Here are four key locations within an SI (Spark Ignition) engine cylinder where unburnt hydrocarbons (HCs) are commonly formed:
🔧 1. Crevice Volumes (e.g., Piston Ring Lands and Cylinder Head Gasket Area)
-
What happens: Air-fuel mixture enters narrow gaps (crevices) during compression.
-
Result: Flame front cannot penetrate these tight spaces due to quenching, so fuel remains unburnt.
-
Example areas:
-
Between piston and cylinder wall
-
Around the spark plug threads
-
Gasket regions
-
🔧 2. Near the Cylinder Wall (Wall Quenching Zone)
-
What happens: The flame loses heat rapidly to the cool cylinder wall, which quenches the flame.
-
Result: Incomplete combustion near walls leaves behind unburnt HCs.
-
Occurs more in: Cold-start conditions or engines with low wall temperature
🔧 3. In the Piston Head Recesses or Bowl (Dead Zones)
-
What happens: Poor air motion or turbulence in recessed areas prevents full combustion.
-
Result: Local fuel-rich pockets or low flame speed lead to HC formation.
-
Affected by: Poor combustion chamber design or carbon buildup
🔧 4. Late Burning or Incomplete Combustion Zones
-
What happens: Some areas may burn too slowly, especially near the end of the expansion stroke.
-
Result: The burning is cut off by the opening of the exhaust valve, leaving partially burned or unburnt fuel.
-
Common in: Poor ignition timing or lean mixtures
✅ Summary Table:
Location | Reason for HC Formation |
---|---|
Crevice volumes | Flame cannot enter; fuel trapped unburnt |
Near cylinder walls | Flame quenched by cold surfaces |
Piston bowl/recesses (dead zones) | Poor mixing or turbulence; local rich mixtures |
Late burning zones | Combustion interrupted before completion |
Unburnt hydrocarbons are a major pollutant and are minimized using design improvements, fuel injection control, and catalytic converters.
0 Comments:
Post a Comment
Thank you for the comment