Engine Cooling and Systems

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Questions and Answers

What does the variable $K$ represent in the equation for calculating the quantity of cooling water required?

Constant depending on compression ratio and specific water consumption (correct)

Heat transferred to the coolant

Percentage of energy going to the coolant

Permissible temperature rise of the cooling water

What is the total energy input to the petrol engine as calculated in the example?

100 kW

384.615 kJ/s (correct)

30 kJ/s

115.385 kJ/s

Which of the following percentages represents the heat loss to coolant for the diesel engine?

30%

26.5%

31%

26% (correct)

How much cooling water is required for the diesel engine?

0.668 kg/s Signup and view all the answers

Which engine has a higher percentage of energy going to the coolant?

Petrol engine with 30% Signup and view all the answers

What is the primary reason for cooling an engine?

To prevent excessive overheating of engine parts Signup and view all the answers

What may happen if the piston head is kept at high temperature?

Deterioration of lubricating oil properties Signup and view all the answers

Which of the following is a disadvantage of engine cooling?

Difficulty in starting the engine at low temperatures Signup and view all the answers

What is the primary cooling method used in automobile engines?

Water cooling Signup and view all the answers

What is typically used in water cooling systems for cold starting?

Anti-freezing agents Signup and view all the answers

How does finning contribute to air-cooled engines?

Promotes heat transfer by increasing surface area Signup and view all the answers

What may occur due to high local temperatures in an engine?

Lowered operational efficiency Signup and view all the answers

What is the typical fin height maintained in air-cooled engines?

15-25 mm Signup and view all the answers

What is a disadvantage of air cooling compared to water cooling?

Higher combustion noise Signup and view all the answers

Which cooling method utilizes the principle of thermodynamics to enhance heat removal?

Thermo-syphon cooling Signup and view all the answers

What is a primary function of the radiator in a water-cooled engine?

Reject coolant heat to the atmosphere Signup and view all the answers

What is a disadvantage of water cooling methods?

Increased engine weight and size Signup and view all the answers

What effect does higher specific output in water-cooled engines have?

It allows placement flexibility within vehicles Signup and view all the answers

Which method of heat removal is the term 'radiator' incorrectly associated with?

Radiant heat transfer Signup and view all the answers

What advantage does air cooling have regarding engine design?

It has a simpler engine design Signup and view all the answers

What is a disadvantage of using a cooling fan in a water cooling system?

Rising noise level Signup and view all the answers

Study Notes

Engine Cooling

Engine cooling is crucial to prevent overheating of engine components.
Excessive heat can lead to pre-ignition, reduced material strength, and piston seizure.
Lubricating oil deteriorates at high temperatures, causing further damage.
High temperatures cause uneven expansion, potentially resulting in cracking.
High temperatures reduce the density of the fresh air charge, impacting power output.

Disadvantages of Cooling

Low engine temperatures make starting difficult.
Corrosion increases at low temperatures, shortening engine lifespan.
Low temperatures lead to the formation of corrosive acids from fuel combustion, damaging the cylinder barrel.
Optimal engine operation requires a suitable operating temperature.

Cooling Systems

Air Cooling: Air alone directly cools the engine
Air cooling is used for smaller engines needing less weight.
Examples include aircraft, agricultural, and industrial engines.
Cylinder and cylinder heads are finned to increase surface area, promoting heat transfer.
Fin height (15-25 mm) impacts engine size and thermally-stressed parts need adequate fins.
Water Cooling: Water cools the engine
Water is used in car engines.
Coolant flows through a water jacket surrounding the cylinder and head.
Water velocity and flow are important for effective cooling.
Anti-freezing agents (kerosene, alcohol, etc.) are used in cold temperatures.
Cooling methods include thermo-syphon, thermostat, pressurized water, and evaporative cooling.

Cooling System Operation

Engine Cold (Thermostat Closed): Coolant circulates through a bypass to the pump, and back to the engine, not going through the radiator.
Engine Warm (Thermostat Open): Coolant circulates through the radiator, cooled by passing through it.

Advantages and Disadvantages of Air Cooling

Advantages: Lightweight engine, simpler design, less sensitive to climate, better warm-up, reduced carbon deposits, easier control.
Disadvantages: Higher combustion noise, lower volumetric efficiency, and higher cylinder head temperature.

Advantages and Disadvantages of Water Cooling

Advantages: Higher latent heat of water enables more heat removal from hot spots, higher volumetric efficiency, easier to place anywhere in the vehicle, higher output
Disadvantages: Increased weight and size of the engine, needs more maintenance.

Radiator

The radiator's function is to transfer coolant heat to the atmosphere.
Heat transfer occurs via conduction and forced convection, not radiation.
The cooling effect is achieved by dividing the hot coolant into fine streams that then heat the large metal surfaces of the radiator.

Fan

Fans maintain adequate air flow across the radiator, especially at low speeds and during idling.
Disadvantages: Increased noise level, higher power consumption, and possibility of overcooling.

Quantity of Cooling Water

Quantity of required cooling water is calculated using the formula: Mf = QBP /(K * ΔΤ).
QBP is the heat transferred to coolant, ΔT is permissible temperature increase, and K is a constant dependent on compression ratio and water consumption.

Solved Example

Calculation of cooling water required for a 100 kW petrol and diesel engine with water temperature increase of 30°C.
Thermal efficiencies and percentages of heat loss to coolant are used in the calculations.

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Description

This quiz covers essential concepts of engine cooling, discussing its importance in preventing overheating and the effects of temperature on engine performance. It also explores the disadvantages of inadequate cooling and various cooling systems, such as air cooling. Test your knowledge about maintaining optimal engine conditions and the impacts of temperature on engine efficiency.