Experimental study on the flammability limits of natural gas/air mixtures at elevated pressures and temperatures

•A novel apparatus for measuring the flammability limits of natural gas at high pressures and temperatures was developed.•Effects of temperatures and pressures upon the flammability limits of natural gas were investigated.•The results showed that both temperature and pressure had a marked effect upon the UFL.•The effect of temperature and pressure on LFL was slight compared with the effect on UFL.•The fitting equations of flammability limits as a function of pressure or temperature were obtained.