Suppression of methane / air flame propagation in large scale pipelines by clouds of ultrafine powders

Explosion suppression of methane / air mixtures with methane concentration 9. 5% in volume by various ul- trafine powders were conducted in a 32. 4 m long pipelines with an internal diameter of 357 mm,the self-developed suppressor were applied to discharge the powders and the array of ionization probes were used to measure the flame propagation velocity. Results indicated that flame propagation can be mitigated when different mass of ultrafine ABC powder were discharged with 125 ms in trigger time,the flame propagation can be suppressed entirely while 800 g ul- trafine ABC powder was discharged. The order of ultrafine ABC,ultrafine SiO2 ,normal partial size ABC and ultrafine Mg(OH)2 powders can be concluded in the suppression efficiency from the present experiments,the flame can’ t be inhibited 100% when the trigger time is above critical.