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NOx Technical Code

MARPOL Annex VI requires all diesel engines installed after 1st January 2000, with a power output of more than 130 kw to be tested and issued with an Engine International Air Pollution Prevention (EIAPP) certificate and an approved NOx Technical File. 

The approved Technical File provides details of the allowable engine components settings, operating values and allowable adjustments which ensure the engine will continue to operate within the acceptable NOx emission limits. 

This EIAPP certificate and approved Technical File stays with the engine and remains valid for its marine life. 

Periodic verification surveys are carried out by the classification to confirm the engine continues to operate within the on-board NOx emission limits.

If any adjustment, part replacement and modifications are carried out, which influences NOx emission characteristics should be recorded chronologically in an engine’s record book of engine parameters. ID numbers of all such components used are to be recorded.

The ID numbers are stamped on these parts and record them before fitting them to the engine

For Eg: the ID number of a cylinder liner usually stamped just above the scavenge ports, on the injection nozzle of a fuel injector valve. The location of ID numbers of these components will be mentioned in the NOx technical code.

When adjusts are made on FQS(Fuel Quality Setting)/ VIT (variable Injection timing) and for operational reasons, the limits mentioned in the Nox Technical file should not be exceeded.

The following are the list of components and settings that influence the NOx Emission:
a) Fuel injection timing
b) Fuel injector nozzle
c) Fuel pump plunger & barrel
d) Fuel cam
e) Exhaust cam
f) Cylinder cover
g) Piston crown
h) Cylinder liner
i) Turbocharger
j) Compressor wheel / turbine rotor
k) Diffuser / nozzle ring
l) Aux blower
m) Scavenge air cooler
n ) Governor
o) Shim thickness to change the compression ratio and if shims used on the fuel pump

The above guide lines are applicable for the auxiliary engines also.

The Code will apply to any diesel engine with a power output of 130 kW and above installed on a ship whose keel was laid on or after 1 January 2000, or any diesel engine with a power output of 130 kW and above which has undergone a major conversion on or after 1 January 2000, except those intended solely for emergency use. Major modification means the maximum continuous rating of the engine is increased by more than 10% or the engine is replaced by a new engine built on or after 1 Jan 2000.


According to MARPOL Annex VI
This regulation shall apply to:
(i) each diesel engine with a power output of more than 130 kW which is installed on a ship constructed on or after 1 January 2000
(ii) each diesel engine with a power output of more than 130 kW which undergoes a major conversion on or after 1 January 2000.

This regulation does not apply to:
(i) emergency diesel engines, engines installed in lifeboats and
any device or equipment intended to be used solely in case
of emergency
(ii) engines installed on ships solely engaged in voyages within
waters subject to the sovereignty or jurisdiction of the
State the flag of which the ship is entitled to fly, provided
that such engines are subject to an alternative NOx control
measure established by the Administration.


What is major conversion ?

(i) the engine is replaced by a new engine built on or after 1 January 2000
(ii) any substantial modification made to the engine
(iii) the maximum continuous rating of the engine is increased by more than 10%.



The maximum NOx allowed on engines are as follows:

From 1st January 2000 to 31st December 2010 (Outdated):

For engines less than 130RPM : 17g/kWh
For Engines between 130 and 2000 rpm, a formula is used:45 × n-0.2 g/kWh
For engines above 2000 rpm: 9.8g/kWh

From 1st January 2011 to 31st December 2015 the limits change (Outdated):
For engines less than 130RPM: 14.4g/kWh
For Engines between 130 and 2000 rpm: 44 × n-0.23 g/kWh
For engines above 2000 rpm: 7.7g/kWh

After 2016 ......Currently this is followed:
For engines less than 130RPM: 3.4g/kWh
For Engines between 130 and 2000 rpm: 9 × n-0.2 g/kWh
For engines above 2000 rpm: 2.0g/kWh

where n = rated engine speed (crankshaft revolutions per minute).


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