Simulation Study On Combustion And Explosion Characteristics Of Hydrogen-Doped Premixed Gas And Confined Space Explosion Release

Because of its clean,low-carbon and renewable characteristics,hydrogen energy is considered to be the preferred alternative energy source to achieve the"carbon peak"and"carbon neutral"goals in the 14th Five-Year Plan.It is of great significance for the transformation of China’s shipbuilding industry to green ships and low-carbon navigation.Hydrogen production and refueling station is convenient and integrated,which can effectively solve the problems of high cost of hydrogen transportation and urban energy shortage.Bioethanol reforming to produce hydrogen is a mature technology and is considered to be an important source of green hydrogen.Meanwhile,natural gas blending technology reduces the cost of hydrogen transportation and promotes the development and utilization of hydrogen.However,when hydrogen production and hydrogen refueling is carried out in stations,there is a risk of leakage of ethanol/blended natural gas in confined spaces,which can easily cause combustion and explosion accidents when encountering ignition sources.Explosion relief devices are widely used in confined spaces such as various industrial plants and large equipment to provide rapid pressure relief after an explosion to protect the building and equipment.Therefore,the study of the combustion characteristics,explosion characteristics and explosion relief process of hydrogen-doped premixed gas in confined spaces is an important prerequisite to promote the full-scale application of hydrogen production and hydrogen refueling stations.In this paper,the combustion and explosion characteristics of hydrogen/ethanol/methane premixed gas at 20%,50%and 80%of ethanol at atmospheric pressure（hydrogen always accounts for 20%of the hydrogen-methane mixture）,with initial temperatures of 370 K,400 K and 450 K and equivalence ratios of 0.7-1.4 are investigated using the constant pressure method based on the constant volume combustion bomb platform.In addition,the process of high pressure explosion in confined space was numerically simulated.The details of the study are as follows:First,the variation law of hydrogen-doped premixed flame propagation under different working conditions was experimentally studied.The results show that the peak of LBV（Laminar Burning Velocity）of laminar combustion velocity shifts to the low equivalent ratio side with the increase of ethanol blending ratio and reaches the peak near the equivalent ratio of 1.2.The decrease of LBV is greater when the C₂H₅OH ratio is greater than 50%and the C₂H₅OH continues to increase.The LBV of the premixed flame can keep increasing as a power function with increasing temperature ratio（T₀/T_i）.Secondly,the effect of different working conditions on the explosion characteristics of premixed gas was experimentally studied.The results show that the maximum explosion pressure and the maximum pressure rise rate are peaked in the range of 1.3-1.4 equivalent ratios.The increase of the initial temperature makes the maximum explosion pressure,maximum pressure rise rate and explosion time become smaller.The maximum explosion pressure increases linearly with the increase of ethanol ratio and decreases linearly with the increase of the initial temperature.In addition,the deflagration index values were less than10 MPa·m/s under all experimental conditions.Again,simulations were performed to study the characteristics of the hydrogen-doped premixed gas flame structure and dynamics.The experimentally obtained LBVs are in good agreement with the simulation results.The sensitivity coefficients,adiabatic flame temperatures,production rates of relevant combustion substances and radical molar fractions at different operating conditions were investigated by Chemkin software.The analysis results showed that the radical reaction R1（H+O2=O+OH）always contributed to the LBV of the hydrogen-doped premixed flame and had the largest effect.The adiabatic flame temperature reaches a maximum at an equivalence ratio of 1.1,which is smaller than the equivalence ratio corresponding to the experimental LBV peak due to the large heat loss in the experiment.Finally,simulations are carried out to investigate the effect of different venting pressures and vent diameters on the explosion pressure relief process of ternary gas mixtures in confined spaces.The temperature field distribution,velocity field distribution and pressure changes inside and outside the confined space after the explosion were studied under different operating conditions.The results show that the higher the opening pressure,the faster the gas propagation speed,the higher the temperature of the external venting area,and the wider the impact.As the diameter of the vent becomes larger,the external high temperature area becomes significantly larger,the external gas flow slows down,but the formation of a vortex ring-like velocity field is larger.The greater the opening pressure of the vent,the larger the diameter of the vent,the faster the pressure drop in the restricted space,the higher the pressure peak in the external vent area,the better the effect of the vent.