Heavy-Duty Supplemental Emissions Test (SET)

The Supplemental Emissions Test (SET) is a 13-mode steady-state engine dynamometer test, first introduced by the US EPA as part of the 1998 consent decrees with US heavy-duty engine manufacturers and then included in the 2007 emission standards for heavy-duty engines. In addition to FTP testing, consent decree engines subject to US EPA 2004 emission standards and model year 2007 and later engines must also demonstrate compliance when tested over the steady-state SET test. There are several versions of this test cycle:

• A discrete mode cycle (DMC), and
• Two ramped mode cycles (RMC).

The discrete mode cycle SET is equivalent to the European Stationary Cycle (ESC). It was the test used for engine testing under the 1998 consent decrees.

The ramped mode test is performed as a continuous cycle with ramped transitions between the individual modes. The 2007 ramped mode cycle SET was applicable to 2007-2009 heavy-duty engines, where manufacturers could use either the 2007 RMC-SET or the discrete mode DMC-SET. While the RMC test contains the same operating modes and weightings as the discrete mode test, their order is different and the transition between modes is defined.

For 2010 and later model year heavy-duty engines, manufacturers must use the 2010 RMC-SET [40 CFR Part 86.1362]. It is similar to the 2007 ramped mode SET with the exception that the order in which the modes are run is the same as for the discrete mode SET and ESC cycles. For the 2010 model year only, manufacturers could continue to use the 2007 ramped mode SET as long as it did not adversely affect the ability to demonstrate compliance with emission standards.

In the federal Phase 2 GHG standards, the RMC-SET was changed for GHG certification to reflect the continuing trend in engine down-speeding. In the final rule for 2027 and later heavy-duty engines, the applicability of this updated RMC-SET cycle was extended to criteria pollutants. The duration of the steady-state points at speed C was shortened and that of speed A was lengthened [40 CFR Part 1036.510].

Table 1 summarizes two ramped mode SET cycles. Speeds A, B and C are defined in the same way as for the ESC cycle.

In 2016, the EPA introduced an additional set of weighting factors for the SET test [2918]. The two sets of weighting factors are shown in Table 2. Weight (A) represents the original weights (identical to those of the ESC), while weight (B) represents the additional set of weights. The weighting factors (B)—developed to account for the downspeeding trend in heavy-duty engines—are used for testing of engine CO₂ emissions for the purpose of EPA Phase 2 GHG emission standards. Weighting factors (A) continue to be used for the purpose of pollutant (CO, HC, NOx, PM) emission testing.