A numerical study of ignition limits for methane-air mixtures
A detailed numerical study on ignition limits for methane-air mixtures is performed, using two mathematical models. One model allows the pressure to be uniform. The effect of the initial pressure wave induced by the spark on flame propagation is analyzed. The dependence of the minimum ignition energy for a stoichiometric methane-air mixture on the ignition parameters is studied in great detail. The value of the minimum ignition parameters is studied in great detail. The value of the minimum ignition energy is found to depend on the initial blast wave for short ignition times. It is also found that for small ignition kernels, the minimum ignition energy remains constant as the kernel size is decreased. Heat diffusion is found to contribute to the increase in minimum ignition energy for long ignition times, but it helps ignite the mixture for small kernel sizes. A minimum ignition energy 70 times smaller than the reported experimental value is found. The existence of a lean flammability limit for methane-air mixtures in the absence of gravity is then proven. It is found that when radiation heat loss from CO{sub 2} and H{sub 2}O band emission is accounted for, a mixture limit is reached below which no flame propagates. A small but non-zero limit burning velocity is obtained at this limit. For sublimit mixtures, a special type of flame propagation known as self-extinguishing flames is found. The numerical results are compared to the available experimental data, and the agreement is generally good.
- Research Organization:
- Brown Univ., Providence, RI (United States)
- OSTI ID:
- 5404724
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
400800* -- Combustion
Pyrolysis
& High-Temperature Chemistry
AIR
ALKANES
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
COOLING
DETONATION WAVES
DISPERSIONS
ENERGY TRANSFER
FLAME PROPAGATION
FLUIDS
GASES
HEAT TRANSFER
HYDROCARBONS
HYDROGEN COMPOUNDS
IGNITION
MATHEMATICAL MODELS
METHANE
MIXTURES
ORGANIC COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PRESSURE EFFECTS
SHOCK WAVES
WATER