Basic structure
They have a cylinder, piston, crankshaft, valves, and a spark plug, just like a 4-stroke engine. However, the key difference lies in the number of strokes required to complete one combustion cycle.
Cycle of operation
- Intake:
- The intake valve opens
- Piston moves downward
- Fuel (petrol) and air mixture is drawn into the cylinder.
- Compression and Power:
- Both the intake and exhaust valves are closed
- The piston moves upward, compressing the fuel-air mixture significantly
- At the peak of compression, the spark plug ignites the fuel-air mix
- The expanding gases push the piston downward, generating power
- Exhaust:
- The piston moves up, pushing the exhaust gases towards the exhaust valve
- The exhaust valve opens, and the exhaust gases escape from the cylinder.
Additional stroke (power)
The primary distinction of a 3-stroke engine is the introduction of an additional power stroke. This additional power stroke is achieved through the use of a special piston called the "floating piston" or the "free-floating piston."
The floating piston is smaller and lighter than the main piston. During the compression stage, it is attached to the main piston and assists in compressing the air-fuel mixture. However, during the power stroke, the floating piston separates from the main piston, allowing the compressed gases to rapidly expand and generate additional power.
This arrangement allows for more efficient energy extraction and utilization of fuel-air mixture energy, resulting in increased power output compared to a typical 2-stroke engine.
Benefits:
- Fuel Efficiency: Due to the additional power stroke, 3-stroke engines have the potential to be more fuel-efficient compared to traditional 2-stroke engines.
- Power Output: The additional power stroke also leads to an increase in power output and torque. This makes them suitable for applications requiring high performance and greater torque.
Applications:
3-stroke engines are generally used in specific niche applications where power density and fuel efficiency are of utmost importance, such as:
- High-performance motorcycles
- Racing engines
- Small UAVs (Unmanned Aerial Vehicles)
- Certain industrial machineries
