In July 2008, Union Pacific Railroad (UP) and Electro-Motive Diesel, Inc. (EMD) began discussions to jointly investigate the potential for exhaust gas recirculation (EGR) on a small group of re-powered UP locomotives, to assess the potential for EGR as a technology to meet the oxides of nitrogen (NOx) requirement in US Environmental Protection Agency (EPA) Tier 4 locomotive emissions regulations on newly-manufactured future diesel locomotives effective January 1, 2015 [1].

After several years of research, engineering and experimental testing, EMD began delivering to UP in late-2011 nine SD59MX experimental locomotives equipped with prototype EGR technology as a first step to achieving Tier 4 NOx reductions, plus a tenth SD59MX unit equipped with both the EGR technology and an experimental whole-engine aftertreatment package to migrate toward Tier 4 particulate matter (PM) levels on future new Tier 4 locomotives. Compared to today’s Tier 2 emission limits, the EGR equipped SD59MX produces 42 percent less NOx, a significant step toward the development of new Tier 4 locomotives.

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