Proceedings of the Europort Diesel Engine Symposium'93 ""MOTOR2000"

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1 EUROPORT DIESEL ENGINE SYMPOSIUM '93 - MOTOR 2000

16th & 17th November 1993/Amsterdam

An Overview of the Environmental Situation Conceming

Combustion Engines

J.5. Carlton *

Abstract

The paper considers the emergence of diesel engine exhaust eniissicm regulatipns for

the marine industry and some of the implications of introducing these regulations.

The discussion centres on four interrelated aspects: the fonnat and possible structure

of regulations tpgether with the methods of implementation; the availability of

technology to meet these requirements; the implications for safety and the design of

ships. The arguments are primarily centred on the immediate concerns of the oxides

of nitrogen and sulphur, h o w l e r , the paper also examines the issues suirounding

the PÜier exhaust gas speaes.

Introduction

In recent years there hàs been a growing public awareness of the importance of the

sea's riesoùroes and the influsice of pollution on these resources. Legislative and

technical activities conceming ships have traditionally focused on üte pollution of the

sea. Howeyer, latterly äie 'dean ship' philosophy, which introduced the wider

conœpts of air pollution and contributions to the global 'greenhouse effecf, has

assiuned a niuch greater importance. In response to public (pinion, govenunents are

coitsidering the form and means of implementiiig legislation in the marine Held; the

Intemational Mantime Organization (IMO) effectively began formal consideration of

this matter during the 29th Session of tiie Marine Environmental Protection

Committee (MEPC) in 1990,

Senior Principal Stûveyor and Head of Technical Inyestigabon, l^opulsion and &iyironinantal Engineering Departinent Uoyd's Register, London and also Chainnan of the CM AC Exhaust Enüssion Contrats Workihg Group.

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2 The devélopment of the marine d i ^ e l engine has to a very large extent been

dominated by the pursuit of enhanced fuel efficiency. Whilst this has had a beneficial

influCTce on carbon dioxide emissions, the reverse is true for the oxides of nitrogen

(NO^) due to the trend> amongst other parameters, of increasing cylinder pressures

and temperatures and decreasing crankshaft speeds for slow speed engines which

lead to conditions which promote the formation óf NO^ within the cylinder. Coupled

with this aspect, the trends in recent years with regard to fuel quality have been

ecohoxnically rather environmentally driven. Consequentiy, following on from the

public and governmental interest in envirorunental consavation, cpnsiderable public

sector and privately funded research has been initiated; a summary, althou^ not

complete, of some of the known work being tmdertaken in Europe is given ih [1].

This overview cpn^ders the parallel development of legislative and technological

activity and eöideavPurs to draw conclusions based on the extensive work cunentiy

being imdertak^ in this field.

Emission Regulations

In the short tierm, legislative and regulatory intarest is centring oh lintitations for the

oxides of nitrogen and sülphür, however, it may be that controls for caibon dioxide,

hydrocarbons and particulate einisisicms will feature in the medium to long tenn;

perhaps in dte form of an iterative cyde.

Currentiy, there are several proposals for the limitations of the oxides of hitrogjen and

sulphur; some regionally based and those of an international character, the most

notable of which are those currentiy being formulated by IMG. The riature of the

NO^ proposal h-om IMO is still a matter for agreement during the cozriihg year or so.

One proposal, however, which has been widely quoted and was submitted for

consideration durihg MEPC.30 is titat of a 30% reduction m total N O . emissions from

the marine industry by the year 2000. Such a concept presents a formidable challa:ige

for the marine industry; not so much for new engines where a reduction Of this

order is possible within the foreseeable development of engineermg tedmology, but

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for existing toimage. Although cunent thirücing is prindpally centred oh measüries

for new engines, tiie current ratk) óf new fo existing ships shows that a ppinparatively

limited overall effect on NO^ can be achieved in the short term from regulations

aimed at new ships alone. Table 1 shows the number of new ships built dihihg 1992

as compared to existing ships for all known vessels of 100 toimœ DWT and over

from Lloyd's Register's data base of ship statistics:

New Vesseb En<>tlng Vesaäs Vesseb laid up

Wmdwr of Slips 1422 78304 441

Table 1 - Numbers of Vesels over 100 tonnes DWT in 1992

Based on this d a ^ and sub-grouping the ships info slow and medium speed engines,

tlie potential for overall reductipn can be estmiated using tiie enüssion factors

presented in [2]. This shows, for example, that if a 30% reduction in the N O .

emissions was introduced for new engines this would lead to an overall marine

industry reduction of around 1 % in the first year. Alternatively, if the reduction were

inaeased to 80% then this would pnly cprrespond to approximately a 2.5% reduction.

Clearly, tiiese effects would then be cumulative in successive years as fleet

replacement took place.

Geographical factors, tiie distributipii and nature of industrial conurbations and

public p^ceptioh highlight particular areas of the globe as being particularly sensitive

from an enviroiunaital and ecological point of view. Notable in this respect are parts

of the western seaboard of the Urüted States of America and the Baltic Sea. In

additiori, maritime transport pattems tend to concentrate tragic in particular sea areas

such as the English Channel and Straits of Malacca. Emission densities in these

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4 regions can locally be relatively high as seen, for example, i n [3J. Qearly, from the

marine industry viewpoint, due to its international character, e?diaust ernission

regulations are best framed such that a single coinmon system of emission controls

applies throughout tiie world wherever regulations are required. The IMO through

the forum of the Marine Environmental Protection Committee is an obvious

mechanisih for this, assuniing that a satisfactory level of agreement can be reached.

Ahy difierent approach involving administrations working separately will introduce

additional complexity into rriaritime operaticm, in terms of both the implementation

and the auditing of compliarice to regulations, and this will ultimately be reflected

ih transport coste and operational flexibility. Nevertheless, from thé foregoing

discussion it is clear that soihe areas will require special attention and this pould be

achieved tiirough a spedal area framework similar to that used i n the MARPOL

73/78 Convention [4],

In the case of particular ports, many aie consid^ing and some have impleniented

environniehtal schemes as a meajis of controllihg emissions from ships vàîdïst in the

areas u i u i ^ thdr jurisdiction. The need for undertaîong this action dearly depends

on the relative significance of marine enüssions compared to those from land based

sources and the prevailing climatic and geographic infiuences. In the particular case

studied in [5] the need is dearly less than in other areas subject to intense inarine

activity.

When formulating emission regulations, whether these are on a global, regional or

local level, it is particularly impprtant that a consistent framework is adopted and

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tiiat the details of the regulations reflect the cunent or antidpated engineering

capabilities at the time of their introduction. $ubsequentiy, regulations can then be

sti^ngthened and maintained to be 'in-line' with the developrhent of tedinoiogy for

newbuildings.

The additional levels of complexity introduced by sonrie abatement technologies riiust

be viewed in the context pf the operational safety of the vessel as well as in terms of

their environmoital benefit. The cunent and predicted short-fall of qualified engineer

officers [6] is critical ih this respect; particularly where a technique danahds ain

in-depth knowledge of engine operation, chraxücal processes or the handling of

potentially hazardpus substeoices. As a general prihdple it should be ensured that

the technology assodated with the abatement tedmiques adopted is comparable with

that of the systems ih which it is to be installed; in particular, the r ^ t i v e l y siniple

systems assodated with some smaller vessels should not be unduly aictimbef ed with

highly complex emission control equiprhent Furthérmore, legislative requirements

should be l>ased on diaracteristics proven by service conditions ^ o e , frequentiy,

these may invalidate the results obtained in the ixipre carfully controlled test-bed

conditions.

Characterisation of N O . Emissions

The formation of oxides of lütrogen occurs as a result of dther the oxidation of

molecular nitrogen in the combustion air or of orgarüc rütrogen in the fud. In the

latter case, it would be antidpated that the bulk of the or^mic rütrogen would be

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6 oxidised within the combustion proems and, dejTendent upon the hature of the fuel,

orgarüc rütrogen may account for a sigrüficant proportion of the total N O . enüssions,

particularly for engines op>erating on heavy fud.. When considering the oxidation of

atmospheric nitrogen the reaction will be influenced by Ipcal œnditions in the

combustion chamber with inaeased production of lütric oxide (NO) favoured at high

temperatures ahd optimal air-to-fud ratios. Subsequentiy, during the passage of the

gases through the exhaust system a proportion of the lutric OJdde will be converted

to lütrogen dioxide (NO^); typically this will be of the order of 5 to 10%.

^multaneously, a limited proportion óf lütrous pxide (NjO) will also be formed.

After expulsion from the exhaust stack, furtiier oxidation of the nitric oxide will

continue uhder ambiént conditions tp form additional amounts of nitrogen dioxide.

Conditions within the combustion chamber greatly influence tiie formation of lütric

oxide. Peak pressures and temperatures, injection rate and time for the combustion

process are inajor détenhinante in the basic processes of N O . formation. The average

steady state émission factors reported i n [2], and reproduced for cony^ence below,

illustrate tiie distinction between the broad categories pf slow speed and medium

speed engines measured under normal service operating conditions.

[ Canbustfon Spvctes Médium %aed Slow Spaed

foxides of Nitrogen (NOk) Carbon Monoxide (CO) 1 Hydiocazbon (HO 13^ 1.8 0.6 Î8.7

2.1 OS

Table 2 - Emission Factors for Medium and Slow Speed Diesd Engines (g/kW.h)

Independentiy, attempts by two nujor engine manufacturer assodations [7,8 and 9]

to characterise N O . emissions from engines have led to tiie development of limitation

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proposals dep>endént On design crankshaft speed. Both the European and Japanese

proposals are derived from the rnonitoring of the anission behaviour of current

engine designs and result in proposals for N O . linüte having a coinmon mathematical

form fbr engine speeds below 1200 rpm as follows:

NOx = x.(RPM) '' g/kWh Equ. 1

where the coeffidents x and y are shown in Table 3.

ORIGIN

X

_y

EUROMOT:

1) At MCR using Z3iesel Fuel 30.97 0.167

ii) At Propeller U w (E3 Cyt^) using 3423 0.167

OLesdFud JAPAN:

At MCR Coonditipn 45.00 02

Table 3 - EUROMOT and JICEF N O . Limitation Proposals

frispection of the values quoted in Table 3 shows that the Japahese proposal leads to

a more relaxed liinitatfon> particulariy for low RPM values, tiian dther of tiie

EUROMOT proposals. At higher RPM values there is a tendency for the Japanese

and EIJROMOT-Ë3 cyde curves to converge. However, both equations are intehded

to represent a valid Umit on NO. emissions. The difrérènce in the coeffidents x and

y reflect^ therefpre, differing views between the Japanese and European

mahufacturers on the extrapolation of their existing databases of engine emissions

towards achievable levds at the time of implementation of the legislation.

Equation 1 has an exponential chara.cter and, consequentiy, when thé revolutions tend

toward low values then the proposed liimting mission values tend to inaease.

Wlulst this relationship follows the underlying laws of physics over the speed range

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8 pf the engines upon which it was based, deairly, this tendency, if extrapolated too far

towards the origin, leads both to enoneous limiting values and also to a

misrepresentation of the undalying physics. Consequentiy, there is a need för an

upper bound on emission levels to be introduced for very low rotational speeds.

An aitemative view on N O . emission limit characterisation has been expressed by one

major medium speed diesd engine manufactura* group and this has foimd s t i j ^ r t

with some ship Owners. This is to establish a common N O . emission limit in the

regioii of 12-14 g/kWh which is independeht Of rotational speed, size or otha- factors

and to ap>proach this constant emission state by means of a step-wise approach based

on ship type and duty.

The N O . characterisation so far discussed rdates to new engines under test bed

conditions. In the case of marine engines thé in-sa^rice performance is normaUy

cydic ih its character dependihg on the period between overhauls which is frequentiy

related to docking cycles. N O . emissions reflect this periodic maintenance sdiedule

along with other combustion spedes; the most notable being carbon monoxide and

hydrocarbons. In the case, however, of N O . emissions a reduction in concentration

of the order of 3ÖQ to 400 ppm is quite possible over a maihtenance cyde. In addition

to the nonnal periodic maintenance cycle, engine modifications which may occur

during the Ufe of the vessd can also influence N O . production. For example, the use

of difrerent atcnhisers can introduce variations of the order of 10% in N O . production.

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^^.•••"^^.••"•••^'-v'w,

ambient conditions are also known to affect tiie N O . ahissipns cpnsiderably. In test

bed trials on a medium speed diesd engine [10] the influaice of ambient and recdver

air temperature, barometric pressuie and air humidity was investigated. From this

research it was demonstrated that NO. emissions can bé more than 40% higher in the

wintar in Northern Europe than in the tropics using tiie same engine at the sarne

power. Such a result> therefore, has much significance for the implementation of any

N O . limitation proposals ih terms of the need for the introdUctfon of suitable

oonection factors.

N O , Reduction Techniqaes

N O . reduction tedmiques essentially faU into :two categories; primary methods

involving action within the engine and secondary methods which dther address the

cleaning up of tiie exhaust gases pr, altemativdy, tiie reduction of emissipns by

changing the opa'ational characteristics of the ship. A sdection of thé primary

reduction metiiods a^^ailable can be seen in Table 4.

Engine Timing

Ddàyed Fud Injection

Injection Rate Characteristics

Charge Air Pressure Increase

Charge Air Temperatiu-e Deaease

Exhaust Gas Redrculatipn

Multi-Point Injection

Cómbüstioh Air Conditioiüng

Inlet Air Hurhidification

Oil Fud-Water Emulsions

Oil Fud-Water Sequential or Simultaneous In ection

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10 In tiie case of new nijachiiiery installations, their design, given suffident development

resources, could be expected to achieve a nonünal 30% reduction m N O . production

by primary methods. Notwithstanding this, many of the tedmiques Usted in Table

4 are ciirrehtiy the subject of research and develppment initiative; for example, the

adtievement of an appropriate balance between N O ^ and particulate emissions

and their dependence on f u d injection rate. Altemativdy, the attainment of an

optimal balance between oil-fuel and wabâr quantities and timing m sequaitial or

simultaneous injection methods for slow speed engines. In the case of water injection

inethods the provision of suffident quantities pf high grade water is a complemaitary

consideration which n<eed not riecessarily be a problem on large ships but may be

more difficult to achieve on smaUer vessels.

Engines designed and buüt l>efpre the mid 1970s were generaUy less fUd effident and

had relativdy low N O . levels within their exhaust gases; tiierefore, their potential

for devdoping further reductions in the óxidtó of nitrogen is Umited today. For more

recent designs, reductions varipitsly estimated at between 5^10% may be possible

without tiie use of emission abatenient devices. For these existing engines, greater

reductions, pos^bly up to 30%, may be achievable, but only by the use of additional

equipment or through substantial modification. It is, however, potentially dangerous

tp arbitrarily ihtrodiice N O . abatemäit tedmiques on these older engines. For

ecample, water based em;ülsion aiid injection techiiiques or> altemativdy, the ùse of

delayed injection tinting can, if extended too far, lead to unreUabiUty and difficulties

in starting, with consequent safety impUcations.

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In genaal terms a reduction in N O . by means of primary abatement measures is

likdy to lead to a detrimaital effect on specific f u d consumptipn. This in turn leads

to an increase in runniiig costs and to increased carbon dioxide production. Fiuther

r e s ^ r à i is requfred before definitive estimates can be made, however, based on

current information a reduction of the order of 10% in N O . would sfeem to imply a

one or two percent inaease ih specific f u d consumption.

In tenns of swndary methods, selective catalytic reduction techniques (SCR) are

showing considerable potential in their abiUty to e^ectivdy reduce.NO. emissions as

witnessed by the iheasüréments reported in [11]. In this work, reductions in N O . of

around 96% together with significant h y d r o c ^ ^ n emissicm reductions of the order

of 84 to 91% were reported for a 2300 tonne feny operating on gas oU. Cunentiy,

however, SCR uiüte have a sulphur-exhaust temperature window which confines

their operation to a region of low sülphüï- fuels, generaUy bdow 0.6 to 0.7%, and to

mecUimi and high speed aigines with exhaust temperatures in tiie range 290 to 500

d ^ C. Sigrüficant work is beihg undertaken to extend the siilphur tolarance of these

units to levds of 2% and above which, if successful, wiU enhance their tolerance to

thé Wider spectrum of marine fuds in coinmon use. AdditionaUy, the Ufe of the

catalyst elements discussed in [11] is iiidicating that operatmg liyes in excess of 20000

hours may be possible. If subject to wider vaUdation^ this coupled with a better

tolerance to sulphur in fuels is particularly encouraging for a more gaiierai acceptance

of tiie techrtique.

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12 for a particular ship, however, in cases where a strict saüing schedule is required, a

vessd's speed requirement is largely a weather dominated parameter. This technic{ue

may in tum cUctate that less frdght capabiUty is avaUable or, altemativdy, that more

ships are required with a consequent detrimental effect on emissicms. Such a

solution, nevertheless, by taking into account the nominaUy ciibic relationship of

propulsicm power requirement with ship speed may, but not necessarily wiU, lead to

an overaU reduction m eriiissipns depending upon the ship speed and size, harbour

dzes and frdght capadty requiremente. AdditionaUy, a factor common to aÜ

operaticmal soluticms of this type, as opposed to machinery mcxiification, is the

degree to which they can be effectivdy rhonitored.

Other Pollutant Spedes

In adcliticm to N O . cónsiclërations, whidi as far as the air poUution debate is

concerned has largdy dominated discussion, other spedes heed recognition and

consideration. PrincipaUy, tiiese are the oxides of sulphur, cartxm dioxide, carbon

moncodcle, hydrocarlx^ns, particulates and microppUutants; this latter term being tiiat

gaieraUy used for those spedes present in trace quantities ahd typicaUy indude the

polyaromatic hydrocarbons (PAHs), nitro-polyaromatic hydrocarlxms (n-PAHs),

polychlorinated biphenyls (PCBs), jxilychlorinated dibenzodioxins (PCDDs) and

polychlorinated dibenzofurans (PCDFs). Of Üiése other pollutant spedes those of tiie

oxides of sulphur and carbori dioxide have perhaps recdved most consideration i n

terms of marine air

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poUutioh-The oxides of sulphur (SO.) OTiginate directiy from the sulphur cpiitait of the fuel

used and in general terms the rnass sulphur input into the engine equals that output

in the exhaust, ^ a r t from a relativdy insigrüficant amount which is converted to

caldum sulphaite through the Use of alkaUhe lubricants. The prindpal SO. cOmpcmeht

is sulphur dioxide

(SO2),

with sulphur trioxide

(SÔ3)

forming to a much lesser extent

The most convenient way of reducdhg the SO. emissipns appears to l?e tiirough ttie

GQitirol of the sulphur content of ihe f u d since this, as far as the ship is concemed,

deals with the problem at source. Clearly, this is not tiie case with respect to the

r^nery. Fud sulphur limite can dther be applied on a gfobal or regicmal basis aind

curraitly the r ^ p n a l approach appears to be finding favour; typicaUy, in this

context a region inight form a geographical area such as the North Sea. VA^tiün these

regions the imposition of a comparatively stringent f u d siüphur linüt in marine terms

may be Ukdy to lead, for intanaticmal trädihg vessds, to an extension of the dual

f u d prindple. This in tum raises furtha* questions of marine safety iritroduced by

the absolute need to esnsure f u d ccnnpatibiUty and the wider consequences that can

rësult in the event of f u d rdated problaris arising. Therefore, coihddent with the

introduction of any regionaUy t>ased fuel restrictions the appropriate safety measures

need to be simultanepusly addressed. AdditionaUy, the sighificahoe of the siilphur

content inforinaticm which would need to be ccmtained on Bunker Receipt would

need careful attention by aU parties.

Global capping of f u d sulphur levels is a rhatter with far reaching poUtical and

techno-economic csOnseqUences. The sulphur content of tiie majcniiy of residual f u d

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14 OÜS is found to vary between 1.5 and 4.0% worldwide whereas in North Western

Europe they are found to have values in the range 2.3 to 33% based cm LR's

é)q)erience As a consequence capping Urnits wül need to ccmsider these range of

sulphur content if they are to have any effect. As such the current ISO 8217

specification does not represent a real liniitation on currait fuds.

Carbon dioxide (COj) is a direct result of the fundamental combustion process and

iis a pirimary function of the c{uantity of f u d consumed. Ite ccmtrol, theréfore, has to

a very large extent to be implemented through the means of efficiency optimisation;

that is, by means of the fundamental prime mover effidaicy; the optimisaticm,

disposition and use of eh^r^ based auxiUary systems and the hydrcxlynamic

effidàicy of the ship. This, therefore, raises the concepte of system complexity, as

ccmsidered previously, and also the bounds of present knowledge and experience in

ship design. The situation with aiergy based auxiliary systems such as exhaust heat

recovery systenis, shaft drivai auxiliaries ahci so on is w d l known and the overaU

plant effidency and successful in-service operation are function of good design,

mahuÊscture and maintenance. Whilst significant progress in this area has been made

there is stül potential for further improvanent In order to appredably enhance

hydrodynamic propulsion effidency a fuller understanding of the thick boundary

laya- at the stem of the vessd is required. Until this is achieved only limited

improvements eah be made, nevertheless, sigrüficant energy savings have been

repctrted andi vaUdated by sea trials in certain instances of fitting some flow

augmentation aind recovery devices. For example, the fitting of a Grim vane whed

in the case of two frön ore caniers demcmstrated, on the basis of sea trials analysed

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15 by LR, propulsive effidency improvanente in the region of 10 to 12%.

Notwithstanding a pleasing residt of this type, the potential for improvement is

always a unic]ue function of the incUvidual ship's propulsion paraimetas. Simikrly,

some flow control devices haVe yidded worthwhile résulte, however, as outUned

above Ûi&i dedgn currentiy depends, to a very large exterit> on empiricism.

In geheral terms it is, therefore, considered that the route towards CQz reduction is

to be found in the design optimisation óf Üie total ship unit and an integrated

transport infrastructure. In this respect both the minimisation of CC^ emissions and

the reduction of f u d coste Ue, in prindple, within the same objective.

Implementation Procedures

Ccmsideraticsi is cunaitly iTeing given to the definition pf different categories of

engine, based on power output> for tiie irnplementatipn of N O . regulations. These

prcKedures rdy on a mixtiue of type approval and survey procedures with the

unda'lying framework of ISO 8178 acting as the supporting procedure and they will

be contained wititin the MARPOL framework. This basis provides a way forward

which is consistent with the conventional maritime approach to inspecticm and, as

such, establishes for the ship operator a meahs of corhpliance with regulatory

procedures. These procedures recogrtise tiiat it is ultimatdy the flag state authorities

which wiU be responsible for the enforcement of €»diaust anission regulations but,

as in the case of tiie SOLAS ahd MARPOL réqUfrëmâite, the lACS affiliated

dassification spcieties are frequentiy bést placed to act as the approval ahd

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16 verification agente in view of their independence and worldwide represaitation

which is synonymous with the intematiprial character of the marine industry.

In framing regulattons requiring the in-service assessment of exhaust emissions it

must be recognised that these can only be undertaken whai the vessd is at sea: this

is ih contrast, for exarhple, to the existing MARPOL requiremente whidi can l>e

implemented with the vessd in port. Where in-service trials are to be imdertaken for

regulatory compUanœ purposes it is probable that spedaUst personnd would be

recpiired to travd with the ship and this may involve extended pericxls at sea when

the vessd's trading pattem predudes short duration trips. Altemativdy^ if a

continuous mcmitoring approach were adopted this would, of necaisity, be under the

control of the vessd's Ghief Engineer who would be respcmsible for ensuring the

conect functioning, verificaticm, through pericxlic calibration, and maintenanœ of the

ecjuipment In this case the Chief Engineer's rejxsrte would be subject to scrutiny by

a ccmtrolUng authority, potentiaUy through the existing continupus survey schemes

operated by the major dassification scxieties.

It may be that a combination of two approaches is the most satisfactory option where

the bulk of the monitoring is done by a continuous approach with occasional

independent checks. However, in recognising tiie workload imposed by the pericxUc

exhaust emission inspection requirements, a balance must be drawn between the

rec{Uirèmente of the responsible authorities to check for possible non-compliance and

the dismption caused to the vessel's operatmg scheditie by such re(]uiremaite.

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, 17

Conduding Rémarks

Frpm tiie foregping discussion a saies of coiKlusicms cóncerhing any proposed

exhaust emission régulaticms can be identified. These are as foUows;

i) A unified system of emisdon controls shpuld l7e introduced throu^out

the world wherever regulation is reqiured and the most appropriate

means to adiieve tiiis is through the Intematicmal Maritime

Organization.

U) It is unlikdy that a major short term reducticm on afr pollution from

marine sources wiU result from the intrcxiucticm of abatement measures

confined to new ships alone. This effect wiU, however, be cumulative

as fleet replacement over the years takes efiect

iii) Regulations should refiect the current or antidpated techitolo^cal

capabiUties at the time pf thefr mtrcxluction anci then be strengthened

and maintained 'in-line' with future research and devdopment for

newbuildings. Furthamore, they should be based on vaUdated service

pafprmance of the abatemait technologies.

iv) The levd of technology assodated with abatement techniques should be

comparable with that of the systems in which they aré installed.

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18 v) There is cunentiy a diversity of opinion on the most appropriate form

for N O . limite.

vi) In-service N O . eniissfons are subject to ccmsiderable variations through

maintenance cydes, the mcxiifications carried out during the life of the

ship and from ambient ccmditions.

V Ü ) For new engines the achievement of a 30% reduction in currént levels

pf N O . ahissioris could be attainable. This is not, howeva-, the case for

existing engines where reductions variously estimated at between 5 anci

10% may be possible It is, however, potaitiaUy dangerous to

aifbitfarily introduce N O . abatëmait techniques on older engines.

viii) A reduction in N O . emissiprts of> for example, 10% would, based on

current informaticm, be generally expected to lead to a one or two

percent increase in specific f u d constm:iption.

ix) Sdective catalytic reducticm techniques have demcmstrated a potential

as a seconciary method of N Ô . and hydrocarbcm reduction for

applications within a window defined by low sulphur content and

exhaust tempa'a;tures betweai 290 and 500 deg C.

x) Sfow steaming may, but not necessarily wiU> lead to an overall

reduction in emiissiohs depending on the size of a vessel and ite sipeed.

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freight requiremente and harbour avaüability.

xi) SO. emission reduction is most likely to be achieved through r ^ c m a l

restriction asscxiated with a global capping limit. This wiU rec^uire the

simultaneous addressing of appropriate saféty measures in ttiie case of

regional restrictions and attaition to the level set for ^obal capping if

it is to be effective.

X Ü ) CO^ reducticm depends cm the design optimisation pf the total ship uxtit

and an iritegrated transport mfrastmclure and, ther^re, is compatible

in prindple with economic considerations.

xiU) ImplemaitatiOn procedures are likdy to rdy oh a ccmibmation of type

approval and survey procedures and be based on the framework of ISO

8178.

xiv) ResponsibiUty for implementation wiÛ rest with the flag state as the

regulations wiU be set within the MARPOL requirements. However, by

vfrtue of tiidr independence and world wide representation,

classification societies are frequentiy best placed to act as approval and

verificaticm agente.

(21)

20 Acknowledgements

The Author wcmld like to thank the Committee of Lloyd's Register for permission to

publish the paper and also to his riiany coUeagues within LR upon whose work over

the yéars tiie sUbjed matter is based; particularly notable in tins respect are Dr G.L.

Reynokis and Mr A.A. Wright In adcUtion, thanks are also due to the various

members of the CIMAC Working Group on Exhaust Enüssion Controls and the

lOkŒS TCS Ccmuatittee where, through lively debate on these matters, many erf the

ideas have been formed and growh.

REFERENCES

1. Ruxton, T.> Ciu-lton, J.S. & Flameling, T. "A Simunary erf Scmne European

Marine Pollution Research". ICMES 93 Conf. Hamtnirg 1993.

Z Lloyd's Register, "Marine Exhaust Emission Research Programme: Phase II

Transient Emission Trials". Lloyd's Register, London, 1993.

3. Cariton, J.S., Wright, A.A. and Coker, R.J., "Marine Exhaust Emissicms - A

Regicmal Survey erf Emissions in the English Channd". Trans. LMar.E., March

1994.

4. Intanaticmal Maritime Organization, Intematicmal Conventicm for the

I^evention erf PoÛution from Ships,

M A R P O L

^ / 7 8 . International Maritime

Orgahizaticm, London, 1993.

5. Lloyd's Register, "Marine ETchaust Emission Research Programme: Phase n Afr

QuaUty Impact Evaluation". Lloyd's Register, London, 1993.

6. Intanational Shipping Federation "The World Wide Denumd and Supply erf

Seafarers". K F , BIMCO, 1991.

7. EUROMOT, "Thé Regulativem of Exhaust Emissions for Redprocating Intemal

Combustion Engines 91/01", Euromot 1991.

8. EUROMOT, "EUROMOT Proposal on Exhaust Emission Standards for Marine

Engines 93/01", Euromot 1993.

(22)

- 21

9. HacUa*, C , "Ffrst Conespondaiœ Papa- cm Tedmical Requiranente for New

Engines to Deal with NO.", IMO January 1993.

10. Bcxrf, Ph. " NO.-RedUctión of Diesel Engines by CcmcibUstion Afr Ccmditicming".

Paper D67. 20tii Iht O M A C Cong. London 1993.

11. Cooper, D. and Petarson, K. "Emission MàteUremaite from a Urea-based

SCR/cod Catalytic N O . / H C Exhaust Gas Treatment System on Board a Diesd

(23)

MTU Friedrichshafen

I T T t U

Deutsctie Aerospace

Measures for Reducing Noxious

Exhaust Emissions in High-speed,

High-performance Diesel Engines

Symposium "Motor 2000"

Amsterdam

November 1993

(24)

Dr.'Ing. Christoph Teetz

Measures for Reducing Noxious Exhaust Emissions

in High-speed, High-performance Diesel Engines

Symposium "Motor 2000"

Amsterdam

November igg3

Introduction

If one considers the material and energy iised during the manufacture and

oper-ation of a diesel ehgine, one will see that the diesel engine is a relatively

environmentally friendly machine over the length of its service l i f e , figore 1

• Environmentally safe materials such as cast iron, steel and aluminum a r é

machined (asbestos ahd cadmium are replaced).

• Conventional manufacturing procedures, environmental aspects can be

controlled;

• High proportion of recyclable materials;

• Long service l i f e ;

• High thermal efficiency.

(25)

Exhaust from Diesel Engines

The exhaust of internal-combustion engines contains components which are - or

may be dangerous to man and the environment. Legislators therefore define

-or are in the process of defining - different limits f-or the various

applica-tion areas; this process is not yet concluded but i s , rather, presently a very

dynamic one.

The components of the exhaust from a diesel engine must be evaluated,

figure 2:

molecules of Ng, Og and HgO are already present in the atmosphere and can be

considered non-harmful. CO2, also a natural part of the atmosphere, presents

a borderline c a s é : i t is not poisonous, however. It contributes to the

"green-house effect" as its c ö n c e n t r a t i o n in the atmosphere rises. CO, NOx» ^'^

and particulates (primarily carbon) are noxious.

The harmless compohents of diesel exhaust. Including COg, amount to 99.8% by

yolume, figure 3. It should be pointed out that a l l the noxious emissions

amount to only about 0.2% of the total volume. This very small portion of

individual components must be f ü r t h e r reduced. Of this 0.2%, the nitrous

oxides form the largest portion.

The affects of the individual noxious elements d i f f e r . To avoid injury to man

and prevent damage to t h é environment, such noxious elements should be

reduced, figure 4:

• Hydrocarbons form smog ahd can also cause cancer.

• Sulphur dioxide is essentially responsible for acid rain.

• Carbon monoxide is poisonous.

• Particulates - carbon soot - carry toxic agents anci can cause cancer.

• The nitrous oxides NO and Wz are toxic, form smog and participate In the

formation of acid rain.

There are primarily two mechanisms which create the noxious components in

die-sel exhaust, figure 5: CO, HC and particulates result from Ihcoiiqplete

combustion; SO2 and NOx caused by undesirable secondary reactions during

the thennal process.

(26)

Exhaust Legislation

Limits for diesel exhaust have been discussed for about 15 years.

For marine engines, legal limitations have been decided on recently for various

regions, figure 6. Switzerland's Federal Transport Institute (BAV) has

prepared legislation for marine engines with output power exceeding 100 kW

which will implemented for 1994.

The NOx liniit of 10 g/kWh planned for 1994 does not p r e s é n t an unsoivable

challenge for the development of diesel engines. This l i m i t w i l l also be

implemented for Lake Constance - located between Switzerland, Austria and

Germany - however, In 1993.

In California, limits will be implemented for 1995; the discussion is not yet

finished.

Exhaust limits are also being discussed for implementation i n 1996 for

inter-national waters. The target Is to reduce NOx emissions by 30% t i l l the year

2000.

For trucks, (figtire 7) frc>m 1995 on, the limits for the ÉCE 13-step test of

Euro II will have to be met: NOx ^1^^ have to be less than 7 g/kWh, CO less

than 4 g/kWh and HC will have to be under 1.1 g/kWh, and particulates will

have to be below 0.15 g/kWh.

It is to be expected that the exhaust-emission limits for the truck on the road,

diesel locomotives on r a i l s and vessels on inland waterways or near the coasts

w i l l be treated similarly, that i s , the limit figures will tend to approximate

one another as time passes.

The strictest limits at the moment are those of the german "TA-Luft" for

stationary diesel plants, figure 8. The limits were made originally for boiler

plants and are, therefore, referenced to the standard cubic meter o f exhaust

gas, contrary to other applications. The largest restriction taking effect

during the period between 1986 and 1994 will concern the NOx U m i t , a

reduction from 4 to 0,5 g/m^ standard a i r .

(27)

Even today, the permissible proportion of noxious components in the exhaust of a

diesel engine is considerably restricted.

The tendencies in exhaust-emission legislation can be summarized as follows,

figure 9:

a Further r é d u c t i o n of limits for noxious emissions are already subject to

limitation, that Is, NOx, ^h<i particulates,

• Introduction of limits for noxious emissions not presently restricted: SOg

and PAH (polycycUc aromatic hydrocarbons)^

• Reduetion of CO2 (greenhouse effect),

• Spreading of legislation to cover additional application groups,

• Introduction of International l i m i t s .

If the exhaust emissions from MTU diesels are compared with the TA-Luft limits

for stationary plants, i t can be seen that engines which have been "exhaust

optimized" already have emissions which are below the limits presently In

force, figure 10.

The path MTU followed to f u l f i l l the TA-Luft restrictions is explained in

figure 11. The basis is a Series 595 engine Which had been optimized for

consumption and performance, built for NTU's Class IDS application, that i s ,

for fast vessels. The NOx emissions represent 100% In the figure.

By altering

• the compression ratio,

• combustion-chamber geometry, and

• the injection system - particularly by delaying the start of injection,

the NOx emissions were reduced to 50% of the original value. The diagrams

show the consequences on cylinder pressure and heat release during the

combustion process. Specific fuel consumptioh suffered as a result.

Some features of the strategy which was worked out for this application can be

applied to other applications, such as ships.

(28)

The situation Is aggravated by the fact that the limits must not be exceeded

during the drive cycles required for applications like ship, locomotive and

trucks.

In order to f u l f i l l future emissiori limits, i t will be necessary to design a

diesel engine which provides favorable prerequisites for low noxioiis exhaust

emissions. In principle, measures within as well as outside the engine are

possible, figure 12.

With the engine-internal measures, the formation mechanisms in the combustion

chamber are influenced, that Is, the creation of the noxious component is

inhibited by:

• Influencing the gas flow In the crombustion chamber,

• Manipulating the injection parameters,

• Adapting the combustion-chamber geometry, and

• Altering the composition of the combustion a i r .

After treatment of the exhaust gas Is one of the engine-external measures;

noxious exhaust components already formed are reduced in a system downstream

of t h é engine. Because of the special problems relating to the emission of

NOx, particular attention i s given to the reduction of this noxious component

Ejnglne-Internal Measures

With the engine-internal measures, one must differentiate between the

Implementation of conventional and unconventional technologies. Among the

conventional technologies are those measures which have already been long

employed in the development of combustion methods and which have been

introduced into series engine production:

• Adaptation of the combustion chamber;

• Modification of the injection system;

• Adaptation of combustion-chamber swirl.

(29)

The influence of swirl on the emission o f NOx 1s shown in figure 13,

Combustion methods with high swirl, i . e . a high'tangential flow around the

axis of the cylinder, do not promote the reduction of NOx emission. If a

high-performance injection system is used. It is possible to reduce the

emission of NOx reducing the amount of swirl - without increasing

fuel consumption.

Under "unconventional" technologies we mean supplementary measures, some of

which involve considerable additional development effort as well as greater

expense in manufacture and operation of the engine for example:

• Water injection,

• Exhaust recirculation.

Figure 14 illustrates the effect of water injection.

Water is injected into the combustion chamber through a supplementary

injection system before combustion takes p l a c é . Vaporization of the water

lowers the temperature of the cylinder charge, and the resulting steam also

acts as an inert gas. NOx emission can be reduced by 40% without loss of

operating efficiency.

Water can also be injected into the combustion chamber through inlet a i r pipe

or with a fuel/water emulsion.

Testing in MTU's "pre-development" f a c i l i t i e s has shown that the three methods

are roughly equivalent in reducing NOx. emulsion has the additional

advantage that i t has a positive effect on the production of black smoke.

This method is s t i l l in the pre-development stage.

Trials with exhaust recirculation are presently being prepared at MTU,

figure 15. The figure shows data published by Ricardo. With a constant fuel

consumption, the NOx emissions can be reduced by 50%, however the production

of black smoke is a problem.

(30)

Engine-External Measures ^

In order to be able to f i i l f i l l the s t r i c t exhaust-emission limits which are

planned to be imposed by TA-Luft from 1994 onward for stationary plants,

diesels will have to have a exhaust aftertreatment system,

MTU is currently (figure 16) working on a project for the entire Daimler-Benz

concern. Its purpose is to optimize such a system; i t consists primarily of a

particulate f i l t e r , SCR catalytic converters and an oxidation catalytic

converter. Nitrous oxides are reduced with the aid of ammonia.

This method could also be employed with vessels where the weight and volume

of the propulsion plant are not of extreme importance. Good results have been

achieved with various types of catalytic converters, figure 17. Their behavior

d i f f e r s primarily as a function of the converter temperature. The greatest

conversion is reached with a catalytic converter made with elements of

solid-extruded catalytic material for which the conversion rate is over 95%.

The particulate f i l t e r Is biiilt of four chambers in which rod elements wound

with ceramic yarn are located, figure 18. Regeneration i s electro-thermal.

The particulate f i l t e r is not yet ready for series production because:

• regeneration has not beén solved satisfactorily, and

• with continued use, ash particles which carinot be regenerated are deposited

in the f i l t e r and cause excessively high exhaust back pressure.

Figure 19 shows the effectiveness of SCR technology and the particulate

f i l t e r . With SCR technology, the emission of NOx held below the limit of

500 mg per cubic meter of standard a i r . With the aid of the particulate

f i l t e r , a spot concentration below 20 mg per cubic meter of standard air can

be achieved; further development of the particulate f i l t e r i s , however,

necessary for the reasons stated above.

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8 Concept for Combustion Developments

À concept for combustion development based on the legal parameters and

engineering potential has been worked out at MTU, figure 20:

• Operation without exhaust-emission limits

- Target

It is to be expected that differing exhaust emissions will be prescribed for

different applications and regions. For segments of the market, there will be

no limitation, even in the future. In such cases, the engines can be optimized

for fuel consumption.

For applications with unrestricted exhaust emissions, optimum fuel consumption

of <190 g/kWh will be achievable under acceptable exhaust figures.

- Measures

Consistent further development of the engines with regard to potential peak

(combustion) pressures, supercharging efficiency and combustion quality.

• Stationary applications

- Target

In stationary applications, TA-Luft imposes a limit of 500 mg/m^ standard air

for NOx ^''om 1994 onwareï.

Further restrictions are to be expected in Germany; it can already be assumed

that this strict limit will be introduced regionally but not worldwide

-diiring the next ten years.

- Measures

Operation below this figure can be achieved only by using exhaust gas

after-treatment; the engines will be optimized for fuel consumption.

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• Ship, locomotive and truck application

- Target

I expect that the NOx limits for these applications will be set in the

area of 6 to 10 g/kWh and can be fulfilled by 1999 under consideration of

representative load profiles. After the year

2000,

the NOx Umit will lie

below 6 g/kWh.

- Measures

It is desirable that this limit be reached by engine-internal measures while

maintaining acceptable fuel consumption figures. If CO2 emission is taxed,

it may be advisable to meet this limit with engines optimized for fùel

consumption and Install a exhaust gas aftertreatment system. In this regard,

it should be mentioned that the addition of a exhaust gas aftertreatment

system considerably increases both the weight and the Installed volume of the

drive system. Especially in applications in which a customer requires small

overall dimensions and a high power-to-weight ratio, disadvantages result for

the diesel engine if exhaUst gas aftertreatinent is necessary.

Exhaust gas aftertreatment will be optimized on a test stand for complete

engines; the potential for engine-internal measures is determined on three

single-cylinder engine test stands. After the goals are reached with

pre-prototype engines, economical concepts for series engine production must

be developed.

(33)

10 Summary

• It is safe to assume that legislation for exhaust emissions Will be stricter