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From the above:
- Quench distance is inversely proportional to the laminar flame speed.
- For a given fuel- air mixture composition, pressure and temperature,
 is proportional to the Peclet number at the flame quenching conditions.
Quench distance or quench layer thickness depends on several parameters viz., wall geometry, fuel composition, mixture stoichiometry, flame speed, temperature and pressure of the reactants, thermal conductivity and turbulence. Typical quench layer thickness for stoichiometric mixtures of different fuels for laminar flame combustion are given in Table 2.2.
Table 2.2 |
Quench layer thickness,(mm) for different fuel-air mixtures,
 =1, P = 1atm and T = 20 ºC |
Fuel |
, mm |
Hydrogen |
|
Methane |
1.9 |
Propane |
2.1 |
Isooctane |
2.0 |
Methanol |
1.8 |
In engine like conditions, typical two wall quench distance ranges from 0.2 to 1 mm. Peclet number for flame quenching between two parallel plates is nearly 5 times of the single wall quench distance. Thus, the single wall quench layer thickness would be in the range 0.04 to 0.2 mm. For example, in a SI engine operating on normal gasoline, at an average cylinder pressure = 10 bar,  = 0.2 m/s and a = 10-5 m2/s, single wall quench distance is estimated to be about 0.05 to 0.1 mm assuming  and  , to be about equal in Eq. (6.40).
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