1 The NOX certification requirements of regulation 13 of MARPOL Annex VI include dual fuel engines
(those which can simultaneously use both liquid and gas fuels). MEPC 66 adopted
amendments to the NOX Technical Code 2008 in order to specifically
cover certain specific aspects related to the NOX certification of those
engines.
2 MEPC 67 adopted amendments to MARPOL Annex VI which extend the scope of the definition of a marine
diesel engine as given by regulation 2.14 to include gas-fuelled engines installed on
ships constructed on or after 1 March 2016 and also such engines installed as additional
or non-identical replacement engines on or after that date. PPR 2 considered further
amendments to the NOX Technical Code 2008 relating to the
certification of gas-fuelled engines which were subsequently approved by MEPC 68. As
such, these steps may be seen as complementary to the International Code of Safety
for Ships using Gases or other Low-flashpoint Fuels (IGF Code), adopted by MSC
95 in June 2015 (resolution MSC.391(95)).
3 Therefore, the procedures for the certification of engines which use gas as
a fuel, typically natural gas, but also other gases, have now been finalized.
4 Gas-fuelled engines, where ignition is initiated by a spark plug or another
external ignition device, are generally expected to readily meet the Tier III
NOX emission limits and therefore it is possible that engine builders
will seek only Tier III certification for such engines, irrespective of whether they are
to be installed on ships which operate outside or inside Emission Control Areas (ECA)
for NOX as described in regulation 13.6 of MARPOL Annex VI, currently the North
American ECA and the United States Caribbean Sea ECA, both of which will take effect
from 1 January 2016.
5 In the case of dual fuel engines, those engines which use gas fuel in a
pre-mix combustion process with the liquid fuel as the pilot ignition source (as opposed
to gas-diesel engines which use high pressure gas injection directly into the combustion
chamber) are expected to be certified to the Tier III NOX standards when
operating in that arrangement. Consequently, the Technical Files for such engines will
include the restriction that, when operating in the Tier III condition, the liquid fuel
rate will be limited to the certified maximum liquid pilot fuel rate and those engines
will undergo their Tier III Parent Engine test on that basisfootnote. These engines are expected to be certified to
the Tier II NOX standards when operating on liquid fuel oil only. In these
cases, the EIAPP Certificate would be completed for both Tier II (liquid fuel only) and
Tier III (gas fuel with pilot fuel), with a single Technical File giving two different
modes of operation.
6 In terms of the applied Onboard NOX Verification Procedure,
virtually all engines use the Parameter Check Method. In this, the Technical Files will
provide that all replacements and adjustments to the listed components and settings
which affect NOX emissions are to be recorded in a Record Book of Engine
Parameters. This is also the case for engines certified to both Tier II and Tier III,
with replacements and adjustments for both operating conditions being listed. In
addition, amendments to regulation 13 of MARPOL Annex VI approved at MEPC
68 also require that the tier and on/off status of an engine certified to both Tier II
and Tier III or only Tier II on ships subject to regulation 13.5.1 of MARPOL Annex VI should be recorded
together with the date, time and ship's position at entry into and exit from an ECA
under regulation 13.6 of MARPOL Annex VI or when the on/off status
changes within such designated area. It should be noted that prior to entry into an ECA,
sufficient time must be allowed for the tier changeover, to ensure Tier III compliance
upon entry into the ECA, and the Technical File should include a written procedure
showing how the tier change-over is to be done. The ship must also log the fuel oil
change-over as required under regulation 14.6 of MARPOL Annex VI.
7 NOX emissions during operation on pure liquid fuel resulting
from restricted gas supply in cases of failure under paragraph 1.3.10 of the NOX Technical Code 2008 should follow regulation 3.1.2 of
MARPOL Annex VI. This would indicate that if such failure prevents operation on gas
fuel, the ship should take reasonable precautions to minimize emissions by operating at
Tier II NOX levels, if feasible. It should be noted that non-availability of
gas fuel under regulation 18 of MARPOL Annex VI is not regarded
as a failure in this provision.
8 A particular issue for gas or dual fuel engines, including those engines on
gas tankers where boil-off from the cargo tanks is the only source of gas fuel on board,
is the situation immediately following building, before or after dry docking, or when
repairs or maintenance are done on board the ship, when a ship is required to not have
gas fuel or gas cargo on board due to safety requirements. In these particular
situations, a coastal/port State would have discretion with respect to how the ship
would proceed through the ECA. For example, the coastal/port State may allow the ship to
proceed to and/or from the dry dock or repair or maintenance location or from the
shipyard using liquid fuel, without associated Tier III NOX controls,
provided the fuel is SOX ECA-compliant or, alternatively, it may specify some
other conditions for that limited voyage.
9 It is possible that certain auxiliary control devices (ACD), as mentioned
in regulation 13.9 and defined in regulation 2.4 of MARPOL Annex VI, respectively, may be used on
dual fuel and gas-fuelled engines, covering starting and stopping, low load operation
and manoeuvring and reversing operation. During this type of operation, the amount of
liquid fuel used may exceed the maximum amount that the engine was operated on when
certified to the test cycles in appendix II of MARPOL Annex VI, resulting in higher
NOX emissions. These ACDs should be disclosed at the time of Tier III
certification and denoted in the engine's Technical File.