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Methods of operating the marine engines by ultra-low sulfur fuel to aiming to satisfy MARPOLAnnex VI.

INTRODUCTION

Engine fuels are mainly petroleum distillates, which are complex mixtures of different hydrocarbons. Based on the nature and structure of hydrogen carbon molecules are divided into three groups: straight hydrocarbon carbon (saturated and unsaturated); Hydrocarbons (naphthalin); aromatic carbohydrates [1]. Simple carbon hydrocarbons: especially saturated hydrocarbons (especially hydrocarbons or naphthalene) have the highest selfigniting potential. Hydrocarbons of the benzene type have the lowest self-igniting ability. Hydrocarbon naphthalene has the ability to ignite itself between the two families. The naphthalene hydrocarbon content in the fuel component increases fuel viscosity [2,3].

The chemical composition of the group indicates the percentage of different hydrocarbon groups in the composition of the fuel. The content depends on the composition of the fuel. The distillate fuel contains about 30-55% saturated hydrogen carbon, 5-15% naphthalene hydrocarbon, 30-50% aromatic hydrocarbon, with heavy fuel, it contains respectively: 5-50%, 40-70%, and 10-25%. The chemical composition of the group allows the assessment of self-ignition of fuel relative to the self-igniting ability of different fuels [4,7]. The greater the content of fuel, the more saturated hydrocarbon and the less aromatic hydrocarbons are, the higher the ability of self-ignition is (evaluated via the catalytic number). With cruise diesel engines, two types of fuel are produced from petroleum: distillate fuels and heavy fuel [5,8].

Low-viscosity distillate fuels cannot be heated prior to feeding into the diesel engine cylinder. This type of fuel is called diesel fuel and gas turbine fuel. The diesel fuel obtained during the direct distillation of the oil consists of the main fraction boiling at a temperature of 230-345oC. Gas turbine fuel is the fuel obtained by slow-quenching sugar from cracking residual sulfur oil. This type of fuel has low ash, low mechanical impurities content but high sulfur content and resin content. Heavy fuel is the mixture of the remaining oil products when distilled directly from petroleum. Based on the volume and quality of the ingredients, heavy fuel is classified as high viscosity and medium viscosity. Due to the high viscosity of heavy fuel, a drying system is required in the fuel system [10].

The reduction in nitrogen oxide, sulfur oxide, carbon dioxide and particulate emissions is considered as an extremely large challenge for the designers of the engines while they are facing the international regulations and controls tightly aiming at reducing the pollutants from exhaust gas of engine. As specified in Annex VI of MARPOL, modified or supplemented, diesel engines with a capacity of 130 kW or more are installed on ships set up on January 1, 2004, operating in the NOx control area of vessels in North America and the Caribbean Sea in the United States, they must meet the level III of NOx emissions in accordance with the Technical Code for the Control of Nitrous Oxide Emissions from Marine Diesel Engines (NOx Law). The NOx emission limit (g/kWh) specified in the NOx Law depends on the engine's maximum revolutions (rpm) as shown in the diagram above [4,11]. Level I and II emission standards apply globally, while level III standards apply only to NOx control areas from existing ships (North America and the Caribbean Sea Region of the United States). In the future, if the International Maritime Organization (IMO) issues a new NOx control zone, level III emission standards will apply to ships. NOx emission limits for Level III include: SCR; Exhaust gas recirculation system (EGC); Use alternative fuels, such as liquefied natural gas (LNG).

The North American--Emission Control Areas (ECA) in accordance with Annex VI have been amended and supplemented by the International Convention for the Prevention of Pollution from Ships (MARPOL) which entered into force on 1 January August 2012, under which strict control of sulfur oxide ([SO.sub.x]) emissions, nitrous oxide (NOx) and particulates from ships operating off the coast of Canada, the United States, territorial waters French (Saint-Pierre and Miquelon) will be strictly implemented. Amendment of Annex IV--MARPOL (Prevention of Air Pollution from Ships) establishes North America's ECA which is officially in force from 01/08/2012. To date, three ECAs have been established globally, two of other ECA are [SO.sub.x]--eCa in the Baltic Sea and the North Sea [4,12]. The ECA and SECA are shown in Figure 1.

A fourth area, ECA of the Caribbean Sea of the United States, includes the waters adjacent to the coast of Puerto Rico and the US Virgin Islands, established under MARPOL amendments adopted in July 2011, It is expected to take effect on January 1, 2013 and 12 months later, January 1, 2014. The new ECA of the United States of America has entered into force. Within the ECA, Fuel oil (expressed as% m/m--means by weight) does not exceed 1.00% m/m, falling to 0.10% m/m on or after January 1, 2015. Outside ECA is 3.5% m/m, down to 0.50% m/m as from 1 January 2020. This date may be postponed to January 2025 depending on the results of the fuel oil quality assessment to be completed by 2018. In fact, this means that, in an ECA, ships must use lower sulfur fuel oil. In addition, the ship may use any "suitable material or equipment, alternative fuel oil, operating procedures or suitable methods" to at least ensure effective emission reductions equivalent to the membership of Annex VI of the MARPOL regulation. The Sulfur Emission Control Areas (SECAs) currently are listed with the Baltic Sea, The North Sea, the English Channel and waters within 200 nautical miles from the coast of USA, the coastal waters around Puerto Rico and the U.S. Virgin Islands (the US Caribbean ECA) and Canada.

The conversion of fuel during the ship operation may meet some problems related to fuel properties like viscosity, lubrication, flashpoint, and effect direct on the quality of combustion process. A matter is shown that, the sulfur content in fossil fuel is inversely proportional to the kinematic viscosity, thus resulting in reducing the amount of oil supplied to the engine and affecting the engine performance. It is necessary to investigate the effects of ultra low sulfur fuels on marine diesel engines and find out effective methods to ensure the safety operation of engines. The aim of this paper is to carry out the introduction of some low-sulfur fuel such as fossil ultra low sulfur fuel or biofuels applied to the marine engines to reduce the toxic emission.

Low-Sulfur Fuel For Marine Engine:

There are international standards recognized for identifying the characteristics and composition of the fuels used for marine engine. ISO 8217, British standard BS6843-1: 1996 and the American standard ASTM D-975 are the most widely used standards. In ISO standards, fuels are separated by viscosity, such as RME 180, RMF 180 and RMH 380, RMK 380 ... etc. The lower the fuel number is, the lower the specific mass and the less the impurities are, and thus the price is also higher. Low-sulfur fuel mentioned above includes Marine Gas Oil (MGO), which is defined as DMA, DMX or DMZ. Besides, Marine Diesel Oil (MDO) can be defined as DMB grade in ISO 8217-2012. This standard for marine fuels includes three different grades based on the distillation (DM) and residual (RM). The properties of fuels contained the maximum 0.1% sulfur limit are shown in Table 1. Diesel engine manufacturers generally set the fuel viscosity range for the engine. These include the minimum viscosity and maximum viscosity applied to the fuel at high pressure pumps under running conditions. For heavy fuel with high viscosity, the required viscosity is achieved by heating the fuel. At normal temperatures, distillate fuels often have limited viscosity. Low sulfur fuel tends to have a viscosity around the lower limit of allowable viscosity. The minimum viscosity of fuel for different types of engines is listed below:

* Low speed diesel engines (speeds below 400 rpm): 2 cSt is the minimum viscosity.

* Medium speed diesel engines (speed from 400 rpm to below 1400 rpm): The viscosity is from 1.8 to 3.0 cSt

* High-speed diesel engines (1.400 rpm or higher): 1.4-1.5 cSt is the minimum viscosity, it depends on or DMA.

Regulations around the world are beginning to require the use of ultra-low sulfur fuels. In the United States, this requirement has been applied to automotive engines, which will be applied to railroad engines and eventually ship engines. Marine engines conforming to the EPA Tier 4 emission standards require the use of ultra-low-sulfur fuel oils (ULSFO). EPA predicts that the adoption of new regulations will promote the reduction of sulfur content in the available fuel in the market. ULSFO is regulated differently in the world. The sulfur content of ULSFO is typically 15 parts per million (ppm) for USA / Canada, 10 ppm for Europe, Australia and New Zealand; and 50 ppm in other countries. The price of ULSFO is shown in Figure 2. Some key characteristics of ULSFO with less than 0.1% of sulfur can be found in Table 2.

During desulfurization, the fuel's ability of lubricating decreases because of low viscosity. The viscosity of ULSFO is extremely low in comparison with the viscosity of heavy fuel oil (C) and marine diesel oil (A). Low viscosity may result in low lubricity. This will affect the pumps and other equipment in the fuel system. To avoid too low lubricity in diesel fuel, the minimum fuel lubricity standard was adopted in 2005. The refining process also reduces the density of the fuel, resulting in the calorific value of the fuel is estimated to be around 1%. Since automotive engines use ULSD fuel, fuel system equipment is designed based on the characteristics of ULSD fuel. This is very different to marine engines because they are usually designed to operate on higher viscosity and viscous fuels. Thus, the use of ULSD on marine engines is a challenge for engine designers and ship engine engineers.

The Effect Of Low-Sulfur Fuel On Ship Engine Operation:

3.1. Thermal stress:

As the ship engine converts from HFO fuel to low sulfur fuels, it faces a huge change in fuel temperature. HFO fuel must be heated up before being supplied to the engine, otherwise ULSFO even need to be cooled. The shorter the transition time is, the greater the effect of thermal stress is. As converting from HFO to MGO contained 0.1% S, the temperature of the fuel drops at least 60[degrees]C. The load of the engine can be reduced to 25%- 40% and conversion time is 30-60 minutes. Therefore, the velocity of reducing temperature is about 1 2[degrees]C/min to avoid heat stress.

3.2. Low lubrication:

During the operation of the marine engines, if the viscosity of the fuel falls below the required level, it will have many negative effects. Sulfur is able to combine with other components in fuel into lubricating compounds. Reduced sulfur content leads to reduced fuel lubrication. During the conversion of fuel, temperature variability is very high, affecting viscosity and fuel lubrication. Low viscosity reduces the film thickness between the plunger and the barrel in the high-pressure pump; this will lead to the abrasion, and cause pump failure. To overcome this, it can be used a lubrication system for high-pressure pump or use a high pressure pump coated wolfram-carbon.

3.3. Incompatibility

Mixing of two fuels can lead toincompatible matter, especially as mixing of heavy fuel and low sulfur distillate fuel. If incompatibility occurs, it can lead to the obstruction in the filter, separators and injection nozzles of high-pressure pump, which result in losing the power even stop, endangering to the ship. The problem of incompatibility emerged by the difference in the stability reserves of the fuels. For example, HFO fuels usually with high aromatic hydrocarbons and asphaltenes may create precipitate like heavy mud as mixing, so it causes the obstruction.

Solution Of Using Ultra Low-Sulfur Fuel Oils In Marine Engines:

4.1. Installation of cooler or chiller:

As the ship engine is operated with ULSFO, one of the ways aiming at keeping the kinematic viscosity higher than the minimum is to equip the fuel cooler to keep the fuel temperature below 40[degrees]C. This is especially necessary when operating the ship engines in the summer or in the tropics where the temperature of the engine room and fuel tanks can exceed this temperature. The used coolant is water at a temperature between 36[degrees]C and 38[degrees]C. Cooler is installed at some locations on the fuel system. It can be installed on the oil return line from the engine to the mixing tank to eliminate the amount of heat supplied to the fuel as circulating. Figure 3 shows the recommended locations to install coolers. For the lowest viscosity distillates, a cooler may not be enough to cool the fuel sufficiently due to the cooling water available onboard. In such a case, it is recommended to install a so-called 'chiller'. The chiller principle is shown in Figure 4.

This installation is applied when the fuel supplied to the engine is at satisfactory temperature, and the cooler is only responsible for removing the heat of the return fuel. Welding can be installed at the fuel supply pipe to the engine. The sudden drop in fuel temperature should be avoided. The temperature of the fuel at the output of cooler is controlled through the flow of the coolant. In this way, the temperature of the fuel will be gradually reduced to the required temperature during the fuel conversion.

For the lowest viscosity distillates, a cooler may not be enough to sufficiently cool the fuel as the cooling water available onboard is typically LT cooling water (36oC). In such cases, it is recommended to install a so-called 'Chiller' which removes heat through vapor-compression or an absorption refrigeration cycle. When converted to ULSFO, the filter can be changed to suit the specific fuel content of the new fuel. A separate filter can be used to filter HFO fuel and low sulfur fuels. Normally, fuel like ULSFO does not require filtering except in some cases manufacturer requirement. Typical processes for reducing Si-Al catalyst include regular discharge of sediment in tanks, and other appropriate methods. The carried out test can detect the number and the size of the catalytic particle, allows suitable filtering process.

4.2. Using blend of ULSFO and biodiesel:

ULSFO is a high cost, so higher sulfur fuels are preferred. The ship will be equipped with a dual fuel system to ensure that ULSFO are used in the ECA, and higher sulfur fuels will be used outside ECA. However, this method still uses high sulfur fossil fuels. In this paper, the authors propose a solution using a mixture of biodiesel fuel and ULSFO. Low viscosity ULSFO fuel is blended with high viscosity biodiesel fuel to produce a suitable viscosity fuel that does not need to be cooled but contains extremely low sulfur content. Using this method not only saves the cost of installing the cooling system but also significantly reduces the toxic emissions from the use of bio-fuels. However, the ship engine may be used only bio-fuels that are without sulfur content. This system is shown in Figure 5.

Conclusion:

MARPOL Annex VI provides a legal regulation for the reduction of sulfur in fuel and associated time. Some issues related to vessel operation need to be considered to ensure the safe and efficient operation of the vessel when converting the fuel. There are also a number of engine operating procedures to be followed to ensure short-term and long-term operation of distillate fuel without damaging the fuel system and the mechanical parts of ship engine. The use of ultra-low sulfur fuels requires the use of support devices to maintain the kinematic viscosity in the operating range of the high-pressure pump group to avoid damaging and temperature-shocking equipment and system.

REFERENCES

[1.] ABS., 2015. Fuel switching advisory notice.

[2.] CIMAC, 2013. Guideline for the operation of marine engines on low sulphur diesel

[3.] http://www.maritimesymposium-rotterdam.nl/uploads/Route

[4.] INTERTANKO, 2013. Recommendations on the Hazard Assessment of Fuel Changeover Processes.

[5.] MAN Diesel & Turbo, 2014. Operation on low sulfur fuel.

[6.] http://www.marinediesels.info/2_stroke_engine_parts/Other_info/annex_vi.htm

[7.] Wain, K.S., J.M.Perez, E.Chapman, A.L.Boehman, 2005. Alternative and low sulfur fuel options: boundary lubrication performance and potential problems. Tribology International, 38: 313-319.

[8.] Hazrat, M.A., M.G.Rasul, M.M.K.Khan, 2015. Lubricity Improvement of the Ultra-low Sulfur Diesel Fuel with the Biodiesel. Energy Procedia, 75: 111-117.

[9.] Yu, X., K.Zha, R.Florea, M.Jansons, 2012. Comparison of In-Cylinder Soot Evolution in an Optically Accessible Engine Fueled with JP-8 and ULSD. SAE International., pp: 1315.

[10.] Nargunde, J., C. Jayakumar, A. Sinha, K. Acharya, 2010. Comparison between Combustion, Performance and Emission Characteristics of JP-8 and Ultra Low Sulfur Diesel Fuel in a Single Cylinder Diesel Engine. SAE Technical.

[11.] Chandrasekharan, J., N.Jagdish, S.Anubhav, B.Walter, A.H.Naeim, S.Eric, 2011. Effect of Biodiesel, Jet Propellant (JP-8) and Ultra Low Sulfur Diesel Fuel on Auto-Ignition, Combustion, Performance and Emissions in a Single Cylinder Diesel Engine. Journal of Engineering for Gas Turbines and Power, 134(2): doi:10.1115/1.4003971.

[12.] Sane, S., T.Badawy, N.Henein, 2017. Autoignition and Combustion of ULSD and JP8 during Cold Starting of a High Speed Diesel Engine. SAE Technical., pp: 0797, 2017, https://doi.org/10.4271/2017-01-0797.

(1) Viet Dung Tran, (2) Anh Tuan Le, (3) Van Huong Dong, (3,4) Anh Tuan Hoang

(1) College of Maritime I, Haiphong, Vietnam.

(2) Hanoi University of Science and Technology, Hanoi, Vietnam.

(3) Ho Chi Minh University of Transport, Ho Chi Minh, Vietnam.

(4) Ho Chi Minh College of Transport III, Ho Chi Minh, Vietnam.

Received 14 September 2017; Accepted 15 October 2017; Available online 30 October 2017

Address For Correspondence:

Viet Dung Tran, College of Maritime I, Faculty of Mechanical Engineering, Haiphong, Vietnam E-mail: dungtranviet1979@gmail.com

Caption: Fig. 1: SECA and ECA for ship operation

Caption: Fig. 2: The cost of ULSFO in the world

Caption: Fig. 3: The cooler is installed after the circulating pumps in fuel system

Caption: Fig. 4: Chiller principle

Caption: Fig. 5: Duel fuel system for marine engine
Table 1: Key properties of fuels in the ISO standard for marine fuels,
ISO 8217-2012 [5]

Key characteristics   Unit                 Limit     DMA

Density at            kg/[m.sup.3]         Max       890
  15[degrees]C
Viscosity at          m[m.sup.2]/s (cSt)   Min       2
  40[degrees]C                             Max       6
Viscosity at          m[m.sup.2]/s (cSt)   Max       --
  50[degrees]C
Sulfur                % m/m                Max       1.5
Flash point           [degrees]C           Min       60
Pour point (winter)   [degrees]C           Max       -6
Acid number           mg KOH/g             Max       0.5
Al+Si                 ppm m/m              Max       --
Lubricity             [micro]m             Max       520

Key characteristics   DMZ       DMB       RMA10     RMB30     RMD80

Density at            890       900       920       960       975
  15[degrees]C
Viscosity at          3         2         --        --        --
  40[degrees]C        6         11        --        --        --
Viscosity at          --        --        10        30        80
  50[degrees]C
Sulfur                1.5       2         Max. 0.1% in SECA
Flash point           60        60        60        60        60
Pour point (winter)   -6        0         0         0         30
Acid number           0.5       0.5       2.5       2.5       2.5
Al+Si                 --        --        25        40        40
Lubricity             520       520       --        --        --

Table 2: Key characteristics of examples of new types
of fuels with less than 0.1 % S (ULSFO) [5]

Key characteristics   Unit                 Limit     Supplier A

Density at            kg/[m.sup.3]         Max.      895-915
  15[degrees]C
Viscosity at          m[m.sup.2]/s (cSt)   Min.      40
  40[degrees]C                             Max.      75
Viscosity at          m[m.sup.2]/s (cSt)   Max.      --
  50[degrees]C
Sulfur                % m/m                Max.      0.1
Flash point           [degrees]C           Min.      70
Pour point (winter)   [degrees]C           Max.      15-30
Acid number           mg KOH/g             Max.      0.1
Al+Si                 ppm m/m              Max.      <0.3
Lubricity             [micro]m             Max.      <320

Key characteristics   Supplier B   Supplier C   Supplier D

Density at            870-930      928          910
  15[degrees]C
Viscosity at          --           45           --
  40[degrees]C                     65           --
Viscosity at          8-25         30-40        65
  50[degrees]C
Sulfur                0.1          0.1          0.095
Flash point           60-80        70           60
Pour point (winter)   18-21        20-25        20
Acid number           0.1-0.2      2.5          2.5
Al+Si                 12-15        10-20        17
Lubricity             --           --           520

Key characteristics   Supplier E

Density at            845
  15[degrees]C
Viscosity at          --
  40[degrees]C        --
Viscosity at          8.8
  50[degrees]C
Sulfur                0.03
Flash point           70
Pour point (winter)   21
Acid number           0.04
Al+Si                 <1
Lubricity             328
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Author:Tran, Viet Dung; Le, Anh Tuan; Dong, Van Huong; Hoang, Anh Tuan
Publication:Advances in Natural and Applied Sciences
Article Type:Report
Date:Oct 1, 2017
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