**3. Sea ship classification and quantification**

The sulphur ECA limit which entered into force in 1 January 2015 can be met using a lowsulphur fuel with sulphur below 0.1 %. The global limit, outside sulphur ECA, can be met using fuel with sulphur content below 0.5 %, which will be required from 2020. The date of the global limit reduction may be changed to 2025 as a result of a feasibility review to be

In order to comply with the requirements of Regulation 14 of MARPOL, the burning of lowsulphur fuel oils (LSFOs) was introduced. There is also an EU regulative about the sulphur content in marine gas oil. Namely, in accordance with EU's marine fuel sulphur directive (1999/32/EG, Article 4 with amendment as per directive 2005/33/EC), the sulphur content in marine gas oil within the territorial waters of an EU member state may not exceed 0.1 % by weight. This applies to all ships regardless of flag. As of 1 January 2010, the sulphur content of any marine fuels may never exceed 0.1 % by weight for ships in port with the exception of

For ships continuously operating on low-sulphur fuel oil and for those that may be fitted with an exhaust cleaning system, there is no issue. However, for ships which burn heavy fuel oil with 3.5 % sulphur content and are not equipped with scrubbing equipment, the problem of compliance is much greater as large quantities of fuel are being mixed during the oil change‐ over to low-sulphur fuel oil. MARPOL Annex VI Regulation 14 requires those ships using separate low-sulphur fuel to comply with this regulation and in entering or leaving an Emission Control Area, shall carry a written procedure showing how the fuel oil changeover is to be done, allowing sufficient time for the fuel oil service system to fully flushed out all fuel oils exceeding the applicable sulphur content prior to entry into a sulphur Emission Control Area. The volume of low-sulphur fuel oils in each tank as well as the date, time and position of the ship when any fuel oil changeover operation is completed prior to the entry into an ECA or commenced after exit from such an area shall be recorded in such logbook as prescribed by

Furthermore, ships are also an important source of greenhouse gas (GHG) pollutants. According to the Green House Gas study by the IMO consensus, international shipping emitted 843 million metric tonnes of carbon dioxide, 2.7 % of the global CO2 emissions in 2007. Including domestic shipping and fishing ships larger than 100 gross tonnes (GT),2 the amount would increase to 1.019 billion tonnes, i.e. 3.3 % of the global CO2 emissions. At the present trend, this percentage could go two or three times higher from the present by

In order to control this CO2 emission from shipping, the first formal CO2 control regulations were adopted by the IMO at the 62nd session of the Marine Environment Protection Committee (MEPC) in July 2011. The amendments to MARPOL Annex VI included the addition of Chapter 4 on regulations on energy efficiency for ships to make mandatory the Energy Efficiency Design Index (EEDI) for new ships and the Ship Energy Efficiency Management Plan (SEEMP)

2 Gross tonnage (GT) determined under the IMO 1969 Tonnage Convention represent the total volume of of ship's enclosed spaces measured in register tonne (RT) where 1RT=100 f3 or 2,83 m3, conversely. Net tonnage (NT) determined under the IMO 1969 Tonnage Convention represents the volume of cargo spaces (cargo holds and cabins)

conducted no later than 2018 (see Figure 2).

short stays in port (up to 2 h).

170 Current Air Quality Issues

the Annex VI Regulation.

2050 emissions [8, 9].

in register tonne (RT).

As per rules of the Shipping Classification Societies, ship is defined as 'a floating unit intended for sea-going service with length greater than 12 meters and with GT greater than 15, or which carries more than 12 passengers. The present definition does not apply to ships of war and troopships'. Marine ocean-going ships are generally very large ships designed for deepwater navigation. Depending on the nature of their cargo, ships can be divided into different categories, classes and types. A majority of these ships can be classified as one of the following: tanker, bulk carrier, container ship, ro-ro ship, general cargo ship, reefer ship and passenger ship. There are also smaller ship types, which are not included in the largest categories of ship, as fishing ships intended and equipped for fishing or exploiting other living resources of the sea; tugs, a ship specially constructed and equipped for towing and/or rescuing and salvage of ships or other floating units; ships used by authorities which include the following types: pilot boats, rescue ships, police boats, custom boats, etc.; training ships provided for training of marine personnel gaining training and practical marine experience to develop seafaring skills suitable for a professional career at sea and provided with special equipment and arrangements suitable for that purpose (teaching rooms, accommodation spaces for teachers and trainees, etc.); research ship, a ship without cargo spaces, engaged in scientific research, noncommercial expeditions and surveys, carrying scientists, technicians and members of expeditions, and provided with special equipment and arrangements suitable for that purpose (i.e. laboratories, accommodation for research personnel, etc.); supply ship, a ship mainly intended and equipped for the carriage of special personnel, special materials and equipment which are used to provide facilities to offshore units and other marine installations, as well as to provide assistance in performing special activities; and icebreakers and recreational ships such as yachts classified as recreational craft for personal or commercial use, having hull length greater than 12 m, having facilities and accommodation for extended navigation, authorised to carry not more than 12 passengers, excluding crew. The following is a brief description of the characteristics of the main types of ocean-going ships:

*Tanker* is a merchant ship designed to transport liquids or gases in bulk. The major types of tanker ship include the oil tanker, the chemical tanker and gas carrier.

*Oil tanker* is a ship which is constructed primarily to carry oil in bulk and comes in two basic types: the crude carrier, which carries crude oil, and the clean product tanker, which carries the refined products, such as petrol, gasolene, aviation fuel, kerosene and paraffin. Tankers also include ship types such as combination carriers. Combination carrier is a general term applied to ships intended primarily to carry oil or dry cargoes, including ore, in bulk (ore/oil ships, oil/bulk/ore – OBO). These cargoes are not carried simultaneously. Generally they are constructed with a single deck, two longitudinal bulkheads and a double bottom throughout the cargo length area and intended primarily to carry ore cargoes in the centre holds or of oil cargoes in centre holds and wing tanks.

*Chemical tankers* are ships which are constructed generally with integral tanks and intended primarily to carry chemicals in bulk.

*Gas carrier* can be divided into two types: the *LNG tanker* carries liquified natural gas and the *LPG tanker* carries liquified petroleum gas. Tankers can range in size of capacity from several hundred deadweight tons (DWT),3 which include ships for servicing small harbours and coastal settlements, to the real giants of several hundred thousand DWT: the VLCC (very large crude carrier) of between 200,000 and 300,000 DWT and the ULCC (ultra large crude carrier) of over 300,000 DWT.

*Bulk carriers* are sea-going self-propelled ships which are constructed and intended primarily to carry dry cargoes in bulk such as ore, coal, pulp, rock, cement, scrap metal, grain, flour, rice, fertilisers, sugar or any cargo that travels in bulk. Bulk carriers range from about 25,000 DWT ('handysize') through the medium-size ('Panamax') ships of about 75,000 DWT, to the giant ('capesize') ships of over 200,000 DWT.

*Container ships* are a type of dry cargo ships specially designed and equipped with the appropriate facilities for carriage of containers. They carry standardising container at 20-feet long (TEU – twenty-foot equivalent unit) or 40-feet long (FEU – forty-foot equivalent unit). Today's container ships are being built to take up to18,000 TEU.

*Ro-ro (roll on/roll off)* is a cargo ship (ferry) specifically designed for the carriage of vehicles, which embark and disembark on their own wheels, and/or goods on pallets or in containers which can be loaded or unloaded by means of wheeled vehicles. Another type of ro-ro is a passenger ship (ROPAX). The acronym ROPAX (roll-on/roll-off passenger) describes a ro-ro ship built for freight vehicle transport along with passenger accommodation. Ro-ro ships have built-in ramps that allow the cargo to be efficiently rolled on and off the ship when in port. The ramps and doors may be stern-only, bow and stern or side for quick loading.

<sup>3</sup> Deadweight tonnage (also known as deadweight abbreviated to DWT) is a measure of how much weight a ship is carrying or can safely carry. It is the sum of the weights in metric tonnes of cargo, fuel, freshwater, ballast water, provisions, passengers and crew.

*General cargo ship* is a ship intended for the carriage of general cargo which will not be carried in containers.

*Refrigerated cargo ship or reefer ship* is a ship (excluding liquefied gas carriers and fishing ships) specially intended to carry permanently refrigerated cargoes such as fruits, vegetables, dairy products, fish and meat and has fixed refrigeration installations and insulated holds. Excluding the temperature control, the reefers are similar to other dry cargo ships or containers.

*Passenger ship* as per rules of the ship's classification society is a self-propelled ship with a permission to carry more than 12 passengers, specially designed and equipped for that purpose, with a single or multi-deck hull and superstructure and with cabin accommodation for passengers.

As of 1 January 2013, there were 48,732 merchant ships (597,709,000 GT) involved in interna‐ tional trade, registered under the flags of over 150 nations (see Figure 4).

**Figure 4.** Number of the main types of ocean-going ships in the world merchant fleet as of 1 January 2013 (source: http://www.statista.com)

#### **3.1. Ship engines**

to carry not more than 12 passengers, excluding crew. The following is a brief description of

*Tanker* is a merchant ship designed to transport liquids or gases in bulk. The major types of

*Oil tanker* is a ship which is constructed primarily to carry oil in bulk and comes in two basic types: the crude carrier, which carries crude oil, and the clean product tanker, which carries the refined products, such as petrol, gasolene, aviation fuel, kerosene and paraffin. Tankers also include ship types such as combination carriers. Combination carrier is a general term applied to ships intended primarily to carry oil or dry cargoes, including ore, in bulk (ore/oil ships, oil/bulk/ore – OBO). These cargoes are not carried simultaneously. Generally they are constructed with a single deck, two longitudinal bulkheads and a double bottom throughout the cargo length area and intended primarily to carry ore cargoes in the centre holds or of oil

*Chemical tankers* are ships which are constructed generally with integral tanks and intended

*Gas carrier* can be divided into two types: the *LNG tanker* carries liquified natural gas and the *LPG tanker* carries liquified petroleum gas. Tankers can range in size of capacity from several

coastal settlements, to the real giants of several hundred thousand DWT: the VLCC (very large crude carrier) of between 200,000 and 300,000 DWT and the ULCC (ultra large crude carrier)

*Bulk carriers* are sea-going self-propelled ships which are constructed and intended primarily to carry dry cargoes in bulk such as ore, coal, pulp, rock, cement, scrap metal, grain, flour, rice, fertilisers, sugar or any cargo that travels in bulk. Bulk carriers range from about 25,000 DWT ('handysize') through the medium-size ('Panamax') ships of about 75,000 DWT, to the giant

*Container ships* are a type of dry cargo ships specially designed and equipped with the appropriate facilities for carriage of containers. They carry standardising container at 20-feet long (TEU – twenty-foot equivalent unit) or 40-feet long (FEU – forty-foot equivalent unit).

*Ro-ro (roll on/roll off)* is a cargo ship (ferry) specifically designed for the carriage of vehicles, which embark and disembark on their own wheels, and/or goods on pallets or in containers which can be loaded or unloaded by means of wheeled vehicles. Another type of ro-ro is a passenger ship (ROPAX). The acronym ROPAX (roll-on/roll-off passenger) describes a ro-ro ship built for freight vehicle transport along with passenger accommodation. Ro-ro ships have built-in ramps that allow the cargo to be efficiently rolled on and off the ship when in port.

3 Deadweight tonnage (also known as deadweight abbreviated to DWT) is a measure of how much weight a ship is carrying or can safely carry. It is the sum of the weights in metric tonnes of cargo, fuel, freshwater, ballast water, provisions,

The ramps and doors may be stern-only, bow and stern or side for quick loading.

which include ships for servicing small harbours and

the characteristics of the main types of ocean-going ships:

cargoes in centre holds and wing tanks.

primarily to carry chemicals in bulk.

hundred deadweight tons (DWT),3

('capesize') ships of over 200,000 DWT.

Today's container ships are being built to take up to18,000 TEU.

of over 300,000 DWT.

172 Current Air Quality Issues

passengers and crew.

tanker ship include the oil tanker, the chemical tanker and gas carrier.

The power needed on ships is generated through main and auxiliary engines often called prime mover in the literature and can be sorted as diesel engine, gas turbine, steam turbine and electric motor. The diesel engine is the most common prime mover in the merchant marine, mainly due to its low fuel consumption in comparison with other prime movers. Power ranges between 0.25 MW for the smallest high-speed engines and 100 MW for the for the biggest lowspeed marine diesel engines. The main advantages of diesel engines are the following: it is relatively insensitive to fuel quality; it can be operated by light fuel as well as the heaviest residual fuels; and it has high reliability and high efficiency. In the other hand, the main disadvantages of diesel engines are pollutant emissions, low power-to-weight ratio if com‐ pared with gas turbine and vibration and noise.

From the application viewpoint, three main types of diesel engines are available: low-speed diesel engines (rpm<200), medium-speed diesel engines (200<rpm<1000) and high-speed diesel engines rpm>1000).

From the construction viewpoint, two types can be distinguished: two-stroke low-speed engines and four-stroke engines (medium or high speed). Low-speed diesel engines are dominant in the deep sea tanker, bulk carrier and containership sectors. Such types of engines are used as ship's propulsion engine without gearbox, i.e. directly connected to the propeller shaft system. These engines are currently the most efficient in terms of the specific fuel consumption, but NOx emission level from these engines is very high in comparison with medium- or high-speed marine diesel engines (see Figure 5b). The diesel engines have specific fuel consumptions around 160–185 g/kWh, against the 220–240 g/kWh of gas turbines and 300 g/kWh of steam turbines (see Figure 5a).

Medium-speed engines are used for auxiliaries such as alternators and for the main propulsion engine, with a gearbox to provide a propeller speed reduction, for smaller cargo ships, ferries, passenger cruise liners, ro-ro carriers, supply ship, icebreakers, etc., while high-speed engines are used as propulsion and for auxiliaries in smaller ships as fishing ships, tugs, pilot ships, recreational ships, etc.

**Figure 5.** a) Specific fuel consumption of prime movers b) NOx emission ratio for prime movers

#### **3.2. Marine diesel engine: Type and working principles**

residual fuels; and it has high reliability and high efficiency. In the other hand, the main disadvantages of diesel engines are pollutant emissions, low power-to-weight ratio if com‐

From the application viewpoint, three main types of diesel engines are available: low-speed diesel engines (rpm<200), medium-speed diesel engines (200<rpm<1000) and high-speed

From the construction viewpoint, two types can be distinguished: two-stroke low-speed engines and four-stroke engines (medium or high speed). Low-speed diesel engines are dominant in the deep sea tanker, bulk carrier and containership sectors. Such types of engines are used as ship's propulsion engine without gearbox, i.e. directly connected to the propeller shaft system. These engines are currently the most efficient in terms of the specific fuel consumption, but NOx emission level from these engines is very high in comparison with medium- or high-speed marine diesel engines (see Figure 5b). The diesel engines have specific fuel consumptions around 160–185 g/kWh, against the 220–240 g/kWh of gas turbines and 300

Medium-speed engines are used for auxiliaries such as alternators and for the main propulsion engine, with a gearbox to provide a propeller speed reduction, for smaller cargo ships, ferries, passenger cruise liners, ro-ro carriers, supply ship, icebreakers, etc., while high-speed engines are used as propulsion and for auxiliaries in smaller ships as fishing ships, tugs, pilot ships,

Slow speed diesel engine Medium speed diesel engine

20

0

40

60

N

Ox [g/kg fuel]

80

100

120

140

**a) b)**

0% 25% 50% 75% 100%

Power

High speed diesel engine Gas turbine

0% 25% 50% 75% 100% Power

**Figure 5.** a) Specific fuel consumption of prime movers b) NOx emission ratio for prime movers

pared with gas turbine and vibration and noise.

g/kWh of steam turbines (see Figure 5a).

diesel engines rpm>1000).

174 Current Air Quality Issues

recreational ships, etc.

150

200

250

SFC

[g/kWh]

300

350

400

The diesel engine is reciprocating internal combustion engine where chemical energy of the fuel is converted into thermal energy by means of combustion reactions of the fuel, and then the thermal energy is converted into mechanical work. The actual cycle inside the engine can be done either in four strokes (two crank revolutions) or in two strokes (one crank revolution) [11]. A stroke is defined as the distance travelled by the piston between the top dead centre (TDC) and the bottom dead centre (BDC). Cycles in the four-stroke engine are compression, power, exhaust and intake strokes. During compression stroke, the piston moves upwards from BDC to TDC. Inlet and exhaust valves are closed, and the combustion air is compressed and thus increases air pressure and temperature (110 to 220 bar and 600 °C to 800 °C depending on the type of engine). Fuel is injected several crank degrees before TDC and ignited by the high temperature of the compressed air. Combustion starts at the end of the compression stroke. The combustion is continued over a considerable crank angle after TDC, while the combustion gases expand and perform work on the piston, forcing it down. This is power stroke. Towards the end of the stroke, the exhaust valve opens which releases the combustion gases into the exhaust manifold or exhaust gas receiver. Thereafter during the exhaust stroke, the piston moves from BDC to TDC. The exhaust valve is open and the rest of the combustion gases are forced out of the cylinder by the upward stroke of the piston. The gases that remain in the cylinder are dispelled by a scavenging process; the inlet valve is opened early, whereas the exhaust valve is closed late, so that both are open at the same time (overlap period). Thereafter during the intake stroke, the piston moves downwards from TDC to BDC. The inlet valve is open and the exhaust valve closed, while the cylinder is filled with a charge of fresh air and thereafter is ready for the compression stroke. A complete cycle takes four strokes. However, the power stroke is the only useful one, which suggests that there is a useful stroke every two crank revolutions.

Slow-speed marine diesel engine (65–200 rpm) operates on the two-stroke cycle. This means that this engine has one working or power stroke per every crank revolution. The main difference comparing two-stroke with the four-stroke cycle is that charging and exhaust take place without the piston enforcing the process. During the compression stroke, the inlet ports and exhaust valve are closed and a volume of air is trapped into the cylinder. The piston moves upwards to TDC, thus compressing this combustion air and causing a temperature and pressure rise (110 to 160 bar and 600 °C to 800 °C depending on the type of engine) that is sufficient to ignite the fuel that has been injected few degrees before TDC. At the end of the compression stroke, combustion starts and continues several degrees during power stroke. The combustion gases expand and perform work on the piston, forcing it down from TDC to BDC. At the end of expansion, exhaust valve opens and combustion gases blow down to exhaust receiver pressure. By the time the inlet ports are open, the cylinder pressure will have reached a pressure lower than that of the scavenging air, so scavenging starts. These processes take place in one stroke. Scavenging, which starts while the piston moves downwards, is completed while the piston moves upwards. Both the inlet ports and exhaust valve are opened, and fresh air from scavenging air receiver enters the cylinder, forcing the exhaust gases out. The scavenging and compression processes take place in another stroke. The process described here is for uniflow scavenging. It is necessary to compress the scavenging air by the turbo‐ charger in order to scavenge the cylinder. The principal scheme of a turbocharged marine diesel engine is shown in Figure 6 as in [12]. Turbocharger (TC) is composed of the compressor (C) driven by the gas turbine (T) that receives its power from the heat energy of the exhaust gases flowing through. The compressor and the turbine are directly coupled and they are built together in a common housing. The gas turbine, usually one-stage axial type, is located after an exhaust gas receiver (EGR) which collects the exhaust gases from all the engine cylinders. The one-stage centrifugal-type compressor feeds compressed air through scavenging air cooler into scavenging air receiver (SAR) that supplies all the engine cylinders.

**Figure 6.** Principal scheme of turbocharging marine diesel engine

#### **3.3. Types of fuel oils for marine diesel engine**

Marine diesel engines use three types of liquid fuels standardised by ISO 8217 fuel standard for marine distillate fuels as gas oil (GO) with max. density of 890 kg/m3 at 15 °C, marine diesel oil (MDO) with max. density from 890 to 900 kg/m3 at 15 °C and heavy fuel oil (HFO) with max. density from 920 to 1010 kg/m3 at 15 °C as in [13]. ISO 8217 fuel standard for marine distillate fuels also defines the values of the essential properties of each type of the fuel. The most important properties of marine fuels are as follows:

**•** Kinematic viscosity, expressed as mm2 s-1, is a measure for the fluidity of the fuel at 50 °C. The viscosity of a fuel decreases with increasing temperature. The moment the fuel leaves the injectors, the viscosity must be within the limits prescribed by the engine manufacturer in order to obtain an optimal spray pattern; otherwise, it will lead to poor combustion, deposit formation and energy loss.

