Lesson Notes By Weeks and Term - Senior Secondary 2

Automobile: A petrol engine

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TERM – 1ST TERM

WEEK ONE

Class: Senior Secondary School 2

Age: 16 years

Duration: 40 minutes of 5 periods each

Date:

Subject: AUTO MECHANICAL

Topic: AUTOMOBILE: A PETROL ENGINE

SPECIFIC OBJECTIVES: At the end of the lesson, pupils should be able to

I.) Define a petrol engine

II.) Describe the two-stroke cycle operation of the engine

III.) Discuss the working principles of a two-stroke cycle operation

INSTRUCTIONAL TECHNIQUES: Identification, explanation, questions and answers, demonstration, videos from source

INSTRUCTIONAL MATERIALS: Videos, loud speaker, textbook, pictures,

INSTRUCTIONAL PROCEDURES

PERIOD 1-2

PRESENTATION

TEACHER’S ACTIVITY

STUDENT’S

ACTIVITY

STEP 1

INTRODUCTION

The teacher explains the meaning of Petrol Engine and identify the two ways an engine operates.

Students listens attentively to the teacher                                                                          

STEP 2

EXPLANATION

Teacher discusses the working principles of a petrol engine

Students exhibit attentiveness and active engagement

STEP 3

NOTE TAKING

The teacher writes a summarized

note on the board

The students

copy the note in

their books

 

NOTE

AUTOMOBILE: A PETROL ENGINE

A petrol engine, also known as a gasoline engine, is an internal combustion engine that operates by burning a mixture of fuel and air. In a petrol engine, fuel, usually gasoline, is mixed with air in the engine's combustion chamber, compressed, ignited by a spark plug, and then burned to create power. A petrol engine can operate using either a two-stroke cycle or a four-stroke cycle.

Two stroke cycle operation

The two-stroke cycle operation is a type of internal combustion engine operation where the four strokes of intake, compression, power, and exhaust occur within just two strokes of the piston.

The working sequence of a two-stroke cycle operation

  1. Intake/Compression Stroke:

   - As the piston moves downward on its first stroke, it uncovers the intake port.

   - Simultaneously, a mixture of fuel and air is drawn into the crankcase from the carburetor or fuel injector.

   - The upward movement of the piston compresses this mixture in the crankcase.

  1. Power/Exhaust Stroke:

   - As the piston reaches the bottom of its stroke, it uncovers the exhaust port while covering the intake port.

   - The compressed air-fuel mixture in the crankcase is forced through the transfer ports into the combustion chamber.

   - At the same time, the piston uncovers the spark plug, igniting the compressed mixture.

   - The combustion of the mixture generates high pressure, driving the piston downward with considerable force.

   - As the piston moves downward, it pushes the remaining exhaust gases out through the exhaust port.

  1. Scavenging and Fresh Charge Admission:

   - Towards the end of the power stroke, the piston uncovers the transfer ports while still covering the exhaust port.

   - The incoming fresh air-fuel mixture from the crankcase is pressurized by the descending piston, displacing the remaining exhaust gases out of the cylinder through the exhaust port.

   - The fresh mixture enters the combustion chamber, displacing the exhaust gases completely, and preparing for the next cycle.

  1. Repeating the Cycle:

   - The upward stroke of the piston repeats the cycle by covering the transfer ports, compressing the fresh mixture in the crankcase, and setting up for the next power stroke.

EVALUATION: 1. What is a petrol engine?

  1. Identify the two operations of the petrol engine
  2. Discuss the working principle of a two-stroke cycle operation

CLASSWORK: As in evaluation

CONCLUSION: The teacher commends the students positively