Expected Regulations of IMO NOx Tier III


Expected Regulations of IMO NOx Tier III


Tier I and Tier II are global requirements to reduce nitrogen-oxide emissions (NOx) for diesel engines whereas Tier III standards only apply to current existing Emission Control Areas (ECAs) (North American and US Caribbean Sea).

The IMO Tier III requirements by approximately 76% in comparison to a Tier II engine, apply to new vessels and engines.  In future, the Tier III standards will apply to ships with keel-laying on or after the date of adoption of such an ECA.


The global Tier II limits (2011) did not pose much of a challenge to engine-makers but, for the Tier III compliance they need to apply NOx-reduction measures using other engine technologies as follows:

  1. Selective catalytic reduction (SCR) systems.  This is a method for purification of NOx from an engine’s exhaust gas.
  2. Exhaust gas recirculation (EGR).  This is still a relatively new technology developing a competitive option for NOx compliance.
  3. Alternative fuels such as liquefied natural gas (LNG).

The NOx certification does not take into account, the technology that is connected to the engine and the exhaust gas system.  It is the sole responsibility of one applicant  for the application of certification for the combined engine and post-treatment system, regardless of how many manufacturers are involved.

“Super-yachts” (vessels of 24m and above, but of less than 500 GT, which are designed and solely used for recreational purposes) constructed before 1st January 2021 and all yachts smaller than 24 m, irrespective of construction date, are exempt from Tier III.

In the case of engine replacements, the new engine has the option of meeting Tier II requirements if it does not achieve compliance with Tier III as stated in Reg.13 para 5.1.1.  However, this is subject to case by case approval.

As Tier III requirement applies to vessels with keel-laying on or after 1 January 2016 and not a retroactive requirement, it will not be applicable to existing engine installations.  The new building plans have to incorporate the technological solution options – such as SCR, EGR or LNG.

Source: DNV GL