# data[].attributes.body
By the end of this lesson, students will be able to explain the four strokes of an internal combustion engine (intake, compression, power, exhaust) and describe the function of each stroke.

# data[].attributes.body
Students will:
- Identify key engine components
- Understand the timing of each stroke
- Explain the transformation of energy in the engine

# data[].attributes.body
Essential Question: How does a car's engine convert fuel into motion? Students discuss in pairs and share their ideas using a Padlet wall.

# data[].attributes.body
Teacher demonstrates the four strokes using an interactive animation and explains each phase.

# data[].attributes.body
In groups of 3, students create a physical model of the four strokes using simple materials (syringes, balloons). Teacher circulates to provide support.

# data[].attributes.body
Students explore this interactive engine simulation to understand the timing and movement of components.

# data[].attributes.attachment_link.readable_text
Four Stroke Engine

The four stroke engine was first demonstrated by Nikolaus Otto in 1876, hence it is also known as the Otto cycle. The technically correct term is actually four stroke cycle. The four stroke engine is probably the most common engine type nowadays. It powers almost all cars and trucks.

The four strokes of the cycle are intake, compression, power, and exhaust. Each corresponds to one full stroke of the piston; therefore, the complete cycle requires two revolutions of the crankshaft to complete.

Intake

During the intake stroke, the piston moves downward, drawing a fresh charge of vaporized fuel/air mixture. The illustrated engine features a poppet intake valve which is drawn open by the vacuum produced by the intake stroke. Some early engines worked this way; however, most modern engines incorporate an extra cam/lifter arrangement as seen on the exhaust valve. The exhaust valve is held shut by a spring (not illustrated here).

Compression

As the piston rises, the poppet valve is forced shut by the increased cylinder pressure. Flywheel momentum drives the piston upward, compressing the fuel/air mixture.

Power

At the top of the compression stroke, the spark plug fires, igniting the compressed fuel. As the fuel burns it expands, driving the piston downward.

Exhaust

At the bottom of the power stroke, the exhaust valve is opened by the cam/lifter mechanism. The upward stroke of the piston drives the exhausted fuel out of the cylinder.

Ignition System

This animation also illustrates a simple ignition system using breaker points, coil, condenser, and battery.

A number of visitors have written to point out a problem with the breaker points in my illustration. In this style ignition circuit, the spark plug will fire just as the breaker points open. The illustration appears to have this backwards.

In fact, the illustration is correct; it just moves so fast it's difficult to see! Here's a close-up of the frames just at the point the plug fires:

My original intent was to accurately show that the points need to remain closed for only a fraction of a second, called the dwell. By illustrating this, I inadvertently obscured the overall operation of the circuit. Perhaps someday I'll prepare a more detailed illustration of the ignition system alone.

Larger four stroke engines usually include more than one cylinder, have various arrangements for the camshaft (dual, overhead, etc.), sometimes feature fuel injection, turbochargers, multiple valves, etc. None of these enhancements changes the basic operation of the engine.

# data[].attributes.attachment_link.description
Animated illustration and description of the four stroke engine.

# data[].attributes.body
Students complete a diagram labeling activity, identifying the position of the piston and valves in each stroke.

# data[].attributes.body
Advanced students can compare four-stroke and two-stroke engines, creating a Venn diagram of similarities and differences.

# data[].attributes.body
Students write one sentence explaining which stroke they think is most crucial and why.

# data[].attributes.body
Using Padlet's collaboration features, students post one new thing they learned and one question they still have.

# data[].attributes.body
Students research and create a simple infographic showing real-world applications of four-stroke engines.

# data[].attributes.body
Complete the worksheet on calculating engine displacement and compression ratios.

# data[].attributes.body
Watch the suggested video and identify each stroke as it occurs in a real engine.

# data[].attributes.attachment_link.title
4 Stroke Combustion 4K SLOW MOTION | 33,000 FPS | Clear Engine Cylinder