This Unified Interpretations document (UI MPC125 Rev.1 CLN) was published on 1 May 2023 and is to be uniformly implemented by IACS Societies no later than 1 January 2024.
Paragraph 220.127.116.11 of the NOx Technical Code (NTC) 2008 states that the engine group can be defined by certain characteristics and specifications, in addition to those mentioned in paragraph 4.3.8 for an engine family.
When engines are equipped with an SCR system to reduce NOx emissions, not all parameters mentioned in paragraph 4.3.8 apply to every engine in the group.
Specifically, the individual cylinder displacement should vary within a 15% range, and the number of cylinders and cylinder configuration may only apply in certain cases, such as when used with exhaust gas cleaning devices.
Engines with an SCR system may have different cylinder numbers and arrangements within the engine group. Instead, parameters such as the SCR space velocity (SV), catalyst block geometry, and catalyst material can be used to replace the cylinder-related parameters.
This interpretation allows for the variation in cylinder numbers and arrangements within an engine family, as long as the applicant can demonstrate that it results in equal or lower NOx emissions compared to the parent engine.