Influence of initial pressure and temperature on flammability limits of hydrogen–air

• Lower flammability limits of hydrogen–air decrease as initial pressures increase from 0.1 to 0.4 MPa.
• Decrement of LFL with initial temperature from 21 to 90 °C at 0.4 MPa is less than 0.25%.
• Lower flammability limit of hydrogen–air at 0.1 and 0.4 MPa are 4 and 1.25%(V/V) respectively.
• Upper flammability limits of hydrogen–air increase with initial pressure and temperature.
• Upper flammability limit of hydrogen–air at 90 °C and 0.4 MPa is 93%(V/V).

This paper presents data on the lower and upper flammability limits of hydrogen–air mixtures at elevated temperature and pressure. A 5-L explosion vessel, an ignition system, and a transient pressure measurement sub-system were used in this study. Through a series of experiments carried out, the lower and upper flammability limits of hydrogen–air mixtures at different initial pressures and temperatures have been studied and the influence of initial temperature and pressure on the lower and upper flammability limits of hydrogen–air mixtures has been analysed and discussed. It was found that the decrement of the LFLs of hydrogen–air with the initial temperature from 21 to 90 °C at the initial pressure of 0.1 MPa is less than 1%, the decrement of the LFLs with the initial temperature from 21 to 90 °C at 0.2 MPa is less than 1%, the decrement of the LFLs with the initial temperature from 21 to 90°Cat 0.3 MPa is less than 0.66%, and the decrement of the LFLs with the initial temperature from 21 to 90 °C at 0.4 MPa is less than 0.25%. The lower flammability limits of hydrogen–air mixtures at the pressures of 0.1 and 0.4 MPa are 4 and 1.25%(V/V), respectively. The upper flammability limits of the hydrogen–air mixtures increase with the initial pressure and temperature. The upper flammability limit of the hydrogen–air mixtures at 90 °C and 0.4 MPa reaches 93%(V/V) which is much higher than that (76%(V/V)) at 21 °C and 0.1 MPa.