Figure 1. 2-stroke internal combustion engine As the name implies, the two strokes engine only requires two piston movements (one cycle) in order to generate power. The engine is able to do and produce power after one cycle because the exhaust and intake of the gas occurs simultaneously, as seen in Figure 1. There is a valve for the intake stroke that opens and closes due to changing pressures. In addition, due to its frequent contact with moving components, the fuel is mixed with oil to add lubrication, allowing smoother strokes. Overall, a two-stroke engine contains two processes:1. Compression stroke: The inlet port opens; the air-fuel mixture enters the chamber and the piston moves upwards compressing this mixture. A spark plug ignites the compressed fuel and begins the power stroke.
2. Power stroke: The heated gas exerts high pressure on the piston, the piston moves downward (expansion), waste heat is exhausted.
The thermal efficiency of these gasoline engines will vary depending on the model and design of the vehicle. However in general, gasoline engines convert 20% of the fuel (chemical) energy to mechanical energy—in which only 15% will be used to move the wheels (the rest is lost to friction and other mechanical elements). Compared to four stroke engines, two strokes are lighter, more efficient, have the ability to use lower-grade fuel, and more cost-efficient. Therefore, the lighter engines results in a higher power-to-weight ratio (more power for less weight). However, they lack the maneuverability possible in four stroke engines and require more lubrication. This makes two stroke engines ideal for ships (need to carry a lot of cargo), motorcycles, and lawn mowers—whereas a four stroke would be ideal for automobiles like cars and trucks.
QUESTIONS:
1. What does the two strokes engine requires in its movement?
2. What are the differences between the compression and power strokes processes?
3. Notwithstanding with a model and a design of vehicle, how does the thermal efficiency of gasoline works in an engine?
4. Explain, why is the two stroke engine ideal for ships’ machinery?​