Amendments to the NOx Technical Code for Marine Diesel Engines
In December 2025, Lloyd’s Register Group Limited announced important amendments to the NOx Technical Code for marine diesel engines, as adopted by the International Maritime Organisation (IMO) in April 2025 during MEPC 83.
These amendments affect:
- Shipowners;
- Ship operators;
- Ship managers;
- Ship masters;
- Shipbuilders;
- Ship manufacturers.
Key Changes
The amendments include changes to the re-certification process for marine diesel engines, the introduction of multiple engine operational profiles (MEOP), and clarification of existing engine test cycles. The changes are effective as follows:
- New Engines: For individual or parent engines not previously certified, the amendments take effect from January 1, 2028.
- Family Engines: For member engines in a certified engine family or group before January 1, 2028, compliance with new requirements must be demonstrated by January 1, 2030.
- Existing Engines: For currently certified engines undergoing substantial modification from January 1, 2028.
- Identical Replacements: For identical engine replacements after January 1, 2028, the NOx Technical Code version during the issuance of the Engine International Air Pollution Prevention (EIAPP) Certificate applies unless equipped with MEOP.
- Clarifications regarding existing test cycle requirements have no specified effective dates.
Controls on Multiple Engine Operational Profiles. The amendments allow the use of more than one operational profile for specific engine applications, covering various load scenarios (e. g., generator engines operating “at sea” or during “cargo handling“). This is aimed at optimizing fuel usage.
Source: LLoyd’s Register
Rational Emission Control Strategy. The document stresses the necessity for an effective emission control strategy, ensuring that values of relevant test cycles reflect a linear progression between mode points under normal operating conditions. Limits are established on how much NOx emissions can deviate from the intermodal line.
Clarifications on Emission Test Cycles. Changes include updates to engine type descriptions, replacing terms like “main” and “auxiliary” with “propulsion” and “non-propulsion” to create a clearer classification. A flow chart illustrating these updates has been added as Appendix IX.
Action for Shipowners and Operators. Shipowners and operators should review the new amendments and test requirements to ensure compliance with the updated NOx Technical Code.
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