Lesson Note on Petrol Engine – Four Stroke Cycle: Four Stroke Cycle Engine Operation for SS2

Class: Senior Secondary School 2 (SS2 / SSS 2)
Term: 1st Term
Week: 2
Age: 16 years
Duration: 45 minutes
Subject: Auto Mechanic Work
Curriculum Theme: Engine Systems
Previous Lesson: Petrol Engine – Two Stroke Cycle: Two Stroke Cycle Operation.
Topic: PETROL ENGINE – FOUR STROKE CYCLE.
Subject Matter: Meaning of PETROL ENGINE – FOUR STROKE CYCLE (definition of four stroke cycle petrol engine), four stroke cycle engine (intake stroke, compression stroke, power stroke, exhaust stroke)

Specific Objectives

By the end of the lesson, pupils should be able to:

Cognitive Domain:

• Define a four-stroke cycle petrol engine.
• State the four strokes of a petrol engine in the correct order.
• Describe the events that occur during each stroke.

Affective Domain:

• Appreciate the working principle of a four-stroke petrol engine.
• Show interest in the mechanics of internal combustion engines.

Psychomotor Domain:

• Illustrate the piston and valve positions for each stroke.
• Identify the key components involved in the four-stroke cycle on a diagram or live engine.

Social Domain:

• Work cooperatively in groups to discuss the engine cycle.
• Share observations and understanding of the engine’s operation.

Reference Materials

The following resources were used in planning this lesson:

• Senior Secondary Schools Education Curriculum
• State Unified Scheme of Work
• Automobile Engineering by Kirpal Singh
• https://www.youtube.com/watch?v=F7P_5X4v8W8
• https://auto.howstuffworks.com/engine.htm

Instructional Materials

The teacher will teach this lesson with the aid of:

• Live engine (if available)
• Charts illustrating the four-stroke cycle
• Posters showing engine components
• Diagrams of piston and valve movements

Rationale for the Lesson

This lesson helps pupils understand the fundamental working principles of petrol engines found in many vehicles. Knowing how these engines operate is important for future mechanics and for anyone driving or maintaining a car.

Prerequisite/Previous Knowledge

Pupils should have a basic understanding of what an engine is and its purpose in a vehicle.

Lesson Content/Board Summary

PETROL ENGINE – FOUR STROKE CYCLE

Definition of a Four-Stroke Cycle Petrol Engine

A four-stroke cycle petrol engine is an internal combustion engine that completes a cycle of operations (intake, compression, power, and exhaust) in four movements of the piston (two up, two down) and two complete revolutions of the crankshaft.

The Four Strokes of a Petrol Engine

The four strokes are:

• Intake Stroke (Suction Stroke):
• Piston Movement: Moves downwards from Top Dead Centre (TDC) to Bottom Dead Centre (BDC).
• Valve Status: Intake valve is open, exhaust valve is closed.
• Action: A mixture of air and fuel is drawn into the cylinder due to the vacuum created by the downward moving piston.
• Crankshaft Rotation: 180 degrees.
• Compression Stroke:
• Piston Movement: Moves upwards from BDC to TDC.
• Valve Status: Both intake and exhaust valves are closed.
• Action: The air-fuel mixture is compressed, increasing its temperature and pressure. This prepares it for efficient combustion.
• Crankshaft Rotation: 180 degrees (total 360 degrees from start).
• Power Stroke (Combustion/Expansion Stroke):
• Piston Movement: Moves downwards from TDC to BDC.
• Valve Status: Both intake and exhaust valves are closed.
• Action: Just before the piston reaches TDC on the compression stroke, the spark plug ignites the compressed air-fuel mixture. The resulting explosion forces the piston downwards, producing power. This is the only stroke that produces work.
• Crankshaft Rotation: 180 degrees (total 540 degrees from start).
• Exhaust Stroke:
• Piston Movement: Moves upwards from BDC to TDC.
• Valve Status: Exhaust valve is open, intake valve is closed.
• Action: The upward movement of the piston pushes the burnt gases (exhaust fumes) out of the cylinder through the open exhaust valve.
• Crankshaft Rotation: 180 degrees (total 720 degrees or two complete revolutions from start).

Teaching Methods/Instructional Techniques

Discussion, Lecture, Demonstration, Question and Answer, Visual Aids

Instructional Procedures

Step 1: Introduction

Time: 5 minutes
Teaching Skill: Set Induction
Teacher’s Activity: The teacher greets the pupils and asks them what they know about car engines and how they work. The teacher then introduces the topic: PETROL ENGINE – FOUR STROKE CYCLE.
Pupils’ Activity: Pupils respond to the questions and listen attentively to the introduction.
Learning Point: Pupils recall prior knowledge and are prepared for the lesson.

Step 2: Definition of a Four-Stroke Cycle Petrol Engine

Time: 7 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher defines a four-stroke cycle petrol engine, explaining that it completes its cycle in four piston movements and two crankshaft revolutions.
Pupils’ Activity: Pupils listen, take notes, and define the four-stroke cycle petrol engine.
Learning Point: Pupils understand the basic definition of the engine type.

Step 3: Intake Stroke

Time: 7 minutes
Teaching Skill: Illustration/Description
Teacher’s Activity: The teacher explains and illustrates the intake stroke, describing the piston’s downward movement, the opening of the intake valve, and the drawing in of the air-fuel mixture.
Pupils’ Activity: Pupils observe the illustration, describe the events of the intake stroke, and ask questions for clarification.
Learning Point: Pupils understand the first step of the engine cycle.

Step 4: Compression Stroke

Time: 7 minutes
Teaching Skill: Explanation
Teacher’s Activity: The teacher explains the compression stroke, detailing the piston’s upward movement, the closing of both valves, and the compression of the air-fuel mixture.
Pupils’ Activity: Pupils listen, take notes, and describe the compression stroke.
Learning Point: Pupils understand how the air-fuel mixture is prepared for combustion.

Step 5: Power Stroke

Time: 7 minutes
Teaching Skill: Demonstration
Teacher’s Activity: The teacher explains and demonstrates the power stroke, emphasizing the spark ignition, the explosion, and the forceful downward movement of the piston that generates power.
Pupils’ Activity: Pupils observe the demonstration, describe the power stroke, and identify it as the work-producing stroke.
Learning Point: Pupils understand how power is generated in the engine.

Step 6: Exhaust Stroke

Time: 7 minutes
Teaching Skill: Description
Teacher’s Activity: The teacher explains the exhaust stroke, describing the piston’s upward movement, the opening of the exhaust valve, and the expulsion of burnt gases.
Pupils’ Activity: Pupils listen, take notes, and describe the exhaust stroke.
Learning Point: Pupils understand how waste gases are removed from the cylinder.

Step 7: Evaluation/Review

Time: 5 minutes
Teaching Skill: Questioning/Assessment
Teacher’s Activity: The teacher evaluates the learning by asking the following questions:

1. Define a four-stroke cycle petrol engine.
2. List the four strokes of a petrol engine in their correct order.
3. Describe what happens during the Intake Stroke.
4. Explain the main event that occurs during the Power Stroke.

Pupils’ Activity: Pupils answer orally and in writing.

Learning Point: Pupils demonstrate understanding of the lesson.

Step 8: Conclusion

Time: 5 minutes
Teaching Skill: Summarization
Teacher’s Activity: The teacher summarizes the main points of the lesson by briefly reviewing the four strokes and their sequence. The teacher then assigns homework for pupils to draw and label a diagram of the four-stroke cycle.
Pupils’ Activity: Pupils listen to the summary and copy the homework assignment.
Learning Point: Pupils consolidate their understanding of the engine cycle.

Lesson Keywords

• Four-Stroke Cycle – A complete cycle of operations in an internal combustion engine, consisting of intake, compression, power, and exhaust strokes.
• Intake Stroke – The stroke where the air-fuel mixture is drawn into the cylinder.
• Compression Stroke – The stroke where the air-fuel mixture is compressed.
• Power Stroke – The stroke where combustion occurs, forcing the piston down and producing power.
• Exhaust Stroke – The stroke where burnt gases are expelled from the cylinder.
• TDC (Top Dead Centre) – The highest point the piston reaches in the cylinder.
• BDC (Bottom Dead Centre) – The lowest point the piston reaches in the cylinder.

Differentiation

For pupils who grasp the concept quickly, the teacher can challenge them to explain how a two-stroke engine differs from a four-stroke engine. For pupils needing more support, the teacher can provide simplified diagrams and allow for peer-tutoring.

Note for teachers using this lesson plan

Ensure that visual aids like charts or a live engine are available and clearly visible to all pupils. Encourage pupils to actively participate in describing each stroke and to ask questions. Emphasize the sequence and the role of valves and the spark plug in each stroke. Practical demonstration with a working model or animation would greatly enhance understanding.