State any four important types (shapes) of combustion chambers common in SI engines?

 Here are four important types (shapes) of combustion chambers commonly used in Spark Ignition (SI) engines:

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1. 🔵 Hemispherical Combustion Chamber (Hemi Head)

• Shape: Dome-shaped like half a sphere

• Features:

  • Allows large valves for better airflow

  • Good swirl and turbulence

  • Promotes efficient combustion

• Advantages: High volumetric efficiency and power output

• Used In: High-performance and racing engines

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2. 🔷 Wedge-Shaped Combustion Chamber

• Shape: Angled or wedge-like structure

• Features:

  • Simpler design

  • Generates squish and swirl during compression

  • Helps in faster flame propagation

• Advantages: Compact, good for efficient combustion and emission control

• Used In: Many production cars

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3. 🟩 Bathtub or Heart-Shaped Combustion Chamber

• Shape: Resembles a bathtub or heart

• Features:

  • Promotes good squish and turbulence

  • Central spark plug placement improves flame travel

• Advantages: Better fuel-air mixing and combustion efficiency

• Used In: Modern compact SI engines

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4. ⚫ Pent-Roof Combustion Chamber

• Shape: Like a sloped pentagon

• Features:

  • Used with multi-valve (typically 4-valve) cylinder heads

  • Allows central spark plug placement

  • Efficient airflow and flame propagation

• Advantages: Excellent power and emissions balance

• Used In: Most modern fuel-injected engines

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✅ Summary Table:

Combustion Chamber Type	Key Feature	Common Application
Hemispherical (Hemi)	High power, large valves	Sports/Performance engines
Wedge-shaped	Simple design, good turbulence	General purpose engines
Bathtub/Heart-shaped	Good squish, compact	Compact car engines
Pent-roof	Supports 4-valve heads, efficient	Modern multi-valve engines

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Each combustion chamber design aims to optimize power, efficiency, emissions, and flame propagation in an SI engine.