Lesson Notes By Weeks and Term v4 - SHS 3
INTRODUCTION TO ENGINE TECHNOLOGY
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INTRODUCTION TO ENGINE TECHNOLOGY
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Subject: Applied Technology
Class: SHS 3
Term: 1st Term
Week: 2
Grade code: 3.1.1.LI.3
Strand code: 1
Sub-strand code: 1
Content standard code: 3.1.1.CS.1
Indicator code: 3.1.1.LI.3
Theme: AUTOMOTIVE TECHNOLOGY
Subtheme: INTRODUCTION TO ENGINE TECHNOLOGY
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Welcome, students. Today, we are going to explore how a car engine "breathes." Just like humans need clean air to live and have energy, an engine needs a constant supply of clean air to burn fuel and produce power. Think about the cars you see every day on our roads – the tro-tros in Madina, the taxis in Kejetia, or the private cars on the motorway. They all depend on an efficient air intake system to work properly. Especially in Ghana, with our dusty roads and the Harmattan season, understanding how an engine gets its air and keeps it clean is crucial for performance, fuel savings, and longevity.
The Air Intake System is a network of components designed to deliver clean, filtered air to the engine's cylinders for combustion. For fuel to burn, it needs oxygen, which it gets from the air. The ideal air-to-fuel ratio for a petrol engine is approximately 14.7 parts air to 1 part fuel (14.7:1) by mass. The intake system's job is to provide the correct amount of clean air to maintain this ratio.
Let's break down the journey of air through the main components, in the order it travels. Main Components and Their Functions
Analogy: Think of the engine's intake system like your own breathing system. You breathe in air through your nose/mouth (Air Inlet), your nose hairs filter out dust (Air Filter), your throat controls how much air goes in (Throttle Body), and the air travels down your windpipe (Intake Manifold) into your lungs (Cylinders). Air Inlet / Air Duct What it is: The opening, often located in the front grille or engine bay, where air from the atmosphere first enters the system. It is connected to the air filter housing by a plastic or rubber tube. Function: To draw in the coolest, densest air possible from outside the hot engine bay. Cooler air is denser, meaning it contains more oxygen molecules per unit volume, which leads to better combustion and more power. Air Filter / Air Cleaner What it is: A device containing a filter element, usually made of pleated paper, foam, or cotton gauze, housed in a plastic or metal box. Function: This is the engine's "nose hair" or "face mask." Its critical job is to trap dust, dirt, pollen, insects, and other debris from the air before it enters the engine. Ghanaian Context: On our dusty laterite roads or during the Harmattan, the air is filled with fine particles. A high-quality, clean air filter is essential to prevent this abrasive dust from entering the engine, where it can cause rapid wear on pistons, rings, and cylinder walls, leading to expensive damage. Consequence of a Dirty Filter: A clogged filter restricts airflow. The engine struggles to "breathe," leading to: Reduced Power: Less air means less oxygen for combustion. Poor Fuel Economy: The engine's computer may inject the normal amount of fuel for the expected amount of air, leading to a "rich" mixture (too much fuel, not enough air). This unburnt fuel is wasted and goes out the exhaust, costing the driver more money. Increased Emissions: Incomplete combustion produces more smoke and pollutants like carbon monoxide. Mass Airflow (MAF) Sensor What it is: An electronic sensor located in the air duct between the air filter and the throttle body. It has a small, heated wire or film that is cooled by the incoming air. Function: It measures the mass (how much) and density of the air entering the engine. It sends this information to the Engine Control Unit (ECU), which is the engine's computer or "brain." The ECU then uses this data to calculate precisely how much fuel to inject to maintain the optimal 14.7:1 air-fuel ratio. Importance: It is a key sensor for modern fuel-injected engines, ensuring efficiency and low emissions. Throttle Body What it is: A valve located before the intake manifold. It contains a butterfly valve (a metal plate) that pivots to open and close. Function: It acts as the "gate" that controls the *volume* of air entering the engine. It is connected to the accelerator pedal (the "gas pedal"). When you press the accelerator, the butterfly valve opens, allowing more air in. The ECU detects this and injects more fuel, causing the engine to produce more power and the car to accelerate. When you release the pedal, the valve closes, restricting airflow, and the engine returns to idle speed. Intake Manifold What it is: A series of pipes or runners that branch out from the throttle body. Function: Its job is to evenly distribute the air from the throttle body to each of the engine's cylinders. A well-designed manifold ensures that each cylinder receives the same amount of air for balanced and smooth engine operation. Intake Valves What they are: Mechanical valves located inside the cylinder head, one or two per cylinder. Function: These are the final "doors" that open to allow the air-fuel mixture into the combustion chamber (the cylinder) at the precise moment of the intake stroke. They then close tightly to seal the chamber for compression and combustion. Summary of the Air's Journey (Step-by-Step) Cool air is drawn from the atmosphere through the Air Inlet. The air passes through the Air Filter, where dust and debris are removed. The clean air flows past the MAF Sensor, which measures its mass and sends the data to the ECU. The air then reaches the Throttle Body, where the butterfly valve, controlled by the driver's accelerator pedal, regulates how much air can proceed. The air enters the Intake Manifold, which channels and distributes it equally to each cylinder. Finally, as the piston moves down on the intake stroke, the Intake Valve(s) for that cylinder open, and the air is drawn into the cylinder to be mixed with fuel for combustion.
Guided Practice (With Solutions)