Experimental Study On The Effect Of Release Port Properties On Spontaneous Ignition Of High-Pressure Hydrogen Release

The excessive use of fossil fuels has caused environmental pollution and climate change.Hydrogen,as a zero-pollution,highly efficient,and widely available renewable clean energy,is of strategic significance to energy transition.Currently,the mainstream method for hydrogen storage and transportation is high-pressure gas storage.However,due to hydrogen’s properties,such as its high risk of leakage,hydrogen embrittlement,low ignition energy,and wide combustion range,the use of hydrogen poses safety hazards.In addition,in the event of a high-pressure hydrogen leak,ignition may occur without any apparent external ignition source,which can lead to further hydrogen fires or explosions,posing significant obstacles to the safe utilization of hydrogen.Therefore,it is necessary to conduct extensive research on high-pressure hydrogen leakage and spontaneous ignition phenomena.Experimental studies were conducted to comprehensively study the shock wave propagation and spontaneous ignition characteristics of high-pressure hydrogen under different conditions of the release port properties including different shapes,materials,and sizes.Firstly,the impact of the shape and length-width ratio of the release port on highpressure hydrogen leakage and spontaneous ignition was explored by changing the shape of the release port,including circular,square with a length-width ratio of 1,slit with a length-width ratio of 2 and 3.The results showed that the shock wave intensity and speed under non-circular release port conditions were smaller than those under circular release port conditions.The larger the length-width ratio,the stronger the weakening effect on the shock wave,and the higher the minimum release pressure required for hydrogen spontaneous ignition.However,under non-circular release port conditions,the mixing effect of hydrogen gas and air inside the tube would be enhanced,thereby increasing the strength of the hydrogen spontaneous ignition flame.The weakening effect of the change in the release port shape would inhibit the occurrence of hydrogen spontaneous ignition,while the strengthening effect of gas mixing would promote the occurrence of hydrogen spontaneous ignition.The two effects are in opposition,jointly affecting hydrogen spontaneous ignition.Compared with circular release port conditions,under the square release port conditions with a length-width ratio of 1,there was no significant change in ignition flame strength.Under the slit release port conditions with a length-width ratio of 2,the gas mixing effect was much stronger and the ignition flame strength of hydrogen was significantly increased.Under the slit release port conditions with a length-width ratio of 3,the ignition flame strength of hydrogen was slightly increased.Secondly,the self-ignition of high-pressure hydrogen gas leakage under different burst disk materials conditions incorporating the factor of vent area was studied.When the release port area was 79 mm2,under the nickel burst disk condition,the opening degree of the burst disk,shock wave and flame intensity were greater than those under the stainless steel burst disk condition.When the release port area was 79 mm2,there was no significant difference in the shock wave intensity and speed between the nickel and aluminum burst disk conditions.However,when the release port area was 177 mm2,the shock wave intensity,shock wave speed,and flame intensity under the nickel burst disk condition were slightly greater than those under the aluminum burst disk condition,and the flame appeared earlier.When the inlet area was the same,the shock wave pressure and velocity increase with the opening degree of burst disk,and the possibility of hydrogen self-ignition is higher.When the vent area decreased,the opening degree of burst disks under different materials conditions decreased,and the shock wave intensity and possibility of hydrogen self-ignition were reduced.Finally,a study was conducted on the spontaneous ignition of high-pressure hydrogen leakage under different releasing areas,taking into account the factors of inlet shape.The results show that for a square inlet,a slit-shaped inlet with a length-width ratio of 2,and a slit-shaped inlet with a length-width ratio of 3,reducing the inlet area leads to a significant decrease in the shock wave intensity and speed as well as the flame intensity and speed inside the tube,and will weaken the enhancement effect of the increased release pressure on the maximum flame intensity.Under the condition of reduced inlet area,the variation of the length-width ratio of the slit-shaped inlet has no effect on the propagation of shock waves and flame intensity of high-pressure hydrogen.The influence of the variation of inlet area under different inlet shapes on the minimum release pressure required for spontaneous combustion of high-pressure hydrogen is different.This effect is smaller under the conditions of a square inlet and a slit-shaped inlet with a length-width ratio of 3,but larger under the condition of a slit-shaped inlet with a length-width ratio of 2.