Marpol Annex VI - NOx Clause

  • The relevant clause of MARPOL Annex VI was designed to ensure that engine design for low NOx can achieve the standards.
  • Large, efficient slow speed engines face the biggest challenges, and so are permitted greater emissions.
  • New NOx emissions standards come into effect on May 20 2006
  • For the full text of MARPOL Annex VI see INDEPTH below or visit www.imo.org

INDEPTH
“(3) (a) Subject to the provision of regulation 3 of this Annex, the operation of each diesel engine to which this regulation applies is prohibited, except when the emission of nitrogen oxides (calculated as the total weighted emission of N02) from the engine is within the following limits:
(i) 17.0 g/kW h when n is less than 130 rpm
(ii) 45.0 x n(-0.2) g/kW h when n is 130 or more but less than 2000 rpm
(iii) 9.8 g/kW h when n is 2000 rpm or more where n = rated engine speed (crankshaft revolutions per minute).

This translates into the IMO NOx curve shown below (diagram from EPA)

Maximum Allowable NOx Emissions For Marine Diesel Engines

When using fuel composed of blends from hydrocarbons derived from petroleum refining, test procedure and measurement methods shall be in accordance with the NOx Technical Code, taking into consideration the test cycles and weighting factors outlined in appendix II to this Annex.
(b) Notwithstanding the provisions of sub-paragraph (a) of this paragraph, the operation of a diesel engine is permitted when:
(i) an exhaust gas cleaning system, approved by the Administration in accordance with the NOx Technical Code, is applied to the engine to reduce onboard NOx emissions at least to the limits specified in sub-paragraph (a), or
(ii) any other equivalent method, approved by the Administration taking into account relevant guidelines to be developed by the Organization, is applied to reduce onboard NO, emissions at least to the limit specified in sub-paragraph (a) of this paragraph.”