Effect of low temperature on the flammability limits of methane/nitrogen mixtures

An experimental setup was established to measure the flammability limits of flammable gases at low temperatures. The flammability limits of methane/nitrogen mixtures in air were measured at atmospheric pressure and wide temperature range from 150 to 300 K. The estimated uncertainty of the experimental values was 0.2 vol%. The results reveal that as initial temperature decreases, the upper flammability limits (UFL) decrease while the lower flammability limits (LFL) increase. Therefore, the critical flammability ratio (CFR) decreases as the initial temperature decreases. In addition, the variation in the UFL is more sensitive than that in the LFL as the molar ratio of nitrogen to methane increases. In addition, an extended Le Chatelier’s formula with higher-order and temperature terms was proposed to correlate and predict the flammability limits at each temperature. The calculated values conformed to the experimental results for both the LFL and the UFL.