Effects of hydrogen concentration on the vented deflagration of hydrogen-air mixtures in a 1-m3 vessel

We experimentally investigated the pressure buildup and flame behavior during the vented deflagration of hydrogen-air mixtures with concentrations ranging from 13% to 39% that were centrally ignited in a 1-m³ rectangular vessel with a 500 mm × 400 mm top vent. The performance of some available models for estimating the maximum reduced overpressure was experimentally evaluated. The maximum reduced overpressure increased from approximately 3 kPa to 100 kPa as hydrogen concentration increased from 13 to 39%. Turbulent pressure oscillations with frequencies of 200–300 Hz triggered by external explosions were observed in our tests with 22–39% hydrogen-in-air mixtures. Molkov's best-fit and conservative models predict the maximum reduced overpressure well for lean and rich hydrogen mixtures, respectively. The average speed of the external flame first decreases to a minimum value with the fireball expanding to its maximum size and then increases. As hydrogen concentration increases, the maximum length and duration of the external flame increases and decreases, respectively.