Lesson Notes By Weeks and Term v4 - SHS 2
INTRODUCTION TO ENGINE TECHNOLOGY
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INTRODUCTION TO ENGINE TECHNOLOGY
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Subject: Applied Technology
Class: SHS 2
Term: 1st Term
Week: 5
Grade code: 2.1.1.LI.6
Strand code: 1
Sub-strand code: 1
Content standard code: 2.1.1.CS.1
Indicator code: 2.1.1.LI.6
Theme: AUTOMOTIVE TECHNOLOGY
Subtheme: INTRODUCTION TO ENGINE TECHNOLOGY
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Welcome, learners. Today, we are discussing the lifeblood of every vehicle engine: the lubricating oil. In Ghana, where our cars, trotros, and okadas are essential for daily life, understanding how to properly care for an engine is crucial. Using the right oil and ensuring the engine can "breathe" properly through its ventilation system can be the difference between a vehicle that lasts for many years and one that needs expensive repairs. This lesson will empower you to make informed decisions about vehicle maintenance, saving you or your family money and protecting our environment.
This lesson is divided into two main parts: Engine Lubricating Oil and Crankcase Ventilation. Part A: Engine Lubricating Oil
The oil in an engine is not just for making things slippery. It performs several critical jobs at once.
i. Functions of Engine Oil Lubrication: This is the primary function. Engine oil creates a thin, protective film between moving metal parts (like pistons in cylinders, and crankshaft bearings). This film drastically reduces friction, which prevents parts from wearing out and reduces the energy wasted as heat. Cooling: While the coolant system does most of the cooling, engine oil plays a vital role by absorbing heat from areas the coolant cannot reach, such as the bottom of the pistons and the crankshaft bearings. It then carries this heat to the oil pan (sump), where it can cool down. Cleaning (Detergency): As fuel burns, it creates by-products like soot and carbon. Engine oil contains special additives called detergents that clean these deposits off internal engine parts, preventing them from building up and causing damage. Sealing: The oil helps to form a tight seal between the piston rings and the cylinder walls. This is important to keep the high-pressure combustion gases in the combustion chamber (to produce power) and prevent them from leaking into the crankcase. Corrosion Prevention: Combustion can create acidic by-products. The oil contains additives that neutralise these acids and form a protective layer on metal surfaces to prevent rust and corrosion. Holding Contaminants (Dispersancy): The oil not only cleans away contaminants but also holds them in suspension (like sugar dissolved in water). These tiny particles are then carried to the oil filter, where they are trapped and removed. This prevents the particles from clumping together to form damaging "sludge".
ii. Properties of Engine Oil Viscosity: This is the most important property of lubricating oil. Viscosity is a measure of a fluid's resistance to flow. Think of the difference between water and honey. Honey is more "thick" and flows slowly; it has a high viscosity. Water is "thin" and flows easily; it has a low viscosity. Engine oil viscosity changes with temperature. When the engine is cold, the oil is thicker (higher viscosity). When the engine gets hot, the oil becomes thinner (lower viscosity). The challenge is to find an oil that is thin enough to flow quickly during a cold start but thick enough to protect the engine when it is at its hot operating temperature. Viscosity Index (VI): This is a number that indicates how much the oil's viscosity changes with temperature. An oil with a high Viscosity Index changes very little with temperature. This is very desirable. An oil with a low Viscosity Index thins out a lot when it gets hot. This is not good for engine protection. Modern oils have high VI.