1. Intake and Compression Stroke:
* Intake: As the piston moves downwards, a mixture of fuel and air is drawn into the crankcase through the intake port. This is facilitated by the reduction in pressure caused by the descending piston.
* Compression: The piston continues downwards, compressing the fuel-air mixture in the crankcase.
* Transfer: Near the bottom of the stroke, the piston uncovers a transfer port, allowing the compressed fuel-air mixture to flow into the combustion chamber (above the piston) through a passageway called the transfer port.
* Exhaust: At the same time, the exhaust port is opened by the rising piston, allowing some of the burnt exhaust gases to escape.
2. Power and Exhaust Stroke:
* Power: A spark plug ignites the compressed fuel-air mixture in the combustion chamber, causing an explosion that drives the piston downwards. This downward motion is the power stroke that delivers the engine's power output.
* Exhaust: As the piston moves upwards, the exhaust port is further opened, allowing the remaining exhaust gases to escape. This is the exhaust stroke.
* Scavenging: The fresh fuel-air mixture entering the combustion chamber from the transfer port helps to push out the remaining exhaust gases in a process called scavenging.
Key differences from a four-stroke engine:
* No separate valves: Two-stroke engines use ports in the cylinder wall for intake and exhaust, instead of valves.
* Lubrication: The fuel-air mixture in a two-stroke engine includes oil for lubrication.
* Simpler design: Two-stroke engines are typically simpler in design and have fewer moving parts compared to four-stroke engines.
Benefits of two-stroke engines:
* Lightweight and compact: Due to their simpler design, two-stroke engines are often smaller and lighter than four-stroke engines with similar power outputs.
* High power-to-weight ratio: Two-strokes can deliver high power for their size, making them suitable for applications like motorcycles and small engines.
* Simple operation: The lack of valves makes them easier to maintain.
Drawbacks of two-stroke engines:
* Higher emissions: They produce more harmful emissions (especially unburned hydrocarbons) than four-stroke engines.
* Less fuel-efficient: They consume more fuel than four-stroke engines for a given amount of power.
* More noise: They can be noisier than four-stroke engines due to the design of the exhaust system.
In summary, a two-stroke engine relies on two strokes of the piston to complete a cycle of intake, compression, power, and exhaust. While they are relatively simple and powerful, they suffer from higher emissions and lower fuel efficiency compared to four-stroke engines.
