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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
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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
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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.
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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.