Petrol works by being mixed with air and ignited inside an engine's combustion chamber, creating expanding gases that push a piston to generate power.
Here's a more detailed look at the process, primarily within a spark-ignited system, which is the most common type for petrol engines:
The Core Principle: Combustion
The power from petrol comes from the process of combustion, essentially controlled burning. When petrol burns rapidly in a confined space, it produces a large amount of hot, expanding gas. This expansion is what drives the engine's moving parts.
Steps in a Spark-Ignited Engine
As described in the reference, in a spark-ignited system, the process involves several key steps:
1. Fuel Injection and Mixing
- The fuel is injected into the combustion chamber (or sometimes the intake manifold just before it).
- This fuel, typically petrol (gasoline), is then combined with air. The precise ratio of air to fuel is crucial for efficient and clean combustion.
2. Compression
- A piston moves upwards within the cylinder, compressing the air/fuel mixture. This increases the temperature and pressure, making the mixture easier to ignite powerfully.
3. Ignition
- The air/fuel mixture is ignited by a spark from the spark plug. This precisely timed spark initiates the rapid combustion.
4. Power Stroke
- The rapid burning and expansion of gases push the piston downwards with great force. This motion is transferred through a connecting rod to a crankshaft, causing it to rotate. This rotating motion is the engine's output power, which ultimately drives the vehicle's wheels.
5. Exhaust
- After the power stroke, the piston moves upwards again, pushing the spent combustion gases (exhaust) out of the cylinder through an exhaust valve. These gases are then expelled from the vehicle's exhaust system.
These steps repeat rapidly in each cylinder of the engine, creating continuous power.
Key Components Involved
- Combustion Chamber: The space where fuel is burned.
- Piston: A cylindrical component that moves up and down inside the cylinder.
- Spark Plug: Creates the spark to ignite the mixture.
- Valves: Control the flow of air/fuel mixture into and exhaust gases out of the chamber.
- Crankshaft: Converts the piston's linear motion into rotational motion.
Petrol vs. Other Fuels
While gasoline is the most common transportation fuel, the reference notes that alternative fuel options use similar components and engine systems. For example, engines running on natural gas or LPG often also use a spark ignition system like petrol engines. Diesel engines, however, work differently, using compression ignition rather than a spark.
Summary Table: Spark-Ignited Engine Cycle
| Step | Action | Purpose |
|---|---|---|
| Intake | Air/Fuel enters combustion chamber. | Prepare for combustion. |
| Compression | Piston compresses air/fuel mixture. | Increase pressure & temperature for ignition. |
| Power | Spark ignites mixture, gases expand. | Piston is pushed down, generating power. |
| Exhaust | Piston expels spent gases. | Clear chamber for the next cycle. |
Understanding how petrol works in this cycle is fundamental to understanding how most cars and many other vehicles are powered.
For more on how the entire engine operates, you can learn about the Internal Combustion Engine.
