Definition of flame speed, SL
•Temperature profile through flame
•Product density is less than the reactant density so that by continuity the velocity of the burned gases is greater than the velocity of the unburned gases
•For a typical hydrocarbon-air flame at atmospheric pressure, the density ratio is about 7
•Convenient to divide the flame into two zones
1.Preheat zone: little heat is released
2.Reaction zone: most of the chemical energy is released
2.a Thin region of fast chemistry
•Destruction of fuel molecules and creation of intermediate species
•Dominated by bimolecular reactions
•At atmospheric pressure, fast zone is usually less than 1 mm
•Temperature and species concentration gradients are very large
•The large gradients provide the driving forces for the flame to be self-sustaining, i.e. diffusion of heat and radical species from the reaction zone to the preheat zone
2.b Wider region of slow chemistry
•Chemistry is dominated by three-body radical recombination reactions, such as the final burn-out of CO via CO + OH → CO2 + H
•At atmospheric pressure, this zone may extend several mm
Definition of flame speed, SL
•Temperature profile through flame
•Product density is less than the reactant density so that by continuity the velocity of the burned gases is greater than the velocity of the unburned gases
•For a typical hydrocarbon-air flame at atmospheric pressure, the density ratio is about 7
•Convenient to divide the flame into two zones
1.Preheat zone: little heat is released
2.Reaction zone: most of the chemical energy is released
2.a Thin region of fast chemistry
•Destruction of fuel molecules and creation of intermediate species
•Dominated by bimolecular reactions
•At atmospheric pressure, fast zone is usually less than 1 mm
•Temperature and species concentration gradients are very large
•The large gradients provide the driving forces for the flame to be self-sustaining, i.e. diffusion of heat and radical species from the reaction zone to the preheat zone
2.b Wider region of slow chemistry
•Chemistry is dominated by three-body radical recombination reactions, such as the final burn-out of CO via CO + OH → CO2 + H
•At atmospheric pressure, this zone may extend several mm
การแปล กรุณารอสักครู่..