MARPOL Annex VI • Regulation 13

NOx Compliance Infographic

Interactive TST study recap for MCA Engineering Oral preparation: NOx tiers, T1/T2/T3 vessel definitions, EIAPP / Technical File control, ECA triggers and practical reduction methods.

Regulation

Annex VI Reg. 13

Scope

>130 kW engines

Certification

EIAPP + Tech File

Focus

Tiers I / II / III

What this infographic is for

This module turns NOx compliance into an oral-exam answer structure. The correct answer is not only “SCR or EGR”; it is the full compliance chain from MARPOL Annex VI Regulation 13, through EIAPP certification, to the approved NOx Technical File, physical engine parts and the evidence available during survey.

Define T1, T2 and T3 vessels using correct Tier terminology.
Explain when Tier III applies and when Tier II still applies outside a NOx ECA.
Link NOx-critical components, settings and record keeping to certification.
Compare SCR, EGR, Miller timing, HAM, DWI and water-in-fuel systems.

Exam warning

Tier level is based on ship construction date and, for Tier III, operation in a NOx ECA. Do not state that every modern ship is “Tier III everywhere”. Outside a NOx ECA, Tier II controls apply unless another specific requirement applies.

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1. ScopeReg. 13 basics 2. T1 / T2 / T3Definitions + limits 3. PaperworkEIAPP + Technical File 4. VerificationParameter checks 5. NOx ECAsTier III triggers 6. Reduction methodsSCR / EGR / water 7. Oral trapsChief Engineer answer

Section 1

Regulation 13 scope: what NOx compliance actually controls

Application headline

MARPOL Annex VI Regulation 13 controls nitrogen oxide emissions from installed marine diesel engines of more than 130 kW, other than engines used solely for emergency purposes. It applies irrespective of the ship’s tonnage.

>130 kWInstalled enginesEmergency engines excluded

Why NOx forms

Thermal NOx forms when combustion has high peak temperature, available oxygen and sufficient residence time. The “diesel dilemma” is that the conditions that improve combustion efficiency can also increase NOx formation.

High temperatureOxygenResidence time

Exam wording

“Regulation 13 is the MARPOL Annex VI control for NOx from marine diesel engines. I would first confirm the engine is within scope, then prove compliance through the EIAPP Certificate, the approved Technical File, NOx-critical parts and settings, and the survey verification method.”

Section 2

T1 / T2 / T3 vessel definitions and NOx Tier limits

Important wording: “T1 / T2 / T3 vessel” is useful training shorthand, but the official requirement is based on engine NOx Tier, ship construction date, engine rated speed and, for Tier III, operation in a NOx ECA.

T1 / Tier I

Tier I vessel

Training shorthand for a ship constructed on or after 1 January 2000 and before 1 January 2011, with applicable installed marine diesel engines certified to Tier I limits.

T2 / Tier II

Tier II vessel

Training shorthand for a ship constructed on or after 1 January 2011. Tier II is the global NOx level for applicable engines, including when a Tier III-capable ship operates outside a NOx ECA.

T3 / Tier III

Tier III vessel

Training shorthand for a ship / engine required to meet Tier III when operating in a designated NOx ECA, subject to the relevant construction-date trigger for that ECA.

Tier	Construction trigger	n < 130 rpm	130 ≤ n < 2000 rpm	n ≥ 2000 rpm	Exam trap
Tier I	On / after 1 Jan 2000	17.0 g/kWh	45 × n^-0.20	9.8 g/kWh	Older certified engines may still be valid if maintained within the approved Technical File.
Tier II	On / after 1 Jan 2011	14.4 g/kWh	44 × n^-0.23	7.7 g/kWh	Tier II applies globally; it is also the default outside NOx ECAs for Tier III ships.
Tier III	ECA construction-date trigger	3.4 g/kWh	9 × n^-0.20	2.0 g/kWh	Tier III applies only to specified ships while operating in a NOx ECA.

How to answer T1 / T2 / T3

“T1, T2 and T3 are shorthand for Tier I, Tier II and Tier III NOx compliance. Tier I starts from 1 January 2000, Tier II from 1 January 2011, and Tier III is the strict ECA standard triggered by construction date and operation inside a NOx Emission Control Area.”

Section 3

Certification chain: EIAPP, IAPP and the Technical File

Reg. 13 Legal requirement for NOx control

EIAPP Engine-specific certification

Tech File Approved parts, settings and limits

Record Book Changes and parameter evidence

IAPP Ship-level Annex VI certification

EIAPP Certificate

Proves the specific engine, parent engine, group or family has been certified to the applicable NOx Tier and duty cycle under the NOx Technical Code.

NOx Technical File

The approved identity of the engine. It lists NOx-critical components, settings, operating values and onboard verification method.

Record Book of Engine Parameters

Used to record changes, replacement components and parameter evidence where the Parameter Check Method is used.

Chief Engineer-level point

NOx compliance can be broken by an unapproved “like-for-like looking” injector, fuel pump, cam, timing change, charge-air modification or SCR / EGR bypass if it is outside the approved Technical File and not class/flag approved.

Section 4

Onboard NOx verification methods

Engine Parameter Check Method

Most common in service. Surveyor verifies NOx-critical components, settings and operating values against the approved Technical File.

Simplified Measurement Method

Uses onboard emission measurements under defined conditions as an alternative verification route where approved.

Direct Measurement and Monitoring

Continuous or direct monitoring route where the installation and procedure are approved in line with the NOx Technical Code.

Survey check	What examiner may ask	Engineer answer
Fuel injector / pump IDs	“How do you prove the parts are compliant?”	Match serials / ID numbers to the approved Technical File and record book evidence.
Injection timing / cam setting	“Why does timing matter?”	It changes combustion temperature and NOx formation; unapproved setting change can invalidate compliance.
SCR / EGR status	“Can you bypass the system?”	Only as permitted by approved arrangements and records; illegal bypass or disabled alarms is a PSC red flag.
Missing Technical File	“What if the file is missing?”	The compliance chain is incomplete; contact owner/maker/class/flag and do not rely on memory or a generic manual.

Section 5

Tier III and NOx Emission Control Areas

Tier III operating rule

Tier III controls apply only to specified ships while operating in a designated NOx ECA. Outside those areas, Tier II controls apply. This is one of the most common oral exam traps.

Inside NOx ECA = Tier IIIOutside = Tier II

Current ECA expansion

Canadian Arctic and Norwegian Sea ECAs entered into force on 1 March 2026 under MEPC.392(82). The Canadian Arctic NOx trigger uses 1 January 2025; the Norwegian Sea uses 1 March 2026 with contract / keel / delivery date wording.

NOx ECA	Tier III construction trigger	Operational point
North American ECA	Ship constructed on / after 1 Jan 2016	Tier III required while operating in the ECA.
US Caribbean Sea ECA	Ship constructed on / after 1 Jan 2016	Applies around Puerto Rico and US Virgin Islands.
Baltic Sea ECA	Ship constructed on / after 1 Jan 2021	Tier III applies inside the NOx ECA.
North Sea ECA	Ship constructed on / after 1 Jan 2021	Tier III applies inside the NOx ECA.
Canadian Arctic ECA	Ship constructed on / after 1 Jan 2025	Added by MEPC.392(82); entered into force 1 Mar 2026.
Norwegian Sea ECA	Ship constructed on / after 1 Mar 2026	Contract on/after 1 Mar 2026, keel on/after 1 Sep 2026, or delivery on/after 1 Mar 2030.

Scenario wording

“A Tier III-capable ship may operate to Tier II outside a NOx ECA. Entering the ECA makes the Tier III arrangements operationally relevant, so I must verify the SCR/EGR or approved equivalent is available, alarms and records are in order, and any exemption/bypass is approved and logged.”

Section 6

NOx reduction methods: compare the engineering options

SCR

After-treatment. Urea decomposes to ammonia, which reacts over catalyst to convert NOx into nitrogen and water. Needs correct exhaust temperature window and dosing.

EGR

In-cylinder formation reduction. Cooled, cleaned exhaust is returned to intake, reducing oxygen concentration and peak combustion temperature.

Miller timing

Early inlet valve closing reduces effective compression temperature. Often paired with high-efficiency turbocharging.

DWI / water-in-fuel

Water absorbs heat during combustion, reducing peak flame temperature. Requires water quality, control and maintenance discipline.

HAM

Humid Air Motor saturates charge air with water vapour, thermally diluting combustion and reducing NOx formation.

Low-NOx tuning

Injection timing, pressure, charge air and combustion optimisation can reduce NOx but may affect fuel consumption, smoke and thermal loading.

Method	Reduces NOx by	Main operational risk
SCR	Chemically reducing NOx after combustion	Low exhaust temperature, urea deposits, catalyst fouling, ammonia slip.
EGR	Reducing oxygen and peak combustion temperature	Soot, acidic washwater, corrosion, blower/charge-air fouling.
Water methods	Absorbing latent heat and lowering flame temperature	Water quality, injector wear, corrosion, control failure.
Miller / tuning	Lowering effective compression/combustion temperature	May affect starting, load response, thermal efficiency or smoke.

Section 7

Oral exam traps and Chief Engineer answer structure

Common traps

Calling Regulation 13 a SOx/fuel-sulphur rule.
Saying Tier III applies globally to all new ships.
Ignoring engine rated speed when quoting limits.
Replacing NOx-critical parts without checking the Technical File.
Confusing the ship-level IAPP certificate with the engine-specific EIAPP certificate.
Assuming SCR/EGR can be bypassed without approval, records and alarm management.

Strong oral answer flow

Identify Regulation 13 and engine scope.
State the applicable Tier from construction date and ECA operation.
Reference EIAPP, NOx Technical File and IAPP.
Explain approved NOx-critical components/settings.
Describe verification method and record evidence.
Explain reduction technology and operational checks.

Model answer

“For NOx compliance I would start with MARPOL Annex VI Regulation 13. For each installed marine diesel engine over 130 kW, excluding solely emergency engines, I would identify the applicable Tier from the ship construction date and operating area. I would then verify the EIAPP certificate, approved NOx Technical File, component IDs, injection timing and any SCR/EGR or water-based reduction system. Any changes to NOx-critical parts must be approved and recorded, otherwise the engine may no longer match its certified condition.”

Source trail

Primary references

Exam focus

Use the references to support the logic: law → certificate → technical file → physical engine → records → survey evidence. This is the structure examiners expect from a management-level marine engineer.