Lesson Notes By Weeks and Term v5 - Grade 11

Lesson Video

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Performance objectives

• Describe the function of cooling system components.
• Explain the purpose and components of the lubrication system.
• Describe the fuel delivery process in a petrol engine.
• Identify common faults in these systems.
• Differentiate between air and liquid cooling.

Lesson summary

This week, we delve into the crucial systems that keep an engine running smoothly and efficiently: the cooling, lubrication, and fuel systems. These systems work in concert to manage the intense heat, friction, and fuel delivery required for internal combustion. Understanding these systems is vital, not just for aspiring mechanics, but also for any South African relying on vehicles for transportation, agriculture, or industry. Faulty systems can lead to breakdowns, costly repairs, and even hazardous situations. In a country where many depend on vehicles for livelihood, understanding basic engine maintenance is a valuable skill.

Lesson notes

2.1 Cooling System Engines generate a lot of heat during combustion. If this heat isn't managed, it can damage engine components, cause pre-ignition, and ultimately lead to engine failure. The cooling system removes excess heat, maintaining the engine at its optimal operating temperature (typically between 80-100°C for liquid-cooled engines).

Types of Cooling Systems: Air Cooling: Relies on air flowing over finned surfaces of the engine to dissipate heat. Common in motorcycles and some older vehicles. Less efficient than liquid cooling, especially in hot climates like certain parts of South Africa.

Liquid Cooling: Uses a coolant (typically a mixture of water and antifreeze) to absorb heat from the engine block and cylinder head. The heated coolant then flows to a radiator, where the heat is transferred to the air. More efficient and provides more even temperature distribution. More common in modern vehicles.

Components of a Liquid Cooling System: Engine Block and Cylinder Head Water Jackets: Channels cast into the engine block and cylinder head through which coolant flows, absorbing heat.

Water Pump: Circulates the coolant throughout the system. Usually belt-driven.

Radiator: A heat exchanger that transfers heat from the coolant to the air. Consists of a core (made of tubes and fins) and tanks.

Thermostat: A temperature-sensitive valve that controls the flow of coolant to the radiator. It remains closed when the engine is cold, allowing it to warm up quickly. Once the engine reaches operating temperature, the thermostat opens, allowing coolant to flow to the radiator.

Radiator Cap: Maintains pressure within the cooling system. Pressure increases the boiling point of the coolant, improving cooling efficiency. Contains a pressure relief valve to prevent over-pressurization.

Coolant Reservoir (Expansion Tank): Allows for expansion and contraction of the coolant as it heats up and cools down.

Coolant Hoses: Connect the various components of the cooling system.

Coolant: Usually a mix of water and antifreeze/coolant concentrate. Antifreeze prevents freezing in winter and raises the boiling point in summer, while corrosion inhibitors protect the cooling system components.

Operation of a Liquid Cooling System: The water pump circulates coolant through the water jackets in the engine block and cylinder head. The coolant absorbs heat from the engine. The heated coolant flows to the thermostat. If the engine is cold, the thermostat remains closed, and the coolant bypasses the radiator, circulating only within the engine. Once the engine reaches operating temperature, the thermostat opens, allowing coolant to flow to the radiator. In the radiator, heat is transferred from the coolant to the air flowing through the radiator core. The cooled coolant returns to the engine to absorb more heat. 2.2 Lubrication System The lubrication system reduces friction and wear between moving engine parts. Without lubrication, the metal surfaces would rub directly against each other, generating excessive heat and causing rapid wear and eventual seizure.

Functions of Lubrication: Reduces friction Reduces wear Cools engine components (removes heat) Cleans engine components (suspends contaminants) Seals combustion gases Dampens noise Components of a Lubrication System: Oil Pan (Sump): A reservoir that holds the engine oil.

Oil Pump: Circulates oil throughout the engine. Typically gear-driven or rotor-driven.

Oil Filter: Removes contaminants from the oil.

Oil Pressure Relief Valve: Prevents excessive oil pressure.

Oil Galleries: Passages in the engine block and cylinder head through which oil flows.

Spray Nozzles: Direct oil onto specific components, such as piston skirts and cylinder walls.

Lubrication Methods: Splash Lubrication: An older method where the connecting rods have dippers that splash into the oil in the oil pan, lubricating the cylinder walls, pistons, and connecting rod bearings. Less efficient than pressure lubrication. Found in older or smaller engines.

Pressure Feed Lubrication: The most common method. The oil pump forces oil through the oil filter and oil galleries to the various engine components under pressure. This ensures adequate lubrication even at high engine speeds and loads. Operation of a Pressure Feed Lubrication System: The oil pump draws oil from the oil pan. The oil is pumped through the oil filter to remove contaminants. The filtered oil flows through the oil galleries to the main bearings, connecting rod bearings, camshaft bearings, and valve train components. Oil is sprayed onto the cylinder walls and piston skirts to lubricate these components. Oil returns to the oil pan by gravity. 2.3 Fuel System (Petrol Engine) The fuel system in a petrol (gasoline) engine delivers the correct amount of fuel to the engine at the right time for efficient combustion. Components of a Fuel System (Petrol Engine): Fuel Tank: Stores the fuel.

Fuel Pump: Transfers fuel from the fuel tank to the engine.