The Four-Stroke Engine
Lesson notes
Overview
Intake, compression, power and exhaust strokes repeat to turn fuel into rotation. This topic is rated beginner and is number 16 of 93 in Engineering. Core ideas and first intuitions. No prior knowledge needed.
What you are seeing
The panel above shows the steps of a process, laid out in order. Click a step to see what happens next. The animation is drawn live from the model, so everything you see responds to the sliders. Press Space to pause, use Restart to replay from the start, and change the speed to slow down quick events.
In depth
A petrol engine works in four strokes of the piston: intake draws in the fuel–air mixture, compression squeezes it, the spark ignites it and the hot gas pushes the piston down in the power stroke, and the exhaust stroke expels the gases. Only one stroke in four produces work, so several cylinders are staggered to give smooth running. The ideal Otto cycle has an efficiency of 1 − r^(1−γ), which rises with the compression ratio.
Reading the relationship
The expression "Otto cycle" is a compact summary of the idea. It uses the symbols O, t, o, c, y, l; name what each one stands for before you start. Then use the sliders to see how changing one quantity changes the others.
A guided exploration
1. Run the animation once with the default settings and describe in words what happens. 2. Change one slider at a time and note which quantity responds most. 3. Push each slider to its extreme and decide whether the result still makes sense.
Try this
Start by only moving one slider at a time. Say aloud what you expect, then check.
Common pitfalls
Always ask what the safety margin is and which assumption would break the design first. Idealised models hide losses, noise and limits.
How it connects
It builds on “Efficiency of Machines”, the topic before it in Engineering. Once you are comfortable, continue with “The Refrigeration Cycle”.
Why it matters
Engineers use this idea to design structures, machines and systems that are safe, efficient and reliable.
Where you might use it
- Revising “The Four-Stroke Engine” before a class, exam or certification
- Designing safe structures, machines and control systems that must work reliably
- Diagnosing faults in electrical, mechanical or signal-processing equipment
- Checking that a design meets safety margins before it is built or deployed
Frequently asked questions
What is The Four-Stroke Engine?
Intake, compression, power and exhaust strokes repeat to turn fuel into rotation. It is a beginner topic in Engineering.
How do I use the The Four-Stroke Engine simulation?
The panel at the top shows the steps of a process, laid out in order. Click a step to see what happens next. Move the sliders one at a time, then press Space to pause the animation and look closer.
What does the formula mean?
The expression Otto cycle packs the idea into symbols. Name each symbol first, then change one quantity with the sliders and see which others respond.
Who is this topic for?
Core ideas and first intuitions. No prior knowledge needed. If the quiz feels hard, reread the lesson notes and try the previous topic first.
What should I learn before this?
Start with “Efficiency of Machines”, the previous topic in Engineering. Each topic in a subject builds on the ones before it.
How do I track my progress?
Press “Mark as learned” on this page. Progress is stored only in this browser and is never sent anywhere. The Browse page can show topics you have learned or still need to learn.
Quick quiz
More in Engineering
See all →The Refrigeration Cycle
A refrigerant absorbs heat inside and releases it outside by cycling through evaporation and condensation.
The Jet Engine
Air is compressed, mixed with fuel, burned and expelled to push the aircraft forward.
Heat Exchangers
Two fluids exchange heat through a thin wall without mixing.