Energy Flow Modeling

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The Environmentally Friendly Ship, 28 - 29 February 2012, London, UK

2011: The Royal Institution of Naval Architects

FUEL CONSUMPTION AND AIR EMISSIONS PREDICTION BY ENERGY FLOW

MODELING ONBOARD SHIPS: APPLICATION ON A MODERN BULK CARRIER SHIP

K. Chatzitolios, Bureau Veritas, FranceM. Claudepierre, Bureau Veritas, France

A. Leblanc, Bureau Veritas, France

SUMMARY

Energy efficiency and air pollution prevention are the two main driving forces for future ship designs. A number ofsolutions for reducing fuel oil consumption and air emissions are presented in the paper and a possible ranking of energy

saving measures and NOx reduction measures is proposed. The challenge that is faced by designers today is to optimally

combine some of these measures in order to obtain a fuel efficient and environmentally friendly ship.

With this in mind, Bureau Veritas has developed a ship modeling platform (SEECAT) to effectively simulate the

different energy systems (diesel engines, propulsion system, steam production, cooling system, waste heat recovery etc.)and the energy transformations shared between them (fuel, heat, steam, mechanical power). The simulation is performed

in time domain according to a pre-selected operational profile allowing for real time monitoring of fuel consumption and

of CO2, NOx and SOx emissions.The methodology of component-oriented modeling is described in this paper and theenergy model of a bulk carrier is presented. The results of comparative simulations for the given model are analyzed andthe potential uses of energy flow simulation in the optimization of ship design are also discussed.

1. INTRODUCTION

1.1 ENVIRONMENTAL REQUIREMENTS

The requirements for the environmental performance of aship are wider than the objectives of just CO2 reduction.

The scope of emissions reduction shall also embrace the

existing and forthcoming environmental regulations,

including the additional environmental requirements for

NOx, SOx and PM emissions.

1.2 EXHAUST GAS EMISSIONS FROM A

TYPICAL MARINE DIESEL ENGINE

Marine diesel engine exhaust gases contain oxygen,

nitrogen and carbon dioxide (CO2) which are produced

from the combination of fuel with the oxygen duringcombustion. They also contain water vapour form

reaction between the hydrogen in the fuel and the oxygen

in the scavenge air and carbon monoxide (CO) produced

by the incomplete combustion of the fuel. There is also

sulphur dioxide (SO2), generated by the reaction of

sulphur present in the fuel and oxygen, and nitrogen

oxides (NOx), produced during the combustion process

at high temperature between nitrogen and oxygen. Some

hydrocarbons and volatile organic vapours are also

present in small quantities as a result of imperfect

combustion.

The exhausts gases of a typical marine diesel engine

contain also a mixture of solids carbons, soot, ash, heavy

metals, precipitated sulphur oxides, corrosion particles

and partially combusted hydrocarbon from fuel and

lubricating oil. These derivatives are all classed as

Particle Matters (PM).

1.3 POLLUTANT EMISSIONS REGULATIONS

IN THE MARINE INDUSTRY

International regulations have been put in place for the

shipping industry by the United Nations, in order to offera consistent scheme to the Maritime community. The

United Nations Marine Branch, the International

Maritime Organization, has encompassed the pollutant

and GHG regulations in the Annex VI of the MARPOL

73/78, which stipulate the regulation for the exhaust gas

emissions (NOx, SOx, PM and CO2).

Since July 2011, the consolidated MARPOL has

included in Annex VI, additional regulations on CO2,

under the name: Regulations on Energy Efficiency for

Ships. These new regulations, described later on the

paper, will enter into force for new and existing ships onthe first of January 2013.

Other regulations on emissions reduction include,

amongst others, the EC Directive 2005(33), California

Air Resources Board (CARB), EPA, and local

jurisdictions such as Port Administrations.

1.4 NOx EMISSIONS LIMITS (IMO)

The Annex VI provides a step by step approach to reduce

the emissions of NOx in a three Tiers approach1. The

original emission limit is referred to as Tier I, the current

is the Tier II which entered into force in 2011 while the

third, Tier III, will be introduced in 2016. The NOx

limits of Regulation 13 of MARPOL Annex VI for the

three Tiers are given in Table 1.

1

Applicable to all Diesel engines with a power outputgreater than 130kW but excluding engines used in

emergency situations.


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Table 1: IMO NOx limits.

Tier Date NOx limit (g/kWh)

N


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In order to simplify the administrative tasks for crews, it

is recommended that the monitoring of the ships EEOIshould be carried out by shore staff, utilizing data

obtained from existing required records such as the

official log-books and oil record books.

The basic expression of the EEOI for a voyage is givenbelow:

Dm

CFC

EEOI

oc

j

Fjj

=

arg

(1)

When calculating the EEOIfor a period or for a number

of voyages the following expression may be used:

)(

)(

argi

i

ji

Dm

CFC

EEOI

oc

Fjij

=

(2)

Where:

j: is the fuel type

i: is the voyage number

FCi j: is the mass of consumed fuel j at voyage i

CFj3: is the fuel mass to CO2 mass conversion factor for

fuel j

mcargo: is the cargo carried (tonnes).

D: is the distance in nautical miles corresponding to thecargo carried.

2. AIR POLLUTANTS REDUCTION

MEASURES

2.1 GENERAL

The following paragraphs list the most common

technologies available today for reduction of polluting air

emissions and GHGs. It is important to note that a wide

approach should be considered when targeting in

emissions reduction measures as some solutions for CO2

or NOx reduction technologies may be detrimental toother environmental issues and should in any case not

impair the ships safe operation. Therefore before

adoption of a given emission reduction device, it is

necessary to check if there is a risk of transferring

environmental impact from one form to another.

2.2 NOx REDUCTION MEASURES

Emissions of NOx from diesel engines can be reduced by

a number of measures, addressing the mitigation of peak

combustion temperatures, minimizing the combustion

3 Considered according to IMO MEPC.1/Circ.681, dated

17 August 2009.

period where gases are at their highest temperatures and

minimizing also the concentration of oxygen presentinitially in the charge air.

These measures may include and combine fuel and water

emulsion, modification of the charge air such as

humidification (HAM), exhaust gas recirculation (EGR)

and modification of the combustion process such as theMiller timing.

Another way to reduce NOx emissions is by post

treatment of the exhaust gasses (i.e. selective catalytic

reduction).

The choice of one technology amongst others willdepend on the type of engine (2 strokes or 4 strokes) and

the targeted NOx reduction, keeping in mind that the

performance of the engine may be also affected resulting

in higher CO2 emissions4.

2.2 (a) Selective Catalytic Reduction (SCR)

The principle behind SCR is, as a post treatment method,

to inject ammonia (NH3) in the exhaust gases, and drive

them on a bed of specific catalytic components, at a

specific temperature, in order to combine NOx with NH3

to produce benign nitrogen and water. The amount of

ammonia needed depends on the amount of NOx

produced and consequently on the engine load. For easier

storage and safety, the ammonia can be stored as urea

and dissolved in water before use.

2.2 (b) Exhaust Gas Recirculation (EGR)

This method is already in use for a while on cars and

trucks using 4 stroke Diesel engines. The principle

behind EGR is to cool and recirculate part of the exhaust

gases, which contain oxygen, water and carbon dioxide.

The produced inert gas (water and CO2) will absorb heat

during the combustion and increase the heat potential of

the cylinder charge, thus reducing the temperature during

combustion. Also the reduced oxygen content of the air

present in the combustion chamber is also contributing toreduce the combustion temperature and so the NOx

combination. The two processes work together to

globally decrease the combustion temperature which

lowers the produced NOx. However this method needsclean fuels or intermediate scrubbing, in order to avoid

potential issues caused by internal cylinder deposits frompollutants included in the recirculated gases. This process

may require up to 40% recirculation of the exhaust gas.

EGR are claimed from engine manufacturers to reach a

NOx level reduction up to 80-90% (some are coupled

with a water mist system), thus enabling new generation

engines to comply with Tier III requirements.

4

Generally, the NOx and CO2 emissions are in counterbalance, with the decrease of the first leading to the

increase of the other and vice versa.


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2.2 (c) Water In Fuel

The principle behind the so called wet method of

reducing NOx is to add water in the fuel, and to provoke

their emulsion. During combustion the water is

evaporated and the moisture helps to cool down the

combustion chamber.This process is already in use today. If considered as aretrofit measure, its application may require some

modifications, as for example the injection pump and the

fuel injectors might need to be replaced because for the

given power output the amount of injected liquid

increases.

This process is recognised to be able to reduce NOx

emissions up to 30%.

2.2 (d) Humid Air Motor (HAM)

The principle is similar as above but with thehumidification instead of the scavenge air. This process

increases the inert gas fraction heat capacity and lowers

the oxygen content. As a result, the combustion is slower

and the combustion temperature is reduced. The SFOC is

almost unaffected.

The total NOx reduction is up to 40%, however this

reduction is diminished at full engine load and at low

loads. The water consumption is higher than for direct

water injection, and very clean water is required in order

to avoid fouling and corrosion of charge air compressor

and air duct system. Also, the waste heat recovery

potential is affected and less cooling water heat isavailable for the production of clean water. Corrosion

can occur in the air duct system with high sulphur fuel

(>3%).

2.2 (e) Miller Process

The principle behind this method is to close the inlet

valve before the piston reaches bottom dead centre. The

expansion of the scavenging air in the cylinder generatesa lower air temperature. The target is to obtain a lower

gas combustion temperature. As already mentioned, the

higher the combustion gas temperature, the larger the

quantity of generated NOx. The reduction of NOxemissions obtained by the Miller principle is up to 15%-

20%.

2.2 (f) Direct Water Injection

The principle is to inject water directly in the cylinder

through a dedicated independent injection system. It

enables the engine to receive large amount of waterwithout compromising the power output.

Advantages are a low water consumption compared to

HAM, and the water quality is less crucial. Also the air

duct system can be left unaffected without risk ofspecific corrosion. The heat recovery potentiality is not

affected by the system and there is a good long term

experience with low sulphur fuels. But there is an impacton the fuel consumption, and the system is more

complicated compared to Humidification Air Motor.

Piston top and injector may be impacted by corrosion

with high sulphur fuels (>1.5%).

A high NOx reduction level up to 50% is achievable.

2.3 RANKING

In order to class and benchmark the different types of

NOx reducing systems the following ranking is

proposed. It gives an order of magnitude of potential

NOx emissions reduction in percentage.

Table 3: NOx rating grades

Letter Order of magnitude in NOx reduction

A NOx Reduction > 80% (Tier III)

B 50%< NOx Reduction < 80%

C 20%< NOx Reduction < 50%

D NOx Reduction < 20%

Table 4: Rating of NOx reduction measures

NOx emissions reduction devices Potential

emission

reduction

Selective Catalytic Reduction (SCR) A

Exhaust Gas Recirculation (EGR) B

Water in Fuel C-

Humid Air Motor (HAM) C

Direct Water Injection (DWI) C+

Miller process D

2.4 SOx REDUCTION MEASURES

2.4 (a) Scrubber

Exhaust-gas scrubbing system can be employed to reduce

the level of sulphur dioxide. Two main principles exist:

open-loop seawater scrubbers and closed-loop scrubbers.

Both scrubber concepts may also remove PM. Scrubbing

of exhaust gases requires extra energy estimated between

1 to 2% of the engine nominal power.

Particulate matters (PM) which are caught in the

seawater have a significant environmental impact if

released in the sea. The IMO fix limits and Port State

requirements for effluent discharges may also impair the

future use of open loop seawater scrubbers.

2.4 (b) Low Sulphur Fuels

Low sulphur fuel obtained by blending HFO with diesel

fuels is the most effective way to reach the IMO and EU

levels without adding expensive and complicated

devices. However, the risk of uncertain availability fromrefineries, high price associated with a need for


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additional installations on-board for low sulphur fuel,

and to inject additive for lubrication of the injectionpump for example, also using different lube oil for the

engine, make this solution not desirable by many.

LNG as a fuel is an appropriate solution because of the

absence of sulphur emissions. (Sulphur present in theextracted methane is eliminated during the liquefactionprocess). It has the advantage to produce less GHG

emissions than conventional fuels, even though the 22%

lower CO2 emissions is reduced to 16 to 20% lower net

greenhouse gas emissions due to methane slip (which

depends on employed engine technology).

3. GHG REDUCTION METHODS

GHG emissions can be reduced either by reducing the

fuel oil consumption (i.e. by improving the energy

efficiency) or by the use of low carbon fuels such as

LNG.

3.1 ENERGY EFFICIENCY IMPROVEMENT

METHODS

There are many different practices and technologies for

saving energy on-board a ship and thus reducing GHG

emissions. Those measures can be classed in three

categories:

The operational measures, or best practices, such asslow steaming and arrival just in time.

The maintenance level improvement measures, notimpacting on the design and integrity of the ship,

such as hull cleaning and propeller polishing.

The technical measures, impacting on the design, byadding Energy Saving Devices components to the

installations (such as the Engine) or outside the hull

(propeller optimisation for example).

Hereafter some of the Energy Saving Devices are

presented and classed in a tentative ranking which is

based on literature and experience feedback.

3.1 (a) Operational Measures

Slow steaming: is the adoption of a lower speed for an

existing ship. The potential of energy saving is large, as

much as 30% depending on initial design speed and

speed reduction order of magnitude. However the

potential to reduce speed is not limitless. It is not

recommended to operate engines at low load without

adjustments under the engine manufacturer control. The

minimum load depends on the technical specification of

the manufacturer for each individual engine.

Electronically controlled engines are more flexible and

can generally be operated at lower loads than

mechanically controlled engines. Where it is intended tochange the operating conditions of the propulsion plant,

it should be ascertained that the propulsion plant is free

from harmful torsional vibrations throughout the entireoperating speed range of the engine. NOx emissions

may also be affected. In addition, there are commercial

and minimum safe speed considerations which

complicate the matter further, but these are out of the

scope of this paper.

Weather routing systems: are widely used by owners

for a long time. It is therefore estimated that the saving

potential is not more than 2 % for most realistic scenarios

from what is already a widely spread practice nowadays.

Also the saving potential largely depends on the trade

route.

Just in time arrival: the objective is to ameliorate the

communication with the next port to call in order to get

the maximum notice of berth availability and thus

facilitate the use of optimum speed.

(Model test or CFD based) Trim optimization: trim

optimization tools are based on model test results, large

measures on-board campaign and/or CFD calculations of

large set of different combinations of draught, trim and

speed. It improves the efficiency of the operation of the

ship. However, when based on model tests results and/or

CFD simulations, it is recommended that such

application to be consolidated by a sea test campaign of

the ship, or from a reference ship to validate the expected

saving potential.

3.1 (b) Maintenance Level Improvement Measures

Regular maintenance of hull and propellers increases the

vessel performance by reducing hull fouling and

propeller friction.

Propeller cleaning and polishing or even appropriate

coating may significantly increase fuel efficiency.

Silicone Painting may improve propulsion efficiency by

hull friction reduction. However this type of paint is verydelicate and may be damaged easily, thus impairing the

initial performances.

Fluor polymer foul release coating, associated with acareful dry-docking cycle follow up, may improve the

hull efficiency by minimising the average hull roughnessgrowth, thus minimising the frictional resistance

evolution.

3.1 (c) Basic Optimization Techniques (CFD)

The use of CFD code computation studies for optimisingthe ships hydrodynamic performances can be done

during the design process of the ship with a wide range

of possibilities, or after its building due to changes of

displacement, trim or speed leading to non-adapted

bulbous bow or stern shapes.


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A propeller with hull integration study consists in a

parametric CFD study in order to optimise the thrustdeduction factor and the wake. Stern shape and propeller

location may also be studied. The expected gain can be

up to 10% depending on the stern hull shape.

3.1 (d) Energy Saving Devices on Propeller

CLT propeller: principle is to fix endplates fitted with

minimum resistance in sight of higher efficiency and

lower vibration and noise level.

Propeller Boss Cap Fins: the principle behind is to

break up the hub vortex, thus reducing the energy losses.

Mewis duct: is a combination of a pre-swirl stator and

wake equalizing duct. It has a power reducing potential

up to 4 %.

Pre Swirl Stator: is composed of a fixed set of bladespositioned upstream of the propeller. The blades have

different pitch angles. It affects the inflow by reducing

the rotational losses, also having a positive effect on the

wake.

Contra-rotating propellers: combine recuperation of

rotational energy losses with better propeller loading.

However, contra-rotating propellers also have larger

areas in general, and more bearings losses. In addition

the mechanical complexity makes the decision to install

contra-rotating propellers very difficult. The potential

gain is recognised to be about 4%.

3.1 (e) Waste Heat Recovery Systems (WHR)

A waste heat recovery system uses thermal heat losses

from the exhaust gas for either electricity generation or

additional propulsion with a shaft motor. It is generally

installed on the main engine. This is the most potentially

efficient system for improving the energy efficiency of a

2 stroke engine propulsion system. It is also positively

used on-board large cruise vessels having 4 strokesengines and electric plants for providing extra power or

steam to propulsion and hotel loads.

It is estimated that fuel savings of 8% can be obtained byenergy recovery from exhaust gas. For ships with PTI,

the saving potential is estimated at 10%.

3.1 (f) Engine Tuning

Optimised electronic engine control will use the

potentials of common rail injection and two stage turbo

charging to improve engine efficiency in the whole rangeof operation. However, the engine improvements are

currently dominated by the upcoming stringer

requirements to reduce NOx emissions. This may act

against fuel efficiency improvement, because of lower

combustion temperatures and increased back pressurefrom exhaust gas cleaning systems.

3.1 (g) Variable Turbine Area (VTA)

The principle is to use a variable turbine area that will be

extended to a larger range of loads, specifically at part

load and low load. The variation of area extends from a

minimum and progressively increase until the scavenging

air pressure reaches its normal MCR value.

3.1 (h) Turbocharger Cut-Out

It is applicable mostly to larger engines with two to four

turbochargers; this option is based on cutting out one of

these units in the lower load range. In contrast with

exhaust gas bypass, there is thus no fuel consumptionpenalty in the high load range as all turbochargers are in

operation. The cutting-out or cutting-in of a turbocharger

has to be effected with the engine at dead slow or

stopped.

3.1 (i) Exhaust Gas Bypass (EGB)

The principle is that a small turbocharger is more suitable

for the engine at low load, thus reaching normal MCR

scavenging air pressure at a partial load. Above the

chosen partial load, the exhaust gas is bypassed so that

the scavenging air pressure will not exceed the normal

MCR value.

3.1 (j) Engine Derating

The principle is to derate the installed propulsion power

in order to save fuel. If the same speed is to be

maintained as before then a more powerful engine shouldbe chosen (performed only in the design stage) otherwise

the ship speed will decrease accordingly (performed for

ships in operation). In the latter, a minimum power is to

be maintained for safety reasons to ensure

manoeuvrability and course keeping capability in adverse

conditions.

3.2 LOW CARBON FUELS

LNG contains more hydrogen and less carbon than fuel

oils, since the carbon factor of methane (CH4) is lower

than diesel oil or heavy fuel oil, so emissions of CO2 are

reduced. However, methane slip5

can generateinvoluntary emissions of unburned gas which will reduce

the GHG reduction due to the Global Warming Potentialof methane generally acknowledged as much as 20 to 25

times equivalent to CO2.

3.3 RANKING

In order to class and benchmark the different types ofenergy saving measures among others, a ranking is

proposed. It gives an order of magnitude of potential

5

Methane slip is the incomplete combustion of methanein the cylinders and the consequent release of unburned

methane in the atmosphere.


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energy saving in percentage. The grades are based on an

analysis of the available claims and results in the publicdomain crossed with experience and sea proven

feedbacks and reviews from the authors.

Table 5: Energy saving grades

Letter Order of magnitudeA Saving > 20%

B 10


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The hull efficiency, nh, is calculated as follows:

w

t

h

=

1

1 (3)

The wake fraction coefficient w and the thrust deduction

coefficient t may be calculated with an empirical methodor can be input directly by the user. Then the

hydrodynamic performance of the propeller is computedby the propeller module which derives from the

dimensionless thrust (KT) and torque (KQ) parameters,

the torque (Q), thrust (T) and the rotary velocity (n) to be

delivered to the shaft module:

42Dn

TKT

= (4)

52Dn

QK

Q

= (5)

Where D is the propeller diameter and the water

density.

The propeller efficiency n0, is then calculated by the

following expression:

JK

K

Q

T

2

10 = (6)

And the advance number of the propeller is expressed:

nD

VaJ= (7)

Where Va is the speed of advance of the propeller.

To take into account the interaction between the hull and

the propeller, the power delivered from the engine to thepropeller (PD) is connected to the effective power (PE)

needed to drive the vessel with the following expression:

PE=PD nhn0nr8, (8)

Where nh is the hull efficiency, n0 the propeller efficiencyand nr is the relative rotative efficiency.

The required engine power (PS) is then calculated by the

expression:

PS=PD/ns (9)

Where ns is the shaft efficiency.

With the estimation of the required engine power, the

main engine load is calculated and thus the fuel oil

8 The product nhn0nris usually referred to as QPC(quasi-

propulsive-efficiency)

consumption and the exhaust gas emissions (exhaust

mass flow of CO2, NOx & SOx). The fuel consumptionis calculated via the brake specific fuel consumption

(BSFC) curve which is a function of the engine load. A

correction ratio is used to adapt to the specific

characteristics of the fuel. The global efficiency is

calculated by the expression:

= 1/(LHV x BSFC) (10)

WhereLHV9

is the Low Heat Value of the fuel andBSFC

is the Brake Specific Fuel Consumption.

Account for losses calculation is also made. The thermalpower given to the cooling circuit is calculated and can

be reused for water production, or preheating needs. The

exhaust gasses from the engine can be reused for energy

production according to their heating potential.

4.2 ELECTRICITY NETWORK MODELING

The tool emulates the electricity need considering several

operating modes. The electricity need (Pload) isdetermined by the electrical balance given for each

operating mode. The rated electric power (Pr) is adjusted

by the service total factor of use (ku) for the different

operating cases, so that Pload = Pr x ku. The navigation

module indicates for each calculation step the actual

operating mode and the electricity module selects the

corresponding service factor which is multiplied by the

total power which corresponds to the electrical powerneed. The electrical power need is transmitted to the

electrical producers, the diesel generators (diesel engineand alternator). The load of the engine is adjusted to

achieve the electrical power required by the ship. A PMS(Power Management System) module calculates the

auxiliary engine load to achieve the necessary power. It

can also select the number of engines in operation and

their corresponding load.

4.3 STEAM NETWORK MODELING

The tool emulates the steam need considering several

operating modes. The steam need (Qsteam) is

determined by the steam balance given for each

operating mode. The rated steam mass flow (Qr) isadjusted by the service total factor of use (Lf) for the

different operating case. The navigation module indicates

for each calculation step the actual operating mode of the

ship and the steam module chooses the corresponding

service factor which is multiplied by the total mass flow.

The required mass flow is then calculated as Qsteam =

Qr x Lf.

The required steam is transmitted to the steam producers.

The priority is given to the exhaust gas operation of the

9 Considered for this paper with the value: LHV = 42,700

kj/kg


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composite boiler10. If the waste heat recovery steam

production is enough to supply the steam need, the boileris not using fuel to operate (this is usually the case for

regular sailing operation). The waste heat recovery boiler

steam production is determined by the load of the main

engine. When the steam production from the waste heat

recovery boiler is not sufficient, the boiler can supply thedemand. The production depends on the load of the

boiler. The fuel consumption of the boiler is determined

by the boiler efficiency taking into account the

combustion efficiency and the efficiency recovery from

the exhaust gases into the chamber.

In the same logic as the one described above, everyphysical component of the ship which interacts in the

various energy transformations and consequently affects

the overall efficiency (and emissions) of the ship could

be modeled.

5. CASE STUDY

Some of the optimization steps described in Section 3

have been applied on a 57,500 Tons bulk carrier(designed in 2008) using the energy flow calculations

described in Section 4. The main particulars of the ship

are presented in Table 7.

Table 7: Main particulars of the case study vessel

Length over all (Loa) 219.80 m

Length between perpendiculars 212.00 m

Moulded breadth 32.26 m

Moulded depth 16.40 m

Design draught 11.22 mDeadweight at design draught 57,500 t

5.1 BASIC OPTIMIZATION TECHNIQUES

During the concept design stage, the resistance of the

ship is estimated using the design characteristics which

are available at this stage of the design11. These include

the initial lines plan of the vessel and a chosen propeller

of D=6.5m in diameter. The design speed of the ship is

considered at 14kn at the laden draft of 11.22m.

The resistance prediction calculations are performedaccording to the Holtrop & Mennen methodology for a

range of speeds [4], [5]. The resulting resistance for each

speed is presented in Table 8.

10In the case of the bulk carrier model used in the study,

a composite boiler is the only steam producing unit.11 At this point it is assumed that no hull form

optimization has been performed using CFD calculationsor model tests. Accordingly, the speed-power curves of

the ship are not yet available.

Table 8: Total resistance Rt for each ship speed Vs

Vs [kn] Rt [kN]

11 417

11.5 458

12 502

12.5 55013 603

13.5 661

14 726

14.5 800

15 882

15.5 974

16 1078

The wake fraction coefficient w, the thrust deduction

coefficient t and the relative rotative efficiency nR can be

estimated with various methods or can be provided

directly based on similar designs. In this case, the

Holtrop & Mennen prediction formulae are used [4], [5].

The open water efficiency n0 of the propeller is

calculated for a B-series propeller and the shaft

efficiency is taken at 0.99. The shaft power Ps and the

relative propeller (and engine) speed N is then calculated

for every ship speed.

The resultant propeller curve (Figure 1) corresponds to a

light running propeller (LR) for a clean hull and a calm

sea [6]. Since this condition is only comparable to the

ships sea trials, it is common practice to incorporate an

additional 15% power margin12 which reflects the added

resistance due to weather conditions. The propeller curve

corresponds now to a heavy running propeller (HR) and

this condition is analogous to the real operation of the

ship. The two curves are depicted graphically in figure 1.

For the desired ship speed of 14kn, the required shaft

power is estimated at Ps=8,188kW and N=87.1Rpm and

this operational point on the heavy running propellercurve corresponds to the engines CSR (continuous

service propulsion point). By adding another 15% engine

margin13 we arrive on the engines SMCR (specified

maximum continuous rate). Based on this point

(Ps=9633kW, N=91.7Rpm) the selection of the engine is

now possible and in this instance the MAN 5S60MC-C8

is chosen. In figure 1, the above mentioned engine pointsare shown together with the engines layout diagram and

SFOC14 [7].

12 This power margin is often referred to as the sea-

margin and can vary depending on the ship type. It will

also account for a fouled hull and propeller for the in-

service operation of the ship.13 It is common practice to add this 10%-15% operational

margin for the engine.14 SFOC data used in this study correspond to ISO

Ambient Conditions.


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Figure 1: Propeller and engine matching

With the information acquired up to this point (speed-power curves, propeller characteristics & engine), the

initial energy model of the ship is created using SEECAT

(Figure 2). The daily FOC (Fuel Oil Consumption) of

the ship is then calculated with SEECAT at 32.8MT/day

for a laden speed of 14kn and a sea margin of 15% (toreflect in-service conditions). This consumption refersonly to the main engine as at this point the diesel

generators are not yet considered.

Figure 2: Initial energy model

5.1 (a) Optimum Propeller Diameter

With the aim of obtaining the best possible propulsive

efficiency (QPC), the maximum propeller diametershould normally be chosen. Oftentimes the maximum

desirable propeller diameter is restricted due tooperational issues15. In this case, after an investigation of

all possible loading conditions, during the initial design

stage, a propeller of maximum diameter D=6.7m isfinally chosen.

The effect of an increased propeller diameter on the

propeller curves and the CSR and SMCR points is

depicted in Figure 3. As expected, the propeller curves

have been shifted to the left, at the lower Rpm range. Inorder for the ship to obtain the service speed of 14kn, the

15

Generally it is required that the propeller should befully immersed under all loading conditions including

sailing in ballast.

new CSR corresponds now to a power of Ps=8041kW at

N=82.7Rpm (i.e. at 80% of SMCR). Consequently theFOC is now calculated at 32.5MT/day for a laden speed

of 14kn.

Figure 3: Propeller and engine matching for increased

propeller diameter.

5.1 (b) Engine Derating

The next step is to use a more powerful engine, derated

at the same SMCR. In Figure 4 is shown the propeller

and the engine matching points for both the 5S60MC andthe more powerful 6 cylinder 6S60MC.

Figure 4: Propeller and engine matching points for the 5

and 6 cylinder engines.

The FOC for the 6 cylinder engine is now calculated at

31.6MT/day for a laden speed of 14kn and the same seamargin of 15%.

5.1 (c) Electronic Engine

The use of an electronic engine at the same SMCR and

SCR that were chosen above (in order to obtain the sameship speed) resulted in a further reduction of FOC. The

FOC with an MAN 6S60ME-C8 engine is calculated at

30.9MT/day [8].

With the optimization steps described in 5.1(a), 5.1(b)

and 5.1(c) an efficiency gain of 5.8% has been obtained

in terms of daily fuel consumption.

5.1 (d) Hull Form Optimization

The computations described previously have been based

on the initial hull form of the vessel for which there has

not been made any optimization attempts using CFDsoftware or model tests. The effect of hull form


11/15



optimization for this particular ship will be presented

hereafter.

During the basic design stage, the initial hull lines have

been examined and optimized with the cooperation of

MARIN with the use of its non-linear potential flow

computer program RAPID [9]. The main aspect of theoptimization consisted of transforming the original V-shaped aft body of the ship to the so-called Hogner

shape, with more pronounced roundings in the bilge of

the gondola and a more narrow upper part of the gondola.

This transformation of the aft part is aiming mainly to the

improvement of the wake field in the propeller rather

than reducing the resistance of the ship. The overalldecrease in the resistance was calculated at around 3%-

4%16 [9].

For the optimized hull form, model tests were performed

by MARIN, comprising of resistance and self-propulsion

tests. The results of resistance extrapolation are given inTable 9 for various ship speeds [9].

Table 9: Results of resistance tests

Vs [kn] Rt [kN]

11 436

11.5 478

12 523

12.5 567

13 611

13.5 658

14 709

14.5 776

15 873

15.5 1000

16 1163

The comparison between the estimated resistance (with

Holtrop & Mennen methodology) of the initial hull form,the measured resistance of the optimized hull form using

model tests and the estimated resistance of the optimized

hull form using again the Holtrop & Mennen method is

presented graphically in Figure 5. The estimated

resistance seems to be in good agreement with the model

test results17

. An underestimation of the resistance

(compared to the model tests) can be observed for shipspeeds below 13.5kn and above 15kn while the opposite

is calculated for the speed range between 13.5kn and

15kn.

16 The calculated wave resistance decreased by 25%, but

for a bulk carrier sailing at a Froude number of 0.16, thewave resistance is about 15% of the total resistance.17 For the given speed of 14kn, the difference is 1.4%.

Figure 5: Comparison of resistance calculation

The final propeller curves for sea trial performance

prediction and for service performance prediction18 that

resulted from the model tests and the relative propeller

open water tests are presented graphically in figure 6.

The SMCR is considered at the lowest possible range for

the 6S60ME engine (Ps=9660kW, N=89Rpm) and the

CSR for a service ship speed of 14kn is taken at 83% ofthe SMCR. With this input, the FOC is calculated by

SEECAT at 30.7MT/day. The fact that the hull form

optimization did not achieve an impressive improvement

in the resistance of the ship and consequently to the

predicted daily consumption, should be attributed to thesuccessful initial design process.

Figure 6: Final propeller curves and engine layout.

At this stage of the design process, the use of any energy

saving device similar to the ones described in 3.1(d)

should be considered. The efficiency gain of any suchdevice ought to be verified with CFD calculations and or

model tests. The verified efficiency gains can then betransferred to SEECAT for further evaluation of the

energy benefits for the ship.

5.2 OPTIMIZATION WITH SCENARIO

ANALYSIS IN SEECAT

With the optimized hull form and propeller and with the

chosen engine it is now possible to perform an energy

optimization approach using scenario analysis. This

optimization process could be performed also for an

18 Including the 15% sea margin relative to the sea trials.


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existing ship in service (i.e. for the purpose of developing

the SEEMP). The analysis requires the use of anavigational profile as an input in SEECAT which will

be analysed based on time domain calculations. For the

ship of this case study, the following navigational profile

is considered (separated in three legs):

1. In the first leg of the trip, the ship travels for7,000nm at the loaded draft of 11.22m from the

port of departure to the port of arrival. At this

draft the payload is estimated at 54,178Ton

2. In the second leg of the trip the ship unloads itscargo at the arrival port.

3. In the last leg, the ship returns to its departureport after traveling for 7,000nm at a mean

ballast draft of 7.92m19.

It is now necessary to create the complete energy modelof the ship, where all the energy consumers (electrical &

steam) should be input in SEECAT for each leg of the

navigational profile described above, together with the

characteristics of the Diesel Generators (D/G) and the

boilers or any other energy producing module (i.e. waste

heat recovery system etc.). For the ship under

consideration, three diesel generators are considered and

one composite boiler. The energy model of the ship is

depicted in Figure 7.

Figure 7: The energy model of the ship.

For illustration purposes, each part of the navigational

profile described above will be considered separately.

For the design speed of 14kn the cumulative FOC for the

first leg of the trip (500 hours) is shown in Figure 8. The

depicted graph concerns only the consumption of the

main engine for propulsion needs.

19 The 3rd leg of the trip has been chosen mainly for

illustration purposes since the ship will eventually spenda large part of its operational life in the ballast condition.

Figure 8: Cumulative fuel consumption of the main

engine for the loaded condition

From the calculated electrical and steam balance in

SEECAT, the total cumulative fuel oil consumption ofthe D/Gs and the boiler is estimated and presented in

Figure 9. From the electrical balance it is estimated that

during normal sailing one D/G is operating at 92% of its

full power20. The total fuel oil consumption is computed

at 699.4tons (for in-service performance prediction

including the 15% sea-margin).

Figure 9: Cumulative fuel oil consumption of the D/G

and the boiler for the loaded condition.

The fuel oil consumption for the second leg of the trip

(cargo unloading) is given in Figure 10. From the

electrical balance, it is estimated that in order to meet the

required electrical demand, two D/Gs are operating at53% of their full load

21.

Figure 10: Cumulative fuel oil consumption of the D/Gand the boiler during loading operations

For the last leg of the trip, the ballasted return, a shipspeed of 14.5kn is considered. The cumulative fuel oil

consumption of the main engine is given in Figure 11,

while in Figure 12 the corresponding cumulative fuel oilconsumption of the D/Gs and the boiler is presented. It is

to be noted that ballast exchange operations have been

considered in the latter case of the return trip. From the

estimated power balance, an increased power demand of

21.9% is calculated compared to the normal sailing

20 Considering also an alternators efficiency of

approximately 92%21

A mean unloading rate of 1200tons/hr has beenconsidered. The given ship does not have own means of

unloading its cargo


13/15



condition, requiring two D/Gs in operation for the ballast

exchange (due to the operation of the ballast pumps). Theincreased fuel consumption during ballast exchange takes

place in the time domain between 300 and 310 hours but

it is not visible in the scale of figure 12.

Figure 11: Cumulative fuel consumption of the main

engine for the return trip

Figre 12: Cumulative fuel oil consumption of the D/G

and the boiler for the return trip

The cumulative NOx and SOx emissions for the

complete round trip (loaded trip, harbour unloading &

ballast return) are presented in Figure 1322.

Figure 13: Cumulative NOx and SOx emissions.

The EEOI is calculated according to (1) for the round trip

at EEOI1=5.64 gCO2/ton-mile.

While this EEOI value has been calculated for only one

trip, the fact that the 3rd

leg of the navigational profile is

chosen as a large ballast trip, of the same miles as the

payload trip, this value could potentially reflect an in-

service EEOI value of the ship.

22 Regarding the NOx emissions, the main engine and the

D/Gs are IMO Tier II compliant and for the SOx

emissions, 3.5% HFO has been considered for the firstand the third leg of the navigational profile and 0.1%

MGO while in port.

5.2 (a) Slow Steaming

To investigate the effect of slow steaming in the vessels

energy efficiency and emissions, the previous scenario is

repeated with a speed of 13.3kn in the first leg of the trip

and 12.5kn for the 3rd leg (ballast return). The total

consumption for regular sailing and slow steaming isdepicted in Figure 14. The steeper consumption curve ofregular sailing evinces the hourly fuel gains of slow

steaming.

The time penalty for slow steaming is also evident from

the same figure, with the delayed arrival to the discharge

port and the overall delay of the trip, as compared toregular sailing. If this late arrival triggers for example a

delay in the unloading of the ship, then the economic

benefits of slow steaming may vanish. This fact points

out that the time factor should be carefully considered

when optimizing the energy efficiency of the ship

considering real navigational scenarios (i.e. for SEEMP).

Figure 14: Comparison between regular sailing and slowsteaming.

The relevant reduction in NOx23 and SOx emissionswhile slow steaming can be seen in figures 14 and 15.

Fig 15: NOx emissions

Figure 16: SOx emissions

The EEOI for the round trip is now calculated at

EEOI2=4.74 gCO2/ton-mile.

23 Considering the same NOx performance for the engine

as for regular sailing.


14/15



5.2 (b) Engine Tuning

As mentioned in 3.1(f) there are also engine tuning

possibilities that could influence the fuel consumption of

the engine (although constrained to certain extend due to

NOx restrictions). If the scenario of paragraph 5.2(a) is

repeated with the same engine, but this time the engine ispart-load optimized at 70% of SMCR

24, using for

example an EGB system (see 3.1(i)), then the SFOC will

be lower at the engine load required for slow steaming at

12kn. This is shown in Figure 16 where the cumulative

fuel oil consumption is given for the time domain

between 200 and 250 hours in the case of slow steaming

with the high load optimized engine (scenario 5.2(a)) andwith the relative part load optimized engine at 70% of

SMCR. The graph reveals the small gain in the fuel

consumption in the case of the part load optimization.

Figure 17: Part load and high load optimization (slow

steaming).

In Figure 18, the same comparison is made but this time

with an increased power demand (i.e. due to heavy

weather). The consumption for the part load optimized

engine is now slightly increased.

Figure 18: Part load and high load optimization (heavy

weather)

It becomes obvious that there is not one simple solutionwhen it comes to energy efficiency optimization and

many scenarios should be investigated based on the

intended operational profile of the ship.

5.2 (c) Other Considerations

With this kind of (time domain) scenario analysis using

the energy model of the ship it is possible to examine

also other factors which influence the ships energy

efficiency and air emissions. For example the energy

24 One of the benefits of the electronic engines, as

compared to the camshaft controlled ones, is also thewide range of load operation for which they can be

optimized for.

gains of arriving without delay at the port (just in time)

and loading/unloading at arrival as compared to delaysand increased harbour waiting times, can be simulated

(partly presented in 5.2(a)). Or the effect of weather

routing rather than steaming in heavy weather could be

predicted25.

Other factors which could influence the ships energyefficiency and environmental footprint can be also

investigated when considering the energy model of the

ship. For example, a scrubber system can be added as a

module in the energy model of the ship, with the

beneficial impact on the SOx and PM emissions but also

with the increase in fuel consumption due to theoperation of the scrubber unit (i.e. due to pump operation

etc.). It is actually possible to model every system that

interacts in the energy transformations on-board the ship

(i.e. waste heat recovery systems, steam turbines etc.).

6. CONCLUSIONS

Air emissions reduction is a major issue for the marine

industry concerning both the existing fleet but also the

designs that are currently on the drawing board. The

emissions coming from the exhaust gases of the ships can

be separated into those that add to the environmental

pollution (NOx, SOx and PM) and to those fuelling the

global warming of the atmosphere (CO2, NH3). The IMO

has put forth limits for the pollutant emissions from ships

which are presented and discussed in Section 1. There

are several solutions today in the industry that can help

reduce the pollutant emissions from ships. The SOx

emissions solely depend on the level of sulphur in thefuel and to this end the measures are focused either on

the use of better (distilled) fuels or on the post treatment

of exhaust gasses. For the NOx reduction, there are also

other measures focusing on the engine technology. A

number of measures are introduced in Section 2 and are

ranked based on their reduction potential.

The GHG emissions are closely connected to the energy

efficiency of the ship. As ships become more energyefficient, the GHG emissions are reduced for the cargo

transferred. The IMO will make the EEDI and the

SEEMP mandatory for new and existing ships from

January 2013 in order to improve the energy efficiencyof the global fleet, with the purpose of reducing the

global warming potential arising from ships. There aremany available solutions today to improve the energy

efficiency of ships. Some of these options are introduced

in Section 3 and are ranked based on their improvement

potential.

25 Provided the accurate prediction of the ships added

resistance in the waves. This can be estimated with CFD

calculations or by real measured data for the ship underconsideration or can be approximated with the use of

empirical formulae.


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2011 Th R l I i i f N l A hi

It is obvious that with a great number of solutions at

hand, a tool of simulating the energy and emissionsperformance of the ship becomes necessary. The

software SEECAT (Ship Energy Efficiency Calculation

& Analysis Tool), developed by Bureau Veritas, is a ship

energy modeller, using energy flow calculations, which

can be used to create the energy model of a ship in orderto predict its energy efficiency and the level of its airemissions. SEECAT utilizes a user-defined navigational

profile which facilitates the examination of the energy

performance of the ship in a time domain scenario

analysis. The methodology of energy flow modelling

with SEECAT is described in Section 4.

The application of energy flow modelling is presented

for a bulk carrier in Section 5 using basic optimization

steps and scenario analysis in order to demonstrate the

potential of energy flow calculations. The tool can be

used both for predicting the given energy status of a ship

(i.e. an existing ship) and also for optimizing its energyefficiency (and emissions) by evaluating different

measures under different scenarios. As a future

development, the predicted results should be also verified

by measurements on-board ships under various situations

(calm sea, heavy weather, slow steaming etc.).

7. ACKNOWLEDGEMENTS

The authors wish to thank the designers of the ship used

for the case study of the present paper: Mr D. Chalkias,

Mr N. Papapanagiotou and Mr N. Protonotarios for

providing the necessary information used for the energy

model of the ship in SEECAT and relevant informationon the optimization steps followed during the initial and

basic design stage.

8. REFERENCES

1. Second IMO GHG Study 2009.2. MEPC.1/Circ.684, 17 August 2009.3. KUIKEN, K., Diesel Engines For Ship Propulsion

And Power Plants, 20084. HOLTROP, J., MENNEN, G.G.J., An

Approximate Power Prediction Method, 1982.

5. HOLTROP, A Statistical Re-Analysis ofResistance and Propulsion Data, 1984.

6. CARLTON J., Marine Propellers and Propulsion,2007.

7. MAN B&W, S60MC-C8-TII Project Guide, 2010.8. MAN B&W, S60ME-C8-TII Project Guide, 2010.9. MARIN Report No22155-1-DT, dated Feb. 20089. AUTHORS BIOGRAPHY

Kostantinos Chatzitolios holds the current position of

product manager at Bureau Veritas and is based in the

Head Office, in Paris. He is responsible for the

international business development in the field of

container ships and dry bulk carriers. He joined Bureau

Veritas in 2005 after obtaining a Diploma in Naval

Architecture and Marine Engineering from the National

Technical University of Athens. Before moving to Sales

& Marketing Management in 2011, he has worked as

hull surveyor for the Bureau Veritas plan approval office

in Greece. During this period he has dealt with stability

and hull matters of bulk carriers, oil tankers and

passenger ships. In the period 2009-2010 Konstantinosunderwent training for surveyor on board and obtained

his surveyors certificate in 2010. Since 2010,

Konstantinos holds also an MBA degree from the Athens

University of Economics & Business.

Martial Claudepierre holds the current position of

Marine Leader for Environmental Services at Bureau

Veritas with the primary role of providing technical and

managerial leadership in the development of

Environmental Rules and Services.

He has a Master Engineer Degree in Mechanical applied

to Naval Shipbuilding. Prior to joining Bureau Veritas in

2006, he has been working for 12 years in two majorFrench civilian and military navy shipyards.

Aude Leblanc holds the current position of Engineer at

Bureau Veritas. She is responsible for the machinery

development. She joined Bureau Veritas in 2009 after

obtaining an Engineer Master Degree from INSA Lyon.

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