Table of Contents
Marine Engineers Question and Answer Series Part 3
Marine engineering is a challenging and exciting field that involves the design, construction, and maintenance of ships and other marine vessels. To succeed, marine engineering requires technical knowledge, practical skills, and hands-on experience. The third part of the Marine Engineers Questions and Answers series allows marine engineers to test their knowledge and showcase their expertise in the field.
This series will cover various topics, including Diesel Engine, Turbocharger, Fuel, and Oil. The questions will range from basic to advanced and will challenge marine engineers to demonstrate their understanding of key concepts and applications in marine engineering.
Whether you are a seasoned marine engineer or a beginner, this series provides a valuable learning opportunity to expand your knowledge and skills in this area. Get ready to put your marine engineering expertise to the test and take your career to the next level.
Read the related topic:- 300 Top Questions and Answers for Marine Engineers Interview Part-2.
Marine Engineers Question and Answer on Diesel Engine, Turbocharger, Fuel, Oil
Q 1- What method is commonly used to lubricate bearings in small high-speed diesel engines?
Ans- Splash lubrication is a standard method of lubricating bearings in small high-speed diesel engines. In this system, oil is splashed or thrown inside the engine by moving the crankshaft and other rotating parts. The oil then covers and lubricates the bearings, reducing friction and wear.
This lubrication system is simple and effective, and it can work well in small, low-power engines that don’t generate much heat. However, it’s unsuitable for larger engines or engines subjected to high temperatures and heavy loads, as the oil may not reach all parts of the engine or provide enough lubrication to prevent damage.
Q 2– What is the purpose of the inlet grid provided within the exhaust gas casing in the gas flow path before entry to the turbocharger?
Ans- Particles and other debris may have accumulated in the exhaust gas. The inlet grid helps prevent the turbocharger’s damage and prolong its lifespan. It can also help improve the overall performance of the turbocharger by providing a clean and unobstructed flow of exhaust gases, which is essential for the turbocharger to function efficiently. Additionally, the inlet grid can help reduce emissions by removing larger particulate matter from the exhaust stream before entering the turbocharger.
Q 3- What is the main function of tie rods in constructing large, low-speed diesel engines?
Ans- Tie rods are essential in constructing large, low-speed diesel engines. They are designed to accept most firing loads from the projectile forces generated during operation. The tie rods are a critical link in the engine’s load path, transmitting the firing forces from the piston and cylinder to the engine block and other structural components.
The tie rods are subjected to high-stress levels during engine operation and must be made from solid, durable materials that can withstand these loads. A failure of the tie rods can result in significant damage to the engine and even cause the engine to seize. Therefore, it is essential to properly maintain and inspect the tie rods to ensure their continued reliability and safety.
Q 4- Which factor determines the lower limit of thrust bearing clearance?
Ans- The lower limit of thrust bearing clearance is governed by the requirement to allow the thrust pads to tilt and generate an oil wedge. In a thrust bearing, the oil wedge is the thin layer of oil that forms between the moving and stationary surfaces of the thrust pads. The oil wedge helps reduce friction and wear between the moving and stationary surfaces and helps carry away heat generated by the friction.
There must be sufficient clearance between the moving and stationary surfaces to allow the thrust pads to tilt and generate the oil wedge. If the clearance is too small, the thrust pads will not be able to tilt and create the oil wedge, which can result in increased friction, wear, and heat generation. If the clearance is too large, the oil wedge is too thin to reduce friction and dissipate heat, reducing engine efficiency and performance.
Therefore, it is essential to maintain the proper thrust bearing clearance to ensure the reliable and efficient operation of the engine. This can typically be achieved by adjusting the thrust bearing clearances during engine assembly and periodically checking and adjusting the clearances during routine maintenance.
You may like to read our related post: 300 Top Questions and Answers for Marine Engineers Interview Part 2.
Q 5- Which causes lead to cracking of the piston crown?
Ans– All three of the reasons listed below can result in the cracking of the piston crown.
A. Deposits in cooling spaces: Deposits in the cooling areas around the piston can cause local hot spots and increased thermal stress on the piston crown, which can lead to cracking.
B. Impingement of fuel due to faulty injection: Impingement of energy onto the piston crown due to faulty fuel injection can cause local overheating and increased thermal stress, leading to cracking.
C. Insufficient piston cooling oil flow: Insufficient piston cooling oil flow can increase piston temperature and thermal stress, leading to cracking.
In addition to these reasons, other factors that can contribute to the cracking of the piston crown include high levels of mechanical stress, high combustion pressures, and high operating temperatures. It is essential to properly maintain and monitor the engine to minimize the risk of piston crown cracking and ensure reliable and efficient engine operation.
Q 6- What does the NLGI number of grease indicate?
Ans- (NLGI) The National Lubricating Grease Institute has established a standardized system for classifying grease consistency, known as the NLGI consistency grade. The NLGI consistency grade is based on the fluidity or thickness of the grease and is expressed as an NLGI number on a scale from 000 to 6.
A grease with an NLGI number of 000 is fluid and often called an oil. A grease with an NLGI number of 6 is stiff and often called a paste. The NLGI consistency grade provides a simple and effective way to compare and select greases with the desired consistency for a particular application.
Generally, greases with a lower NLGI number are used in applications where a liquid grease is required, such as in centralized lubrication systems or where low viscosity is needed for ease of pumping. Greases with a higher NLGI number are used in applications requiring stiffer grease, such as in gearboxes or bearings, where the grease must provide a better seal and resist displacement.
Choosing the correct NLGI consistency grade for a particular application is essential to ensure adequate lubrication and minimize the risk of equipment failure.
Q 7- Which layer in thin shell bearings gives fatigue strength?
Ans- The overlay layer of a thin shell bearing provides its fatigue strength. A thin shell bearing, also known as a babbitted bearing, is made by pouring a soft, ductile metal, such as tin or lead, over a rigid backing material, such as steel. The overlay layer is a sacrificial layer that provides a low-friction surface for the moving parts to slide, while the backing material provides the necessary structural strength and rigidity.
The overlay layer is designed to deform plastically under high loads and high loading frequencies, absorbing the energy generated by the load and preventing the formation of cracks that could lead to bearing failure. The thickness and composition of the overlay layer are carefully engineered to provide the desired fatigue strength level while maintaining low friction and good wear resistance.
In summary, the overlay layer of a thin shell bearing provides both the low-friction surface for the moving parts to slide on and the fatigue strength to resist repeated loading without cracking or failing.
Q 8- What type of bearings are most commonly used for a Modern Diesel Engine’s main and connecting rod bearings?
Ans- Precision insert bearings, or precision journal bearings, are commonly used for the main and connecting rod bearings in modern diesel engines. These types of bearings provide high precision and stability, essential for the smooth operation of diesel engines under heavy loads and high speeds. Precision insert bearings are designed to handle high radial loads and are well suited for applications in demanding environments, such as diesel engines.
Q 9- Which engine component reduces cylinder oil consumption?
Ans- Using anti-polishing or flame rings in diesel engines can help reduce cylinder oil consumption. Anti-polishing rings are placed in the engine’s cylinder liners above the piston rings. Their purpose is to prevent the piston rings from “polishing” the cylinder liner surface, which can lead to increased oil consumption. By reducing the amount of cylinder liner wear, anti-polishing rings can help maintain the engine’s oil control and reduce oil consumption.
Similarly, flame rings are designed to reduce oil consumption by preventing oil from entering the combustion chamber and being burned as fuel. They create a barrier between the engine’s oil scraper ring and the combustion chamber, preventing oil from entering and burning. By reducing the amount of oil burned, flame rings can help to improve engine efficiency and reduce oil consumption.
Q 10- What happens if the tappet clearance between the rocker arm tappet and the exhaust valve stem is too large?
Ans- If the tappet clearance between the exhaust valve stem and the rocker arm tappet is excessive, the valve will open later and close earlier than it should. The tappet clearance is the gap between the rocker’s arm and the top of the valve stem, which is critical to properly operating the valvetrain.
When the tappet clearance is too large, the rocker’s arm takes longer to transfer the camshaft’s motion to the valve, causing the valve to open later. Similarly, when the valve closes, the rocker’s arm pushes against it, causing it to close earlier. Too large a clearance can reduce engine performance and efficiency and increase engine noise and wear.
Maintaining the correct tappet clearance is essential to ensure the proper operation of the valvetrain. This is typically done by adjusting the rocker arm and the valve lash.
Q 11- Which conditions can cause poor performance on the main engine?
Ans- The following three conditions can lead to reduced power developed by a main engine.
A. High scavenge air temperature: High scavenge air temperature can reduce the amount of air available for combustion, reducing engine power. High temperatures can cause air to expand, reducing its density and volume.
B. Dirty air suction filter of a turbocharger: A choked air suction filter of a turbocharger can restrict airflow into the engine, reducing the amount of air available for combustion. Starvation of charge air can lead to reduced engine power, decreased engine efficiency, and increased engine wear.
C. Blow by in one or more units: Blow past refers to leaking air or combustion gases past the piston rings and into the crankcase. Blowby of flue gases reduces the amount of air and fuel available for combustion, which can result in reduced engine power. Blowpast can also increase engine wear and reduce engine efficiency.
Q 12- What types of diagrams are indicators of the effectiveness of Exhaust and scavenging processes?
Q 13-What separates the piston chamber from the crankcase in a 2-stroke engine?
Ans- In a 2-stroke engine, the diaphragm separates the piston chamber from the crankcase. The diaphragm is a flexible, disc-shaped component between the piston chamber and the crankcase. It helps create a sealed combustion chamber and prevent oil from entering it.
Q 14- What gauges are commonly used to evaluate main bearing clearance?
Ans-A telescopic feeler gauge is commonly used to evaluate main bearing clearance in an internal combustion engine. Main bearings support the crankshaft and play a critical role in the engine’s operation. The clearance between the Crankshaft main journal and main bearings must be carefully controlled to ensure smooth and efficient engine operation.
Q 15- What is the best arrangement for a diesel engine in continuous operation?
Ans- A duplex filter unit should be the best arrangement for a continuous-operation diesel engine because changing filter elements would not interrupt engine operation. A duplex filter unit is an arrangement in which two filter elements are used in a single housing. This arrangement is often used in continuous-operation diesel engines because it provides a backup filter that can be used when the primary filter becomes clogged or needs to be changed.
Q 16- How does a modern 4-stroke medium-speed marine diesel engine exhaust valve spindle rotate?
Ans- In modern 4-stroke medium-speed marine diesel engines, exhaust valve spindles are rotated using Rotocaps. A Rotocap is a specialized component designed to provide rotary motion to the valve spindle, which helps ensure smooth and efficient valve operation.
Q 17- What impact will the occurrence of microbiological growth in marine fuel have?
Ans- Microbiological growths in marine fuel are common, and they can be highly detrimental to equipment and operating processes. Microbes, such as bacteria and fungi, can grow in a ship’s fuel system and cause various problems, including contamination of the fuel, formation of deposits, and corrosion of fuel system components.
Q 18- What is the function of the tie rod?
Ans- The functions of the tie rod are: To avoid fatigue failure, the engine components are highly compressed so that the tensile stresses acting during the ignition stroke do not exceed this precompression.
Q 19- Which type of crankshaft is significantly lighter for similar power requirements?
Ans- Semi-built, all-welded crankshafts are often lighter than traditional cast crankshafts for similar power requirements. The semi-built crankshaft design typically consists of separate crank throws connected by welding rather than being cast as a single piece. This design allows for greater flexibility in material selection and manufacturing processes, and it can result in lighter, more compact crankshafts.
Q 20- How does the Bendix drive unit, drive gear, or pinion come off the flywheel after the engine is started?
Ans- A Bendix drive is a starter mechanism commonly used in internal combustion engines. It uses a small pinion gear that engages with the teeth on the engine’s flywheel. When the starter motor is operated, the pinion rotates and transfers its motion to the flywheel, which rotates the engine’s crankshaft and starts the engine.
Once the engine starts, the flywheel’s speed increases, which can cause the pinion to disengage from the flywheel. This phenomenon is because the pinion is designed to disengage when its rotational speed exceeds the flywheels. Disengagement of pinion from the flywheel teeth prevents damage to the starter motor and the drive mechanism.
Blog Conclusion
In conclusion, the Marine Engineer Question and Answer series Part 3 has provided valuable insights into the exciting field of marine engineering. Through exploring a range of topics, including the responsibilities of marine engineers, the daily routine of these professionals, and the various career paths available within the field, we have gained a deeper understanding of what it means to be a marine engineer.
We have learned that marine engineers are critical in ensuring ships’ and other maritime vessels’ safe and efficient operation. They are responsible for maintaining and repairing these vessels’ various systems and components, including engines, electrical, and navigation systems. They also help ensure ships comply with all relevant regulations and safety standards.
