Turbocharging and Engine Components

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Questions and Answers

What type of lube oil pump is typically used in small marine engines?

Positive displacement type (correct)

Centrifugal type

Diaphragm type

Electrically driven

What is the purpose of telescopic pipes in a large slow-speed main propulsion diesel engine?

Prevent lube oil contamination of the cooling water

Cool the lube oil

Prevent water contamination of the lube oil (correct)

Reduce crankcase pressure

What is a potential consequence of excessive axial thickness in a piston ring?

Difficulty in forming a proper oil wedge (correct)

Twisting of the ring in its groove

Excessive oil scraping from the cylinder liner

Increased wear on the cylinder liner

Which type of wear on a cylinder liner is considered adhesive wear?

Scoring Signup and view all the answers

What is the primary function of relief valves on cylinder heads of marine diesel engines?

Prevent excessive pressure buildup in the combustion chamber Signup and view all the answers

What factor does the operation of a pulse pressure turbocharger rely on?

Pressure pulses generated by the exhaust system Signup and view all the answers

Which of these factors contribute to the penetration of fuel droplets during injection?

All of the above Signup and view all the answers

How does increasing the storage temperature affect catalytic fines?

Increases catalytic fines Signup and view all the answers

Which of the following directly contributes to the cracking of a piston crown?

All of the above Signup and view all the answers

What is the primary function of the overlay layer in a thin shell bearing?

Provides fatigue strength Signup and view all the answers

What does the NLGI number of grease primarily indicate?

The consistency of the grease, i.e., how fluid or non-fluid it is Signup and view all the answers

Why are precision insert bearings widely used in modern diesel engines for main and connecting rod bearings?

They offer excellent wear resistance and durability Signup and view all the answers

What is the primary function of load sensing devices in diesel engines driving alternators?

Prevent excessive fluctuations in engine speed Signup and view all the answers

Which of the following statements about cylinder oil consumption is FALSE?

The use of anti-polishing rings or flame rings increases cylinder oil consumption Signup and view all the answers

Which of the following bearing types is MOST commonly used for main and connecting rod bearings in modern diesel engines?

Precision insert Signup and view all the answers

In a uniflow scavenged marine 2-stroke diesel engine, how are the scavenge ports in the cylinder liner machined?

Only for a part of the circumference, at an angle almost tangential to the circumference of the liner Signup and view all the answers

What is the purpose of cooling supercharged air in an engine?

To increase its density and prevent moisture entry Signup and view all the answers

Which material is commonly used for intake valves in diesel engines?

Low-alloy steels Signup and view all the answers

Why must turbocharger bearings be renewed periodically?

They are prone to failure from metal fatigue Signup and view all the answers

What type of compressor is typically used in modern marine turbochargers?

Radial flow Signup and view all the answers

What is a significant disadvantage of using water as a cooling medium for pistons?

Chemical treatment is required Signup and view all the answers

What is the primary function of thrust bearings in an engine?

Prevent axial movement of rotating components Signup and view all the answers

In comparison to exhaust valves, which characteristic makes intake valves less susceptible to wear?

They are less exposed to corrosive gases Signup and view all the answers

Which design feature contributes to the complexity of piston designs compared to using water as a cooling medium?

Water cooling requires additional fittings and tubes Signup and view all the answers

Study Notes

Turbocharging

Supercharged air is cooled to increase its density and keep peak temperature and exhaust gas temperature within limits.
This cooling prevents moisture from entering the engine.

Bearings

Piston pin bushing is an example of a solid bearing.
Turbocharger bearings must be renewed after a preset number of hours, regardless of condition, due to cyclic loading and metal fatigue.

Valves

Intake valves in diesel engines can be made from low-alloy steels because they are less affected by corrosive exhaust gases.
Exhaust valves are more prone to wear and require more durable materials.

Turbochargers

Modern marine turbochargers use radial flow compressors.

Cooling Systems

Water as a cooling medium for pistons has disadvantages, including chemical treatment requirements, higher thermal stresses, and more complicated piston design.

Fuel Injection

Factors affecting penetration of fuel droplets during injection include quality of atomization, injection temperature, and scavenge air pressure.

Lube Oil Systems

Lube oil pumps in small marine engines are usually positive displacement type.
Telescopic pipes to the piston are designed to prevent contamination of lube oil by water.
Excessive axial thickness of a piston ring can lead to difficulty in forming an oil wedge.

Cylinder Liners

Scuffing is an adhesive type wear of a cylinder liner.
Cylinder heads are provided with relief valves to relieve excessive pressure within the combustion chamber.

Turbocharger Operation

Pulse pressure turbochargers work by creating pressure pulses in the exhaust system.

Piston Crowns

Cracking of piston crowns can be caused by deposits in cooling spaces, impingement of fuel due to faulty injection, or insufficient piston cooling oil flow.

Grease

The NLGI number of grease indicates its consistency, i.e., how fluid or non-fluid it is.

Bearings (continued)

The overlay of a thin shell bearing gives it its fatigue strength.
Precision insert bearings are widely used for main and connecting rod bearings of modern diesel engines.

Cylinder Oils

Fuel oil sulfur level is an important criterion for choosing the TBN level of cylinder oil.
Excessive cylinder oil feed can lead to harmful deposits in piston top land area.

Speed Control

Load sensing devices ensure prompt correction of speed of diesel engines driving alternators without massive fluctuations.

Scavenging

In uniflow scavenged marine 2-stroke diesel engines, scavenge ports in a cylinder liner are machined only for a part of the circumference, at an angle almost tangential to the circumference of the liner.

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Description

This quiz covers turbocharging, bearings, and valves in diesel engines, including their functions and maintenance.