FIRST REPORT IN PRELIM 2ND SEMESTER

BY: JAY MARK B. ANUTADEEP3B BSMT

REPORT IN MARINE POWER

OBJECTIVES• Describe the 2-stroke diesel engine cycle• Describe the 4-stroke diesel engine cycle• Describe the operating principle of marine

diesel engine• Describe the advantages and disadvantages

of a slow-speed diesel engine• Explain the cause of scavenge fires and how

they are dealt with• Describe the methods Asupercharging• Describe the fuel oil system from bunker

tank to injection• Describe the lubrication system

I. THE 2-STROKE DIESEL CYCLE• A two-stroke engine cycle undergoes different

processes in order to served its functions, these processes are:

1. Intake2. Crankcase compression3. Transfer exhaust4. Compression5. Power

INTAKE

The fuel/air mixture is first drawn into the crankcase by the vacuum that is created during the upward stroke of the piston. The illustrated engine features a poppet intake valve; however, many engines use a rotary value incorporated into the crankshaft.

CRANKCASE COMPRESSION

During the downward stroke, the poppet valve is forced closed by the increased crankcase pressure. The fuel mixture is then compressed in the crankcase during the remainder of the stroke.

TRANSFER EXHAUST

Toward the end of the stroke, the piston exposes the intake port, allowing the compressed fuel/air mixture in the crankcase to escape around the piston into the main cylinder. This expels the exhaust gasses out the exhaust port, usually located on the opposite side of the cylinder. Unfortunately, some of the fresh fuel mixture is usually expelled as well.

COMPRESSION

The piston then rises, driven by flywheel momentum, and compresses the fuel mixture. (At the same time, another intake stroke is happening beneath the piston).

POWER

At the top of the stroke, the spark plug ignites the fuel mixture. The burning fuel expands, driving the piston downward, to complete the cycle. (At the same time, another crankcase compression stroke is happening beneath the piston.)

Video Presentation

II. THE 4-STROKE DIESEL CYCLE

• A four-stroke engine cycle undergoes different processes in order to served its functions, these processes are:

1. Intake2. Compression3. Power4. Exhaust

INTAKEDuring the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated engine features a poppet intake valve which is drawn open by the vacuum produced by the intake stroke. Some early engines worked this way; however, most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring (not illustrated here).

COMPRESSION

As the piston rises, the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives the piston upward, compressing the fuel/air mixture.

POWER

At the top of the compression stroke, the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward.

EXHAUST

At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of the cylinder.

Video Presentation

III. OPERATING PRINCIPLES OF MARINE DIESEL PROPULSION

The Diesel Engine• One of the places where diesel engines play an

important role is the shipping industry. Diesel engines are known by the name of compression ignition engines due to technical reasons. Rudolf Diesel (German Engineer), the brain behind the invention of the diesel engine.

Diesel Marine Engines• Marine engines are those which are used in

marine vehicles namely boats, ships, submarines and so forth. Both 2-stroke as well as 4-stroke engines are used in the marine industry. The engines used for the main propulsion or turning the propeller/s of the normal ships are usually slow speed 2-stroke engines while those used for providing auxiliary power are usually 4-stroke high speed diesel engines.

IV. THE ADVANTAGES AND DISADVANTAGES OF SLOW-SPEED DIESEL ENGINE

Advantages• Inexpensive fuel cost

Disadvantages• Viscos fuel consumption

V. THE CAUSE OF SCAVENGE FIRES AND HOW TO DEAL WITH IT

The Purpose of ScavengingScavenging is the removal of

exhaust gases by blowing in fresh air; thus, efficient scavenging is essential to ensure a sufficient supply of fresh air for combustion.

THE CAUSE OF SCAVENGE FIRE

• Cylinder oil can collect in the scavenge space of an engine. Unburned fuel and carbon may also be blown into the scavenge space as a result of defective piston rings, faulty timing, a defective injector, etc. 

A build-up of this flammable mixture presents a danger as a blow past of hot gases from the cylinder may ignite the mixture, and cause a scavenge fire. A loss of engine power will result, with high exhaust temperatures at the affected cylinders. The affected turbo-chargers may surge and sparks will be seen at the scavenge drains.

HOW TO DEAL WITH IT?

• Once a fire is detected the engine should be slowed down, fuel shut off from the affected cylinders and cylinder lubrication increased. All the scavenge drains should be closed. A small fire will quickly burn out, but where the fire persists the engine must be stopped. A fire extinguishing medium should then be injected through the fittings provided in the scavenge trunking. On no account should the trunking be opened up.

STEPS IN DEALING SCAVENGE FIRESScavenge fires are extremely dangerous and

it is important that quick and effective action is taken to rectify the situation.

1. Engine revolutions must immediately be reduced to a minimum.

2. If possible the fuel is to be cut off from the cylinder unit concerned.

3. If more than one cylinder is involved then it will be more effective if the engine is stopped and the turning gear engaged and continuous turning commenced.

CONTINUED……..1. The cylinder lubricators are then to be

advanced to the maximum setting on the effected cylinders.

2. Turbocharger air intakes are to be blanked off.

3. Scavenge space relief valves where possible can be secured, and isolating flaps shut.

4. All external scavenge space surfaces must be carefully scrutinised for outbreaks of fire and strategic cooling applied as necessary.

5. There are various types of scavenge space fire extinguishing systems in use i.e. steam, dry powder, and CO2.

VI. THE METHODS OF SUPERCHARGING

Video Presentation

VII. THE FUEL SYSTEM FROM BUNKER TANK TO INJECTION

Video Presentation

VIII. THE LUBRICATION SYSTEM

“Lubricating oil for a marine diesel engine achieves two objectives; it must cool and lubricate.”

FUNCTION OF LUBRICATION

The lubrication system of an engine provides a supply of lubricating oil to the various moving parts in the engine. Its main function is to enable the formation of a film of oil between the moving parts, which reduces friction and wear. The lubricating oil is also used as a cleaner and in some engines as a coolant

LUBRICATING OIL SYSTEMLubricating oil for an engine is stored in the bottom of the crankcase, known as the sump, or in a drain tank located beneath the engine . The oil is drawn from this tank through a strainer, one of a pair of pumps, into one of a pair of fine filters. It is then passed through a cooler before entering the engine and being distributed to the various branch pipes. 

The branch pipe for a particular cylinder may feed the main bearing, for instance. Some of this oil will pass along a drilled passage in the crankshaft to the bottom end bearing and then up a drilled passage in the connecting rod to the gudgeon pin or crosshead bearing. 

Large slow-speed diesel engines are provided with a separate lubrication system for the cylinder liners. Oil is injected between the liner and the piston by mechanical lubricators which supply their individual cylinder, A special type of oil is used which is not recovered. As well as lubricating, it assists in forming a gas seal and contains additives which clean the cylinder liner. 

CYLINDER LUBRICATION

On a two stroke crosshead engine lubricating oil is supplied to the main bearings and camshaft and camshaft drive. A separate supply is led via a swinging arm or a telescopic pipe to the crosshead where some of it is diverted to cool the piston (travelling up and back through the piston rod), whilst some is used to lubricate the crosshead and guides, and the rest led down a drilling in the connecting rod to the bottom end or crankpin bearing. Oil is also used to operate the hydraulic exhaust valves.

VIDEO PRESENTATION

IX. GENERALLY ACCEPTED MARITIME TERMS

1. Swept Volume-Swept volume can be defined as the volume swept by the engine piston during one stroke.Swept volume is also the product of piston area and stroke.2. Clearance Volume-Clearance volume can be defined as the volume that remains in the cylinder when the engine piston is in the top-centre position.-Clearance volume can also be defined as the difference between the total cylinder volume and the swept volume. The space covered by the clearance volume also forms the combustion chamber.

3. Compression RatioCompression ratio can be defined as the value obtained by dividing the total cylinder volume by the clearance volume.4. Volumetric efficiencyVolumetric efficiency can be defined as the ratio of the volume of air drawn in to the cylinder to the swept volume.5. Scavenge EfficiencyScavenge efficiency can be defined as the ratio of the volume of air in the cylinder at the start of the compression to the volume swept by the piston from the top edge of the ports to the top of the strokes.

6. Air Charge RatioAir charge ratio can be defined as the ratio of the air contained in the cylinder at the start of the compression to the swept volume of the piston. It is also known as air mass ratio or air supply ratio.7. Natural aspirationNatural aspiration is a term which mainly applies to four stroke engines and is defined as the process by which air charge is brought in to the engine cylinder by only the downward movement of the piston without using other aids.8. SuperchargingSupercharging is a term used to indicate that the weight of the air supplied to the engine has been considerably increased for greater fuel usage and power production per stroke.It is also noted that supercharged engines produce more power as compared to non supercharged engines having the same stroke and speed.

~FIN~

Shalom!