Near flammability limits behavior of methane-air mixtures with influence of flammable gases and nitrogen: An experimental and numerical research

The flammability limit is a key parameter used to evaluate the combustion characteristics and explosion risk of flammable gases mixtures. In this work, the flammability limit of a methane with mixed flammable gases was measured in a standard cylindrical equipment, and the effect of inert gas on the flammable limit was studied as well. Moreover, the GRI-Mech3.0 mechanism was employed to obtained the thermodynamic and chemical kinetic parameters by using the PREMIX code. The experimental results show that the addition of gaseous fuel can reduce the flammability limit of methane, rise the explosion risk of methane, and increase the amount of inert gas needed for complete inertization. Thermodynamic and chemical kinetic analyses showed that with the increase in the volume fraction of the mixed gas, the peak flame temperature and the flammability exponent gradually increased when approaching the lower flammability limit. The peak flame temperature and the flammability exponent gradually decreased when approaching the upper flammability limit. Sensitivity analysis indicated that the competition between chain branching reaction R38 and chain termination reaction R35 had an important effect on the lower flammable limit, while that competition effect between R38 and R52 dominated the upper flammability limit. The influence of flammable gas on the flammability limit of methane was mainly determined by changing the thermodynamic characteristic of the mixed gas and the competition between the chain reaction. These results will supplement the corresponding flammability limit database and help to prevent potential explosion hazards.