Cooling and Lubrication MCQ Quiz - Objective Question with Answer for Cooling and Lubrication - Download Free PDF

Explanation:

Mist Lubricating System

Definition: A mist lubricating system is a type of lubrication system where the lubricant is atomized into fine droplets or mist and then delivered to the engine components. This mist is carried by an airstream and is directed towards the components requiring lubrication. The primary purpose of this system is to ensure that all moving parts receive adequate lubrication to reduce friction and wear, thereby enhancing the engine's performance and longevity.

Working Principle: In a mist lubricating system, the lubricant (usually oil) is mixed with air to create a fine mist. This mist is then transported through the engine's air intake system and distributed to various engine components, such as the piston, cylinder walls, and crankshaft. The mist lubricates these parts by forming a thin film of oil on their surfaces, which reduces friction and wear. After performing its lubricating function, the mist is either burned along with the fuel or expelled through the exhaust system.

Advantages:

• Ensures even distribution of lubricant to all engine components, resulting in reduced friction and wear.
• Simple and cost-effective design, making it easy to maintain and operate.
• Effective in engines with complex geometries where direct lubrication may be challenging.

Disadvantages:

• May result in higher oil consumption compared to other lubrication systems.
• Potential for environmental pollution due to the expulsion of oil mist in the exhaust gases.
• Requires careful control of the oil-to-air ratio to ensure proper lubrication without excessive oil consumption.

Applications: Mist lubricating systems are commonly used in two-stroke petrol engines, which are found in various applications such as motorcycles, chainsaws, and small outboard motors. These engines have high-speed operation and require effective lubrication to prevent excessive wear and overheating.

Explanation:

Dry Sump Lubrication System

Definition: A dry sump lubrication system is a method used to lubricate and cool the moving parts of an engine, particularly in high-performance and racing applications. Unlike a wet sump system, where oil is stored directly in the engine's oil pan, a dry sump system uses an external reservoir for storing the oil.

Working Principle: In a dry sump lubrication system, oil is circulated through the engine by pumps. These systems typically use multiple pumps: a pressure pump to supply oil to the engine and one or more scavenge pumps to return oil from the engine back to the external reservoir. This ensures that oil does not accumulate in the engine, reducing the risk of oil starvation during high-speed maneuvers.

Correct Option Explanation (Option 2):

In a dry sump lubrication system, oil is returned to the storage tank by the action of a scavenge pump. The scavenge pump actively pumps the oil from the engine's crankcase or other low points back to the external oil reservoir. This is crucial because, in high-performance engines, maintaining proper lubrication under extreme conditions can be challenging. The scavenge pump ensures that oil does not remain in the engine, which could lead to issues like oil foaming, starvation, or excessive oil accumulation that might impair performance.

Scavenge pumps are typically more robust than the pressure pumps because they need to handle aerated oil (oil mixed with air) and ensure it is efficiently returned to the reservoir. This active pumping mechanism ensures that the oil flow remains consistent, even under high G-forces or during aggressive driving conditions. By constantly removing oil from the engine and returning it to the reservoir, the scavenge pump helps maintain optimal lubrication and cooling, which is vital for engine longevity and performance.

Advantages:

• Improved oil control and reduced risk of oil starvation in high-performance applications.
• Allows for lower engine profiles, improving aerodynamics and center of gravity.
• Better cooling and lubrication due to the external reservoir and active oil circulation.

Disadvantages:

• More complex and expensive compared to wet sump systems.
• Requires additional components, such as multiple pumps and an external reservoir.

Applications: Dry sump lubrication systems are commonly used in racing cars, high-performance sports cars, aircraft engines, and other applications where maintaining consistent oil pressure and lubrication under extreme conditions is critical.

Analysis of Other Options:

Option 1: Centrifugal force separates oil from air.

This option suggests that centrifugal force is used to separate oil from air, which is not a common method for returning oil to the storage tank in a dry sump system. While centrifugal force might play a role in certain oil separation mechanisms within the engine, it is not the primary method for actively returning oil to the storage tank.

Option 3: Oil remains in the engine block indefinitely.

This is incorrect as it contradicts the fundamental purpose of a dry sump lubrication system. The dry sump system specifically aims to prevent oil from remaining in the engine block indefinitely. The scavenge pump actively removes oil from the engine to avoid issues related to oil accumulation, such as foaming, starvation, and inefficient lubrication.

Option 4: Gravity drains oil directly to the crankcase.

In a dry sump system, gravity drainage to the crankcase is not sufficient to return oil to the external storage tank. While gravity might assist in moving oil to lower points within the engine, the scavenge pump is necessary to actively transport the oil back to the reservoir, especially under dynamic conditions where gravity alone cannot ensure consistent oil flow.

Option 5:

This option is not provided in the statement, but it is important to note that any other mechanism would still need to actively manage oil flow to maintain proper lubrication and cooling in a dry sump system.

Conclusion:

The correct option, option 2, accurately describes the role of the scavenge pump in a dry sump lubrication system. This pump is essential for actively returning oil from the engine to the external reservoir, ensuring optimal performance and reliability in high-stress conditions. Understanding the advantages and disadvantages of dry sump systems, as well as the importance of the scavenge pump, is crucial for anyone involved in the design, maintenance, or operation of high-performance engines.

Explanation:

Lubricating System in Light-Duty Engines

Splash system: 

• Used in lightduty, slowspeed engines (<250 rpm)
• Lubricating oil is stored at the bottom of the engine crankcase and maintained at a predetermined level.
• The oil is drawn by the pump and delivered through a distributing pipe into the splash trough located under the big end of all the connecting rods.
• These troughs are provided with overflows and oil in the trough is therefore kept at a constant level.
• A splasher or dipper is provided under each connecting rod cap which dips into oil in the trough at every revolution of the crankshaft and the oil is splashed all over the interior of the crankcase, into the pistons, and onto the exposed portion of cylinder walls.
• The oil dripping from the cylinder is collected in the sump where it is cooled by the air flowing around. The cooled air is then recirculated.
• A splash system of lubrication is employed for the camshafts, piston rings, and tappets.

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Advantages:

• Simplicity in design and construction, making it easier to manufacture and maintain.
• Cost-effective due to fewer components and simpler assembly.
• Effective lubrication for light-duty applications where the engine does not operate under extreme conditions.

Disadvantages:

• Not suitable for high-performance or heavy-duty engines where more precise and reliable lubrication is required.
• Less efficient at higher speeds and loads, as the splashing method may not provide adequate lubrication to all parts.

Applications:

• Splash wet sump lubricating systems are commonly used in small engines, such as those in lawnmowers, small motorcycles, and compact generators. These applications benefit from the simplicity and cost-effectiveness of the splash system.

Additional InformationOption 1: Splash and pressure lubricating system

This system combines the splash method with a pressure feed. It is more complex and provides better lubrication compared to the splash wet sump system alone. It is used in some light-duty engines but is more common in engines that require higher reliability and efficiency.

Option 2: Dry sump lubricating system

Dry sump systems are typically used in high-performance and racing engines. They use an external reservoir for the oil and a pump to circulate the oil throughout the engine. This system is more complex and expensive, making it less suitable for light-duty engines.

Option 4: Pressure feed wet sump lubricating system

This system uses a pump to circulate oil from the sump to various engine components under pressure. It provides reliable lubrication but is more complex and costly compared to the splash wet sump system. It is used in engines that require more precise lubrication.

Explanation:

Flash Point:

• The flash point of a substance is the lowest temperature at which it can vaporize to form an ignitable mixture in air. It is a crucial parameter in determining the fire hazard of fuels and lubricants. A lower flash point indicates higher flammability, which is a significant safety concern during storage, handling, and use.

Pour Point:

• The pour point is the lowest temperature at which a liquid (such as oil or fuel) will pour or flow under specific conditions. This property is critical for understanding the low-temperature performance of lubricants, ensuring they remain fluid enough to provide adequate lubrication in cold environments. The pour point helps in selecting the appropriate lubricant for applications in varying climatic conditions.

Fire Point:

• The fire point is the temperature at which the vapors of a lubricant or oil will continue to burn for at least five seconds after ignition by an open flame. Unlike the flash point, which indicates the temperature at which vapors can ignite momentarily, the fire point indicates a sustained combustion temperature, providing a more comprehensive understanding of the fire hazards associated with the substance.

Explanation:

Radiators in IC Engine Systems

Definition: Radiators in Internal Combustion (IC) engine systems are critical components designed to dissipate heat from the engine coolant to the atmosphere, maintaining optimal engine operating temperatures. Efficient cooling is essential to prevent overheating, which can lead to engine damage or failure.

Types of Radiators: The two primary types of radiators used in IC engine systems are the tubular core type and the cellular core type.

Tubular Core Type Radiator:

The tubular core type radiator consists of a series of tubes through which the engine coolant flows. These tubes are surrounded by thin metal fins that increase the surface area for heat dissipation. The air passes over the fins and tubes, carrying away the heat from the coolant. This type of radiator is known for its efficiency in transferring heat and its ability to handle higher pressures.

Key Features:

• High heat transfer efficiency due to the increased surface area provided by the fins.
• Durable construction, often made from materials like aluminum or copper.
• Ability to handle higher pressures and temperatures.

Advantages:

• Effective in maintaining engine temperature within a narrow range.
• Capable of dissipating large amounts of heat, making them suitable for high-performance engines.
• Relatively easy to manufacture and maintain.

Disadvantages:

• Can be prone to clogging if not properly maintained, affecting performance.
• Higher manufacturing costs compared to simpler designs.

Applications: Tubular core radiators are commonly used in automotive and industrial applications where efficient heat dissipation is crucial. They are particularly favored in high-performance vehicles and heavy-duty machinery.

Cellular Core Type Radiator:

The cellular core type radiator, also known as a honeycomb radiator, consists of a series of small passages or cells through which the coolant flows. The design resembles a honeycomb structure, providing a large surface area for heat exchange. Air passes through the cells, absorbing the heat from the coolant and dissipating it into the atmosphere.

Key Features:

• Honeycomb structure provides a large surface area for heat transfer.
• Lightweight construction, often made from aluminum or other lightweight materials.
• Compact design, making them suitable for applications with space constraints.

Advantages:

• Efficient heat transfer due to the large surface area.
• Lightweight and compact, making them ideal for use in smaller vehicles or applications with limited space.
• Lower manufacturing costs compared to tubular core radiators.

Disadvantages:

• Less durable than tubular core radiators, with a higher likelihood of damage from debris or impacts.
• Can be more challenging to clean and maintain due to the small cell size.

Applications: Cellular core radiators are commonly used in passenger cars, motorcycles, and other applications where space and weight are significant considerations. They are also used in some industrial equipment where compact and lightweight cooling solutions are needed.

Correct Option Analysis:

The correct option is:

Option 1: Tubular core type and cellular core type.

This option correctly identifies the two primary types of radiators used in IC engine systems. Both types are widely used due to their respective advantages in heat dissipation and design characteristics.

Additional Information

To further understand the analysis, let’s evaluate the other options:

Option 2: Tubular core type and reciprocating core type.

This option is incorrect because there is no widely recognized radiator type known as a reciprocating core type. Radiators do not operate on a reciprocating mechanism.

Option 3: Reciprocating core type and rotating core type.

This option is also incorrect because neither reciprocating core type nor rotating core type are recognized types of radiators used in IC engine systems. These terms do not apply to radiator technology.

Option 4: Rotating core type and cellular core type.

This option is incorrect because rotating core type is not a recognized type of radiator. The correct type is tubular core, not rotating core.

Conclusion:

Understanding the types of radiators used in IC engine systems is essential for recognizing their design and operational characteristics. The tubular core type and cellular core type radiators are the primary types used, each with its own advantages and applications. The tubular core type is known for its high heat transfer efficiency and durability, while the cellular core type is favored for its lightweight and compact design. Proper maintenance and selection of the appropriate radiator type are crucial for ensuring optimal engine performance and longevity.

Concept:

• Whenever the engine is started from cold, the coolant temperature has to be brought to the desired level in order to minimize the warm-up time.
• This purpose is achieved by a thermostat fitted in a system which initially prevents the circulation of water below a certain temperature through the radiator so that the water gets heated up quickly.
• When the preset temperature is reached, the thermostat allows the water to flow through the radiator.

Explanation:

Petroil (Petro-oil lubrication system): In this method, the lubricating oil is mixed with petrol and fed into the engine cylinder during the suction stroke. The droplets of the partials cause the lubricating effect in the engine cylinder.

This method of lubrication is used in small engines like motorcycles and scooters. The system of lubrication is used in scooters and motorcycles, particularly for two-stroke engines about 3 to 6% of lubrication oil is added with petrol is the petrol tank.

The petrol evaporates when the engine is working. The lubricating oil is left behind in the form of mist. The parts of the engine such as piston, cylinder walls and connecting rod are lubricated by being waited with the oil mist left behind.

Splash lubrication system: The splashing action of oil maintains a fog or mist of oil that drenches the inner parts of the engine such as bearings, cylinder walls, pistons, piston pins, timing gears etc. The splash oil then drips back into the sump.

This system is commonly used in a single-cylinder engine with the closed crankcase.

Explanation:

There are two types of cooling systems used for cooling the IC engines.

1. Liquid or indirect cooling system
2. Air or direct cooling system

Air or direct cooling system:

• In an air-cooled system, a current of air is made to flow past the outside of the cylinder barrel, the outer surface area of which has been considerably increased by providing cooling fins.
• This method is mainly applicable to engines in motorcycles, small cars, airplanes, and combat tanks where the motion of the vehicle gives a good velocity to cool the engine.
• In bigger units, a circulating fan is also used.
• The value of the heat transfer coefficient between metal and air is appreciably low.
• As a result of this, the cylinder wall temperatures of the air-cooled cylinders are considerably higher than those of the water-cooled type.

Liquid or indirect cooling system:

• In this system, mainly water is used and made to circulate through the jackets provided around the cylinder, cylinder head, valve ports and seats where it extracts most of the heat. It is used for heavy vehicles.

Water cooling is carried out by the following five methods:

(a) Director non-return system

(b) Thermosyphon system

(c) Forced circulation cooling system

(d) Evaporative cooling system

(e) Pressure cooling system

Evaporative cooling system:

• This is predominately used in stationary engines and in many types of industrial engines.
• In this system, the engine will be cooled because of the evaporation of the water in the cylinder jackets into steams.

Thermosyphon system:

• In this system, the circulation of water is due to the difference in temperature of the water. So, in this system pump is not required but water is circulated because of density difference only.

Forced circulation cooling system:

• This system is used in many vehicles like cars, buses, trucks and other heavy vehicles. Here, the circulation of water takes place with convection currents helped by a pump.

The primary purpose of the lubrication system is to lubricate sliding surfaces and reduce friction losses in the engine, whilst secondary issues are involved with heat transfer.

These are mainly classified into two categories:

A. Non-positive displacement pumps:

• Centrifugal pump is a non-positive displacement pump. In this there is a relative motion between the fluid and motor. It imparts velocity energy to the fluid, which is converted to pressure energy upon exiting the pump casing.
• These pumps are also known as hydro-dynamic pumps. In these pumps the fluid is pressurized by the rotation of the propeller and the fluid pressure is proportional to the rotor speed. 
• These pumps cannot withstand high pressures and generally used for low-pressure and high-volume flow applications.
• These pumps are primarily used for transporting fluids and find little use in the hydraulic or fluid power industries.

B. Positive displacement pumps:

• Positive displacement pump is a pump in which there is a physical displacement of boundary of fluid mass.
• These pumps deliver a constant volume of fluid in a cycle. The output fluid flow is constant and is independent of the system pressure (load).
• These pumps are used in most of the industrial fluid power applications.
• Important positive displacement pumps are gears pumps, vane pumps and piston pumps.

Explanation:

Petroil (Petro-oil lubrication system): In this method, the lubricating oil is mixed with petrol and fed into the engine cylinder during the suction stroke. The droplets of the partials cause the lubricating effect in the engine cylinder.

This method of lubrication is used in small engines like motorcycles and scooters. The system of lubrication is used in scooters and motorcycles, particularly for two-stroke engines about 3 to 6% of lubrication oil is added with petrol is the petrol tank.

The petrol evaporates when the engine is working. The lubricating oil is left behind in the form of mist. The parts of the engine such as piston, cylinder walls and connecting rod are lubricated by being waited with the oil mist left behind.

Splash lubrication system: The splashing action of oil maintains a fog or mist of oil that drenches the inner parts of the engine such as bearings, cylinder walls, pistons, piston pins, timing gears etc. The splash oil then drips back into the sump.

This system is commonly used in a single-cylinder engine with a closed crankcase.

Concept:

Flash Point: The flash point of a volatile material is the lowest temperature at which vapors of the material will ignite when given an ignition source.

Fire Point: The fire point of a fuel is the lowest temperature at which the vapor of the fuel will continue to burn for at least 5 seconds after ignition by an open flame. The main difference in fire and flashpoint is that at the flashpoint a substance will ignite briefly, but vapor might not be produced at a rate to sustain the fire.

Flashpoint and fire points are related to high-temperature characteristics of the fuel and tell the behavior of fuel at high temperatures.

Cloud Point: Cloud point is the temperature at which oil becomes cloudy or hazy when oil is cooled at a specified rate.

Pour Point: It is the temperature at which oil just ceases to flow. The pour point of the liquid is the lowest temperature at which it becomes semi-solid and loses its flow characteristics.

Cloud point and pour point are related to low-temperature characteristics of the fuel and tells the behavior of fuel at low temperatures.

Explanation:

• In the radiator, the hot coolant enters from the engine and it gets cooled down by the atmospheric air
• So there is a requirement of material with high thermal conductivity and also corrosion resistance with coolant
• So copper tubes are used due to high thermal conductivity

Concept:

The function of a lubrication system is to provide a sufficient quantity of cool, filtered oil to give positive and adequate lubrication to all the moving parts of an engine. The various lubrication systems used for internal combustion engines may be classified as:

• Mist lubrication system
• Wet sump lubrication system
• Dry sump lubrication system

Mist lubrication system:

• In two-stroke engines, mist lubrication is used where crankcase lubrication is not suitable. In a two-stroke engine, as the charge is compressed in the crankcase, it is not possible to have the lubricating oil in the sump. Hence, mist lubrication is adopted in practice.
• In such engines, the lubricating oil is mixed with the fuel, the usual ratio being 3% to 6%. The oil and fuel mixture is inducted through the carburetor.
• The fuel is vaporized and the oil (mist form) goes through the crankcase into the engine cylinder. The mist from the oil strikes the crankcase walls, lubricates connecting rod bearings, and the remaining oil lubricates the piston, piston rings, and the cylinder.

Wet sump lubrication system:

In the wet sump system, the bottom of the crankcase contains an oil pan or sump from which the lubricating oil is pumped to various engine components by a pump. After lubricating these parts, the oil flows back to the sump by gravity. There are three varieties in the wet-sump lubrication system.

• the splash system
• the splash and pressure system
• the pressure feed system

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Dry Sump Lubrication System:

Explanation:

Pressure Cap:

• In normal atmospheric conditions, water boils at 100°C.
• In higher altitude height the atmospheric pressure is low and water boils at a temperature below 100°C.
• To increase the boiling temperature of the water the pressure of the cooling system is increased.
• This is achieved by providing pressure caps to seal the system.
• The coolant loss, due to evaporation is also minimized, by using a pressure cap.
• It also permits the engine to operate at a higher temperature so that better efficiency of the engine is achieved.
• The pressure cap is fitted in the filler neck portion on the top of the radiator tank. If the pressure is increased by 15 P.S.I., the boiling temperature raises to 113°C.

Explanation:

Splash system: 

• Used in light-duty, slow-speed engines (<250 rpm)
• Lubricating oil is stored at the bottom of the engine crankcase and maintained at a predetermined level.
• The oil is drawn by the pump and delivered through a distributing pipe into the splash trough located under the big end of all the connecting rods.
• These troughs are provided with overflows and oil in the trough is therefore kept at a constant level.
• A splasher or dipper is provided under each connecting rod cap which dips into oil in the trough at every revolution of the crankshaft and the oil is splashed all over the interior of the crankcase, into the pistons, and onto the exposed portion of cylinder walls.
• The oil dripping from the cylinder is collected in the sump where it is cooled by the air flowing around. The cooled air is then recirculated.
• A splash system of lubrication is employed for the camshafts, piston rings, and tappets.

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