NOx compliance for retrofitted engines in ECA zones

If a diesel engine installed on board a vessel has to be replaced by a non-identical diesel engine, the replacement engine has to comply with IMO Tier III emission regulations for installations after the 1 January 2016, when trading in the two dedicated NOx ECA Zones (North America, US Carribbean Sea Area). The market is only starting to respond to this demand, and it may be difficult to find a suitable replacement engine complying with Tier III. DNV GL explains in this technical news how to handle this issue.


Relevant for shipyards, suppliers, flag states and owners/managers of vessels with diesel engines.

DNV GL has already informed about the new requirements and recommended actions related to IMO Tier III. This issue focuses on the situation if an IMO Tier III compliant engine is not available. Vessels constructed on or after 1 January 2016, intending to sail in the North American or US Carribbean Sea Area, need to comply with Tier III requirement. We recommend the following steps:

1. Contact DNV GL

If you are in the situation that the engine, which you intend to install as a non-identical replacement engine, does not comply with IMO Tier III, first contact DNV GL through DATE (Direct Access to Technical Experts), which is available in our customer portal My DNV GL. Please consider that the engine only needs to comply with Tier III if sailing in a NOx ECA.

2. Check if a Tier II engine could be allowed as an exception 

MARPOL Annex VI allows the use of a Tier II replacement engine instead of a Tier III engine if certain criteria are met. In general, the criteria are related to the unavailability of a suitable engine with Tier III certification and, at the same time, to the nonfeasibility of retrofitting a Tier II engine due to various reasons related to engine performance, ship performance or ship safety. 

3. Provide your reasons for not choosing a Tier III engine 

Inform DNV GL of what prevents a Tier III engine from being installed and provide evidence. Please document the search for a Tier III engine and explain why the closest available engine with respect to size or performance is not appropriate for the ship. The search should also include engines produced by manufacturers other than the original engine’s manufacturer. DNV GL will assist you in submitting this documentation to the flag state administration with the aim of receiving endorsement. Endorsement would mean that the replacement engine is officially allowed to comply only with IMO Tier II instead of IMO Tier III. Once endorsed, the documentation should be kept on board with the engine’s EIAPP Certificate and approved IMO NOx Technical File.

MARPOL Annex VI regulation provides for an exemption from IMO Tier III in regulation 13.2.2 if certain criteria are met. These criteria are listed in IMO MEPC.230(65):

  • An engine with similar rating complying with Tier III is not commercially available.
  • If a Tier II engine would have to be retrofitted with a NOxreducing device to meet Tier III, the NOx-reducing device cannot be installed on board due to size restrictions or due to the fact that extensive heat release could have an adverse impact whilst additional ventilation/insulation is not possible.
  • A Tier III engine would not be a feasible replacement with regard to the ship’s characteristics such as drive shafts, reduction gears, cooling systems, exhaust and ventilation systems, and propeller shafts.
  • A Tier III engine would not be a feasible replacement with regard to electrical systems for diesel generators (indirect drive systems), and other ancillary systems and ship equipment that would affect the choice of an engine.
  • A Tier III engine would not be feasible concerning engine adjustment/ matching needed to meet boundary conditions and performance data necessary for SCR operation at all relevant load points.
  • A Tier III engine would not be feasible in multi-engine (twin engine) arrangements where engines are installed as matched pairs (or more) as propulsion engines and where matching is necessary to ensure comparable manoeuvring.
  • A Tier III engine would not be feasible because it would increase the ship’s electrical demand beyond the installed capacity.
  • A Tier III engine would not be feasible because it would require modifications to the ship’s structure which would weaken its structural stability below the acceptable level.
  • A Tier III engine would not be feasible because of other reasons stated by the ship owner and to be taken into consideration by the flag state administration. These reasons could be, for example, that the SCR device would require an excessive urea storage capacity relative to bunker capacity or that the SCR device is not to increase engine weight/volume by more than an unjustifiably low percentage.

The following reasons do not justify the use of a Tier II engine:

  • Warranty period
  • Life expectancy
  • Cost
  • Production lead time


MARPOL 73/78 Revised Annex VI
Nox Technical Code 2008
IMO MEPC.230(65)

DNV GL Technical and Regulatory News:
- IMO NOx Tier III requirements to take effect on 1 January 2016
- Upcoming environmental regulations for emissions to air - IMO NOx Tier III


Email to Environmental Certification

As a DNV GL customer you can directly submit any questions through our DATE service (Direct Access to Technical Experts) via My DNV GL.