MARPOL Annex VI Regulation 13 establishes a three-tier engine-certification regime for marine diesel engines, with the maximum permitted NOx emission rate set as a function of the engine’s rated rotational speed n in rpm. The applicable tier is determined by the engine’s installation date and (for Tier III) by the engine’s current operating area.
Tier-applicability rules
| Engine installation date | Applicable tier outside NECA | Applicable tier inside NECA |
|---|---|---|
| Before 1 January 2000 | not regulated | not regulated |
| 1 January 2000 – 31 December 2010 | Tier I | Tier I |
| 1 January 2011 – NECA effective date | Tier II | Tier II |
| On or after NECA effective date | Tier II | Tier III |
NECA effective dates: North American NECA and US Caribbean Sea NECA from 1 January 2016; Baltic Sea NECA and North Sea NECA from 1 January 2021.
Tier limits as a function of rated speed
Each tier has a piecewise-defined limit as a function of the engine’s rated rotational speed n in rpm:
$$ \text{NOx}_\text{limit} = \begin{cases} A_\text{low} \& n < 130 \\ K \cdot n^{p} \& 130 \le n < 2000 \\ A_\text{high} \& n \ge 2000 \end{cases} $$| Tier | $A_\text{low}$ (g/kWh) | $K$ | $p$ | $A_\text{high}$ (g/kWh) |
|---|---|---|---|---|
| Tier I | 17.0 | 45 | $-0.2$ | 9.8 |
| Tier II | 14.4 | 44 | $-0.23$ | 7.7 |
| Tier III | 3.4 | 9 | $-0.20$ | 2.0 |
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $\text{NOx}_\text{limit}$ | Maximum permitted cycle-weighted NOx | g / kWh | result |
| $n$ | Engine rated rotational speed | rpm | EIAPP Certificate |
| $A_\text{low}$, $A_\text{high}$ | Constant limits at low / high rated speed | g / kWh | MEPC.176(58) Reg 13 Table |
| $K$, $p$ | Tier-specific coefficient and exponent for medium rated speed | - | MEPC.176(58) Reg 13 Table |
Compliance margin
$$ \text{Margin} = \text{NOx}_\text{limit} - \text{NOx}_\text{certified} $$where $\text{NOx}_\text{certified}$ is the cycle-weighted NOx from the engine’s EIAPP Certificate. Positive margin = compliant; negative margin = non-compliant.
Worked examples
| Engine | Rated speed (rpm) | Installation year | Operating area | Tier | Limit (g/kWh) |
|---|---|---|---|---|---|
| Slow-speed two-stroke (95 rpm), 2024 install, in Baltic NECA | 95 | 2024 | inside NECA | Tier III | 3.4 |
| Slow-speed two-stroke (95 rpm), 2024 install, mid-Atlantic | 95 | 2024 | outside NECA | Tier II | 14.4 |
| Slow-speed two-stroke (95 rpm), 2008 install, anywhere | 95 | 2008 | any | Tier I | 17.0 |
| Medium-speed (720 rpm), 2018 install, in Baltic | 720 | 2018 | inside NECA | Tier II (Baltic NECA effective 2021) | 9.7 |
| Medium-speed (720 rpm), 2022 install, in Baltic NECA | 720 | 2022 | inside NECA | Tier III | 1.7 |
| High-speed (3000 rpm), 2024 install, in NECA | 3000 | 2024 | inside NECA | Tier III | 2.0 |
Sources
- IMO MARPOL Annex VI Regulation 13.
- IMO Resolution MEPC.176(58) - Amendments to MARPOL Annex VI (revised Annex VI with the 3-tier NOx framework). 10 October 2008.
- IMO Resolution MEPC.177(58) - NOx Technical Code 2008. 10 October 2008.
- IMO Resolution MEPC.272(69) - 2016 Amendments to the NOx Technical Code 2008. 22 April 2016.
- IMO Resolution MEPC.286(71) - Baltic and North Sea NECA designation. 7 July 2017.
- IMO MEPC.1/Circ.795 - Unified interpretations to MARPOL Annex VI. 22 May 2015.
See also
Related wiki articles: