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1.
This paper investigates the effects of hydrogen additions on spontaneous ignition of high-pressure hydrogen released into hydrogen-air mixture. Hydrogen and air are premixed with different volume concentrations (0%, 5%, 10%, 15% and 20% H2) in the tube before high-pressure hydrogen is suddenly released. Pressure transducers are employed to detect the shock waves, estimate the mean shock wave speed and record the shock wave overpressure. Light sensors are used to determine the occurrence of high-pressure hydrogen spontaneous ignition in the tube. A high-speed camera is used to capture the flame propagation behavior outside the tube. It is found that only 5% hydrogen addition could decrease the minimum storage pressure required for spontaneous ignition from 4.37 MPa to 2.78 MPa significantly. When 10% or 15% hydrogen is added to the air, the minimum storage pressure decreases to 2.81 MPa and 1.85 MPa, respectively. When hydrogen addition increases to 20%, the spontaneous ignition even takes place at burst pressure as low as 1.79 MPa inside the straight tube.  相似文献   

2.
The shock wave dynamics, spontaneous ignition and flame variation during high-pressure hydrogen release through tubes with different cross-section shapes are experimentally studied. Tubes with square, pentagon and circular cross-section shapes are considered in the experiments. The experimental results show that the cross-section shape of the tube has no great difference on the minimum burst pressure for spontaneous ignition in our tests. In the three tubes with length of 300 mm, spontaneous ignition may occur when overpressure of shock wave is 0.9 MPa. When the spontaneous ignition is induced in a non-circular cross-section tube, the possible turbulent flow in the corner of the tube increases can promote the mixing of hydrogen and air, thus producing more amount of the hydrogen/air mixture. As a result, both the peak light signal and flame duration detected in the non-circular cross-section tubes are more intense than those in the circular tube. The smaller angle of the corner leads to a more intensity flame inside tube. When the hydrogen flame propagates to the tube exit from the circular tube, the ball-like flame developed near tube exit is relatively weak. In addition, second flame separation outside the tube is observed for the cases of non-circular cross-section tubes.  相似文献   

3.
Spontaneous ignition induced by high-pressure hydrogen release is one of the huge potential risks in the promotion of hydrogen energy. However, the understanding of the microscopic dynamic characteristics of spontaneous ignition, such as ignition initiation and flame development, remains unresolved. In this paper, the spontaneous ignition caused by high-pressure hydrogen release through a tube is investigated by two-dimensional numerical simulation at burst pressure ranging from 2.67 to 15 MPa. Especially, the thermal and species characteristics in hydrogen shock-induced ignition under different strengths of shock wave are discussed carefully. The results show that the stronger shock wave caused by higher burst pressure leads to larger heating area and higher heating temperature inside the tube, increasing the possibility of spontaneous ignition. The shortening effect of initial ignition time and initial ignition distance will decrease with the increase of the burst pressure. Ignition will be initiated when the temperature is raised to about 1350–1400 K under the heating effect of shock waves. It is also found that the ignition occurs under the lean-fuel condition firstly on the upper and lower walls of the tube. The flame branch after spontaneous ignition is observed in the mixing layer. Two ignition kernels show different characteristics during the process of combustion and flow. The evolution of HRR and mass fraction of key species (OH, H, HO2) are also compared to identify the flame front. The mass fraction of H has the better trend with HRR. It is suggested that H radical is a more reasonable choice as the indicator of the flame front.  相似文献   

4.
5.
Hydrogen is expected to be an alternative energy carrier in the future. High-pressure hydrogen storage option is considered as the best choice. However, spontaneous ignition tends to occur if hydrogen is suddenly released from a high-pressure tank into a tube. In order to improve the safety of hydrogen application, an experimental investigation on effects of CO2 additions (5%, 10% and 15% volume concentration) on the spontaneous ignition of high-pressure hydrogen during its sudden expansion inside the tube has been conducted. Pressure transducers are used to record the pressure variation and light sensors are employed to detect the possible spontaneous ignition. It is found that the shock wave overpressure and the mean shock wave speed are almost the same inside the tube for different CO2 additions under the close burst pressures. For cases with more CO2 additions, the ignition detected time is longer and the average speed of the flame, the maximum value of light signals and the detected duration time of spontaneous ignition are smaller. It is shown that minimum burst pressure required for spontaneous ignition increase 1.47 times for 15% CO2 additions. The minimum burst pressure required for spontaneous ignition increases from 4.37 MPa (0% CO2) up to 6.41 MPa (15% CO2). With the increasing of CO2 additions, it requires longer distance and longer time for hydrogen and oxygen to mix and thus longer ignition delay distance/time. The results showed that additions of CO2 to air have a good suppressing effect on hydrogen spontaneous ignition.  相似文献   

6.
A high-pressure hydrogen jet released into the air has the possibility of igniting in a tube without any ignition source. The mechanism of this phenomenon, called spontaneous ignition, is considered to be that hydrogen diffuses into the hot air caused by the shock wave from diaphragm rupture and the hydrogen-oxidizer mixed region is formed enough to start chemical reaction. Recently, flow visualization studies on the spontaneous ignition process have been conducted to understand its detailed mechanism, but such ignition has not yet been well clarified. In this study, the spontaneous ignition phenomenon was observed in a rectangular tube. The results confirm the presence of a flame at the wall of the tube when the shock wave pressure reaches 1.2–1.5 MPa in more than 9 MPa burst pressure and that ignition occurs near the wall, followed by multiple ignitions as the shock wave propagates, with the ignitions eventually combining to form a flame.  相似文献   

7.
The tendency of spontaneous ignition of high-pressure hydrogen during its sudden release into a tube is one of the main threats to the safe application of hydrogen energy. A series of investigations have shown that the tube structure is a key factor affecting the spontaneous ignition of high-pressure hydrogen. In this paper, a numerical study is conducted to reveal the mechanism of spontaneous ignition of high-pressure hydrogen inside the tube with local contraction. Large Eddy Simulation, Renormalization Group, Eddy Dissipation Concept, 37-step detailed hydrogen combustion mechanism and 10-step like opening process of burst disk are employed. Three cases with burst pressures of 3.10, 4.90, and 8.45 MPa are simulated to compare against the pervious experimental study. The spontaneous conditions and positions agree well with the experimental results. The numerical results indicate that shock wave reflection takes place at the upstream vertical wall of contraction part. The interacted-shock-affected region is generated at the tube center because of the subsequent shock wave interaction. The forward reflected shock wave couples with normal shock wave and increases the pressure of leading shock wave. The sudden contraction of tube blocks the propagation of hydrogen jet and decreases the speed from supersonic flow to subsonic flow. More flammable mixture is generated inside the contraction part, as a results, the length of the flame is increased. Two mechanisms are proposed finally.  相似文献   

8.
A series of experiments were conducted to study the pressure and combustion characteristics of the high-pressure hydrogen during the occurrence of spontaneous ignition and the conversion from spontaneous ignition to a jet fire and explosion. Different initial conditions including release pressure (4–10 MPa), tube diameter (10/15 mm), and tube length (0.3/0.7/1.2/1.7/2.2/3 m) were tested. The variation of the pressure and flame signal inside and outside of the tube and the development of the jet flame were recorded. The experimental results revealed that the minimum ignition pressure required for self-ignition of hydrogen at different tube diameters decreased first and then increased with the extension of tubes. The minimum ignition pressure for tubes diameters of 10 mm and 15 mm is no more than 4 MPa and the length of the tubes is L = 1.7 m. The minimum release pressure required for spontaneous ignition of a tube D = 15 mm is always lower than that of a tube D = 10 mm at the same tube length. When the spontaneous ignition occurred, it did not absolutely trigger the jet fire. The transition from spontaneous ignition to a jet fire must go through the specific stages.  相似文献   

9.
Increasing hydrogen storage pressure brings high economic benefits and high risks. Pressurized hydrogen leakage spontaneous ignition experiment is an important means to reveal the mechanism of hydrogen leakage spontaneous ignition and improve the safety of hydrogen storage equipment. However, due to the extremely high cost and danger of ultra-high pressure, there is a serious lack of experimental data. In this paper, a pressure-ratio equivalent (PRE) method of experiments is proposed based on the theory of the shock tube problem. By keeping the hydrogen-air pressure ratio constant while reducing the absolute pressure of air and hydrogen, the difficulty of the experiment is greatly reduced. The effectiveness of the PRE method is evaluated theoretically and experimentally. The results show the PRE method retains the ignition characteristics of hydrogen leakage spontaneous ignition largely when the air pressure is within 0.05–0.1 MPa. It is found the pressure ratio of hydrogen to air dominates the leakage spontaneous ignition process. In the experiments of different air pressures, the shock Mach numbers are close to theoretical values. In addition, leakage spontaneous ignition of hydrogen mixed with 30% (vol.) CO is found in experiments using the PRE method, with pressure ratios of up to 250. This indicates that when the storage pressure is high enough, there is also a risk of spontaneous ignition of syngas from high-pressure leakage. The PRE method can widely broaden the pressure scope of experimental research on leakage spontaneous ignition, and it provides a new idea for obtaining the experimental data of gas high-pressure leakage spontaneous ignition.  相似文献   

10.
运用扩散点火理论对高压氢气泄漏到下游管道内的自燃点火情况进行了分析。利用激波管流动理论讨论了氢气射流前端激波加热区域的参数变化情况,分析了前沿激波强度、均匀区压力和温度与初始压力的关系,给出了高压氢气泄漏到下游管道后,预测前沿激波强度、均匀区压力和温度的数学方程,建立了判断高压氢气泄漏到下游管道内是否发生自燃点火的函数表达式。提出了理论点火临界压力的概念,计算发现氢气的理论点火临界压力明显低于其他几种常见的气体燃料。讨论了影响泄漏自燃发生的可能因素,结果可为预防高压储氢泄漏自燃提供科学依据。  相似文献   

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