Experimental assessment on the explosion pressure of CH4-Air mixtures at flammability limits under high pressure and temperature conditions

•Explosion characteristics during HPAI were investigated up to 15 MPa and 100 °C.•Pm, (dP/dt)max, and KG increased with the initial pressure.•Explosion pressure slightly reduced at high temperature conditions.•Monitoring the CH4 concentration can eliminate the explosion risk during HPAI.•Pm is higher at stoichiometric concentration and can be applied in NG engines. High-pressure air injection technique has been extensively used for enhanced oil recovery in oilfields. Yet, it is of great concern on the process safety in terms of the explosion of natural gas-air mixtures. To deeply understand the explosion characteristics in the air injection procedure, explosion experiments for methane (a main component of natural gas) and air mixture were conducted using a cylindrical vessel at elevated pressure and temperature situations. The explosion pressure, the pressure rise rate and deflagration index of CH4 and air mixtures in a closed chamber were investigated under pressure up to 15 MPa and temperature up to 100 °C, and the effect of CH4 concentration on explosion pressure was also examined. The results of this research can provide useful data to quantify the dependency of explosion risk parameters on pressure, temperature and gas concentration. The experimental results indicate that the explosion pressure at flammability limits of CH4 gradually increases with initial pressure, while it can be slightly declined at elevated temperatures. The pressure rise rate and deflagration index increase at high pressures, but these values become lower at higher temperatures. At lower flammability limits and upper flammability limits of CH4-air mixtures, the explosion pressure can be greatly reduced due to the presence of insufficient combustible gas or high content of inerting gas (N2). The explosion pressure data reported in this study can provide guidelines for the prevention and mitigation of explosion disasters in high-pressure air injection process.