Exhaust stroke

Definition

The exhaust stroke is the phase in an internal combustion engine cycle where the spent combustion gases are expelled from the combustion chamber, preparing for the next intake of fresh air-fuel mixture. This stroke is crucial as it ensures that the engine operates efficiently by clearing out residual gases that can hinder performance and power output. The proper functioning of this stroke directly affects the overall efficiency and emissions of the engine.

5 Must Know Facts For Your Next Test

1. During the exhaust stroke, the exhaust valves open, allowing gases from combustion to exit the cylinder.
2. This stroke occurs after the power stroke and is essential for maintaining engine performance by preventing exhaust gas buildup.
3. The timing of the exhaust stroke is critical for efficient engine operation and is precisely coordinated with other strokes through the camshaft.
4. Exhaust strokes can vary in duration and efficiency depending on engine design, including factors like valve timing and exhaust system configuration.
5. Properly designed exhaust systems can enhance performance by improving gas flow and reducing back pressure during this stroke.

Review Questions

• How does the exhaust stroke impact overall engine efficiency and emissions?
  • The exhaust stroke directly impacts engine efficiency by ensuring that spent gases are effectively expelled from the combustion chamber. If this phase is not performed correctly, residual gases can mix with fresh air-fuel mixtures during intake, leading to incomplete combustion, reduced power output, and higher emissions. By efficiently clearing out combustion byproducts, the exhaust stroke allows for a cleaner intake charge, which optimizes fuel use and minimizes harmful emissions.
• Discuss how changes in valve timing can affect the effectiveness of the exhaust stroke.
  • Changes in valve timing can significantly affect how effectively the exhaust stroke clears out spent gases from the cylinder. If exhaust valves open too late or close too early, it can lead to incomplete expulsion of gases, which may result in a loss of performance and increased emissions. Optimizing valve timing through technologies like variable valve timing systems can enhance airflow during this phase, improving overall engine efficiency and responsiveness.
• Evaluate how advancements in exhaust system design have influenced modern internal combustion engines' performance during the exhaust stroke.
  • Advancements in exhaust system design have greatly influenced modern internal combustion engines by improving gas flow dynamics during the exhaust stroke. Features like high-flow catalytic converters, tuned headers, and variable geometry exhaust systems reduce back pressure and enhance scavenging effects. This leads to more effective removal of spent gases, resulting in improved performance, better throttle response, and lower emissions. Such innovations play a key role in meeting stringent emission standards while maximizing engine efficiency.

Related terms

Intake Stroke: The phase in an internal combustion engine cycle where the air-fuel mixture is drawn into the combustion chamber as the piston moves down.

Compression Stroke: The stage in the engine cycle where the piston compresses the air-fuel mixture, raising its temperature and pressure before ignition.

Power Stroke: The portion of the engine cycle when combustion occurs, pushing the piston down and generating power for the crankshaft.