Compression stroke

Definition

The compression stroke is a phase in the operation of an internal combustion engine where the piston moves upward in the cylinder, compressing the air-fuel mixture before ignition occurs. This stroke is crucial as it increases the pressure and temperature of the mixture, making it more volatile and efficient for combustion. The effectiveness of this process significantly impacts the engine's power output and efficiency.

5 Must Know Facts For Your Next Test

1. During the compression stroke, the piston reduces the volume of the air-fuel mixture, increasing its density and improving combustion efficiency.
2. Higher compression ratios generally lead to more efficient engines, as they allow for greater energy extraction from the combustion process.
3. The timing and duration of the compression stroke are critical; improper timing can lead to issues like knocking or pre-ignition.
4. Compression strokes can vary between different engine types, such as gasoline versus diesel engines, with diesel engines typically having higher compression ratios.
5. Efficient compression strokes can lead to lower emissions and better fuel economy, making them a key focus in engine design and optimization.

Review Questions

• How does the compression stroke impact overall engine performance?
  • The compression stroke directly affects engine performance by increasing the pressure and temperature of the air-fuel mixture. A more effective compression stroke leads to better combustion, resulting in higher power output and efficiency. Inadequate compression can lead to incomplete combustion, reducing both performance and fuel economy.
• Discuss the differences between compression strokes in gasoline engines compared to diesel engines.
  • In gasoline engines, the compression ratio is typically lower, ranging from 8:1 to 12:1, while diesel engines operate at much higher ratios, often exceeding 14:1. This difference is due to the way each engine ignites fuel; gasoline engines use spark plugs for ignition, while diesel engines rely on high compression to ignite fuel. As a result, diesel engines experience more significant temperature rises during the compression stroke, which contributes to their efficiency.
• Evaluate how advancements in technology have influenced the design of compression strokes in modern internal combustion engines.
  • Advancements in technology have greatly influenced the design of compression strokes through improved materials, precision engineering, and electronic controls. For example, variable valve timing allows for optimized intake and exhaust valve operation during different engine speeds, enhancing compression efficiency. Additionally, computer-aided design techniques enable engineers to simulate and analyze combustion processes, leading to innovations like turbocharging that enhance air intake and ultimately improve the effectiveness of the compression stroke.

Related terms

Intake stroke: The phase in which the piston moves downwards to draw in the air-fuel mixture into the cylinder.

Power stroke: The stage in which the ignited air-fuel mixture expands, forcing the piston down and producing power.

Engine efficiency: A measure of how well an engine converts fuel energy into useful work, often impacted by the effectiveness of the compression stroke.