NOx Technical Code: Certification of Ammonia and Multi-Fuel Engines (MEPC 84)

NOx: modification and recertification, phased multiple-profile requirements, the non-carbon fuels project and the separate EEDI track.

Operational Explanation

The NOx Technical Code governs testing, surveys and EIAPP certification of engines subject to regulation 13. Distinguish NOx modifications and profiles, the non-carbon fuels project and EEDI verification.

Substantial modifications and profiles can also concern conventional diesel engines, not only ammonia and dual-fuel engines.

Workstream one: multiple operational profiles, already adopted

Resolution MEPC.397(83), adopted on 11 April 2025 at MEPC 83, amends the NOx Technical Code 2008 and is titled “Use of multiple engine operational profiles for a marine diesel engine, including clarifying engine test cycles”. Tacit acceptance on 1 September 2026, entry into force on 1 March 2027. Beware the two-date trap: 1 September 2026 is the acceptance date, not the entry into force.

MEPC.397(83) enters into force on 1 March 2027; paragraph 4 distinguishes application by EIAPP date. A new individual engine or previously uncertified parent of an Engine Family or Engine Group: no later than 1 January 2028. A new member with its parent certified before 2028: demonstrate family/group compliance before member certification, no later than 1 January 2030. No blanket application to engines already holding an EIAPP: substantial modification from 2028 follows amended definition 1.3.2 and the EIAPP date; an identical replacement installed from 2028 uses the Code version linked to the original EIAPP, unless the replaced engine already had multiple profiles, in which case chapter 8 applies.

MEPC.408(84) enters into force on 1 September 2027, adding entries 9f, 10g and 11e to the IAPP Supplement. Its paragraph 4 refers to the application dates in MEPC.397(83), paragraph 4: no blanket renewal of every Supplement on 1 September 2027.

Modification and recertification: section 7.2 already in force

MEPC.398(83) has been in force since 1 September 2026. It retains former chapter 7 as section 7.1 and adds 7.2 for installed engines substantially modified or certified to a different Tier. The route admits an individual engine or Engine Group, not Engine Family. Agree the test plan with the Administration before scheduling the test (7.2.10). The nominal 100% load point may not fall below 85% of rated power under the plan; otherwise defer the test (7.2.5). Even at an accepted reduced load, retain the test cycle’s 100% point weighting factor in the calculation. Replace the nameplate if rated power or speed changes (7.2.4).

The NOx non-carbon fuels project and the separate EEDI track

The NOx project for non-carbon fuels, such as ammonia and hydrogen, is distinct from adopted instruments. The official MEPC 84 summary confirms approval for subsequent adoption. As of 15 September 2026 it is not an amendment in force. The full final text of the new methods is not documented here, so no requirements or commencement date are anticipated. Methanol and ethanol contain carbon and fall outside this specific project.

The third track is EEDI: MEPC.411(84), paragraphs 4.2.3–4.2.4 and footnote 3, addresses primary fuel, specific fuel consumption and documents, including liquid-fuel dual-fuel engines. The Administration makes the final primary-fuel decision; manufacturer and verifier supply and examine evidence. This is not a new NOx rule.

Regulatory Reference

MEPC.408(84) text checked in the reproduction in ClassNK T1378, attachment 2. On 15 September 2026 the direct IMO PDF still contains an awaiting-certification notice. The adopted text confirms commencement, the application cross-reference and new IAPP Supplement entries.

Scope of Application

Engines subject to regulation 13, including conventional engines, in relevant modification, recertification or profile cases. The non-carbon fuels project and EEDI verification have separate scopes; they do not apply indiscriminately to every EIAPP.

Procedure / How to Complete It

1. Identify original engine, identical/non-identical replacement, addition, modification or new Tier. Check regulation 13.2 and the recognized organization's authorization.
2. MEPC.398(83) has been in force since 1 September 2026. It retains former chapter 7 as section 7.1 and adds 7.2 for installed engines substantially modified or certified to a different Tier. The route admits an individual engine or Engine Group, not Engine Family. Agree the test plan with the Administration before scheduling the test (7.2.10). The nominal 100% load point may not fall below 85% of rated power under the plan; otherwise defer the test (7.2.5). Even at an accepted reduced load, retain the test cycle’s 100% point weighting factor in the calculation. Replace the nameplate if rated power or speed changes (7.2.4).
3. MEPC.397(83) enters into force on 1 March 2027; paragraph 4 distinguishes application by EIAPP date. A new individual engine or previously uncertified parent of an Engine Family or Engine Group: no later than 1 January 2028. A new member with its parent certified before 2028: demonstrate family/group compliance before member certification, no later than 1 January 2030. No blanket application to engines already holding an EIAPP: substantial modification from 2028 follows amended definition 1.3.2 and the EIAPP date; an identical replacement installed from 2028 uses the Code version linked to the original EIAPP, unless the replaced engine already had multiple profiles, in which case chapter 8 applies.
4. Where chapter 8 applies, identify each profile and its authorized conditions in the Technical File. Use it only within those conditions; record its identifier and evidence that its conditions were met, plus the date and time each change is completed. Multiple profiles do not mean multiple fuels or free choice of calibration.
5. MEPC.408(84) enters into force on 1 September 2027, adding entries 9f, 10g and 11e to the IAPP Supplement. Its paragraph 4 refers to the application dates in MEPC.397(83), paragraph 4: no blanket renewal of every Supplement on 1 September 2027.
6. The third track is EEDI: MEPC.411(84), paragraphs 4.2.3–4.2.4 and footnote 3, addresses primary fuel, specific fuel consumption and documents, including liquid-fuel dual-fuel engines. The Administration makes the final primary-fuel decision; manufacturer and verifier supply and examine evidence. This is not a new NOx rule.
7. For ammonia/hydrogen agree the route with the Administration and authorized organizations; the future project is not a NOx exemption.

Practical Example

A conventional diesel being recertified to a new Tier follows section 7.2: agree the plan before scheduling the test. If the highest point cannot reach at least 85%, defer the test. For methanol/diesel dual-fuel also assess the EEDI primary fuel, without equating it to the NOx non-carbon fuels project.

What Typically Goes Wrong

Common Mistakes Mistake Library

• Engine Family is not Engine Group: section 7.2 does not admit the former.
• For an identical replacement, the removed engine's profiles matter.
• Commencement of instruments 397/408 does not mean application to every engine.
• Authorized profile, conditions and records must match.
• EEDI primary fuel does not mean NOx classification.

What the PSCO Checks

Operational Tips

• Maintain an engine–certification–Code version–date matrix.
• Separate adoption, entry into force and application.
• Agree tests and documentation before committing the operational window.

Preparation checklist

Educational checklist. This summary supports learning and preparation only. It does not replace the vessel’s approved procedures, manuals, statutory documents, company SMS, or applicable official requirements. Completing it demonstrates neither compliance nor readiness for an inspection: it shows that a list has been read, not that the ship is in order. Always verify the current documents carried on board.

• Identify original engine, identical/non-identical replacement, addition, modification or new Tier. Check regulation 13.2 and the recognized organization's authorization.
• MEPC.398(83) has been in force since 1 September 2026. It retains former chapter 7 as section 7.1 and adds 7.2 for installed engines substantially modified or certified to a different Tier. The route admits an individual engine or Engine Group, not Engine Family. Agree the test plan with the Administration before scheduling the test (7.2.10). The nominal 100% load point may not fall below 85% of rated power under the plan; otherwise defer the test (7.2.5). Even at an accepted reduced load, retain the test cycle’s 100% point weighting factor in the calculation. Replace the nameplate if rated power or speed changes (7.2.4).
• MEPC.397(83) enters into force on 1 March 2027; paragraph 4 distinguishes application by EIAPP date. A new individual engine or previously uncertified parent of an Engine Family or Engine Group: no later than 1 January 2028. A new member with its parent certified before 2028: demonstrate family/group compliance before member certification, no later than 1 January 2030. No blanket application to engines already holding an EIAPP: substantial modification from 2028 follows amended definition 1.3.2 and the EIAPP date; an identical replacement installed from 2028 uses the Code version linked to the original EIAPP, unless the replaced engine already had multiple profiles, in which case chapter 8 applies.
• Where chapter 8 applies, identify each profile and its authorized conditions in the Technical File. Use it only within those conditions; record its identifier and evidence that its conditions were met, plus the date and time each change is completed. Multiple profiles do not mean multiple fuels or free choice of calibration.
• MEPC.408(84) enters into force on 1 September 2027, adding entries 9f, 10g and 11e to the IAPP Supplement. Its paragraph 4 refers to the application dates in MEPC.397(83), paragraph 4: no blanket renewal of every Supplement on 1 September 2027.
• The third track is EEDI: MEPC.411(84), paragraphs 4.2.3–4.2.4 and footnote 3, addresses primary fuel, specific fuel consumption and documents, including liquid-fuel dual-fuel engines. The Administration makes the final primary-fuel decision; manufacturer and verifier supply and examine evidence. This is not a new NOx rule.
• For ammonia/hydrogen agree the route with the Administration and authorized organizations; the future project is not a NOx exemption.

FAQ

Related Topics

Last substantive revision of this page: 15 September 2026 · page fingerprint 177e0ec3f91d