ISO 8178-4

Introduction

The ISO 8178-4 standard—titled “Reciprocating internal combustion engines — Exhaust emission measurement, Part 4: Steady-state and transient test cycles for different engine applications”—is an international standard for exhaust emission measurement from nonroad (spelled non-road in the standard) engines. It is used for emission certification and/or type approval testing in many countries, including the United States, China, India, Japan, and the European Union. Depending on the legislation, the cycle can be defined by reference to the ISO 8178 standard, or else by specifying a test cycle equivalent to ISO 8178 in the national legislation (as it is the case with the US EPA regulations).

The first edition of the standard was published in 1996 and updated in 2007, 2017, and 2020. The original standard (ISO 8178-4:1996) defined several steady-state (discrete mode) engine dynamometer test cycles for different applications of nonroad engines.

The scope of the standard was significantly extended in 2017 (ISO 8178-4:2017). Some key changes include the addition of ramped mode versions for many of the ISO 8178 steady-state cycles, as well as certain transient test cycles for nonroad engines.

The transient test cycles that are now covered by ISO 8178 include the NRTC cycle for diesel engines and the LSI-NRTC cycle for large spark ignited engines.

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.

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

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.

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

Locomotive Test Cycle (Type F)

ISO 8178 defines Type F cycle for locomotive testing, Table 5. This cycle has been modified on several occasions.

In the first edition of the standard (ISO 8178-4:1996), the Type F weighting factors were 0.25 at rated speed & 100% torque, 0.15 at intermediate speed & 50% torque, and 0.60 for idle. In the second edition (ISO 8178-4:2007), the rated speed point was reduced from 0.25 to 0.15 and the intermediate speed point was increased from 0.15 to 0.25, based on measurements on in-service locomotives in Europe. Additionally, the idling point was changed from “no load” to 5% of torque to account for the engine driving the air brakes compressor and other electrical loads.

In ISO 8178-4:2017, the load points have been defined based on percent power, rather than percent torque, in alignment with EU emission standards for nonroad mobile machinery (the test cycle F for Stage III A/B locomotives was based on %torque, while the cycle for Stage V locomotives is based on %power).

Snowmobiles and TRU Engines

Other test cycles found in ISO 8178 include Type H for snowmobiles and Type I for transport refrigeration units (TRU), Table 6.