency and power for the end-user. The next generation of clean diesel power plants is nearly here.
“The EPA has estimated that Tier 4 implementation across all power ranges will reduce the U.S. annual emissions inventory by hundreds of thousands of tons of PM and NOx and make a major contribution to improving the air quality of the nation,” explains Clint Schroer, off-highway communications manager for Cummins Inc. (one of the pioneer makers of diesel engines starting in 1919). “But we also remain focused on providing outstanding customer value while meeting these tough emission standards. We have invested significantly in a broad technology portfolio that extends from air intake to exhaust after-treatment systems. This technology base, which enables us to focus on achieving a low initial cost for the OEM and the lowest cost of operation for the equipment owner, will result in delivering improved fuel economy and higher power outputs along with a cleaner burning engine.”
Getting Standard
With industry comes pollution. From agricultural and textile innovations to the advent of the internal combustion engine, the industrial revolution of the last 300 years has increased our impact on the environment with contaminants such as noise, heat, energy and chemical substances.
The U.S. EPA was created in 1970 under President Richard Nixon, charged with protecting human health and safeguarding the natural environment. But it wasn’t until 1994 that the first federal standards for new off-highway or non-road diesel engines were adopted for engines more than 50 hp (37 kW) to be phased in from 1996 to 1999. Today, the EPA only regulates 0.3 percent of an engine’s total product of complete combustion. The rest (99.7 percent) of the engine exhaust is made up of natural elements in the air such as nitrogen, oxygen and water vapor.
“The primary focus of the Tier standards is the reduction of the oxides of nitrogen and particulate matter. For Tier 4, NOx and PM will be reduced by more than 90 percent when compared with current Tier 3 emissions regulations,” says Doug Laudick, product manager at John Deere Power Systems, a company with more than 90 years of off-highway engine experience.
Tier 1 standards for equipment under 50 hp and increasingly more stringent Tier 2 and Tier 3 standards for all equipment had a phase-in schedule from 2000 to 2008. The first three emission standards were generally met by using advanced engine designs such as electronic controls, high-pressure fuel systems, new turbocharger designs, air-to-air aftercooling and in-cylinder solutions to control pollutants, with no or only limited use of exhaust gas after-treatment systems. This meant little or no redesign of the outside envelope of the engine. But with Tier 4, after-treatment systems will be added to the engine to further control NOx and PM pollutant levels.
“Increasingly stringent emissions regulations drive the need for increasingly complex engines,” Laudick says. “While the emission regulations for each power category are different, it is likely that nearly all will require some sort of after-treatment to achieve Tier 4. Changes to the base engine and the addition of after-treatment may mean that OEMs will need additional time to adopt these next-generation engines. In anticipation, John Deere has communicated our technology choices earlier and well in advance of the regulation compliance date.”
There are two deadlines for Tier 4 off-highway diesel engines — Interim and Final. The initial Interim standards deal with PM compliance, while the Final standards deal with NOx and HC compliance. For engines 25 to 74 hp, Interim Tier 4 has already started, and because the regulations vary by horsepower, different engines will require different technologies. For example, the John Deere 2.4L PowerTech M and PowerTech E, both rated between 25 and 74 hp, are already Interim Tier 4 compliant, but they do not use the new after-treatment technologies (as discussed in the sidebar).
Most diesel engines emission reductions for 74 hp and below are using advanced in-cylinder combustion systems without the need for exhaust after-treatment for that power band. It’s the bigger diesel power plants (75 to 751 hp) that will see the latest new emission gizmos.
“The most stringent reductions apply across the 174- to 751-hp power categories with 90 percent PM and 45 percent NOx reductions,” says Schroer. “At Tier 4 Final, NOx emissions are reduced by a further 45 percent to bring a total NOx reduction of 90 percent compared to Tier 3.”
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