1. Combustion Efficiency: In a four-stroke engine, the combustion process occurs over four distinct strokes - intake, compression, power, and exhaust. This allows for a more complete combustion of the fuel-air mixture, resulting in better fuel efficiency and fewer emissions. On the other hand, a two-stroke engine combines the intake and exhaust strokes with the compression and power strokes, leading to less efficient combustion and higher emissions.
2. Thermal Efficiency: The thermal efficiency of an engine refers to how much of the heat energy from the fuel is converted into usable mechanical energy. Four-stroke engines have a higher thermal efficiency compared to two-stroke engines because they can trap and expand the gases more effectively during the power stroke. This results in more power output from the same amount of fuel.
3. Mechanical Efficiency: Mechanical efficiency relates to the amount of energy lost due to friction and other mechanical inefficiencies within the engine. Four-stroke engines typically have better mechanical efficiency than two-stroke engines because they have fewer moving parts and a smoother running cycle. This reduces the energy lost to friction and other mechanical issues, leading to improved overall efficiency.
4. Emissions: Two-stroke engines produce higher levels of emissions compared to four-stroke engines. Because of their combined strokes, two-stroke engines allow some of the unburned fuel-air mixture and exhaust gases to escape during the scavenging process. This results in higher emissions of hydrocarbons (HC), carbon monoxide (CO), and particulate matter (PM). Four-stroke engines, with their separate intake and exhaust strokes, are better at containing and expelling the exhaust gases, leading to lower emissions.
5. Durability: Four-stroke engines generally have a longer lifespan and require less frequent maintenance compared to two-stroke engines. This is due to the more efficient and controlled combustion process of four-stroke engines, which leads to reduced wear and tear on the engine components. Additionally, the lubricating system in four-stroke engines is more effective in reducing friction and ensuring proper lubrication of the engine parts.
In summary, while two-stroke engines may be simpler in design, four-stroke engines offer significantly better fuel efficiency, thermal efficiency, emissions control, and durability.
As a result, four-stroke engines are predominantly used in vehicles, generators, and other applications where efficiency and environmental impact are key considerations.
