Experimental study of the pressure and temperature dependence on the upper flammability limit of methane/air mixtures

The flammability limits of methane/air mixtures are investigated experimentally at pressures up to 5500 kPa and temperatures up to 200 degrees C. Two different criteria based on the maximum explosion pressure are used to define the flammability limit, the tangent criterion and the min-max criterion. It is shown that the min-max criterion should be used to determine the upper flammability limit (UFL), because the tangent criterion underestimates the UFL at initial pressures higher than ambient. In the pressure-temperature range tested second order pressure dependences and linear temperature dependences of the UFL are found. The temperature dependence of the UFL is influenced by the initial pressure which is in contrast with previous findings. (C) 1997 Elsevier Science B.V.