Influences of concentration gradients and ignition positions on unconfined inhomogeneous hydrogen explosion

This work aims at investigating the inhomogeneous hydrogen cloud explosion in unconfined spaces. The influences of concentration gradient and ignition position on the explosion were studied. Different initial inhomogeneous hydrogen clouds with vertical concentration gradients were prepared by controlling the injection rate and ignition time. Results show that the explosion flame at the equivalent concentration zone has higher temperature, faster propagation and more intense combustion reaction. With the decrease of the concentration gradient, the flame is faster and higher in temperature. The max explosion temperature increases from 905.9 °C to 1000.8 °C. The shapes of flame and temperature field in the gas cloud change from mushroom-shaped to ellipsoidal and then to spherical. The maximum overpressure (Pmax), maximum rise rate of overpressure ((dP/dt)max) and positive impulse (I) increase significantly with the decrease of concentration gradient. While ignited with different ignition positions, the flame propagation from the equivalent concentration zone to the flammability limit zone is inhibited by the concentration gradient. Central ignition induces the most intense and shortest explosion process and causes the highest temperature. Generally, central ignition induces larger Pmax and I in the vicinity of the cloud. Non-central ignition extends the impact areas of explosion.