Experimental Study Of The Effect Of Hydrogen Concentration On Explosion Venting Of Hydrogen-air Mixtures

Hydrogen is known as the gas which has the world’s smallest density and the smallest relative molecular mass, its mass is only1/14of the air. Under normal temperature and pressure, hydrogen is a highly flammable, colorless, odorless and tasteless gas.Water is the product of the combustion of hydrogen, So hydrogen as fuel has the advantages of clean, no pollution to the environment, the conversion efficiency is very high after the reaction, the water that is produced from hydrogen can also be used as the raw material for preparing hydrogen. In the future,hydrogen is likely to become the secondary energy as important as the electric which is indispensable for human.Under room temperature, the properties of hydrogen is stable, and is not easy to react with other substances. But when conditions change (such as lighted, heated, using a catalyst, etc.), the situation is different. The explosion limit range of hydrogen is very large, when the volume fraction of hydrogen in the air is in the range of4%to75%, just encountered the fire, it will explode immediately. Therefore, in daily life, once the use of hydrogen or improper storage, fire and explosion accidents can be caused easily. In the event of accident, the consequence is extremely serious. So the hydrogen combustion explosion characteristics and rules have a great significance on the safety storage and transportation of the hydrogen.In this study, constant volume bomb which has single venting explosion port is used as venting explosion container. High speed camera, schlieren system, pressure sensor are be used to study on the single port venting explosion of hydrogen-air premixed gas. Different hydrogen-air equivalence ratio on the venting process of combustion and various pressure variation, the rupture time and the external flame are be analyzed, the conclusions are as follows:(1).In each equivalence ratio of hydrogen-air premixed gas, the ratio has a substantial impact on the changes of the internal pressure and the peak value of the combustion bomb.And there is a critical equivalent ratio of1.6. Under the critical equivalent ratio, the internal pressure of combustion bomb reaches the maximum, when equivalence ratio is less than1.6, with the increase of equivalent ratio, internal peak pressure gradually increases,it reachs the maximum value at1.6. When equivalence ratio is greater than1.6, with the further increase of equivalence ratio, peak pressure begins to become smaller.(2).Equivalent ratio also has a great impact on the rupture time, there is also a critical equivalent ratio of1.4. Under this equivalence ratio, the shortest rupture time is Tmin=7.4ms. When equivalence ratio is less than1.4, with the increase of equivalent ratio, the rupture time gradually shortens; when equivalence ratio is greater than1.4, the rupture time becomes long.(3).In each equivalence ratio of hydrogen-air premixed gas, the ratio has a substantial impact on the changes of the pressure of the vent. When the equivalent ratio was1.6, the rising rate of pressure at the vent is the fastest, In the sides of the equivalence ratio1.6,the the rising rate of pressure all decreased.(4).Equivalent ratio has a great influence on the development of external flame of venting explosion port. With the equivalence ratio increases, the maximum length of the external flame gradually becomes longer. Until the equivalence ratio increases to4, the maximum length of external flame reaches the maximum value1.83m, with further increase of equivalence ratio, the maximum flame length gradually shortenes.