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Emission Test Cycles

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 is applicable to 2007-2009 heavy-duty engines. While it contains the same operating modes and weightings as the discrete mode test, their order is different and the transition between modes is defined. For 2007-2009 model year engines, manufacturers could use either the 2007 ramped mode SET or the discrete mode SET.

For 2010 and later model year heavy-duty engines, manufacturers must use the 2010 ramped mode SET. 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.

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

Table 1
Ramped mode cycle SET
RMC Mode2007-20092010 & later
Time, sSpeedTorque, %Time, sSpeedTorque, %
1aSteady-state170Warm idle0170Warm idle0
1bTransition20Linear transitionLinear transition20Linear transitionLinear transition
2bTransition20ALinear transition20Linear transitionLinear transition
3bTransition20ALinear transition20BLinear transition
4bTransition20ALinear transition20Linear transitionLinear transition
5bTransition20Linear transitionLinear transition20ALinear transition
6bTransition20BLinear transition20ALinear transition
7bTransition20BLinear transition20Linear transitionLinear transition
8bTransition20BLinear transition20BLinear transition
9bTransition20Linear transitionLinear transition20Linear transitionLinear transition
10bTransition20CLinear transition20CLinear transition
11bTransition20CLinear transition20CLinear transition
12bTransition20CLinear transition20CLinear transition
13bTransition20Linear transitionLinear transition20Linear transitionLinear transition
14Steady-state168Warm idle0168Warm idle0

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.

Table 2
SET weighting factors
ModeEngine SpeedLoad, %Weight A, %Weight B, %
1Low idle01512
Total A speed2345
Total B speed3938
Total C speed235