- IMO Adopts NOx Code Amendments at MEPC 83.
- New NOx Certification Rules to Apply From 2028.
- MEPC 83 Clarifies NOx Engine Certification Framework.
The Marine Environment Protection Committee (MEPC 83) of the International Maritime Organisation met in April 2025 and made some important updates to the NOx Technical Code 2008 through Resolution MEPC.397(83). These amendments mainly focus on the re-certification process for marine diesel engines, provide clearer guidelines for multiple engine operational profiles (MEOP), and clarify how existing emission test cycles should be applied, reports LR.
Entry-Into-Force and Application Dates
Here’s how the amendments will roll out:
- Starting from January 1, 2028: This applies to new individual or parent engines that haven’t been certified before.
- By January 1, 2030: This is for new member engines that are added to an engine family or group that was certified before January 1, 2028, as long as the family or group meets the new standards.
- From January 1, 2028: This applies to existing certified engines that undergo significant modifications.
- For identical replacements after January 1, 2028: The version of the NOx Technical Code that was in effect at the time of EIAPP certification will still apply, unless the replacement engine uses MEOP.
Clarifications regarding existing test cycle requirements don’t have specific effective dates.
New Controls on Multiple Engine Operational Profiles
The amendments officially acknowledge the use of multiple engine operational profiles in the NOx certification process. This is particularly relevant for engines that operate under various load conditions, like generator engines used for “at sea” and “cargo handling” scenarios. While multiple profiles are permitted, the certification method takes the highest NOx emission value from each mode point across all operational profiles to calculate a composite NOx value. To accommodate this, a new Chapter 8 has been introduced to the NOx Technical Code.
Strengthening Emission Control Strategy Requirements
The new amendments focus on how emission control strategies are handled. Now, applicants need to show that their engines maintain a generally linear relationship between test cycle mode points throughout their load-speed range, unless auxiliary control devices are necessary for safety or operational reasons. There are also new limits on how much deviation from this intermodal line is acceptable, and it’s up to the applicants to define the operating ranges based on how the engine is intended to be used.
Clarified Application of Emission Test Cycles
The amendments aim to clear up any confusion. Instead of changing the test cycles, they revise the descriptions of engine types. The terms “main” and “auxiliary” engines have been swapped out for “propulsion” and “non-propulsion,” creating a straightforward classification system. This adjustment offers clear guidance on which test cycle should be applied in every situation. Plus, there’s a handy decision flow chart included as Appendix IX in the NOx Technical Code to help navigate these changes.
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Source: LR
