Emission Test Cycles: ISO 8178 - DieselNet

Nonroad, Utility, and Marine Engines

Discrete Mode Steady-State Cycles

The ISO 8178-4 includes a collection of steady-state engine dynamometer test cycles (designated as type C1, C2, D1, D2, etc.) designed for different classes of engines and equipment. Each of these cycles represents a sequence of several steady-state modes with different weighting factors.

The ISO 8178 test cycle—or its 8-mode schedule C1 in particular—is also referred to as the Non-Road Steady Cycle or Non-Road Steady-state Cycle (NRSC).

Table 1 summarizes many of the steady-state cycles. Each of these cycles consists of a selection of the 11 modes shown. These modes have been derived from the 13 mode UN-ECE R49 cycle. ISO 8178-4:1996 included a 13-mode cycle, the A cycle, that reflected UN-ECE R49. Until ISO 8178-4:2007, the “universal test cycle” or “B cycle” referred to a cycle consisting of all 11 modes shown in Table 1 but with no weighting factors. With emissions data collected over this universal test cycle, emissions values for the other cycles in Table 1 could be calculated using the appropriate weighting factors for the respective application. This avoided duplication of test runs if the same engine was used in different applications.

It should be noted that the mode numbers for each cycle in Table 1 start at 1 and increment by 1 to the maximum number of modes in that test cycle. They do not necessarily correspond to the B cycle mode numbers.

Table 1Steady-state discreet mode ISO 8178 test cycles—weighting factors

Mode Number(B cycle)	1	2	3	4	5	6	7	8	9	10	11
Torque, %	100	75	50	25	10	100	75	50	25	10	0
Speed	Rated speed					Intermediate speed					Lowidle
Nonroad vehicles
Type C1	0.15	0.15	0.15	-	0.10	0.10	0.10	0.10	-	-	0.15
Type C2	-	-	-	0.06	-	0.02	0.05	0.32	0.30	0.10	0.15
Constant speed
Type D1	0.30	0.50	0.20	-	-	-	-	-	-	-	-
Type D2	0.05	0.25	0.30	0.30	0.10	-	-	-	-	-	-
Utility, lawn and garden
Type G1	-	-	-	-	-	0.09	0.20	0.29	0.30	0.07	0.05
Type G2	0.09	0.20	0.29	0.30	0.07	-	-	-	-	-	0.05
Type G3	0.90	-	-	-	-	-	-	-	-	-	0.10
Marine application
Type E1	0.08	0.11	-	-	-	-	0.19	0.32	-	-	0.30
Type E2	0.20	0.50	0.15	0.15	-	-	-	-	-	-	-
Notes: Engine torque is expressed in percent of the maximum available torque at a given engine speed Rated speed is the speed at which the manufacturer specifies the rated engine power Intermediate speed is the maximum torque speed if it occurs between 60% and 75% of the rated speed or 60% of the rated speed if it is lower or 75% of the rated speed if it is higher

The engine operating modes and their weighting factors for ISO 8178 test cycles for marine propeller law applications are listed in Table 2.

Table 2ISO 8178 marine application propeller law test cycles

Type E3, Mode #	1	2	3	4
Power, %	100	75	50	25
Speed, %	100	91	80	63
Weighting factor	0.2	0.5	0.15	0.15
Type E4, Mode #	1	2	3	4	5
Speed, %	100	80	60	40	Idle
Torque, %	100	71.6	46.5	25.3	0
Weighting factor	0.06	0.14	0.15	0.25	0.4
Type E5, Mode #	1	2	3	4	5
Power, %	100	75	50	25	0
Speed, %	100	91	80	63	Idle
Weighting factor	0.08	0.13	0.17	0.32	0.3

Ramped Mode Cycles

In addition to discrete mode cycles, the ISO 8178-4:2017 standard introduced ramped mode cycles (RMC). RMCs provide a method for performing a steady-state test in a pseudo-transient manner and consist of a series of steady state modes with a linear transition between them. The relative total time at each mode and its preceding transition match the weighting of the discrete-mode cycle. The mode change time is part of the new mode (including the first mode). In some cases, modes are not run in the same order as the discrete-mode NRSC or are split to prevent extreme changes in temperature. Two examples for variable speed and constant speed engines are shown in Table 3 and Table 4.

The percent torque in the tables is relative to the maximum torque at the commanded engine speed. The advance from one mode to the next should occur over a 20 second transition phase, with a linear progression from both the torque and speed settings of the current mode to the torque and speed setting of the next mode. The intermediate engine speed is the same as that for the discreet-mode cycle.

Table 3RMC-C1 9-mode test cycle for variable-speed engines

RMC Mode	Time in Mode, s	Engine Speed	Torque, %
1a Steady state	126	Idle	0
1b Transition	20	Linear transition	Linear transition
2a Steady state	159	Intermediate	100
2b Transition	20	Intermediate	Linear transition
3a Steady state	160	Intermediate	50
3b Transition	20	Intermediate	Linear transition
4a Steady state	162	Intermediate	75
4b Transition	20	Linear transition	Linear transition
5a Steady state	246	100%	100
5b Transition	20	100%	Linear transition
6a Steady state	164	100%	10
6b Transition	20	100%	Linear transition
7a Steady state	248	100%	75
7b Transition	20	100%	Linear transition
8a Steady state	247	100%	50
8b Transition	20	Linear transition	Linear transition
9 Steady state	128	Idle	0

Table 4RMC-D2 5-mode test cycle for constant-speed engines

RMC Mode	Time in Mode, s	Engine Speed	Torque, %
1a Steady-state	53	Engine governed	100
1b Transition	20	Engine governed	Linear transition
2a Steady-state	101	Engine governed	10
2b Transition	20	Engine governed	Linear transition
3a Steady-state	277	Engine governed	75
3b Transition	20	Engine governed	Linear transition
4a Steady-state	339	Engine governed	25
4b Transition	20	Engine governed	Linear transition
5a Steady-state	350	Engine governed	50

Ramped mode cycles apply to C1, C2, D2, E2, E3, E5, F, G1, G2, H and I test cycles.