Comparison of Exhaust Emissions from Application of the Ramped Modal Cycle and Steady-State Nonroad Test

With input from industry, the United States Environmental Protection Agency (US EPA) has developed ramped modal versions of its steady-state certification duty cycles for land-based nonroad diesel engines. The Ramped Modal Cycle (RMC) calls for gathering gaseous and particulate emissions continuously over the cycle, while the steady-state test specifies that samples be taken for only a portion of the time at each mode. The RMC test was developed in part to capture discrete regeneration events associated with advanced catalyst systems like NO_x adsorbers that are anticipated to meet future nonroad emission standards.¹ To compare the emission levels between these two tests, a 5.9 liter medium-heavy-duty on-highway diesel engine rated for 260 hp @ 2500 rpm, was run at EPA's National Vehicle and Fuel Emissions Laboratory (NVFEL), derated to 180 hp @ 2500 rpm, to simulate the configuration of a typical nonroad engine. This engine was equipped with both PM and NO_x control devices that are likely to be applied for meeting future long-term emission standards. The goal of this testing was to determine if the RMC emissions with a 2014-like engine and catalytic system correlated to the established 8-mode steady-state test.