Scavenging and Turbocharging (Questions & Answers)

By Maklub Al Mostofa

Q. What is scavenging? Name the types of scavenge used for large two stroke engine. Describe the advantage of Uniflow scavenging.

SCAVENGING:
It is the removal of residual exhaust gas and its replenishment with fresh air in an internal combustion of the engine. The fresh air intake and exhaust gas expel operation are not simultaneous fully but some degrees of overlap period are provided for better efficiency.
There are 3 types of scavenging process.
1. Loop scavenging
2. Cross scavenging
3. Uniflow scavenging

Loop scavenging:
In this type of scavenging air passes over the piston crown and rises to form a loop. Ports are cut in the cylinder liner wall for this operation. The scavenge ports and exhaust ports are in the same side of the liner. Read more

Enclosed Space Entry

By Maklub Al Mostofa

Enclosed Space:

For the purpose of this Guide, an ‘Enclosed Space’ is defined as a space that has the following characteristics:

  • Limited openings for entry and exit.
  • Unfavourable natural ventilation.
  • Not designed for continuous worker occupancy

Enclosed spaces include, but are not limited to:

    • Cargo spaces
    • Double bottoms
    • Fuel tanks
    • Ballast tanks
    • Cargo pump-rooms
    • Cargo compressor rooms
    • Cofferdams
    • Chain lockers
    • Void spaces
    • Duct keels
    • Inter-barrier spaces
    • Boilers
    • Engine crankcases
    • Engine scavenge air receivers
    • Sewage tanks
    • Read more

The Origin of Shipping & Insurance

By F. R. Chowdhury

Shipping is one of the oldest businesses in the world. Risk management and insurance is also equally old business. They are closely linked with one another. In fact the development of insurance took place in support of the shipping industry.

In the early days the ship-owner, trader and ship-captain was a single entity. A rich influential person got a ship built, procured some commodity that is readily available in his area and then sailed to another place for business. He would normally barter the goods in exchange of commodity available in the new land. Gradually gold and then coins and currency became medium of exchange. Fortune favours the brave. The pioneer in shipping gradually became a rich man. He was not anymore ready to undergo all the rolling and pitching at sea. He employed a trusted man as the captain of his ship. He still remained owner of the ship and the cargo. However, those days with no radio telecommunication there was no way for him to know anything until the ship was sighted on the horizon again. Some time the ship was never seen again – either lost at sea or hijacked by pirates.
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Wärtsilä EnergoProFin Propeller

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Image Credit: Wärtsilä

The efficiency of the ship’s propeller is an important part of a ship’s overall propulsion efficiency. The Wärtsilä EnergoProFin has become a popular retrofit solution to improve the propulsion efficiency and hence improve the fuel efficiency of many ships already in service.The Wärtsilä EnergoProFin solution, a propeller cap with fins that rotates together with the propeller to produce fuel savings of up to 5%.
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Ignition Quality Parameters of Slow Speed Diesel Engine

Ignition quality parameters:

  1. Energy
  2. Viscosity
  3. Maximum firing pressure.
    4. Injection delay
    5. Ignition delay .

1. Energy comparison

• The injection pump is a volumetric pump
• The higher the density the more energy it contains per volume unit
• The density difference between HFO and MDO is larger than the difference in net calorific value

2.  Viscosity comparison

  • The viscosity of MDO is lower than the viscosity of HFO (even HFO is heated)
    • Lower viscosity fuels result in more internal leakage in the injection pump from the high pressure side to low pressure side.
    • Internal leakage has to be compensated by giving more fuel rack

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High Pressure Water Mist (Hyper Mist) System

  • Mandatory in passenger ships with GT > 500 and cargo ships with GT >2000, for fire extinguishing in machinery spaces of category A with volume > 500 m3 (IMO MSC/Circ.913).
  • System introduced as an alternative to the Halon systems (prohibited in 1994) for fire fighting in machinery spaces of category A and cargo pump rooms. This fire extinguishing process is based in 3 mechanisms:
    –  Cooling of the flames
    –  Reduction of the oxygen content by the displacement of the air by the expansion
    of the water vapor
    –  Diminution of the radiating heat
  • The pressurized water in contact with the fire vaporizes and it is converted into steam. This process absorbs much energy lowering the temperature of the fire and the pressurized water expands about 1700 times taking the air away from the fire. These systems require a water consumption 6 to 10 times lower than a traditional sprinkler system
  • It shall be activated automatically by 2 different types of detectors:
    flame and smoke.

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DIESEL ENGINE CRANKCASE EXPLOSION

INTRODUCTION:

For any fire to begin, the fire tringle needs to be completed. To complete a fire tringle there must be present of a combustible material, oxygen or air to support combustion and a source of heat in proportional ratio and within the flammable limits, the reaction which causes fire or explosion becomes cyclic.

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Image Credit: www.brighthubengineering.com

Crankcase explosion normally occurs in trunk engine in which the lubricating oil used in the bearings is splashed around the crankcase and broken down into moderate size particles.
The main cause of crankcase explosions are the development of hot spots at various places in the crankcase. Due to the reciprocating motion of the piston the lubricating oil in the crankcase is splashed in the air.
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Diesel Engine Scavenge Fire

INTRODUCTION: 

For any fire to begin, the fire tringle needs to be completed. To complete a fire tringle there must be present a combustible material, oxygen or air to support combustion and a source of heat at a temperature high enough to start combustion.
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Source: www.marinediesels.info

In the case of scavenge fires:
 the combustible material is oil. The oil can be cylinder oil which has drained down from the cylinder spaces, or crankcase oil carried upwards on the piston rod because of a faulty stuffing box. In some cases the cylinder oil residues may also contain fuel oil. The fuel may come from defective injectors, injectors with incorrect pressure setting, fuel particles striking the cylinders and other similar causes.
 The oxygen necessary for combustion comes from the scavenge air which is in plentiful supply for the operation of the engines.
 The source of heat for ignition comes from piston blow-by, slow ignition and afterburning, or excessive exhaust back pressure, which causes a blowback through the scavenge ports.
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Cylinder Lubrication System

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Cylinder lubrication in a low-speed main propulsion diesel engine:

Cylinder lubrication For marine diesel engines operating on residual fuels containing sulphur, cylinder lubrication must generally serve the following purposes:
■ Create and maintain an oil film to prevent metal to metal contact between the cylinder liner and piston rings.
■ Neutralise sulphuric acid in order to control corrosion.
■ Clean the cylinder liner, and particularly the piston ring pack, to prevent malfunction and damage caused by combustion and neutralisation residues.

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Problems in Boilers

Boiler-Maintenance-Repair94926492aff64df7962dc137ded70501

Image Credit:www.globalspec.com

 

Some common boiler problems are described below:

Fires

Cleanliness of the heat recovery surfaces after the boiler can often be judged by observing the gas pressure differential above and below. Any significant rise in this value should be attended to. Whilst good combustion conditions will minimise the risk, deposits allowed to accumulate in this area are a fire risk and, should fire take hold undetected, it can prove impossible to control and can wreck the heat exchanger, or even the whole boiler. There is plenty of evidence of soot fires leading on to hydrogen fires.

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Fuel Injector of Diesel Engines

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Image Credit: www.riceweightloss.com

Older loop scavenged engines may have a single injector mounted centrally in the cylinder head. Because the exhaust valve is in the centre of the cylinder head on modern uniflow scavenged engines the fuel valves (2 or 3) are arranged around the periphery of the head.
The pressure at which the injector operates can be adjusted by adjusting the loading on the spring. The pressure at which the injectors operate vary depending on the engine, but can be as high as 540bar.

FUEL INJECTOR

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Carbon Steel Alloys

metal-pipes
Image Credit: Taybro Alloys Stainless Steel

Carbon is the most important component in commercial steel alloy. Increasing carbon content increases hardness and strength and improves hardenability. But carbon also increases brittleness and reduces weldability because of its tendency to form martensite.

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Bunkering Procedure

Bunkering Procedure

The actual Bunkering operation is carried out with bunker checklists. In this article, emphasis is made on the checklists, safety precautions, SOPEP locker & SOPEP equipments, temperature & density correction to calculate the quantity of oil bunkered. Formula for calculation has been included.

Bunkering Oil

Earlier we learnt about the bunkering and what is means. Now we will study the process of actual bunkering operations and the practical details of the process of bunkering oil. All types of ships needs fuel oil, lub oil etc and hence it is important for everyone to understand the actual process of bunkering.
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MARPOL Annex VI- Emissions Control Development

Introduction:

IMO ship pollution rules are contained in the “International Convention on the Prevention of Pollution from Ships”, known as MARPOL 73/78. On 27 September 1997, the MARPOL Convention has been amended by the “1997 Protocol”;, which includes Annex VI titled “Regulations for the Prevention of Air Pollution from Ships”. MARPOL Annex VI sets limits on NOx and SOx emissions from ship exhausts, and prohibits deliberate emissions of ozone depleting substances.

The IMO emission standards are commonly referred to as Tier I…III standards. The Tier I standards were defined in the 1997 version of Annex VI, while the Tier II/III standards were introduced by Annex VI amendments adopted in 2008, as follows:

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Bismilla-hir-Rahma-nir-Rahim

 images (1)images (1)images (1)Surah Alaq:

surah_al-alaq

Meaning in English:

  1. Recite with the name of your Lord Who created,
  2. He made man from the clot of blood,
  3. Recite, for your Lord is the Most Generous,
  4. Who taught writing by the pen.
  5. Taught man what not.
  6. Yes, undoubtedly, man transgresses.
  7. Because, he thought himself self-sufficient.
  8. Read more