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  • Lloyds Register of Shipping Page 1 of 27

    Emissions of Nitrogen Oxidesfrom Marine Diesel Engines

    Questions and Answers

    July 2002

  • Emissions of Nitrogen Oxides (NOx) from Marine DieselEngines Jul 2002

    Questions and Answers


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    Lloyd's Register of Shipping, 2002

  • Emissions of Nitrogen Oxides (NOx) from Marine DieselEngines Jul 2002

    Questions and Answers


    This document has been prepared as a usefulsource of information for surveyors dealing withthe implementation of MARPOL 73/78 Annex VIRegulation 13 and the NOx Technical Code.

    The information contained has been assimilatedfrom many sources and is by no means exhaustive.

    A simple questions and answers format has beenadopted although some items have been includedin the form of notes with all common areas beinggrouped into sections.

    Each question is clearly differentiated from itssubsequent answer or note by the style of text.Questions are introduced in larger bold italicstext. Where sections of Annex VI or the NOxTechnical Code have been quoted a reference isgiven with the text appearing italicised.

    The questions and answers are for internal useonly. Their formulation is aimed at providingsurveyors with information which will allow themto deal with client enquiries.

    Lloyds Register of Shipping71 Fenchurch StreetLondon EC3M 4BSTelephone 020 7709 9166Telex 88379 LR LON GFax 020 7488 4796Web site



    Section Page

    1 General Aspects 3

    2 Control of NOx Emissions 4 - 8

    3 IAPP, EIAPP, flag states, 9 - 13MARPOL Annex VI and theNOx Technical Code

    4 On-Board Verification Procedures 14 - 15

    5 Engine Specifics 16 - 18

    6 Conformity of Production 19 - 20Procedures

    7 Pre-certification Testing 21 - 24

    8 Parent, Family & Group Engine 25 - 26Concepts

  • Emissions of Nitrogen Oxides (NOx) from Marine DieselEngines Jul 2002

    Questions and Answers

    1. General Aspects

    1.1 What are oxides of nitrogen (NOx)?99% of engine intake air is comprised of nitrogen(N2) and oxygen (O2). The nitrogen remainslargely unreacted in the diesel engine combustionprocess, however a small percentage is oxidised toform exhaust gases containing various oxides ofnitrogen, predominantly nitric oxide (NO) withsmaller amounts of nitrogen dioxide (NO2) andminor concentrations of nitrous oxide (N2O). Theterm oxides of nitrogen, or nitrogen oxides (NOx)is used to group both the NO and NO2components.

    1.2 Are oxides of nitrogen (NOx) harmful?Nitric oxide (NO) is relatively inert and onlymoderately toxic but is readily oxidised to form themore harmful gas nitrogen dioxide (NO2). As anemission species oxides of nitrogen (NOx) are ofconcern for several reasons. They are responsiblefor acid deposition, respiratory illness in humansand in association with sunlight and organicmaterial, the formation of photochemical oxidants,namely ozone (O3) and smog.

    Ozone in itself has detrimental effects on humanhealth, vegetation and crop yields, and contributesin the degradation of certain materials. Ozone isalso a greenhouse gas, controlling the amount ofthe suns UVB radiation from reaching the earthssurface and so contributes to the problem of globalwarming.

    1.3 How are NOx formed?NOx are formed during the combustion processwithin the burning fuel sprays. At these elevatedflame or combustion temperatures nitrogen is nolonger inactive and reacts with oxygen to formnitric oxide (NO) and nitrogen dioxide (NO2). Theimmediate reaction is the formation of NO. Later inthe process, during expansion and in the exhaustsystem, part of the NO will convert to form NO2.NOx is controlled by local conditions in the spray,with temperature and oxygen concentrations beingthe dominant influences. The higher thetemperature and the longer the residence time athigh temperature, the more NOx will be created.

    1.4 When are NOx formed?The stoichiometric quantity of air is defined as thatquantity of air containing the minimum theoreticalamount of oxygen required to fully convert all thefuel into completely oxidised products, i.e. forcomplete combustion. The ratio of the actualfuel/air ratio to the stoichiometric fuel/air ratio isan informative parameter for defining thecomposition of a fuel mixture. This ratio is termedthe fuel/air equivalence ratio, , and is thusdefined:

    ( )( ) =FA




    The critical equivalence ratio of the local mixture offuel and air for NOx formation is close to 1, i.e.maximum NOx creation occurs when the localair/fuel ratio is close to stoichiometric.

    The critical time perio

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