How Combustion Engines Work
Transforming fuel into motion, one stroke at a time.
Introduction
An internal combustion engine is a heat engine where the combustion of a fuel occurs with an oxidizer (usually air) in a confined space called a combustion chamber. This combustion generates high-temperature, high-pressure gases, which directly apply force to a component of the engine, such as a piston, to move it over a distance, thereby generating mechanical energy. This is the fundamental principle behind how most cars, motorcycles, and many other machines move.
Key Components
Before exploring the engine's cycle, let's identify its main parts. Hover over the labels to highlight the components in the diagram.
- Cylinder Block: The main body of the engine, containing the cylinders.
- Piston: A cylindrical component that moves up and down within the cylinder, converting gas pressure into mechanical force.
- Connecting Rod: Connects the piston to the crankshaft, transmitting the piston's linear motion.
- Crankshaft: Converts the up-and-down (reciprocating) motion of the pistons into rotational motion, which powers the vehicle.
- Cylinder Head: Sits atop the cylinder block, sealing the combustion chamber and housing the valves and spark plug.
- Intake Valve: Opens to allow the fuel-air mixture into the cylinder.
- Exhaust Valve: Opens to allow spent combustion gases to exit the cylinder.
- Spark Plug: Ignites the compressed fuel-air mixture.
The Four-Stroke Cycle
Most modern gasoline engines operate on a four-stroke cycle, meaning the piston completes four distinct movements (strokes) for each power-generating combustion event.
Interactive Engine Cycle
Click "Next Stroke" to advance through the four stages of the engine cycle.
Intake Stroke
The piston moves downwards, creating a vacuum. The intake valve opens, allowing a mixture of fuel and air to be drawn into the cylinder. The exhaust valve remains closed.
Engine Process Flow
This flowchart summarizes the sequence of events in a four-stroke internal combustion engine.