The Best Tutorial on All About Marine Diesel Engines Theory

All About Marine Diesel Engines Theory

Diesel Engines & Systems

DIESEL ENGINE BASICS is a necessary read for anyone who wants to gain an understanding of diesel engines. This post will explore the basics of diesel engines and help you to understand what is going on inside them. We will also cover the different parts of a diesel engine and give you some tips on how to keep them running smoothly.

In this post on DIESEL ENGINE BASICS, i will discuss about the basics of Marine Diesel Engines. . This post will be useful for the engineering students.

Combustion process takes place inside the cylinder of an Internal combustion Engine. A Diesel engine reforms the heat power in to mechanical power.  
Following are the example of these types of engines.

• Diesel Engines
• Gas Turbines.

Advantages of ICE over ECE

1. Simple in mechanical design
2. Enhanced Power weight ration
3. Lower initial cost
4. Less requirement of cooling water
5. Occupies less space
6. Higher economy
7. Low maintenance

CONSTRUCTION OF AN INTERNAL COMBUSTION ENGINE

In ICE (Internal Combustion Engine, transformation of motions takes place.. This process is achieved through connecting rod.

The piston fits closely n the cylinder liner. The leakage of gases is prevented by installing piston rings into circumferential grooves of the piston. Usually, the cylinder is bored into the cylinder liners, and in large Diesel Engines, a separately manufactured cylinder liner is inserted in the cylinder block.

Combustion takes place in the space in the upper part of cylinder liner above the piston.

The Crankshaft and pistons are connected through the connecting rod.

The reciprocating of the piston is conveyed through connecting rod, makes the crankshaft to rotate around its axis.

The Crankshaft is supported by main bearings fitted in a cylinder block. The uneven torques produced by the engine is smoothened by a flywheel fitted at the drive end of the Crankshaft.

Engine is provided with a pan at the bottom end, known as the sump of engine. In wet sump type of the engines, oil gets collected in to this pan/sump.

1. Spark Ignition Engines.
2. Compression-Ignition Engines

Spark Ignition Engines:-In, this type of Internal Combustion Engine combustion process, takes place by the spark plug igniting the air-fuel mixture, and generally, petrol engines are the typical examples.
Compression-Ignition Engines:- An Engine in which injected fuel in to the cylinders is ignited by the high temperature of the compressed air and the combustion takes place. The expansion of combustion gases acts on the top of the piston and causes the vertical or horizontal movement through the connecting rod transmitting the movement to rotate Crankshaft.  Production of mechanical energy is by the conversion of fuel chemical energy. Because of the process of ignition, these type of internal combustion engines are also known as Diesel Engines.

In a Diesel Engine production of mechanical energy is by the conversion of fuel chemical energy.
Due to this process, Compression ignition engines are also known as Diesel Engines..
Classification of the Diesel engines is as per the listed below categories.

1. Diesel Engine By use.
2. Diesel Engine By Speed
3. Diesel Engine By Design
4. Diesel Engine By Size

By use: – By application, DIESEL ENGINE BASICS are categorized.

1. Marine: – In marine, Diesel Engines are used for propulsion and power generation purpose.
2. Industrial: – In Industries, Diesel Engines are used for Power generation as DG sets, For driving the compressors and Pumps.
3. Automotive: – Diesel Engines For land transport.
4. Traction: – For locomotives and trains.

By Speed:- Weight and capacity of Diesel Engine are determined by the speed of Engine. There are the following three types of speed classes for Diesel Engines.

• High-Speed Diesel Engines– Engines above 1000 RPM
• Medium Speed Diesel Engines– Engines from  400 to 1000 RPM
• Slow Speed Diesel Engines– Below 400 RPM

Design:– DIESEL ENGINE BASICS are again sub-classified as per the following designs.

• For Stroke/Two Strokes.
• Piston action- Single acting, Double acting and opposed piston arrangements.
• Cylinder arrangements.
• Kind of fuel (Heavy fuel, Low Sulfur, High-speed Diesel, Gaseous, and Dual fuel.
• Natural aspirated and turbocharged.

Why Aren’t V Engines Commonly Used as Propulsion Engines?

V engines are not commonly used as propulsion engines in large marine vessels for several reasons:

1. Space and Size Considerations:
   V engines typically have a more compact design than inline engines, which is useful in vehicles but less practical for ships. Marine vessels, particularly large ones like tankers or container ships, have ample vertical space in the engine room. This makes inline engines, which are taller but easier to maintain and provide higher power, more suitable for marine propulsion.
2. Lower Power Density:
   Marine vessels require engines capable of producing very high power over long periods, and inline engines, especially the large slow-speed 2-stroke engines, are more efficient at delivering high torque and power at low RPMs. V engines, being designed more for compactness and higher RPMs, do not match the performance needs of marine propulsion systems.
3. Maintenance Complexity:
   Inline engines are easier to maintain in the marine environment due to their simpler design. V engines, with their dual-bank cylinder arrangements, can complicate maintenance in a ship’s engine room, making them less ideal for the rigorous operational needs of large vessels.
4. Thermal Efficiency and Durability:
   The slow-speed diesel engines commonly used in ships (like long-stroke inline engines) provide better fuel efficiency and thermal efficiency than V engines. Marine engines often need to operate at lower RPMs for fuel economy, and V engines are generally optimized for higher-speed operation, where they are less fuel-efficient.

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Is It Possible to Have an Engine with a Stroke-Bore Ratio of 1:1?

Yes, it is possible to have an engine with a stroke-to-bore ratio of 1:1, though it is uncommon. In such an engine, the stroke length (the distance the piston travels within the cylinder) is equal to the bore (the diameter of the cylinder).

Advantages of a 1:1 Stroke-Bore Ratio:

1. Balanced Performance:
   Engines with a 1:1 stroke-to-bore ratio offer a balanced compromise between power and torque. This ratio allows the engine to have good torque at low speeds (due to the moderate stroke length) while maintaining higher power output at higher RPMs.
2. Compact Design:
   Engines with a 1:1 stroke-bore ratio tend to be more compact in size, offering a middle ground between the compactness of short-stroke engines and the torque advantage of long-stroke engines. This could be beneficial in applications where both power and space efficiency are important.
3. Smoother Operation:
   A 1:1 ratio can result in smoother engine operation because the balance between stroke length and piston speed reduces the chances of high vibration. This makes the engine quieter and more comfortable for operators.

Drawbacks of a 1:1 Stroke-Bore Ratio:

• Not Optimized for Either Extreme: While a 1:1 ratio is balanced, it doesn’t excel in specific areas. Engines with longer strokes (stroke > bore) are better for high-torque, low-RPM applications (like marine engines), while shorter stroke engines (bore > stroke) are better for high-RPM, high-power applications.
• Fuel Efficiency May Suffer: In marine applications, long-stroke engines are preferred for fuel efficiency because they extract more energy from each combustion cycle. A 1:1 engine may not match the efficiency of a super long stroke engine in this regard.

Working cycles:

• Two-Stroke Diesel Engines
• Four Stroke Diesel Engines

Two-Stroke Diesel Engine (DIESEL ENGINE BASICS): – This type of engine completes a power cycle in two strokes of Piston Movement and one revolution of Crankshaft. In a two-stroke engine end of combustion and starting of compression stroke take place simultaneously;

Four Stroke DIESEL ENGINE BASICS :- In this type of Engine, the Piston completes the following four strokes in two revolutions of the Crankshaft.

• Intake Stroke: – This stroke is also known as suction or induction stroke. This stokes starts at the top dead center and finishes at the bottom dead center. During the Piston, Air’s downward movement is sucked, and in the turbocharged engines,, the air is forced with positive pressure inside the cylinders.
• Compression: – Compression stroke begins at BDC (Bottom dead centre) and ends just at the end of suction stroke. In this stroke, the piston compresses the air to a pressure between 32 to 50 bar and the temperature in the range of 600⁰
• Ignition Stroke:- his stroke is also known as Power/Combustion stroke. This stroke starts in the 2^nd revolution of the crankshaft. During this stroke, the Chemical Energy of fuel’s mechanical energy pushes the piston downward, transmitting the power to the crankshaft.
• Exhaust:– This stroke is also known as exhaust expulsion stroke.  Exhaust stroke begins at BDC (Bottom dead centre) and finishes at

Notations used by MAN B&W engines

MAN – Germany – Maschinenfabrik Augsburg Nurnberg,
B&W – Denmark – Burmeister & Wain Motorfabrik A/S

The merger of above two Giants is now known as Man B&W.

MAN B&W ENGINE Specifications:

774VT2BF(S)

7 – Number of cylinders
74 – Cylinder diameter in cm
V – Single acting 2-stroke
T – Cross Head
2B – Degree of Turbocharging
F – Marine applicationS – Stationary Application

7K74EF

7 – Number of cylinders
K – Two stroke cross head
74 – Cylinder diameter in cm
E/G – Engine model/Hydraulically Operated Exhaust Valve
F – Marine application

7L80GFCA

7 – Number of cylinders
L – Long stroke
80 – Cylinder diameter in cm
G – Engine model/Hydraulically Operated Exhaust Valve
F – Marine Application
C – Constant pressure turbocharging
A – Engine rating

7L80GB/E

7 – Number of cylinders
L – Long stroke
80 – Cylinder diameter in cm
G – Engine Model/Hydraulically Operated Exhaust Valve
B – Engine rating
E – Economy layout

7S80MC

7 – Number of cylinders
S – Super long stroke
80 – Cylinder Diameter in cm
MC – Engine model/Programme

6K90MC-C/S

6 – Number of cylinders
K – Two stroke cross head
90 – Cylinder diameter in cm
MC – Engine model/Programme-
C – Short stroke container ship application-
S – Stationary Application

5L60MC MK-5

5- Number of cylinders
L – Long stroke
60 – Diameter of cylinder in cm
MC – Engine Programme
MK 5 – Engine version/Mark Number

6S90ME-C 9 GI TII

6 – Number of cylinders
S – Stroke/bore ratio – (G – ‘Green’ Ultra long stroke, S – Super long stroke,
L – Long stroke, K – short stroke)
90 – Diameter of the Cylinder in mm
M – Engine programme series
E – Concept – (E – Electronically controlled, C – Camshaft controlled)
C – Design – (E – Exhaust valve controlled by camshaft, C – Compact engine)
9 – Mark NumberGI – Fuel injection concept – (“blank” – Fuel oil only, GI – Gas injection)TII – Emission regulation – (TII – IMO Tier level)
Stroke/ Bore ratio:
K – Short stroke (approximately ratio = 2.8)
L – Long stroke (approximately ratio = 3.2)
S – Super long stroke (approximately ratio = 3.8)
G – Ultra long stroke (approximately ratio=4.7)

Major DIESEL ENGINE BASICS Components

• Cylinder Block
• Base Frame
• Crankshaft
• Connecting Rod
• Piston
• Cylinder Liner
• Cylinder Head
• Flywheel
• Camshaft
• Valve Train
• Fuel Injection Pump
• Fuel Injector
• Vibration Damper

Cylinder Block

A Cylinder Block is made of Cast Iron as a single unit in the liquid-cooled type engines. Block is designed to provide the following.

• Rigid frame with string structure to house the Cylinder Liners.
• Water passage.
• Lube oil Passages.
• Cylinder block supports the crankshaft and camshaft bearings..

Crankshaft

• Solid forged: – One to four throw crankshafts are made from a single ingot.
• Semi built:- In Semi-built Each pair of webs and crank-pin joining them are on one piece, and the separate journals are shrunk in.
• Built:-Built-up crankshaft comprises separate webs, crank-pins, and journals.

 Functions of Crankshaft

• Crankshaft transforms the motion of the piston to flywheel. From flywheel the power is transferred to the Alternator or propeller.
• The throw of the Crankshaft controls the piston stroke.
• Transmits drive to Camshaft for operating the valves, Fuel Pumps as per the timing of Engine.
• Transmits the drive to all the lube oil, fuel oil, and water pumps.

Crankshaft components

• Crank-throw:-
• Crank-webs
• Main-bearing Journal
• Connecting-rod Big-end (Crank-pin) Journals

Connecting Rod

• Big End
• Small End

Big End: – Big end of the connecting rod is attached to crankshaft through crank pin.

Small End:-   Small end of the connecting rod and piston are attached to each other through gudgeon pin ( Piston Pin).

Piston

• Connecting rod attaches the piston with crankshaft.
• Expanding gases on completion of Power stroke transmit the force to Piston downward and the movement is transmitted to Crankshaft.

The piston has two parts.

• Piston Crown
• Piston Skirt

   Characteristics of a Piston

•  Piston should be capable of rapid movement without any friction. With a running clearance in hot position should form a sealing surface?
• Should have less weight to work with minimum inertia forces.
• Should have enough strength to transmit the firing loads without getting distorted.

• Ring should form a seal between working surface of cylinder liner and piston.
• Amount of oil and scrape of the excess oil is performed by piston design.
• The piston rings should be able to transfer the combustion heat to the cooling water through cylinder liners.

Piston Rings

• Top ring ( Fire ring)
• 2^nd Ring ( Compression and oil control)
• 3^rd Ring ( Compression)
• 4^th Ring ( Oil scrapper ring)

Cylinder Liners-ENGINE BASICS FOR ENGINEERS

Engine Cylinders are popularly known as the liners. There are two type of liners based on their cooling design and fitment in cylinder blocks.

1. Dry liners
2. Wet liners

Dry Liners;- This type of design of liners is not cooled directly by the cooling water as is not exposed to the water circulation. Water circulates through the cavities. These type of cylinders are with thin wall design and are shrunk fit in the cylinder blocks. Tight fit of cylinders is beneficial since there are no chances of the cylinders suffering the corrosive effect.

Wet Liners.;- These type of cylinders are directly cooled by the cooling water circulating  around  the external surface of the cylinders. The water leakage sealing is affected by the Orings fitted in the grooves. There is also one metallic sealing rings provided between the cylinder block and cylinder liners.

These liners have the better cooling effect due to the direct conduction of heat. These liners have one serious drawback of getting affected by the corrosion and erosion due to the cooling water. In such type of cylinders, special attention need to taken to maintain the cooling water standards as per the manufacturers recommendations.

Cylinder Head-ENGINE BASICS FOR ENGINEERS

• It reduces the vibration through inertia by normalising it in each firing stroke.
• To control the unbalance forces on the crankshaft and maintain the regular speed, Fly wheel is mounted on the crankshaft –end.
• The gears on the flywheel facilitate the engagement of starting motor and crankshaft.

Flywheel weight is concentrated towards the outer circumference. It stores the energy due to the angular momentum while in rotation. Rotational speed changes are resisted by Flywheel. Flywheel gains momentum in the power stroke of the engine and maintains the even speed in the other three strokes of the engine. Flywheel also dampens the process of torsional vibration.
By choosing the suitable weight of Flywheel engine can work smoothly at various workloads.

Camshaft

I hope the post on DIESEL ENGINE BASICS has been useful to students.

The Best Book On Diesel Egines

Fundamentals of Medium/Heavy Duty Diesel Engines

Pounder’s Marine Diesel Engines and Gas Turbines

Lamb’s Questions and Answers on the Marine Diesel Engine

A Pocket Book of Marine Engineering: Questions and Answers

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Marine Engineers Tools and working gears

Rechargeable LED Flashlight

Vibration Meter

Men’s Long Sleeve Zip-Front Coverall

Timberland Men’s Pit Boss 6 Inch Steel Safety Shoes

Blog Conclusion

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