Page 82: of Maritime Reporter Magazine (April 1998)

PROPULSION UPDATE the realities of shipboard service, particularly that the analyzers and the associated equipment will need to be robust, reliable and suffi- ciently simple to operate and maintain without specialist skills or training. Additionally, due to the variations that will occur between different sets of readings, there will be a need for an allowance over the NOx limit as given in Annex VI, the magnitude of which will need to be taken into account, the probable relaxation in some of the analyzer and associat- ed equipment specifications as compared to test bed equipment and also the effect of using resid- ual fuel oil in most cases (with an inherent tendency to higher NOx emissions) rather than a distillate <3 Underwriters Laboratories Inc.® una

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Nevertheless, it must always be borne in mind that a total reliance on onboard monitoring or associat- ed equipment fail to function cor- rectly, giving either no reading or worse still an anomalous output, the continued service of the ship could be in question until the prob- lem, inevitable occurring at some remote location, could be fully resolved.

So just how much variation in

NOx measurements could be expected? Figures 1 and 2, based on measurements undertaken by

Working Group members, illus- trate two examples of the variabil- ity which can be encountered when measuring the brake specif- ic NOx emissions from marine engines. Figure 1 (page 75) shows the emissions from two slow-speed engines as measured at the time of delivery and, in the case of Engine

Two, again after 18 months of operation. Figure 2, (page 75) shows the emission from four nom- inally identical medium-speed engines installed on a ferry under in-service conditions at two differ- ent dates some nine months apart.

In both cases the emissions bands were between 1.0 - 2.0 g/kWh, which represents up to around +/- eight percent of the actual emis- sion values determined. Since the analytical equipment used and the procedures adopted in both instances were more comparable to those which would normally be used under test bed conditions it is evident that a wider range of emis- sion results would be expected when using the type of equipment and procedures that may eventu- ally be stipulated within the NOx

Monitoring Guidelines with a con- sequent need for a corresponding allowance when monitoring NOx under onboard conditions. The measurement of brake specific

NOx emission rates is no different to other analytical procedures, such as those used in tiil fuel test- ing, with a consequent need to allow engines to meet the Annex

VI limits and when setting the acceptance criteria for NOx

Monitoring as a means? of onboard verification.

The NOx emission profile from a particular engine under standard- ized conditions are set by the design, adjustment and usage of that engine. The NOx emissions do not tend to increase over time.

The engine builder should ensure that the Parameter Check method

Maritime Reporter/Engineering News