Four-stroke cycle

Definition

The four-stroke cycle is a thermodynamic process that describes the operation of an internal combustion engine, consisting of four distinct strokes: intake, compression, power, and exhaust. Each stroke plays a crucial role in converting fuel into mechanical energy, facilitating efficient engine operation. Understanding this cycle is key to grasping how internal combustion engines generate power and how they are designed for performance and efficiency.

5 Must Know Facts For Your Next Test

1. The four strokes are: intake (drawing in air-fuel mixture), compression (compressing the mixture), power (igniting the mixture to create power), and exhaust (expelling spent gases).
2. Each complete cycle requires two revolutions of the crankshaft, with each stroke occurring in sequence to maintain continuous engine operation.
3. The four-stroke cycle is essential for optimizing fuel efficiency and minimizing emissions in modern internal combustion engines.
4. Engines designed with a four-stroke cycle generally produce smoother power delivery compared to two-stroke engines, which have a simpler cycle.
5. The design and timing of each stroke are critical for maximizing performance and reliability, often regulated by components like camshafts and timing belts.

Review Questions

• How does each stroke in the four-stroke cycle contribute to the overall function of an internal combustion engine?
  • Each stroke in the four-stroke cycle plays a vital role in the engine's operation. During the intake stroke, the engine draws in an air-fuel mixture. The compression stroke then compresses this mixture, increasing its temperature and pressure. The power stroke ignites this compressed mixture, generating force that drives the piston down. Finally, the exhaust stroke expels the spent gases from the combustion process, allowing for a new cycle to begin. Together, these strokes enable continuous power generation.
• Compare and contrast the four-stroke cycle with a two-stroke cycle in terms of efficiency and power output.
  • The four-stroke cycle is generally more fuel-efficient than a two-stroke cycle because it allows for complete combustion and more effective expulsion of exhaust gases. In contrast, a two-stroke cycle completes a power stroke every revolution of the crankshaft, leading to higher power output but at the cost of increased emissions and reduced fuel efficiency due to incomplete combustion. This makes four-stroke engines preferable for applications requiring efficiency and lower emissions.
• Evaluate how advancements in technology have influenced the design and performance of four-stroke engines in recent years.
  • Advancements in technology have significantly enhanced the design and performance of four-stroke engines. Innovations such as variable valve timing improve efficiency by optimizing the timing of intake and exhaust strokes based on engine speed. Additionally, computer-controlled fuel injection systems ensure precise fuel delivery, improving combustion efficiency and reducing emissions. These technologies not only enhance power output but also contribute to compliance with stricter environmental regulations, making modern four-stroke engines more efficient and cleaner than ever before.

Related terms

Internal Combustion Engine: An engine that generates mechanical energy through the combustion of fuel with air, resulting in a series of controlled explosions.

Piston: A cylindrical component that moves within the engine cylinder, transferring force from the combustion process to the crankshaft.

Combustion Chamber: The area within the engine where fuel and air mix and ignite, creating the pressure necessary to drive the piston.