The Otto cycle, also known as the four-stroke cycle, is a thermodynamic process that powers gasoline engines. It consists of four distinct strokes: intake, compression, power, and exhaust.
Intake Stroke
- Intake valve opens: The intake valve opens, allowing air to enter the cylinder.
- Piston moves down: The piston moves down, creating a vacuum that draws in the air-fuel mixture.
Compression Stroke
- Intake valve closes: The intake valve closes, trapping the air-fuel mixture inside the cylinder.
- Piston moves up: The piston moves upward, compressing the mixture.
- Temperature and pressure increase: As the mixture is compressed, its temperature and pressure increase significantly.
Power Stroke
- Spark plug ignites: The spark plug ignites the compressed air-fuel mixture, causing a rapid expansion of hot gases.
- Piston moves down: The expanding gases push the piston down, generating power that rotates the crankshaft.
Exhaust Stroke
- Exhaust valve opens: The exhaust valve opens.
- Piston moves up: The piston moves upward, expelling the burnt gases through the exhaust valve.
Cycle Repetition
After the exhaust stroke, the intake valve opens again, and the cycle repeats.
Practical Applications
The Otto cycle is the foundation for most gasoline-powered engines, including:
- Cars: The most common application of the Otto cycle is in internal combustion engines found in cars.
- Motorcycles: Motorcycles also use Otto cycle engines.
- Lawn mowers: Small gasoline engines in lawn mowers and other equipment are based on the Otto cycle.
Key Components
- Intake valve: Controls the flow of air-fuel mixture into the cylinder.
- Exhaust valve: Controls the flow of burnt gases out of the cylinder.
- Piston: Moves up and down within the cylinder, converting the pressure from the combustion process into mechanical energy.
- Crankshaft: Converts the linear motion of the piston into rotational motion.
- Spark plug: Ignites the air-fuel mixture.
Efficiency and Limitations
The Otto cycle is a relatively efficient process, but it has some limitations:
- Heat loss: Some heat energy is lost to the engine block and surrounding air.
- Incomplete combustion: Not all of the fuel is burned completely, resulting in some energy loss.
- Limited compression ratio: The compression ratio of an Otto cycle engine is limited by the tendency for knocking (premature ignition) at high compression ratios.
