Effect Of Ignition Locations On Vented Explosion Characteristic Of Premixed Hydrogen-air Mixtures

At present, fossil fuels are still the main source of energy and chemistry product. However, the consumption of fossil fuel will cause serious environment problems, as global warming and greenhouse effects. As a clean energy, hydrogen can solve these problems. However, the work system of hydrogen has several security issues due to its wide flammable range and high burning rate. Vented explosion is a measure to weaken the loss of explosion, when pressure peak is higher than a presupposed value, the presupposed film will burst so that the high pressure gas can eject from the vessel. The correct and safe vented explosion design of hydrogen work system can improve the safety of hydrogen fuel.Experiments were carried out to investigate the effect of ignition location and vent burst pressure on pressure profile and flame propagation during explosion venting of hydrogen-air mixtures. Four piezoelectric pressure transducers are used to measure pressure-time histories and high speed camera is employed to record the vented flame outside the vessel. Several conclusions can be summarized by the means of analyzing the flame velocities and peak pressures of three ignitions and different vent burst pressures.1 Central ignition leads to the highest flame areas, flame propagation velocity and the highest peak pressures; the flame propagation velocity, the flame areas and the peak pressures of rear ignition were medium; front ignition resulted in the lowest flame areas, flame propagation velocity and peak pressures. For front ignition, the pressure profile has three peak pressures which corresponding to the following three successive stages, but for central ignition and rear ignition, only first and third peak pressure can be find.2 The peak pressures and the flame areas totally increase with bursting pressure. Overpressure measurements made inside the chamber show clearly that the acoustic oscillation occurs in this study. The internal pressures have been influenced by the external explosion.3 The photographs demonstrate the occurrence of external explosion. For rear ignition, the velocities of emerging flame and the levels of external explosion are always highest, the distances from vent to location of external explosion are farthest accordingly. For front ignition, however, the levels of external explosion are lowest and external explosion sites are nearest from vent, the results of central ignition are medium.4 With vent burst pressure increasing, the distances from vent of external explosion show little change, and the effect of acoustic oscillation is weaken, but the levels of external explosion are firstly enhanced and then weaken with the increase of the vent burst pressure. Because of the effect of acoustic oscillation, internal pressure signal shows significant oscillation of front ignition when vent is open. Moreover, external pressure signals of central and rear ignitions also present oscillations due to external explosion.