The International Maritime Organisation’s MEPC 83  adopted a number of amendments to the NOx Technical Code 2008 in Resolution MEPC.397. They cover the re-certification process for marine diesel engines and include the use of multiple engine operational profiles, as well as clarifying existing engine test cycles

• For new individual or parent engines not previously certified, these amendments apply from 1 January 2028.
• For a new member engine to an engine family or group that was certified before 1 January 2028, it will need to be shown that the engine family or group meet the new requirements by 1 January 2030.
• For existing certified engines, these amendments apply if the engine is subject to substantial modification on or after 1 January 2028.
• In the case of identical replacement of an engine on or after 1 January 2028, the version of the NOx Technical Code at the time of the Engine International Air Pollution Prevention (EIAPP) Certificate is issued continues to apply unless the replaced engine is equipped with MEOP.
• Amendments also clarify the application of existing test cycle requirements, so do not have specified effective dates

.Controls on multiple engine operational profiles 

Alternative MEOP have been used in the NOx certification process for some time, for example, where a particular engine is certified for both Tier II and Tier III, or a non-propulsion engine is to be used in more than one (i.e. E3 and D2) duty application.

These amendments allow for more than one engine operational profile for a particular engine duty application, thereby covering several differing load scenarios: for example, a generator engine “at sea” or “cargo handling” conditions, leading to fuel optimisation.

However, in this instance, the highest NOx emission value at each mode point in the relevant test cycle across all the engine operational profiles is used in a composite approach to give the actual NOx certification value.

To cover these situations, a new Chapter 8 has been added to the NOx Technical Code.

Application of a rational emission control strategy  

An irrational emission control strategy is where the mode points values of relevant test cycles do not represent the intermodal values. Since the 2008 revision of MARPOL Annex VI, there has been an explicit prohibition on the use of irrational emission control strategies. However, there were no specific provisions in the NOx Technical Code to cover that issue.

These amendments require applicants for NOx certification to demonstrate that the engine’s control arrangements are such that, under normal operating conditions, there is a generally linear progression between the mode points over the entire operating load–speed range other than were declared auxiliary control devices function to ensure engine safety or operability.

Furthermore, limits are set on the extent to which the NOx emissions may increase away from the intermodal line. It is for the applicant to define, according to the intended usage of an engine, as to how far from that intermodal line the engine is to operate and those power – speed values.

Clarifications on use of emission test cycles 

These amendments are to the engine type descriptions, not to the actual test cycles or weighting factors as given in the NOx Technical Code. Hence the terms “main” and “auxiliary” have been replaced by “propulsion” or “non-propulsion”, as now defined, to provide a clear binary choice. This binary choice has been used to provide clear and unambiguous direction as to which test cycle applies in all instances. A flow chart illustrating this process has been added as Appendix IX to the Code.

What shipowners and operators should do now

Please review the new amendments and test requirements and act as necessary to ensure you remain compliant.