A Combustion chamber is an important component of an Internal combustion engine. It plays a vital role in engine performance and its knock properties.

Types of combustion chamber:

The combustion chamber is classified based on fuel type and injection method.

For Spark Ignition (SI) Engines
For Compression Ignition (CI) Engines
Special Types (Used in Gas or Dual-Fuel Engines)

Also Read: What type of combustion chambers are used n gas turbine engines?

Lets discuss in detail:

1. For Spark Ignition (SI) Engines:

(Common in petrol/gasoline engines)

A. Hemispherical Combustion Chamber (Hemi Head)

Dome-shaped chamber allowing large valves and a central spark plug. Known for high power and efficient combustion.

Shape: Half-sphere dome
Features:
- High volumetric efficiency
- Large valves can be accommodated
- Centrally located spark plug ensures good flame travel
Advantages:
- Excellent power output and efficiency
- Reduces knocking
Disadvantages:
- Complex and expensive cylinder head
- Higher surface area leads to more heat loss

B. Pentroof Combustion Chamber

Sloped roof-like design with four valves. Promotes better air-fuel mixing and is common in modern engines.

Shape: Roof-like structure with inclined valves (resembles a house roof)
Features:
- Allows 4-valve-per-cylinder configuration
- Compact and efficient
Advantages:
- Promotes swirl and better air-fuel mixing
- More efficient combustion
Used in: Most modern high-performance engines

C. Wedge Combustion Chamber

Shape: Wedge-like chamber with one flat surface
Features:
- Simple design
- Helps in squish and swirl motion
Advantages:
- Cost-effective and compact
Disadvantages:
- Less efficient flame propagation compared to hemispherical

D. Bowl-in-Piston Type

Shape: Recess (bowl) in the piston crown
Features:
- Used in engines with high compression ratios
Advantage:
- Improves turbulence and mixing
Common in: Some performance and race engines

2. For Compression Ignition (CI) Engines:

(Common in diesel engines)

A. Direct Injection (DI) Combustion Chamber

Fuel is injected directly into the main combustion chamber.
Features:
- Bowl-shaped recess in piston crown to promote air-fuel mixing
Advantages:
- Higher fuel efficiency
- Better thermal efficiency
Disadvantages:
- Higher NOx emissions
- Requires high injection pressure

B. Indirect Injection (IDI) Combustion Chamber

Fuel is first injected into a pre-combustion chamber
Types:
- Pre-combustion Chamber
- Swirl Chamber
- Turbulence Chamber

a. Pre-combustion Chamber

Small chamber connected to main chamber via narrow passage
Initial combustion starts here, then spreads
Good cold-start behavior

b. Swirl Chamber

Promotes strong air swirl before fuel injection
Improves mixing and combustion

c. Turbulence Chamber

Uses rapid movement of air/fuel for efficient ignition
Often found in older diesel engines

3. Special Types (Used in Gas or Dual-Fuel Engines)

A. Pre-Chamber Combustion System (Active Pre-Chamber)

Small pre-chamber contains its own injector/spark plug
Jets of hot gases ignite main chamber mixture
Used in lean burn or hydrogen/natural gas engines
Improves efficiency and lowers NOx

Also Read: Read more about pre-combustion chamber in detail.

Comparison table:

Type	Used In	Efficiency	Emissions	Complexity
Hemispherical	Petrol (SI)	High	Medium	High
Pentroof	Petrol (SI)	Very High	Low	Medium
Wedge	Petrol (SI)	Medium	Medium	Low
DI Chamber	Diesel (CI)	High	High NOx	High
IDI Chamber	Diesel (CI)	Medium	Low	Medium
Pre-Chamber (Active)	Gas/Dual Fuel	High	Low	High