Flame Speed: The rate of expansion of flame front in combustion chamber is known
as flame speed. (Or, The minimum time
taken for complete combustion in combustion chamber)
Importance of Flame Speed:
1. It affects
Combustion Process.
2. Higher the
combustion efficiency.
3. High Fuel Economy can be achieved.
Factors effecting Flame Speed:
1. Turbulence
2. Compression
ratio
3. Inlet
Temperature & Pressure
4. Air-Fuel
ratio.
5. Engine
Speed.
1. Turbulence:
- Helps in mixing & accelerates chemical reaction in dissimilar manner in combustion chamber.
2. Compression:
- High compression ratio increases the pressure and temperature of mixture.
- This reduces the initial phase of compression and hence less ignition advance is needed.
- High pressure & temperature of the compressed mixture, speeds up the second phase of compression.
- Increased compression ratio reduces the clearance volume & leads to increase the peak pressure and temperature of mixture and reduces the total combustion duration.
- Thus the engine with higher compression ratio has higher Flame Speed.
3. Inlet Temperature & Pressure:
- Flame speed increases with an increase inlet temperature & pressure.
- The higher value of these forms a better homogeneous mixture which helps in increasing the flame speed.
4. Air-Fuel ratio:
- The higher flame speed is obtained with standard air-fuel mixture.
- When there is linear or rich mixture, flame speed decreases & leads to release if less thermal energy.
5. Engine Speed:
- When engine speed increases, flame speed increases due to turbulence, swirl squish & tumble.