The EMD four-stroke engine was resurrected in 2015 to meet EPA Tier 4 emissions regulations.
Development of the H-engine was announced in 1994 as a railway locomotive specific engine - the design was influenced by the transition to AC traction motors, which had increased adhesion and tractive effort characteristics, allowing an increase in usable power to be usefully converted traction - thus the new design was to have 6,000 horsepower (4,500 kW) available for traction - a 6000 hp locomotive design would allow one to replace two of the very common 3000 hp SD40-2 locomotives.
EMD had investigated the potential of four-stroke designs in 1984, building two prototype 4,500 horsepower (3,400 kW) 16 cylinder 854H engines (with 854 cu.in.
Eight engines were produced and tested at the Transportation Technology Center under the management of the Association of American Railroads in Pueblo, Colorado.
To meet EPA Tier 4 emission standards for nitrogen oxides (NOx), manufacturers rely on one of two methods: exhaust gas recirculation (EGR), where exhaust gases are cooled and recirculated back through the combustion cycle, or selective catalytic reduction (SCR) using urea-based diesel exhaust fluid, which converts NOx in the catalytic converter to elemental nitrogen and water.
Although EGR requires a diesel particulate filter, it is the preferred solution for Class I operators, as SCR adds another consumable with handling and storage issues by maintenance personnel.
Although EMD had experimented with modifying the 710 to meet Tier 4, the prototype proved to be too heavy and inefficient to be practical.
[12] Other new features are an EGR system to reduce exhaust emissions and double-walled fuel injection to increase safety.